Mesomorphic Order in Polymers - American Chemical Society

13 Mesomorphic Order i n Block Copolymers from α-Amino Acids and Other Monomers and i n Copolymers from

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α-Amino Acids ANDRÉ D O U Y and B E R N A R D G A L L O T Centre de Biophysique Moléculaire, C.N.R.S., 1 A , Avenue de la Recherche Scientifique, 45045 Orléans Cedex, France F o r more t h a n t e n years we have been interested by t h e s y n t h e sis and t h e structure o f b l o c k c o p o l y m e r s ( 1 , 2 ) . I n 1973, we have t h o u g h t t h a t c o p o l y m e r s with one or two p o l y p e p t i d e b l o c k s w o u l d be o f h i g h interest b o t h in a technological and in a biological p o i n t o f v i e w . Due to their ability to exhibit a large r a n g e o f c o n f o r m a t i o n s , p o l y p e p t i d e c h a i n s s h o u l d be a b l e t o confer t o c o p o l y m e r s a large variety o f new technological properties on one hand, and to mimic t h e b e h a v i o u r o f membranous proteins on t h e other hand (3). So we have synthesized and studied by X - r a y diffraction, Electron M i c r o s c o p y and Infrared S p e c t r o s c o p y t h e following t y p e s o f c o p o l y m e r s : c o p o l y m e r s w i t h a c a r b o h y d r a t e and a p e p t i d e b l o c k , c o p o l y m e r s w i t h a polyvinyl b l o c k and a polypeptide b l o c k , random and b l o c k c o p o l y m e r s o f two different α amino acids. In this p a p e r , we give t h e principle of the synthesis of the three classes of copolymers and we sum up the principal characte ristics of their mesomorphic structures. Copolymers w i t h a s a c c h a r i d e

b l o c k and a p e p t i d e

block

The f i r s t c l a s s o f mesomorphic c o p o l y m e r s t h a t we have s y n t h e s i z e d and s t u d i e d a r e c o p o l y m e r s w i t h a h y d r o p h i l i c s a c c h a r i d e b l o c k and a h y d r o p h o b i c p e p t i d e b l o c k . I n t h e s e c o p o l y m e r s , t h e saccharide block i s a carbohydrate f r a c t i o n of a g l y c o p r o t e i n . A g l y c o p r o t e i n c a n be d e s c r i b e d a s a g r a f t c o p o l y m e r i n w h i c h a s m a l l number o f c a r b o h y d r a t e c h a i n s a r e g r a f t e d t o a p e p t i d e s k e l e t o n . S y n t h e s i s . We have used a s g l y c o p r o t e i n Ovomucoid e x t r a c t e d f r o m Hen egg w h i t e (40 . The e n z y m a t i c d e g r a d a t i o n o f Ovomucoid g i v e s a m i x t u r e o f c a r b o h y d r a t e s . T h e i r f r a c t i o n a t i o n by column c h r o m a t o g r a p h y p r o v i d e s two g l y c o amino a c i d s w h i c h a r e b o t h t e r m i n a t e d by an A s p a r a g i n r e s i d u e ( 5 ) . The α f r a c t i o n ( 0 ] has a m o l e c u l a r w e i g h t o f 1850 and c o n t a i n s 10 s u g a r r e s i d u e s ; t h e 3 f r a c t i o n Cϋβ3 has a m o l e c u l a r w e i g h t o f 3200 and c o n t a i n s 16 r e s i d u e s (5_3 . U s i n g t h e α amine f u n c t i o n o f t h e t e r m i n a l A s p a r a g i n r e s i d u e a

0-8412-0419-5/78/47-074-165$05.00/0 © 1978 American Chemical Society

In Mesomorphic Order in Polymers; Blumstein, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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o f t h e g l y c o - a m i n o - a c i d s G and 0^ we have i n i t i a t e d t h e p o l y m e r i z a t i o n o f t h e NCAs o f b e n z y l - L - g l u t a m a t e and c y n n a m y l - L - g l u t a m a t e and p r e p a r e d c o p o l y m e r s c o n t a i n i n g between 14 % and 86 % o f p o l y p e p t i d e (_6) . a

