X-ray Studies of the Structure of Cellulose Complexes - ACS

Chapter 12

X-ray Studies of the Structure of Cellulose Complexes John Blackwell, David Kurz, Mao-Yao Su, and David M. Lee Department of Macromolecular Science, Case Western Reserve University, Cleveland, OH 44106-2699

X-ray methods have been used to investigate the structures of crystalline complexes of cellulose I and II with diamines. The structures of three complexes: ramie cellulose I complexed with ethylenediamine and 1,3-diaminopropane, and cellulose II complexed with hydrazine, have been refined by linked atom least squares methods. Interaction with the low molecular weight specimens disrupts both the hydrogen bonding and hydrophobic forces between the cellulose chains. The results show that i nallthree cases the cellulose chains rearrange from quarter stagger to zero staggered (in r e g i s t e r ) packing. The complexes consist of a series of sheets of chains separated by hydrogen bonded complexing molecules. The p a r a l l e l - I antiparallel-II chain polarity is maintained in the complexes of the two forms of cellulose.

The e x i s t e n c e o f c r y s t a l l i n e complexes o f c e l l u l o s e and c e r t a i n low m o l e c u l a r weight compounds has been known s i n c e t h e 1930*s, and s e v e r a l s t u d i e s o f t h e i r s t r u c t u r e s by X - r a y methods have been r e p o r t e d s i n c e t h a t time (1-6)· These s t r u c t u r e s a r e o f c u r r e n t r e l e v a n c e i n v i e w o f t h e renewed i n t e r e s t i n o r g a n i c solvents f o r c e l l u l o s e : i n t h e l a s t 15 y e a r s s e v e r a l new s o l v e n t systems have been r e p o r t e d , i n c l u d i n g d i m e t h y l s u l f o x i d e - p a r a formaldehyde 0 7 ) , N-methylmorpholine-N-oxide ( 8 ) , h y d r a z i n e a t elevated temperature and p r e s s u r e ( 9 ) , and l i t h i u m chloridedimethylacetamide ( 1 0 ) . A n a l y s i s of the s t r u c t u r e of c e l l u l o s e s o l v e n t complexes p r o v i d e s a d e t a i l e d m o l e c u l e model f o r t h e polymer s o l v e n t i n t e r a c t i o n . T h i s paper d e s c r i b e s o u r a n a l y s e s of t h e s t r u c t u r e s o f c e l l u l o s e complexed w i t h ethylenediamine, h y d r a z i n e , and 1,3-propylenediamine.

0097-6156/87/0340-0199$06.00/0 © 1987 American Chemical Society

200

THE STRUCTURES OF CELLULOSE

Our p r e s e n t i n v e s t i g a t i o n s o f the s t r u c t u r e o f c e l l u l o s e complexes has been made p o s s i b l e by the i n c r e a s e d knowledge of the s t r u c t u r e s of the uncomplexed forms i n the l a s t t e n y e a r s . F i g u r e 1 shows the r e f i n e d s t r u c t u r e of c e l l u l o s e I d e r i v e d by Gardner and B l a c k w e l l (11) , based on the X - r a y i n t e n s i t y d a t a f o r f i b e r s drawn from the c e l l w a l l o f the sea a l g a V a l o n i a v e n t r i cosa. T h i s m a t e r i a l has a m o n o c l i n i c u n i t c e l l w i t h d i m e n s i o n s j i = 16.34Â, b = 15.72Â, c = 10.38À ( f i b e r a x i s ) , and Ύ = 9 7 . 0 ° , c o n t a i n i n g d i s a c c h a r i d e s e c t i o n s o f e i g h t c h a i n s (as f i r s t p r o p o s e d by H o n j o and Watanabe (_1_2). H o w e v e r , o n l y a few weak r e f l e c t i o n s a r e seen w i t h odd h and/or k i n d i c e s ( t h e r e s t a r e a b s e n t ) and hence a two c h a i n u n i t c e l l w i t h the a and _b dimen s i o n s reduced by h a l f can be used as an adequate a p p r o x i m a t i o n t o the f u l l s t r u c t u r e . T h i s two c h a i n u n i t c e l l i s the Meyer and M i s c h (13) u n i t c e l l o b s e r v e d f o r o t h e r n a t i v e c e l l u l o s e s , and i t seems l i k e l y t h a t the e x t r a r e f l e c t i o n s ( w i t h odd h and/or k) a r e not seen f o r t h e s e due t o the lower c r y s t a l l i n i t y and c r y s t a l l i t e size. F o r V a l o n i a c e l l u l o s e , odd o r d e r 001 r e f l e c t i o n s a r e absent and the space group i s P2^, p o i n t i n g to a 2^ h e l i c a l con f o r m a t i o n f o r the c h a i n i n the c r y s t a l l i n e r e g i o n s . In the a n a l y s i s of the s t r u c t u r e o f c e l l u l o s e I , the most i m p o r t a n t f e a t u r e t o be d e t e r m i n e d was the p o l a r i t y of a d j a c e n t c h a i n s , i . e . do the c h a i n s i n the two c h a i n c e l l have the same ( p a r a l l e l ) o r o p p o s i t e ( a n t i p a r a l l e l ) sense? Both k i n d s o f model were s e t up and r e f i n e d u s i n g t h e l i n k e d atom l e a s t s q u a r e s (LALS) r o u t i n e s (14) t o o b t a i n the b e s t agreement between the o b s e r v e d and c a l c u l a t e d X - r a y i n t e n s i t i e s . The b e s t model f o r c e l l u l o s e I was found to be an a r r a y o f p a r a l l e l c h a i n s , as can be seen i n F i g u r e 1: the b e s t a n t i p a r a l l e l model c o u l d be r e j e c t e d a t a s i g n i f i c a n c e l e v e l o f 0.005%, i . e . , the p a r a l l e l model i s p r e f e r r e d by 200 t o 1. The two c h a i n s have the same basic conformation, r i g h t down t o the t g o r i e n t a t i o n s of the pendant-CHÔH g r o u p s , and a r e s t a g g e r e d by 0.265^, c o n s i s t e n t w i t h the a p p r o x i m a t e q u a r t e r s t a g g e r f i r s t proposed by Meyer and Mark ( L 5 ) . E a c h g l u c o s e r e s i d u e i s i n v o l v e d i n two intra m o l e c u l a r hydrogen bonds: 0 3 - Η · · · 0 5 , as f i r s t p r o p o s e d by Hermans £ t a l . (1_6) f r o m s t u d y o f s p a c e f i l l i n g m o d e l s and 02-Η···06', which was s u g g e s t e d t o a c c o u n t f o r the d i c h r o i s m of the 0-H s t r e t c h i n g modes i n the p o l a r i z e d i n f r a r e d s p e c t r a (17, 18). The c e l l u l o s e c h a i n i n e v i t a b l y has a r e l a t i v e l y s t i f f extended c o n f o r m a t i o n due to the $ - ( 1 , 4 ) - l i n k a g e s , and these i n t r a m o l e c u l a r bonds on b o t h s i d e s o f the g l y c o s i d i c linkage f u r t h e r s t a b i l i z e the c o n f o r m a t i o n . The c h a i n s a r e l i n k e d i n s h e e t s by 06-Η···03 i n t e r m o l e c u l a r bonds a l o n g the _b a x i s . How e v e r , t h e r e i s no i n t e r m o l e c u l a r bonding a l o n g the ab d i a g o n a l s nor a l o n g the a_ a x i s , and the s t r u c t u r e must be s t a b i l i z e d i n these d i r e c t i o n s by h y d r o p h o b i c f o r c e s , e.g. between the f a c e s o f the g l u c o s e r i n g s . F i g u r e 2 shows the s t r u c t u r e o f c e l l u l o s e I I , which was d e t e r m i n e d i n a s i m i l a r manner based on the i n t e n s i t y data f o r F o r t i s a n rayon (19). The u n i t c e l l i s m o n o c l i n i c w i t h d i m e n s i o n s a = 8.01Â, _b = 9.04Â, £ = 10.36À ( f i b e r a x i s ) , and Ύ = 117.1°; the space group i s a p p r o x i m a t e l y P2^ and the c e l l con t a i n s d i s a c c h a r i d e r e p e a t s of two c h a i n s . In t h i s case the b e s t agreement between o b s e r v e d and c a l c u l a t e d X - r a y i n t e n s i t i e s was ,

