Reactions of Coordinated Ligands and Homogeneous Catalysis

12 Effects of Metal Ions on Imidazole Catalysis of the Mutarotation of Glucose NORMAN C. LI and LUCY JEAN University, Pittsburgh,

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Duquesne

Pa.

The rates of mutarotation of glucose in the absence and presence of imidazoles and metal ions have been measured at 25° and pH 4 to 7. Under the experimental conditions, only the imidazole free bases serve as catalysts, and the rate constants of mutarotation obey the equations k = 0.0104 + 1.14 (imidazole) and k = 0.0104 + 0.14 (benzimidazole). The difference in catalytic coefficients is related to the difference in pK's. In the presence of metal ions which complex with the imidazoles, the rates of mutarotation decrease because of decrease in the concentration of imidazole free base. The concentrations of the latter derived from kinetic data, agree with values calculated from equilibrium pH data. Glucosamine hydrochloride is glucose with a hydroxyl group replaced by -NH +. From pH 4 to 7, the basic amino group in glucosamine serves as an intramolecular catalyst. In the presence of metal ions, rates of mutarotation decrease; the effect of metal complexation is smaller for glucosamine than for intermolecular catalysis by imidazole. A mechanism for the intramolecular catalysis of mutarotation is proposed. 3

p u r d et al.

(8)

h a v e m e a s u r e d t h e r e a c t i v i t y o f i m i d a z o l e k i n e t i c a l l y b y its a b i l i t y

to c a t a l y z e t h e h y d r o l y s i s o f p - n i t r o p h e n y l a c e t a t e i n t h e a b s e n c e a n d p r e s e n c e o f Zn(II)

or

Cu(II)

determined

of m e a s u r i n g A

ion.

The

interaction

the

c o n c e n t r a t i o n of i m i d a z o l e

s i m i l a r s t u d y is r e p o r t e d h e r e o n t h e

catalyze the Cd(II),

between

imidazole

and

f r o m the rate d a t a a n d f r o m e q u i l i b r i u m p H values;

and

mutarotation Ca(II)

ions.

mutually

was

methods

compatible.

ability of i m i d a z o l e a n d b e n z i m i d a z o l e

of D - g l u c o s e The

free b a s e are

m e t a l ions the two

in the

metal

ions

absence

and

themselves

at

presence a

of

concentration

0 . 0 2 M d o not c a t a l y z e the m u t a r o t a t i o n a n d the d e c r e a s e i n the rate of c a t a l y s i s i n t h e p r e s e n c e o f m e t a l i o n s is d u e to i n t e r a c t i o n

Ni

Busch; Reactions of Coordinated Ligands Advances in Chemistry; American Chemical Society: Washington, DC, 1962.

of

imidazole

between imidazole

174

to

(II),

and

LI AND JEAN metal ions. lated

175

Metal Ion Effect on Imidazole Catalysis

T h e concentrations

f r o m the

rate d a t a

are

of i m i d a z o l e a n d b e n z i m i d a z o l e free base

i n satisfactory

derived f r o m equilibrium p H data.

agreement

with

the

calcu-

concentrations

T h e results of a n i n t r a m o l e c u l a r catalysis

m u t a r o t a t i o n a n d of t h e m e t a l i o n effects are

of

presented.

Experimental Materials. obtained

Imidazole, benzimidazole, and

from

the

Eastman

Kodak

Co., and

glucosamine

used

without

hydrochloride

after d r y i n g for several d a y s over a n h y d r o u s c a l c i u m c h l o r i d e . nickel nitrate


glyoxime.

and nickel chloride were

Stock solutions of

analyzed b y precipitation with

S t o c k solutions of c a d m i u m nitrate

were

were

further purification, dimethyl-

analyzed gravimetrically

by

c o n v e r s i o n to c a d m i u m s u l f a t e . Measurement.

Rotations were measured with a R u d o l p h

electric polarimeter operating f r o m a s o d i u m v a p o r l a m p . through 20-cm. 0.1°.