Structure• B l o c k copolymersϋ ΕΒ and O^EB, where t h e h y d r o p h o b i c p o l y p e p t i d e b l o c k CEB) i s a p o l y ( b e n z y l - L - g l u t annate) b l o c k , e x h i b i t mesophases i n d i m e t h y l s u l f o x i d e f o r DMSO c o n c e n t r a t i o n s r a n g i n g f r o m z e r o t o a l i m i t v a l u e w h i c h depends upon t h e c o m p o s i t i o n o f t h e c o p o l y m e r and t h e n a t u r e o f t h e c a r b o h y d r a t e b l o c k ( 2, 6_) . The s t u d y by l o w a n g l e X - r a y d i f f r a c t i o n o f t h e s e mesophases p r o v i d e s X-ray p a t t e r n s e x h i b i t i n g i n t h e i r c e n t r a l r e g i o n a s e t o f s h a r p l i n e s w i t h B r a g g s p a c i n g s i n t h e r a t i o 1,2,3,4,5.., c h a r a c t e r i s t i c o f a layered s t r u c t u r e . This l a m e l l a r s t r u c t u r e results from t h e s u p e r p o s i t i o n o f plane, p a r a l l e l , e q u i d i s t a n t sheets ; e a c h s h e e t c o n t a i n s two l a y e r s : one o f t h i c k n e s s ûf\ f o r m e d by t h e c a r b o h y d r a t e b l o c k , t h e o t h e r o f t h i c k n e s s d f o r m e d by t h e p o l y p e p t i d e b l o c k s ; t h e r e i s a p a r t i t i o n o f t h e s o l v e n t between t h e two l a y e r s : 70 % o f t h e s o l v e n t i s l o c a l i z e d i n t h e c a r b o h y d r a t e l a y e r (J3) . F u r t h e r m o r e , i n t h e p o l y p e p t i d e l a y e r , t h e p e p t i d e c h a i n s a r e i n an α h e l i x c o n f o r m a t i o n a s i s d e m o n s t r a t e d by I n f r a r e d s p e c t r o s c o p y and X - r a y d i f f r a c t i o n and a r e a s s e m b l e d on a b i d i m e n s i o n a l h e x a g o n a l a r r a y f o r c o p o l y m e r s w i t h an 0^ s a c c h a r i d e b l o c k a s i s r e v e a l e d by X r a y s ( 6 ) . When t h e m o l e c u l a r w e i g h t o f t h e p o l y p e p t i d e b l o c k i n c r e a s e s , t h e t o t a l t h i c k n e s s o f a s h e e t and t h e t h i c k n e s s de o f t h e p o l y p e p t i d e l a y e r b o t h i n c r e a s e l i n e a r l y w h i l e t h e t h i c k n e s s d/\ o f t h e c a r b o h y d r a t e l a y e r remains- n e a r l y c o n s t a n t . The e f f e c t o f t h e s o l v e n t c o n c e n t r a t i o n on t h e g e o m e t r i c a l parameters o f t h e l a m e l l a r s t r u c t u r e i s s i m i l a r f o r a l l t h e copo l y m e r s s t u d i e d and i s I l l u s t r a t e d i n F i g . 1 f o r t h e c o p o l y m e r Og EB.33 w h i c h c o n t a i n s 62 % o f p o l y p e p t i d e . When t h e DMSO c o n c e n t r a t i o n i n c r e a s e s : t h e t o t a l t h i c k n e s s d o f a sheet i n c r e a s e s , t h e t h i c k n e s s d/\ o f t h e c a r b o h y d r a t e l a y e r a l s o i n c r e a s e s , w h i l e t h e t h i c k n e s s de o f t h e p o l y p e p t i d e l a y e r r e m a i n s n e a r l y c o n s t a n t .


α

B

Copolymers w i t h a p o l y v i n y l

b l o c k and a p o l y p e p t i d e

block

The second c l a s s o f mesomorphic c o p o l y m e r s t h a t we have s y n t h e s i z e d and s t u d i e d c o n s i s t s o f c o p o l y m e r s w i t h a p o l y v i n y l b l o c k and a p o l y p e p t i d e b l o c k . I n t h e s e c o p o l y m e r s t h e f i r s t b l o c k i s a p o l y s t y r e n e o r a p o l y b u t a d i e n e b l o c k and t h e s e c o n d b l o c k i s a hydrophobic o r a h y d r o p h i l i c p o l y p e p t i d e block. Synthesis. The p o l y v i n y l b l o c k ( p o l y b u t a d i e n e o r p o l y s t y r e n e ) i s s y n t h e s i z e d by a n i o n i c p o l y m e r i z a t i o n , t h e n t h e c h e m i c a l m o d i f i c a t i o n o f t h e l i v i n g ends p r o v i d e s a p o l y m e r t e r m i n a t e d by a p r i m a r y amine f u n c t i o n w h i c h I s used t o i n i t i a t e t h e p o l y m e r i z a t i o n o f t h e NCA o f t h e d e s i r e d α amino a c i d ( 7 , 8 ) .


