Effects of Ascorbic Acid on the Nitrosation of Dialkyl Amines

24 Effects of Ascorbic Acid on the

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Nitrosation of Dialkyl Amines YOUNG-KYUNG KIM, STEVEN R. TANNENBAUM, and JOHN S. WISHNOK Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, MA 02139 Ascorbic acid is known to inhibit the nitrosation of secondary amines. A computer model has been developed to predict the amount of nitrosamine formed under conditions that are experimentally inaccessible. The computer-calculated rates for N-nitrosomorpholine formation using rate and equilibrium constants from the literature agree well with experimental values in the absence of and presence of ascorbic acid under anaerobic conditions. In the aerobic system the inhibitory efficiency of ascorbic acid is lower, and the nature of the interactions among the various components of the mixtures is less well understood. The use of ascorbic acid for inhibition of N-nitroso compound formation both in vitro and in vivo is briefly reviewed.

A s c o r b i c a c i d , i n a d d i t i o n to its k n o w n a n d p o t e n t i a l b i o l o g i c a l p r o p e r ties, is a n a c t i v e a n d i n t e r e s t i n g o r g a n i c c h e m i c a l i n its o w n r i g h t . Its s t r o n g r e d u c i n g a b i l i t i e s ( 1 ), i n p a r t i c u l a r , h a v e s t i m u l a t e d interest i n the possible use of ascorbic a c i d as a n i n h i b i t o r of n i t r o s a t i o n reactions a n d , c o n s e q u e n t l y , as a means of r e d u c i n g h u m a n exposure to c a r c i n o genic N - n i t r o s o c o m p o u n d s . M o s t substances c o n t a i n i n g t h e Ν — N O f u n c t i o n a l i t y are c a r c i n o genic i n at least one a n i m a l species

(2,3)

a n d these c o m p o u n d s

are,

therefore, p r o b a b l y h u m a n carcinogens as w e l l . N - N i t r o s o c o m p o u n d s are not often f o u n d i n n a t u r e , a l t h o u g h t h e y are o c c a s i o n a l l y d e t e c t e d i n some i n d u s t r i a l e n v i r o n m e n t s (4,5).

How

ever, several N - n i t r o s o a m i n e s h a v e b e e n r e g u l a r l y d e t e c t e d i n a w i d e v a r i e t y of foods (6)

a n d a n extensive r e s e a r c h effort has c o n s e q u e n t l y 0065-2393/82/0200-0571$06.00/0 © 1982 American Chemical Society

In Ascorbic Acid: Chemistry, Metabolism, and Uses; Seib, P., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.

572

ASCORBIC

ACID

b e e n d i r e c t e d t o w a r d the d e t e c t i o n a n d i d e n t i f i c a t i o n of these substances, the e l u c i d a t i o n of the routes of t h e i r f o r m a t i o n , a n d t h e e v a l u a t i o n of the h u m a n h e a l t h h a z a r d s p o s e d b y n i t r o s a m i n e

exposure.

O n e result of these investigations has b e e n a r e a l i z a t i o n t h a t nitroso c o m p o u n d s c a n f o r m u n d e r a w i d e v a r i e t y of c o n d i t i o n s

detailed

N-

from

r e a c t i o n of nitrosatable nitrogens w i t h a n y of several n i t r o s a t i n g species (7-13).

A s w i l l be

later, c o m p l e x e q u i l i b r i a a m o n g

n i t r o s a t i n g agents c a n arise f r o m

2

f o r m e d i n v i v o b y b a c t e r i a l r e d u c t i o n of nitrate, N 0 " (14). 3


several

n i t r i t e i o n , N 0 ~ , w h i c h is r e a d i l y

amines, i n a d d i t i o n , are w i d e l y d i s t r i b u t e d i n foods ( 1 5 ) .