The

on

the

mutarotation

over two half lives.

h y d r o c h l o r i d e i n the presence m e t a l salt,

200

was

photo-

circulated

t u b e s w i t h g l a s s e n d p l a t e s , f r o m a b a t h m a i n t a i n e d at 2 5 . 0 °

runs

dependence

Model

Water

it w a s n e c e s s a r y

D-glucose showed

of

In studies o n the

mutarotation

of v a r y i n g c o n c e n t r a t i o n s

to a d d t h e

alkali

first,

excellent of

±

first-order

glucosamine

of s o d i u m h y d r o x i d e a n d

then the

metal

salt,

to

avoid

precipitation.

Results and

Discussion

T h e r a t e c o n s t a n t , k, o f m u t a r o t a t i o n is g i v e n b y t h e e q u a t i o n

*

t

=

° (RT^RZ)

l o g ,

w h e r e t is t i m e i n m i n u t e s , a n d R , R ( )

final

, and R

œ

(

are t h e initial a n g l e of rotation,

t

e q u i l i b r i u m a n g l e , a n d t h e a n g l e at t i m e f, r e s p e c t i v e l y .

Roo) vs.

t g i v e straight lines a n d the rate constant,

k,

is r e p r o d u c i b l e t o

T h e rates of m u t a r o t a t i o n of g l u c o s e , i n the p r e s e n c e zole a n d of 0 to 0 . 2 3 0 M stant d a t a are g l u c o s e vs.

P l o t s of l o g

1

)

the

{R

t

—

±2 /c r

of 0 to 0 . 2 3 8 M

imida-

b e n z i m i d a z o l e at 2 5 ° , h a v e b e e n m e a s u r e d ; t h e r a t e c o n -

g i v e n i n T a b l e I.

L i n e a r plots of the

o b s e r v e d rate constants

the m o l a r i t y of i m i d a z o l e or b e n z i m i d a z o l e ( I m or B I m )

for

are o b t a i n e d .

T h e straight lines f o l l o w the equations k = ko + k

where k and k

are i n m i n .

0

free bases,

1

and

k

+

0

fc

* B i

(2

(BIm)

m

and k

Ini

(Im)

lm

(3)

are the catalytic coefficients of the

m m

imidazole a n d benzimidazole, respectively,

T h e values of k

im

A

-

=

k

and

fc

BIm

i n liters p e r m o l e m i n u t e .

a r e l i s t e d i n T a b l e I.

p l o t of the o b s e r v e d rate constants

for glucose w i t h T

tration of i m i d a z o l e , does not y i e l d a straight line.

I

m

, the total

concen-

T h i s is s h o w n b y t h e v a l u e s o f

k' l i s t e d i n T a b l e I, w h e r e k' = T h e constancy of the values of

(k — k )/T 0

k

lm

and

(4)

lm

k , BIm

rather than the values of

T a b l e I s u g g e s t s t h a t t h e b a s i c f o r m o f i m i d a z o l e o r b e n z i m i d a z o l e is t h e s p e c i e s , a n d t h a t t h e i m i d a z o l i u m o r b e n z i m i d a z o l i u m i o n is n o t . t i o n is i n a g r e e m e n t

w i t h t h a t of G u r d

(8)

This

in

interpreta-

a n d of B r u i c e a n d S c h m i r (3)

c a t a l y z e d hydrolysis of p - n i t r o p h e n y l acetate b y i m i d a z o l e .

k',

catalytic

on

the

Bronsted and Guggen-


ADVANCES IN CHEMISTRY SERIES

176 Table I.

Imidazole Catalysis of Mutarotation of D-Glucose, 0.27Μ, 25° A.

(Im), M

(Him*),

0.000 0.030 0.040 0.050 0.080

Imidazole, p K

M

A

= 7.08 k'

k

0.000 0.150 0.079 0.150 0.158

0.0104 0.0458 0.0568 0.0667 0.0977 Av.

Β.


(BIm)

Benzimidazole, p K

0.000 0.075 0.0375 0.150 0.150

A

1.14

= 5.53

k

^Blm

k'

0.0104 0.0138 0.0161 0.0171 0.0125

0.14 0.14 0.13 0.14

0.03 0.08 0.03 0.05

(HBIm^)

0.000 0.025 0.0375 0.050 0.080

Av.

heim

(2)

in the a c i d dissociation constant, K . =

10- , k 5

A

— 2 X 10~ .

