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VOLUME 5 NO. 1 JANUARY 1997

A s c i e n t i f i c journal published by U n i v e r s i t i Putra M a l a y s i a P r e s s

Pertanika Journal of Science and Technology •



About the Journal Pertanika, the pioneer journal of UPM, began publication in 1978. Since then, it has established itself as one of the leading multidisciplinary journals in the tropics. In 1992, a decision was made to streamline Pertanika into three journals to meet the need for specialised journals in areas of study aligned with the strengths of the university. These are (i) Pertanika Journal of Tropical Agricultural Science, (ii) Pertanika Journal of Science and Technology and (ui) Pertanika Journal of Social Science and Humanities.

Reviews are critical appraisals of literature in areas that are of interest to a broad spectrum of scientists and researchers. Review papers will be published upon invi­ tation. •

The (Ihicf Editor

Aims and Scope Pertanika Journal of Science and Technology welcomes full papers and short communications in English or Bahasa Melayu in the fields of chemistry, physics, mathematics and statistics, engineering, environmental control and manage­ ment, ecology and computer science. It will be published twice a year in January and July.

Pertanika Journal of Science and Technology

Universiti Putra Malaysia 43400 UPM Serdang, Selangor Darul Ehsan MALARIA Tel: 9486101 Ext: 1325; Fax (60S) 9483745 •

Articles must be reports of research not previously or simultaneously published in other scientific or technical journals. Communications are notes of a significant finding intended for rapid publication. It should not exceed five double spaced typewritten pages and must be accompanied by a letter from the author justifying its publication as a communication.

EDITORIAL BOARD

Submission of Manuscript Three complete clear copies of the manuscript are to be submitted to

Proofs and Offprints Page proofs illustration proof, the copy-edited manuscript and an offprint order form will be sent to the author. Proofs ,must be checked very carefully within the specified time as they will not be proofread by the Press editors. Authors will receive 20 offprints of each article. Additional copies can be ordered from the Secretary of the Editorial Board by filling out the offprint order form.

INTERNATIONAL PANEL MEMBERS |

Prof. Dr. Mohamed Suleiman - Chief Editor Faculty of Science and Environmental Studies

Prof. D.J. Evans Parallel Algorithms Research Centre

Prof. Abang Abdullah Abang Ali Faculty of Engineering

Prof. F. Halsall University College of Swansea

Assoc. Prof. Dr. Low Kun She Faculty of Science and Environmental Studies

Prof. S.B. Palmer University of Warmick

Assoc. Prof. Dr. Mohamad Ismail Yaziz Faculty of Science and Environmental Studies

Prof. Dr. Jerry L. Mc Laughlin Purdue University

Dr. Mansor Hashim

Prof. Dr. John Loxton MacQuarie University

Faculty of Science and Environmental Studies Dr. Isa Daud Faculty of Science and Environmental Studies Assoc. Prof. Dr. Abu Talib Othman Faculty of Science and Environmental Studies Sumangala Pillai - Secretary Universiti Pertanian Malaysia Press

Prof. U A . Th. Brinkman Vrije Universiteit Prof. A.P. Cracknell University of Dundee Prof. AJ. Saul University of Sheffield Prof. Robert M. Peart University of Florida Prof. J.N. Bell Impherial College of Science, Technology and Medicine Prof. Yadolah Dodge University De Neuchatel Prof. W.E. Jones University of Windsor

Published by Universiti Putra Malaysia Press ISSN No: 0128-7680 Printed by: Medan Press Sdn. Bhd.

Prof. A.K. Kochar UMIST

Pertanika Journal of Science & Technology Volume 5 No. 1 1997 Contents

Equilibrium Relative Humidity-Equilibrium Moisture Content Isotherms of O i l Palm Kernels - Muhammad Hakimi Ibrahim, Wan Ramli Wan Daud, Mohd Shihabuddin Ismail and Meor Zainal Meor Talib Kesan Pelarut Terhadap Pemalar O p t i k Larutan Organik Laser Dye - W. Mahmood Mat Yunus dan Zulkifly Man Thermal Conductivity o f Carbon Pellets Prepared from O i l Palm Bunches - Mohamad Deraman and Ramli Omar Characterization o f Fine and Coarse Atmospheric Aerosols i n Kuala L u m p u r - M. Rashid, A. Rahmalan and A. Khalik Pendekatan Ionik dalam Menulis Struktur Lewis - Wan-Yaacob Ahmad dan Mat B. Zakaria Solution Properties o f Polysaccharides from Anacardium occidentals - Mat B. Zakaria, Zainah Ab. Rahman and Nik Noor Aini Nik Mahmood Confidence Intervals for Parallel Systems with Covariates - Ayman Baklizi, Isa Daud and Noor Akma Ibrahim A Natural Dye in a Mesophase Region o f Cetyltrimethylammonium Bromide/Octan-l-ol/Water System - Hamdan Suhaimi, Faujan B.H. Ahmad, Mohd Zaizi Desa and Laili Che Rose Peleraian Buah Sawit dari Tandan Menggunakan Kaedah Kimia - Desa Ahmad, Hishamuddin Jamaludin dan Gan Leng Sim Chemical Constituents o f Vitex ovata (Verbenaceae) - Irmawati Ramli, Ahmad Sazali Hamzah, Norio Aimi and Nordin Hj. Lajis Prediction and Determination o f Undrained Shear Strength o f Soft Clay at Bukit Raja - Jamal Mohd. Amin, Mohd. Raihan Taha, Jimjali Ahmed, Azmi Abu Kassim, Azmi Jamaludin and Jamilah Jaadil

ISSN:0128-7680 © Penerbit Universiti Pertanian Malaysia

Pertanika J. Sci. & Technol. 5(1): 1-6 (1997)

Equilibrium Relative Humidity-Equilibrium Moisture Content Isotherms of Oil Palm Kernels 2

Muhammad Hakimi Ibrahim, Wan Ramli Wan Daud, Mohd Shihabuddin Ismail and Meor Zainal Meor Talib 2

2

Pusat Pengajian Teknologi Industri Universiti Sains Malaysia 11800; Minden, Pulau Pinang, Malaysia 2

Jabatan Kejuruteraan Kimia & Proses Universiti Kebangsaan Malaysia 43600 UKM Bangi, Selangor, Malaysia Received 2 October 1993

ABSTRAK Lengkung sesuhu kelembapan nisbi keseimbangan-kandungan lembapan keseimbangan ( E R H - E M C ) atau lengkung sesuhu lembapan pepejal penting dalam pengeringan, pencampuran pepejal, pembungkusan dan storan bahan tersebut. Lengkung sesuhu E R H - E M C kernel kelapa sawit ditentukan dengan menggunakan sebuah kebuk sekitaran malar untuk beberapa gabungan kelembapan nisbi (30%-90%) dan suhu udara (30° 70°C). Lengkung sesuhu ini dapati memadani persamaan-persamaan Hasley dan Henderson.

ABSTRACT Equilibrium relative humidity-equilibrium moisture content ( E R H - E M C ) or moisture isotherms of solids is important in the drying, solid mixing, packaging and storage of such material. E R H - E M C isotherms of oil palm kernels are determined by using a constant environmental chamber for several combinations of air relative humidity (30-90%) and temperature (30-70°C). The isotherms are found to fit the Hasley and Henderson equations well. Keywords: equilibrium relative humidity, equilibrium moisture content, isotherms, oil palm kernels

INTRODUCTION E q u i l i b r i u m moisture content and e q u i l i b r i u m relative h u m i d i t y relation­ ship or sorption and desorption isotherms are used i n post-harvest processes and the food industry for a n u m b e r o f purposes, w i t h d r y i n g , m i x i n g , packaging and storage being the m a i n fields o f application (Gal 1983). I n d r y i n g operations desorption isotherms determine the lowest possible moisture content attainable at the process temperature. D e t e r m i n a t i o n o f

Muhammad Hakimi Ibrahim, Wan Ramli Wan Daud, Mohd Shihabuddin Ismail and Meor Zainal Meor Talib

the E R H - E M C isotherms has become a very c o m m o n practice i n food laboratories due to an increased awareness o f its i m p o r t a n c e for characterizing the state o f water i n foods, namely its availability for biological, physical, and chemical changes (van den Berg and B r u i n 1978; Rockland and Nishi 1980). Brooker et al. (1974) observed that moisture sorption and desorption characteristics o f a material are influenced by many factors such as the origin, composition, and history o f the material and the methodology o f measurement. Speiss and W o l f (1983) concluded that E R H - E M C isotherms of the same material from different sources usually differ widely and are comparable only w i t h qualification. Different objectives i n measuring the isotherms complicate the issue further, and have resulted i n a great variety of measurement methods. G r a v i m e t r i c , manometric and h y g r o m e t r i c procedures for obtaining the isotherms have been well described i n detail by various workers such as T a y l o r (1961), Toledo (1973), L a b u z a (1974), Gal (1975, 1983), T r o l l e r and Christian (1978), and Neuber (1981). Attempts to define a microcrystalline cellulose ( M C C ) as a reference material, a reference method and thus a reference isotherm as reported by Speiss and W o l f (1983) have been o f l i m i t e d success because o f the need to use standard equipment. G a l (1983) argued that isotherms o f other workers should not be used unless all relevant data are d u l y quoted and there is a close correspondence between the substance for w h i c h the isotherm had been determined and that to w h i c h i t is applied. T h i s c o n d i t i o n is h a r d l y ever fulfilled and a p p l i c a t i o n oriented s o r p t i o n / d e s o r p t i o n i s o t h e r m measurement by laboratories involved i n the application o f such data has become more i m p o r t a n t . E q u i l i b r i u m between the ambient and the sample is achieved either by the static method where the sample is allowed to come to e q u i l i b r i u m i n still moist air or by the dynamic method where the air is mechanically moved. The static method has been used extensively i n the past, b u t its m a i n drawback is the relatively long e q u i l i b r a t i o n time o f up to several weeks. Furthermore at high relative h u m i d i t y and temperature, samples o f biological material, especially agricultural products, may become m o u l d y before equilibrium is attained. T h e dynamic method is faster and is thus to be preferred. The desorption data are fitted to the Hasley's and Henderson's equations. Hasley's equation (Hasley 1948; Iglesias et al. 1975) is given by

where y

e

2

is the E R H , X

e

is the E M C and A

Y

and A

Pertanika J. Sci. & Technol. Vol. 5 No. 1, 1997

2

are

constants.

Equilibrium Relative Humidity-Equilibrium Moisture content Isotherms of Oil Palm Kernels

Henderson's equation (Henderson 1952) is given by

l-y

e

=

exp[-B X?>] 2

(2)

where B\ and B are constants. T h e choice o f the use o f these t w o equations instead o f m u c h more recent ones is determined by the ease i n w h i c h the constants can be determined. T h e constants are estimated by using a least square fitting a l g o r i t h m . T h e aptitude o f each equation is evaluated by using the mean relative percentage modulus, E, w h i c h is defined by 2

(3) w h e r e y ( ) 2i\\c\y are respectively the experimental and the predicted values o f the e q u i l i b r i u m relative h u m i d i t y and N is the n u m b e r o f experimental data. e

meas

e(cal)

MATERIALS AND METHODS E q u i l i b r i u m between the air and the sample was achieved by using an envi­ ronmental chamber ( I S U Z U model (i-2501); air at approximately 1 m/s was forced a r o u n d the sample for about 24 h at fixed relative air h u m i d i t y and temperature. T h e w o r k i n g range for air relative h u m i d i t y and temperature was 20-90% and 3 0 - 7 0 ° C respectively. T h e size o f o i l p a l m kernels used was o f the range 11.2-12.5 m m . After the completion o f the e q u i l i b r a t i n g period, the e q u i l i b r i u m moisture content o f the sample was determined according to the A S A E S352.2; a p p r o x i m a t e l y 10 g o f the sample i n five replicates were dried i n an electric oven at 103°C for 72 h .

RESULTS AND DISCUSSION I t is observed that e q u i l i b r i u m i n the constant e n v i r o n m e n t a l chamber is approached after about 16 h . A l l desorption experiments are carried over a time interval o f 16 h to ensure e q u i l i b r i u m is reached before measurements are made. Fig. 1 and 2 show the desorption isotherms o f oil p a l m kernels at 3 0 - 7 0 ° C fitted w i t h Hasley's and Henderson's models respectively. Both graphs depict the typical sigmoid shape w h i c h indicates multi-layers adsorption o f water i n a macroporous material. Both Hasley's and Henderson's models show better fit at temperatures of 40 and 3 0 ° C compared to higher temperatures. T h i s trend can be seen i n T a b l e 1 where the relative deviations are tabulated against all the temperatures. T h i s phenomenon could be accounted for by kernel o i l losses at higher temperatures because o i l can be seen exuding from the sample at these temperatures.

PertanikaJ. Sri. & Technol. Vol. 5 No. I , 1997

•i

Muhammad Hakimi Ibrahim, Wan Ramli Wan Daud, Mohd Shihabuddin Ismail and Meor Zainal Meor Talib

0.01

0.03

0.05

0.07

0.09

0.11

0.13

0.15

EMC (kg/kg )

+ 70*c

3

sere • 5C1—•Br—•S—>N kerana keafinan elektron yang meningkat mengarah kepada penjuru atas sebelah kanan j a d u a l berkala (Jadual 1). E m p a t unsur tapak kepada segitiga enam unsur tadi pada pepenjuru C—>P—•Se—>I j u g a m e n y u m b a n g kepada anion-anion sebatian ionik tetapi pada tahap yang agak rendah.

