etcheverry 1997

8/3/2019 Etcheverry 1997

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E L S E V IE R Carbohydrate Research 302 (1997) 131 - 138

CARBOHYDRA T ERESEARCH

Synthesis and characterization o f oxovanadium (IV)com plexes w ith saccharides

S u s a n a B . E t c h e v er r y , P a t r ic ia A . M . W i l l ia m s , E n r i q u e J . B a r a n *Centro de Quimica Inorgdnica (CEQUINOR), Facultad de Ciencias Exactas, Universidad Nacional deLa Plata, C. Correo 962, 1900-La Plata, Argentina

Rec eived 20 January 1997; accepted in revised form 4 April 1997

A b s t r a c t

O x o v a n a d i u m ( I V ) c o m p l e x e s o f t h e m o n o s a c c h a r i d e s D - g l u c o s e a n d D - f r u c t o s e , a n d t h ed i s acch a r i d es s u c r o s e an d t u r an o s e , w e r e o b t a i n ed i n aq u eo u s s o l u t i o n a t p H 1 2 . T h e i r s o l i ds o d i u m s a lt s w e r e p r e c i p it a t e d w i t h ab s o l u t e e th a n o l a n d c h a r a c t e r i z e d b y U V - V I S , I R , a n dd i f f u s e r e f l ec t an ce s p ec t r o s co p i e s . M ag n e t i c s u s cep t i b i l i t i e s a t r o o m t em p er a t u r e w er e a l s od e t e r m i n ed . T h e L : M s t o i ch i o m e t r y , a s d e r i v ed f r o m s p ec t r o p h o t o m e t r i c t i tr a t io n s , w as 2 : 1f o r a l l s a c c h a r i d e s e x c e p t f o r t h e o - f r u c t o s e c o m p l e x , w h i c h w a s 3 : 1 . T h e a n a l y t i c a l a n dm a g n e t i c d a t a a l s o s h o w t h a t i n t h e s o l i d s ta t e t h e co m p l ex o f t h is l i g an d s h o w s a d i f f e r en tb eh av i o r , g en e r a t i n g a d i n u c l ea r s p ec i e s b r i d g ed b y a s u g a r m o l ecu l e , w h e r eas a l l t h e o t h e rc o m p l e x e s a r e m o n o n u c l e a r . 1 9 97 E l s e v i e r S c i e n c e L t d.Keywords." VO 2+ complexes; M onosaccharide complexes; Disaccharide complexes; Electronic spectra; Vibra-tional spectra

1 . I n t r o d u c t i o nV a n a d i u m i s a m i c r o n u t r i e n t e l e m e n t w h i c h h a s

b e e n s h o w n t o p r o d u c e s e v e r a l i m p o r t a n t b i o l o g i c a le f f ec t s in l iv i n g o r g an i s m s [ 1 - 5 ] . I ts d e f i c i e n cy cau s esg r o w t h r e t a r d a t i o n an d s k e l e t a l d e f o r m a t i o n s i n an i -m a l s . I t h a s a l s o b e e n s u g g e s t e d t h a t v a n a d i u m m a yp l a y a r o l e i n t h e r e g u l a t i o n o f ( N a , K ) - A T P a s e s ,p h o s p h o r y l t r a n s f e r a s e s , a d e n y l a t e c y c l a s e , a n d p r o -t e i n k i n as es , an d i t s p o s s i b l e p a r t i c i p a t i o n i n h o r -m o n e , b o n e , g l u c o s e , a n d l i p i d m e t a b o l i s m h a s a l s ob e e n d i s c u s s e d [ 1 , 4 -6 ] . A n u m b e r o f s im p l e a n dc o m p l e x v a n a d i u m ( I V ) a n d v a n a d i u m ( V ) c o m p o u n d sh a v e s h o w n i n s u l i n -m i m e t i c a c t i o n s in a n i m a l s a n d i nd i f f e r en t t y p es o f cu l t u r ed ce l l s [ 3 - 8 ] . D es p i t e t h e

* Corresponding a uthor

r e l e v a n c e o f t h e b i o a c t i v it y o f v a n a d i u m d e r iv a t iv e s ,t h e i n v o l v e d m e c h a n i s m s o f a c t i o n a r e p o o r l y u n d e r -s tood .

I n p a st y e a r s w e h a v e r e p o r t e d a n u m b e r o f s t u d ie st h a t h a v e i d e n t i f i e d a n d c h a r a c t e r i z e d c o m p l e x e sf o r m e d b y a c t i v e v a n a d i u m s p e c i e s w i t h d i f f e r e n ti m p o r t a n t b i o m o l e c u l e s . S i n c e c a r b o h y d r a t e s a r e t h em o s t a b u n d a n t c o m p o u n d s i n n a t u r e a n d a r e d i r e c t l yi n v o l v ed i n s ev e r a l i m p o r t an t f u n c t i o n s l i k e t h e r eg u -l a t i o n o f m e t a l f l o w t h r o u g h ce l l w a l l s [ 9 ] , w e h av er ecen t l y i n i t i a t ed s t u d i e s t o ex am i n e t h e i n t e r ac t i o n o fb i o l o g i c a l l y r e l e v a n t v a n a d i u m s p e c i e s w i t h s i m p l ec a r b o h y d r a t e s [ l 0 - 1 4 ] .

A l t h o u g h t h e r e a r e m an y a r t i c l e s d ea l i n g w i t h t h ei n t e r ac t i o n s o f s acch a r i d es w i t h n o n - t r an s i t i o n m e t a l s ,i n f o r m a t i o n a b o u t t h e i n t e r a c t i o n o f c a r b o h y d r a t e sw i t h t r an s i t i o n m e t a l i o n s i s s ca r ce [ 9 ] . T h i s m ay b e

000 8-62 15/ 97/$ 17. 00 1997 Elsevier Science Ltd. All r ights reserved.Pl l S 0 0 0 8 - 6 2 1 5 ( 9 7 ) 0 0 1 3 2 -8


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13 2 S.B. Etche ver ~ et al. / Carbohydrate Research 302 (1997) 13 1-138CH2OH

IHOCH2 O OH H./i----O H HOCH,

HO H H OH OH H

Fru S u c

HO~O HH OH

~___H0H HOCH2 0 OH

H O H20HH OH

Gtc Tur

Fig. 1. Schem atic structures o f saccharides: Fru = f l -D-fructofu ranose ; Glc = a-D-glucopyranose; Suc = sucrose;Tur = OZ-D-glucopyranosyl-(1~ 3)-/3-o-fructofuranose.

