Fiber Diffraction Methods - American Chemical Society

24 Ultrastructureof Curdlan NOBUTAMI KASAI Department of Applied Chemistry, Faculty of Engineering, Osaka University, Yamadakami, Suita, Osaka 565 JAPAN TOKUYA HARADA

Downloaded by EMORY UNIV on February 26, 2016 | http://pubs.acs.org Publication Date: November 17, 1980 | doi: 10.1021/bk-1980-0141.ch024

Institute of Scientific and Industrial Research, Osaka University, Yamadakami, Suita, Osaka 565 JAPAN

1.

Introduction During the studies on Alcaligenes faeoalis var. myxogenes

10C3, Harada and co-workers found that a spontaneous mutant, 10C3K produces an insoluble exocellular polysaccharide (1).

This

polysaccharide i s entirely composed of D-glucosyl residues which are connected almost exclusively by

β-(1->3)-linkages.

This and

the similar glucan formed by some strains of Agrobacterium are named Curdlan because they form i r r e v e r s i b l y , r e s i l i e n t gel when heated i n water. Because of interesting and specific properties

of the g e l ,

curdlan has many potential uses not only i n food industry but also as a f i l m , a fiber, a support for immobilizing enzymes and a binding agent i n tobacco product etc. (2).

Besides these, an

antitumor activity(3) has been reported. In connection with these uses the conformation of curdlan molecule i n solution and i n gel and the ultrastructure of aggre gates of curdlan molecules are considered very important.

This

paper deals with conformational studies on curdlan molecules by means of l i g h t scattering,

13

C NMR, X-ray d i f f r a c t i o n , and

morphological studies using an electron microscope. 0-8412-0589-2/80/47-141-363$05.25/O © 1980 American Chemical Society In Fiber Diffraction Methods; French, Alfred D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

364

2.

1).

FIBER DIFFRACTION

Conformation of Curdlan Molecule in

METHODS

Solution

j

Conformation i n a cadoxen- water mixture (4) For the l i g h t

scattering

s t u d y , H i r a n o et al.

divided

a

c u r d l a n sample i n t o n i n e f r a c t i o n s by f r a c t i o n a l p r e c i p i t a t i o n a t 25°C w i t h c a d o x e n *

a s a s o l v e n t and a p r o p a n o l - w a t e r ( 3 : 1 b y volume)

m i x t u r e as a p r e c i p i t a n t .

The l i g h t

s c a t t e r i n g measurement

was

c a r r i e d o u t i n t h e 1:1 w a t e r - d i l u t e d c a d o x e n a t 25°C. From t h e m e a s u r e d s c a t t e r i n g

i n t e n s i t i e s H i r a n o et

al.


o b t a i n e d t h e a n g u l a r dependence o f t h e i n f i n i t e - d i l u t i o n scattering

intensity

(K /RQ)^ O

of the zero-angle reduced then determined z-average

and t h e c o n c e n t r a t i o n d e p e n d e n c e

0

scattering

intensity

the values o f weight-average

2

(K /RQ)Q+Q.

They

Q

molecular weight

2

mean-square r a d i u s o f g y r a t i o n

coefficient A

reduced

*,

and s e c o n d

o f t h e f r a c t i o n by t h e u s u a l method.

The

M

y]9

virial

results

are presented i n Table I . The v a l u e s o b t a i n e d f o r

a r e about

one o r d e r o f m a g n i t u d e

l a r g e r than t h e r e p o r t e d number-average m o l e c u l a r w e i g h t s d e t e r m i n e d b y t h e method o f Manners et al. (5_) 2

Figure 1 g i v e s the molecular weight d a t a p o i n t s may be f i t t e d b y a s t r a i g h t 2

2

< 5 > | = 3.2 x 1 0 ~ M

d e p e n d e c e o f ^.

The

l i n e as shown i n F i g . 1. 0

-

W

5 3

( i n nm).

F i g u r e 1 i n c l u d e s t h e d a t a f r o m c e l l u l o s e i n t h e same s o l v e n t ( 7 ) . A t f i x e d Af , w

the values o f

f

f o r c u r d l a n a r e about

one

those f o r c e l l u l o s e , i n d i c a t i n g that the c u r d l a n molecule

assumes

a more c o i l e d f o r m t h a n d o e s t h e c e l l u l o s e m o l e c u l e i n 1:1 diluted

water-

cadoxen.

