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A deuterium magnetic resonance study of chain disorder in lamellar phases of mixed chain length Tang, Wendy Wai Sau 1981

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A DEUTERIUM MAGNETIC RESONANCE STUDY OF CHAIN DISORDER IN LAMELLAR PHASES OF MIXED CHAIN LENGTH by WENDY WAI SAU jTANG B. S c . , U n i v e r s i t y o f Hong K o n g , 1979 T H E S I S SUBMITTED IN P A R T I A L F U L F I L M E N T OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF S C I E N C E i n THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CHEMISTRY We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE U N I V E R S I T Y OF B R I T I S H COLUMBIA O c t o b e r , 1981 ©Wendy Wai Sau Tang, 1981 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head of my department o r by h i s o r her r e p r e s e n t a t i v e s . I t i s understood t h a t c o p y i n g or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a llowed without my w r i t t e n p e r m i s s i o n . Department of The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date Oct J&.ft DE-6 (2/79) A b s t r a c t D e u t e r i u m nmr i s u s e d t o i n v e s t i g a t e t h e t e m p e r a t u r e d e p e n d e n c e o f t h e o r i e n t a t i o n a l o r d e r o f s m a l l a m o u n t s o f p e r d e u t e r a t e d p o t a s s i u m c a r b o x y l a t e s o f d i f f e r i n g c h a i n l e n g t h s d i s s o l v e d a s g u e s t s i n t h e p r o t i a t e d h o s t p o t a s s i u m p a i m i t a t e . A d d i t i o n a l l y , s a m p l e s c o n t a i n i n g l i p i d s o f a s i n g l e c h a i n l e n g t h e q u a l t o t h a t o f e a c h g u e s t a r e s t u d i e d f o r c o m p a r i s o n . L o n g c h a i n g u e s t s h a v e t h e same o r i e n t a t i o n a l o r d e r a s t h e h o s t u p t o t h e 15th p o s i t i o n , w h i l e t h e r e s t o f t h e c h a i n i s o r i e n t a t i o n a l l y d i s o r d e r e d . S h o r t c h a i n g u e s t s a r e r e s t r i c t e d i n s i d e t h e h o s t a n d t h e r e i s l e s s i n t e r a c t i o n o f t h e p o l a r h e a d w i t h w a t e r t h a n i n t h e s i n g l e c h a i n l e n g t h s a m p l e s . P h a s e s e p a r a t i o n i n v o l v i n g a r a p i d e x c h a n g e o f m o l e c u l e s b e t w e e n a l a m e l l a r p h a s e a n d a p o s s i b l y i s o t r o p i c p h a s e y i e l d s u n e x p e c t e d l y l o w s p l i t t i n g s f o r t h e s h o r t c h a i n g u e s t s a t l o w e r t e m p e r a t u r e a n d w i t h h i g h e r w a t e r c o n t e n t . Table of Contents Page Abstract i L i s t of Figures i V Acknowledgements vii Chapter 1 Introduction 1 2 Theory 2.1 Deuterium nmr i n the absence of molecular motion 10 2.2 Deuterium nmr i n the presence of rapid anisotropic molecular motion 13 2.3 Deuterium nmr of p o l y c r y s t a l l i n e samples 14 3 Experimental 3.1 Materials 16 3.2 Sample preparation 16 3.3 NMR spectroscopy 18 Z+ Results 4.1 Guest samples Cn 21 4.2 Pure samples Pn 29 3 Discussion 3.1 Models of the host-guest mixture 5.1.1 Review of the host behavior 3 5 5.1.2 Proposed Models 36 5.2 Analysis of the proposed model 36 in 5.3 Comparison between Cn and Pn samples 5.3.1 Comparison of the average s p l i t t i n g s and the d i s t r i b u t i o n parameter 5.3.2 Comparisons f o r i n d i v i d u a l chain p o s i t i o n s 5«4 L i p i d - w a t e r i n t e r a c t i o n 5.4.1 For chain l e n g t h comparable to and longer than that of the host 5.4.2 For s h o r t chains 5.5 Phase separation 5.5.1 Phase separation e f f e c t on the guest 5.5.2 Phase separation e f f e c t on the host 6 Summary and Conclusion 7 Table 1: Composition of samples References iV L i s t of Figures Figure Page 1 General features of the phase diagram i n the potassium palmitate-water system. 2 2 (a) Schematic representation of the geometry and the coordinate system i n a l i p i d b i l a y e r . (b) Orientation of the s t a t i c magnetic f i e l d with respect to the p r i n c i p a l coordinate system of the e l e c t r i c f i e l d gradient. 12 3 Theoretical powder pattern for a deuterium nucleus i n a symmetric e l e c t r i c f i e l d gradient (T\ =0) 15 4 Schematic diagram of the s o l i d echo pulse sequence. 5 Calibration graph for sample temperature 6 Representative DMR spectra of CD^ and CD^ i n (a) C22 at 77°C (b) PI 6 at Gk°C 22 7 Temperature dependence of the spectral s p l i t t i n g s (A-Oi ) for the guest potassium caproate, caprate, higher water content caprate, laurate, palmitate and behenate. 23 8 Temperature dependence of the spectral s p l i t t i n g s (a-iK ) for the samples containing l i p i d s of a single chainlength (Pn, n=lO, 12, 16, 22). 30 18 20 V 9 Variation of the r e l a t i v e s p l i t t i n g ( j ^ ) along the hydrocarbon chain for C6, CIO, C12, Cl6 and C22 samples at 49°C and 143°C(methyl group s p l i t t i n g s are not shown). 38 10 Temperature dependence of the average s p l i t t i n g <C^^y for (a) Cn sample * (n=6, 10, 12, 16, 22) (b) Pn sample (n=10, 12, 16, 22) 40 11 Temperature dependence of the r a t i o of the average s p l i t t i n g betwaen Cn and Pn 12 Temperature dependence of the d i s t r i b u t i o n parameter £^z for (a) Cn sample (n=6, 10, 12, 16, 22) (b) Pn sample ' (n=10, 12, 16, 22) 44 13 Temperature dependence of the r a t i o of the d i s t r i b u t i o n parameter between Cn and Pn samples( ^* C n ). 45 ^1 Pn 14 (a) Variation of the spectral s p l i t t i n g along the hydrocarbon chain for i ) C10, P10, P16; i i ) C12, P12, P16; . m ) Cl 6, P16; i v ) C22, P22, P 1 6 . (b) Variation of the r a t i o of the spectral s p l i t t i n g between Cn and Pn sample along the hydrocarbon chain (^ .^'^ y) for ( i ) caprate, ( i i ) laurate, ( i i i ) palmitate, and (iv) behenate. 47 V i 15 Model for the lipid-water i n t e r f a c e . 53 16 Spectral s p l i t t i n g (£\) 2 ) of the d-CD2 group plotted against guest chain length at 143°C, 104°C, 77°C, 58°C and z+5°C. 56 17 Temperature dependence of the spectral s p l i t t i n g )} of (a) D 20 (b) o(-CD2 (c) W-CD2 for Cn samples(n=6, 10, 12, 16, 2 2 ) . 58 18 Phase diagram of the sodium laurate-water system. 60 i v i i A c k n o w l e d g e m e n t s F i r s t o f a l l , I w i s h t o a c k n o w l e d g e my g r e a t r e s e a r c h s u p e r v i s o r , D r . E . E l l i o t t B u r n e l l f o r h i s p a t i e n c e , e n t h u s i a s m a n d h e l p t h r o u g h - o u t t h e c o u r s e o f t h i s w o r k . I h a v e g r e a t l y b e n e f i t e d f r o m h i s m e t h o d i c a l i n s t r u c t i o n a n d a d v i s e . I am v e r y g r a t e f u l t o D r . T i m o t h y P. H i g g s a n d D r . V i n o d K. G u j r a l f o r p r o v i d i n g h e l p i n p r e p a r a t i o n o f t h e s a m p l e s , a n d D r . A l e x L . M a c k a y f o r t h e t e c h n i c a l a s s i s t a n c e . I a l s o e x p r e s s my s i n c e r e g r a t i t u d e t o D r . H a k a n W e n n e r s t r o m a n d D r . J a m e s H. D a v i s f o r many f r u i t f u l d i s c u s s i o n s . F i n a l l y , I t h a n k my p a r e n t s a n d Kan S z e t o f o r t h e i r c o n t i n u i n g e n c o u r a g e m e n t a n d m o r a l s u p p o r t . 1 C h a p t e r 1 I n t r o d u c t i o n T h e p r i n c i p a l c o n s t i t u e n t s o f b i o l o g i c a l membranes a r e t h e p o l a r l i p i d s a n d p r o t e i n s ( 1 ) . T h e e s s e n t i a l s t r u c t u r a l r e p e a t i n g u n i t s a r e t h e p h o s p h o l i p i d m o l e c u l e s i n a b i l a y e r a r r a n g e m e n t . G l o b u l a r p r o t e i n s may l o c a l i z e a t one o r t h e o t h e r o f t h e two s u r f a c e s o f t h e l i p i d b i l a y - e r o r may p a s s f r o m one s i d e t o t h e o t h e r . I n o r d e r t o u n d e r s t a n d t h e f u n d a m e n t a l p h y s i c a l p r o p e r t i e s o f t h e b i o l o g i c a l s y s t e m s , m o d e l membranes a r e f r e q u e n t l y e m p l o y e d ( 2 - 4 ) t o make q u a n t i t a t i v e m e a s u r e m e n t a n d t h e o r e t i c a l i n t e r p r e t a t i o n much e a s i e r . M o d e l s w h i c h h a v e s i m i l a r i t i e s i n s t r u c t u r e t o t h e r e a l b i o l o g i c a l membranes c a n be made f r o m d i s p e r s i o n s o f l i p i d s i n w a t e r . I n c l u d e d i n t h i s g r o u p o f m o d e l membranes a r e t h e s o a p - w a t e r s y s t e m s , w h i c h a r e m i x t u r e s o f f a t t y a c i d s a l t s a n d w a t e r . Due t o t h e a m p h i l p h i l i c n a t u r e o f s o a p m o l e c u l e s , w h i c h c o n t a i n h y d r o p h i l i c h e a d g r o u p s a n d h y d r o p h o b i c p a r a f f i n i c c h a i n s , m i x t u r e s o f s o a p a n d w a t e r f o r m a v a r i e t y o f l y o t r o p i c l i q u i d c r y s t a l p h a s e s a s t h e t e m p e r a t u r e a n d t h e c o m p o s i t i o n a r e v a r i e d . T h e m e s o p h a s e s a r e c h a r a c t e r i z e d b y t h e e x i s t e n c e o f l o n g r a n g e o r d e r a n d s h o r t r a n g e d i s o r d e r . T h e m o l e c u l a r d y n a m i c s o f t h e i n d i v i d u a l m o l e c u l e s i n t h e s i m p l e s o a p - w a t e r s y s t e m s w i t h i n t h e v a r i o u s p h a s e s a r e v e r y f a s c i n a t i n g , a n d 2 s t u d i e s o f t h i s t y p e o f m o d e l membrane a r e o f g r e a t i n t e r e s t i n t h e i r own r i g h t . T h e s o a p m o l e c u l e s h a v e a g e n e r a l t e n d e n c y t o a g g r e g a t e i n s u c h a way t h a t t h e h y d r o p h i l i c h e a d g r o u p i s a n c h o r e d a t t h e l i p i d - w a t e r i n t e r f a c e w h i c h s e p a r a t e s t h e a q u e o u s a n d p a r a f f i n i c r e g i o n . T h e l o n g r a n g e o r g a n i z a t i o n o f s o a p - w a t e r m e s o p h a s e s h a s b e e n s t u d i e d by X - r a y t e c h n i q u e s ( 5 ) . T h e g e n e r a l f e a t u r e s o f t h e p h a s e d i a g r a m a r e i l l u s t r a t e d i n f i g . 