( c e - D - g l u c o p y r a n o s y l- ( 1 ~ 3 ) - D - f r u c t o se ) w e r e p u r -c h a s e d f r o m S i g m a a n d u s e d a s s u p p l i e d .

V O C 1 2 ( 5 0 % s o l u t i o n ) w a s o b t a i n e d f r o m C a r l oE r b a .

U V - V I S a b s o r p t i o n s p e c t r a w e r e m e a s u r e d o n aH e w l e t t - P a c k a r d 8 4 5 3 d i o d e - a r r a y s p e c t r o p h o t o m -e t e r u s i n g 1 - c m q u a r t z c e l ls . I R s p e c t r a w e r e r e c o r d e do n a P e r k i n - E l m e r 5 8 0 B s p e c tr o p h o t o m e te r u si n gt h e K B r p e l l e t t e c h n i q u e . D i f f u s e r e f l e c t a n c e s p e c t r aw e r e o b t a i n e d w i t h a S h i m a d z u U V - 3 0 0 i n s t r u m e n tu s i n g M g O a s a n i n t e r n a l s t a n d a r d . R o o m t e m p e r a -t u r e m a g n e t i c s u s c e p t i b i l i t i e s w e r e m e a s u r e d w i t h aC a h n 2 0 0 0 b a l a n c e c a l i b r a t e d w i t h H g [ C o ( S C N ) 4 ]a n d u s i n g a f i e l d s tr e n g t h o f 6 k G . C a n d H a n a l y s e sw e r e d o n e o n a C a r l o E r b a 1 1 0 8 e l e m e n t a l a n a l y z e r ;v a n a d i u m w a s d e t e r m i n e d b y t h e t u n g s t o p h o s p h o -v a n a d i c m e t h o d a n d s o d i u m b y fl a m e p h o t o m e t r y .

e x p l a i n e d b y t h e l o w r e a c t i v it y o f t h e h y d r o x y l g r o u p so f s u g a r s a t a c i d i c o r n e u t r a l p H v a l u e s . C o m p l e x a -t i o n o f t h e V O 2 + c a t i o n w i t h s u g a r s i s f a c i l i ta t e d b yt h e p r e s e n c e o f c a r b o x y l a t e g r o u p s i n a d d i t io n t oh y d r o x y l m o i e t i e s , a s f o u n d i n a c i d i c c a r b o h y d r a t e s[ 1 1 ,1 3 ] . I n th e c a s e o f n e u t r a l s u g a r s , c o m p l e x a t i o n i sf a v o r e d b y b a s i c m e d i a a n d t a k e s p l a c e o n l y w i t hm o l e c u l e s p o s s e s s i n g a d j a c e n t c i s - h yd r o xy l g r o u p s[15 ,16] .

T h e a i m o f t h e p r e se n t w o r k w a s t h e s y n t h e s i s a n dc h a r a c t e r i z a t i o n o f c o m p l e x e s o f t h eo x o v a n a d i u m ( I V ) c a t i o n w i t h t h e n e u t r a l s u g a r s D -f r u c t o s e , D - g l u c o s e , s u c r o s e , a n d t u r a n o s e ( F i g . 1 ) ,b o t h i n a q u e o u s s o l u t i o n a n d i n t h e s o l i d s t a t e .

2 . Mater ia l s an d meth od sD( d - ) - G l u c o s e , D ( - - ) - f r u c t o s e , s u c r o s e ( / 3 - D - f r u c -

t o f u r a n o s y l a - D - g l u c o p y r a n o s i d e ) , a n d D ( + ) - t u r a n o s e

3 . Exp er imen ta lA l l t h e c o m p o u n d s w e r e p r e p a r e d b y t h e f o l l o w i n g

p r o c e d u r e : 2 m m o l o f t h e s a c ch a r i d e w e r e d i s s o l v e di n d i st i ll e d w a t e r ( 1 0 m L ) . S m a l l a m o u n t s o f so l i dN a O H w e r e a d d e d u n ti l a fi n a l p H o f 1 2 w a s r e a c h e d .O n e m m o l o f V O C1 2 w a s a d d e d t o ea c h a l k a li n es u g a r s o l u t i o n u n d e r c o n s t a n t s t i rr i n g , m a i n t a i n i n g t h ep H o f th e s o l u t i o n a t 1 2 d u r i n g t h e p r o c e s s .

A l t h o u g h t h e r e s u l t i n g s o l u t i o n s w e r e g r e e n , t h es u c r o s e - v a n a d y l s o l u t i o n b e c a m e b r o w n i s h i n a s h o r tt i m e , s u g g e s t i n g r a p i d d e c o m p o s i t i o n . T h e r e f o r e , i t i se s s e n t i a l t o m e a s u r e t h e e l e c t r o n i c s p e c t r a a n d t op r e c i p i t a t e t h e s o l i d c o m p l e x e s i m m e d i a t e l y .