The d o u b l e - l o g a r i t h m i c p l o t s

of intrinsic viscosity

c u r d l a n ( 4 ) and c e l l u l o s e ( 6 ^ 7 ) a g a i n s t M and c e l l u l o s e m o l e c u l e s a r e n o t v e r y

*

half

T r i ( e t h y l e n e diamine) hydroxide,

w

[n] f o r

suggest t h a t t h e c u r d l a n

flexible.

[Cd(en) ](OH) 3

2

In Fiber Diffraction Methods; French, Alfred D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

24.

Table I.

365

Ultrastructure of Curdlan

KASAI A N D H A R A D A

Numerical results from l i g h t scattering measurements on

curdlan fractions i n the 1:1 water-diluted cadoxen at 25°C(£)


Fraction Number

M X10" w

5

2

n

X10 /cm

2

i4 X10Vcm

z

3

2

F-II

6 .83

1.62

3.81

F-III

5 .85

1.49

3.54

F-IV

3 .48

0.751

3.85

F-V

2 .60

0.534

4.38

F-VI

1 .78

0.350

3.71

F-VII

1 .24

0.262

6.58

F-VIII

0 .888

0.159

6.11

F-12-2*

0 .659

0.156

8.13

mol g "

2

*Sample f r a c t i o n a t e d a t T a k e d a C h e m i c a l I n d u s t r i e s . DPn 131 b y t h e method o f Manners et al. (5). —

Polymer Journal

Polymer Journal

Figure 1. Molecular weight dependence of < S > ^ for curdlan in the 1:1 waterdiluted cadoxen at 25°C (4). Data for cellulose (small circles) (1) are also plotted. 2


366

FIBER

DIFFRACTION

METHODS

A c o n s i d e r a t i o n o f t h e m o l e c u l a r c o n f o r m a t i o n u s i n g t h e worml i k e c h a i n model s u g g e s t s t h a t t h e c u r d l a n m o l e c u l e may c o n t a i n h e l i c a l p o r t i o n s b u t , as a whole, t a k e s a r a n d o m - c o i l

conformation

(£).

2).

Conformation i n an alkaline 1 3

F i g u r e 2 shows water


C NMR s p e c t r a o f c u r d l a n ( D P n

540) o f an

s u s p e n s i o n and a l k a l i n e s o l u t i o n r e p o r t e d b y S a i t o et a£.(8).

I t i s noteworthy 1 3

solution

t h a t a t a c o n c e n t r a t i o n o f 0.22M NaOH t h e b r o a d

C NMR s i g n a l s d e c r e a s e t o l e s s t h a n o n e - t e n t h o f t h o s e o f t h e

aqueous s u s p e n s i o n .

T h i s sharp spectrum

random-coil conformation. Ogawa et aZ. ( 9 ) .

This i s consistent with the results of

They d e t e r m i n e d

rotation, intrinsic

i s characteristic of

t h e dependence o f o p t i c a l

v i s c o s i t y , and t h e e x t i n c t i o n a n g l e o f

c u r d l a n s o l u t i o n on c o n c e n t r a t i o n o f NaOH and f o u n d t h e t r a n s i t i o n from o r d e r e d form t o r a n d o m - c o i l

3.

1).

Conformation

i n a b o u t 0.2M.

o f C u r d l a n M o l e c u l e s i n Gel

Conformation i n gel. S a i t o et al.(S) h a v e shown t h a t

observed 2.8,

( F i g . 3B).

1 3

1 3

C NMR s i g n a l s o f g e l c a n be

C peak p o s i t i o n s a r e s h i f t e d d o w n f i e l d b y

3.2, and 0.9 f o r C - l , C-3, and C-4 r e s p e c t i v e l y ,

w i t h those o f w a t e r - s o l u b l e degraded conformation.

compared

polymer i n a random-coil

On t h e o t h e r h a n d , o t h e r C-2, C-5, and C-6 s i g n a l s

remain unchanged.

T h e s e d o w n f i e l d d i s p l a c e m e n t s o f t h e C - l and

C-3 s i g n a l s o c c u r a t c a r b o n s p a r t i c i p a t i n g i n t h e g l u c o s i d i c l i n k a g e s o f (1+3)-$-D-glucan, terms o f a c e r t a i n f i x e d The

and t h i s f a c t c o u l d be e x p l a i n e d i n

conformation.

e n e r g e t i c a l l y p r e f e r r e d c o n f o r m a t i o n s o f (1+3)-$-D-glucan

have been d e t e r m i n e d by S u n d a r a l i n g h a m ( 1 0 ) , and S a t h y a n a r a y a n a and e x t e n d e d shwon t h a t

1 3

and R a o ( 1 2 ) .

helical

Rees and S c o t t ( 1 1 ) ,

According t o these r e s u l t s ,

c o n f o r m a t i o n s a r e most p r o b a b l e .