BLACKWELL ET AL.

F i g u r e 1. S t r u c t u r e of c e l l u l o s e (b) ab p r o j e c t i o n . (Reprinted with permission Wiley

& Sons.)

201

X-ray Studies of Cellulose Complexes

I [11]:

from r e f . 11.

(a) ac p r o j e c t i o n ; Copyright

1974

John

202


b

F i g u r e 2. S t r u c t u r e of c e l l u l o s e I I [19]: (b) ab p r o j e c t i o n . (Reprinted with permission Chemical S o c i e t y . )

from r e f . 19.

(a) ac p r o j e c t i o n ; Copyright

1976

American

12.

BLACKWELL ET AL.

203


o b t a i n e d f o r an a n t i p a r a l l e l c h a i n model. The b e s t contending models w i t h p a r a l l e l c h a i n s gave i n f e r i o r agreement and were a l s o found to be stereochemically unacceptable; constraining the models t o a v o i d such "bad c o n t a c t s " took them f u r t h e r out of con sideration. In the s t r u c t u r e as shown i n F i g u r e 2b, the c o r n e r c h a i n s have a c o n f o r m a t i o n s i m i l a r t o t h a t i n c e l l u l o s e I , w i t h two i n t r a m o l e c u l a r hydrogen bonds (03*-Η···05 and 0 2 - Η · · · 0 6 ) and l i n k e d a l o n g the _b a x i s by an 0 6 - Η · · · 0 3 i n t e r m o l e c u l a r bond. The c e n t e r c h a i n s have o p p o s i t e sense and a r e s t a g g e r e d r e l a t i v e t o t h e c o r n e r c h a i n s by 0.18c^ ( t h e c^ a x i s s e p a r a t i o n o f t h e g l y c o s i d i c oxygens). These c h a i n s have the 0 3 - Η · · · 0 5 i n t r a m o l e c u l a r bond, but the -ChÔH group i s i n the g t c o n f o r m a t i o n so t h a t the second i n t r a m o l e c u l a r bond i s not p o s s i b l e . In t h i s c a s e , the -CHÔH groups a r e bonded 06-Η···02 a l o n g the _b a x i s , and the 02-H groups form a f u r t h e r i n t e r m o l e c u l a r bond 0 2 - H » - » 0 2 a l o n g the l o n g ab d i a g o n a l . T h i s e x t r a i n t e r m o l e c u l a r bond may account f o r the h i g h e r s t a b i l i t y o f c e l l u l o s e I I as compared to c e l l u l o s e I. The p a r a l l e l - I - a n t i p a r a l l e l - I I c o n c l u s i o n was a l s o o b t a i n e d i n independent work by Sarko and co-workers ( 2 0 , 2 1 ) . τ

!