Since the values of K

3

zole are m u c h smaller, 8 X

-

8

A

of glucose b y

increases w i t h

increase

for imidazole a n d benzimida

A

10

k,

T h e s e authors list f o r t r i m e t h y l a c e t i c a c i d :

A

A

0.14

h a v e g i v e n values for the catalysis of the mutarotation

acids a n d h a v e s h o w n that t h e a c i d catalytic constant,

K

0.20 0.39 0.28 0.37

1.18 1.16 1.13 1.09

and 3 X

10

_ G

, respectively, their a c i d

constants w o u l d b e e x p e c t e d to b e s m a l l e r t h a n 1 0

_ 3

.

catalytic

A n y catalysis b y the i m i d a -

z o l i u m or b e n z i m i d a z o l i u m i o ntherefore w o u l d b e undetected. Bruice tives, k

îm

and Schmir

(3)

have

s h o w n that

f o r a series

mate measure of base strength, the value of k pK . A

T a b l e I s h o w s t h a t t h i s is i n d e e d t h e c a s e .

Brônsted k

H

constant

eight

times

and Guggenheim

andp K

A

larger

(2)

than

that

A

is a n a p p r o x i -

should increase w i t h increase in

îm

catalytic

of imidazole deriva

d e p e n d s o n the base strength of the catalyst a n d since p K

Imidazole, p K

A

=

7.08, has a

of b e n z i m i d a z o l e , p K

A

=

5.53.

have obtained a linear relationship between l o g

f o r a series o f c a r b o x y l i c a c i d s i n t h e p K

A

range of 2 to 5, w h e r e k

]{

is

the carboxylate anion basic catalytic constant for the mutarotation of glucose a n d K

A

is t h e a c i d d i s s o c i a t i o n c o n s t a n t

of the a c i d .

O u r results f o r i m i d a z o l e a n d

b e n z i m i d a z o l e fit f a i r l y w e l l i n t o t h e B r ô n s t e d p l o t . F o r t h e m u t a r o t a t i o n o f g l u c o s e i n a q u e o u s m e d i a a n d at 2 5 ° , L i et al. obtained the equation k — 0.0102 + tion (9)

is k =

4- 0 . 2 5 8

(H+).

0.0104 +

0.283

( H + ), w h i l e K u h n a n d Jacob's

0 . 3 3 4 ( H + ) a n d H u d s o n ' s e q u a t i o n (6)

is k =

(12) equa-

0.0096

T h e p H r a n g e o f t h e e x p e r i m e n t a l s o l u t i o n s l i s t e d i n T a b l e I is

f r o m 4 . 8 5 t o 6 . 8 , a n d it is o b v i o u s t h a t t h e c a t a l y t i c e f f e c t o f h y d r o g e n i o n i n o u r experiments

is e n t i r e l y n e g l i g i b l e .

Using

i m i d a z o l e a n d b e n z i m i d a z o l e as c a t a -

lysts, o u r e q u a t i o n s a r e : k = 0.0104 +

1.14 ( I m )

(5)

k = 0.0104 + 0.14 ( B I m )

(6)

A s c h e m e f o r the i m i d a z o l e catalysis of t h e m u t a r o t a t i o n of glucose, similar to the " c o n c e r t e d " m e c h a n i s m p r o p o s e d b y S w a i n a n d B r o w n

(13),

is s h o w n b e l o w ,

i n w h i c h a p r o t o n is t r a n s f e r r e d f r o m t h e υ - g l u c o s e t o i m i d a z o l e o r b e n z i m i d a z o l e a n d f r o m the H

2

0 ( r e p r e s e n t e d as a n a c i d ) t o t h e D - g l u c o s e i n t h e r a t e - d e t e r m i n i n g

step.


LI AND JEAN

177


H

OH

H

lm

HIm

Ο

+

G H — C — O H

H — G — O H

HO—G—Η

Ο

+

H

2

O H -

HO—G—Η

0

H — G — O H

H — G — O H .J

H—G

H — G — O H

(7)

GH OH

GH OH

2

2


H o w e v e r , t h e m e c h a n i s m g i v e n i n E q u a t i o n 7 is n o t n e c e s s a r i l y t h e c o r r e c t one.

E i g e n arid M a a s s

i m i d a z o l e to y i e l d stant o f 1 0 sec.

M~

1

5

M

_

sec.