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By t h i s way we have p r e p a r e d t h e f o l l o w i n g c o p o l y m e r s : p o l y b u t a d i e n e - p o l y ( b e n z y l - L - g l u t a m a t e ) (BG), p o l y s t y r e n e - p o l y ( b e n z y l L-glutamate) (SG), polybutadiene-poly(carbobenzoxy-L-lysine) (BCK), p o l y s t y r e n e - p o l y ( c a r b o b e n z o x y - L - l y s i n e ) (SCK), p o l y s t y r e n e poly ( L-leucine ) (SL), polybutadiene-poly(N -hydroxypropyl-L-glutamine) (BGH), p o l y b u t a d i e n e - p o l y ( L - l y s i n e ) ( B K ) , p o l y s t y r e n e - p o l y ( L - l y s i n e ) (SK) and p o l y s t y r e n e - p o l y ( L - g l u t a m i c a c i d ) (SE) .


5

Structure. C o p o l y m e r s BG, SG, S L , BCK and SCK e x i . i b i t l i q u i d c r y s t a l l i n e s t r u c t u r e s i n t h e d r y s t a t e and i n c o n c e n t r a t e d s o l u t i o n i n d i f f e r e n t s o l v e n t s : dioxane, d i c h l o r o ethane, d i c h l o r o propene... F o r a l l c o p o l y m e r s s t u d i e d ( c o p o l y m e r s c o n t a i n i n g between 18 % and 83 % o f p o l y p e p t i d e ) t h e l i q u i d c r y s t a l l i n e s t r u c t u r e s a r e a l w a y s l a m e l l a r and a r e v e r y s i m i l a r t o t h e s t r u c t u r e o f s a c charide-peptide block copolymers. I n the l a m e l l a r s t r u c t u r e o f c o p o l y m e r s w i t h a p o l y v i n y l b l o c k and a h y d r o p h o b i c polypeptide b l o c k , each sheet o f t h i c k n e s s d r e s u l t s from the s u p e r p o s i t i o n o f two l a y e r s : one o f t h i c k n e s s d/\ f o r m e d by t h e p o l y v i n y l c h a i n s i n a more o r l e s s random c o i l c o n f o r m a t i o n , t h e o t h e r o f t h i c k n e s s dg f o r m e d by t h e p o l y p e p t i d e c h a i n s , i n an α h e l i x c o n f o r m a t i o n , a r r a n g e d i n an h e x a g o n a l a r r a y , and g e n e r a l l y f o l d e d C2_,_7,_8) . The l a m e l l a r c h a r a c t e r o f t h e s t r u c t u r e , t h e α h e l i x c o n f o r m a t i o n o f t h e p o l y p e p t i d e c h a i n s and t h e i r h e x a g o n a l p a c k i n g a r e demonstrated, as i n the case o f s a c c h a r i d e - p e p t i d e block copoly mers, by X - r a y d i f f r a c t i o n , E l e c t r o n m i c r o s c o p y ( F i g . 2 ) , I n f r a r e d s p e c t r o s c o p y and C i r c u l a r D i c h r o i s m ( 7 ) . The number o f f o l d s o f t h e p o l y p e p t i d e c h a i n s I s d e t e r m i n e d by c o m p a r i s o n o f t h e t h i c k n e s s dβ o f t h e p o l y p e p t i d e l a y e r w i t h t h e a v e r a g e l e n g t h L o f t h e p o l y p e p t i d e chains c a l c u l a t e d from t h e i r degree o f p o l y m e r i z a t i o n and t h e i r α h e l i x c o n f o r m a t i o n 12,7) . The number o f f o l d s o f t h e p o l y p e p t i d e c h a i n s i s g o v e r n e d by t h e m o l e c u l a r w e i g h t and t h e c o m p o s i t i o n o f t h e c o p o l y m e r and by t h e n a t u r e o f t h e b l o c k s . The number o f f o l d s i n c r e a s e s w i t h t h e p o l y p e p t i d e c o n t e n t o f t h e copo l y m e r : f o r i n s t a n c e , f o r c o p o l y m e r s SG o f d i f f e r e n t c o m p o s i t i o n but w i t h a l l a m o l e c u l a r w e i g h t o f 25000 f o r t h e p o l y s t y r e n e b l o c k , t h e number o f f o l d s i n c r e a s e s f r o m 0 f o r a p e p t i d e c o n t e n t o f 31 % t o 5 f o r a p e p t i d e c o n t e n t o f 71 %. F u r t h e r m o r e , t h e number o f f o l d s i s higher i f the p o l y p e p t i d e chain i s l i n k e d t o a p o l y s t y r e ne c h a i n t h a n t o a p o l y b u t a d i e n e one (_9) . F i g . 3 i l l u s t r a t e s t h e b e h a v i o u r o f t h e g e o m e t r i c a l parameters of the l a m e l l a r s t r u c t u r e versus s o l v e n t c o n c e n t r a t i o n f o r copoly mers w i t h a p o l y v i n y l b l o c k and a h y d r o p h o b i c p o l y p e p t i d e b l o c k . As i n t h e c a s e o f s a c c h a r i d e - p e p t i d e c o p o l y m e r s , when t h e s o l v e n t c o n c e n t r a t i o n i n c r e a s e s , t h e t o t a l t h i c k n e s s d o f a s h e e t and t h e t h i c k n e s s d/\ o f t h e p o l y v i n y l l a y e r b o t h I n c r e a s e , w h i l e t h e t h i c k n e s s dg o f t h e p o l y p e p t i d e l a y e r r e m a i n s n e a r l y c o n s t a n t .