2

Satu pasangan elektron bukan pengikatan atau pasangan pencil yang selama ini ditandakan sebagai dua titik atau dua pangkah, boleh diwakilkan oleh satu garisan pendek sendeng kepada sesuatu atom seperti yang pernah dipakai oleh Eberlin and Monroe (1982), Pardo (1989) dan Ahmad Omar (1992). Garisan-garisan itu boleh disambung membentuk sesiku bersudut jika terdapat lebih daripada satu pasangan elektron bukan ikatan atau pasangan pencil bagi mcmpcrccpatkan lagi proses pcnulisan.

PertanikaJ. Sci. 8c Technol. Vol. 5 No. 1, 1997

45

Wan-Yaacob Ahmad dan Mat B. Zakaria

Kesemua sepuluh unsur d i atas j u g a merupakan segitiga dengan unsur sulfur terletak d i tengahnya. Unsur hidrogen j u g a m e n y u m b a n g kepada anion (hidrida) tetapi ia berada d i luar segitiga i n i . Gabungan antara anion-anion i n i dan kation pada nisbah tertentu hingga j u m l a h cas-cas berlawanan adalah sifar, memberikan formula sebatian ionik. S t r u k t u r sebatian ionik apabila semua elektron petala luar anionnya d i t u n j u k k a n dipanggil struktur Lewis sebatian tersebut. JADUAL1 Anion monoatom yang biasa ditemui dalam sebatian ionik binari Kala\Kumpulan

1

1 2 3 4 5

H'

14

4

c-

15

3

*N -

16

2

os2

2

17

F

cr

Se -

r ASPEK IONIK DALAM SPESIES KOVALEN

M o l e k u l atau ion poliatom diketahui terbit daripada perpaduan d i antara unsur-unsur bukan logam yang diketahui m e m p u n y a i ciri keafinan elektron tinggi dan keupayaan pengionan rendah. O l e h i t u atom-atom i n i , apabila bergabung membentuk spesies kovalen, t i d a k menerima serta t i d a k melepaskan sepenuhnya elektron-elektron valensi mereka. Sebaliknya elektron-elektron i n i dikongsikan d i kalangan atom-atom d a l a m bentuk pasangan-pasangan elektron ikatan. U n t u k mengatasi masalah tolakan elektrostatik d i antara dua elektron yang bercas sama d a l a m ikatan kovalen, setiap elektron mengambil keadaan spin berlawanan d i samping ia tertarik kepada kedua-dua nukleus berjiran seperti yang disarankan oleh teori L e w i s . U n t u k m e m e n u h i k e p e r l u a n p e r a t u r a n o k t e t A b e g g , sebahagian daripada elektron valensi atom-atom kovalen tertentu terpaksa mengambil peranan sebagai pasangan pencil. Selain i t u , k e t u m p a t a n elektron ikatan yang menyambungkan dua atom t i d a k l a h terbahagi sama rata dalam kesemua ikatan. Bagi ikatan antara dua atom yang berbeza, ketumpatan elektron adalah lebih b e r t u m p u ke arah atom yang lebih kuat menarik pasangan elektron ikatan i a i t u a t o m elektronegatif. I k a t a n sebegini dikatakan mempunyai ciri ionik dengan atom elektronegatif m e m i l i k i k u t u b separa negatif sementara atom yang satu lagi b e r k u t u b separa positif. J i k a diteliti .spesies-spesies kovalen tak organik ringkas, h a m p i r semua atom penyumbang terutamanya atom-atom yang mengelilingi atom pusat, datang daripada unsur hidrogen dan sepuluh unsur penjuru atas sebelah kanan j a d u a l berkala dalam segitiga C — > N — > 0 — > F — • C I — > B r — > C 46

Pertanika J. Sci. &Technol. Vol. 5 No. 1, 1997

Pendekatan Ionik dalam Menulis Struktur Lewis

dengan a t o m S berada d i tengahnya. Sebagai contoh perhatikan molekul atau ion kovalen (atom yang bergaris adalah atom pusat) N H , H C O , C O S , NCS", N O C 1 , F N 0 , N N O , O O O , A1F ", P B r , N S F , C1F , C 1 0 , BrF ~, I F , I I I " , IOF5, X e O F , C r 0 C l dan sebagainya. Selain daripada i t u , tolak atom duplet hidrogen, semua atom yang mengelilingi atom pusat adalah menepati peraturan oktet Abegg d a l a m semua struktur Lewis mereka i a i t u mereka m e n u n j u k k a n persekitaran l a p a n a t a u empat pasangan elektron berbentuk pasangan elektron ikatan dan pasangan pencil. Pada pihak lain, atom pusat ada yang m e m a t u h i peraturan oktet Abegg, ada yang berkeadaan pra-oktet dan ada pula yang m a m p u mencapai keadaan pasca-oktet, bergantung kepada kedudukan atom pusat d i d a l a m j a d u a l berkala. 3

2

3

2

4

6

7

4

2

3

3

4

2

M e n g i k u t pendekatan tradisi, struktur Lewis molekul neutral atau ion p o l i a t o m d i l i h a t sebagai datang daripada pempasangan elektron-elektron valensi d i antara atom-atom neutral atau antara atom-atom neutral dan ion-ion m o n o a t o m . Berikutnya, struktur Lewis spesies kovalen boleh j u g a dianggap sebagai d a t a n g daripada gabungan d i antara ion-ion monoatom, i a i t u k a t i o n dan anion m o n o a t o m . Syaratnya ialah penjumlahan cas i o n ion p e n y u m b a n g mestilah sama dengan cas bersih spesies kovalen. O l e h sebab atom-atom yang mengelilingi atom pusat spesies kovalen sentiasa m e m a t u h i peraturan oktet Abegg dan u m u m n y a merupakan atom-atom yang p a l i n g elektronegatif serta b e r k u t u b separa negatif maka semasa menerbitkan struktur Lewis spesies kovalen tersebut mereka wajar d i l i h a t sebagai anion seperti yang lazim d i t e m u i d a l a m sebatian ionik. J a d i atom sulfur yang berada d i bawah atom oksigen d a l a m k u m p u l a n 16, j i k a ia w u j u d sebagai atom luar spesies kovalen, d i l i h a t sebagai ion oktet sulfida sementara a t o m C I , Br, I sebagai klorida, b r o m i d a , iodida kerana mereka berada d i bawah unsur fluorin d a l a m k u m p u l a n 17. A t o m pusat yang biasanya datang daripada unsur-unsur yang lebih

2

I SI " ICli" Sulfida Klorida

IBri" ill* Bromida Iodida

elektropositif d i l i h a t sebagai kation. K a t i o n atom pusat m e n g a m b i l nilai cas tersendiri i a i t u apabila ia d i j u m l a h k a n dengan cas-cas anion akan menghasilkan cas bersih spesies kovalen yang sedang d i t u m p u k a n . J i k a nilai cas positif kation adalah sama dengan bilangan elektron valensi atom pada keadaan neutral maka atom pusat tersebut tidak m e m p u n y a i sebarang elektron valensi yang tinggal. Satu pasangan elektron valensi masih terdapat pada kation atom pusat apabila nilai cas positif kation adalah dua u n i t k u r a n g daripada bilangan elektron valensi a t o m sama d a l a m keadaan n e u t r a l . Pasangan-pasangan elektron valensi pada k a t i o n i n i akan Pertanika J . Sci. & Technol. Vol. 5 No. 1, 1997

47

Wan-Yaacob Ahmad dan Mat B. Zakaria

menjelma sebagai pasangan pencil pada atom pusat d a l a m struktur Lewis akhir sesuatu molekul atau ion poliatom. Cas-cas positif pada kation a t o m pusat dan cas-cas negatif pada atom pengeliling yang diperolehi j i k a a t o m pusat adalah lebih elektropositif adalah sama dengan nombor atau keadaan pengoksidaan a t o m - a t o m kovalen d a l a m m o l e k u l n e u t r a l a t a u i o n poliatom. Pengkoordinatan satu pasangan elektron daripada setiap anion kepada k a t i o n a t o m pusat menyebabkan a t o m - a t o m l u a r d a n a t o m pusat bersambung dengan ikatan sigma (a). K e m u n c u l a n setiap ikatan a akan meneutralkan seunit cas berlawanan i a i t u satu cas positif kation atom pusat dan satu cas negatif anion atom pengeliling. A t o m pusat dengan beberapa pasangan elektron, atau sebaliknya, sekarang bercas f o r m a l lebih rendah daripada cas kation asal sebanyak bilangan anion yang terbabit atau sebanyak bilangan ikatan a yang dibentuk. A t o m - a t o m luar sekarang yang mempunyai tiga pasangan elektron dan satu ikatan a masih menepati keadaan oktet Abegg serta bercas formal satu u n i t kurang negatif daripada cas anion asal. Struktur spesies kovalen yang menunjukkan ikatan-ikatan a dan pasangan-pasangan elektron bukan pengikatan hasil daripada proses d i atas dinamakan struktur elektron asas bagi spesies kovalen tersebut. 3

LANGKAH-LANGKAH MENDAPATKAN STRUKTUR E L E K T R O N ASAS SPESIES KOVALEN Berdasarkan perbincangan d i d a l a m bahagian sebelum i n i , d i p e r t u r u n k a n ringkasan langkah-langkah yang perlu d i i k u t i u n t u k memperolehi struktur elektron asas sesuatu molekul atau ion p o l i a t o m sebatian tak organik ringkas: (.1) M u l a - m u l a kenalkan atom pusat spesies kovalen tersebut. A t o m pusat biasanya terdiri daripada unsur tunggal yang elektropositif. A t o m atom yang mengelilingi atom pusat yang merupakan unsur elektronegatif N , O , S, F, C I , Br, I d i l i h a t masing-masing sebagai ion n i t r i d a (cas 3-); oksida, sulfida (cas 2-); fluorida, klorida, b r o m i d a , iodida (cas 1-). A t o m hidrogen yang berikatan terus kepada atom pusat d i l i h a t sebagai ion hidrida (cas 1-).

Cas ionik ialah cas pada ion monoatom atau cas bersih pada ion poliatom. Setiap unit cas adalah setara dengan cas proton atau elektron yang bernilai ± 1 . 6 0 x 10" C . Cas formal adalah cas kiraan bagi atom-atom yang berikatan kovalen antara mereka. Pasangan elektron bukan pengikatan dianggap kepunyaan atom tempat ia melekat. Hanya satu daripada dua elektron ikatan adalah kepunyaan atom tadi. Jadi, atom tersebut mempunyai elektron daripada jumlah ikatan dan semua elektron bukan pengikatan yang terdapat padanya. Atom kovalen bercas formal seunit positif atau negatif jika ia mempunyai elektron yang kurang atau lebih seunit daripada atom itu sendiri dalam keadaan bebas dan neutral. 19

48

Pertanika J. Sci. & Technol. Vol. 5 No. 1, 1997

Pendekatan Ionik dalam Menulis Struktur Lewis

(2) A t o m pusat sebagai kation m e m p u n y a i cas yang apabila d i j u m l a h k a n dengan cas-cas anion d a l a m (1) mestilah sama dengan cas bersih spesies kovalen. Sama ada kation atom pusat m e m p u n y a i pasangan elektron atau sebaliknya bergantung kepada bilangan elektron valensi yang dikeluarkan daripada atom neutralnya. (3) K a t i o n atom pusat dengan pasangan elektron atau sebaliknya memperolehi semula ikatan a melalui pengkoordinatan pasangan elektron daripada anion-anion. Cas positif kation atom pusat dan cas negatif anion a t o m pengeliling akan terneutral seunit bagi setiap ikatan a yang dibentuk. A t o m - a t o m luar (kecuali H) sekarang m e m p u n y a i satu ikatan a dan tiga pasangan elektron b u k a n pengikatan. S t r u k t u r spesies kovalen yang d i perolehi hingga langkah i n i d i n a m a k a n struktur elektron asas spesies kovalen. J u m l a h ikatan a dan pasangan elektron pada sesuatu a t o m pusat struktur elektron asas sesuatu spesies kovalen dengan cepat dapat memberi tahu jenis o r b i t a l h i b r i d yang dipakai oleh a t o m pusat u n t u k b e r t i n d i h dengan o r b i t a l a t o m pengeliling bagi membentuk ikatan a i t u sendiri. Pasangan elektron pula akan berada d i d a l a m o r b i t a l h i b r i d sebagai pasangan pencil. A t o m pusat struktur elektron asas m e m p u n y a i o r b i t a l h i b r i d sama ada sp, sp , sp , sp d atau sp d j i k a ia m e m p u n y a i j u m l a h ikatan o dan pasangan elektron sebanyak 2,3,4,5 atau 6. K e h a d i r a n ikatan p i (n) d i atas ikatan a struktur elektron asas t a d i adalah bergantung kepada beberapa perkara lain yang akan dijelaskan k e m u d i a n d a l a m bahagian contoh penulisan struktur Lewis m o l e k u l neutral atau ion p o l i a t o m . Bagi m e m u d a h k a n perbincangan selanjutnya, spesies kovalen akan dikelaskan berdasar kepada kedudukan atom pusat d i d a l a m j a d u a l berkala. A t o m pusat molekul neutral atau i o n p o l i a t o m terbahagi kepada empat kategori i a i t u (1) spesies kovalen dengan atom pusat t e r d i r i daripada unsur baris pertama k u m p u l a n 14, 15 d a n 16, i a i t u C, N d a n O ; (2) spesies kovalen dengan atom pusat daripada unsur k u m ­ p u l a n 2 dan 13; (3) spesies kovalen dengan a t o m pusat daripada unsur baris kedua dan ke atas d i antara k u m p u l a n 14-18; d a n (4) spesies kovalen dengan atom pusat yang t e r d i r i daripada unsur logam peralihan.