1

(4,

5)

h a v e f o u n d that the reaction b e t w e e n glucose a n d

imidazolium - 1

a n d glucose

anion has a second-order

rate

con

, w h i l e t h e r a t e c o n s t a n t f o r t h e r e v e r s e r e a c t i o n is 2 X

10

1 0

T h u s t h e i o n i z a t i o n e q u i l i b r i u m is e s t a b l i s h e d b e f o r e m u t a r o t a t i o n o f

- 1

g l u c o s e c a n o c c u r , a n d i t is p o s s i b l e t h a t t h e c a t a l y t i c a c t i o n o f i m i d a z o l e i n v o l v e s the p r e - e q u i l i b r i u m between glucose a n d imidazole, f o r m i n g the i m i d a z o l i u m ion

a n d glucose

anion, a n d the subsequent

reaction

between

them

cat

How

(7).

ever, the reaction of glucose anion w i t h i m i d a z o l i u m i o n cannot b e distinguished stoichiometrically f r o m a reaction between glucose a n d imidazole. The

effects

mutarotation

of m e t a l

ions o n i m i d a z o l e a n d b e n z i m i d a z o l e catalysis

o f g l u c o s e a r e s h o w n i n T a b l e s II a n d I I I , r e s p e c t i v e l y .

centration of i m i d a z o l e ( I m ) or b e n z i m i d a z o l e ( B I m ) free base two ways: and

f r o m p H of the experimental solution a n d the p K

f r o m the rate constants

columns

6

and 7

using

Equation 5

o f T a b l e s II a n d III, t h a t

o r 6.

A

of the

T h e con

is c a l c u l a t e d i n of the imidazole,

It is s e e n ,

the concentration

b y comparing

of i m i d a z o l e or

b e n z i m i d a z o l e f r e e b a s e c a l c u l a t e d f r o m t h e r a t e d a t a is i n g o o d a g r e e m e n t the

concentration

from

rate data,

zole) +

2

calculated from the equilibrium

i t is a s s u m e d t h a t t h e m e t a l

complexes d o not catalyze

p H data.

ions, M +

the mutarotation

2

, a n d the

of glucose.

s u m p t i o n w a s tested b y m e a s u r i n g the rate of mutarotation Ni(N0 ) , 3

and in 0 . 0 1 M C a ( N O

2

: i

) . 2

T h e rate

F r o m t h e increase i n p H a n d rate constant

(metal-imida-

T h e f o r m e r as

of glucose in 0 . 0 1 M

constants

i n these

0 . 0 1 0 4 a n d 0 . 0 1 0 5 , r e s p e c t i v e l y , e s s e n t i a l l y t h e s a m e as i n p u r e

(Im)]

with

In the calculation

media

are

water.

[with c o n s e q u e n t increase i n free

i n g o i n g f r o m e x p e r i m e n t 1 t o 4 i n T a b l e I I , i t is s e e n t h a t t h e s t a b i l i t y o f

the imidazole complexes

is i n t h e o r d e r :

Ni+

>

2

Cd+

2

»

Ca+ . 2

agreement w i t h the order of f o r m a t i o n constants of these complexes t h e f i n d i n g (11) imidazole.

(1),

This

t h a t t h e r e is n o a p p r e c i a b l e i n t e r a c t i o n b e t w e e n c a l c i u m i o n a n d

M o r e o v e r , i n a solution w i t h a n initial c o m p o s i t i o n of 0 . 2 3 8 M

zole a n d 0 . 1 5 8 M

is i n

and with

H C 1 , k w a s f o u n d to b e 0 . 0 9 7 7 m i n . -

i n c r e a s e i n k f o r this s o l u t i o n i n t h e p r e s e n c e o f 0 . 0 2 0 M

1

imida

( T a b l e I ) , so t h a t t h e

C a ( N 0 ) 3

2

(experiment

4

i n T a b l e II) a m o u n t s to o n l y 3.6%. T a b l e s II a n d III d e m o n s t r a t e constant free

a n d p H decrease

a b u n d a n t l y that i n a g i v e n m e d i u m the rate

(with a c c o m p a n y i n g decrease i n the concentration

imidazole or b e n z i m i d a z o l e )

with

increase

i n concentration

of

of metal i o n .