T h e s o l i d c o m p l e x e s w e r e o b t a i n e d f r o m t h e g r e e ns o l u t i o n s b y s u c c e s s i v e a d d i t i o n s o f a b s o l u t e e t h a n o l ,d i s c a r d i n g t h e s u p e r n a t a n t u n t i l a m i c r o c r y s t a l l i n es o l id w a s f o r m e d . T h e h y g r o s c o p i c s o d i u m s a lt s w e r e

Table 1Elemental analys is (%) for VO2+-sacchafide com plexes 1- 4Complex Formula C H V Na1 C30Hs003 2V2Na 6 4H 20 Calcd 29.17 4.70 8.26 11.18Found 28.57 4.74 8.66 11.202 C 12 HzlO 14VN a3 " 5H 20 24.04 5.17 8.51 11.5224.84 4.79 8.34 11.883 C24H41024 VNa 3 H20 33.82 5.05 5.99 8.1033.12 5.41 5.70 8.644 C 24 H 4 1 0 2 4 V N a 3 . 3 H 2 0 32.44 5.29 5.74 7.7932.95 5.47 5.45 7.33


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S.B. Etcheverry et al. / Carbohydrate Research 302 (1997) 131-138 13 3k e p t i n a n o v e n a t 6 0 C . T h e r e s u l t s o f e l e m e n t a la n a l y s e s a r e g i v e n i n T a b l e 1 .

4 . R e s u l t s a n d d i s c u s s i o n

T h e e l e m e n t a l a n a l y s e s a r e c o n s i s t e n t w i t h t h ef o l l o w i n g f o r m u l a t i o n s f o r t h e s o l i d s o d i u m s a l t s :N a 6 [ ( V O ) 2 ( F r u ) 5 ] . 4 H 2 0 ( 1) , N a 3 [V O ( G l c )2 O H ] "5 H 2 0 ( 2) , N a 3 [ V O ( S u c ) z O H ] . H 2 0 (3 ), a ndN a 3 [ V O ( T u r ) zO H ] 3 H 2 0 ( 4) .E l e c t ron i c spe c t ra . - -Compl e x e s 1 a n d 2 s h o w t h ew e l l - k n o w n t h r e e - b a n d p a t t e r n ( T a b l e 2 ) c h a r a c t e r i s -t i c o f t h e c o o r d i n a t i o n o f t h e V O 2 + c a t i o n t h r o u g hf o u r d e p r o t o n a t e d O H g r o u p s o f t w o s u g a r li g a n d s[ 1 0 , 1 3 , 1 5 - 1 7 ] .

C o m p l e x 4 s h o w s a n e l e c t ro n i c s p e c t r u m s i m il a r tot h o s e o f 1 a n d 2 , b u t t he U V a b s o r p t io n o v e r l a p s w i tht h e b a n d c e n t e r e d a t ~ 4 0 0 n m c a u s i n g a s m a l li n c r e a s e i n i t s i n t e n s i t y ( T a b l e 2 ) . O n t h e o t h e r h a n d ,c o m p l e x 3 , w i t h a n o n - r e d u c i n g s u g a r a c t i n g a s al i g a n d , s h o w s a g r e a t e r o v e r l a p p i n g w i t h t h e U Va b s o r p t i o n t h a n 4 , i t b e i n g d i f f i c u l t t o g e t t h e e x a c tp o s i t io n o f th e b a n d p l a c e d at ~ 4 2 0 n m .

I t i s in t e res t ing to poin t ou t tha t our resu l t s d i f fe rf r o m t h o s e o b t a i n e d b y S r e e d h a r a e t a l . [ 1 8 ] a n d R a oa n d K a i w a r [ 1 9 ] f o r th e V O 2 + c o m p l e x e s w i t h g l u -c o s e a n d f r u c t o s e . T h e m a i n d i f f e r e n c e i s t h e l a c k o fthe b 2 ---> a t t rans i t ion in the i r e l ec t ro nic abso rp t ions p e c t r a a s w e l l a s i n t h e d i f f u s e r e f l e c t a n c e s p e c t r a .T h e y p o s t u l a te a p e n t a c o o r d i n a t e d v a n a d y l ( I V ) c a t i o ni n t h e s o l i d s t a t e . O n t h e o t h e r h a n d , t h e i r a q u e o u ss o l u t i o n s p e c t r a w e r e o b t a i n e d a t a p H < 1 2. N e v e r -t h e l e s s , t h e r e p o r t e d d a t a f o r o t h e r r e l a t e d s y s t e m s

[ 9 , 1 0 , 1 3 ] s h o w t h a t t h e s u g a r c o o r d i n a t i o n t o t h eV O 2 c a t i o n i s s t r o n g l y p H d e p e n d e n t . A l l t h e s erepo r t s agree w i th the fac t tha t , a t pH > 11 , thec o o r d i n a t i o n s p h e r e c o n s i s t s o f t w o s a c c h a r i d e s w i t ht w o d e p r o t o n a t e d O H g r o u p s p e r s u g a r . U n d e r t h e s ec o n d i t i o n s t h e s p e c t r a o f s o l u t i o n s a n d s o l i d s ( i nc a s e s w h e r e t h e y w e r e m e a s u r e d ) e x h i b i t t h e w e l l -k n o w n t h r e e - b a n d p a t t e r n .

Spec trophotometr ic t i t rat ions . - -These t i t ra t ionsw e r e c a r r i e d o u t a t p H 1 2 w i t h 0 . 0 2 M s o l u t i o n s o ft h e s u g a r s a n d l i g a n d t o m e t a l r a t i o s v a r y i n g f r o m10:1 to 1 :1 . The resu l t s show tha t the s to ich iomet ryo f t h e c o m p l e x e s i s 2 :1 ( L : M ) i n a l l c a s e s e x c e p t f o rt h e f r u c t o s e c o m p l e x , w h i c h w a s 3 : 1 . T h e d i f f e r e n tc o o r d i n a ti o n b e h a v i o r o f f r u c t o s e w i t h V O 2 h a s a l sob e e n o b s e r v e d i n t h e s o l i d s t a t e . I n t h i s c a s e t h e r e i so n e f r u c t o s e m o l e c u l e b r i d g i n g t w o m e t a l c e n t e r s ,w i t h e a c h m e t a l c e n t e r a l s o c o o r d i n a t e d t o t w o o t h e rf r u c t o s e m o i e t i e s .