CONTOH-CONTOH PENULISAN STRUKTUR LEWIS SPESIES K O V A L E N A. Spesies Kovalen Dengan Atom Pusat Unsur C, N dan 0 A t o m gas nadir neon d i h u j u n g kanan baris pertama d a l a m k u m p u l a n 18 j a d u a l berkala tidak membentuk entiti kovalen dengan mana-mana unsur kerana ia m e m i l i k i konfigurasi elektron oktet (4-pasangan) yang cukup stabil d i samping m e m p u n y a i saiz yang kecil. U n s u r fluorin yang berada sebelah k i r i neon d a l a m k u m p u l a n 17, atas ciri monovalensinya seperti PertanikaJ. Sci. 8c Technol. Vol. 5 No. 1,

1997

49

Wan-Yaacob Ahmad dan Mat B. Zakaria

unsur hidrogen, membentuk satu ikatan a sahaja dengan m e n g a m b i l ked u d u k a n luar molekul atau ion poliatom. A t o m hidrogen dan fluorin tidak pernah bertindak sebagai atom pusat d i dalam mana-mana spesies kovalen. A t o m - a t o m polivalensi C, N dan O daripada baris pertama d i d a l a m k u m p u l a n 14, 15 dan 16 membentuk pusat d i d a l a m banyak molekul atau ion poliatom, misalnya C H , C C 1 , C O , H C N , H C O , C O C l , C 0 , C S , COS, N C O " , NCS", C 0 " , N H , N C 1 , N H " , N H , N O , N O F , N O F , NOC1, N 0 , C N O , F N 0 , N 0 C 1 , N 0 , N N O , NNN~, N 0 , H N 0 , H 0 , H 0 , F 0, OOO. 4

4

2

2

2

+

3

3

3

2

2

2

+

4

3

+

2

2

2

2

3

3

+

2

3

2

Contoh 1: CH4 Setiap satu daripada empat atom H molekul gas metana C H d i l i h a t sebagai ion h i d r i d a . Bagi mengimbangi cas bersih sifar molekul metana, a t o m C d i l i h a t sebagai bercas 4 + . Pada keseluruhannya, molekul metana berada sebagai ion C : 4H". Cas-cas pada atom C dan H bagi ion C : 4 H " bukan merupakan keadaan/nombor pengoksidaan masing-masing atom dalam C H kerana atom luar H adalah kurang elektronegatif daripada atom pusat C. A t o m C metana adalah berkeadaan pengoksidaan songsang 4 - dan atom H adalah 1 + . I o n C d i dalam ion C : 4 H " tidak mempunyai sebarang elektron valensi yang tertinggal kerana semua empat elektron valensi atom C neutral dikeluarkan. Pengkoordinatan setiap pasangan elektron pada ion h i d r i d a kepada ion C menghasilkan struktur elektron asas molekul C H (1) yang mempunyai empat ikatan a karbonhidrogen. A t o m C dengan 4 pasangan elektron pengikatan m e m i l i k i empat orbital h i b r i d sp . Struktur 1 yang tidak m e m p u n y a i sebarang cas f o r m a l merupakan struktur Lewis bagi C H . A t o m C d a l a m struktur 1 m e m p u n y a i persekitaran elektron4 oktet neon sementara atom-atom H pula menyerupai konfigurasi duplet helium. 4

4 +

4 +

4

4 +

4 +

4 +

4

3

4

H

H

I

109.25* I

H-C—H H

1

;?C~H H

1.091 A 2

Kesemua empat ikatan a karbon-hidrogen m e m p u n y a i panjang sama iaitu 1.091 A ( K e n n a r d 1982). Bagi menurunkan tolakan elektrostatik empat ikatan a C - H ke tahap m i n i m u m , masing-masing ikatan C - H akan mengarah ke penjuru-penjuru tetrahedron sempurna dengan sudut H - C - H 109.25° seperti dalam struktur 2.

50

Pertanika J . Sci. & Technol. Vol. 5 No. 1, 1997

Pendekatan Ionik dalam Menulis Struktur Lewis

Contoh 2: 0

3

M o l e k u l ozon 0

banyak terdapat d i kawasan stratosfera

3

dan

berfungsi

menyerap cahaya u l t r a l e m b a y u n g tenaga tinggi yang boleh mengakibatk a n kanser k u l i t d a r i p a d a sampai ke permukaan b u m i . D u a atom O luar molekul 0

3

dianggap berupa oksida yang m e m p u n y a i j u m l a h cas 4-. O l e h

i t u , a t o m pusat O ozon adalah bercas 4 + bagi menghasilkan molekul yang tidak bercas. Sekarang m o l e k u l ozon boleh d i l i h a t sebagai ion 0

4

+

:

2

20 ".

A t o m pusat d a n a t o m luar ozon dengan atom sama tidak m e m p u n y a i n o m b o r pengoksidaan daan sifar. I o n 0

4

+

4 4- dan 2-. A t o m - a t o m i n i berkeadaan pengoksi-

adalah kekurangan empat elektron daripada atom O

neutral yang m e m p u n y a i 6 elektron valensi. J a d i ia masih

mempunyai

sepasang elektron valensi. J i k a semua pasangan elektron d i t u n j u k k a n , i o n 0

4

+

2i oi

2

: 2 0 " adalah seperti d a l a m struktur 3. 4*

2-

51 oi

3

> |j

u

\o—o—q\

N

11

\o—o=o>

4

Pengkoordinatan

II

]

'

( o = o — o j

5

_ (0=0=0)

6

7

satu pasangan elektron daripada setiap ion oksida

struktur 3 kepada ion 0 4 + membentuk i k a t a n a struktur 4 dengan cas 2oksida t u r u n kepada cas

formal

1-, manakala cas 4 +

pusat 0

4

+

turun

kepada cas formal 2 + . Pusat s t r u k t u r elektron asas ozon (4) dengan satu pasangan tidak berikatan dan 2 i k a t a n a ( j u m l a h 3 pasangan elektron) 2

m e m p u n y a i tiga o r b i t a l h i b r i d sp d i d a l a m petala valensi 2. O l e h sebab satu o r b i t a l 2s dan dua o r b i t a l 2p a t o m O d i h i b r i d k a n u n t u k memberikan 2

o r b i t a l sp , a t o m O pusat struktur 4 yang bercas formal 2 + masih m e m i l i k i satu o r b i t a l 2p kosong. Pergerakan satu pasangan elektron daripada a t o m O luar s t r u k t u r 4 ke arah atom O pusat d a r i arah kanan atau k i r i meng­ hasilkan satu i k a t a n % dan melibatkan peneutralan

seunit cas setentang

m e m b e r i k a n struktur 5 dan 6. Perubahan daripada

struktur 4 kepada

struktur 5 atau 6 menukar atom O pusat daripada keadaan elektron sekstet kepada keadaan oktet. S t r u k t u r semua oktet 5 dan 6 adalah struktur Lewis bagi 0 . Satu pasangan elektron pada a t o m O bercas formal 1- s t r u k t u r 5 3

dan 6 tidak boleh d i k o o r d i n a t k a n seterusnya kepada a t o m O pusat bercas formal 1 + kerana o r b i t a l - o r b i t a l kosong a t o m pusat berada d a l a m petala 3 tenaga tinggi m e l i b a t k a n o r b i t a l 3s3p3d. J i k a keadaan sebaliknya berlaku, s t r u k t u r 5 dan 6 bertukar kepada s t r u k t u r 7. S t r u k t u r Lewis ozon (5 dan 6) dengan a t o m pusat sama-sama m e m ­ p u n y a i satu pasangan elektron pencil serta dua pasangan elektron ikatan a tetapi berbeza d a r i segi kedudukan ikatan n d i antara a t o m pusat d a n a t o m luar serta j u g a berbeza t a b u r a n pasangan elektron b u k a n pengikatan pada a t o m - a t o m luar d i n a m a k a n struktur resonans bagi molekul ozon. Panjang ikatan O - O

1.278 A d i d a l a m molekul 0

3

yang lebih rendah

PertanikaJ. Sci. & Technol. Vol. 5 No. 1, 1997

daripada 51

Wan-Yaacob Ahmad dan Mat B. Zakaria

2

panjang ikatan tunggal O - O d i dalam ion 0 ~ (1.49 A) ataupun d a l a m H 0 (1.48 A) m e m b u k t i k a n bahawa molekul ozon tidak boleh d i w a k i l i oleh struktur elektron asas berikatan tunggal 4. Panjang ikatan O - O (1.278 A) dalam ozon yang melebihi panjang ikatan dubel d a l a m 0 (1.208 A) pula menunjukkan bahawa struktur semua ikatan dubel 7 j u g a tidak sesuai mewakili molekul ozon. L a g i p u n kita tahu bahawa atom pusat O d i d a l a m struktur 5 dan 6 mempunyai orbital 3s3p3d kosong yang m e m p u n y a i tenaga lebih tinggi daripada tenaga o r b i t a l valensi 2s2p yang dipakai u n t u k membentuk konfigurasi elektron pada atom O pusat struktur 5 dan 6. Fakta perbezaan tenaga yang besar i n i j u g a menyebabkan a t o m pusat daripada unsur C, N atau O hanya berkeadaan oktet sepenuhnya, dengan orbital h i b r i d sama ada sp, sp ataupun sp . Panjang ikatan O - O 1.278 A d i dalam 0 yang h a m p i r sama panjang dengan ikatan tertib 1.5 d a l a m 0 " (1.26 A) dan terletak d i antara panjang ikatan tertib 1 ( 0 ~ ; 1.49 A) dan tertib 2 setara ( 0 ; 1.208 A) ( K e n n a r d 1982) menyokong kuat kewujudan tertib ikatan 1.5 bagi ikatan O - O d i dalam ozon. 2

2

2

2

2

3

3

2

2

2

2

O l e h sebab kedua-dua struktur resonans 5 dan 6 adalah bersimetri cermin maka masing-masing struktur memberikan sumbangan yang sama kepada struktur resonans h i b r i d ozon. Berikutan i t u , setiap satu daripada dua segmen kanan dan k i r i struktur 5 dan 6 adalah d i w a k i l i oleh satu ikatan tunggal dan satu ikatan dubel. O l e h i t u setiap satu daripada dua ikatan O - O d i dalam ozon mengambil tertib ikatan purata (1 + 2 ) / 2 = 1.5 sebagai struktur h i b r i d resonannya. Dengan mengambil purata, atom O pusat struktur h i b r i d daripada dua struktur resonans 5 dan 6 adalah bercas formal ( l + l ) / 2 = 1 + sementara setiap atom O luar m e m p u n y a i cas formal purata (-1 + 0 ) / 2 = 1/2-. Sama j u g a hujung-hujung O struktur 5 dan 6 m e m p u n y a i purata elektron bukan pengikatan (4 + 6)/2 = 5 elek­ tron, manakala pusat O pula adalah (2 + 2)/2 = 2 elektron. M o l e k u l ozon boleh dibayangkan sebagai m e m p u n y a i struktur h i b r i d resonans 8 dengan setiap ikatan O - O m e m p u n y a i satu ikatan a dan satu ikatan 0.5K, sementara atom O tengah dengan satu pasangan pencil, dua ikatan a, dan dua ikatan 0.571 adalah bercas formal 1 + manakala masing-masing a t o m O luar dengan l i m a elektron bukan pengikatan, satu ikatan a, dan satu ikatan 0.57t adalah bercas formal 1/2-. Kesemua atom O struktur h i b r i d 8 bagi ozon masih berkeadaan oktet seperti struktur penyumbang 5 dan 6.

15.

L

2

7

8

A

^o-

*^Tj^Oj*

8

116.8*

(

mewakili ikatan O.Stc)

9 K e w u j u d a n satu pasangan pencil dan dua ikatan tertib 1.5 pada atom O pusat struktur h i b r i d resonans ozon 8 menyebabkan molekul ozon ber52

Pertanika J . Sci. & Technol. Vol. 5 No. 1, 1997

Pendekatan Ionik dalam Menulis Struktur Lewis

bentuk bengkok (struktur 9) dengan sudut i k a t a n O - O - O 116.8° ( K e n n a r d 1982) u n t u k mencapai tolakan elektrostatik yang m i n i m u m .