T h i s is as e x p e c t e d , b e c a u s e t h e r e is g r e a t e r c o m p l e x a t i o n i n a g i v e n m e d i u m w h e n the concentration of the m e t a l i o n increases. The ing

m e t a l c o m p l e x o f b e n z i m i d a z o l e is m u c h less s t a b l e t h a n t h e c o r r e s p o n d

complex of imidazole.

experiment

T h u s a comparison of experiment

1 i n T a b l e III shows that starting

1 i n T a b l e II a n d

w i t h e q u a l concentrations

u n c h a r g e d l i g a n d , t h e ratios o f the c o m p l e x e d l i g a n d p e r m o l e o f N i ( I I )


of the

are e q u a l


178 Table II.

Effects of Metal Ions on Imidazole Catalysis of Mutarotation of Glucose at 25°

Initial Total Concn. Expt. No.


1 2 3 4 5 6 7 8

Metal salt Ni(N0 NiCl Cd(N0 Ga(N0 NiCl , Gd(N0 Ni(N0 Ni(N0

)

3

2

3

2

2

3

3

3

2

2

2

Table III.

From H

From rates

0.025 0.026 0.037 0.079 0.061 0.066 0.008 0.013

0.025 0.027 0.037 0.080 0.060 0.066 0.010 0.015

P

0389 0413 0532 1013 0785 0851 0223 0273

0 0 0 0 0 0 0 0

6.28 6.29 6.45 6.78 6.67 6.70 5.90 6.11

158 158 158 158 158 158 120 120

0 0 0 0 0 0 0 0

k, Min.-'

pH

HCl

0.238 0.238 0.238 0.238 0.238 0.238 0.150 0.150

0.020ΛΤ 0.020 ) , 0.020 ) 0.020 0.006 ) 0.006 ) 0.010 ) 0.007 2 )

3

2

(Im)

Imida zole

Effect of Ni(ll) on Benzimidazole Catalysis of Mutarotation of Glucose at 2 5 °

Initial Total Molar Concn. Expt. No. 1 2 3 4 5 6

Ni(N0 )

3 2

HCl

0.230 0.230 0.200 0.200 0.150 0.120

0.150 0.150 0.150 0.150 0.100 0.090

0.020 0.010 0.020 0.010 0.010 0.020

to 2 . 7 5 a n d 1 . 1 5 , r e s p e c t i v e l y , L a n e a n d Q u i n l a n (10)

k, Min.-'

H

P

From rates

0.056 0.070 0.031 0.040 0.042 0.016

0.057 0.069 0.032 0.043 0.040 0.018

P

0.0184 0.0200 0.0149 0.0164 0.0160 0.0129

5.10 5.20 4.84 4.95 5.15 4.78

From H

for the imidazole a n d benzimidazole

complexes.

carried out p H titration of b e n z i m i d a z o l e i n the presence

of N i ( I I ) , a n d reported

that they

hydrolysis of the metal ion. that t h e N i (II)

(BIm)

Benzimi dazole

could not study the complexation

In our experiments

ion d i d not hydrolyze.

because of

t h e p H v a l u e s a r e l o w e n o u g h so

T h e weaker

complex-forming ability of

b e n z i m i d a z o l e , as c o m p a r e d w i t h i m i d a z o l e , m a y b e a s c r i b e d t o t h e s m a l l e r p K

A

a n d possible steric h i n d r a n c e i n the f o r m e r l i g a n d . G l u c o s a m i n e h y d r o c h l o r i d e is g l u c o s e atom 2 replaced b y —N H + . 3

with the hydroxyl group

o n carbon

W h e n a n a l k a l i is a d d e d t o a n a q u e o u s s o l u t i o n o f

g l u c o s a m i n e h y d r o c h l o r i d e , g l u c o s a m i n e is p r o d u c e d , a n d t h e b a s i c a m i n o a c t s as a n i n t r a m o l e c u l a r c a t a l y s t f o r t h e m u t a r o t a t i o n o f g l u c o s e . shown in Table I V .

T h e rate constant of mutarotation

group

T h e results are

o f g l u c o s a m i n e is a l i n e a r

function of the s o d i u m h y d r o x i d e concentration; i n each r u n 0.500 g r a m of glucos a m i n e h y d r o c h l o r i d e is a d d e d t o 1 0 m l . o f t h e a l k a l i s o l u t i o n .