!

f

The above r e s u l t s have o b v i o u s i m p l i c a t i o n s f o r the b i o s y n t h e s i s of c e l l u l o s e m i c r o f i b r i l s . The p a r a l l e l c h a i n s t r u c t u r e o f c e l l u l o s e I r u l e s o u t any k i n d o f r e g u l a r l y f o l d e d c h a i n s t r u c t u r e , and r e v e a l s the m i c r o f i b r i l s to be extended chain polymer s i n g l e c r y s t a l s , which l e a d s to optimum t e n s i l e p r o p e r ties. Work by Brown and co-workers (22) on the mechanism o f b i o s y n t h e s i s p o i n t s to s y n t h e s i s of a r r a y s o f c e l l u l o s e c h a i n s from banks of enzyme complexes on the c e l l w a l l . These complexes produce a bundle o f c h a i n s w i t h the same s e n s e , which c r y s t a l l i z e almost i m m e d i a t e l y a f t e r w a r d s to form c e l l u l o s e I m i c r o f i b r i l s ; t h e r e i s no o p p o r t u n i t y t o r e a r r a n g e t o form a more s t a b l e a n t i p a r a l l e l c e l l u l o s e I I s t r u c t u r e . E l e c t r o n m i c r o s c o p y by H i e t a et_ a l . (23) c o n f i r m s the p a r a l l e l sense of c e l l u l o s e c h a i n s w i t h i n the i n d i v i d u a l m i c r o f i b r i l s : s t a i n s r e a c t i v e a t the r e d u c i n g end o f the c e l l u l o s e m o l e c u l e s t a i n o n l y one end o f the m i c r o f i b r i l . The p e r c e i v e d d i f f i c u l t y w i t h the p a r a l l e l - I : a n t i p a r a l l e l - I I model c o n c e r n s the I I I c o n v e r s i o n by M e r c e r i z a t i o n . Reversal o f c h a i n p o l a r i t y i s r e l a t i v e l y easy to u n d e r s t a n d d u r i n g r e g e n e r a t i o n v i a complete d i s s o l u t i o n , but l e s s so where c e l l u l o s e I i s s i m p l y s w o l l e n i n c a u s t i c soda. One p o s s i b l e mechanism would i n v o l v e r e g u l a r c h a i n f o l d i n g , but t h i s i s i n c o n s i s t e n t w i t h the mechanical p r o p e r t i e s of M e r c e r i z e d c o t t o n . I t i s important to note however t h a t the s w e l l i n g i n v o l v e s f i b r i l s which themselves a r e b u n d l e s of many m i c r o f i b r i l s . The c h a i n s w i t h i n an i n d i v i d u a l m i c r o f i b r i l w i l l h a v e t h e same s e n s e , b u t t h e c o t t o n m a c r o f i b r i l p r o b a b l y c o n s i s t s of a 50/50 m i x t u r e o f up and down microfibrils. E l e c t r o n m i c r o s c o p y by W i l l i s o n and Brown (24) on the c e l l w a l l s o f G l a u c o c y s t i s show a w i n d i n g of m i c r o f i b r i l s around the c e l l . A s i m i l a r mechanism f o r c o t t o n would l e a d t o e q u a l numbers of up and down c h a i n s t h a t a r e packaged i n t o m i c r o f i b r i l s i n w h i c h a l l the c h a i n s have the same s e n s e . Hence the mechanism f o r M e r c e r i z a t i o n p r o b a b l y i n v o l v e s rearrangement of extended c h a i n s . On s w e l l i n g , the c h a i n s a r e s e p a r a t e d and l o s e t r a c k of t h e i r p r e v i o u s n e i g h b o r s . T h e n on r e m o v a l o f t h e s w e l l i n g agent the c h a i n s a r e more l i k e l y t o r e u n i t e w i t h a n t i p a r a l l e l n e i g h b o r s due t o the h i g h e r s t a b i l i t y o f c e l l u l o s e I I .

204


At t h i s p o i n t the major f e a t u r e s of the s t r u c t u r e s of c e l l u l o s e I and I I can be c o n s i d e r e d t o be s o l v e d . N e v e r t h e l e s s , q u e s t i o n s remain, e s p e c i a l l y as r e g a r d s the d i f f e r e n c e s between the i n f r a r e d , Raman, and s o l i d s t a t e NMR s p e c t r a o b t a i n e d f o r d i f f e r e n t n a t i v e c e l l u l o s e s , a l l o f which appear t o have the c r y s t a l s t r u c t u r e s shown i n F i g u r e 1. T h i s has been a f u r t h e r m o t i v a t i o n f o r our analyses of the s t r u c t u r e s of c e l l u l o s e s o l v e n t complexes, which a r e d e s c r i b e d below. Experimental Materials. D e l i g n i f i e d n a t i v e ramie f i b e r s were o b t a i n e d from D r . R.V. A l l i s o n o f U.S.D.A., B e l l e G l a d e , F L . Mercerized s p e c i m e n s w e r e p r e p a r e d by r e p e a t e d s o a k i n g s i n 22% a q u e o u s sodium h y d r o x i d e s o l u t i o n s s e p a r a t e d by thorough washings i n water u n t i l no more than a t r a c e of r e s i d u a l c e l l u l o s e I c o u l d be d e t e c t e d i n the X - r a y p a t t e r n . F o r t i s a n r a y o n f i b e r s were the g i f t o f Dr. L. L a n i e v e o f C e l a n e s e C o r p o r a t i o n . Reagent grades of e t h y l e n e d i a m i n e and h y d r a z i n e were purchased from Eastman Kodak Co., 1,2- and 1,3- p r o p y l e n e d i a m i n e from F i s h e r S c i e n t i f i c Co. These r e a g e n t s were d r i e d u s i n g m o l e c u l a r s i e v e s . Complex