1. Weight Percent of Water Figure 1 : General features of the phase diagram i n the potassium palmitate-water system. (Copied from Bloom et a l . J . Chem. Phys. £ £ ( 1 9 7 7 ) , 3 0 1 2 . ) A c c o r d i n g t o t h e i r a r r a n g e m e n t a n d c o n f o r m a t i o n . , t h e m o l e c u l e s a r e c l a s s i f i e d a s f o l l o w s : 1. O r d e r e d c h a i n p h a s e s T h e s e p h a s e s a r e g e n e r a l l y o b s e r v e d w i t h low w a t e r c o n t e n t (< 20 w e i g h t p e r c e n t ) a n d a t low t e m p e r a t u r e . T h e s t r u c t u r e e l e m e n t s a r e s y m m e t r i c m o n o l a y e r s , a n d t h e c h a i n s a r e i n t e r d i g i t a t e d . G e l ( L E ) p h a s e T h i s p h a s e h a s t h e l a m e l l a r s t r u c t u r e w h e r e t h e m o l e c u l e s a r e a r r a n g e d i n p l a n e s o f b i l a y e r s s e p a r a t e d by w a t e r l a y e r s . T h e s o l i d - l i k e , a l l t r a n s h y d r o c a r b o n c h a i n s a r e p e r p e n d i c u l a r t o t h e l a m e l l a e , a n d t h e r e i s no i n t e r c o n v e r s i o n b e t w e e n c o n f o r m a t i o n s . C o a g e l ( L i ' ) p h a s e T h i s p h a s e o c c u r s a t l o w e r t e m p e r a t u r e a n d t h e s t r u c t u r e ' i s s i m i l a r t o t h a t o f t h e g e l p h a s e e x c e p t t h a t t h e s t i f f h y d r o c a r b o n c h a i n s a r e t i l t e d a t a n a n g l e w i t h r e s p e c t t o t h e n o r m a l t o t h e l a m e l l a e . 2. L i q u i d c r y s t a l l i n e p h a s e s T h e p a r a f f i n i c c h a i n s a r e s u f f i c i e n t l y f l e x i b l e t h a t t h e y f i t a l o t o f d i f f e r e n t n e i g h b o u r i n g c o n d i t i o n s . T h e m o l e c u l e s c a n a g g r e g a t e i n l a m e l l a e , r i b b o n s , r o d s o r s p h e r e s p e r i o d i c a l l y a l o n g o n e , two a n d t h r e e d i m e n s i o n s . T h e y u n d e r g o a n i s o t r o p i c t r a n s l a t i o n a l d i f f u s i o n a n d r a p i d 4 r o t a t i o n a l d i f f u s i o n about an a x i s p e r p e n d i c u l a r t o the i n t e r f a c e . These d i f f u s i o n a l motions a r e accompanied by a l k y l group g a u c h e - t r a n s c o n f o r m a t i o n a l m o t i o n s . L a m e l l a r (La) phase B e i n g a s m e c t i c A l i q u i d c r y s t a l , t h i s phase c o n s i s t s of p l a n a r , p a r a l l e l and e q u i d i s t a n t l i p i d b i l a y e r s s e p a r a t e d by water l a y e r s . The l a y e r s e x t e n d over l a r g e d i s t a n c e s , commonly of the o r d e r of m i c r o n s or more. The h y d r o c a r b o n c h a i n s a r e l i q u i d - l i k e and h i g h l y d i s o r d e r e d . On the a v e r a g e , the c h a i n s a r e o r i e n t a t e d p e r p e n d i c u l a r t o the l i p i d - w a t e r i n t e r f a c e . T r a n s l a t i o n a l d i f f u s i o n of the soap m o l e c u l e s i s c o m p a r a t i v e l y r a p i d (6) (D ~ 10' 6 cm 2 s - 1 ) . Hexagonal (Ho) phase  0 T h i s phase c o n t a i n s rod-shaped m i c e l l e s of i n d e f i n i t e l e n g t h packed i n a hexagonal a r r a y s e p a r a t e d by a c o n t i n u o u s water r e g i o n . The soap m o l e c u l e s d i f f u s e t r a n s l a t i o n a l l y a l o n g and around the i n f i n i t e l y l o n g c y l i n d e r s . C u b i c (Qo) phase The Qo phase o c c u r s between the Ho and the Lo phases. I t i s a " v i s c o u s - i s o t r o p i c " phase, the s t r u c t u r e of which has not been w e l l - e s t a b l i s h e d . There may be groups of m i c e l l e s packed i n some s o r t of c u b i c a r r a y . They may c o n s i s t of s h o r t s u r f a c t a n t or water rods j o i n e d t o form a 5 c o n t i n u o u s n e t w o r k . R a p i d d i f f u s i o n o f t h e s o a p m o l e c u l e s a l o n g t h i s n e t w o r k o f c u b i c s y m m e t r y i s e q u i v a l e n t t o i s o t r o p i c m o t i o n o f t h e m o l e c u l e s f r o m a n NMR p o i n t o f v i e w M i c e l l a r p h a s e T h e m i c e l l e s h a v e a s p h e r i c a l s t r u c t u r e i n w h i c h t h e c a r b o x y l g r o u p s o f s o a p m o l e c u l e s f a c e t h e a q u e o u s e n v o i r o n m e n t a n d t h e h y d r o c a r b o n c h a i n s e x t e n d i n w a r d s t o w a r d s t h e c e n t r e o f t h e m i c e l l e . I s o t r o p i c m o t i o n i s d e t e c t e d by nmr due t o t h e r a p i d t r a n s l a t i o n a l d i f f u s i o n o f t h e l i p i d s a n d t h e t u m b l i n g m o t i o n o f t h e m i c e l l e s . T h e s h o r t r a n g e d y n a m i c s o f t h e l i p i d s i n e a c h p h a s e h a v e b e e n i d e n t i f i e d by m a g n e t i c r e s o n a n c e ( 7 - 8 ) a n d o t h e r t e c h n i q u e s ( 9 ) . T h r e e l a m e l l a r p h a s e s , t h e l i q u i d c r y s t a l l i n e ( L a ) , g e l {Lp) a n d c o a g e l ( L * ' ) , a r e o f p a r t i c u l a r i n t e r e s t . NMR p r o v i d e s r e l i a b l e q u a n t i t a t i v e d a t a a b o u t t h e m o t i o n a n d t h e c o n f o r m a t i o n o f t h e c h a i n s . T h e m o l e c u l a r p r o p e r t i e s c a n be d e s c r i b e d by t h e o r d e r p a r a m e t e r a n d t h e c o r r e l a t i o n t i m e f o r e a c h s e g m e n t on t h e h y d r o c a r b o n c h a i n . T h e m a i n e x p e r i m e n t a l q u a n t i t y t h a t a l l o w s m e a s u r e m e n t o f t h e o r d e r p a r a m e t e r f o r e a c h m e t h y l e n e s e g m e n t i s t h e s p l i t t i n g o f t h e nmr a b s o r p t i o n l i n e ( e x p l a i n e d i n t h e o r y s e c t i o n ) d u e t o t h e n u c l e a r d i p o l e d i p o l e o r t h e q u a d r u p o l e i n t e r a c t i o n . T h e l i p i d 6 b i l a y e r s h a v e b e e n i n v e s t i g a t e d i n d e t a i l u s i n g d e u t e r i u m nmr on a v a r i e t y o f b i n a r y s y s t e m s , i n c l u d i n g p o t a s s i u m o r s o d i u m l a u r a t e ( 1 0 - 1 1 ) , p o t a s s i u m p a l m i t a t e ( 1 2 ) a n d p o t a s s i u m s t e a r a t e ( 1 3 ) . I t i s f o u n d t h a t t h e o r d e r p a r a m e t e r s o f t h e m e t h y l e n e g r o u p s a r e f a i r l y c o n s t a n t f r o m t h e p o l a r h e a d g r o u p t o a b o u t t h e m i d d l e o f t h e h y d r o c a r b o n c h a i n . A f t e r t h i s p o s i t i o n , t h e o r d e r p a r m e t e r s o f t h e r e m a i n i n g m e t h y l e n e g r o u p s d e c r e a s e r a p i d l y . H e n c e a p l o t o f t h e o r d e r p a r a m e t e r v e r s u s c a r b o n p o s i t i o n shows a ' p l a t e a u ' . A t h i g h t e m p e r a t u r e , o r on a d d i t i o n o f w a t e r , t h e r e i s a r e d u c t i o n i n t h e a v e r a g e o r d e r o f t h e c h a i n s a n d a l s o a r e d u c t i o n i n t h e s i z e o f t h e p l a t e a u r e g i o n . Many c h e m i c a l f a c t o r s may a f f e c t t h e e x p e r i m e n t a l l y d e t e r m i n e d o r d e r p a r a m e t e r p r o f i l e s . T h e s e may i n c l u d e v a r i a t i o n o f t h e p o l a r h e a d g r o u p s , i s o t o p i c s u b s t i t u t i o n , o r h e t e r o g e n e i t y o f c h a i n l e n g t h s . T h e e f f e c t o f h e t e r o g e n e i t y o f c h a i n l e n g t h s on t h e e x p e r i m e n t a l l y d e t e r m i n e d o r i e n t a t i o n a l o r d e r p a r a m e t e r s h a s b e e n e x a m i n e d p r e v i o u s l y . C h e n e t a l . ( 1 4 ) s t u d i e d s m a l l a m o u n t s o f a g u e s t c a r b o x y l i c a c i d o r c a r b o x y l a t e i n a n o r i e n t e d l y o m e s o p h a s e c o n t a i n i n g a c o n s t a n t r a t i o o f s o d i u m d e c y l s u l p h a t e , d e c a n o l , s o d i u m s u l p h a t e a n d w a t e r . T h e s e s t u d i e s were p e r f o r m e d a t a s i n g l e t e m p e r a t u r e , 3 4 ° C . I t was f o u n d t h a t t h e d e g r e e o f o r d e r o f t h e ex-p o s i t i o n o f e a c h g u e s t s p e c i e s i n c r e a s e s w i t h i n c r e a s i n g 7 c h a i n l e n g t h u p t o t h a t p o i n t w h e r e t h e l e n g t h o f t h e g u e s t c h a i n a p p r o x i m a t e l y m a t c h e s t h a t o f t h e h o s t , a t w h i c h p o i n t no f u r t h e r i n c r e a s e i s o b s e r v e d . T h e s e r e s u l t s were e x p l a i n e d a s e i t h e r a d e c r e a s e i n t h e f r e e d o m o f c o n f o r m a t i o n a l m o t i o n s a s t h e c h a i n i s l e n g t h e n e d o r a d e c r e a s e i n t h e a m p l i t u d e o f o s c i l l a t i o n s o f t h e a v e r a g e c h a i n a x i s a b o u t t h e n o r m a l t o t h e i n t e r f a c e . I n a s t u d y o f F o r r e s t e t a l . ( l 5 ) on t h e e f f e c t o f h e t e r o g e n e i t y o f c h a i n l e n g t h s , l o n g c h a i n g u e s t s were d i s s o l v e d i n t h e h o s t s o d i u m d e c y l s u l p h a t e . The f i r s t f o u r m e t h y l e n e p o s i t i o n s o f t h e l o n g c h a i n g u e s t s h a v e h i g h e r o r i e n t a t i o n a l o r d e r t h a n t h e h o s t . F r o m t h e 4 t h p o s i t i o n t o t h e e n d o f t h e h o s t c h a i n , t h e g u e s t a n d t h e h o s t h a v e s i m i l a r o r i e n t a t i o n a l o r d e r p r o f i l e s . T h e r e a f t e r , t h e e x c e s s c h a i n l e n g t h s o f t h e g u e s t s h a v e l o w a n d s t e a d i l y d e c r e a s i n g o r i e n t a t i o n a l o r d e r . I t was s u g g e s t e d t h a t t