C peaks o f m o l e c u l e s

wide

I t has been

i n the r i g i d double- o r t r i p l e -


24.

KASAI AND HARADA

helical narrow

conformation are completely

1 3

C peaks have been r e p o r t e d

(16,17). should

The are

lost(13-15).

1 3

C NMR v i s i b l e

t othe s i n g l e - h e l i c a l

l i n e w i d t h s o f C-1--C-5

1 3

However, r a t h e r

f o rsingle helical

These f a c t s suggest t h a t t h e

be a s c r i b e d

367

Vltrastructure of Curdlan

molecules portion

region.

C resonance peaks i n t h e g e l

a b o u t 150 H z , w h i c h a r e r a t h e r b r o a d i n c o m p a r i s o n w i t h

those

o f a l k a l i n e s o l u t i o n (0.22M N a O H ) ( F i g . 2D) a n d a l s o w i t h t h o s e o f the

lower molecular weight f r a c t i o n ( F i g . 3A).


i n t e g r a t e d peak i n t e n s i t i e s pressed) with

(with nuclear

Overhauser e f f e c t s u r -

t h o s e o f t h e c o r r e s p o n d i n g p e a k s i n t h e 0.22M NaOH

s o l u t i o n , i n which the curdlan

molecules are considered

r a n d o m - c o i l c o n f o r m a t i o n , i t was e s t i m a t e d 1 3

C

By c o m p a r i n g t h e

peaks account f o r o n l y

carbons o f t h e t o t a l

i n v i s i b l e portion o f the

zones o f t h e g e l n e t work

that these observed

20-30 and 6 0 % f o r t h e C-1--C-5 a n d C-6

gel, respectively. 1 3

t o have

C should

Hence, t h e r e m a i n i n g

be a s c r i b e d t o t h e j u n c t i o n

and t o r e s i d u e s

located closelyt o

these junctions. These r e s u l t s l e a d t o a c o n c l u s i o n

that the v i s i b l e

p e a k s a r e due t o t h e s i n g l e h e l i c a l p o r t i o n .

C NMR

The N M R - i n v i s i b l e

p o r t i o n o f the g e l i s present as m u l t i - h e l i c a l 2).

1 3

junction-zones.

Conformation i n and u l t r a s t r u c t u r e o f a n o r i e n t e d g e l . As

t h e X - r a y d i f f r a c t i o n d i a g r a m s o f a n o r i e n t e d g e l ( F i g . 6)

are p o o r l y crystal

crystalline,

i t has been u s e f u l t o conduct

X-ray

s t r u c t u r e a n a l y s e s o f o l i g o m e r o f 3-(1+3)-D-glucan.

molecular structures o f laminarabiose

The

and i t s a c e t y l d e r i v a t i v e

have been d e t e r m i n e d . (1) L a m i n a r a b i o s e (18) As

shown i n F i g . 4, t h e m o l e c u l e s o f l a m i n a r a b i o s e

have a

c o n f o r m a t i o n , d i f f e r e n t from t h e f u l l y - e x t e n d e d one, which i s s t a b i l i z e d by an i n t r a m o l e c u l a r

f

h y d r o g e n b o n d b e t w e e n 0-4 --H a n d

o

«

0 - 5 [ 2 . 7 8 6 ( 7 ) A] {Cf. i n t r a m o l e c u l a r

0-2

r i n g - t o - r i n g confromation can be d e s c r i b e d -37.5°) a c c o r d i n g

f

0 - 2 = 3 . 9 2 0 ( 6 ) A ) . The a s ( $ , ¥ ) = (27.9°,

t o t h e d e f i n i t i o n o f S a t h y a n a r a y a n a and R a o ( 1 2 ) ,



368

FIBER

120

100

80

60

DIFFRACTION

40PPm

METHODS

0 Biochemistry

Figure 2.