Kedua-dua

i k a t a n O - O tertib 1.5 adalah sama panjang i a i t u 1.278 A. N a m p a k n y a pasangan pencil pada a t o m O pusat ozon berada d a l a m r u a n g o r b i t a l 2

h i b r i d sp

yang lebih besar daripada r u a n g gabungan satu i k a t a n a dan

satu i k a t a n 0.57C (tiga elektron) bagi setiap satu daripada dua i k a t a n O - O yang menghala ke penjuru-penjuru satah trigon sehingga pasangan pencil mengenakan tolakan elektrostatik yang lebih kuat. A k i b a t n y a sudut ikatan O - O - O m o l e k u l bengkok ozon 0

3

mengecut 3.2° daripada sudut satah

trigon sempurna 120°. S t r u k t u r h i b r i d 9 bagi ozon m e m p u n y a i kelemahan tersendiri d a r i segi kewujudan " d w i r a d i k a l " pada masing-masing s t r u k t u r kanonik yang sepat u t n y a m e m b a w a kepada kehadiran sifat paramagnetisme. O z o n d i k e t a h u i tidak m e m p u n y a i sifat paramagnetisme. tersebut dapat menerangkan

W a l a u bagaimanapun,

struktur

ciri sudut i k a t a n dan panjang i k a t a n ozon

seperti yang dijelaskan sebelum i n i . I a j u g a dapat menjelaskan

pemben-

t u k a n bahan perantara molozonida daripada penambahan ozon ke atas i k a t a n dubel C = C secara b u k a n ionik tidak seperti j i k a kita memakai m a n a - m a n a s t r u k t u r resonans " i o n i k " 5 atau 6 ozon. P e r t i n d i h a n antara o r b i t a l - o r b i t a l p pada kedua-dua a t o m C i k a t a n dubel C = C dengan o r b i t a l p pada kedua-dua a t o m O h u j u n g ozon dengan setiap o r b i t a l dianggap mengandungi

satu

elektron

d w i r a d i k a l 9)

akan

(bagi ozon

memberikan

dua

ia d a t a n g

ikatan a

daripada

C-O

elektron

d i dalam

aduk

molozonida. D u a elektron yang membentuk dua i k a t a n 0.571 struktur 9 akan bergerak ke a t o m O tengah membentuk pasangan pencil kedua pada a t o m tersebut d i d a l a m bahan perantara molozonida. D u a pasangan pencil pada masing-masing a t o m h u j u n g struktur 9 terus kekal hingga ke d a l a m molozonida. Selain daripada i t u fakta bahawa ozon m e m p u n y a i m o m e n d w i k u t u b sungguhpun m o l e k u l i n i terbentuk daripada unsur yang sama dapat diterangkan oleh struktur h i b r i d 9. Hasil paduan dua m o m e n i k a t a n O-O

ozon y a n g sama tetapi tidak saling m e m a d a m k a n

memberikan

m o m e n d w i k u t u b bersih 0.53 D yang agak signifikan (Nelson et al. 1982). Contoh 3:

N0 2

Gas nitrus oksida N 0 , d i p a k a i antaranya sebagai pengaruh anestesia serta 2

merta ( 8 0 % N 0 , 2 0 % 0 ; U.S.P.) d a n pada peratusan rendah u n t u k 2

2

mengekalkan anesthesia. M o l e k u l neutral N 0 , dengan a t o m luar sebagai 2

i o n n i t r i d a d a n oksida m e m p u n y a i j u m l a h cas 5- sehingga a t o m N pusat m e n g a m b i l cas 5 + , memberikan i o n N

5

+

3

2

: N " ; 0 ' . R a t i o n a t o m pusat N

5

+

tidak m e m p u n y a i sebarang elektron valensi a t o m N neutral (lima elektron). Pembetukan i k a t a n a daripada i o n n i t r i d a serta i o n oksida kepada k a t i o n a t o m pusat N

5+

m e m b e r i k a n struktur elektron asas 10 bagi nitrus oksida.

A t o m pusat N s t r u k t u r 10 dengan dua i k a t a n a dan berkeadaan empat Pertanika J . Sci. 8c Technol. Vol. 5 No. 1, 1997

53

Wan-Yaacob Ahmad dan Mat B. Zakaria

elektron mempunyai dua orbital h i b r i d sp (n = 2) d i samping dua o r b i t a l 2p kosong. Mengingatkan bahawa atom N pusat struktur 10, yang k u r a n g empat elektron daripada keadaan oktet serta bercas formal, datangnya daripada unsur baris pertama d a l a m k u m p u l a n 15, maka ia boleh dikoordinatkan dua kali bagi mencapai struktur keadaan semua oktet 11, 12 dan 13. Struktur Lewis 11 dan 13 terbit daripada pergerakan 2 pasangan elektron struktur elektron asas 10 kepada atom N pusat, masingmasing daripada atom N k i r i dan atom O kanan. S t r u k t u r Lewis 12 j u g a terbit daripada pergerakan 2 pasangan elektron struktur 10 tetapi kali i n i setiap pasangan datangnya daripada masing-masing atom N k i r i dan atom O kanan.

|N=N—6]

11

12

Cas formal 2- yang tinggi pada atom N luar struktur 13 akan menurunkan kestabilan struktur i t u kerana kenaikan cas formal pada satusatu atom sama ada cas negatif ataupun cas positif akan menaikkan keupayaan elektrik d i sekitar atom tersebut. Selain i t u , kemunculan cas formal bertanda sama iaitu 1 + pada masing-masing atom N pusat serta atom O d i sebelahnya d i dalam struktur 13 akan merendahkan lagi kestabilan strukturnya. K e w u j u d a n cas-cas formal yang bertanda sama pada atom-atom berjiran sama ada sama positif atau sama negatif akan menaikkan tenaga coulomb atom-atom mereka. Cas formal positif pada atom eletronegatif seperti cas formal 1 + pada atom O luar struktur 13 t u r u t menyumbang kepada ketidakstabilan atom seterusnya ketakstabilan keseluruhan struktur 13. Kestabilan kedua-dua struktur 11 dan 12 adalah tinggi dan h a m p i r sama kerana struktur 11 mempunyai atom N dan O luar bercas formal sifar dan 1- sementara taburan mereka d a l a m struktur 12 adalah berkeadaan menyongsang. D i kalangan tiga struktur resonans 11, 12 dan 13 bagi nitrus oksida, struktur 13 tidak m e n y u m b a n g langsung kepada struktur h i b r i d resonansnya. A k i b a t n y a , ikatan N - N nitrus oksida mempunyai tertib ikatan purata d i antara tertib ikatan tripel dan tertib ikatan dubel struktur 11 dan 12 iaitu 2.5 sementara ikatan N - O nitrus oksida m e m i l i k i tertib ikatan purata d i antara tertib ikatan tunggal dan tertib ikatan dubel i a i t u 1.5. Purata cas-cas formal dan elektron b u k a n pengikatan pada atom-atom setara d i dalam struktur resonans 11 dan 12 menghasilkan struktur h i b r i d resonans nitrus oksida seperti d i d a l a m struktur 14.

[N=N^O>

5-1

(--

mewakili ikatan 0.5*)

Pertanika J . Sci. & Technol. Vol. 5 No. 1, 1997

Pendekatan Ionik dalam Menulis Struktur Lewis

JADUAL 2 Perbandingan panjang ikatan beberapa bahan yang mengandungi ikatan nitrogen-nitrogen dan nitrogen-oksigen Molekul

Ikatan N=N N-N N-N N =N N = 0 N-O NO N-O

N2 N 0 N* N F NOF N 0 N0 HONO 2

+

2

2

Tertib ikatan

2

2

2

Panjang ikatan/A

3 2.5 2.5 2 2 1.5 1.5 1

1.0975 1.126 1.116 1.25 1.13 1.186 1.188 1.46

D a t a panjang i k a t a n beberapa sebatian yang m e m p u n y a i ikatan setara d i antara a t o m - a t o m seperti i k a t a n d a l a m molekul nitrus oksida (Jadual 2) ( K e n n a r d 1982) d i d a p a t i menyokong hujah kestabilan struktur resonans yang berasaskan idea cas formal. Sebagaimana yang telah disebutkan, ketiga-tiga struktur resonans 11, 12 dan 13 tidak m e n y u m b a n g secara sama kepada struktur h i b r i d resonansnya. J i k a i n i terjadi, tertib ikatan masingmasing sambungan N - N (1.126 A) dan N - O (1.186 A) nitrus oksida adalah dua i a i t u m e n g h a m p i r i panjang ikatan N = N d a l a m N F (1.25 A) dan panjang i k a t a n N = 0 d a l a m N O F (1.13 A ) . Panjang ikatan tertib 2.5 N - N d a l a m N 0 (1.126 A) adalah h a m p i r sama dengan panjang ikatan tertib sama dalam N (1.116 A) tetapi berada d i antara panjang ikatan tripel d a l a m N (1.0975 A) dan panjang ikatan dubel N = N d i d a l a m N F (1.25 A ) . I k a t a n - i k a t a n N - O tertib 1.5 d a l a m spesies N 0 dan N 0 m e m p u n y a i panjang i k a t a n h a m p i r sama (1.186 A dan 1.188 E) tetapi mereka berada antara panjang i k a t a n dubel N = 0 d a l a m N O F (1.13 E) dan panjang i k a t a n tunggal N - O d a l a m H O N O (1.46 A ) . 2

2

2

+

2

2

2

2

2

2

B. Spesies Kovalen dengan Atom Pusat dari Unsur Kumpulan 2 dan 13 Entiti B e H , BeCl , BeCl ", B H , BBr , BC1 , B F , B H ~ , BF ", B ( O H ) A 1 F , A 1 C 1 , A l B r , A1H ~, A 1 F adalah mewakili spesies kovalen dengan a t o m pusat (bergaris) berasal daripada unsur k u m p u l a n 2 dan 13 j a d u a l berkala. Unsur-unsur d a l a m k u m p u l a n i n i sungguhpun secara u m u m n y a j a t u h d a l a m kategori unsur logam kecuali unsur metaloid B tetapi keafinan elektron dan keelektronegatifan a t o m - a t o m adalah meningkat bergerak ke atas bagi k u m p u l a n . O l e h i t u , unsur-unsur i n i m e m p u n y a i ciri b u k a n logam yang bertambah. Gabungan unsur-unsur i n i dengan unsur-unsur b u k a n logam seperti H , N , O , F, C I , Br, S menghasilkan spesies kovalen. 2

2

2

4

2

6

3

3

3

4

4

3

3_

3

2

6

2

6

4

6

PertanikaJ. Sci. & Technol. Vol. 5 No. 1, 1997

55

Wan-Yaacob Ahmad dan Mat B. Zakaria

Contoh 4: BeCl'c

[4] CONFIDENCE INTERVALS

This section describes two methods o f obtaining approximate intervals for the regression parameters. These approximations are based on the asymptotics o f the maximum likelihood estimator (Kalbfleisch and Prentice 1980; Lawless 1982). A P P R O X I M A T E I N T E R V A L S BASED O N T H E A S Y M P T O T I C NORMALITY Intervals based on the asymptotic normality are widely used. Most o f the common statistical packages use this kind o f approximation. These intervals are easy to calculate and they are reasonably accurate when the sample is large. A two-sided confidence interval for j8. is given by

A

- z

( 1

_

a / 2 )

s

(A), A

+

z _ (L

A/2)S

(A)]

[5]

where i = 0, 1, p respectively, and where s(.) denotes the sample standard deviation for the given estimator, and a denotes the nominal level o f the confidence interval.

Pertanika J. Sci. 8c Technol. Vol. 5 No. 1, 1997

79

Ayman Baklizi, Isa Daud and Noor Akma Ibrahim

C O N F I D E N C E I N T E R V A L S BASED O N I N V E R T E D LIKELIHOOD RATIO TESTS These confidence intervals are constructed using the fact that, asymptotically, -2 log (R(f3.)); (i = 0, 1, p ) , has a chi-squared distribution with one degree of freedom (Vander Wiel and Meeker 1990), where for p = 1 with parameters jS , j8j we have 0

L

/ L

R(PO) = T ( ( P O . P I )

(PO.P.))

[6]

R(P,) = ' K " ( L ( P O , P ) / L ( P O . P ) )

m

I

1

where L denotes, the likelihood function, and likelihood estimators o f j3 and 0

/J , 0

fa

are the maximum

. The bounds o f these intervals are given

as the solutions o f

•Slog^fc)) - X ( , . „ , , ) = 0. 2

[8]

These intervals are somewhat complicated to compute; however, Venzon and Moolgavkar (1988) provide an efficient algorithm to compute the bounds. T H E SIMULATION STRUCTURE The simulation structure adopted here has m = 3. I t is restricted to the case of two parameters, and fi equal to 1. The sample size is varied as 20, 30, and 40. The level o f significance a is taken to be 0.05. The covariate values are taken on an equally spaced lattice, 0, 0.2, ... , 1.8. Four censoring mechanisms are considered: exponential censoring, uniform censoring, singly type 1 censoring, and type 1 censoring, with three censoring proportions in each case, that is, 0.1, 0.3, and 0.5. There were 5000 replications for each simulation run, as suggested by Piegorsch (1987). The simulation program was written i n FORTRAN with double precision. The maximum likelihood estimator was found using the Newton-Raphson method; necessary and sufficient conditions for the existence o f the maximum likelihood estimator are given i n Hamada and Tse (1988). The maximum likelihood estimator is unique because the log-likelihood function is concave; this property follows from the concavity o f log(g) where g is the density function o f u. See equation [ 2 / ] , Burridge (1981). The method o f Venzon and Moolgavkar (1988) was used to obtain the bounds o f the intervals based on inverted likelihood ratio tests. Intervals based on the asymptotic normality were obtained using the formula given i n equation [5] with estimates o f the standard deviations obtained from the inverse o f the observed information matrix. The simulation results are given i n Tables 1, 2, 3, and 4. x

80

PertanikaJ. Sci. 8c Technol. Vol. 5 No. 1, 1997

TABLE 1 Observed error rates of confidence intervals for regression parameters based on 5000 samples under singly type 1 censoring 0o