h e t a i l s o f t h e l o n g c h a i n g u e s t s p a r t i c i p a t e i n t h e d i s o r d e r e d r e g i o n a t t h e c e n t r e o f t h e b i l a y e r r a t h e r t h a n i n s e r t t h e m s e l v e s i n t o t h e o p p o s i t e s i d e o f t h e b i l a y e r . I n a s t u d y by C h a r v o l i n e t a l . ( l 6 ) , s o a p s w i t h d i f f e r e n t c h a i n l e n g t h s (C10 o r C14) w e r e a d d e d t o t h e l a m e l l a r p o t a s s i u m s t e a r a t e ( C 1 8 ) h o s t a t 7 0 ° C . The two l a m e l l a r C14 a n d C18 p h a s e s a p p e a r t o t a l l y m i s c i b l e . M i x t u r e s o f t h e s e . two s o a p s s t i l l e x i s t a s a l a m e l l a r s t r u c t u r e . F o r l a r g e g u e s t c o n c e n t r a t i o n s i n t h e C18-C10 8 was m i x t u r e s , t h e l a m e l l a r p h a s e i s no l o n g e r s t a b l e S e p a r a t i o n o f t h e two d i f f e r e n t c h a i n l e n g t h m o l e c u l e s d e t e c t e d by X - r a y d i f f r a c t i o n . M e l y e t a l . ( 1 7 ) u s e d d e u t e r i u m nmr t o s t u d y t h e s e same s y s t e m s a t 6 0 ° C i n t h e p r e s e n c e o f 6.2 m o l e s w a t e r p e r m o l e s o a p . T h e y o b s e r v e d t h a t t h e f i r s t few m e t h y l e n e g r o u p s n e a r t h e p o l a r h e a d a r e n o t a f f e c t e d by t h e p r e s e n c e o f c h a i n s o f d i f f e r e n t c h a i n l e n g t h . O n l y t h e l a s t few m e t h y l e n e g r o u p s a n d t h e m e t h y l g r o u p a r e p e r t u r b e d by t h e h o s t . T h e s h o r t c h a i n s a r e a l i t t l e more c o n s t r a i n e d a n d t h e l o n g c h a i n s l e s s c o n s t r a i n e d t h a n f o r t h e same m o l e c u l e i n a s a m p l e o f s i n g l e c h a i n l e n g t h . I n a n o t h e r s t u d y Beckmann e t a l . ( l 8 ) i n v e s t i g a t e d t h e c h a i n o r i e n t a t i o n a l o r d e r o f t h e h o s t p o t a s s i u m p a l m i t a t e u n d e r t h e e f f e c t o f l o n g o r s h o r t c h a i n g u e s t s . T h e i r e x p e r i m e n t a l r e s u l t s g i v e a s i m p l e q u a l i t a t i v e p i c t u r e o f t h e m i x e d c h a i n l e n g t h s y s t e m . A t h i g h t e m p e r a t u r e , t h e s h o r t c h a i n g u e s t s g i v e r i s e t o more f l u i d i t y a n d t h e l o n g c h a i n g u e s t s g i v e r i s e t o l e s s f l u i d i t y t o w a r d s t h e m e t h y l e n d o f t h e h o s t c h a i n . A t l o w t e m p e r a t u r e , t h e e f f e c t o f l i p i d - w a t e r i n t e r a c t i o n i s i m p o r t a n t i n d e t e r m i n i n g t h e o r i e n t a t i o n a l o r d e r o f t h e h o s t c h a i n . T h e s e s t u d i e s l e a v e many q u e s t i o n s u n a n s w e r e d . I t i s o f g r e a t i n t e r e s t t o e x a m i n e c r i t i c a l l y t h e e x p l a n a t i o n o f t h e d e p e n d e n c e o f t h e o - m e t h y l e n e s p l i t t i n g s on 9 c h a i n l e n g t h o f C h e n e t a l . ( 1 4 ) , a n d t o i n v e s t i g a t e t h e e f f e c t o f h e t e r o g e n e i t y o f c h a i n l e n g t h on t h e d e u t e r i u m nmr o f t h e m o l e c u l e s i n t h e l a m e l l a r p h a s e i n d e t a i l a s a f u n c t i o n o f t e m p e r a t u r e a n d c h a i n p o s i t i o n . Beckmann e t a l . ( l 8 ) h a v e w e l l d e t e r m i n e d t h e b e h a v i o r o f t h e h o s t a t v a r i o u s t e m p e r a t u r e s , b u t f u r t h e r i n v e s t i g a t i o n i s r e q u i r e d on t h e b e h a v i o r o f t h e g u e s t s . F o r t h i s p u r p o s e , we s h a l l s t u d y ? t h e o r i e n t a t i o n a l o r d e r o f g u e s t c h a i n s o f d i f f e r e n t l e n g t h u s i n g a g u e s t c o n c e n t r a t i o n t h a t d o e s n o t p e r t u r b t h e h o s t o r d e r s i g n i f i c a n t l y . D e u t e r i u m nmr i s u s e d t o o b s e r v e t h e o r i e n t a t i o n a l o r d e r o f e a c h m e t h y l e n e g r o u p on t h e c h a i n s i n p e r d e u t e r a t e d p o t a s s i u m c a p r o a t e , c a p r a t e , l a u r a t e , p a l m i t a t e a n d b e h e n a t e w h i c h h a v e b e e n a d d e d a s 1 m o l e % g u e s t t o t h e h o s t p r o t i a t e d p o t a s s i u m p a l m i t a t e . P e r d e u t e r a t e d s o a p s o f s i n g l e c h a i n l e n g t h t h e same a s t h a t o f t h e g u e s t s a r e a l s o s t u d i e d f o r c o m p a r i s o n . 10 Chapter 2 o Theory o 2.1. Deuterium nmr in the absence of molecular motion. In an applied magnetic f i e l d H e, the t o t a l spin Hamiltonian- for a deuterium with nuclear spin 1=1 i s dominated by Zeeman and quadrupolar interactions. The dipolar interactions and indire c t spin-spin couplings are e s s e n t i a l l y n e g l i g i b l e . Hence, the Hamiltonian can be written as H = H2 + Hg. Because in f i e l d s normally used the quadrupolar interaction i s much smaller than the Zeeman interaction, only the f i r s t order perturbation i s considered in solving the energy l e v e l s ( l 9 ) . In a r i g i d s o l i d in the absence of molecular motion, the energy lev e l s are then given by Em - - T l U t ^ [ 3 m ' - K I + t ) l [ icn\9^ * 1 s J e v n z f ] M where 6 and 0 are the Euler angles defining the e l e c t r i c f i e l d gradient ( e T g ) tensor with respect to the magnetic f i e l d H,, m i s t h e magnetic quantum 'number which i s +1, ( 11 or -1 for 1=1, v0 i s the Larmor frequency, i s the guadrupolar coupling constant, and n i s the asymmetry parameter which i s a measure of the deviation of the efg from a x i a l symmetry ( f i g . 2 ) . The asymmetry parameter for the C-D bonds as obtained from t h e o r e t i c a l c a l c u l a t i o n s and c r y s t a l studies(20-24) is less than 0.05. Hence, to a good approximation, n can be neglected, and the energy lev e l s for one s p e c i f i c deuteron can be written as _ N -^ a / 3 cos 8 - 1 v E-, - v. T ^ 2 ; E . - -4 (HP) _ N -Oa / 3 COS 0 - 1 x E., * ' ^  + T ( 2 5 [2] The t r a n s i t i o n s are governed by the selection rule Am=+1 or - 1 , so that there are two resonance frequencies in the NMR spectrum: The separation between these two l i n e s i s the quadrupolar s p l i t t i n g Ava and A-Oa " I Va V 2 ' 2K ^ 2 ' [4] 12 Figure 2. (a) Schematic r e p r e s e n t a t i o n of the geometry i n a l i p i d b i l a y e r . n i s the normal to the b i l a y e r . n i s the~angle between the magnetic f i e l d Hp and n, 9 i s the angle between the C-D bond d i r e c t i o n and Hp and 6 n i s the angle between the C-D bond d i r e c t i o n and n. (b) O r i e n t a t i o n of the magnetic f i e l d d i r e c t i o n r e l a t i v e to the p r i n c i p a l coordinate system of the e l e c t r i c f i e l d g r a d i e n t . where eQ i s the n u c l e a r q u a d r u p o l e moment, eq i s the e l e c t r i c f i e l d g r a d i e n t a t the d e u t e r i u m n u c l e u s , and h i s P l a n c k ' s c o n s t a n t . 2.2. Deuterium nmr i n the pr e s e n c e of r a p i d a n i s o t r o p i c  m o l e c u l a r m o t i o n . The a n i s o t r o p i c m o t ions of the CDg groups i n the c h a i n s i n c l u d e r o t a t i o n a l d i f f u s i o n of the whole m o l e c u l e about an a x i s of a t l e a s t 3 - f o l d symmetry, the t r a n s l a t i o n a l d i f f u s i o n of the m o l e c u l e s i n the p l a n e of the b i l a y e r , and the a l k y l groups g a u c h e - t r a n s c o n f o r m a t i o n a l motions w i t h i n the m o l e c u l e s . The r a t e of t h e s e a n i s o t r o p i c motions i s much f a s t e r than the time s c a l e ( r o u g h l y e q u a l t o M2irAi/ Q) ~ 10 " 6 s ) of the d e u t e r i u m nmr e x p e r i m e n t . T h e r e f o r e , t h e time average of (3 c o s 2 6 - 1 ) / 2 must be c o n s i d e r e d . By u s i n g the a d d i t i o n theorem(25) f o r the s p h e r i c a l h a r m o n i c s , the mot i o n s a r e s e p a r a t e d i n t o two independent components, and the time average of (3 c o s 2 e -1)/2 can be w r i t t e n a s : / 3 c o s 2 e - 1 x _ / 3 cos'0n - 1 v / 3 cos a i l -1 \ 2 / ~ >• Z 2 > where n i s the a n g l e between the magnetic f i e l d Ho and the normal n t o the b i l a y e r s u r f a c e , and e n i s the a n g l e between the C-D bond d i r e c t i o n and n. Then the q u a d r u p o l a r s p l i t t i n g o f a d e u t e r o n on the n t h p o s i t i o n w i l l be: The o r d e r parameter f o r the n t h p o s i t i o n i s d e f i n e d as SCH=Sn = < [ 6 ] , which i s a measure of the time average f l u c t u a t i o n of the C-D bond a x i s w i t h r e s p e c t t o the normal n, and i s d e t e r m i n e d by the o r i e n t a t i o n a l o r d e r of the C-D bond i n the n t h p o s i t i o n of the h y d r o c a r b o n c h a i n . 2.3. Deuterium nmr of p o l y c r y s t a l l i n e samples. For randomly o r i e n t e d samples, the normals t o the l a m e l l a e make random a n g l e s w i t h the magnetic f i e l d H„, and a l l v a l u e s of cos n a r e e q u a l l y p r o b a b l e . The shape of the s o - c a l l e d 'powder-type' nmr spectrum t h a t i s o b t a i n e d i s an average over the resonances of a l l p o s s i b l e v a l u e s of c os n. I t i s a broad a b s o r p t i o n c u r v e g i v e n by the f u n c t i o n qiv+) where T2 i s the s p i n - s p i n r e l a x a t i o n t i m e , v i s the 15 frequency and the i n t e g r a l i s over a l l possible orientations. Equation 7 i s plotted in f i g 3. Frequency (in kHz) Figure 3: Theoretical powder pattern f o r a deuterium nucleus i n a symmetric e l e c t r i c f i e l d gradient. In the presence of dipolar broadening of the spectra, the measured peak to peak values are less than the actual s p l i t t i n g s ( 2 6 ) . Hence the peak positions are read s l i g h t l y to the side of the spectral peaks in order to correct p a r t i a l l y for t h i s systematic error. The separation between the two s i n g u l a r i t i e s i s then . ^ a S J [ 8 ] , This expression shows that the quadrupolar s p l i t t i n g Av i s proportional to the order parameter S„. Therefore the order parameters for the methylene deuterons on a hydrocarbon chain can be obtained d i r e c t l y from the measured quadrupolar s p l i t t i n g s Ay. Hence whatever one says about quadrupolar s p l i t t i n g s , one could imply about order parameters. 