Formation

C e l l u l o s e complexes were p r e p a r e d by s o a k i n g the t a u t f i b e r s i n the i n d i v i d u a l l i q u i d complexing agents f o r 1 - 3 6 hours f o l l o w e d by vacuum d r y i n g . The s o a k i n g time was t h a t n e c e s s a r y t o remove a l l t r a c e s o f the uncomplexed c e l l u l o s e i n t h e X - r a y p a t t e r n . E t h y l e n e and p r o p y l e n e d i a m i n e c o n t e n t s were d e t e r m i n e d by e l e c t r i c a l a n a l y s e s performed by G a l b r a i t h L a b o r a t o r i e s , K n o x v i l l e , TN. H y d r a z i n e c o n t e n t s w e r e d e t e r m i n e d by a d d i t i o n o f t h e specimen t o 0.1N h y d r o c h l o r i c a c i d f o l l o w e d by p o t e n t i o m e t r i c t i t r a t i o n a g a i n s t 0.1N sodium h y d r o x i d e s o l u t i o n . X-ray

Diffraction

Wide a n g l e X - r a y d i f f r a c t i o n p a t t e r n s were r e c o r d e d on Kodak No S c r e e n X - r a y f i l m u s i n g n i c k e l f i l t e r e d CuKa r a d i a t i o n and a S e a r l e t o r o i d a l f o c u s i n g camera. The d - s p a c i n g s were c a l i b r a t e d w i t h sodium f l u o r i d e . The i n t e n s i t i e s o f the X - r a y r e f l e c t i o n s were d e t e r m i n e d from an x-y g r i d o f o p t i c a l d e n s i t y o b t a i n e d using a scanning o p t i c a l densitometer. These d a t a were c o r r e c t e d for background and f o r the L o r e n t z and p o l a r i z a t i o n effects. O v e r l a p p e d i n t e n s i t i e s were a p o r t i o n e d i n the r a t i o of the c a l culated intensities. Unobserved reflections, i . e . predicted r e f l e c t i o n s t o o weak t o be d e t e c t e d , were a s s i g n e d an i n t e n s i t y of o n e - h a l f t h e background ( t h r e s h o l d ) but i n c l u d e d i n the d a t a o n l y when t h e c a l c u l a t e d i n t e n s i t y exceeded the background. The atomic c o o r d i n a t e s f o r t h e c e l l u l o s e c h a i n were based on those used by Kolpak and B l a c k w e l l (19) i n t h e i r r e f i n e m e n t o f the s t r u c t u r e o f c e l l u l o s e I I , w i t h minor adjustments i n the g l y c o s i d i c t o r s i o n angles to f i t the s l i g h t l y d i f f e r e n t f i b e r r e p e a t s . The N-N b o n d l e n g t h i n h y d r a z i n e was s e t a t 1.44Â a s i n t h e c r y s t a l s t r u c t u r e d e t e r m i n e d by C o l l i n and Lipscomb ( 2 5 ) ; the

12.

BLACKWELL ET AL.


205

bond l e n g t h s and a n g l e s i n t h e y l e n e d i a m i n e were those used by Y o k o z u k i and K u s h i t a (26) f o r gas d i f f r a c t i o n s t u d i e s ; the s t r u c t u r e of 1,3 diaminopropane was based on t h a t f o r t r i m e t h y l e n e diamonium h y d r o c h l o r i d e due t o Hirokawa ejt al· (27 ) . R e s u l t s and

Discussion

The u n i t c e l l s determined i n t h i s and o t h e r l a b o r a t o r i e s f o r c e l l u l o s e I and I I complexes w i t h e h t y l e n e d i a m i n e and h y d r a z i n e a r e l i s t e d i n t a b l e s 1 and 2. T a b l e 3 shows our u n i t c e l l s f o r the 1,2- and 1,3- diaminopropane complexes f o r which t h e r e have been no p r e v i o u s p r o p o s a l s . As c a n be seen i n t a b l e 2, a number of u n i t c e l l s have been proposed f o r c e l l u l o s e I-hydrazine complexes o v e r the years. Some of t h i s d i v e r s i t y i s almost c e r t a i n l y due t o poor q u a l i t y d a t a , which can be indexed i n d i f f e r e n t ways. Nevertheless, v i s u a l comparison shows t h a t our p a t t e r n s a r e s i g n i f i c a n t l y d i f f e r e n t from those p u b l i s h e d p r e v i o u s l y , which p r o b a b l y r e f l e c t s the f a c t t h a t we used h y d r a z i n e c o n t a i n i n g no more than 3% water, as compared t o up to 40% i n e a r l i e r work. So f a r we have p r e pared t h r e e d i f f e r e n t c e l l u l o s e I I - h y d r a z i n e complexes, two f o r F o r t i s a n ( d e s i g n a t e d A and B) and one f o r M e r c e r i z e d ramie. There may be some r a t i o n a l e f o r t h i s : complex A has o n l y been o b t a i n e d u s i n g anhydrous h y d r a z i n e , and the F o r t i s a n and Merceri z e d ramie have d i f f e r e n t m o r p h o l o g i e s . However, i t seems l i k e l y t h a t a l l t h r e e complexes can be formed by both specimens once the p r e p a r a t i o n c o n d i t i o n s are b e t t e r understood. We a r e i n v e s t i g a t i n g the s t r u c t u r e s o f these complexes u s i n g the r e f i n e m e n t methods a p p l i e d to c e l l u l o s e s I and I I , as desc r i b e d above. In the next s e c t i o n s we d e s c r i b e the r e s u l t s of t h e s e a n a l y s e s f o r t h r e e complexes: ramie c e l l u l o s e I - e t h y l e n e diamine [ ( 2 8 ) , ramie c e l l u l o s e 1-1,3-propanediamine ( 2 9 ) , and F o r t i s a n c e l l u l o s e I I - h y d r a z i n e A, which a r e the most c r y s t a l l i n e complexes p r e p a r e d t o d a t e . Ramie C e l l u l o s e