13

C NMR spectra of curdlan(DPn 540) in water suspension (A) and alkaline solution (90° pulse, repetition time 0.6 s) ($)

B

C u r d l a n ( D P n 540)

A

Degraded

C-4 C-2

polymer

C-6

C-3

C-l

-J

110

100

90

80

70

60

L_

50 ppm(TMS) Biochemistry

13

Figure 3. C NMR spectra of curdlan and of a degraded polymer (DPn 13) in solution (90° pulse, repetition times 1 s for A and 0.6 s for B) (8)


24.

KASAI AND HARADA

369



H(C-6-2)

fHc-e'-i)

^(0-4')

H

!7H(C-6-l)

(C-5)(

H(C-5')£

/0-1'B H(C-2)

0-1 a

1

H(O-l'a) Ha(C-l')

0-W

Carbohydrate Research

Figure 4.

Molecular structure of laminarabiose (IS)

The C and O atoms are shown as thermal ellipsoids with 50% probability level, and the H atoms are represented as spheres with B = 0.75 A . Atoms that are related to the a-anomer molecule (~38%) and the water of crystallization (~19%) associated with the a-anomer molecules are shown in squares. 2


370

and

FIBER DIFFRACTION

METHODS

i t i s l o c a t e d i n t h e c o m p a r a t i v e l y low e n e r g y r e g i o n o f

energy contour diagram o f

the

B-(1+3)-glucan(12).

1

(2) M e t h y l

2,3,4,6,2 ,4',6'-hepta-tf-acetyl-$-l>laminarabioside(19).

B e c a u s e h y d r o g e n bonds a r e p r o h i b i t e d by t h e a c e t y l the molecules

have a f u l l y - e x t e n d e d c o n f o r m a t i o n 1

and

groups

the

inter-

1

o x y g e n d i s t a n c e s a r e 0-4 •••-0-5=3.224(14) and

0-2 •••-0-2=3.604

o

(14) A ( F i g . 5 ) . as

The

r i n g - t o - r i n g conformation

($ ,V) = (42.5°, 4.7°),

and

can be

described

i t i s a l s o l o c a t e d i n the

other


c o m p a r a t i v e l y low e n e r g y r e g i o n i n t h e e n e r g y c o n t o u r m a p ( 1 2 ) . (3)

Curdlan

a.

Room temperature

structure

T a k e d a et al.(20)

prepared

a

f i l m s p e c i m e n , r e g e n e r a t i n g f r o m a IN NaOH s o l u t i o n o f c u r d l a n (DPn=400).

T h i s f i l m was

A f i b r o u s s p e c i m e n was uniaxially

s w o l l e n i n w a t e r a t room

o b t a i n e d by s t r e t c h i n g t h e s w o l l e n

(draw r a t i o 3.5 : 1 ) .

o f t h e wet,

has a c r o s s - l i k e

t h e l a y e r s 0, 3, and 4.

appearance

average

2 were much w e a k e r t h a n t h o s e

A t o t a l o f 17 o b s e r v e d

be i n d e x e d by an o r t h o r h o m b i c

diagram

molecule.

f e a t u r e o f the diagram i s t h a t the

o f t h e l a y e r s 1 and

film

center o f the f i b e r

a simple h e l i c a l s t r u c t u r e f o r the

Another s i g n i f i c a n t intensities

The

f i b r o u s s p e c i m e n ( F i g . 6A)

that suggests

temperature.

reflections

of

could

u n i t c e l l w i t h a=26.4, fr=16.4 and

o

£=22.65 A n o t be

( f i b e r a x i s ) ; but the c o r r e s p o n d i n g

space group c o u l d

determined.

R e f e r r i n g t o a c y l i n d r i c a l P a t t e r s o n f u n c t i o n a l ) computed from the i n t e n s i t y

distribution

o f t h e f i b e r d i a g r a m , and

also

c o n s i d e r i n g the s t a n d a r d geometry o f the D-glucose r i n g ( 2 2 ) conformations crystal

a b o u t t h e 3-(1+3) l i n k a g e o b t a i n e d by t h e

s t r u c t u r e analyses of laminarabiose(18)

d e r i v a t i v e ( 1 9 ) , r e a s o n a b l e m o d e l s o f 7/1

and 6/1

and

and

single

i t s acetyl

single

helices

o

w i t h f i b e r r e p e a t p e r i o d o f 2 2 . 6 5 A ( f u l l y - e x t e n d e d model) c o u l d be c o n s t r u c t e d .

The

F o u r i e r t r a n s f o r m o f each h e l i x

was

c a l c u l a t e d u s i n g t h e e q u a t i o n g i v e n by K l u g et al.(23). results

The

f o r the r e l a t i v e magnitude o f the i n t e n s i t i e s o f the


7/1


24.