16 C h a p t e r 3 E x p e r i m e n t a l 3.1. M a t e r i a l s P a l m i t i c a c i d ( C a l b i o c h e m A g r a d e ) was u s e d t o p r e p a r e p o t a s s i u m p a l m i t a t e w i t h o u t f u r t h e r p u r i f i c a t i o n . O t h e r a c i d s w e r e d e u o t e r a t e d a n d p u r i f i e d by D r . T . P . H i g g s a n d D r . V . K . G u j r a l i n t h i s l a b o r a t o r y . T h e f a t t y a c i d s t o be d e u t e r a t e d w e r e p l a c e d i n a two nectk f l a s k w i t h p a l l a d i u m on c h a r c o a l a n d h e a t e d t o 1 8 0 ° C . D e u t e r i u m g a s was p a s s e d o v e r t h e s u r f a c e c o n t i n u o u s l y a t a b o u t 35 c c . p e r m i n u t e f o r a week. D e u t e r a t e d a c i d s w e r e t h e n p u r i f i e d by s i l i c a g e l c h r o m a t o g r a p h y , a n d a n a l y s e d b y mass s p e c t r o s c o p y a n d h i g h r e s o l u t i o n nmr ( 2 7 ) . 3.2. S a m p l e p r e p a r a t i o n 0 T h e p o t a s s i u m s a l t s w e r e p r e c i p i t a t e d f r o m e t h a n o l by t h e a d d i t i o n t o t h e c o r r e s p o n d i n g f a t t y a c i d o f 1.05 e q u i v a l e n t o f p o t a s s i u m h y d r o x i d e i n v e r y c o n c e n t r a t e d a q u e o u s s o l u t i o n . F o r t h e s h o r t c h a i n p o t a s s i u m s a l t s w h i c h w e r e d i f f i c u l t t o c r y s t a l l i z e o u t , 0.95 e q u i v a l e n t o f KOH was a d d e d , a n d t h e e x c e s s a c i d s w e r e w a s h e d away w i t h d i e t h y l e t h e r . P o t a s s i u m s a l t s w e r e t h e n 17 r e c r y s t a l l i z e d from ethanol and vacuum dried at room temperature. Any impurity i s l i k e l y to be fat t y acids of di f f e r e n t chainlength. However, Beckmann et al.(18) have found that 1 % of the long or short chain guests do not af f e c t the order parameter of the host potassium palmitate s i g n i f i c a n t l y . Samples were prepared by weighing the s a l t s into a constricted pyrex sample t u b e [ l ] . Another c o n s t r i c t i o n was made to prevent the evaporation of w a t e r f l l ] . Water (containing 1 % D2O) was measured accurately using a syringe and injected onto the surface of the s a l t s [ I I l ] . The tube was evacuated and f i l l e d with nitrogen before sealing. Mixing was achieved by heating in an oven at 110°C for a couple of weeks and by centrifuging many times through the c o n s t r i c t i o n in the sealed glass tube[IV]. Samples were frozen using l i q u i d nitrogen before the f i n a l s e a l i n g f V ] . ' . [1] 1 A I A l l the samples, except C10' which has higher water content, contain ~ 6.3 moles of water per mole of s a l t . 18 The samples containing one mole percent guest of chainlength n in the host potassium palmitate are denoted by Cn, while the samples containing a single perdeuterated soap of chainlength n are denoted by Pn. Detailed compositions of the samples are l i s t e d in table 1 (p.64). 3.3. NMR spectroscopy Deuterium NMR experiments using the quadrupolar echo as described by Davis et al.(28) were carr i e d out on a Bruker CXP-200 pulse NMR spectrometer. This method involves a two-pulse quadrupolar echo sequence as shown below: F-T SOLID ECHO FOR t >2T Figure k'- Schematic diagram of a s o l i d echo pulse sequence. An i n i t i a l pulse which rotates the magnetization by 90° i s followed at a time T by a second pulse whose rf magnetic f i e l d i s s h i f t e d in phase r e l a t i v e to that of the f i r s t pulse by 90° and which also rotates the nuclear spins by an angle 90°. A c h a r a c t e r i s t i c signal c a l l e d the 1 9 Q u a d r u p o l a r e c h o i s o b s e r v e d a t t i m e 2T. F o u r i e r T r a n s f o r m a t i o n o f t h e q u a d r a t u r e s i g n a l s t a r t i n g a t t h e t o p o f t h e q u a d r u p o l a r e c h o g i v e s a n a l m o s t s y m m e t r i c s p e c t r u m . Due t o t h e i n a c c u r a c i e s o f t h e p u l s e l e n g t h s a n d t h e p u l s e p h a s e s , t h e r e i s a s m a l l amount o f f r e e i n d u c t i o n s i g n a l f r o m t h e s e c o n d p u l s e . T h i s s i g n a l o c c u r s i f t h e p u l s e l e n g t h s a r e n o t e x a c t l y 9 0 ° , o r i f t h e p h a s e s do n o t b e a r e x a c t l y t h e c o r r e c t r e l a t i o n t o t h e r e c e i v e r p h a s e . I t i s n e c e s s a r y t o e l i m i n a t e t h i s f r e e i n d u c t i o n s i g n a l by a l t e r n a t i n g t h e p h a s e a t t h e f i r s t p u l s e b e t w e e n 0° a n d 1 8 0 ° a n d t h a t o f t h e s e c o n d p u l s e b e t w e e n 9 0 ° a n d 2 7 0 ° . A n y c o h e r e n t n o i s e w i l l a l s o be e l i m i n a t e d ( 2 9 ) . S p e c t r a w e r e o b t a i n e d i n t h i s s t u d y u s i n g t h e f o l l o w i n g s e t u p : a p u l s e w i d t h o f 8 us, p u l s e s p a c i n g o f 100 us a n d r e p e t i t i o n t i m e o f 0.2 s . E x p e r i m e n t s w e r e c a r r i e d o u t a s a f u n c t i o n o f t e m p e r a t u r e m a i n l y i n t h e l a m e l l a r p h a s e on r e s o n a n c e a t 30.7 MHz. Due t o t h e m i n u t e amount o f p e r d e u t e r a t e d s o a p i n t h e Cn s a m p l e s , a g r e a t number o f s c a n s ( t y p i c a l l y 5 0 , 0 0 0 ) w e r e r e q u i r e d t o g i v e a s p e c t r u m o f g o o d s i g n a l t o n o i s e r a t i o . T h e p r o b e h e a d a n d t h e a i r f l o w h e a t i n g s y s t e m w e r e p r o v i d e d w i t h t h e s p e c t r o m e t e r . T h e t e m p e r a t u r e a t t h e s a m p l e d i f f e r s f r o m t h e r e a d i n g on t h e t e m p e r a t u r e c o n t r o l u n i t . T h i s d i s c r e p a n c y i s l a r g e a t v e r y h i g h t e m p e r a t u r e , 20 and c o r r e c t i o n s have been a p p l i e d . Temperature c a l i b r a t i o n was c a r r i e d out as f o l l o w s . One j u n c t i o n of a c o p p e r / c o n s t a n t a n thermocouple i s p l a c e d i n s i d e an empty sample tube p l a c e d i n the probe a t the same p o s i t i o n where the sample n o r m a l l y i s , the o t h e r j u n c t i o n i s p l a c e d i n an i c e - w a t e r b a t h . The r e s u l t i n g v o l t a g e on a m i l l i v o l t m e t e r i s then c o n v e r t e d t o temperature u s i n g the c a l i b r a t i o n t a b l e f o r c o p p e r / c o n s t a n t a n (Handbook of Chem. and Phys. 40 P . 2 6 2 3 ) . The r e s u l t i n g c a l i b r a t i o n graph i s shown i n f i g . 5. Sample 1 6 0 | Temperature / °C 140-120 H 100 80 -| 60 40 20 i 1 140 160 Dial Temperature Figure 5: Calibr a t i o n graph for the temperature of the samples. 21 0 C h a p t e r 4 R e s u l t s D e u t e r i u m NMR was u s e d t o e x a m i n e e a c h s a m p l e a s a f u n c t i o n o f t e m p e r a t u r e f r o m 4 5 ° C t o 1 6 0 ° C . T h e s p e c t r a l s p l i t t i n g s b e t w e e n t h e two 9 0 ° p o w d e r p a t t e r n s i n g u l a r i t i e s ( f i g . 3 ) o f t h e d e u t e r i u m i n D 2 0 , CD-, a n d CD3 a r e m e a s u r e d . M o s t o f t h e s i n g u l a r i t e s a r e r e s o l v e d i n e a c h s a m p l e . E a c h s p l i t t i n g i s a s s i g n e d t o a g r o u p u s i n g t h e p r e v i o u s l y o b s e r v e d f a c t t h a t t h e g r e a t e r t h e s p l i t t i n g , t h e c l o s e r t h e g r o u p i s t o t h e p o l a r h e a d ( 3 0 ) . S p e c t r a w e r e o b t a i n e d f r o m t h e one m o l e p e r c e n t g u e s t s a m p l e s (Cn) a n d t h e s a m p l e s ( P n ) o f a s i n g l e c h a i n l e n g t h e q u a l t o t h a t o f e a c h g u e s t . 4.1. G u e s t s a m p l e s , Cn F i g . 6a shows a r e p r e s e n t a t i v e s p e c t r u m f r o m one o f t h e g u e s t s a m p l e s . Powder p a t t e r n s a r i s e f r o m d e u t e r i u m a t d i f f e r e n t c a r b o n p o s i t i o n s . T h e s p e c t r a l s p l i t t i n g s a r e g r e a t l y t e m p e r a t u r e d e p e n d e n t , a s o b s e r v e d i n f i g 7 w h i c h shows how t h e s p e c t r a l s p l i t t i n g s o f a l l t h e Cn s a m p l e s v a r y w i t h t e m p e r a t u r e . S p l i t t i n g s o f m e t h y l e n e s e g m e n t s n e a r t h e p o l a r h e a d g r o u p i n c r e a s e w i t h t e m p e r a t u r e t o a maximum a n d t h e n d e c r e a s e on f u r t h e r i n c r e a s i n g t h e t e m p e r a t u r e . E x c e p t f o r t h e s h o r t c h a i n g u e s t s C6 a n d C10, s p l i t t i n g s o f t h e m e t h y l e n e g r o u p s <near t h e m e t h y l e n d o f 22 Figure 6: Representative deuterium nmr spectra of methylene and methyl groups i n (a) C22 at 77°C (210 000 scans) (b) P16 at 64°C ( 27900 scans) 23 kHz 1 1 1 » 1 1 1 1 1 1 1— 35 62 89 116 143 170 Temperature (C) Figure 7a. Temperature dependence of the spectral s p l i t t i n g s ( A"0 ) for the guest potassium caproate (C6). [The methyl group s p l i t t i n g i s ^ O . ] 21* Ai/ kHz 3CH 20H Temperature (C) Figure 7b. Temperature dependence of the spectral s p l i t t i n g s (A-i) ) for the guest potassium caprate(C10). 25 kHz i ^ » i i • i » • 62 89 116 143 170 Temperoture (C) ;ure ?c. Temperature dependence of the spectral s p l i t t i n g s C A - p ) for higher water content caprate(ClO'). 