9.
WULFF
Molecular
Molecular
Recognition
Imprinting
in
- a New
Polymers
189
Approach
To p r e p a r e s p e c i f i c c a v i t i e s w i t h f u n c t i o n a l groups i n a " d i s c o n t i n u a t e words" a r r a n g e m e n t s e v e r a l y e a r s ago we i n t r o d u c e d a new a p p r o a c h ( 1 9 - 2 3 ) . The f u n c t i o n a l g r o u p s t o be i n t r o d u c e d were bound t o a s u i t a b l e t e m p l a t e m o l e c u l e i n t h e form of p o l y m e r i z a b l e v i n y l d e r i v a t i v e s . T h i s monomer t h e n was c o p o l y m e r i z e d u n d e r s u c h c o n d i t i o n s t h a t h i g h l y c r o s s l i n k e d p o l y m e r s were formed h a v i n g c h a i n s i n a f i x e d a r r a n g e m e n t . A f t e r r e m o v a l of the t e m p l a t e , f r e e c a v i t i e s were formed ( s e e F i g u r e 2 ) . They p o s s e s s e d a shape and an a r r a n g e m e n t of f u n c t i o n a l g r o u p s c o r r e s p o n d i n g to t h a t of t h e t e m p l a t e . The f u n c t i o n a l g r o u p s i n t h i s p o l y m e r a r e l o c a t e d a t q u i t e d i f f e r e n t p o i n t s of the polymer c h a i n and t h e y a r e h e l d i n a s p a t i a l r e l a t i o n s h i p by c r o s s l i n k i n g . T h i s approach to p r e p a r e a c a v i t y c o n t r a s t s w i t h the use of a low m o l e c u l a r w e i g h t m o i e t y c a r r y i n g the d e s i r e d stereochemical information (4-9). Our method r e s e m b l e s to some e x t e n t t h a t of D i c k e y ( 2 4 , 2 5 ) , who d e m o n s t r a t e d t h a t s i l i c a g e l , p r e p a r e d from sodium s i l i c a t e and a c e t i c a c i d i n t h e p r e s e n c e o f m e t h y l o r a n g e , had a s p e c i f i c a f f i n i t y f o r methyl orange i n the p r e s e n c e of e t h y l , n - p r o p y l and n - b u t y l i s o m e r s . See " I m p r i n t i n g i n M o d i f i e d S i l i c a s " f o r more d e t a i l s . In c o n t r a s t to D i c k e y ' s work, u s i n g our method n o t o n l y a r e i m p r i n t s o f t h e s u b s t a n c e s o b t a i n e d , but i t i s p o s s i b l e a t t h e same time to i n t r o d u c e f u n c t i o n a l g r o u p s i n t o the c a v i t i e s i n a s p e c i f i c a r r a n g e ment. T h i s i n c r e a s e s s p e c i f i c i t y and b r o a d e n s t h e a p p l i c a b i l i t y of t h e method. One example i l l u s t r a t i n g the p r i n c i p l e i s d e s c r i b e d i n somewhat g r e a t e r d e t a i l . Monomer 1 was u s e d to some e x t e n t f o r the o p t i m i z a t i o n of the method. The t e m p l a t e i s pheny1-a-D-mannopyranoside, t o w h i c h two m o l e c u l e s of 4 - v i n y l p h e n y l b o r o n i c a c i d a r e bound by e s t e r l i n k a g e s to two h y d r o x y l g r o u p s e a c h . Compared t o F i g u r e 2 , t h i s i s a s i m p l e r c a s e w i t h o n l y two i d e n t i c a l f u n c t i o n a l g r o u p s being involved. B o r o n i c a c i d was c h o s e n as a b i n d i n g group b e c a u s e i t u n d e r g o e s e a s i l y r e v e r s i b l e i n t e r a c t i o n s with d i o l groups. S i n c e t h e r e i s a c h i r a l t e m p l a t e , the a b i l i t y to c r e a t e the s t e r i c a r r a n g e m e n t i n the c a v i t y can be t e s t e d ( a f t e r r e m o v a l of the t e m p l a t e ) by the a b i l i t y of the p o l y m e r to r e s o l v e a r a c e m i c m i x t u r e of template molecules. The monomer 1 was c o p o l y m e r i z e d by f r e e r a d i c a l i n i t i a t i o n i n t h e ~ p r e sence of an i n e r t s o l v e n t w i t h a l a r g e amount of a b i f u n c t i o n a l c r o s s l i n k i n g a g e n t . Under t h e s e c o n d i t i o n s , m a c r o p o r o u s p o l y m e r s were o b t a i n e d w h i c h possessed a permanent p o r e s t r u c t u r e , a h i g h i n n e r s u r f a c e a r e a , and good a c c e s s i b i l i t y . A d d i t i o n a l l y , low p o l y m e r s w e l l a b i l i t y would i m p l y l i m i t e d m o b i l i t y o f the p o l y m e r chains. From a p o l y m e r of t h i s t y p e , 40 t o 90% o f t e m p l a t e m o l e c u l e s can be s p l i t o f f by t r e a t m e n t w i t h water or a l c o h o l (see F i g u r e 3 ). I f t h i s polymer i s