Dif fuse re f lec tance spec t ra. - - I t c a n b e s e e n f r o mT a b l e 2 t h a t t h e f o u r s o l i d c o m p l e x e s a l s o e x h i b i t t h et h r e e - b a n d p a t t e r n , a s e x p e c t e d . T h e i n t e r a c t i o n b e -t w e e n s u c r o s e a n d t h e v a n a d y l ( I V ) c a t i o n i n t h e s o l i dc o m p l e x a l s o p r o d u c e s a d i s p l a c e m e n t o f t h e b 2 ~ eb a n d t o t h e r e d , a s o b s e r v e d i n s o l u t i o n .

Magnet ic suscept ibi l i t i es . - -The m a g n e t i c b e h a v i o ro f c o m p l e x e s 2 , 3 , a n d 4 i s s im p l e a n d t h e / z e f e v a l u e sa r e c l o s e t o t h a t e x p e c t e d f o r t h e ' f r e e ' V O 2 ( d ~)c a t i o n ( 1 . 7 3 M . B . ) ( T a b l e 2 ) . O n t h e o t h e r h a n d , t h er o o m t e m p e r a t u r e m a g n e t i c m o m e n t o f c o m p l e x 1i n d i c a t e s e x t e n s i v e q u e n c h i n g o f th e V O 2 s p i n m o -m e n t . E l e m e n t a l a n a l y s i s o f t h i s c o m p l e x s u g g e s t st h a t t h e c o u p l i n g b e t w e e n t h e v a n a d y l c a t i o n s o c c u r s

Table 2Electronic absorpt ionsolution aComplex

spectra and effect ive magnet ic mom ents ( /Xef ) of the VO2+-saccharide com plexes in aqu eousA ( nm ) ( e , M - l c m - 1 ) ~eff (M.B.)b 2 ~ a I b 2 ~ b I b 2 ~ e1 424 (29.8) 518 (13) 686420 520 672

2 418 (24.7) 508 (11) 700420 518 6873 420? (45) 520 (16) 748420 525 7854 424 (21) 510 (14) 698420 515 678

(36.2) 1.26

(22.5) 1.75

(15.7) 1.70

(27.7) 1.73

a Underl ined values are from diffuse reflectance spectra of the sol ids .


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13 4 S.B. Etchev er~ et al. / Carbohydrate Research 302 (1997) 131-1 38t h r o u g h a f r u c t o s e l i g a n d . A c c o r d i n g t o t h e e x p e r i -m e n t a l t.Z eff v a l u e ( T a b l e 2 ) , t h e d i s t a n c e b e t w e e n t h et w o m e t a l l i c c e n t e r s s h o u l d b e s h o rt , s u g g e s t i n g t h a tt h e b r i d g i n g l i g a n d m a y u s e t w o a d j a c e n t d e p r o t o -n a t e d O H g r o u p s f o r c o o r d in a t i o n . H o w e v e r , i n th ec a s e o f t h e e l e c t r o n i c s o l u t i o n s p e c t r a , t h e o b s e r v e db a n d s c o u l d b e d u e t o a m o n o m e r i c ( 3 : 1 ) s p e c i e sr e s u l ti n g f r o m t h e p a r t ia l r u p t u r e o f t h e b r i d g e d d i m e ri n s o l u t i o n .

I n fr a r ed s p e c t r a . - - T h e I R s p e c t r a o f t h e o b t a i n e ds o li d s w e r e r e c o rd e d d o w n t o 2 0 0 c m - z a n d c o m -p a r e d w i t h t h o s e o f th e f r e e l i g a n d s . T e n t a t i v e a s s i g n -m e n t s f o r t h e s u g a r l i g a n d s a c c o r d i n g t o t h e l i t e r a t u r e[ 2 0 - 2 7 ] , a n d s o m e c h a r a c t e ri s t ic c h a n g e s i n th e c o r n -

p l e x b a n d s , a r e s h o w n i n T a b l e s 3 a n d 4 f o r t h em o n o - a n d d i - s a c c h a r i d e s , r e s p e c t i v e l y .

A l l o f th e f r e e l ig a n d s e x h i b i t i n t e r m o l e c u l a r h y -d r o g e n b o n d s b e tw e e n 3 4 0 0 a n d 3 2 00 c m - ~ . U p o nc o m p l e x a t i o n , t h e r e i s a b r e a k a g e o f t h e H - b o n d s a n dt h e s h a r p a n d w e l l - r e s o l v e d b a n d s o f th e f r e e l ig a n d sa r e lo s t . O u r s p e c t r a a g r e e w i t h t h o s e p r e v i o u s l yr e p o r t e d f o r s a c c h a r i d e s c o o r d i n a t e d t o t ra n s i t i o nm e t a l s [ 1 9 ,2 8 , 29 ] . A l l o f t h e m s h o w a b r o a d b a n dc e n t e r e d a r o u n d 3 4 0 0 c m - l a n d a s h o u l d e r at ~ 2 9 0 0c m - 1 . T h e o t h e r r e g i o n s a r e d i s c u s s e d s e p a r a t e l y f o re a c h l i g a n d a n d i t s v a n a d y l ( I V ) c o m p l e x .

F r u c t o s e / V O 2+ c o m p l e x . - - T h e I R b a n d s o f f ru c -t o s e ( F i g . 2 ) , l o c a t e d a t 9 2 2 , 8 7 0 , a n d 7 8 3 c m - ~ ,

T a b l e 3B and pos i t i ons a and t en t a t i ve a s s i gnm en t o fc o m p l e x e s t h e I R s p e c t ra o f t h e m o n o s a c c h a r i d e l i g a n d s a n d m o n o s a c c h a r i d e / V O 2 +F r u c to s e F r u c t o s e / V O 2+ G l u c o se G l u c o s e / V O 2 + A s s i g n m e n t1469 s h , w 1460 s 14 58 m 6 ( C H 2 )1449 s h , w 14 53 m 1441 s h1 4 2 9 m 1 4 1 0 m 1 42 3 s h1408 s h 14 15 m1399 m1377 w 1377 m 1377 m 1376 m1338 s 1338 sh 1341 m 1338 w1299 w 1293 w1267 m 1277 w 1273 w1250 s h 125 6w 1258 vw1232 sh 1224 w1202 w 1203 w1176 m 1177 w1 1 5 0 s 1 15 6 w 1 1 4 9 m 1 1 3 7 m1130 sh1093 s h 1096 s h 1111 m l l 1 3 m1078 s 10 78m 1066 s1054 s 1051 s 1050 s 1046 s1028 sh 1023 vs 1027 vs995 vs 1003 vs see t ext