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d


0/3Eb.3 3

Figure 1. Variation with DMSO concen tration of the parameters of the lamellar structure of the copolymer ΟβΕΒ.33 with a saccharide block of the β type and a poly (benzyl-h-glutamate) content of 62%. (Q) Total thickness d of a sheet; (A) thickness d of the carbohydrate layer; (O) thickness d of the peptide layer (6).

•

Δ

Ο

A

E

10

20

30

Figure 2. Example of electronic micrographs provided by copolymers polybutadienepoly(benzyl-L-glutamate). White stripes, polypeptide layers; black stripes, polybutadiene layers stained with Osmium.


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Random and b l o c k c o p o l y m e r s o f two α amino a c i d s


The t h i r d c l a s s o f mesomorphic c o p o l y m e r s we have s y n t h e s i z e d and s t u d i e d a r e random and b l o c k c o p o l y m e r s o f two d i f f e r e n t α amino a c i d s . Synthesis. U s i n g h e x a m e t h y l amine a s i n i t i a t o r , we have c o p o l y m e r i z e d , i n DMF s o l u t i o n , t h e Ν-carboxy-anhydride (NCA) o f b e n z y l - L - g l u t a m a t e w i t h t h e NCAs o f t h e f o l l o w i n g amino a c i d s : cinnamyl-L-glutamate, carbobenzoxy-L-lysine, L - l e u c i n e , Q L-phenyl a l a n i n , L-phenyl a l a n i n . To o b t a i n b l o c k c o p o l y m e r s , we c o p o l y m e r i z e s u c c e s s i v e l y t h e NCAs o f t h e two α amino a c i d s . A t t h e end o f t h e p o l y m e r i z a t i o n o f t h e f i r s t b l o c k we p r o t e c t t h e NH2 t e r m i n u s by an G - n i t r o p h e n y l s u l p h e n y l g r o u p t o a l l o w i t s f r a c t i o n a t i o n and i t s c h a r a c t e r i z a t i o n . A f t e r e l i m i n a t i o n o f t h e p r o t e c t i n g group we p o l y m e r i z e t h e NCA o f t h e s e c o n d amino a c i d . To o b t a i n random c o p o l y m e r s , we p o l y m e r i z e s i m u l t a n e o u s l y t h e NCAs o f t h e two amino a c i d s and we f o l l o w t h e c o p o l y m e r c o m p o s i t i o n d u r i n g p o l y m e r i z a t i o n t o be s u r e t h a t i t r e m a i n s n e a r l y c o n s t a n t and t h a t t h e r e i s no f o r m a t i o n o f b l o c k s . Structure. A l l t h e random and b l o c k c o p o l y m e r s we have s y n t h e s i z e d e x h i b i t l i q u i d c r y s t a l l i n e s t r u c t u r e s i n dioxane. We have n o t s t u d i e d t h e c h o l e s t e r i c p h a s e s f o u n d between about 50 \ and 80 % o f s o l v e n t f o r some c o p o l y m e r s , b e c a u s e X-Ray d i f f r a c t i o n p a t t e r n s o f t h i s phase a r e v e r y p o o r (one o b s e r v e s o n l y a band a t l o w a n g l e s ) and do n o t a l l o w a d e t a i l e d a n a l y s i s o f the c h o l e s t e r i c s t r u c t u r e . On t h e c o n t r a r y , f o r d i o x a n e c o n c e n t r a t i o n s s m a l l e r t h a n about 50 % t o 60 %, l o w a n g l e X-Ray d i f f r a c t i o n p a t t e r n s e x h i b i t sets o f sharp l i n e s which a l l o w t h e d e t e r m i n a t i o n o f t h e s t r u c t u r e o f t h e mesophases. I n t h e s e mesophases, t h e p o l y p e p t i d e c h a i n s a r e i n an α h e l i x c o n f o r m a t i o n a s i t i s d e m o n s t r a t e d by I n f r a r e d s p e c t r o s c o p y (from t h e p o s i t i o n o f t h e c h a r a c t e r i s t i c bands Amide I ana Amide I I ) and by X-Ray d i f f r a c t i o n ( f r o m t h e v a l u e o f t h e mass p e r l e n g t h u n i t MO) ) . I n t h e s e mesophases, t h e p a c k i n g o f t h e h e l i c e s , deduced f r o m low a n g l e X-Ray p a t t e r n s depends upon t h e t y p e o f c o p o l y m e r ( r a n dom o r b l o c k ) , t h e c o m p o s i t i o n o f t h e c o p o l y m e r and t h e n a t u r e o f the b l o c k s . 1) H o ^ o p o l y m e r s _ o f _ b e n z y l - L - g l u t a m a t e . Homopolymers o f b e n z y l - L - g l u t a m a t e e x h i b i t , a s i t i s w e l l known, an h e x a g o n a l s t r u c t u r e f o r m e d by α h e l i c e s p a c k e d i n a b i d i m e n s i o n a l h e x a g o n a l a r r a y . The d i s t a n c e between t h e a x i s o f two n e i g h b o u r i n g h e l i c e s i n c r e a ses w i t h t h e d i o x a n e c o n c e n t r a t i o n a s i t i s shown on t h e F i g u r e 4. The domain o f s t a b i l i t y o f t h e h e x a g o n a l s t r u c t u r e v a r i e s s l i g h t l y with the m o l e c u l a r weight o f t h e polymer.