I-Ethylenediamine

Some 39 independent r e f l e c t i o n s a r e o b s e r v e d i n the f i b e r diagram of ramie c e l l u l o s e I - e t h y l e n e d i a m i n e complex, and t h e r e a r e a f u r t h e r 36 t h a t a r e p r e d i c t e d w i t h i n the range o f t h e s e d a t a , but which a r e t o o weak t o d e t e c t . E l e m e n t a l a n a l y s i s i n d i c a t e s the p r e s e n c e of one e t h y l e n e d i a m i n e per g l u c o s e r e s i d u e and d e n s i t y c o n s i d e r a t i o n s r e q u i r e d i s a c c h a r i d e u n i t s of two c h a i n s per u n i t cell. The major f e a t u r e s o f the i n t e n s i t y d a t a a r e determined by the c e l l u l o s e c h a i n s t h e m s e l v e s . Refinements o m i t t i n g the comp l e x i n g m o l e c u l e s show t h a t the s t r u c t u r e c o n s i s t s of s t a c k s o f c h a i n s a l o n g the _b a x i s , and t h a t t h e s e a r e " i n r e g i s t e r " , i . e . there i s zero stagger. T h i s i s a l s o apparent from the f a c t t h a t v e r y few r e f l e c t i o n s w i t h odd h i n d i c e s a r e d e t e c t e d , i n d i c a t i n g t h a t we a r e d e a l i n g w i t h e s s e n t i a l l y a one c h a i n s t r u c t u r e , i . e . the two c h a i n s a l o n g the _b a x i s , t o g e t h e r w i t h t h e i r a s s o c i a t e d e t h y l e n e d i a m i n e s , have a p p r o x i m a t e l y the same s t r u c t u r e .

206


Table 1 Proposed U n i t C e l l s f o r C e l l u l o s e

Cellulose I (Ramie) Cellulose I (Cotton) Cellulose I (Ramie) Cellulose II (Regenerated) Cellulose II (Mercerized)

E t h y l e n e d i a m l n e Complexes

a (A)

b (Â)

c (Â)

12.16

13.1

10.3

Ref.

*

1

135.2

* 12.2

12.3

10.3

137.0

6

12.37

9.52

10.35

117.8

28

12.81

18.27

10.34

118.0

28

13.42

8.41

10.34

119.1

28

* A c u t e a n g l e used i n the o r i g i n a l

paper.

Table 2 Proposed U n i t

Cells for Cellulose

a (Â) Cellulose I 10.9 (Ramie) Cellulose I 9.1 (Ramie) Cellulose I 9.68 (Cotton) Cellulose I 9.19 (Ramie) Cellulose II A 9.37 (Fortisan) Cellulose II Β 8.84 (Fortisan) Cellulose II 9.48 ( M e r c e r i z e d Ramie)

Hydrazine

Complexes

γο

b (Â)

c (Â)

10.9

10.3

127.7

10.38

114.7

8.1

Ref.

*

1 3

* 9.96

10.3

125.2

6

16.39

10.37

97.4

30

19.88

10.39

120.0

30

23.76

10.38

120.0

30

15.39

10.37

96.4

30

Acute a n g l e used i n the o r i g i n a l

paper.

Table 3 Proposed U n i t C e l l s f o r C e l l u l o s e Diaminopropane Complexes

Ramie 1,2diaminopropane Ramie 1,3diaminopropane F o r t i s a n 1,2diaminopropane F o r t i s a n 1,3diaminopropane

a (Â)

b (A)

c (A)

γο

4.72

11.55

10.38

92.8

4.54

12.22

10.38

90.0

4.61

22.95

10.38

90.7

4.57

23.90

10.38

93.1

12.

BLACKWELL ET AL.