9 7 6 s 9 7 0 w 6 ( C C H ) , p9 2 5 s 9 2 5 v s v ( V = O )9 2 2 m 6 ( C C H ) , f9 1 3 m 6 [ C ( l ) H ] , p870 m 858 w844 w

6[ C ( 2 ) H ]oJ ( C H 2)6 ( C O H ) + r [ C ( 1 ) H 2 O H ]r ( C H 2 )6 ( C H 2 + C O H )v ( C O ) , fv ( C O ) , pv ( C O ) e n d ov ( C O ) e x o

8 3 6 m 6 [ C ( I ) H ] , a818 m v ( C C ) , p783 s 786 vw 774 m 791 m v~(COC)741 w 729 w 737 sh685 m , b 709 s h 693 s h627 m 664 s h 646 m594 s h 613 s h 621 m 603 m570 m 561 m 579 w544 m 555 w 548 m523 s h 523 m 538 w

a In cm 1 ; V S, ve r y s t r ong ; s , s t r ong ; m , m ed i um ; w , w eak ; vw , ve r y w eak ; b , b r oad ; s h , s hou l de r ; p , py r anos e ; f , f u r anos e .


5/8

S.B. Etcheverry e t al . / Carboh ydrate Research 302 (1997) 131 -13 8 13 5s u p p o r t t h e / 3 - c o n f i g u r a t i o n o f t h e li g a n d [ 2 0 , 2 4 , 2 5 ] .B e c a u s e o f th e p r e s e n c e o f f u r a n o s e a n d p y r a n o s ec h a r a c t e r is t i c c o n f o r m a t i o n a l b a n d s , w e c a n c o n c l u d et h a t th e s o l i d l i g a n d i s a m i x t u r e o f b o t h c o n f o r m e r s :b a n d s a t 1 2 5 0 , 1 1 7 6 , 9 2 2 , 8 7 0 , a n d 6 8 5 c m - 1 , a n db a n d s a t 1 1 5 0 , 9 7 6 , 8 1 8 , a n d 5 2 3 c m - ~ , c o r r e s p o n dt o f u r a n o s e a n d p y r a n o s e r i n g s , r e s p e c t i v e l y . T a b l e 3s h o w s t h e b a n d a s s i g n m e n t s f o r th e f r e e l i g a n d a n di t s v a n a d y l ( I V ) c o m p l e x .

A s p r e v i o u s l y r e p o r t e d [ 2 8 ] , i n t h e i n t e r a c t i o n o ft r a n si t io n m e t a l s w i t h s a c c h a r i d e s, a b r o a d e n i n g o f

t h e b a n d s c o r r e s p o n d i n g t o th e f o u r c o m p l e x e s i so b s e r v e d . H o w e v e r , t h e f o l l o w i n g s p e c t r a l m o d i f i c a -t i o n s c a n b e o b s e r v e d :

( i) T h e l i g a n d b a n d a t 1 3 3 8 c m - 1 , c o r r e s p o n d i n gt o 6 ( C O H ) + r C ( 1 ) H 2 O H [ 20 ,3 0 ], i s s e n s it iv e tod e u t e r a t i o n , w h i c h c a u s e s a d e c r e a s e i n i t s i n t e n s i t y[ 20 ]. I t s h o w s a s i m i l a r b e h a v i o r a f t e r c o m p l e x a t i o n .

( ii ) T h e f u r a n o s e b a n d a t 1 2 5 0 c m - ~ a p p e a r s a t1 2 5 6 c m - ~ i n th e c o m p l e x . T h e p y r a n o s e b a n d s( 1 1 5 0 I v ( C O ) ] , 1 0 7 8 [v ( C O e x o )] , a n d 8 1 8 [ v ( C C ) ]c m - l ) d i s a p p e a r a f t er c o o r d i n a ti o n .

T a b l e 4B a n d p o s i ti o n s a a n d t e n t a ti v e a s s i g n m e n t o f t h e I R s p e c t r a o f th e d i s a c c h a ri d e l i g an d s a n d d i s a c c h a r i d e / V O 2+ c o m p l e x e sS u cr o se S u c r o s e / V O 2+ T u r a n o s e T u r a n o s e / V O 2 + A s s i g n m e n t1465 m1456 m 1454 m1433 s 1433 sh1374 w 1381 m1 3 4 6 m 1 33 4 s h1322 w1279 w 1287 w

1238 m1208 w1165 sh1126 s1113 s1067 s

1250 vw1240 vw1208 vw1158 sh1139 m1120 sh

1048 s 1049 s1007 sh9 9 4 s 9 9 1 m942 s h 946 s h

F , f i ( C H 2 )1453 m 1452 sh 6(CH2)~u e1433 m 1433 sh F, G1409 m 1417 m F, G1385 m 1372 m F, G, to(CH2)1 3 54 m p ( C H 2 )1335 m 1333 sh F, G p(CH2)~u c1301 w F1288 w1278 m 1262 w1246 m 1247 w F, f1 2 34 s h 6 ( C H 2 + C O H )1201 m 1201 w1143 s 1146 m v (C O ) , p1127 sh F, G , 6(COH)~u c1107 s 1103 s h G , v ( C O ) end o1082 s h 1079 s h F , G , v ( C O ) e xo1057 s 1051 s F, G1042 sh 1034 s G1018 w F, G

G9 6 8 m 9 6 7 w F , 6 ( C C H ) , p8 ( C C H ) , f9 31 s v ( V = O )92 0 sh /3-F, f912 s 880 w 914 s h a - G , p

896 m860 m 856 w 862 m /3-F, f846 s h 838 m 840 w a - G

804 w 773 s h s ee t ex t746 m 750 s h728 w 702 s h 727 s h 735 s h G710 m 704 s h

685 m 698 s h s ee t ex t661 sh 650 m 663 sh G642 w 642 s h585 m 599 m 606 m 571 s h561 m 590 m 561 w G531 s h 526 m 533 m 528 m G , 6 ( C C O ) , p

932 w924 s

a I n cm - ~ ; v s , ve r y s t r ong ; s , s t r ong ; m , m ed i um ; w , w eak ; vw , ve r y w eak ; s h , s hou l de r ; F , f r uc t o s e ; G , g l ucos e ; p ,py r anos e ; f , f u r anos e .