T h e p H values

for t h e e x p e r i m e n t a l solutions v a r y f r o m 3.8 to 6.6 a n d , i n this range, h y d r o g e n or h y d r o x y l i o n catalysis

should b e negligible.

T h e basic

amino group

i n glucos

a m i n e t h e r e f o r e is t h e i n t r a m o l e c u l a r c a t a l y s t a n d t h e d a t a s h o w t h a t t h e — N H + 3

is n o t a c a t a l y t i c

species.

A mechanism for the intramolecular

catalysis

m a y be

represented b y E q u a t i o n 8: H

H

O H \

G I

H—G—ΝΗ·2

ι

HO—G—Η

I

H—G—OH I

H—G

Ο

\

/

I

ι

I

Ο

G

S

H—G—NH +

H

2

0

3

2

(8)

HO—G—H ! H—G—OH

I

H—G—OH

GH OH

+

I

OH"

I

CH OH 2


LI AND JEAN It is e a s y

to see f r o m E q u a t i o n 8 w h y — N H +

i o n does

3

mutarotation :

T h e positively charged

hydroxyl

group

0.0114M

Cd(N0 ) >,

same

179


on carbon 3

1.

i o ncannot

When

no N a O H

t h e rate constant

L

as i n t h e a b s e n c e

extract

is a d d e d ,

of mutarotation

of the metal.

n o t catalyze the

the proton

from the

i n the presence of

is 0 . 0 1 2 2 , p r a c t i c a l l y t h e

T h i s is as e x p e c t e d ,

since n o glucosamine

c o m p l e x is p r e s e n t .

Table IV.

Mutarotation of Glucosamine at 2 5 °

(0.500 g r a m of glucosamine h y d r o c h l o r i d e in 10 m l . of s o d i u m h y d r o x i d e solution)


c

NaOH

—C i K

k, MlTl.

U C 0 8 a m i n e

0.0000 M 0.0202 0.0364 0.0479 The

1

0.0125 0.0221 0.0302 0.0382

catalysis of m u t a r o t a t i o n o f g l u c o s a m i n e h y d r o c h l o r i d e involves a n intra

m o l e c u l a r m e c h a n i s m , a n d s o t h e c a t a l y t i c c o e f f i c i e n t o f g l u c o s a m i n e . £Γ,ΙΝΗ > m u s t 2

have thedimension, m i n . kT where

- 1

,

instead of liters/mole m i n .

= 0.0125 (GlNHa-O

Τ is t o t a l c o n c e n t r a t i o n

glucosamine ( G 1 N H ) . 2

^GINH

2

is 0 - 1 3 m i n .

- 1

(G1NH )

(9)

2

of complexing metal

i o n , is

of glucosamine hydrochloride ( G l N H

: i

+)

In T a b l e I V , Τ = 0 . 2 3 1 9 M a n d the average value of

W i t h t h i s v a l u e o f k \xn i

.

2

a n d , i n the absence

e q u a l to the s u m of the concentrations and

+ *G,NH

T h e t o t a l r a t e is t h e n

G

2

0.0125 ( Τ - (GINHo))

Equation 9 becomes

0.13 (G1NH ) + ψ 2

τ

(10) -

0.0125 +

°·

1

2

(

^

1

Ν

Η

2

)

F o r the data of T a b l e I V , t h e values of k calculated f r o m E q u a t i o n 10 agree w i t h t h e o b s e r v e d k w i t h i n a b o u t 3%. stant s o d i u m h y d r o x i d e c o n c e n t r a t i o n

E q u a t i o n 10 f u r t h e r p r e d i c t s that at c o n (T >

NaOH),

a n increase

in Τ would be

a c c o m p a n i e d b y a d e c r e a s e i n k, a n d t h i s h a s b e e n e x p e r i m e n t a l l y o b s e r v e d . If t h e last s o l u t i o n i n T a b l e I V c o n t a i n s i n a d d i t i o n 0 . 0 2 2 9 M NiCL>, t h e rate constant d r o p s to 0 . 0 3 1 7 a n d 0 . 0 2 7 8 m i n . - , 1