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Figure 3. Variation with dioxane concentration of the parameters of the lamellar structure of the copolymer SG.5 with a polystyrene block of 25,000 and a poly(benzyl glutamate) content of 47%. (Q) Total thickness d of a sheet; (A) thickness d of the polystyrene layer; (O) thickness d of the polypeptide layer. A

B

Figure 4. Variation with dioxane concentration of the parameter of the hexagonal lattice of a homopoly(benzyl-L-glutamate ) with a number average degree of polymerization of 100


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171

e

2) H9î9B9ly I??EË_9f_ÇËEË?È§0? ^yiLl]:y§iD?* ^ have s t u d i e d homopolymers o f c a r b o b e n z o x y - L - l y s i n e w i t h an a v e r a g e d e g r e e o f p o l y m e r i z a t i o n between 50 and 500. They e x h i b i t i n d i o x a n e s o l u t i o n d i f f e r e n t s t r u c t u r e s a s i t has a l r e a d y been r e p o r t e d f o r o t h e r s o l v e n t s (11) F o r d i o x a n e c o n c e n t r a t i o n s between 55 and 70 %, X - r a y p a t terns are c h a r a c t e r i s t i c of a c h o l e s t e r i c structure. F o r d i o x a n e c o n c e n t r a t i o n s between 40 and 55 % and f o r d r y c o p o l y m e r s X - r a y p a t t e r n s e x h i b i t r e f l e x i o n s c h a r a c t e r i s t i c o f an h e x a g o n a l s t r u c t u r e ( B r a g g s p a c i n g s i n t h e r a t i o 1, / 3 , / 4 , / 7 , /ËT. . ) .