0,

SS

CP

M

t

U

T

20

0.1

LR AN

0.0212 0.0154

0.0272 0.0322

0.0484 0.0476

0.0288 0.0288

0.0306 0.0306

0.0594 0.0594

0.3

LR AN

0.0252 0.0164

0.0280 0.0330

0.0532 0.0494

0.0316 0.0298

0.0316 0.0300

0.0632 0.0598

0.5

LR AN

0.0286 0.0112

0.0262 0.0320

0.0548 0.0432

0.0274 0.0234

0.0286 0.0234

0.0560 0.0474

0.1

LR AN

0.0264 0.0218

0.0256 0.0308

0.0520 0.0526

0.0288 0.0284

0.0278 0.0276

0.0566 0.0560

0.3

LR AN

0.0272 0.0194

0.0282 0.0328

0.0554 0.0522

0.0248 0.0240

0.0258 0.0256

0.0506 0.0496

0.5

LR AN

0.0318 0.0188

0.0276 0.0352

0.0594 0.0540

0.0268 0.0246

0.0278 0.0262

0.0546 0.0508

0.1

LR AN

0.0276 0.0230

0.0256 0.0302

0.0532 0.0532

0.0266 0.0266

0.0284 0.0286

0.0550 0.0552

0.3

LR AN LR AN

0.0268 0.0210 0.0308 0.0234

0.0256 0.0302 0.0278 0.0326

0.0524 0.0512 0.0586 0.0560

0.0260 0.0248 0.0294 0.0266

0.0292 0.0282 0.0322 0.0306

0.0552 0.0530 0.0616 0.0572

30

40

0.5

L

U

T

SS = sample size, CP = censoring proportion, M = method, L = lower tail error probability, U = upper tail error probability, T = total error probability, LR = likelihood ratio, AN = asymptotic normality TABLE 2 Observed error rates of confidence intervals for regression parameters based on 5000 samples under uniform censoring

ss

CP

M

L

U

T

20

0.1

LR AN

0.0234 0.0174

0.0264 0.0308

0.0498 0.0482

0.0300 0.0296

0.0268 0.0270

0.0568 0.0566

0.3

LR AN

0.0230 0.0172

0.0260 0.0310

0.0490 0.0482

0.0290 0.0282

0.0276 0.0270

0.0566 0.0552

0.5

LR AN

0.0238 0.0118

0.0254 0.0304

0.0492 0.0422

0.0304 0.0256

0.0298 0.0254

0.0602 0.0510

0.1

LR AN

0.0240 0.0210

0.0268 0.0322

0.0508 0.0532

0.0258 0.0254

0.0246 0.0248

0.0504 0.0502

0.3

LR AN

0.0258 0.0188

0.0284 0.0326

0.0542 0.0514

0.0226 0.0220

0.0278 0.0274

0.0504 0.0494

0.5

LR AN

0.0280 0.0166

0.0288 0.0338

0.0568 0.0504

0.0264 0.0240

0.0286 0.0260

0.0550 0.0500

0.1

LR AN

0.0270 0.0224

0.0256 0.0296

0.0526 0.0520

0.0260 0.0258

0.0285 0.0280

0.0544 0.0538

0.3

LR AN

0.0288 0.0236

0.0244 0.0288

0.0532 0.0524

0.0268 0.0264

0.0306 0.0300

0.0574 0.0564

0.5

LR AN

0.0298 0.0202

0.0272 0.0314

0.0570 0.0516

0.0278 0.0268

0.0322 0.0300

0.0600 0.0568

30

40

L

U

T

SS = sample size, CP = censoring proportion, M = method, L = lower tail error probability, U = upper tail error probability, T = total error probability, LR = likelihood ratio, AN = asymptotic normality 81

TABLE 3 Observed error rates of confidence intervals for regression parameters based on 5000 samples under exponential censoring

ft

ft

SS

CP

M

L

U

T

L

20

0.1

LR AN

0.0236 0.0178

0.0272 0.0324

0.0508 0.0502

0.0296 0.0298

0.0266 0.0266

0.0562 0.0564

0.3

LR AN

0.0250 0.0172

0.0248 0.0300

0.0498 0.0472

0.0294 0.0290

0.0282 0.0270

0.0576 0.0560

0.5

LR AN

0.0248 0.0122

0.0234 0.0284

0.0482 0.0406

0.0302 0.0262

0.0278 0.0240

0.0580 0.0502

0.1

LR AN

0.0252 0.0208

0.0272 0.0326

0.0524 0.0534

0.0246 0.0246

0.0250 0.0250

0.0496 0.0496

0.3

LR AN

0.0254 0.0202

0.0280 0.0326

0.0534 0.0528

0.0232 0.0230

0.0272 0.0262

0.0504 0.0492

0.5

LR _ AN

0.0258 0.0178

0.0270 0.0338

0.0528 0.0516

0.0236 0.0222

0.0242 0.0228

0.0478 0.0450

0.1

LR AN

0.0278 0.0220

0.0256 0.0294

0.0534 0.0514

0.0268 0.0268

0.0278 0.0280

0.0546 0.0548

0.3

LR AN

0.0300 0.0244

0.0252 0.0284

0.0552 0.0528

0.0260 0.0256

0.0294 0.0290

0.0554 0.0546

0.5

LR AN

0.0270 0.0190

0.0270 0.0324

0.0540 0.0514

0.0276 0.0270

0.0308 0.0290

0.0584 0.0560

30

40

T

U

SS = sample size, CP = censoring proportion, M = method, L = lower tail error probability, U • upper tail error probability, T = total error probability, LR = likelihood ratio, AN = asymptotic normality TABLE 4 Observed error rates of confidence intervals for regression parameters based on 5000 samples under type 1 censoring

ft

ft

SS

CP

M

L

U

T

L

20

0.1

LR AN

0.0212 0.0154

0.0272 0.0322

0.0483 0.0476

0.0288 0.0288

0.0306 0.0306

0.0594 0.0594

0.3

LR AN

0.0252 0.0164

0.0280 0.0330

0.0532 0.0494

0.0316 0.0298

0.0318 0.0300

0.0634 0.0598

0.5

LR AN

0.0286 0.0112

0.0262 0.0320

0.0548 0.0432

0.0274 0.0234

0.0286 0.0234

0.0560 0.0474

0.1

LR AN

0.0264 0.0218

0.0256 0.0308

0.0520 0.0526

0.0288 0.0284

0.0278 0.0276

0.0566 0.0560

0.3

LR AN

0.0274 0.0194

0.0280 0.0328

0.0554 0.0522

0.0248 0.0240

0.0260 0.0256

0.0508 0.0496

0.5

LR AN

0.0318 0.0188

0.0278 0.0356

0.0596 0.0544

0.0270 0.0248

0.0278 0.0262

0.0548 0.0510

0.1

LR AN

0.0276 0.0228

0.0256 0.0302

0.0532 0.0530

0.0266 0.0266

0.0284 0.0286

0.0550 0.0552

0.3

LR AN

0.0268 0.0210

0.0256 0.0302

0.0524 0.0512

0.0260 0.0248

0.0292 0.0282

0.0552 0.0530

0.5

LR AN

0.0310 0.0234

0.0278 0.0326

0.0588 0.0560

0.0296 0.0268

0.0321 0.0308

0.0618 0.0576

30

40

U

T

SS = sample size, CP = censoring proportion, M = method, L = lower tail error probability, U - upper tail error probability, T = total error probability, LR = likelihood ratio, AN = asymptotic normality

Confidence Intervals for Parallel Systems with Covariates

D I S C U S S I O N AND C O N C L U S I O N S To judge the adequacy o f a confidence interval in a simulation study, two important observations have to be made: (1) the attainment o f the observed error probability to the nominal one, or at least, conservativeness and, (2) the degree o f symmetry o f the observed lower and upper tail probabilities (Jennings 1987). Tables 1, 2, 3 and 4 show that both intervals tend to achieve the nominal level. They tend to be symmetric for the slope parameter. However, intervals based on the asymptotic normality of the maximum likelihood estimator for the intercept parameter have an observed upper and lower tail probabilities that are highly asymmetric, especially for small samples. O n the other hand, intervals based on inverted likelihood ratio tests have observed upper and lower tail probabilities that are symmetric even for sample size as small as 20, which is an important consideration for one sided confidence limits (Doganaksoy 1991). As the censoring proportion increases, the intervals tend to get shorter and have less coverage probabilities. The form of the censoring mechanism and the proportion of censored cases do not appear to have a clear effect on the relative performance of the two kinds of confidence intervals. REFERENCES BAIN, L.J. 1978. Statistical Analysis of Reliability and Life Testing Models. New York: Marcel Dekker. BURRIDGE, J. 1981. A note on maximum likelihood estimation for regression models using grouped data. Journal of Royal Statistical Society, Series B 43: 41-45. DOGANAKSOY, N. 1991. Interval estimation from censored and masked system failure data. IEEE Transactions and Reliability 40(3): 280-285. DOGANAKSOY, N. and J. SCHMEE. 1991. Comparisons of approximate confidence intervals for the smallest extreme value distribution simple linear regression model under time censoring. Communications in Statistics-Simulation and Computation 120(4): 10851113.

ELANDT-JOHNSON, R. and L . JOHNSON. 1979. Survival Models and Data Analysis. New York: Wiley. HAMADA, M. and S.K. TSE. 1988. A note on the existence of maximum likelihood estimates in linear regression models using interval censored data. Journal of Royal Statistical Society, Series B 50: 293-296. JENNINGS, D.E. 1987. How do we judge confidence-interval adequacy? The American Statistician 41(4): 335-337. KALBFLEISCH, J. and R. PRENTICE. 1980. Statistical Analysis of Failure Time Data. New York: Wiley. KVAM, P. and F. SAMANIEGO. 1993. On estimating distribution functions using nomination samples. Journal of American Statistical Association 88(424): 1317-1322.

IVitanikaJ. Sci. & Technol. Vol. 5 No. 1, 1997

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Ayman Baklizi, Isa Daud and Noor Akma Ibrahim

LAWLESS, J.F. 1982. Statistical Models and Methods for Lifetime Data. New York: Wiley. MEEKER, W.Q. 1987. Limited failure population life tests: Applications to nonintegrated circuit reliability. Technometrics 29(1): 51-65. PIEGORSCH, W. 1987. Performance of likelihood-based interval estimates for twoparameter exponential samples subject to type 1 censoring. Technometrics 29(1): 4 1 49.

VANDER WIEL, S.A. and W.Q. MEEER. 1990. Accuracy of approximate confidence regression

data from accelerated life tests. IEEE Transactions and Reliability 39(3): 346-351. VENZON, D.J. and S.H. MOOLGAVKAR. 1988. A method for computing profile-likelihoodbased confidence intervals. Applied Statistics 37: 87-94.

S4

PertanikaJ. Sci. 8c Technol. Vol. 5 No. 1, 1997

ISSN: 0128-7680 © Universiti Pertanian Malaysia Press

Pertanika J. Sci. & Technol. 5(1): 85-94 (1997)

A Natural Dye in a Mesophase Region of Cetyltrimethylammonium Bromide/Octan-l-ol/Water System

1

1

1

Ham dan Suhaimi, * Faujan B . H . Ahmad, Mohd Zaizi Desa and Laili Che Rose Faculty of Arts and Science University College (UPM) Terengganu Mengabang Telipot, 21030 Kuala Terengganu, Terengganu, Malaysia 2

1

Chemistry Department Centre of Matriculation Studies Universiti Pertanian Malaysia UPM 43400 Serdang, Selangor, Malaysia 2

Received: 10 January 1996

ABSTRAK Satu pewarna semulajadi, kurkumin telah ditambahkan ke dalam satu siri struktur mesofasa hablur cecair lamela yang mengandungi setiltrimetilammonium bromida, oktan-l-ol dan air pada 30°C. Perubahan yang berlaku akibat dari penambahan pewarna tersebut telah diikuti dengan kaedah mikroskop berkutub dan pembelauan sinar X bersudut rendah. Jarak antara lapisan untuk hablur cecair lamela dengan pewarna didapati lebih rendah dari jarak antara lapisan tanpa pewarna pada nisbah isipadu air yang sama. Kesan air dan rantai hidrokarbon dari struktur hablur cecair lamela adalah minima dan penambahan pewarna seterusnya menghalang pembentukan mesofasa tersebut. ABSTRACT A naturally occurring dye, curcumin, was added to a series of lamellar liquid crystal mesophases consisting of cetyltrimethylammonium bromide (CTAB), octan-l-ol and water at 30°C. The changes brought about by the addition of the natural dye were followed by optical microscopy and small angle X-ray diffraction techniques. The interlayer spacings of the lamellar liquid crystal mesophases with the natural dye were observed to be lower than the corresponding structure without dye at the equivalent volume ratio of water. The effect of water and the hydrocarbon chain of the lamellar liquid crystal structure were found to be minimal and further inclusion of curcumin prevented the formation of the mesophase. Keywords: curcumin, lamellar liquid crystal, small angle X-ray diffraction

Hamdan Suhaimi, Faujan B . H . Ahmad, Mohd Zaizi Desa and Laili Che Rose

INTRODUCTION A characteristic feature o f a particular dye, other than its spectrum i n the U V range, is its solubility i n various media. Dyes are colorants which are either partially or completely dissolved in the media o f application (Zollinger 1987). In some applications, such as in inks for j e t printing, waterfastness is desired in an ink which must be water-rich. One way o f attaining this is by formulating inks which harden into a liquid crystal or crystal when applied. The solubilization of dyes into a liquid crystalline structure has over the decades been focused on nonlyotropic or thermotropic liquid crystals due to their importance in colouring liquid crystal display, LCD. Lyotropic liquid crystal structure, however, has not received the corresponding attention it deserves. This amphiphilic structure has special appeal in biological systems such as biomembranes and a part o f an integumentary system known as stratum corneum. It is well documented that the lipids o f human stratum corneum form bilayers which are composed o f sheets o f fatty acids, cholesterol and ceramide layers separated by water layers (Elias 1983; Friberg and Osborne 1985). This molecular arrangement is similar to that o f a lamellar liquid crystal mesophase often observed in the intermediate region o f surfactant/co-surfactant/ water systems (Ekwall 1975). Work on the solubilization o f dye i n lamellar liquid crystals was initiated by Friberg and co-workers (Friberg et al i n press). This work, however, focused on the use o f a synthetic dye, phenol red, as the guest constituent. The present work is concerned with the solubilization o f a naturally occurring dye known as curcumin or l,7-bis(4-hydroxy-3-methoxyphenyl)-l,6-heptadiene-3,5-dione (Fig. 1) in a lamellar liquid crystal mesophase. This investigation arises from the growing concern associated with many synthetic dyes and an awareness o f environment-friendly materials. Curcumin is approved for use as a colorant in food processing ( W H O 1975) and easily extracted from the rhizome o f Curcuma tonga L. (Zingiberaceae).