POLYMERIC REAGENTS A N D
208 Imprinted
CATALYSTS
Biopolymers
The most s p e c i f i c f o r m a t i o n of s h a p e - and s i t e - s e l e c t i v e biopolymers i s occurring i n nature i t s e l f . Highly s p e c i f i c a n t i b o d i e s a r e p r o d u c e d i n r e s p o n s e t o the p r e s e n c e o f antigens. Such an a n t i b o d y forms a s p e c i f i c complex w i t h o n l y the a n t i g e n t h a t evoked i t s f o r m a t i o n . In c h e m i s t r y b i o p o l y m e r s have been used t o p r e p a r e s p e c i f i c s u b s t a n c e s by i m p r i n t i n g o r t e m p l a t e p r o c e d u r e s . S h i n k a i (79^) used w a t e r s o l u b l e s t a r c h and added m e t h y l e n e b l u e as t e m p l a t e . The m i x t u r e was c r o s s l i n k e d i n w a t e r with cyanuric c h l o r i d e . A r e f e r e n c e was p r e p a r e d w i t h o u t t h e dye. The a p p a r e n t b i n d i n g c o n s t a n t f o r m e t h y l e n e b l u e was t w i c e as h i g h f o r the i m p r i n t e d p r o d u c t . A more c a r e f u l i n v e s t i g a t i o n showed t h a t the main d i f f e r e n c e between the two r e s i n s was n o t the b i n d i n g c o n s t a n t b u t the number of the b i n d i n g s i t e s . R e c e n t l y Keyes (80-82) d e s c r i b e d an i n t e r e s t i n g a p p r o a c h to t h e s y n t h e s i s o f s e m i s y n t h e t i c enzymes. A p r o t e i n was p a r t i a l l y d e n a t u r a t e d and t h e n b r o u g h t i n c o n t a c t w i t h an i n h i b i t o r of an enzyme t o be m o d e l l e d . The p r o t e i n was t h e n c r o s s l i n k e d i n t h e p r e s e n c e of the inhibitor. I n t h i s way a p r o t e i n w i t h some of the a c t i v i t y o f the model enzyme was o b t a i n e d . The a c t i v i t y was q u i t e d i f f e r e n t from t h a t of the o r i g i n a l n a t i v e p r o t e i n . I t i s assumed t h a t the p a r t i a l l y d e n a t u r a t e d p r o t e i n b i n d s t h e i n h i b i t o r whereby a new a c t i v e c e n t e r i s formed w h i c h i s s i m i l a r t o t h a t o f t h e model enzyme. In one of s e v e r a l examples t r a n s f o r m a t i o n o f a t r y p s i n to a chymot r y p s i n - a c t i v e p r o t e i n i s d e s c r i b e d w i t h i n d o l e as i n h i b i t o r and g l u t a r a l d e h y d e as c r o s s l i n k i n g a g e n t . The new p r o d u c t showed an i n c r e a s e o f c h y m o t r y p s i n a c t i v i t y of 400% and a d e c r e a s e o f t r y p s i n a c t i v i t y o f 14%. Bunemann, M i i l l e r and c o - w o r k e r s (S3) looked f o r p o l y m e r s w h i c h can b i n d d i s t i n c t s e q u e n c e s o f DNA. They u s e d t h e t a r g e t DNA as t h e t e m p l a t e t o s y n t h e s i z e the complementary p o l y m e r . To the t a r g e t DNA a m i x t u r e o f b a s e - s p e c i f i c dyes c a r r y i n g p o l y m e r i z a b l e a c r y l i c d e r i v a t i v e s was bound. I t was t h e n p o s s i b l e t o c o p o l y m e r i z e t h e s e a c r y l i c d e r i v a t i v e s w h i l e bound to a n a t i v e DNA i n an aqueous s o l u t i o n . The r e s u l t i n g p o l y m e r s were s e p a r a t e d from the t e m p l a t e DNA and a s s a y e d f o r D N A - b i n d i n g s p e c i f i c i t y (8j4) . I t was p o s s i b l e w i t h t h e s e p o l y m e r s to s t r o n g l y i n h i b i t t r a n s c r i p t i o n f r o m t h a t DNA w h i c h had s e r v e d as t e m p l a t e f o r polymer s y n t h e s i s .