Equation

10, it c a n b e c a l c u l a t e d that i n t h e p r e s e n c e

C d ( N 0

respectively.

of 0 . 0 2 2 9 M

)

3

or

2

Using

Cd(II) and

N i ( I I ) , the concentration o f g l u c o s a m i n e free base d r o p s f r o m 0 . 0 4 7 9 M to 0.0371 and

0.0296 M , respectively.

A c o m p a r i s o n of these d a t a w i t h experiments

2 and

3 o f T a b l e II s h o w s c l e a r l y that t h e effects o f m e t a l ions o n i n t r a m o l e c u l a r catalysis o f t h e m u t a r o t a t i o n o f g l u c o s a m i n e h y d r o c h l o r i d e a r e less t h a n t h e c o r r e s p o n d i n g effects o n t h e i n t e r m o l e c u l a r i m i d a z o l e c a t a l y s i s o f t h e m u t a r o t a t i o n o f g l u c o s e . By for

a p H titration m e t h o d , w e h a v e o b t a i n e d l o g Κ = 2.0 a n d 2.5, respectively, λ

t h e f o r m a t i o n constants

of the 1 to 1 C d a n d N i complexes

of glucosamine.

These values are about 0.7 l o g unit lower than the corresponding metal

complexes

o f i m i d a z o l e ( 1 ) , so t h a t t h e m e t a l i o n s w o u l d b i n d g l u c o s a m i n e less s t r o n g l y t h a n i m i d a z o l e , a n d h e n c e w o u l d exert a smaller effect.

Moreover, i n intramolecular

catalysis,

of t h e glucose

the catalytic

a m i n o g r o u p is a l r e a d y

part

m o l e c u l e , so

t h a t t h e c a t a l y t i c i n f l u e n c e w o u l d p r o b a b l y b e r e l a t i v e l y less a f f e c t e d b y t h e p r e s ence o f a m e t a l i o n t h a n i n t h e case o f intermolecular catalysis.

O u r data

also

s h o w that N i (II) h a s a greater effect o n i n t r a m o l e c u l a r catalysis t h a n C d ( I I ) , a n d t h i s is t h e s a m e o r d e r as h a s b e e n o b s e r v e d f o r i n t e r m o l e c u l a r c a t a l y s i s .



160 Acknowledgment

The authors are deeply grateful to M . E i g e n , Max-Planck-Institut fur Physikalische Chemie, Gottingen, Germany, for reading the manuscript a n d making valuable suggestions, and to I. S. K i m for carrying out some of the polarimetric measurements.


Literature Cited (1) Bjerrum, J., Schwarzenbach, G., Sillén, L. G., "Stability Constants," Spec. Pub. 6, Part I, "Organic Ligands," Chemical Society, London, 1957. (2) Brönsted, J. N., Guggenheim, Ε. Α.,J.Am. Chem. Soc. 49, 2554 (1927). (3) Bruice, T.C.,Schmir, G. L., Ibid., 79, 1663 (1957). (4) Eigen, M., Baker Lectures 1961/62, Cornell University, Ithaca, Ν. Y. (5) Eigen, M., Maass, G., private communication. (6) Hudson, C. S., Sawyer, H. L.,J.Am. Chem. Soc. 39, 470 (1917). (7) Kilde, G., Wynne-Jones, W. F. K., Trans, Faraday Soc. 49, 243 (1953). (8) Koltun, W. L., Dexter, R. N., Clark, R. E., Gurd, F. R. N.,J.Am. Chem. Soc. 80, 4188 (1958). (9) Kuhn, R., Jacob, P., Z. physik. Chem. 113, 389 (1924). (10) Lane, T. J., Quinlan, K. P.,J.Am. Chem. Soc. 82, 2994 (1960). (11) Li, N.C.,Chu, T. L., Fujii, C. T., White, J. M., Ibid., 77, 859 (1955). (12) Li, Ν.C.,Kaganove, Α., Crespi, H. L., Katz, J. J., Ibid., 83, 3040 (1961). (13) Swain, C. G., Brown, J. F., Ibid., 74, 2534, 2538 (1952). RECEIVED August 27, 1962. Work supported by the U. S. Atomic Energy Commission through Contract No. AT(30-1)-1922.


Reactions of Coordinated Ligands and Homogeneous Catalysis

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