Fig. 1. Structure of curcumin M E T H O D S AND MATERIALS Materials The constituent materials o f the liquid crystal chosen were octan-l-ol and cetyltrimethylammonium bromide (CTAB) at variable molar ratios in an aqueous system. The surfactant CTAB (MW 364.46 g / m o l ) (>99%) was obtained from Sigma Chemicals and the co-surfactant octan-l-ol (MW 130.23 g / m o l ) (>99%) 86

PertanikaJ. Sci. & Technol. Vol. 5 No. 1, 1997

A Natural Dye in a / octan - I - of/ water system of Cetyltrimethylammonium Bromide

was from Aldrich. No further purification was done prior to usage. The c u r c u m i n ( B D H ) was p u r i f i e d through silica gel c o l u m n u s i n g dichloromethanermethanol (98:2) as the eluent. I t was then recrystallized from ethanol to give a bright orange-yellow crystal. Doubly distilled water was used to prepare the lamellar liquid crystal mesophase. Preparation of Samples The liquid crystal samples used as the host for the study o f the solubilization employing a natural dye as the guest constituent were prepared as follows. First, the surfactant was combined with octan-l-ol at three different surfactant/octanl-ol molar ratios o f 0.66, 0.83 and 1.07 (line a, b and c respectively o f Fig. 2). The samples were mixed by repeated centrifugation in a sealed 7-mm sample tube, vortexed and allowed to equilibrate at 30 ± 0.2°C. For each composition, a series o f samples represented as points on lines a, b and c i n Fig. 2 was prepared with water content i n the range o f 30-40% by weight. For the solubilization o f the natural dye into the lamellar structure, a point on line c of Fig. 2 at 33% by weight o f water was selected and the dye is added to i t directly. For the X-ray measurements, a fixed amount o f 2% w t . / (surfactant + co-surfactant) o f curcumin was added to all the samples series and the water content was adjusted to maintain the initial values at 30-40% by weight. The resulting samples (host + dye) were then allowed to equilibrate overnight at 30 ± 0.2°C. The changes brought about by the above additions o f the dye were followed by optical microscope and small angle X-ray diffraction techniques.

Octan-1-OL

Lamellar Mesophase

/

\

Water Fig. 2.

CTAB

Ternary diagram for the system of cetyltrimethylammonium bromide (CTAB), octan-lol and water, shouting the location of the lamellar liquid crystalline region taken for the X-ray measurements

Small Angle X-ray Diffraction Measurements The interlayer spacings o f liquid crystalline phases were determined by small angle X-ray diffraction method at 30°C. A Kiessig small angle camera from

Pertanika J . Sci. & Technol. Vol. 5 No. 1, 1997

87

Hamdan Suhaimi, Faujan B . H . Ahmad, Mohd Zaizi Desa and Laili Che Rose

Richard Seifert with an Ni-filtered Cu source gradient at 40 kV, 30 used. The reflection was detected by a Tennelec detector system PSD1100). The exposure time for the samples was set to 1000 sec alignment o f the instrument was checked by a lead stearate standard interlayer spacing o f 48.2 A.

mA was (Model and the with an

R E S U L T S AND D I S C U S S I O N The solubility of curcumin to the lamellar liquid crystal over a water concentration of 30-40% is found to be relatively low, i.e. about 2.5% by weight at the higher CTAB/octan-l-ol molar ratio. A n addition o f a large excess o f curcumin beyond the maximum solubility distorts the lamellar structure. The appearance of the sample under the polarized microscope is shown in Plate 1. O u r results also showed a slight reduction or otherwise constant value o f 45.0 A i n the interlayer spacing when curcumin is added directly to the liquid crystal samples (Fig. 3). The interlayer spacings are calculated from the small angle X-ray diffractograms pattern and are plotted against the water ratio in the range of 30-40% by weight. The curcumin is then added to liquid crystalline samples across the points a, b and c o f Fig. 2. The molar ratios o f the surfactant/alcohol for a, b and c are 0.66, 0.83 and 1.07, respectively. A plot o f the interlayer spacings for the compositions with a surfactant/alcohol molar ratio o f 0.66 without curcumin is shown in Fig. 4a. The interlayer spacings observed in these compositions increased linearly with the water content i n the interval used. Equivalent data for systems with surfactant/alcohol molar ratios o f 0.83 and 65 |

56

3g I 0

1

-

i 0.5

i 1

i 1.5

i 2

i 2.5

3

Percentage of Curcumin/(CTAB + Octan-1-ol)

Fig. 3. Interlayer spacing versus curcumin percentage for a sample of initial composition: 50% CTAB, 17% octan-l-ol and 33% water. (% wt)

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A- Natural Dye in a / octan -I- of/ water system of Cetyltrimethylammonium Bromide

*

Plate 1.

Optical pattern at a molar ratio of CTAB to octan l-ol of 1.07: a) before, and b) after, addition of 1.5 wt. % of curcumin, indicating typical lamellar liquid crystalline structures of striated type. The water content for both samples was kept at 32 wt. %

1.07 are shown in Fig. 4b, c respectively. Similar dependence on the water content is observed i n these systems. Inclusion o f curcumin also shows similar dependence on the water content. However, an interesting phenomenon is observed when graph for both systems are plotted together in Figs. 5-7. The interlayer spacings for the liquid crystals containing the curcumin is found to be lower than those without the curcumin with equivalent volume ratio o f water. f

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Hamdan Suhaimi. Faujan B.H. Ahmad, Mohd Zab.i Desa and Laili Che Rose

54

52

-

40 L _ 0.3

1 0.4

1 0.6

1 0.6

1 0.7

1 0.8

Volume Water/ Volume Rest Fig. 4. Interlayer spacing as a function of water volume fraction for CTAB/octan-l-ol molar ratios of a) 0.66, b) 0.83 and c) 1.07, before the addition of curcumin The above results only suggest the location o f the curcumin in the liquid crystal structure (Fig. 3). Since the interlayer spacings and the slopes o f the straight lines (Figs. 5-7) d i d not significantly increase as curcumin was added to the structure, it can be inferred that the curcumin is located between the methylene layer o f the lamellar structure. The results, however, d i d not lend useful information on the dye-water, dye-hydrocarbon interaction nor the whole structure o f the lamellar organization. I n order to obtain such deduction, extrapolation o f the curves in Figs, 5-7 to zero water content and the calculation on the penetration factor become necessary. The values o f the interlayer spacing at zero water (d ) are given i n Table 1. The almost identical values (d ) showed that the presence o f curcumin molecules have little influence on the hydrocarbon chains i n the liquid crystal, suggesting again that curcumin molecules are located between the hydrocarbon layers o f the liquid crystal. The dye-water interaction, on the other hand, is reflected by the extent to which the water penetrates the amphiphilic layer from the polar layer. This may be achieve to a satisfactory extent from the slopes (Table 1) o f Figs. 5-7. However, a better understanding can be made possible by calculating the penetration o f water which is characterized by the penetration factor a. The definition of the penetration factor a by Friberg and co-workers (Friberg et al. 1992) is adopted i n this work and is described here to facilitate understanding and to make clear its vital role in this study. 0

For an added solvent (water i n this case) that is localized entirely i n the polar zone A or methyl zone C (Fig. 8) the penetration factor, a = 0. I f the

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A Natural Dye in a / octan -I- of/ water system of Cetyltrimethylammonium Bromide

0.2

0.4

0.6

Volume Water/ Volume

0.8

1

Rest

Fig. 6. Interlayer spacing as a function of water volume fraction for CTAB/octan-l-ol molar ratio of 0.83, i) before (() and ii) after (() addition of curcumin solvent is partitioned equally into zones A, B, and C (Fig. 8) the penetration fraction, a = 1. For partial penetration into zone B, the penetration factor is defined by d = d [ l + (l ( )

a)R]

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(1)

91

Hamdan Suhaimi, Faujan B . H . Ahmad, Mohd Zaizi Desa and Laili Che Rose

0.2

0.4

Volume

0.6

Water/ Volume

0.8

Rest

Fig. 7. Interlayer spacing as a function of water volume fraction for CTAB/octan-l-ol molar ratio of 1.07, i) before (() and ii) after (() addition of curcumin TABLE 1 Values for the extrapolated interlayer spacings, d , slopes and penetration factor a, for the liquid crystal samples ()

CTAB/Octan-lol Molar Ratio 0.66 0.83 1.07

No Dye

slope Dye

a No Dye

Dye

31.09 33.74 33.91

30.60 31.42 33.53

27.21 24.57 24.80

25.89 26.81 23.53

A

F

Masa Simpan (M) Ralat (b)

3

20457.93

6819.31

939.19* 686.27

0.0001 0.0001

Kemasakan (K) Ralat (b)

2

5192.69

2596.34 261.29

357.58* 0.0001

0.0001

M xK Bahagian (B) Ralat (c)

6 2

1849.45 10.37

308.24 5.9

42.45* 0.71 0.52

0.0001 0.4929 0.6062

6 4 12

9.65 128.59 119.24

1.61 32.15 9.94

0.22 4.43* 1.37

0.9686 0.0030 0.2012

M xB K xB M x Kx B

• Bererti pada paras 1% (b) Analisis varian untuk data peratus peleraian buah pad a lapisan dalam Sumber

Darjah Kebebasan

Hasil Tambah Kuasa Dua

Min Kuasa Dua

Nilai F

Pr > F

Masa Simpan (M) Ralat (b)

3

149486.97

49828.99

6520.18*

0.0001 0.0001

Kemaskan (K) Ralat (b)

2

3723.61

1861.80

243.62* 77.85

0.0001 0.0001

M xK Bahagian (B) Ralat (c)

6 2

154.23 0.29

154.23 0.29

6 4 12

33.48 104.71 286.99

5.58 26.18 23.92

M xB Kx B M x KxB

2018* 0.04 0.01 0.73 3.43** 3.13*

0.0001 0.9626 0.9879 0.6269 0.0128 0.0013

* Bererti pada paras 1% ** Bererti pada paras 5%

Purata peratus peleraian bagi tempoh penyimpanan 9 j a m menunjukkan lapisan luar menghasilkan 79.5 dan 65.5% bagi lapisan dalam. Bagi tempoh penyimpanan 6 j a m purata peratus peleraian untuk lapisan luar adalah 62.5% manakala lapisan dalam hanya 1.7%. I n i menunjukkan pada tempoh tersebut, buah di lapisan dalam masih sukar untuk dileraikan. Purata peratus peleraian pada lapisan luar dan dalam bagi tandan masak adalah masing-masing 91.8 dan 69.8%, 83.0 dan 64.1% bagi tandan kurang masak dan 74.8% dan 55.5% bagi tandan tidak masak (Jadual 4).

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Kesan bahagian terhadap peleraian tidak memberikan perbezaan yang bererti (Jadual 5). Purata peratus peleraian untuk lapisan luar bahagian basal, equatorial dan apikal adalah masing-masing 83.5, 83.3 dan 82.8%. Purata peratus peleraian bagi lapisan dalam pula adalah 63.1% bagi bahagian basal, 63.2% bagi bahagian equatorial dan 63.0% bagi bahagian apikal. Kesimpulannya bahagian pada tandan tidak memberi kesan yang bererti terhadap rawatan yang diberi pada sebarang tempoh simpanan bagi kedua-dua lapisan. JADUAL 3 (a) Analisis varian untuk lapisan luar bagi masa penyimpanan berbeza Kumpulan A B C D

Min

Bilangan

Masa

98.29 92.53 79.46 62.49

27 27 27 27

18 12 9 6

(b) Analisis varian untuk lapisan dalam bagi masa penyimpanan berbeza Kumpulan A B C D

Min

Bilangan

Masa

95.88 89.39 65.45 1.74

27 27 27 27

18 12 9 6

Min bagi huruf (kumpulan) yang berlainan menunjukkan ada perbezaan bererti JADUAL 4 (a) Analisis varian untuk lapisan luar bagi darjah kemasakan yang berbeza Kumpulan A B C

Min

Bilangan

91.78 83.01 74.80

36 36 36

Darjah Kemasakan Masak Kurang Masak Tidak Masak

Min bagi huruf (kumpulan) yang berlainan menunjukkan ada perbezaan bererti (b) Analisis varian untuk lapisan dalam bagi darjah kemasakan yang berbeza Kumpulan A B C

Min

Bilangan

69.77 64.09 55.48

36 36 36

Darjah Kemasakan Masak Kurang Masak Tidak Masak

Min bagi huruf (kumpulan) yang berlainan menunjukkan ada perbezaan bererti 102

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Peleraian Buah Sawit dari Tandan Menggunakan Kaedah Kimia

JADUAL 5 (a) Analisis varian untuk lapisan luar bagi bahagian yang berlainan pada tandan Kumpulan A B C

Min

Bilangan

88.54 83.27 82.79

36 36 36

Darjah Kemasakan Basal Equatorial Apikal

Min bagi huruf (kumpulan) yang berlainan menunjukkan tiada perbezaan bererti (b) Analisis varian untuk lapisan dalam bagi bahagian yang berlainan pada tandan Kumpulan A B C

Min

Bilangan

63.07 63.22 63.06

36 36 36

Darjah Kemasakan . Basal Equatorial Apikal

Min bagi huruf (kumpulan) yang berlainan menunjukkan tiada perbezaan bererti KESIMPULAN Proses peleraian akibat tindak balas bahan kimia, ethephon, berlaku pada lapisan luar terlebih dahulu, di mana lebih 46.9% peleraian berlaku, barulah diikuti oleh lapisan dalam bagi semua darjah kemasakan. Tempoh penyimpanan memainkan peranan penting terhadap peleraian buah. Peleraian buah dalam tempoh 18 j a m didapati melebihi peleraian bagi tempoh 12 j a m dan seterusnya. I n i menunjukkan bahawa dengan memanjangkan tempoh penyimpanan, peleraian buah dapat ditingkatkan. Peleraian dalam tempoh 18 j a m didapati melebihi peleraian menerusi kaedah sapu (Hadi 1994) dan kaedah suntikan (Shahrom 1994). Ethephon yang dituang masuk ke dalam tandan lebih cepat bertindak. Tandan yang masak akan menghasilkan lebih peratus peleraian dalam tempoh yang lebih singkat. Bahagian basal, equatorial dan apikal mempunyai peratus peleraian yang hampir sama bagi setiap tempoh penyimpanan dan darjah kemasakan. Penemuan i n i memberi faedah kepada industri kelapa sawit di masa hadapan yang dapat mengurangkan kos pengendalian dan pengangkutan tandan dari ladang ke kilang. Ruang bagi menampung tandan kosong dapat diisi dengan buah sawit yang telah dileraikan. D i peringkat kilang, skala operasi dapat ditingkatkan dan ruang pemprosesan dapat dikurangkan. Oleh kerana kaedah i n i memendekkan proses pengsterilan, penggunaan sumber tenaga dapat dijimatkan. PENGHARGAAN Pengarang ingin mengucapkan terima kasih kepada Encik Mohammad Ahmad, Encik Saufe Abdul Kadir, Encik Nassarudin dan semua Kakitangan Makmal,

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Fakulti Kejuruteraan dalam menjayakan projek i n i . Ribuan terima kasih juga kepada Puan Rousnafizah, Puan Khatijah dan Encik Faizal A m r i kerana membantu menyiapkan makalah d i atas.