Distance Accuracy
of Two
F u n c t i o n a l Groups
I m p r i n t i n g i n most c a s e s has been u s e d f o r t h e p r e p a r a t i o n of c h i r a l c a v i t i e s w i t h f u n c t i o n a l g r o u p s , and the t e s t f o r a c c u r a c y o f the a r r a n g e m e n t has u s u a l l y been the a b i l i t y t o r e s o l v e the r a c e m a t e of the t e m p l a t e . Thus t h e s e l e c t i v i t y i s a r e s u l t o f the c o m b i n a t i o n o f the e x a c t c a v i t y - s h a p e and t h e e x a c t n e s s of t h e a r r a n g e m e n t of t h e
212
POLYMERIC REAGENTS AND
CATALYSTS
copper i o n s . A f t e r a p r e a r r a n g e m e n t of t h e m a c r o m o l e c u l e s a r o u n d the m e t a l i o n t h i s f a v o r a b l e c o n f o r m a t i o n was s u b s e q u e n t l y f i x e d by means of an i n t e r m o l e c u l a r c r o s s l i n k i n g with butadiene. A f t e r removing the copper i o n s from the c r o s s l i n k e d s o r b e n t w i t h a c i d the p o l y m e r showed an i n c r e a s e d s o r p t i o n c a p a c i t y and an improvement i n i t s k i n e t i c c h a r a c t e r i s t i c s i n comparison with a copolymer c r o s s l i n k e d by t h e same method b u t w i t h o u t t h e a d d i t i o n of a m e t a l i o n . I n d e p e n d e n t l y f r o m t h e R u s s i a n s c i e n t i s t s the J a p a n e s e group of N i s h i d e and T s u c h i d a (92,93) r e p o r t e d t h e c r o s s l i n k i n g o f a m e t a l complex between a poly(4-vinyl- . p y r i d i n e ) l i g a n d ( p a r t i a l l y q u a t e r n i z e d ) and a m e t a l i o n , by a d d i n g 1,4-dibromobutane to the s o l u t i o n . These a u t h o r s r e p o r t e d i n a d d i t i o n improved s e l e c t i v i t y . The r e s i n s showed a p r e f e r e n c e f o r a d s o r b i n g the m e t a l i o n s used as a template. T h i s e f f e c t i s shown i n T a b l e V I . Most s p e c i f i c i s the c o p p e r - r e s i n . The s e l e c t i v i t y f o r c o p p e r i s i n c r e a s e d by a f a c t o r o f 4.8, the Z n - r e s i n shows an i n c r e a s e i n s e l e c t i v i t y o f 3.0, the C d - r e s i n of 2.1 and
Table VI.
A d s o r p t i o n of M e t a l Ions C r o s s l i n k e d P o l y ( 4 - v i n y l p y r i d i n e ) R e s i n s (93)
Resin
Adsorbed Cu
Cross-linked Cross-linked Cross-linked Cross-linked Cross-linked metal i o n
(Cu) (Co) (Zn) (Cd) without
2 +
Metal
Co
52 16 8 9 15
2 +
6 10 6 4 7
Ions, Zn
2 +
8 8 1 1 7 6
% Cd
2 +
9 9 6 8 6
R e s i n s i m p r i n t e d by Cu , Co , Zn , and Cd E q u i l i b r a t i o n i n CH C00H-CH C00Na b u f f e r o f PH 5.5. The u p t a k e p e r c e n t a g e o f an e q u i m o l a r m i x t u r e o f the f o u r m e t a l i o n s , i s l i s t e d above. 3
3
the C o - r e s i n of 1.1 f o r i t s own m e t a l i o n . L a t e r Kabanov and c o - w o r k e r s ^ 4 - 9 6 ^ p r e p a r e d ^ y e s i n s by t h e i r method i m p r i n t e d by Cu , Ni , and Co and f o u n d as w e l l t h a t the s o r b e n t s e x h i b i t e d h i g h e r s e l e c t i v i t y w i t h r e s p e c t t o m e t a l s f o r t h e i o n f r o m w h i c h t h e y were p r e p a r e d . T s u c h i d a and c o - w o r k e r s (9_7) t r i e d s i m i l a r c r o s s l i n k i n g w i t h b r a n c h e d and l i n e a r p o l y ( e t h y l e n e i m i ^ | ) and *f|th p o l y ( v i n y l i m i d a z o l e ) i n the p r e s e n c e of Cu or Co ion t e m p l a t e s , but no enhancement o f s e l e c t i v i t y towards t h e same m e t a l i o n s was a c h i e v e d . The same was t r u e when t h e y p r e p a r e d a p o l y m e r from a monomeric complex (98). In fcbis c a s e t h e m e t a l - 1 - v i n y 1 i m i d a z o l e complex ( f r o m N i ^ , Co o r Zn as the t e m p l a t e ) was c o p o l y m e r i z e d and c r o s s l i n k e d t
+
224
F i g u r e 11. in c a v i t i e s
POLYMERIC R E A G E N T S A N D CATALYSTS
P o l y m e r i m p r i n t e d by 8 (A) and a r e a c t i o n i m p r i n t e d by 8 to p r e p a r e L - t h r e o n i n e (B) .