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136 S.B. Etcheuerry et al . / C a r b o h y d r a t e Research 302 (1997) 131-138

T ( % )i i [

I I I I I I I I I I I I1400 1000 500P ( c m -1 )

Fig . 2 . IR spect r a o f f ruc tose ( above) and o fNa6[ (VO)2(Fru)5].4H20 (below) (1500-200 cm - t r e -gion).

T ( %

T

I I I1 4 0 0 I I I I I I I I I1 0 0 0 500 ( c m -1 )

F i g . 3 . IR s p e c t r a o f g l u c o s e ( a b o v e ) a n dNa3[VO (GIc)2OH] .5H20 (below) (1500-200 crn - I r e-gion).( i i i ) A n o t h e r ch a r ac t e r i s t i c f ea t u r e o f t h e s p ec t r u m

o f th i s co m p l ex i s t h e s t r o n g b an d a t 92 5 cm - ~ ,c o r r e s p o n d i n g t o th e v ( V = O ) s t re t c h i ng [1 1].

T h e f a c t t h a t t h e p r i m a r y O H i s t h e m o s t r e a c t i v eh y d r o x y l s u g a r g r o u p [ 2 0 ] t o g e t h e r w i t h t h e ab o v eo b s e r v a t i o n s a l l o w t h e co n c l u s i o n t h a t t h e co o r d i n a -t i o n t a k e s p l a c e t h r o u g h t h e d e p r o t o n a t e d O H g r o u p s( p H 1 2) o f C ( 1 ) H 2 O H a n d t h e a n o m e r i c C ( 2 ) O H .T h e s p e c t r u m a l s o s h o w s t h a t t h e f r u c t o s e m o i e t i e sa r e p r e s en t a s / 3 - an o m er s i n f u r an o s e f o r m .

G l u c o s e / V O 2 c o m p l e x . -- A c c o r di n g t o t h e p r e -v i o u s l y r e p o r te d I R s p e c t r u m [ 24 ], w e c o n c l u d e t h a tt h e f r ee l i g an d ( D - g l u co s e ) is t h e ce - an o m er ( 8 3 6c m - 1 ) i n t h e p y r a n o s e f o r m ( 9 13 c m - ~ ) ( T a b l e 3 ).I ts co o r d i n a t i o n t o V O 2 + a t p H 1 2 p r o d u ce s t h ef o l l o w i n g ch an g es ( F i g . 3 ) :

( i ) T h e b an d a t 1 3 41 cm - ~ d ec r eas e s i n i n t en s i t yi n a s i m i l a r w a y t o t h a t o b s e r v e d f o r t h ef r u c t o s e / V O 2+ c o m p l e x .

( i i) T h e w eak b an d o f t h e f r ee l i g an d a t 1 0 7 8c m - l , a s s i g n ed to 6 [ C ( 1 ) H ] [2 1 ], s h if t s t o 1 0 6 6 c m - lan d i n c r ea s e s i n i n t en s i t y .

( ii i ) A n e w b an d a t 1 00 3 cm - ~ r e l a t ed , t o d ep r o t o -n a t ed C O H g r o u p s [ 1 3 ] , i s o b s e r v ed .

( iv ) T h e v ( V = O ) s t r e t c h i ng a p p e a r s a t 9 2 5 c m - 'a s a v e r y s t r o n g b an d

T h es e o b s e r v a t i o n s s u g g es t t h a t t h e ca t i o n i sc h e l a t e d b y D - g l u c os e th r o u g h t h e a n o m e r i c O - 1 a n d0 - 2 a t om s , w h i c h a re c is in the c~-anomer .

O u r I R , U V / V I S , a n d d if f u s e r e f l e c t a n c e s p e c t rai n d i ca t e t h a t t h e O H g r o u p a t C - 2 i s d ep r o t o n a t ed , i nco n t r a s t t o p r ev i o u s r e s u l t s [ 1 9 ] . A s s t a t ed ab o v e , t h i sd i f f e r e n c e m a y b e d u e t o t h e f a c t t h a t o u r c o m p l e x e sw e r e p r e p a r e d a t p H 1 2.

S u c r o s e / V O 2 + c o m p l e x . - - S p e c t r a o f t h e f r e es u g a r a n d i ts v a n a d y l ( I V ) c o m p l e x a r e s h o w n i n F i g .4 . T a b l e 4 s h o w s t h e a s s i g n m e n t o f th e o b s e r v e d I Rb an d s o f s u c r o s e . T y p i ca l b an d s o f C ~-D - gl uco se ( 9 1 2 ,8 4 6 c m - ~ ) i n t h e p y r an o s e f o r m , an d / 3 -D - f ru c t os e( 9 2 0, 8 6 0 c m - i ) i n t h e f u ra n o s e fo r m , a s w e l l a ss o m e v i b r a t i o n s ch a r ac t e r i s t i c o f s u c r o s e , c an b e s een[ 26 ]. W e c o n c l u d e t h a t t h e f r u c t o s e r e s i d u e i s i n t h ef u r a n o s e f o r m b e c a u s e o f t h e p r e s e n c e o f t h e 6 8 5c m - ~ b a n d , w h i c h i s c h a r ac t e r is t i c o f d i s a c c h a r id e sw i t h t h i s k i n d o f r e s i d u e [ 2 4 ] .U p o n f o r m a t i o n o f t h e c o m p l e x , t h e f o l l o w i n gm o d i f i ca t i o n s a r e o b s e r v ed :

( i ) T h e b eh a v i o r o f t h e b an d a t 1 3 46 cm - J ( a s -s i g n ed t o p ( C H 2 ) i n s u c r o s e ) i s t h e s am e a s t h a tf o u n d f o r t h e c o n s t i tu e n t m o n o s a c c h a r i d e s .