RUJUKAN ANON. 1985. Palm Oil Factory Process Handbook Bangi: PORIM. ARIFFIN, A.A. 1991. Chemical change during sterilization process affecting strippability and oil quality. Proceedings of Workshop on Quality in the Palm Oil Industry, 16-17 May, PORIM. BURG, F.E. and L.P.K.V. THIMANN. 1959. The physiology of ethylene formation in apples. Proc. Nat. Acad. Sci. 45: 335-344. HADI, S. 1994. Fundamental studies on the field stripping system of oil palm fruitlets. Ph.D. thesis, Universiti Pertanian Malaysia. HARTLEY, C.W.S. 1967. The Oil Palm. London: Longmans. NG, K.T. and A. SOUTHWORTH. 1973. Optimum time of harvesting oil palm fruit. In Advances in Oil Palm Cultivation. Kuala Lumpur, Incorporated Society of Planters. OSTERLI, P.P., R.M. RICE and KW. DUNSTER. 1975. Effect of ethephon on bell pepper fruit ripening. Calif. Agric. 29(7): 3. SAS INSTITUTE INC. 1985. SAS/STAT Guide for Personal Computers. 6th edn. Cary, NC: SAS Institute Inc. SHAHROM, S. 1994. Kajian keberkesanan ethephon ke atas peleraian buah sawit dari tandan, UPM. Laporan Projek Tahun Akhir, Bacelor Kejuruteraan, Universiti Pertanian Malaysia. SHUIB, A.R., ABDUL HALIM HASSAN and AHMAD HITAM. 1989. Development of harvesting

machines for oil palm. PORIM Bulletin 19: 1-7. SOON, CP., MOHD. MAT M I N and QUAH YIN THY. 1990. Possible innovations and agronomic

implications in further mechanisation of oil palm estates. The Planter 66: 420-431. W.A. 1985. Peach quality assessment: fresh and processed. In Evaluation of Quality of Fruits and Vegetables, ed. Harold E. Pattee. Westport: AVI Pub. Co.

S'vSTRUNK,

TJENG, P.D. and R.A. GILLBANKS. 1978. Palm oil mill process description. The Planter 54: 527-549.

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ISSN: 0128-7680 © Universiti Pertanian Malaysia Press

Pertanika J. Sci. & Technol. 5(1): 105-109 (1997)

Chemical Constituents of Vitex ovata (Verbenaceae) 1

2

Irmawati Ramli, Ahmad Sazali Hamzah, Norio Aimi and Nordin H j . Lajis Natural Products Laboratory Department of Chemistry Faculty of Science and Environmental Studies Universiti Pertanian Malaysia 43400 UPM Serdang, Selangor, Malaysia 'School of Applied Sciences Institut Teknologi MARA 40450 Shah Alam, Selangor, Malaysia 2

Faculty of Pharmaceutical Sciences University of Chiba 1-33 Yayoi-cho, Inage-ku Chiba 263> Japan Received: 1 August 1996 ABSTRAK Tiga sebatian, luteolin, asid ursolik dan asid w^a-hidroksibenzoik telah diasingkan daripada daun Vitex ovata. Struktur sebatian tersebut telah dikenalpasti melalui analisis spektroskopi. ABSTRACT Three compounds, luteolin, ursolic acid and ratfto-hydroxybenzoic acid were isolated from the leaves of Vitex ovata. The structures of the compounds were identified using modern spectroscopic techniques. Keywords: luteolin, ursolic acid, meta-hydroxybenzoic Verbenaceae

acid, Vitex ovata,

INTRODUCTION Vitex is a shrub o f family Verbenaceae commonly found throughout the Asia Pacific. There are approximately 140 species distributed in the tropics or subtropics of which 16 have been identified in Peninsular Malaysia (Ng 1978). Some species of this genus such as Vitex negundo, V. cannabifolia, and V. Strieker have been extensively studied (Dutta et al 1983; Zhang et al 1992; Iwagawa et al. 1993). Vitex ovata is a small shrub usually found i n the lowland forest. I t is known locally as tetuban and used for treating dysentery and stomach discomfort (Burkill 1936).

[rmawati Ramli, Ahmad Sazali Hamzah, Norio Aimi and Nordin Hj. Lajis

MATERIALS AND M E T H O D S Plant Materials Vitex ovata was collected from Kuantan, Malaysia and the voucher specimen was deposited at the herbarium of the Biology Department, Universiti Pertanian Malaysia. General Melting points were determined on a Kofler hot stage apparatus and are uncorrected. The UV spectra were recorded on Shidmazu UV-VIS 160 and IR spectra on Perkin Elmer 1600 FTIR spectrometers. Mass spectra were recorded on a Finnigan M A T SSQ 710 spectrometer with ionization being induced by electron impact at 70 eV. ' H - and C-NMR spectra were recorded on a J E O L J N M 500 spectrometer at 500 and 125 MHz, for H and C , respectively. Column chromatography and analytical T L C utilized Merck 7734 and Merck DC-Plastikfollen 60 F , respectively. 1S

]

l3

2M

Extraction of Plant Materials The leaves o f Vitex ovata (5 kg) were soaked i n methanol for 72 hours. The solvent was removed by filtration and fresh methanol was then added. The methanol extracts were combined and evaporated under reduced pressure to give a greenish mass (125 g ) . The crude extract was then partitioned between petroleum ether and water. The aqueous layer was extracted successively with chloroform, ethyl acetate and then butanol. The crude ethyl acetate extract was then subjected to column chromatography on silica gel and eluted with chloroform followed by C H C l : M e O H mixture in increasing polarity. Thirty-six fractions were collected and fractions with a similar pattern on analytical T L C were combined and further purified before the pure compounds were isolated. s

Isolation of Luteolin [1] The combined fractions 13-16 (40 mg) from the column chromatography were subjected to preparative thin layer chromatography on silica gel using CHC1 / M e O H (70:30) as solvent to afford luteolin (12 mg), m.p. 345-348°C (lit. m.p. 328-330°C, Buckingham 1994). UV A. n m ( M e O H , log e): 266.0 (1.22), 333 (0.56); IR V c m ^ K B r disk): 3424,2928, 1656, 1612; 'H-NMR (500 MHz, CDC1 + CD OD)T7.37 (dd, l H J ^ . = 9.0 H z , J . , = 2.4 Hz, H - 6 ) , 6.94 (d, I H , J ^ . « 2.3 Hz, H-2'), 6.93 (d, 1H, J = 9.0 Hz, H-5"), 6.51 (s, H-3), 6.44 (d, 1H, J = 2.4 Hz, H-8), 6.28 (d, I H , J = 2.3 Hz, H-6); "C-NMR (125 MHz, CDC1,+ C D O D , DEPT Experiment): 182.4 (C-4), 164.5 (C-7), 163.9 (C-2), 161.3 (C-5), 157.8 (C-9), 148.8 (C-4'), 144.9 (C3'), 122.5 (C-T), 119.1 (C-6'), 115.2 (C-5'), 112.7 (C-2'), 104.3 (C-10), 102.9 (C3), 99.1 (C-6), 94.1 (C-8); MS m / z ( % ) : 286 ( M , 100), 134 (7), 152 (5); max

max

;1

6

2

3

2

w

M

3

+

106

PertanikaJ. Sci. & Technol. Vol. 5 No. 1, 1997

Chemical Constituents of Vitex ovata (Verbenaceae)

Isolation of Ursolic acid [2] This combined fractions 1-4 from the column chromatography gave a whitish powder, m.p. 269-271°C (lit. m.p. 266-267 °C, Takagi et al 1979). UV A. n m ( M e O H , log e): 470 (0.14), 441 (1.18), 421 (0.17); IR V cm (KBr disk): 3424, 1693, 1540, 1272, 1092, 996: 'H-NMR (500 MHz, CDC1 + CD,OD): 5.24 (m, 1H, H-12), 3.38 (s, 1H, H-3), 2.18 (d, 1 H , J - 11.3 Hz, H 18), 2.02 - 1.15 (m, 22H), 1.14 (s, H-27, Me), 1.08 (s, H-25, Me), 0.96 (s, H-23, Me), 0.95 (s, H-30, Me), 0.90 (d, H-29, M e ) , 0.78 (s, H-24, Me), 0.77 (s, H-26, Me); C - N M R (125 MHz, CDC1 + CD^OD, DEPT Experiment): 181.0 (C-28), 138.4 (C-13), 125.6 (C-12), 79.0 (C-30), 55.4 (C-18), 53.0 (C-5), 47.7 (C-17), 46.6 (C-9), 42.2 (C-14), 41.9 (C-9), 41.4 (C-20, C-19), 39.6 (C-22), 39.4 (C-22), 38.6 ( C - l ) , 34.0 (C-7), 31.0 (C-21), 29.8 (C-15), 28.1 (C-2), 26.0 (C-16), 24.4 (C11), 23.6 (C-27), 21.3 (C-30), 18.4 (C-6), 17.1 (C-29), 17.0 (C-26), 16.9 (C-25), 15.7 (C-24); MS m / z ( % ) : 456 ( M ) , 248 (100), 207 (27), 203 (42.6) 1

max

3

1 8 1 9

B

3

+

Isolation of meta-hydroxybenzoic acid [3] This minor component from combined fractions 14-16 was identified as metahydroxybenzoic acid, melting point 210-213°C (lit. m.p, Wl "C, Buckingham 1992). The C - N M R are similar to those reported in the literature (Scott 1972). B

R E S U L T S AND D I S C U S S I O N Chemical investigations o f the crude ethyl acetate extract of Vitex ovata have resulted in the isolation of three compounds, luteolin [ 1 ] , ursolic acid [2] and m^/rt-hydroxybenzoic acid [ 3 ] . Luteolin, a yellowish amorphous solid has a melting point of 345-348°C. The compound showed a molecular ion peak at m / z 286 which corresponds to molecular formula C _H O . Peaks at m / z 134 and m / z 152 are due to the cleavage o f rings A and B, respectively, of the flavone agylcone. The U V spectrum of the compound showed absorption maxima at 266 n m and 333 nm, typical of a flavone type skeleton. The IR spectra showed strong absorptions at 1656 cm' and 1612 cm' which correspond to the C=C and C = 0 stretchings, respectively. The *H-NMR spectra showed the presence of the aromatic protons of a flavone type compound. Four doublets at 6.94 ppm, 6.93 ppm, 6.44 ppm and 6.28 ppm are due to protons H-2', H-5', H-8 and H-6, respectively. A singlet at 6.51 p p m is due to the isolated proton attached to C-3 whereas a doublet of a doublet at 7.37 ppm is due to a proton at C-6*. Further information to establish the structure was accomplished based on the carbon-13 data o f the compound. Signals at 163.9 p p m and 102.9 p p m are assigned to C-2 and C-3 which are characteristic of a dehydro-type flavone. The chemical shift of a carbonyl carbon at 184.2 ppm is due to the influence of this double bond carbon, C-2 and C-3. Based on these spectral data, the compound is concluded to be luteolin [1] (Harborne and Mabry 1981; Markham 1982). 1

1

10

6

1

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Irmawati Ramli, Ahmad Sazali Hamzah, Norio Aimi and Nordin Hj. Lajis

The U V spectrum o f the second compound showed absorptions at 421, 427, and 444 n m and the IR spectrum exhibited absorptions at 3424 c m (hydroxyl) and 1693 c m (carbonyl). The compound displayed a molecular ion peak at m / z 456 which corresponds to molecular formula C H O . A base peak at m / z 248 is a typical retro Diels Alder cleavage o f an a- or P- type triterpene. Comparison o f the carbon-13 with the literature values for the signals at C-12, C-13, C-18, C-19 and O20 indicated that the compound is an a-type triterpene (Doddrell et al 1974). This conclusion was further supported by the *H-NMR spectrum o f the compound with the doublet at 2.20 p p m having J value o f 11.3 Hz indicating that the protons at C-18 and C-19 are trans to each another. This observation further suggests that the triterpene is o f the a-type and not the type. Based on these spectroscopic data and also by comparison with those reported i n the literature, the compound was assigned as ursolic acid [2] (Romeo et al 1977; Kriwacki and Pitner 1989) . Afea-hydroxybenzoic acid [3] is a white crystalline compound which melted at 210-213°C. The mass spectrum showed a molecular ion peak at m / z 138 which corresponds to molecular formula C H O The IR spectrum showed strong absorptions at 3414 cm' and 1683 c m for the hydroxyl and carbonyl stretchings, respectively. The H - N M R spectra showed the presence o f two doublets at 7.86 p p m and 6.80 ppm. The former is due to H-6 coupled to the proton attached to C-5 (ortho coupling) and the later also shows ortho coupling between H-4 and H-5. A multiplet at 3.31 p p m is due to proton H-5 which is 1

1

S0

7

1

6

48

3

r

1

l

[3] mera-hydroxybenzDic acid

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Chemical Constituents of Vitex ovata (Verbenaceae)

coupled to both H-4 and H-6. The proton attached to C-2 resonates as a singlet at 4.87 p p m . T h e C-spectral data were consistent with those o f the literature (Scott 1972). 13

ACKNOWLEDGEMENTS The authors thank the National Council for Research and Development for financial assistance under the Intensified Research i n Priority Areas (IRPA) Programme.