207

The e t h y l e n e d i a m i n e m o l e c u l e s must be hydrogen bonded t o the c e l l u l o s e c h a i n s (why e l s e w o u l d t h e c o m p l e x e s f o r m and be stable?). S i n c e a l l N-H and 0-H groups a r e r e q u i r e d t o form donor bonds, i t i s c l e a r from the s t e r e o c h e m i s t r y of any p o s s i b l e model t h a t each h y d r o x y l of the g l u c o s e r e s i d u e must be l i n k e d t o a n i t r o g e n v i a a donor o r a c c e p t o r bond. F o r c o n v e n i e n c e we a t t a c h e d the e t h y l e n e d i a m i n e m o l e c u l e a t 03-H by a hydrogen bond w i t h an 0··.Ν d i s t a n c e of 2.8A, and proceeded by t r e a t i n g t h i s as a f l e x i b l e s i d e c h a i n . Models were s e t up i n which the e t h y l e n e diamine^ had t h r e e p o s s i b l e c o n f o r m a t i o n s , c o r r e s p o n d i n g to t r a n s , gauche and gauche f o r the c e n t r a l t o r s i o n a n g l e . F o r complete n e s s , we a l s o c o n s i d e r e d b o t h p a r a l l e l and a n t i p a r a l l e l p a c k i n g of the two c h a i n s i n the u n i t c e l l . The a n t i p a r a l l e l models gave s i g n i f i c a n t l y worse agreement w i t h the o b s e r v e d i n t e n s i t y d a t a than d i d the p a r a l l e l c h a i n models and hence c o u l d be r e j e c t e d . The ( n a t i v e ) c e l l u l o s e I s t r u c t u r e has p a r a l l e l c h a i n s and the complex can be r e s t o r e d t o the o r i g i n a l form s i m p l y by washing i n water. I t seems u n l i k e l y t h e r e f o r e t h a t complex c o n f o r m a t i o n i n v o l v e s a r e v e r s a l o f c h a i n polarity. S i m i l a r l y , models w i t h d i f f e r e n t c o n f o r m a t i o n s f o r the e t h y l e n e d i a m i n e c o u l d a l s o be r u l e d o u t . Beyond t h i s , the r e finement l e d t o f o u r models t h a t c o u l d not be d i s t i n g u i s h e d on the b a s i s o f X - r a y agreement, but of t h e s e , o n l y one model had a l l the 0-H and N-H groups hydrogen bonded, and t h i s i s s e l e c t e d as the f i n a l s t r u c t u r e . The r e f i n e d s t r u c t u r e f o r ramie c e l l u l o s e I - e t h y l e n e d i a m i n e complex i s shown i n F i g u r e 3 and had a c r y s t a l l o g r a p h i c r e s i d u a l of R" = 0.189. As can be seen i n the ac p r o j e c t i o n ( F i g u r e 3b) the two e t h y l e n e d i a m i n e m o l e c u l e s have s l i g h t l y d i f f e r e n t p o s i t i o n s and c o n f o r m a t i o n s , which a c c o u n t s f o r the two c h a i n u n i t cell. C o n s t r a i n i n g the r e f i n e m e n t to g i v e a s t r u c t u r e w i t h i d e n t i c a l c o n f o r m a t i o n s f o r the complexing m o l e c u l e s l e d t o R" = 0.223, and such a model can be r e j e c t e d a t the 0.005% s i g n i f i c a n t level. Comparison o f the s t r u c t u r e of t h i s complex w i t h t h a t o f the o r i g i n a l c e l l u l o s e I shows the e x t e n t o f the rearrangement that has o c c u r r e d . The c h a i n s have s h i f t e d from a q u a r t e r s t a g g e r e d arrangement t o form s t a c k s i n r e g i s t e r , i . e . w i t h z e r o s t a g g e r . Thus the i n t e r a c t i o n w i t h e t h y l e n e d i a m i n e not o n l y breaks the hy drogen bonding network i n the o r i g i n a l s t r u c t u r e but a l s o a f f e c t s the h y d r o p h o b i c f o r c e s between the " s u r f a c e s " o f the r i b b o n l i k e chains. The s t r u c t u r e o f the complex i s v e r y s i m i l a r t o t h a t of c h i t i n i n which the c h a i n s a r e a l s o s t a c k e d i n r e g i s t e r t o form sheets. W i t h i n each s t a c k the c h a i n s have a p p r o x i m a t e l y the same s e p a r a t i o n o f 4.7Â and have a s i m i l a r i n c l i n a t i o n t o the s t a c k i n g plane. In β-chitin, a l l the c h a i n s have the same sense, and the s h e e t s can be s e p a r a t e d t o i n c l u d e water, l e a d i n g t o the forma t i o n o f c r y s t a l l i n e h y d r a t e s t h a t a r e analogous t o the p r e s e n t c e l l u l o s e I - e t h y l e n e d i a m i n e complex. In the l a t t e r s t r u c t u r e , the e t h y l e n e d i a m i n e m o l e c u l e s f i t i n c h a n n e l s between the mole c u l e s t h a t e x i s t i n a z e r o s t a g g e r e d s t r u c t u r e but not i n the case of q u a r t e r s t a g g e r .

208


a F i g u r e 3. complex

S t r u c t u r e o f Ramie c e l l u l o s e I -

( R e p r i n t e d w i t h p e r m i s s i o n from r e f . 30. Wiley

ethylenediamine

[ 3 0 ] : ( a ) 010 p r o j e c t i o n ; (b) ab p r o j e c t i o n .

& Sons.)