26 Ai/ kHz I 1 1 1 1 1 1 1 1 1 r 4 0 H H . 5 i 1 1 1 1 1 j 1 1 1 1— 3 5 6 2 8 9 .116 ' 143 170 Temperature (C) Figure 7d« Temperature dependence of the spectral s p l i t t i n g s (A >> ) for the guest potassium laurate(C12). 27 Au kHz 3CH 20-icH 5^ T 1 i 1 1 1 1 1 r CI6 16 H t r i r 35 62 T r 89 116 143 Temperature (C). 170 Figure 7e. Temperature dependence of the spectral s p l i t t i n g s ( A T ) ) for the guest potassium palmitate(Cl6)• 6 28 Au kHz. -I 1 1 » « ' — 1 r Temperature (C) Figure 7t, Temperature dependence of the sp e c t r a l s p l i t t i n g s ( A ~ ^ ) for the guest potassium behenate(C22). 29 t h e c h a i n a n d o f t h e m e t h y l g r o u p i t s e l f d e c r e a s e m o n o t o n i c a l l y w i t h i n c r e a s i n g t e m p e r a t u r e . F o r t h e two e x c e p t i o n s C6 a n d C 1 0 , t h e r e i s a maximum f o r e v e r y p o s i t i o n i n c l u d i n g t h e m e t h y l g r o u p . T h e 1 7 t h t o 2 1 s t m e t h y l e n e p o s i t i o n s a r e n o t r e s o l v e d i n t h e g u e s t C22 s a m p l e a t h i g h e r t e m p e r a t u r e . F i g . 7 c shows t h e s p l i t t i n g s f o r t h e h i g h e r w a t e r c o n t e n t s a m p l e , C 1 0 ' . T h e s p l i t t i n g s f o r a l l m e t h y l e n e p o s i t i o n s a r e s m a l l e r t h a n f o r t h e l o w e r w a t e r c o n t e n t s a m p l e C 1 0 . T h i s i s e s p e c i a l l y n o t e d a t l o w t e m p e r a t u r e . T h e maxima i n t h e p l o t s o f t h e C10' s a m p l e a r e s h i f t e d t o s l i g h t l y h i g h e r t e m p e r a t u r e . 4.2. P u r e s a m p l e s , Pn Th e s i g n a l t o n o i s e r a t i o s o f t h e s p e c t r a f r o m t h e Pn s a m p l e s a r e b e t t e r t h a n t h o s e o f t h e g u e s t , Cn s a m p l e s ( f i g . 6 b ) . I n t h e same p l o t s a s f i g . 7 f o r t h e p e r d e u t e r a t e d Pn s a m p l e s ( f i g . 8 ) , t h e r e a r e c e r t a i n d i f f e r e n c e s c o m p a r e d t o t h e Cn s a m p l e s . F o r i n s t a n c e , t h e s p l i t t i n g s f o r c a r b o n p o s i t i o n s 3,4 a n d 5,6 a r e a l w a y s v e r y c l o s e a n d n o t a l w a y s r e s o l v e d i n t h e Pn s a m p l e s . A t t e m p e r a t u r e s b e l o w 6 0 ° C , t h e s e s p l i t t i n g s f o r t h e P22 s a m p l e a r e n o t r e s o l v e d . H o w e v e r , f o r t h e C16 a n d P16 s a m p l e s w h i c h g a v e more o r l e s s t h e same s p e c t r a l r e s u l t s , p o s i t i o n s 3,4 a r e e a s i l y d i s t i n g u i s h e d f r o m 5,6 i n b o t h s a m p l e s . T h e a b o v e r e p r e s e n t a t i o n o f t h e r e s u l t s p r o v i d e s c e r t a i n i n f o r m a t i o n a b o u t t h e g u e s t b e h a v i o r . I n o r d e r t o 30 &u kHz k0 —I 30 — 20 — IC — 5 — 2 H 1 -J P10 3 5 — 1 — 6 2 — I — 89 "ni" 143 Temperature (C) 170 F i g u r e 8 a . T e m p e r a t u r e d e p e n d e n c e of t h e s p e c t r a l s p l i t t i n g s (A -0) f o r t h e P10 s a m p l e . 31 Az/ kHz P12 — i , ,, i i , . i — i i — i 1 i 62 89 116 143 170 Temperature (C) Figure 8b. Temperature dependence of the spectral s p l i t t i n g ( A i ) ) for the PI 2 sample. 32 Ai/kHz 40 — Temperature (C) Figure 8c. Temperature dependence of the spectral splittings ( A - p ) for the P16 sample. 33 & v kHz kO -30 -20 -10 5 H 2 —1 1 - 1 P22 22 35 " " I • 62 89 116 Temperature (C) 1 4 3 170 Figure 8d. Temperature dependence of the spectral s p l i t t i n g s ^ ) for the P22 sample. ' 34 u n d e r s t a n d t h e g u e s t a n d t h e h o s t b e h a v i o r a s f u l l y a s p o s s i b l e , i t i s u s e f u l t o e x a m i n e t h e s e r e s u l t s i n v a r i o u s w a ys. T h i s d e t a i l e d i n v e s t i g a t i o n o f t h e r e s u l t s w i l l be d i s c u s s e d i n t h e f o l l o w i n g c h a p t e r . 35 C h a p t e r 5 D i s c u s s i o n 5.1 M o d e l s o f t h e h o s t - g u e s t m i x t u r e 5.1.1 R e v i e w o f t h e h o s t b e h a v i o r R e s u l t s o f t h e s t u d y o f Beckmann e t a l . ( l 8 ) show t h a t 1 % l o n g o r s h o r t c h a i n g u e s t s d o n o t p e r t u r b t h e h o s t t o a n y s i g n i f i c a n t e x t e n t . T h e p r e s e n c e o f 5 % o r more o f t h e g u e s t m o l e c u l e s a l t e r s t h e o r i e n t a t i o n a l o r d e r o f t h e h y d r o c a r b o n c h a i n o f t h e h o s t . A s i m p l e s p a c e p a c k i n g m o d e l p r e d i c t s t h a t t h e a d d i t i o n o f l o n g c h a i n g u e s t s g i v e s r i s e t o a n i n c r e a s e i n s p e c t r a l s p l i t t i n g b e y o n d t h e f o u r t h c a r b o n p o s i t i o n i n t h e h o s t , w h i l e t h e s h o r t c h a i n g u e s t s g i v e an o p p o s i t e e f f e c t . H e n c e t h e s i x t e e n c a r b o n c h a i n s s h o u l d h a v e more f r e e d o m t o move i n t h e p r e s e n c e o f s h o r t c h a i n g u e s t s . T h e r e s u l t s o f Beckmann e t a l . ( l 8 ) a g r e e w i t h t h i s s i m p l e m o d e l a t h i g h t e m p e r a t u r e . H o w e v e r , a t l o w t e m p e r a t u r e t h e o r d e r p a r a m e t e r s o f t h e h o s t c h a i n i n c r e a s e i n t h e p r e s e n c e o f s h o r t c h a i n g u e s t s . T h i s i s p o s s i b l y due t o l o w e r i n g o f t h e w a t e r c o n t e n t o f t h e h o s t p a l m i t a t e i n t h e p r e s e n c e o f t h e g u e s t , a n d t h i s b e h a v i o r w i l l be e x p l a i n e d i n s e c t i o n 5 . 5 . 36 5.1.2 P r o p o s e d m o d e l s O u r c o m p l e m e n t a r y work, w h i c h i s a s t u d y o f t h e b e h a v i o r o f 1 % l o n g o r s h o r t c h a i n g u e s t s , i s an e x t e n s i o n o f t h e s t u d y o f B e c k m a n n e t a l . ( 1 8 ) . I t i s i n t e r e s t i n g t o a s k w h e t h e r o r n o t a s i m p l e , i n t u i t i v e m o d e l c o n s i s t e n t w i t h t h a t o f t h e p r e v i o u s s t u d y c a n e x p l a i n t h e r e s u l t s . T h e h o s t s h o u l d p e r t u r b t h e g u e s t a n d t h i s e f f e c t s h o u l d show u p i n t h e d e u t e r i u m nmr s p e c t r u m . T h e h o s t a n d t h e g u e s t may n o t be a b l e t o p a c k w e l l t o g e t h e r , s o t h a t t h e s h o r t c h a i n s a r e s q u e e z e d o u t o f t h e b i l a y e r c a u s i n g a s e p a r a t i o n o f t h e two t y p e s o f m o l e c u l e s . A l t e r n a t i v e l y , c h a n g e s i n t h e c o n f o r m a t i o n a l a v e r a g i n g w h i c h make t h e s h o r t c h a i n s s t r a i g h t e r a n d l o n g e r a r e l i k e l y . F o r t h e l o n g c h a i n s , m o r e s p a c e t o l o c a t e t h e e x t r a l e n g t h o f t h e c h a i n s m u s t become a v a i l a b l e . T h e f i r s t s i x t e e n c h a i n p o s i t i o n s may c o p y t h e b e h a v i o r o f t h e h o s t w i t h t h e t a i l d o i n g o n e o r more o f t h e f o l l o w i n g : i ) l y i n g a l o n g t h e m i d - p l a n e , i i ) i n s e r t i n g i n t o t h e o p p o s i t e h a l f l a y e r o r i i i ) c u r l i n g u p r a n d o m l y . Our r e s u l t s c a n now be e x a m i n e d i n t e r m s o f t h e a b o v e m o d e l s . 5.2 A n a l y s i s o f t h e p r o p o s e d m o d e l I n t h e p l o t s o f Av v s t e m p e r a t u r e i n f i g . 7 , t h e l o n g c h a i n g u e s t shows r e s u l t s w h i c h a r e q u a l i t a t i v e l y s i m i l a r t o t h e p a l m i t a t e h o s t , b u t t h e C 6 , C 1 0 a n d C 1 0 1 s a m p l e s 37 show some s t r a n g e t e m p e r a t u r e e f f e c t s . I n t h e s e l a t t e r s a m p l e s t h e s p l i t t i n g s a t l o w t e m p e r a t u r e a r e a l l r e l a t i v e l y l o w . T h i s u n e x p e c t e d r e s u l t w i l l be e x p l a i n e d i n d e t a i l i n s e c t i o n 5.5. I n o r d e r t o t e s t t h e p r o p o s e d m o d e l s i n v a r i o u s w ays, f i r s t we e x a m i n e t h e v a r i a t i o n i n o r d e r p a r a m e t e r a l o n g t h e h y d r o c a r b o n c h a i n . F i g . 9 shows t h e s p i t t i n g s r e l a t i v e t o t h e a-CD 2 s p l i t t i n g v e r s u s t h e m e t h y l e n e p o s i t i o n a t 4 9 ° C a n d 1 4 3 ° C . R e l a t i v e p l o t s a r e u s e d b e c a u s e a t low t e m p e r a t u r e t h e s p l i t t i n g o f t h e c-CD 2 o f t h e s h o r t c h a i n g u e s t i s v e r y low c o m p a r e d t o t h a t o f t h e l o n g c h a i n . A t a l l t e m p e r a t u r e s , s p l i t t i n g s f o r t h e s h o r t c h a i n d r o p o f f f a s t e r a t t h e p o l a r h e a d o f t h e c h a i n a n d h e n c e e x h i b i t l e s s o f a p l a t e a u t h a n t h e l o n g c h a i n s . F o r a s p e c i f i c p o s i t i o n a l o n g t h e c h a i n , t h e l o n g e r c h a i n g u e s t s h a v e h i g h e r r e l a t i v e o r d e r p a r a m e t e r t h a n do t h e s h o r t e r c h a i n g u e s t s . F o r a c e r t a i n p o s i t i o n c o u n t i n g b a c k f r o m t h e m e t h y l e n d o f e a c h c h a i n , t h e s h o r t e r c h a i n g u e s t s h a v e l a r g e r r e l a t i v e s p l i t t i n g t h a n d o t h e l o n g e r c h a i n s . T h i s c o u l d i n d i c a t e t h a t t h e s h o r t c h a i n g u e s t s a r e r e s t r i c t e d i n s i d e t h e h o s t , b u t i t c o u l d a l s o be a r g u e d t h a t f o r t h i s p o s i t i o n a t t h e same d i s t a n c e f r o m t h e m e t h y l e n d , t h e s p l i t t i n g s h o u l d be s m a l l e r i n t h e l o n g e r c h a i n , b e c a u s e t h i s p o s i t i o n i s f u r t h e r away f r o m t h e a n c h o r i n g h e a d o f t h e l o n g c h a i n s . I t i s more u s e f u l t o make t h e c o m p