9. W U L F F
61.
62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77. 78. 79. 80. 81. 82. 83. 84. 85. 86. 87.
Molecular Recognition in Polymers
229
Wulff, G.; Dederichs, W.; Grotstollen, R.; Jupe, C. In "Affinity Chromatography and Related Techniques"; Gribnau, T.C.J.; Visser, J.; Nivard, R.J.F.; Eds.; Elsevier: Amsterdam 1982, pp. 207-216. Wulff, G.; Lauer, M.; Bohnke, H. Angew. Chem. 1984, 96, 714-715; Angew. Chem. Int. Ed. Engl. 1984, 23, 741-742. Lauer, M.; Bohnke, H.; Grotstollen, R.; Salehnia, M.; Wulff, G. Chem. Ber. 1985, 118, 246-260. Ferrier, R.J. Adv. Carb. Chem. Biochem. 1978, 35, 31-80. Amicon Corp. "Boronate Ligands in Biochemical Separations"; Amicon Corp., Danvers 1981. Carlsohn, H.; Hartmann, M. Acta Polym. 1979, 30, 420-425. Sarhan, A. Makromol. Chem. Rapid. Commun. 1982, 3, 489-493. Wulff, G.; Sarhan, A.; Gimpel, J.; Lohmar, E. Chem. Ber. 1974, 107, 3364-3376. Wulff, G.; Akelah, A. Makromol. Chem. 1978, 179, 2647-2651. F u j i i , Y.; Matsutani, K.; Kikuchi, K. J. Chem. Soc. Chem. Commun. 1985, 415-417. Damen, J.; Neckers, D.C. Tetrahedron Lett. 1980, 21, 1913-1916. Hopkins, A.; Williams, A. J. Chem. Soc., Perkin Trans. II, 1983, 891-896. Andersson, L.; Sellergren, B.; Mosbach, K. Tetrahedron Lett. 1984, 25, 5211-5214. Takagishi, T.; Klotz, I.M. Biopolymers 1972, 11, 483-491. Takagishi, T.; Hayashi, A.; Kuroki, N. J. Polym. Sci. Polym. Chem. Ed. 1982, 20, 1533-1547. Takagishi, T.; Sugimoto, T.; Hamano, H.; Lim, Y.-J.; Kuroki, N.; Kozuka, H. J. Polym. Sc. Polym. Lett. Ed. 1984, 22, 283-289. Arshady, R.; Mosbach, K. Makromol. Chem. 1981, 182, 687-692. Norrlöw, O.; Glad, M.; Mosbach, K. J. Chromatogr. 1984, 299, 29-41. Shinkai, S.; Yamada, M.; Sone, T.; Manabe, O. Tetrahedron Lett. 1983, 24, 3501-3504. Keyes, M.H. Patent Ger. Offen. 3 147 947, 8.7. 1982. Saraswathi, S.; Keyes, M.H. Polym. Mater. Sci. Engl. 1984, 51, 198-203; Chem. Abstr.1984, 101, 166015 n. See also: Chem. Eng. News 1984, 62, 33. Bünemann, H.; Dattagupta, N.; Schuetz, H.J.; Müller, W. Biochemistry 1981, 20, 2864-2874. Kosturko, L.D.; Dattagupta, N.; Crothers, D.M. Biochemistry 1979, 18, 5751-5756. Crowley, J.I.; Rapoport, H. Acc. Chem. Res. 1976, 9, 135-144. Wulff, G.; Schulze, I. Angew. Chem. 1978, 90, 568570. Wulff, G.; Schulze, I. Isr. J. Chem. 1978, 17, 291297.