F o r d i o x a n e c o n c e n t r a t i o n s between 9 and 23 % X - r a y p a t t e r n s e x h i b i t a s e t o f r e f l e x i o n s w h i c h c a n be i n d e x e d i n a q u a d r a t i c l a t t i c e ( B r a g g s p a c i n g s i n t h e r a t i o 1, /2, / ? , /Ë>, / θ . . ) . A t b o t h ends o f t h e domain o f s t a b i l i t y o f t h e q u a d r a t i c s t r u c t u r e one o b s e r v e s a s m a l l domain o f c o n c e n t r a t i o n where a d e m i x i o n between q u a d r a t i c and h e x a g o n a l s t r u c t u r e s e x i s t s . F o r d i o x a n e c o n c e n t r a t i o n s between 25 and 40 %, i f t h e sam p l e s a r e prepared i n standard c o n d i t i o n s , X-ray p a t t e r n s e x h i b i t a d i f f u s e band w h i c h does n o t a l l o w t h e d e t e r m i n a t i o n o f t h e p a r a meter o f t h e b i d i m e n s i o n a l l a t t i c e ; n e v e r t h e l e s s I n f r a r e d spec troscopy reveals the existence o f helices. I n o r d e r t o r e s o l v e t h e s t r u c t u r e o f t h e p o l y m e r i n t h i s do main o f c o n c e n t r a t i o n s we have used t h e e f f e c t o f t e m p e r a t u r e s on t h e s t a b i l i t y o f t h e d i f f e r e n t s t r u c t u r e s . We have p r e p a r e d a t 80°C mesomorphic g e l s c o n t a i n i n g 50 % o f d i o x a n e and e x h i b i t i n g a w e l l d e f i n i t e h e x a g o n a l s t r u c t u r e , c o o l e d t h e sample a t - 30°C, e v a p o r a t e d t h e s o l v e n t a t - 30°C u n t i l t h e d e s i r e d c o n c e n t r a t i o n and a n n e a l e d t h e sample a t 20°C. By t h i s way we have o b t a i n e d a w e l l organized hexagonal s t r u c t u r e f o r dioxane c o n c e n t r a t i o n h i g h e r t h a n 23 %. We have even been a b l e t o o b t a i n a q u a d r a t i c s t r u c t u r e f o r t h e d r y c o p o l y m e r by e v a p o r a t i o n a t - 30°C o f t h e s o l v e n t o f a sample c o n t a i n i n g 15 % o f d i o x a n e . The q u a d r a t i c s t r u c t u r e i s s t a b l e i n a s m a l l domain o f c o n c e n t r a t i o n and t e m p e r a t u r e . I t s h i g h e s t s t a b i l i t y i s o b s e r v e d f o r d i o x a n e c o n c e n t r a t i o n s o f a b o u t 15 % : t h e q u a d r a t i c s t r u c t u r e i s s t a b l e u n t i l t e m p e r a t u r e s h i g h e r t h a n 90°C. F o r o t h e r d i o x a n e c o n c e n t r a t i o n s t h e t r a n s i t i o n q u a d r a t i c ~> h e x a g o n a l i s o b s e r v e d a t t e m p e r a t u r e s o n l y s l i g h t l y h i g h e r t h a n room t e m p e r a t u r e . On t h e c o n t r a r y , t h e h e x a g o n a l s t r u c t u r e i s s t a b l e u n t i l tem p e r a t u r e s h i g h e r t h a n about 200°C where d e g r a d a t i o n o f t h e p o l y m e r begins. I f the hexagonal s t r u c t u r e i s p a r t i c u l a r l y s t a b l e i t i s not the only s t r u c t u r e p o s s i b l e f o r polymers o f carbobenzoxy-Ll y s i n e . F o r c e r t a i n c o n c e n t r a t i o n s and t e m p e r a t u r e s a q u a d r a t i c s t r u c t u r e a p p e a r s and i t p r o b a b l y c o r r e s p o n d s t o a s p e c i a l c o n f o r m a t i o n o f t h e l a t e r a l c h a i n s . The e l e v a t i o n o f t h e t e m p e r a t u r e i n c r e a s e s t h e t h e r m i c a g i t a t i o n and d e s t r o y s t h e asymmetry o f t h e l a t e r a l c h a i n s l e a d i n g t o on h e x a g o n a l s t r u c t u r e c h a r a c t e r i z e d by a c y l i n d r i c a l symmetry o f t h e l a t e r a l c h a i n s a r o u n d t h e p e p t i d i c chains.