Copyright

1984 John

12. BLACKWELL ET AL.


209

Ramie C e l l u l o s e 1-1,3-diaminopropane Complex The ramie c e l l u l o s e I-1,3-diaminopropane complex s t r u c t u r e i s the most c r y s t a l l i n e o f the diaminopropane complexes so f a r examined, and has a ( m e t r i c a l l y ) o r t h o r h o m b i c u n i t c e l l t h a t can c o n t a i n o n l y one c h a i n which d i c t a t e s a p a r a l l e l c h a i n s t r u c t u r e . Elemental a n a l y s i s and d e n s i t y measurements p o i n t t o one m o l e c u l e of 1,3-diaminopropane per g l u c o s e r e s i d u e . Refinement proceeded i n a manner s i m i l a r t o t h a t d e s c r i b e d above f o r the e t h y l e n e d i a m i n e complex, based on i n t e n s i t y d a t a f o r 24 o b s e r v e d and 12 unobserved r e f l e c t i o n s . I f the c e l l u l o s e c h a i n i s assumed t o have the same backbone c o n f o r m a t i o n as i n the e t h y l e n e d i a m i n e complex, then the s t r u c t u r e i s d e f i n e d by n i n e p o t e n t i a l l y r e f i n a b l e p a r a m e t e r s . The approximate c h a i n o r i e n t a t i o n was r e f i n e d f i r s t b e f o r e the e t h y l enediamines were added. T h e r e a f t e r C-N s e c t i o n s were a t t a c h e d by hydrogen bonds a t two of the t h r e e h y d r o x y l s ( i . e . 1,3-diaminopropane o m i t t i n g the c e n t r a l CH group). T h i s e l i m i n a t e d the p o s s i b i l i t y o f a "bent" complexing molecule t h a t i s hydrogen bonded t o h y d r o x y l on the same c h a i n , and p o i n t e d t o a s t r u c t u r e i n w h i c h the 1 , 3 - d i a m i n o p r o p a n e s a r e bonded between c h a i n s , e i t h e r a l o n g the _b a x i s o r the ab d i a g o n a l s . T w e l v e d i f f e r e n t p o s s i b l e p a c k i n g models were r e f i n e d separ a t e l y , l e a d i n g t o s t r u c t u r e s w i t h R" v a l u e s between 0.147 and 0.194. These were not s t a t i s t i c a l l y d i s t i n g u i s h a b l e , nor were any of them c o m p l e t e l y hydrogen bonded. Note t h a t the r e q u i r e ment t h a t a l l the 0-H and N-H groups must be hydrogen bonded becomes more s e v e r e as the s i z e of the diamine m o l e c u l e i s i n creased. Of the 12 models, the one which came c l o s e s t t o b e i n g c o m p l e t e l y hydrogen bonded was t h a t w i t h the l o w e s t R", f o r which the o n l y d e f e c t was t h a t 06-H d i d not form a donor bond. Howe v e r , the -CH OH o r i e n t a t i o n was not f a r from the o r i g i n a l t g p o s i t i o n i n tne p a r e n t n a t i v e c e l l u l o s e , and i n c o r p o r a t i o n of a c o n s t r a i n t t o r e q u i r e the f o r m a t i o n o f an 06-H-·-02 hydrogen bond l e d t o an a c c e p t a b l e hydrogen bonding network. This f i n a l struct u r e i s shown i n F i g u r e 4. The o n e - c h a i n u n i t c e l l p r e s c r i b e s an u n s t a g g e r e d a r r a y of p a r a l l e l c h a i n s and thus the rearrangement from the o r i g i n a l c e l l u l o s e I s t r u c t u r e t h a t has o c c u r r e d i s v e r y s i m i l a r t o t h a t which o c c u r s on f o r m a t i o n of the e t h y l e n e d i a m i n e complex. A one c h a i n u n i t c e l l i s a l s o seen f o r the 1,2-diaminopropane complex, and t h i s s t r u c t u r e appears to be s i m i l a r , e x c e p t f o r minor modif i c a t i o n s o f the a_ and _b d i m e n s i o n s . 2

F o r t i s a n C e l l u l o s e I I - H y d r a z i n e Complex A This structure p r e s e n t s more d i f f i c u l t problems than those t r e a t e d above. Some 26 r e f l e c t i o n s a r e o b s e r v e d , but these are indexed by a f o u r - c h a i n u n i t c e l l , and t h i s i s i n s u f f i c i e n t d a t a to a l l o w f o r r e f i n e m e n t of the number of parameters n e c e s s a r y t o d e f i n e such a s t r u c t u r e . However, 22 o f these r e f l e c t i o n s can be indexed by a two-chain c e l l and we opted t o work w i t h t h i s as an a p p r o x i m a t i o n t o the f u l l s t r u c t u r e . T i t r a t i o n showed t h a t the h y d r a z i n e c o n t e n t was c l o s e t o one m o l e c u l e p e r g l u c o s e r e s i d u e .


F i g u r e 4. S t r u c t u r e o f Ramie c e l l u l o s e I-1,3-diaminopropane complex: ( a ) _bc p r o j e c t i o n ; (b) ab p r o j e c t i o n showing o n l y half a repeat.

12.

BLACKWELL ET AL.