a r i s o n s 38 Chain position Variation of the r e l a t i v e s p l i t t i n g along the hydrocarbon chain at 4 9 C and 1 4 3 S. (Methyl group s p l i t t i n g s are not shown) C 6 ( 0 ), C 1 0 ( A ) , C 1 2 ( « ) , C 1 6 ( » ) , C 2 2 ( A ) 39 for a p a r t i c u l a r guest used with a sample (Pn) containing only l i p i d s of the same chainlength as the guest considered, and at the same time to compare with the host. 5.3 Comparison between Cn and Pn samples 5.3.1 Comparison of the average s p l i t t i n g s and the  d i s t r i b u t i o n parameter In order to compare the average orientational order of hydrocarbon chains with each other, we use some parameters which r e f l e c t the averages over the whole hydrocarbon chain. Two such parameters are: the average s p l i t t i n g and the d i s t r i b u t i o n parameter In the plot of the average s p l i t t i n g s of the Cn samples vs temperature (fig.10a), the average s p l i t t i n g s decrease monotonically as the temperature increases for C12, C16 and C22. The C6 and CIO average s p l i t t i n g plots exhibit maxima at 90°C anB 65°C respectively. For the lamellar phase, the average s p l i t t i n g increases as the chain gets 40 22-j (Ai/)kHz • ( M kHz 40 6 0 80 100 120 140 160 180 T °C Figure 10: Temperature dependence of the average s p l i t t i n g (a) Cn sample (b) Pn sample 6 ( 0 ) , 1 0 ( A ) , 1 2 ( « ) , 1 6 ( » ) , 2 2 ( A ) 41 s h o r t e r ; t h a t i s , t h e l o n g c h a i n h a s a l o w e r a v e r a g e o r d e r p a r a m e t e r t h a n t h e h o s t a n d t h e s h o r t c h a i n h a s h i g h e r . T h i s r e s u l t a p p l i e s f o r h i g h t e m p e r a t u r e ; t h e s t r a n g e r e s u l t f o r l o w t e m p e r a t u r e i s d i s c u s s e d l a t e r i n s e c t i o n 5.5. T h e t e m p e r a t u r e d e p e n d e n c e o f t h e a v e r a g e s p l i t t i n g o f s i n g l e c h a i n l e n g t h s a m p l e s Pn i s g i v e n i n f i g . 10b. The l o n g e r s i n g l e l e n g t h c h a i n s h a v e l a r g e r a v e r a g e s p l i t t i n g s , a r e s u l t w h i c h i s o p p o s i t e t o t h a t o b s e r v e d f o r t h e Cn s a m p l e s . T h e a v e r a g e s p l i t t i n g s a l l d e c r e a s e a s t e m p e r a t u r e i n c r e a s e s . H o w e v e r , t h e d e p e n d e n c e o f <Av> on t h e c h a i n l e n g t h i s l e s s t h a n f o r t h e Cn s a m p l e s . T h e l a r g e r c h a i n l e n g t h d e p e n d e n c e o f t h e o v e r a l l o r i e n t a t i o n a l o r d e r o f g u e s t c h a i n s seems t o be a d e f i n i t e s i g n o f t h e i r m a n n e r o f p a c k i n g a s t h e y a r e i n t r o d u c e d i n t o a g i v e n h o s t e n v i r o n m e n t / r a t h e r t h a n o n l y a p r o p e r t y d u e t o t h e l e n g t h o f t h e g u e s t c h a i n i t s e l f . T h e h o s t h a s i m p o s e d a s i g n i f i c a n t i n f l u e n c e on t h e g u e s t c h a i n m o l e c u l e s . T h i s e f f e c t s hows u p i n t h e a v e r a g e s p l i t t i n g s . T h e s h o r t g u e s t s a r e r e s t r i c t e d a n d h a v e h i g h e r o r d e r p a r a m e t e r s t h a n when i n s a m p l e s o f e q u a l c h a i n l e n g t h . T h e l o n g c h a i n s h a v e much s m a l l e r s p l i t t i n g s n e a r t h e m e t h y l e n d , s o t h a t t h e a v e r a g e i s t h u s l o w e r e d when t h e y a r e d i s s o l v e d i n t h e h o s t . I n o r d e r t o e x e m p l i f y t h i s r e s u l t , we p l o t t h e r a t i o o f t h e a v e r a g e s p l i t t i n g s , <Av> ( C n ) / <Av> ( P n ) a s a f u n c t i o n o f t e m p e r a t u r e i n f i g 11. T h e r a t i o p l o t shows 42 <A-0 > (Cn) <A -0 > (Pn) Figure 11: Temperature dependence of the r a t i o of the average s p l i t t i n g between Cn and Pn. 10(A), 1 2 ( « ) , I 6 ( * ) t 22(A) A3 t h a t t h e s h o r t g u e s t c h a i n s h a v e 20 t o 30 % h i g h e r a v e r a g e s p l i t t i n g t h a n d o t h e c h a i n s i n t h e s i n g l e c h a i n l e n g t h s a m p l e s , w h i l e t h e l o n g c h a i n g u e s t s h a v e an a v e r a g e s p l i t t i n g 20 % l o w e r . T h e d i s t r i b u t i o n p a r a m e t e r i s e q u i v a l e n t t o t h e s p r e a d a r o u n d t h e a v e r a g e v a l u e . I t i s p l o t t e d a g a i n s t t e m p e r a t u r e i n f i g . 12. T h e s p r e a d o f t h e s p e c t r a l s p l i t t i n g s f o r t h e Cn s a m p l e s ( f i g . l 2 a ) i s shown t o be g r e a t e r b o t h f o r l o n g e r c h a i n g u e s t s a n d a t h i g h e r t e m p e r a t u r e . H o w e v e r , i n e q u i v a l e n t p l o t s ( f i g . 12b) f o r t h e Pn s a m p l e , P16 h a s t h e h i g h e s t d i s t r i b u t i o n p a r a m e t e r among a l l t h e Pn s a m p l e s a t a l l t e m p e r a t u r e s . T h e r a t i o A £ ( C n ) / A 2 ( p n ) i s p l o t t e d v s t e m p e r a t u r e i n f i g . 13 w h i c h shows c l e a r l y t h e d i f f e r e n c e b e t w e e n t h e s p r e a d o f t h e ' s p l i t t i n g s i n t h e two t y p e s o f s a m p l e s . T h e d i s t r i b u t i o n p a r a m e t e r f o r a l l t h e g u e s t s i s h i g h e r t h a n t h a t f o r t h e c o r r e s p o n d i n g s i n g l e c h a i n s a m p l e s . A low v a l u e o f A 2 means t h a t most o f t h e s p l i t t i n g s a r e r o u g h l y e q u a l a s w o u l d be e x p e c t e d i f t h e r e was a p l a t e a u . T h e r e s u l t s f o r t h e r a t i o o f t h e d i s t r i b u t i o n p a r a m e t e r s i n d i c a t e t h a t Cn s a m p l e s e x h i b i t l e s s o f a p l a t e a u t h a n t h e c o r r e s p o n d i n g Pn s a m p l e s . T h e r e a s o n t h a t t h e b e h e n a t e h a s t h e g r e a t e s t r a t i o o f A £ ( C 2 2 ) / A £ ( P 2 2 ) i s t h a t p o s i t i o n s 17 t o 21 a l l h a v e l o w o r i e n t a t i o n a l o r d e r , r e s u l t i n g i n i n c r e a s i n g t h e s p r e a d o f t h e s p l i t t i n g s . F i g u r e 12: Temperature dependence o f the d i s t r i b u t i o n parameter (a) Cn samples; (b) Pn samples. 6 ( 0 ) , 1 0 ( A ) , 1 2 ( » ) , 1 6 ( # ) , 2 2 ( A ) . 4 5 - I F i g u r e 1 5 : ^ ^ ^ ^ , 1 U t ^ i 0 « 0 d f ^ 1 0 ( A ) , 1 2 ( « ) , 16(#>. 2 2 ( A ) 46 5.3.2 C o m p a r i s o n s f o r i n d i v i d u a l c h a i n p o s i t i o n s T h e a b o v e c o m p a r i s o n s ( f i g . 10-13) h a v e g i v e n u s a g e n e r a l i d e a a b o u t t h e o v e r a l l a v e r a g e g u e s t b e h a v i o r . F i g . 7 a n d 9 h a v e e x a m i n e d t h e v a r i a t i o n o f s p e c i f i c d e t a i l s o f i n d i v i d u a l c h a i n s o f t h e Cn s a m p l e s . I t i s b o t h i n s t r u c t i v e a n d i m p o r t a n t t o s t u d y how t h e s e d e t a i l s d i f f e r b e t w e e n t h e two t y p e s o f s a m p l e s (Cn a n d P n ) . P l o t s s i m i l a r t o t h o s e i n f i g . 9 a r e shown i n f i g . 1 4 , w h e r e t h e s p l i t t i n g s a r e p l o t t e d v s c a r b o n p o s i t i o n a t a s e l e c t e d t e m p e r a t u r e , 1 0 4 ° C . I n t h i s f i g u r e , s p e c t r a l s p l i t t i n g s f o r P n, Cn a n d P16 a r e p l o t t e d a s a f u n c t i o n o f c h a i n p o s i t i o n . W i t h i n e x p e r i m e n t a l e r r o r , t h e r e i s no d i f f e r e n c e b e t w e e n t h e C16 a n d P16 s a m p l e , i n d i c a t i n g t h e a b s e n c e o f a l a r g e * i s o t o p e e f f e c t when h y d r o g e n i s s u b s t i t u e d by d e u t e r i u m on t h e c h a i n s . C22 a n d P22 h a v e s i g n i f i c a n t l y d i f f e r e n t o r d e r p a r a m e t e r s . F r o m t h e 3 r d t o t h e 1 5 t h p o s i t i o n , C16 a n d C22 show r o u g h l y e q u a l s p l i t t i n g s e s p e c i a l l y a t h i g h t e m p e r a t u r e . F o r C22, t h e s p l i t t i n g s n e a r t h e m e t h y l e n d a r e much l o w e r t h a n f o r t h e c o r r e s p o n d i n g p o s i t i o n i n t h e P22 s a m p l e . T h i s b e h a v i o r f o r t h e l o n g c h a i n s h a s b e e n o b s e r v e d p r e v i o u s l y i n a s i m i l a r s y s t e m by F o r r e s t e t a l ( 1 5 ) . I t shows t h a t t h e l o n g c h a i n s r o u g h l y f o l l o w t h e o r i e n t a t i o n a l o r d e r o f t h e h o s t up t o a l e n g t h e q u i v a l e n t t o t h a t o f t h e h o s t . T h e r e s t o f t h e c h a i n e i t h e r e x c h a n g e s b e t w e e n p o s i t i o n s a l o n g t h e m i d - p l a n e a n d 0 47 c n ( O ) , p n ( « ) , P I 6 ( A ) . c h a h position 143°C 104°C 5 8 ° C - 4 5 °C < Figure 14: (a) Variation of the spectral s p l i t t i n g s (A^. ) along the hydrocarbon chain for ( i ) caprate, ( i i ) laurate, ( i i i ) palmitate, (iv) behenate. (b) Variation of the r a t i o of the spectral s p l i t t i n g s between Cn samples and Pn s a m p l e s ( f o r ( i ) caprate, ( i i ) laurate, ( i i i ) palmitate, (iv) behenate. 48 ( i i i ) kHz 30-20-1 16 10H a 2H C l6 (0 ) , P i6(#) . b 14 Al/j(C) A i ^ ( P ) u 1.0 -i 1 1•Tf».l>».y V—r 2 4 6 6 1 2 14 chain position 1 4 3 ° c 1 0 4 °c 5 8 ° C - 4 5 ° C 50 i n s e r t s i t s e l f i n t o t h e o p p o s i t e h a l f l a y e r o r i s o r i e n t a t i o n a l l y d i s o r d e r e d . On t h e o t h e r h a n d , t h e s h o r t g u e s t c h a i n s e x h i b i t d i f f e r e n t b e h a v i o r down t h e h y d r o c a r b o n c h a i n . T h e m e t h y l e n e g r o u p s n e a r t h e p o l a r h e a d b e h a v e more l i k e t h e h o s t , w h i l e t h o s e n e a r t h e m e t h y l e n d b e h a v e more l i k e t h o s e i n t h e Pn s a m p l e s . P10 a n d P i 2 s a m p l e s h a v e l o w e r o r d e r p a r a m e t e r t h a n d o e s t h e c o r r e s p o n d i n g g u e s t s a m p l e . T h i s i n d i c a t e s t h a t t h e s h o r t c h a i n s a r e more o r d e r e d when d i s s o l v e d i n a l o n g c h a i n h o s t t h a n when i n t h e p r e s e n c e o f c h a i n s o f e q u a l l e n g t h s . I n o r d e r t o d e m o n s t r a t e more c l e a r l y t h e d i f f e r e n c e b e t w e e n t h e Pn a n d Cn s a m p l e s , we p l o t t h e r a t i o o f t h e s p l i t t i n g s Av (Cn) / Ai> ( P n ) v s c h a i n p o s i t i o n i n f i g . 