KASAI AND HARADA


371

Carbohydrate Research

Figure 5. Molecular structure of methyl 2,3,4,6,2',4',6'-hepata-O-acetyl-p-vlaminarabioside (19). The upper ring is glycosidic residue. Shaded and nonshaded ellipsoids, and small spheres represent C, O, and H atoms, respectively.


FIBER

DIFFRACTION

METHODS


372

Figure 6. The variation of x-rayfiberdiagrams of the wet, fibrous curdlan specimen (DPn 400) dried in the air (20). Starting from the original gel specimen (A), photographs from (B)to(E) were taken at regular intervals (1 hr).


24.

KASAI AND

HARADA


single helix, either left-

373

o r right-handed, agree w i t h

o b s e r v e d peak p o s i t i o n s o f t h e

the

l a y e r s 0, 1, 2, a n d 3 b e t t e r

t h o s e o f 6/1 s i n g l e h e l i c e s .

However, t h e

o f l a y e r s 1 and 2 are

than the observed i n t e n s i t i e s .

greater

F o u r i e r t r a n s f o r m s o f t h e d o u b l e - and were a l s o c a l c u l a t e d u s i n g

the

the observed i n t e n s i t y .

intensities The

t r i p l e - s t r a n d e d 7/1 h e l i c e s

equation

Among them, t h a t o f a t r i p l e - h e l i x

calculated

than

given by Fraser

et al. (24).

showed a r a t h e r good f i t w i t h

However, t h e

calculated intensities o f


l a y e r s 1 a n d 2 a r e v e r y weak, b e i n g a b o u t o n e - h u n d r e d t h o f t h a t at the

equator.

T h e s e f a c t s s u g g e s t t h a t t h e most o f t h e

3 - D - g l u c a n m o l e c u l e i n t h e w e t f i b r o u s s p e c i m e n has helical

s t r u c t u r e and

structure

(Fig. 8).

t h e r e s t has

posed s t r u c t u r e b a s e d on t h e The

X-ray small-angle

a 7/1 s i n g l e

a triple-stranded helical

These r e s u l t s are 1 3

(1-K5)-

c o n s i s t e n t w i t h the

C NMR s t u d i e s m e n t i o n e d

before.

s c a t t e r i n g photograph o f the

s p e c i m e n shows o n l y a d i f f u s e s t r e a k

along

Assuming t h a t the

inhomogeneties i n the

highly dispersed,

uniform, long

arranged p a r a l l e l

t o the

the

pro-

equator

same (Fig.

7).

specimen c o n s i s t s o f

c y l i n d r i c a l m i c e l l e s which

are

s t r e t c h i n g d i r e c t i o n , the diameter o f o

t h e m i c e l l e s was e s t i m a t e d plot(25)

o f the

2

e T-e p l o t ( 2 6 )

t o b e a b o u t 80 A b y t h e

i n t e n s i t y d i s t r i b u t i o n along gives

the

Guinier

equator.

The

a measure o f i n t e r m i c e l l a r d i s t a n c e i n

the

o

e q u a t o r a s a b o u t 120 A. A v a r i a t i o n o f f i b e r diagram, taken a t r e g u l a r i n t e r v a l s , o f a wet

f i b r o u s specimen d r i e d i n the

also given

i n F i g . 6(20).

During the

broadening o f each p a t t e r n destroyed the

f i b e r d i a g r a m s , and

s c a t t e r i n g weakened and

a i r a t room t e m p e r a t u r e , i s

parallel

course o f drying, t h e more and

more t h e d e t a i l s o f

t o t h i s change t h e

f i n a l l y disappeared.

small-angle

These f a c t s suggest

that the m i c e l l e s l o s e i n t r a m i c e l l a r w a t e r ( o r c r y s t a l l i n e by

water)

d r y i n g , which d i s t u r b s the r e g u l a r m o l e c u l a r arrangement

i n s i d e t h e m i c e l l e , and

a t the

same t i m e ,

the

evaporation

m i c e l l a r water causes adjacent m i c e l l e s t o contact

o f inter-

d i r e c t l y , which


374

FIBER

DIFFRACTION

METHODS

Polymer Journal


Figure 7. X-ray small-angle scattering diagram of the wet, fibrous curdlan specimen (DPn 400) (20)

7/1

Helix

Structure of A Micelle

U l t r e s t r u c t u r e o f An O r i e n t e d Gel (Room Temperature)

Figure 8.