172

M E S O M O R P H I C

ORDER

I N

P O L Y M E R S

F i g . 5 i l l u s t r a t e s t h e r e s p e c t i v e domains o f s t a b i l i t y o f t h e q u a d r a t i c s t r u c t u r e ( t r i a n g l e s ] and o f t h e h e x a g o n a l s t r u c t u r e ( c i r c l e s ) a t 20°C. I t a l s o shows t h a t t h e l a t t i c e p a r a m e t e r o f t h e two s t r u c t u r e s i n c r e a s e s w i t h d i o x a n e c o n c e n t r a t i o n . 3) Copolymers__of_çarbobenzoxy-L-lysin te. We have s t u d i e d a l o t o f random and b l o c k c o p o l y m e r s o f c a r b o b e n z o x y l y s i n e and b e n z y l g l u t a m a t e o f d i f f e r e n t c o m p o s i t i o n s . They a l l e x h i b i t an h e x a g o n a l s t r u c t u r e whose t h e l a t t i c e parameter increases with solvent concentration. The f i g u r e s 6 and 7 show t h a t t h e l a w s o f v a r i a t i o n o f t h e d i s t a n c e between t h e a x i s o f t h e n e i g h b o u r i n g h e l i c e s v e r s u s s o l v e n t c o n c e n t r a t i o n a r e t h e same f o r random and b l o c k c o p o l y m e r s o f t h e same c o m p o s i t i o n . The f a c t t h a t random and b l o c k c o p o l y m e r s o f t h e same compos i t i o n p r e s e n t t h e same h e x a g o n a l l a t t i c e w i t h t h e same g e o m e t r i c a l p a r a m e t e r s means t h a t t h e h e l i c e s c a n s l i d e a l o n g t h e d i r e c t i o n o f t h e i r a x i s and t h a t t h e r e i s no phase s e p a r a t i o n between t h e p o l y ( c a r b o b e n z o x y - L - l y s i n e ) and t h e poly(γ-benzyl-L-glutamate) blocks. On f i g u r e 8 we have p l o t t e d t h e v a r i a t i o n o f t h e p a r a m e t e r of t h e hexagonal l a t t i c e f o r homopoly(benzyl-L-glutamate) : curve D, f o r h o m o p o l y ( c a r b o b e n z o x y - L - l y s i n e ) : c u r v e A and f o r random and block copolymers of d i f f e r e n t compositions ; curve Β (copolymers c o n t a i n i n g 33 % o f c a r b o b e n z o x y - L - l y s i n e ) and c u r v e C ( c o p o l y m e r s c o n t a i n i n g 66 % o f c a r b o b e n z o x y - L - l y s i n e ) . One c a n see t h a t t h e d i s t a n c e between t h e a x i s o f t h e h e l i c e s i n c r e a s e s w i t h t h e c a r b o b e n z o x y - l y s i n e (CK) c o n t e n t o f t h e c o p o l y m e r . 4) Çopolymers_of_L-leucin For a l l random and b l o c k c o p o l y m e r s o f L - l e u c i n e and b e n z y l - L - g l u t a m a t e t h a t we have s y n t h e s i z e d and s t u d i e d t h e p o l y p e p t i d e c h a i n s a r e i n an α h e l i x c o n f o r m a t i o n . Random c o p o l y m e r s o f L - l e u c i n e and b e n z y l - L - g l u t a m a t e e x h i b i t an h e x a g o n a l s t r u c t u r e as homopolymers o f b e n z y l - L - g l u t a m a t e do. B l o c k c o p o l y m e r s o f L - l e u c i n e and b e n z y l - L - g l u t a m a t e (LEB) c o n t a i n i n g l e s s t h a n 30 % o f L - l e u c i n e e x h i b i t an h e x a g o n a l s t r u c ture . B l o c k c o p o l y m e r s L.EB c o n t a i n i n g between 40 and 60 % o f Lleucine e x h i b i t a centred rectangular s t r u c t u r e . This structure i s a d e f o r m a t i o n o f an h e x a g o n a l s t r u c t u r e ( s e e F i g . 9) and e a c h e l e m e n t a r y l a t t i c e c o n t a i n s two c h a i n s : one o f e a c h t y p e o f b l o c k . T h i s f a c t i s i n agreement w i t h t h e domain o f c o p o l y m e r c o m p o s i t i o n which g i v e s t h i s centred r e c t a n g u l a r l a t t i c e . The v a r i a t i o n o f t h e p a r a m e t e r s o f t h e c e n t r e d r e c t a n g u l a r a r r a y v e r s u s d i o x a n e c o n c e n t r a t i o n i s shown i s f i g u r e 10. One c a n see t h a t one s i d e o f t h e a r r a y i n c r e a s e s much f a s t e r t h a n t h e other. Conclusion Among t h e mesomorphic c o p o l y m e r s t h a t we have s y n t h e s i z e d and


DOUY

A N D G A L L O T



H

Q

%

Diox.

20

20

Figure 5. Variation with dioxane concentration of the parameter of the hexagonal lattice (Φ) and of the quadratic lattice (A) of polymers of carbob'enzoxy-iAysine

DA 25

CK

30.50

Ο

CK.EEL30.50

EB

·

20

%Diox. 20

40

Figure 6. Variation with dioxane concentration of the param eter of the hexagonal lattice for random and block copolymers with number average degree of polymerization of SO for carbobenzoxy lysine and 50 for benzyl glutamate. (Ο) Block copoly mer CK.EB.30.50; (Φ) random copolymer CK.EB .30.50. r


MESOMORPHIC

25

C K . E B .

CK. E B

4

ORDER IN P O L Y M E R S

100.50 Ο 100.50 ·


20

15

%

20

Die

40

Figure 7. Variation with dioxane concentration of the parameter of the hexagonal lattice for random and block copolymers with number average degree of polymerization of 100 for carbobenzoxy lysine and 50 for benzyl glutamate. (Ο) Block copolymer CK.EB.100.50; (Φ) random copolymer CK.EB,.100.50.

Figure 8. Variation with dioxane concentration of the parameter of the hexagonal lattice of homopolymers, block, and random copolymers of carbobenzoxy-lysine and benzyl glutamate. (Ό) homopolybenzyl glutamate Ε Β. 100; (C) block and random copolymers CK.EB.30.50 and CK.EB .3().50; (B) block and random copolymers: CK.EB.100.50 and CK.EB,-.100.50; (A) homocarbobenzoxy-lysine CK.100. r



DOUY

A N D

G A L L O T


Figure 9. Schematic of the bidimensional rectangular array of poly(\Aeucine)-poly(benzyl-L-glutamate) block co polymers (L.EB). (Φ) Axis of the helices of one type of chains; (O) those of the other type.