1 4 b . A c c o r d i n g t o t h e m o d e l p r e s e n t e d a b o v e , t h e l o n g c h a i n g u e s t s h o u l d h a v e l e s s o r i e n t a t i o n a l o r d e r t o w a r d s t h e m e t h y l e n d o f t h e c h a i n t h a n d o e s t h e same m o l e c u l e i n t h e Pn s a m p l e . M o r e o v e r , w i t h t h e a s s u m p t i o n t h a t t h e o r i e n t a t i o n a l ' o r d e r o f t h e p o l a r h e a d s a r e i n d e p e n d e n t o f c h a i n l e n g t h , t h i s r a t i o p l o t s h o u l d show a l i n e o f n e g e t i v e s l o p e a n d h a v e v a l u e s l e s s t h a n 1 f o r t h e l o n g c h a i n s a m p l e s . T h e s h o r t c h a i n s a m p l e s s h o u l d b e h a v e i n t h e o p p o s i t e manner a n d h a v e h i g h e r o r i e n t a t i o n a l o r d e r t o w a r d s t h e m e t h y l e n d o f t h e c h a i n . H e n c e a l i n e o f p o s i t i v e s l o p e w i t h v a l u e s g r e a t e r t h a n 1 i s p r e d i c t e d . T h e p l o t s o f t h e r a t i o Av ( C 2 2 ) / Av ( P 2 2 ) i n f i g . 1 4 b show t h a t t h e g u e s t o r i e n t a t i o n a l o r d e r d e c r e a s e s more 51 r a p i d l y than t h a t f o r the s i n g l e c h a i n l e n g t h sample as one p roceeds down the hydrocarbon c h a i n . The c u r v a t u r e s i n t h e p l o t s a r i s e because the s p l i t t i n g s of t h e methylene groups from the 17th t o 21st carbon p o s i t i o n s a r e e s s e n t i a l l y e q u a l f o r the guest C22 sample. As p r e d i c t e d , t h e r a t i o of s p l i t t i n g s f o r t h e s e 5 p o s i t i o n s a r e v e r y low. T h i s r e s u l t c o m p l e t e l y a g r e e s w i t h the model proposed from the r e s u l t of f i g . 1 0 . The r a t i o p l o t s i n f i g . 1 4 b ( i ) and ( i i ) f o r the s h o r t c h a i n samples do not c o m p l e t e l y agree w i t h the s i m p l e model p r e s e n t e d above. The c u r v e s do not s t a r t from the v a l u e 1 a t the p o l a r head and t h e r e i s an o b v i o u s c u r v a t u r e . The minimum v a l u e of the r a t i o i s r o u g h l y a t the m i d d l e of the s h o r t c h a i n s . Prom t h i s minimum t o the m e t h y l end, t h e s e p l o t s show l i n e s of p o s i t i v e s l o p e , i n d i c a t i n g t h a t the s h o r t c h a i n g u e s t s are more o r i e n t a t i o n a l l y o r d e r e d towards the m e t h y l end, as p r e d i c t e d . A l s o i n t h i s r e g i o n , C10 and C12 samples both have h i g h e r o r d e r parameter than the c o r r e s p o n d i n g Pn sample, a g a i n a g r e e i n g w i t h the model where the s h o r t c h a i n g u e s t s a r e r e s t r i c t e d i n s i d e the h o s t . However, the n e g e t i v e s l o p e s i n t h e p o l a r head r e g i o n s of the p l o t s i m p l y t h a t t h e r e i s more of a p l a t e a u i n the Pn samples than t h e Cn samples as a l r e a d y i n d i c a t e d i n the r a t i o p l o t s of the d i s t r i b u t i o n parameters ( f i g . 13). T h i s unexpected r e s u l t i s p o s s i b l y due t o the d i f f e r e n c e i n the l i p i d - w a t e r i n t e r a c t i o n among t h e v a r i o u s samples. T h i s 52 e f f e c t w i l l be discussed in the next sections. 5.4 Lipid-water interaction 5.4.1 For chain length comparable to and longer than that .of the host A maximum i s observed for the temperature dependence plots ( f i g . 7) of s p l i t t i n g s of the CD{ groups near the polar head. These results have been obtained in other previous studies (12,31). In the study of Abdolall et aL(3 l ) , i t was explained as a lipid-water interaction e f f e c t . Two rapid interchanging configurations were introduced, namely A and B ( f i g 15). At low temperature, the f i r s t C-C bond i s fixed by the hydrogen bonding between the water and the l i p i d head group. Then the C-D bonds make an angle about 109.5° with the normal to the bilayer (jn). At high temperature, extra thermal energy allows fewer hydrogen bonds and leads to a decrease in the lipid-water i n t e r a c t i o n . The long hydrocarbon chains prefer to l i e perpendicular to the lamellar plane r e s u l t i n g in an angle of 90° between the C-D bonds and i n . A change of population from more A to more B w i l l lead to an increase in order parameter. This arises because S = | (3 co s 2 e - 1)1/2 i s 1/2 for & = 90° and i s 1/3 for G =109.5°. Such increase w i l l reach a maximum at a cer t a i n temperature above which there i s more thermal motion causing more disorder. Therefore the s p l i t t i n g s of the CD2 0 53 Figure 15: Model for the lipid-water interface. (A) Predominant configuration at lower temperature. (B) Predominant configuration at higher temperature. 5k g r o u p s n e a r t h e p o l a r h e a d i n c r e a s e w i t h t e m p e r a t u r e t o a maximum v a l u e a n d t h e n s l o w l y d e c r e a s e ( f i g 7 ) . 5.4.2 F o r s h o r t c h a i n s When t h e s h o r t c h a i n g u e s t i s d i s s o l v e d i n t h e p a l m i t a t e h o s t , t h e g u e s t may be p u l l e d somewhat i n t o t h e b i l a y e r b e c a u s e o f t h e v a c u u m c r e a t e d by t h e s h o r t n e s s o f t h e c h a i n . I n t h i s c a s e , t h e i n t e r a c t i o n o f t h e p o l a r h e a d r e g i o n w i t h w a t e r may.be l e s s t h a n f o r t h e s i n g l e c h a i n l e n g t h s y s t e m , a n d t h e o r i e n t a t i o n o f t h e p o l a r h e a d r e g i o n may be g o v e r n e d m a i n l y by i n t e r m o l e c u l a r f o r c e s b e t w e e n l i p i d c h a i n s . T h i s s i t u a t i o n w o u l d l e a d t o t h e C-D b o n d s i n t h e p o l a r h e a d r e g i o n m a k i n g an a n g l e o f a b o u t 9 0 ° w i t h t h e n o r m a l r u T h i s p u r e l y g e o m e t r i c a l e f f e c t r e s u l t s i n a l a r g e r s p l i t t i n g a n d h e n c e a l a r g e r o r d e r p a r a m e t e r . T h e r e f o r e , t h e o r d e r p a r a m e t e r s f o r t h e s h o r t c h a i n Cn s a m p l e s w i l l be l a r g e r t h a n t h o s e f o r t h e Pn s a m p l e s , e s p e c i a l l y f o r t h e p o l a r r e g i o n o f t h e h y d r o c a r b o n c h a i n . T h e c o r r e l a t e d e f f e c t o f t h e l i p i d -w a t e r i n t e r a c t i o n i s l o s t a s o n e p r o c e e d s t o w a r d s t h e m e t h y l e n d o f t h e c h a i n , g i v i n g r i s e t o a p l a t e a u . As t h e e f f e c t s d u e t o t h e l i p i d - w a t e r i n t e r a c t i o n a r e l a r g e r f o r t h e Pn s a m p l e s t h a n t h e Cn s a m p l e s , t h e Pn s a m p l e s a r e e x p e c t e d t o h a v e a more p r o n o u n c e d p l a t e a u , l e a d i n g t o t h e m i n i m a i n t h e r a t i o p l o t s o f f i g . 1 4 b ( i ) a n d ( i i ) . 55 5.5 Phase s e p a r a t i o n 5.5.1 Phase s e p a r a t i o n e f f e c t on the guest At low t e m p e r a t u r e s , s h o r t guest c h a i n s have u n e x p e c t e d l y s m a l l o r d e r p a r a m e t e r s , as a l r e a d y shown i n f i g . 7 and 1Oa. T h i s r e s u l t a p p l i e s e s p e c i a l l y t o those methylene groups near the p o l a r head group. Chen e t a l . ( 1 4 ) have s t u d i e d the o-CD 2 s p l i t t i n g vs c h a i n l e n g t h of s m a l l amounts of a-d 2 c a r b o x y l a t e s and c a r b o x y l i c a c i d s of v a r i o u s c h a i n l e n g t h s s o l u b i l i z e d i n a m a c r o s c o p i c a l l y o r i e n t a t e d lyomesophase a t a s i n g l e t e m p e r a t u r e , 34°C. The lyomesophase i s a q u a t e r n a r y system c o n t a i n i n g water 50.89 %, d e c a n o l 5.45 %, sodium d e c y l s u l p h a t e 38.14 % and sodium s u l p h a t e 4.36 % by we i g h t . The p l o t of a-CD2 s p l i t t i n g s vs c h a i n l e n g t h i n t h a t system shows a l i n e a r i n c r e a s e w i t h c h a i n l e n g t h up t o a l e n g t h comparable t o t h a t of the host c h a i n , and i s then c o n s t a n t w i t h f u r t h e r i n c r e a s e i n guest c h a i n l e n g t h . In an attempt t o und e r s t a n d t h i s f a s c i n a t i n g b e h a v i o r , we now lo o k a t the same type of p l o t f o r our a-CD 2 group s p l i t t i n g s a t v a r i o u s t e m p e r a t u r e s ( f i g 16). At low t e m p e r a t u r e , a r e s u l t s i m i l a r t o t h a t of Chen e t a l . ( 1 4 ) i s o b t a i n e d . However, a t h i g h e r t e m p e r a t u r e , t h e r e i s v e r y l i t t l e dependence of a-CD2 s p l i t t i n g s on the c h a i n l e n g t h of the g u e s t . In our s t u d y , we have a l s o measured s p e c t r a l s p l i t t i n g s f o r o t h e r methylene p o s i t i o n s . The temperature 56 Figure 1 6 : Spectral s p l i t t i n g of <*-CD2 plotted against guest chain length at 143°C, 10lf°C, 77°C, 55°C and 4 5 ° C 57 d e p e n d e n c e o f t h e q u a d r u p o l a r s p l i t t i n g s o f c-CD^, 0-CD2. a n d D^O a r e p l o t t e d i n f i g . 