A model for the ultrastructure of curdlan gel at room temperature.

The oriented gel consists of micelles, of which the average diameter is about 80 A. Micelle-micelle distance is about 120 A. Area between micelles is filled with water molecules. Micelle interior is packed mostly by 7/1 single helical molecules that are hydrogenbonded to one another by water molecules. The single helical molecule is also probably hydrated. Some parts of the micelle are occupied by molcules of triple-stranded helix, which are also hydrated to some extent.


24.

KASAI AND HARADA


does away w i t h t h e i n h o m o g e n e i t y b. High temperature

i n t h e specimen

375

(Fig. 8).

structure

M a r c h e s s a u l t et al. (27) o b t a i n e d w e a k l y c r y s t a l l i n e a n d o r i e n t e d f i b e r s ( A ) b y e x t r u d i n g a 1 0 % DMSO s o l u t i o n o f c r u d l a n i n t o CH3OH a t room t e m p e r a t u r e a n d w a s h i n g

i ti n water.

f o u n d t h a t t h e same f i b e r a n n e a l e d i n w a t e r , u n d e r

They

tension, at

140°C, i n a s e a l e d bomb, i s o f h i g h e r c r y s t a l l i n i t y a n d o c c u r e d as two r e v e r s i b l e c r y s t a l l i n e p o l y m o r p h s :


h u m i d i t y ( B ) and t h e o t h e r a t h u m i d i t i e s

one a t h i g h

relative

l e s s than 20%(C).

o

The

f i b e r p e r i o d o f 5.79 A f o r (C) t o g e t h e r w i t h t h e r e s u l t s

o f a c o n f o r m a t i o n a l study and t h e v a l u e s o f i t s i n t e n s i t y p o i n t e d t o a t r i p l e - s t r a n d e d 6/1 h e l i c a l T a k e d a et al.(19)

s t r u c t u r e w i t h P6

3

h e a t - t r e a t e d t h e wet f i b r o u s specimen

s e a l e d bomb i n t h e p r e s e n c e o f w a t e r . 120°C t h e a n n e a l e d s p e c i m e n f i b e r diagram

Figure 9.

symmetry

A t temperatures

above

showed a r e m a r k a b l y d i f f e r e n t

(Fig. 9): thef i r s t

ina

X-ray

layer disappered, the f i b e r

X-ray fiber diagrams of heat-treated (>120°C) curdlan specimen (TJFn 400) (20): (A) dried in air and (B) dried in vacuum


376

FIBER

period decreased t o 18.1 A .

DIFFRACTION

METHODS

The a n n e a l e d s p e c i m e n d r i e d i n

2

o

vacuum gave a n o t h e r X - r a y d i a g r a m , h a v i n g a f i b e r p e r i o d o f 5 . 7 A 2

(Table I I ) .

T h e s e two k i n d s o f f i b e r d i a g r a m s

respectively

c o r r e s p o n d t o t h o s e o f (B) and (C) o b t a i n e d b y M a r c h e s s a u l t et al. (27). Triple-stranded helical

s t r u c t u r e was a l s o p r o p o s e d f o r B-

( l + 3 ) - D - g l u c a n b y A t k i n s and P a r k e r ( 2 8 ) .

Blum and S a r k o ( 2 9 )


s t u d i e d the s t r u c t u r e s o f l e n t i n a n , a branched and o f pachyman, a ( 1 + 3 ) - B - D - g l u c a n sidic

(1+3)-B-D-glucan

c o n t a i n i n g a few B - l , 6 - g l u c o -

l i n g a k e s , and p r o p o s e d t h e e x i s t n e c e o f a t r i p l e - s t r n a d e d

helix i n their

structures.

C r y s t a l d a t a and a b r i e f a c c o u n t f o r t h e s t r u c t u r e o f t h r e e forms o f t h e c u r d l a n a r e g i v e n i n T a b l e I I . A schematic r e p r e s e n -

T a b l e I I . A b r i e f account f o r t h e s t r u c t u r e o f t h r e e forms o f Curdlan Room t e m p e r a t u r e or Heat-treated a t temp^.120°C i n a s e a l e d bomb i n the presence o f water, and d r i e d i n a i r d r i e d i n vacuum s

a=b=lSAi

A

o

=Z?= 1 4 . 1

a

A

9

fc=16.4

Fiber Diffraction Methods - American Chemical Society

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