REFERENCES BUCKINGHAM, J. 1992. Dictionary of Organic Compounds. London: Chapman and Hall. BUCKINGHAM, J. 1994. Dictionary of Natural Products. London: Chapman and Hall. BURKILL, I.H. 1936. A Dictionary of the Economic Products of the Malay Peninsula. London: Crown Agents for the Colonies. 13

DODDRELL, D . , P.W. KHONG and K J . LEWIS, 1974. The stereochemical dependence of C-

chemical shifts in olean-12-enes and urs-12-enes as an aid to structural assignment. Tetrahedron Letters 27: 2381-2384. DUTTA, P.K., U.S. CHOUDARY, A.K. CHAKRAVARTY, B . AGHARI and S.C.PAKRASHI. 1983. Studies

on Indian medicinal plants. Part LXXV. Nishindaside: a novel iridoid glycoside from Vitex negundo. Tetrahedron 39(19): 3067-3072. HARBORNE, J.B. and T.J. MABRY. 1981. The Flavonoids: Advances in Research. London: Chapman and Hall. IWAGAWA, T., A. NAKAHARA and M. NAKATANI. 1993. Iridoids from Vitex cannabifolia. Phytochemistry 32: 453-454.

KRIWACKI, R.W. and T.P. PITNER. 1989. Current aspects of practical two-dimensional ( 2 D ) nuclear magnetic resonance (NMR) spectroscopy: applications to structure elucidation. Pharmaceutical Research 6(7): 531-700. MARKHAM, K.R. 1982. Techniques of Flavonoid Identification. New York: Academic Press. NG, F.S.P. 1978. Tree Flora of Malaya. Singapore: Longman. ROMEO, G., P. GIANNETTO and M.C. AVERSA. 1977. Constituents of Satureia calamintha

application of Eu(fod) to the assignments of methyl resonances of triterpenes related to 12-ursene. Organic Magnetic Resonance 9(1): 29-34. 3

13

SCOTT, K.N. 1972. Important aromatic carbon chemical shifts of benzoic acid derivatives. / Amer. Chem. Soc. 94: 8564-8568. TAKAGI, S., M . MASAKI, K. MATSUDA, K . INOUE and Y. KASE. 1979. Studies on the purgative

drugs. (V). On the constituents of the fruits of Prunus japonica Thunb. Yakugaku Zasshi 99(4): 439-442. ZHANG, M., M.J. STOUT and I . KUBO. 1992. Isolation of ecdysteroids from Vitex stricken using RLCC and recycling HPLC. Phytochemistry 31: 247-250.

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Pertanika J. Sci. & Technol. 5(1): 111-126 (1997)

Prediction and Determination of Undrained Shear Strength of Soft Clay at Bukit Raja 1

Jamal Mohd. Amin, Mohd. Raihan Taha, Jimjali Ahmed, Azmi Abu Kassim, Azmi Jamaludin, and Jamilah Jaadil 3

4

Dept. of Civil & Structural Engineering Universiti Kebangsaan Malaysia 43600 Bangi, Selangor, Malaysia l

Pengurusan Lantas Berhad Kuala Lumpur

2

Hussien & K.H. Chong Sdn. Bhd Kuala Lumpur 3

Khairi Consult, Kuala Lumpur.

4

Faculty of Civil Engineering Universiti Teknologi Malaysia Kuala Lumpur Received: 2 January 1992 ABSTRAK Kertas kerja ini membentangkan keputusan kajian untuk meramal dan menentukan kekuatan ricih tak tersalir, s , satu parameter yang amat penting dalam amalam rekabentuk, bagi lempung Klang, Malaysia, s ditentukan menggunakan ujian ricihan bilah di makmal dan di lapangan, dan kaedah main pa tan semula menggunakan radas ricih mudah terus. Ramalan s diperolehi menggunakan prosedur SHANSEP dan model keadaan genting. Satu lubang korek ujian di Bukit Raja Klang, digunakan dalam kajian ini. Perbandingan nilai s menggunakan kaedah-kaedah ini telah dilakukan dan didapati bahawa semtia kaedah menunjukkan arali tuju perubahan s dengan kedalaman yang sama. Kaedah bilah ricih memberikan penganggaran s yang tertinggi, diikuti dengan kaedah mampatan semula, SHANSEP dan kaedah keadaan genting, u

u

u

ABSTRACT This paper presents the results of a study to predict and determine undrained shear strength, s , a very important parameter in design practice, for Klang clay, Malaysia. s is determined using field and laboratory vane shear and recompression method utilizing the direct simple shear (DSS) apparatus. Prediction of s was accomplished using the SHANSEP procedure and the critical state model. A test borehole at Bukit Raja, Klangs, was used for this study. Comparisons of s values obtained by these methods are made. It is found that all the methods employed show the same trend of s with depth. The vane shear test gives die highest estimation of s, followed by the recompression method, SHANSEP method and critical state method. u

u

u

u

Keywords: undrained shear strength, OCR, SHANSEP, critical state, direct simple shear, vane test, recompression

2

M.A. Jamal, T . Raihan, A. Jimjali, A.K. Azmi, J . Azmi and J . Jamilah

INTRODUCTIOIN I n geotechnical design practice, two important considerations which need careful examination are whether construction will cause deformation o f the soil a n d / o r instability due to shear failure. Therefore, an engineer has to ensure that the structure is safe against shear failure in the soil that supports it and does not undergo excessive settlement. Knowledge about the stress-strain behaviour, deformation and shear strength o f the soil is essential. These considerations are more complicated and challenging when dealing with soft clay that is known to be highly deformable and have low shear strength. Shear strength is a very important parameter for the design o f the foundation of a structure. I t can be determined either in the field or in the laboratory, or both. The tests employed in the laboratory may include unconfined compression test, triaxial test, laboratory vane, direct shear box and direct simple shear (DSS) test. In situ tests are normally conducted to test the validity o f the laboratory tests and also for design purposes. The in situ tests available include field vane, standard penetration test, cone penetration test, piezocone and pressuremeter. This paper forms part o f a study to investigate and characterize soft marine clays in Malaysia. A location at Bukit Raja, Klang was chosen for soil sampling and testing. The research was funded by the Intensified Research i n Priority Areas (IRPA) program under RM5. I t is also supported by Universiti Kebangsaan Malaysia (UKM) and the Geotechnical Research U n i t o f the Institute Kerja Raya Malaysia, IKRAM. Methods to predict and determine undrained shear strength, s , o f soft clay are presented. The techniques are SHANSEP, critical state concept, recompression and in situ and laboratory vane shear strength. The first three methods utilize the DSS apparatus. I t is noted that all the methods employed show the same trend with slight differences i n value. I t was also found that the average field and laboratory vane test gives the highest estimation o f s ,followed by recompression method, SHANSEP and critical state predictions, respectively. u

MATERIALS AND M E T H O D S Location of the Study Area The study was conducted at Bukit Raja, Klang, Selangor i n the west coast of Peninsular Malaysia. Fig. 1 shows the location; o f the study area. The profile of the borehole is shown in Fig. 2 it demonstrated that the depth o f the soft clay at Bukit Raja goes down to about 10m before fine sand is encountered. Geology of the Area Geologically, coastal deposits in Peninsular Malaysia have been classified as quaternary deposits from the Cenozoic era. The geology o f the study area consists mainly o f Holocene deposits o f the quaternary period termed Gula formation; this consists primarily o f clay, silt and sand with minor amounts o f 112

Pertanika J . Sci. & Technol. Vol. 5 No. 1, 1997

Prediction and Determination of Undrained Shear Strength of Soft Clay

Fig 1: Location of the study area

gravel, shells and corals. Generally the soft deposits are thicker near the coastline and major river mouth, and become thinner away from the coastline. The thickness may range from 5-30 m (Abdullah et al. 1987). Shells and decayed wood are often found i n the deposits. The predominant clay minerals recorded are koalinite, illite and a mixed layer o f montmorillonite while the important foraminifera belong to the rotalia and nonion species (Mahilah Bibi 1971). The tidal range along the Selangor coast is the highest in Peninsular Malaysia. The recorded difference between the spring and the mean high water spring is 4.1 m i n Port Klang (Bosch 1988). Basic Properties Generally, the colour o f the clay in Bukit Raja is dark grey. Organic materials such as decayed wood and roots are found in the clay to a depth o f 10 m [see M o h d Raihan Taha et al. (1991) for more details].

PertanikaJ. Sci. 8c Technol. Vol. 5 No. 1, 1997

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M.A. Jamal, T . Raihan, A. Jimjali, A.K. Azmi, J . Azmi and J . Jamilah

Fill GWT Stiff clay +roots+silt Stiff clay+roots Soft clay+roots 2

Soft clay + traces of roots Cl

Q

Soft clay Soft clay+fine sand Fine sand 10

50% PL

LL

100%

moisture content

Fig 2: Borehole profile Results o f the Atterberg L i m i t tests are shown i n Table 1 . Plastic limit was in the range o f 30-45% with average value o f 36%. Liquid limit ranges between 75-95% with an average value o f 86%. The water content was mostly found to TABLE 1 Results of some basic soil tests Depth (m) 4.20 5.26 6.20 7.05 8.07 9.07 10.05 11.05 12.07 13.07

114

Moisture Contents (%) 77 78 88 90 84 92 92 97 84 74

Liquid Limit (%)

Plastic Limit (%)

Specific Gravity of Solid Solids

75 84 94 84 82 95 93 90 86 80

30 41 36 35 33 35 36 39 45 30

2.51 2.50 2.50 2.57 2.54 2.62 2.62 2.62 2.70 2.55

Pertanika J . Sci. 8c Technol. Vol. 5 No. 1, 1997

Prediction and Determination of Undrained Shear Strength of Soft Clay

TABLE 2 Comparison of basic properties of different clays Clay

Klang Singapore Bangkok Boston London Weald Norway Leda James Bay

w (%)

LL (%)

PL (%)

PI (%)

Unit weight kN/m

66-107 50-83 68 38.42 32

75-95 50-90 65 45-55 95 55-85 25-36 20-45 26-38

30-45 18-22 24 23-24 30 20-49 17-20 18-24 14-18

41-60 30-50 41 19-31 65 365-46 18-24 5-20 5-18

13.8-15.1 12.7-18.6 12.7-14.7 -

-/ 27-40 28-50 22-38

PL - Plastic limit LL - Liquid limit

J

15.7 16.7-19.6 17.7-19.6

w = Water Content PI * Plastic Index

be almost equal to its liquid limit. This leads to a liquidity index o f unity and therefore indicates the possibility that the soil is normally consolidated. The coordinates o f the plasticity index and liquid limit are mainly concentrates at the upper end along the A-line o f the Cassagrande Chart. Therefore, the clay may be classified as a highly plastic clay, C H or high plastic organic clay, O H . Using the AASHTO system, Klang clay can be grouped under A-7-5. The specific gravity values o f the soil are not consistent due to the existence of line sand, roots and old wood pieces i n some parts. These values are also shown i n Table 1. The average unit weight o f the soil is about 14.35 k N / m . Comparisons o f the index properties with other clays such as London clay, Norwegian clay and Boston Blue clay are given in Table 2. I t can be observed that Klang clay values are higher than those o f the other clays. 3

DSS Apparatus Direct simple shear apparatus available i n U K M is o f type N G I (Norwegian Geotechnical Institute), Model H-12. I n this apparatus, the soil sample is sheared by introducing lateral stress to the top part o f the sample while the bottom remains unmoved. Constant volume tests are performed using an automatic sample height. The primary feature o f this apparatus is the use o f a rubber membrane reinforced by wires. This membrane restrains the changes in its perimeter i n order to ensure uniform distribution o f stress and strain in the sample. The simple shear test gives a better uniform stress-strain relationship compared to the direct shear test. I n addition, the direct shear test creates problems in interpretation o f test results due to the rotation of principal stresses. Further details of this apparatus may be found in Geonor (1968) and Azmi (1991).

Pertanika J . Sci. 8c Technol. Vol. 5 No. 1, 1997

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M.A. Jamal, T. Raihan, A. Jimjali, A.K. Azmi, J. Azmi and J . Jamilah

As various kinds o f construction lead to the application of different loading conditions to the soil, several laboratory tests were developed to reproduce or simulate the loading conditions in the laboratory. The strength measured using DSS apparatus represents the average mobilized strength for embankment stability o f soft clay (Trak et al 1980), soft ground beneath spread footings (Kinner and Ladd 1973), and shaft resistance along pile foundation (Randolf and Wroth 1981). Based on the s of 50 different soft clays, Mayne (1985) observed that the DSS test gave values between that of triaxial compression and triaxial extension tests. u

Prediction of s using SHANSEP Procedure u

The SHANSEP method was first introduced by Ladd and Foott (1974). I t is a procedure that can be used for design purposes and for examining stability o f soft clay that shows a normalized behaviour. A soil parameter is normalized by reducing it to a dimensionless number. Here, a normalized parameter is obtained by dividing s to the in situ effective stress

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