Figure 10. Variation with dioxane concentration of the param eters a and b of the centered rectangular array of the copolymer L.EB.5



176

MESOMORPHIC

ORDER I N P O L Y M E R S

s t u d i e d , c o p o l y m e r s w i t h a s a c c h a r i d e and a p e p t i d e b l o c k a r e o f p a r t i c u l a r i n t e r e s t f o r b i o l o g i s t s . They f o r m s i m p l i f i e d m o d e l s of p r o t e i n s , e s p e c i a l l y membrane p r o t e i n s , a c c o r d i n g t o t h e i r amphipatic character. We a r e now p r e p a r i n g and s t u d y i n g membrane m o d e l s f o r m e d by t e r n a r y s y s t e m s : a m p h i p a t i c b l o c k c o p o l y m e r / l i p i d s / w a t e r . From the i n t e r a c t i o n w i t h o u r p o l y m e r i c models o f l e c t i n s C l e c t i n s a r e p r o t e i n s o r g l y c o p r o t e i n s s p e c i f i c of d i f f e r e n t sugar r e s i d u e s ) we hope t o o b t a i n i n f o r m a t i o n s a b o u t t h e r e s p e c t i v e p a r t s p l a y e d by t h e d i f f e r e n t c a r b o h y d r a t e c h a i n s and t h e p o l y p e p t i d e s k e l e t o n o f g l y c o p r o t e i n s and p e r h a p s h e l p t o t h r o w some l i g h t on p r o b l e m s as i m p o r t a n t as c e l l r e c o g n i t i o n and c e l l c o n t a c t i n h i b i t i o n .

Abstract The structure of random and block copolymers of two α amino acids, and of block copolymers with an amino acid block and a carbohydrate or a vinyl block have been studied by X-ray d i f f r a c tion, electron microscopy, infrared spectroscopy and c i r c u l a r dichroism. Copolymers with a hydrophilic carbohydrate block and a hydrophobic polypeptide block exhibit i n DMSO solution and i n the dry state a lamellar structure ; this lamellar structure con s i s t s of plane, p a r a l l e l , equidistant sheets ; each sheet results from the superposition of two layers : one formed by the carbo hydrate chains i n a disordered conformation, the other formed by the polypeptide chains i n an helical conformation and assembled in a hexagonal or a centred rectangular l a t t i c e . Copolymers with a polyvinyl block (polystyrene or polydiene) and a hydrophobic polypeptide block exhibit a lamellar structure similar to that of copolymers with a carbohydrate and a peptide block, except that their polypeptide chains i n an helical conformation are always hexagonally packed and are generally folded. For random and block copolymers of benzyl-L-glutamate and one of the following amino acids, ε-carbobenzoxy-L-lysine, L-leucine i n the dry state and in dioxane concentrated solution the polypeptide chains are always i n an h e l i c a l conformation, but they are assembled on an hexagonal or a centred rectangular l a t t i c e depending upon the type of copo lymer (random or block), the nature of the blocks and the copoly mer composition. Literature cited 1) Gallot Bernard, Pure Appl. Chem., (1974), 38, 1. 2) Gallot Bernard, "Liquid Crystalline Structure of Block Copoly mers" i n "Liquid Crystalline Order i n Polymers", A. Blumstein Edit., Academic Press, New-York (1978). 3) Billot Jean-Pascal, Douy André, Gallot Bernard, Makromol. Chem., (1976), 177, 1889. 4) Lineaweaver Η., Murray C.W., J. Biol. Chem., (1977) 171, 565. 5) Bayard Bernard, Thèse Doctorat, Lille, France (1974).



13.

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A N D G A L L O T


177

6) Douy André, Gallot Bernard, Makromol. Chem., (1977), 178, 1595. 7) Perly Bruno, Douy André, Gallot Bernard, Makromol. Chem., (1976), 177, 2569. 8) Billot Jean-Pascal, Douy André, Gallot Bernard, Makromol. Chem. (1977), 178, 1641. 9) Douy André, Gallot Bernard, paper i n preparation. 10) Saludjian Pedro, Luzzati V i t t o r i o , "Study of polypeptide-solvent systems" i n "Poly α amino acids", G.D. Fasman Edit., Dekker, New-York (1967). 11) Saludjian Pedro, De Lozé Christiane, Luzzati V i t t o r i o , C.R. Acad. S c i . Paris, 1963) C.256, 4297. RECEIVED December 8, 1977.


Mesomorphic Order in Polymers - American Chemical Society

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