17, w h e r e a l l t h e s a m p l e s a r e g r o u p e d i n t h e same p l o t f o r c o m p a r i s o n . S i n c e t h e r e i s no D^O a d d e d t o t h e C16 s a m p l e , no D2O s i g n a l was o b s e r v e d i n t h i s s a m p l e . W i t h t h e e x c e p t i o n o f t h e u-CDg s p l i t t i n g f o r C12, C16 a n d C22 w h e r e t h e v a l u e s d e c r e a s e m o n o t o n i c a l l y a s t h e t e m p e r a t u r e i n c r e a s e s , a l l t h e p l o t s e x h i b i t m a x i m a. F o r C6 a n d C10 t h e s e maxima s h i f t t o h i g h e r t e m p e r a t u r e w i t h s h o r t e r c h a i n l e n g t h . I n t h e p l o t s o f o-CD^ a n d D^O a t h i g h t e m p e r a t u r e , t h e s p l i t t i n g d o e s n o t v a r y w i t h c h a i n l e n g t h a s a l r e a d y o b s e r v e d i n f i g . 16. A t l o w t e m p e r a t u r e t h e C6 a - C D £ s p l i t t i n g d e c r e a s e s a b o u t 50 % a n d t h e C10 d e c r e a s e s a b o u t 20 % f r o m t h e maximum v a l u e . S i m i l a r b e h a v i o r i s o b s e r v e d f o r DgO a n d 0-CD2 o f t h e s h o r t c h a i n s a m p l e s , w h i l e -the l o n g c h a i n s a m p l e s h a v e t e m p e r a t u r e v a r i a t i o n s i m i l a r t o t h a t o f t h e h o s t . A p o s s i b l e b u t u n l i k e l y e x p l a n a t i o n o f b o t h o u r r e s u l t s a n d t h o s e o f C h e n e t a l . ( l 4 ) i s t h a t a t low t e m p e r a t u r e , t h e r e i s a d e c r e a s e i n t h e e x t e n t o f c o n f o r m a t i o n a l m o t i o n s a s t h e c h a i n s become l o n g e r . H o w e v e r , i t w o u l d be d i f f i c u l t t o e x p l a i n t h e t e m p e r a t u r e d e p e n d e n c e f o r C6 a n d C10 s a m p l e s i n t h i s way. A more p l a u s i b l e e x p l a n a t i o n i s t h a t t h e r e i s p h a s e s e p a r a t i o n a t low t e m p e r a t u r e s i n t h e s a m p l e c o n t a i n i n g s h o r t c h a i n g u e s t s . R a p i d e x c h a n g e o f m o l e c u l e s b e t w e e n a l a m e l l a r p h a s e ( r i c h i n p a l m i t a t e ) a n d some o t h e r , p o s s i b l y i s o t r o p i c p h a s e s ( s ) ( r i c h i n t h e s h o r t c h a i n s o a p s ) w i l l 5 8 30H 2 0 15-12-II 10 9 8 7 6H 4H 3 H •H 1 1 1 I 1-* 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 Temperoture(°C) Figure 1? : Temperature dependence of the s p l i t t i n g s of (a) D 20, (b) d-CD2, (c) ( o-CD 2 for the Cn samples. C 6 ( 0 ) , C 1 0 ( A ) , C 1 2 C B ) , C 1 6 ( # ) , C 2 2 ( A ) . 59 result in s p l i t t i n g s for the short chain which are less than those of the lamellar phase and equal to the population average for each phase. Thus the experimental order parameter i s S e X p t = **St + * ^ where x ^ , x^ are the mole f r a c t i o n of the lamellar and the possibly isotropic phase respectively, and , are their corresponding order parameters. S{ i s zero for an iso t r o p i c phase. The order parameters for the mixed phase sample w i l l then be lower than for the sample containing purely lamellar phase. The s p l i t t i n g s for the palmitate need not be greatly affected (as observed in , ( 1 8 ) ) as long as most of the palmitate i s in the lamellar phase. « J u s t i f i c a t i o n for such rapid exchange can be taken from reference to the well-determined phase diagram for the sodium laurate(32) water-soap system(fig.18 ). The system forms hexagonal and lamellar phases, as well as several intermediate (possibly i s o t r o p i c ) phases. There are also many two phase regions. For a water content of about 35 to 40 weight percent, there i s a mixed phase region (lamellar and possibly i s o t r o p i c ) e x i s t i n g from 60°C to 150°C: The general features of the phase diagram of potassium palmitate should follow that of the similar system, sodium laurate. Mixing of a t h i r d short chain component into the two component potassium palmitate and 60 TEMPERATURE ° C 20 40 60 80 100 WATER CONTENT % Figure 18: Phase diagram of sodium-laurate-water system. (L=lamellar, H=hexagonal, M=micellar, I^ l , I;> i n t e r m e d i a t e phases.) Copied from Madelmont et a l . Bull.Soc. Chim. France.(1974),425. 61 water system c o u l d r e a d i l y modify the phase diagram of potassium p a l m i t a t e so as to b r i n g the system i n t o a two-phase r e g i o n where the second p o s s i b l y i s o t r o p i c phase i s r i c h i n the s h o r t c h a i n s . Our r e s u l t s f o r the CIO' sample show that the s p l i t t i n g s are lower at low temperature as the water content i s i n c r e a s e d . An i n c r e a s e i n the percentage of water b r i n g s the system i n t o the mixed phase r e g i o n at a higher temperature upon c o o l i n g and r e s u l t s i n more of the s h o r t chains being i n the (assumed) i s o t r o p i c r e g i o n . Hence, the e x i s t e n c e of a two-phase r e g i o n , e s p e c i a l l y i n the presence of s h o r t c h a i n guests i s s t r o n g l y i n d i c a t e d . 5.5.2 Phase s e p a r a t i o n e f f e c t on the host Beckmann et a l . (18) have i n v e s t i g a t e d the d i s o r d e r of the host c h a i n i n the presence of long or short c h a i n guests. At low temperature, the host behavior d i d not agree with the simple i n t u i t i v e model proposed. The o r i e n t a t i o n a l order of the host was found to be i n c r e a s e d i n the presence of the short c h a i n (C8) guest. Phase s e p a r a t i o n can e x p l a i n these r e s u l t s i f the p a l m i t a t e c h a i n s are mainly i n the l a m e l l a r phase and the short c h a i n mainly i n the other phase. The i n c r e a s e i n the order parameter of the host then r e f l e c t s the lower water content expected f o r the l a m e l l a r phase. 62 C h a p t e r 6 Summary a n d C o n c l u s i o n D e u t e r i u m nmr s p e c t r a h a v e b e e n o b t a i n e d f r o m l o n g a n d s h o r t c h a i n p o t a s s i u m s a l t s w h i c h a r e d i s s o l v e d a s one m o l e p e r c e n t g u e s t s i n t h e h o s t p r o t i a t e d p o t a s s i u m p a l m i t a t e . C o m p a r i s o n s o f t h e g u e s t s i n t h e h o s t e n v i r o n m e n t w i t h t h e same m o l e c u l e s i n s a m p l e s c o n t a i n i n g a s i n g l e c h a i n l e n g t h h e l p i n u n d e r s t a n d i n g t h e h o s t a n d g u e s t b e h a v i o r . We h a v e e x a m i n e d t h e v a r i a t i o n o f t h e q u a d r u p o l a r s p l i t t i n g s a s a f u n c t i o n o f t e m p e r a t u r e a n d c h a i n p o s i t i o n . A t h i g h t e m p e r a t u r e , t h e r e s u l t s g e n e r a l l y a g r e e w i t h t h e s i m p l e s p a c e p a c k i n g m o d e l t h a t t h e l o n g g u e s t s a r e more o r i e n t a t i o n a l l y d i s o r d e r e d t o w a r d s t h e m e t h y l e n d , a n d t h e s h o r t g u e s t s a r e c o n s t r a i n e d i n s i d e t h e h o s t . I t i s f o u n d t h a t t h e l o n g c h a i n g u e s t s f o l l o w t h e o r i e n t a t i o n a l o r d e r o f t h e h o s t up t o t h e 1 5 t h c h a i n p o s i t i o n , w i t h t h e e x t r a l e n g t h e i t h e r e x c h a n g i n g b e t w e e n p o s i t i o n s l y i n g a l o n g t h e m i d - p l a n e a n d i n s e r t i n g i n t o t h e o p p o s i t e l a y e r o r b e i n g o r i e n t a t i o n a l l y d i s o r d e r e d . T h e s h o r t c h a i n g u e s t s h a v e h i g h e r o r d e r p a r a m e t e r s t h a n t h e same c h a i n s i n t h e i r own e n v i r o n m e n t ( P n s a m p l e s ) . T h e y a r e r e s t r i c t e d i n s i d e t h e h o s t a n d t h e i n t e r a c t i o n o f t h e p o l a r h e a d w i t h w a t e r i s l e s s t h a n i n t h e Pn s a m p l e s . 63 A t low t e m p e r a t u r e , p h a s e s e p a r a t i o n i n v o l v i n g a r a p i d e x c h a n g e o f m o l e c u l e s b e t w e e n a l a m e l l a r p h a s e ( r i c h i n t h e h o s t m o l e c u l e s ) a n d a p o s s i b l y i s o t r o p i c p h a s e ( r i c h i n t h e s h o r t c h a i n m o l e c u l e s ) c a u s e s a s i g n i f i c a n t l o w e r i n g i n o r d e r p a r a m e t e r s o f t h e s h o r t c h a i n g u e s t s . T h i s phenomenon c a n a l s o r e a d i l y e x p l a i n t h e r e s u l t s o f C h e n e t a l . ( l 4 ) t h a t t h e o-CDg. g r o u p s p l i t t i n g s i n c r e a s e w i t h g u e s t c h a i n l e n g t h up t o a l e n g t h c o m p a r a b l e t o t h a t o f t h e h o s t . T h e s e u n e x p e c t e d r e s u l t s a g r e e w i t h t h e s t u d y o f C h a r v o l i n e t a l . ( 1 6 ) w h e r e p h a s e c h a n g e s a r e o b s e r v e d w i t h l a r g e g u e s t c o n c e n t r a t i o n s a t 7 0 ° C . A t low t e m p e r a t u r e , Beckmann e t a l . ( l 8 ) f o u n d t h a t t h e o r d e r p a r a m e t e r s o f t h e h o s t a r e i n c r e a s e d i n t h e p r e s e n c e o f s h o r t c h a i n g u e s t s . T h i s u n e x p e c t e d r e s u l t i s p r o b a b l y due t o p h a s e s e p a r a t i o n r a t h e r t h a n l i p i d - w a t e r i n t e r a c t i o n . I n t h e c a s e o f p h a s e s e p a r a t i o n , t h e p a l m i t a t e h o s t i s m a i n l y i n t h e l a m e l l a r p h a s e a n d t h e s h o r t c h a i n g u e s t s a r e m a i n l y i n t h e p o s s i b l y i s o t r o p i c p h a s e . An i n c r e a s e i n t h e s p l i t t i n g s o f t h e h o s t w i l l be e x p e c t e d , b e c a u s e t h e w a t e r c o n t e n t o f t h e l a m e l l a r p h a s e i s l e s s t h a n t h a t f o r a s i n g l e p h a s e s y s t e m . Table 1 Composition of the samples Samplec mole % Host Guest Water C6 13.38 0 .14 86.49 C10 13.71 0 .14 86.15 CIO' 11.92 0 .12 87 .95 ' C12 13.75 0 .14 86.11 Cl 6 13.20 0 .13 86.67 C22 13.70 0.14 86.15 P10 14.00 — 86.00 P12 14.00 — 86.00 PIS 13.37 — 86.63 P22 0 3 .87 86.13 Cn sample Host: potassium palmitate Guest: potassium soap of chainlength n. Pn sample Host: potassium soap of chainlength n. (Guest not present) 0 65 References ( 1 ) Harvey F. Lodish & James E. 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