211


T h i s b e i n g a complex of c e l l u l o s e I I , one would expect t h e s e two c h a i n s t o be a n t i p a r a l l e l . We d i d c o n s i d e r p a r a l l e l c h a i n models but these always gave i n f e r i o r agreement w i t h the i n t e n s i t y d a t a and c o u l d be r u l e d o u t . I n t e n s i t y c a l c u l a t i o n s q u i c k l y showed t h a t the axes of the two c h a i n s pass through the o r i g i n and 0.0,0.5 i n the ab p r o jection. The h y d r a z i n e s (N-N) were a t t a c h e d by hydrogen bonds a t 02 and t h e i r p o s i t i o n and the -CHÔH o r i e n t a t i o n s were r e f i n e d , s t a r t i n g w i t h the l a t t e r groups i n c o m b i n a t i o n s o f t h r e e s t a g g e r e d p o s i t i o n s ( g t , t g and g g ) . Of the r e s u l t i n g n i n e models, a l l b u t f o u r were r e j e c t e d i n t h a t t h e y were u n a b l e t o f o r m hydrogen bonds f o r a l l the 0-H and N-H g r o u p s . The remaining f o u r , however, were s t a t i s t i c a l l y u n d i s t i n g u i s h a b l e i n terms of t h e i r X - r a y agreement. The model w i t h the l o w e s t r e s i d u a l , R" = 0.207, i s shown i n F i g u r e 5. The major f e a t u r e s o f the s t r u c t u r e a r e the same as i n the o t h e r a c c e p t a b l e models. I t can be seen t h a t the c h a i n s a r e a r r a n g e d i n s t a c k s w i t h the same sense, and s u c c e s s i v e stacks are a n t i p a r a l l e l . The "up" and "down" s t a c k s a r e not i d e n t i c a l , but b o t h a r e s i m i l a r t o those f o r the two c e l l u l o s e I complexes d e s c r i b e d above. The g l y c o s i d i c oxygens of the a n t i p a r a l l e l c h a i n s a r e a l s o a p p r o x i m a t e l y i n r e g i s t e r and t h i s has the e f f e c t t h a t the ChÔH groups on a d j a c e n t c h a i n s a r e o p p o s i t e each o t h e r . Thus t h e r e i s a c h a n n e l between the c h a i n s (between 02 and 03 on a d j a c e n t r e s i d u e s ) and t h i s i s o c c u p i e d by the h y d r a z i n e m o l e c u l e s . T h i s c e l l u l o s e I I complex has a v e r y s i m i l a r s t r u c t u r e t o t h a t o f α - c h i t i n , which a l s o has a n t i p a r a l l e l chains. In the l a t t e r the c h a i n s a r e i n r e g i s t e r a l o n g b o t h the a and b axes, and the " c h a n n e l s " a r e o c c u p i e d by the -NHCOCH^ s u b s t i t u e n t groups. Conclusions For a l l t h r e e complexes d e s c r i b e d above, the e f f e c t o f the comp l e x i n g agent i s to break the i n t e r m o l e c u l a r hydrogen bonds and to r e a r r a n g e the c h a i n s from q u a r t e r s t a g g e r t o i n r e g i s t e r pack ing. These major f e a t u r e s can be determined relatively easily from the X - r a y i n t e n s i t y d a t a , which depend l a r g e l y on the c h a i n s themselves. T h e r e a f t e r the p o s i t i o n s of the complexing m o l e c u l e s a r e more d i f f i c u l t t o d e t e r m i n e . I n each case we have found what appears t o be r e a s o n a b l e s t r u c t u r e i n terms o f X - r a y agreement, s t e r e o c h e m i c a l c o n s t r a i n t s , and the requirement t h a t a l l o f the 0-H and N-H groups s h o u l d be hydrogen bonded. N e v e r t h e l e s s , some competing arrangements cannot be r u l e d o u t , e s p e c i a l l y f o r the F o r t i s a n c e l l u l o s e I I - h y d r a z i n e complex A. T h i s ambiguity may r e f l e c t the f a c t t h a t t h e r e may be some v a r i e t y i n the p o s i t i o n s of the complexing m o l e c u l e s i n the b u l k complex, and a l s o t h e r e a r e c o m p l i c a t i o n s due t o a b s o r p t i o n of water m o l e c u l e s . Acknowledgments T h i s work i s b e i n g s u p p o r t e d by N a t i o n a l S c i e n c e g r a n t No. DMR84-17525 from the Polymer Program.

Foundation,


b-sin?

F i g u r e 5.

S t r u c t u r e of F o r t i s a n c e l l u l o s e I I - hydrazine

complex A [ 2 8 ] :

( a ) 100 p r o j e c t i o n ;

(b) ab p r o j e c t i o n .

( R e p r i n t e d w i t h p e r m i s s i o n from r e f . 28. Wiley

& Sons.)

Copyright

1983 ν

12.

BLACKWELL ET AL.


213

References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30.

Halle, E. Kolloid-Zt. 1934, 69, 324. Trogus, C.; Hess, Κ. Z. Phys. Chem. (Leipzig) 1931, B14, 387. Sakurada, I.; Hutino, K. Kolloid-Zt. 1936, 77, 346. Sakurada, I.; Okamura, S. Kolloid-Zt. 1937, 81, 199. Centola, G. Gass. Chem. Ital. 1938, 68, 825. Creely, J.J.; Segal; L., Loeb, L. J. Polym. Sci. 1959, 36, 205. Johnson, D.L. U.S. Pat. 2 371 359, 1970. Johnson, D.L. Br. Pat. 1 144 048, 1969. L i t t , M.H.; Kumar, G. U.S. Pat. 4,028,132, 1977. Turbak, A.F.; El-Kafrawy, Α.; Snyder, F.W.; Averback, A.B. U.S. Pat. 4 302 252, 1981. Gardner, K.H.; Blackwell, J. Biopolymers 1974, 13, 1975. Honjo, G.; Watanabe, M. Nature, 1958, 326-328. Meyer, K.H.; Misch, L. Helv. Chim. Acta, 1937, 20, 232. Arnott, S.; Wonacott, A. Polymer 1966, 7, 157. Meyer, K.H.; Mark, H. Ber. Dsch. Chem. Ges. 1928, 61Β, 593. Hermans, P.H.; de Booys, J.; Maan, C. Kolloid Zt. 1943, 102, 169. Marrinan, H.J.; Mann, J. J. Polym. Sci. 1956, 21, 301. Jones, D.W. J. Polym. Sci. 1958, 32, 371. Kolpak, F.J.; Blackwell, J. Macromolecules 1976, 9, 273. Sarko, Α.; Muggli, R. Macromolecules 1974, 7, 486. Stipanovic, A.J.; Sarko, A. Macromolecules 1976, 9, 851. Brown, R.M.; Willison, J.H.M.; Richardson, C.L. Proc. Nat. Acad. Sci. U.S.A. 1976, 73, 4565. Hieta, K.; Kuga, S.; Usuda, M. Biopolymers 1984, 23, 1807. Willison, J.H.M.; Brown, R.M. J. Cell Biol. 1978, 77, 103. Collin, R.N.; Lipscomb, W.N. Acta Cryst. 1951, 4, 10. Yokozuki, Α.; Kushita, K. Bull. Chem. Soc. Jpn. 1971, 44, 2926. Hirokawa, S. et a l . Org. Com. Structure Reports 1968, V33B, 26-27. Lee, D.M.; Blackwell, J.; Litt, M.H. Biopolymers 1983, 22, 1383. Kurz, D.; Su, M.-Y.; Blackwell, J. (in preparation). Lee, D.M.; Burnfield, K.E.; Blackwell, J. Biopolymers 1984, 22, 111.

RECEIVED April 9, 1987

X-ray Studies of the Structure of Cellulose Complexes - ACS

Recommend Documents