T (% )

Ti i I i i I I l i I i i

I I I I I I I I I I I I1~o o lOOO 500 U(cm 1 )F i g . 4 . 1R s p ec t r a o f s u c r o s e ( ab o v e ) an dNa3[VO (Suc)2OH] .H20 (below) (1500-200 cm - l r e-gion).


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S.B. Etcheverry et al. / Carbohydrate Research 302 (1997) 131-138 137( ii ) T h e m ed i u m i n t en s i t y b an d a t 1 2 3 8 cm -~

[8 (C H 2 ) + 6 (CO H )] , ch a rac t e r is t ic o f s u c ro s e , d r a s -t i ca l ly decreases in in tens i ty af t er coord inat ion . Thew ea k b a n d o f f r ee s u c ro s e l o ca t ed a t 1 2 0 8 cm -~( c o r r e s p o n d in g t o t h e 1 2 0 2 c m - t b a n d o f a - D -g l u-co s e ) d o es n o t ch an g e u p o n co o rd i n a t i o n , i n co n t r a s tt h at o b s e r v e d in t h e g l u c o s e / V O 2+ c o m p l e x .

( i i i ) The band a t 1067 cm-1 [u (COexo)] behaves ina s i mi l a r man n e r a s i n th e f ru c t o s e co mp l ex , s u g g es t -i n g co o rd i n a t i o n o f t h e ca t i o n t h ro u g h t h e f ru c t o s er e s i d u e o f t h e s u g a r.

( i v) T h e b an d a t 9 3 1 cm -1 can b e a s s i g n ed t o th eu (V = O ) v i b r a t i o n , an d p ro b ab l y o v e r l ap s w i t h t h ean o m er i c b an d s a t 9 2 0 ( f ru c t o se ) an d 9 1 2 cm - I(g lucose) .

F ro m t h e ab o v e o b s e rv a t i o n s w e co n c l u d e t h a t i nt he c o m p l e x N a 3 [ V O ( S u c ) z O H ] . H 2 0 , t hev an ad y l ( IV ) ca t i o n co o rd i n a t e s w i t h t h e f ru c t o s e mo i -e t y o f s u c ro s e . S i n ce s u c ro s e i s a n o n - r ed u c i n g d is ac -ch a r i d e , t h e an o mer i c ca rb o n s o f t h e mo n o s acch a -t i d e s a r e i n v o l v ed i n t h e g l y co s i d i c l in k ag e . T h e h i g hi n s tab i l it y o f t h e co m p l ex i n aq u eo u s s o l u ti o n , w h i chreq u i r e s i t s i mmed i a t e p r ec i p i t a t i o n a f t e r mi x i n g t h er eag en t s i n o rd e r t o av o i d v an ad y l h y d ro l y s i s , s u g -g es t s t ha t , i n t h is ca s e , a s e v en -m em b ered ch e l a ter i n g i s f o rmed , i n v o l v i n g e i t h e r O -1 a n d 0 -4 , o r 0 -3a n d 0 - 6 o f t h e f r u c t o s e m o i e t y . T h e c o o r d i n a t i o ns p h e re i s co mp l e t ed w i t h an h y d ro x y l g ro u p .

Turanose / VO 2 + compl ex.-- Spect ra o f t h e f r eel i g an d an d o f i t s v an ad y l ( IV ) co mp l ex a r e s h o w n i nF i g . 5 . T h e IR s p ec t ru m o f t u r an o s e h as n o t b eenr e p o r te d p r e v i o us l y . T h e b a n d a s s i g n m e n t s w e r e m a d eb y co mp ar i s o n w i t h t h e s p ec t r a o f g l u co s e , f r u c t o s e ,an d s u c ro s e (T ab l e 4 ).

T u ran o s e , l i k e s u c ro s e , s h o w s b an d s w h i ch a r ech a rac t e r i s t i c o f p y ran o s e an d fu r an o s e fo rms . T h eb an d a t 6 9 8 cm -~ i s t y p i ca l o f d i s acch a r i d es w i t h af ructose res idue [24] .

T h e a n o m e r i c r e g i o n ( 9 0 0 - 7 5 0 c m - ~ ) s h o w s t h eg l u co s e r e s i d u e i n t h e a - fo rm, w h i l e t h e f ru c t o s emo i e t y is f o u n d i n t h e / 3 - an o mer i c fo rm. A s o b s e rv edi n th e s u c ro s e s p ec t ru m, t h e b an d s a t 7 7 8 ( a -g l u co s e )an d 7 8 4 cm -~ ( / 3 - f ru c t o se ) a r e ab s en t . Mo reo v e r , t h eb an d a t 8 0 4 cm-~ i s t h e o n l y i n d i ca t i o n o f t h eg lyco s id ic 1 ~ 3 l inkage p resen t in tu ranose . T h i sba nd is also ob ser ve d in (1 ---> 3) o~-dextran and i t i sn o t p r e s en t i n t h e s p ec t ru m o f (1 ~ 4 ) a -d ex t r an[24].

T h e m a j o r f e a t u r e s o f t h e I R s p e c t r u m o f t h et u r a n o s e / V O 2+ c o m p l e x a re :( i) T h e b an d a t 1 3 5 4 cm -1 d ra s ti ca l ly d ec reas es i n

i n t en s it y a f t e r co mp l ex a t i o n , a s ex p ec t ed .

T ( % ) l

1I I I I 1 1 1 1 1 1 1 1

I I I I I I I I I I I I1 4 0 0 1 0 0 0 5 0 0b ' ( c m - '~ )

Fi g . 5 . IR s p ec t r a o f t u r an o s e ( ab o v e ) an dNa3[VO(Tur)2OH]-3H20 (below) (150 0-200 crn - l re-gion).

( ii ) T h e b an d s i n t h e 1 3 0 0 - 1 2 0 0 cm -~ r eg i o n[ (CH 2) + 8(COH)] , in par t i cu lar those tha t ind ica tet h e fu r an o s e fo rm, b eco me w eak e r a f t e r co mp l ex a -t ion.

( i ii ) The b and a t 1201 c m -1 , p resen t in the spec-t ru m o f f r ee a -D -g l u co se , r ema i n s u n ch a n g ed i n th et u r an o s e co mp l ex ( co n t r a ry t o w h a t i s o b s e rv ed i n t h eg l u c o s e / V O 2+ c o m p le x ).

( i v ) T h e s t ro n g b an d a t 9 2 4 cm-J , a s s i g n ab l e t ot h e v ( V = O ) m o d e , m a s k s t h e l i g a n d b a n d s i n t h i sr eg i o n .

A l l o f t h e s e o b s e rv a t i o n s s u g g es t t h a t t h e V O 2+ca t i o n co o rd i n a t e s w i t h t u r an o s e t h ro u g h t h e f ru c t o fu -r an o s e r e s i d u e . T h e ch e l a t e f o rma t i o n p ro b ab l y o c -cu r s t h ro u g h t h e d ep ro t o n a t ed O H g ro u p s a t C-2(an o mer i c ) an d C- l , w h i ch a r e t h e t w o mo s t r eac t i v eg ro u p s .

5 . C on c lu s ion s

As ind ica ted by spec t roph otom et r i c t i tra t ion , a ll o ft h e i n v es t i g a t ed co mp l ex es , ex cep t t h a t o f f r u c t o s e ,r e s p o n d t o a 2 :1 (L : M) s t o i ch i o me t ry in s o l u t i o n . T h ef ru c t o s e co mp l ex ap p ea r s a s a 3 : 1 s p ec i e s . T h es ed i f f e r en ces r em a i n a l s o i n t h e s o l id co m p o u n d s b e -cau s e , w h e reas t h e f ru c t o s e co m p l ex i s a d i mer fo rm edb y t w o (F ru )zV O mo i e t i e s l i n k ed b y a f ru c t o s e b r i d g e(s to ich iomet ry 5 :2 ) , a l l o f the o ther species arem o n o m e r i c .


8/8

138 S.B. Etcheverry e t al . / Carbohydrate Research 302 (1997) 131-138P r ev i o u s s t r u c t u r a l s t u d i e s o n v an ad a t e ( V ) co m -

p l ex es w i t h r i b o s e d e r i v a t i v e s h av e e s t ab l i s h ed ad i s t o r t ed t r i g o n a l b i p y r am i d a l co o r d i n a t i o n s p h e r ea r o u n d t h e m e t a l c e n t e r , w h i c h i s a t y p i c a l g e o m e t r yi n t h e t ran s i t i o n s t a t e i n h y d r o l y t i c en zy m a t i c r eac -t i o n s ( s ee r e f. [ 3 1] an d r e f e r e n ces t h e r e i n ) . O n t h eo t h e r h a n d , o x o v a n a d i u m ( I V ) c o m p l e x e s u s u a l l y e x -h i b i t a s q u a r e p y r a m i d a l c o o r d i n a t i o n w i t h t h e o x y -g en b o n d ed t o v an ad i u m i n t h e ax i a l p o s i t i o n , a l -t h o u g h , i n aq u eo u s s o l u t i o n , t h e co o r d i n a t i o n i s n o r -m a l l y a d i s t o r t e d o c t a h e d r o n b e c a u s e o f t h e w e a kb o n d i n g o f a w a t e r m o l ecu l e i n t h e s i x t h p o s i t i o n .

A l l o f t h e v a n a d i u m ( I V ) / s u g a r c o m p l e x e s c h a ra c -t e r i zed i n t h e p r e s en t s t u d y a r e h ex aco o r d i n a t ed . T h i sco n c l u s i o n i s n o t o n l y s u p p o r t ed b y t h e e s t ab l i s h eds t o i ch i o m e t r i e s b u t a l s o b y t h e s p ec t r o s co p i c b eh av -i o r o f th e c o m p l e x e s .

T h e v a l u e s f o u n d f o r t h e c h a r a c t e r i s t i c v ( V = O )v i b r a t i o n a r e s i m i l a r t o t h o s e p r ev i o u s l y f o u n d i n t h ev a n a d y l ( I V ) c o m p l e x e s o f c h o n d r o i t in s u l f a te A [1 1]an d D - g l u cu r o n i c ac i d [ 1 3 ] , w h i ch a l s o s h o w t h ev ( V = O ) s t r e t c h in g a t ~ 9 3 0 c m - 1 ( b o t h i n a q u e o u ss o l u t i o n an d i n t h e s o l id s t a t e) . T h e ag r eem en t b e -t w een t h e f r eq u en c i e s i n t h e t w o s t a t e s s u g g es t s ,acco r d i n g t o M i ce r a e t a l . [ 1 5 ] , t h a t t h e co o r d i n a t i o ns p h e r e o f t h e V O 2 + ca t i o n co n s i s t s o f f o u r d ep r o t o -n a t e d s u g a r o x y g e n a t o m s w i t h t h e p o ss i b l e p r e s e n c eo f a n o t h e r O H g r o u p ( c o m p l e x e s 2, 3 , a n d 4 ) o r al i g a n d m o l e c u l e ( c o m p l e x 1 ) in t h e s i x t h c o o r d i n a t io npos i t ion .

Acknowledgemen t sT h i s w o r k w a s s u p p o r te d b y C O N I C E T a n d C I -

C P B A a n d b y a p e r s o n a l g r a n t b y F u n d a c i 6 n' A n t o r c h a s ' t o P . A . M . W .

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