Nitrosatable

T h e r e is, t h e r e

fore, a n i n c r e a s i n g interest i n t h e q u e s t i o n of h u m a n exposure to e n d o g e nously formed N-nitroso compounds. If it is f o u n d t h a t e p i d e m i o l o g i c a l l y significant n i t r o s a t i o n m a y o c c u r i n v i v o f r o m reactions of c o m p o u n d s n o r m a l l y present i n the d i e t or as metabolites, t h e n it becomes i m p o r t a n t to d e v e l o p n o n t o x i c m e t h o d s for p r e v e n t i n g these transformations. A s c o r b i c a c i d is k n o w n to react r a p i d l y w i t h n i t r i t e as w e l l as w i t h other n i t r o s a t i n g agents (16).

T h i s , a l o n g w i t h its l o w t o x i c i t y a n d k n o w n

n u t r i t i o n a l i m p o r t a n c e , has n a t u r a l l y l e d to a n e v a l u a t i o n of its usefulness as a n i n h i b i t o r of

n i t r o s a t i o n reactions

We

(17).

have

begun

both

e x p e r i m e n t a l a n d t h e o r e t i c a l studies of the interactions of ascorbic w i t h amines, a m i d e s , a n d n i t r o s a t i n g agents.

acid

O u r a p p r o a c h e s a n d results

are d e s c r i b e d i n the f o l l o w i n g sections. Amine

Nitrosation

T h e n i t r o s a t i o n reactions of a g i v e n a m i n e i n the presence of a c i d c a n be

conceptually

considered

as an i n t e r a c t i n g set of

ascorbic several

separate systems, t h a t is, ( i ) a set of e q u i l i b r i a a m o n g v a r i o u s n i t r o g e n oxides,

( i i ) reactions of nitrosatable n i t r o g e n w i t h e a c h of the v a r i o u s

n i t r o s a t i n g agents, ( i i i ) r e a c t i o n of ascorbic a c i d w i t h o x y g e n , a n d

(iv)

r e a c t i o n of ascorbic a c i d w i t h the n i t r o s a t i n g agents. T h e e q u i l i b r i a a r i s i n g f r o m a q u e o u s n i t r i t e are s h o w n i n S c h e m e 1, w i t h n i t r o s a t i n g species i t a l i c i z e d

(18).

N0 +H ^±HN0 +

2

HN0

2

+ H *± H N0 +

2HN0 HN0

2

2

2

z± H 0 +

+

2

2

*± N O 2

2

s

+

+ H X # NOX

NO

+

H 0 2

+

H 0 2

Scheme 1.


24.

Ascorbic Acid ir Nitrosation of Dialkyl Amines

KIM E T AL.

573

T h e r e l a t i v e i m p o r t a n c e of t h e v a r i o u s n i t r o s a t i n g agents is s t r o n g l y d e p e n d e n t o n t h e p H a n d , i n t h e case of N O X , o n t h e c o n c e n t r a t i o n of the h a l o g e n (e.g., C l " , B r " ) or p s e u d o h a l o g e n , (e.g., S C N " ) , X . A t y p i c a l p H profile for t h e n i t r o s a t i o n of amines has a n i n i t i a l - r a t e m a x i m u m near p H 3.4.

T h i s b e h a v i o r is t h e net r e s u l t of

a n increase i n t h e

c o n c e n t r a t i o n of n i t r o s a t i n g species vs. a decrease i n the c o n c e n t r a t i o n of nitrosatable free a m i n e ( 1 9 )

as the p H is l o w e r e d .

A l t h o u g h the

m a x i m u m i n i t i a l rate u s u a l l y occurs near p H 3.4, m e a s u r a b l e n i t r o s a t i o n Downloaded by UNIV OF MISSOURI COLUMBIA on October 7, 2013 | http://pubs.acs.org Publication Date: June 1, 1982 | doi: 10.1021/ba-1982-0200.ch024

w i l l nonetheless o c c u r over a w i d e p H range. I n t h e p r e s e n c e of catalysts, for e x a m p l e , X =

S C N " , the p H m a x i m u m is s h i f t e d , a n d t h e i n i t i a l rates

f a l l off m o r e s l o w l y as the p H decreases ( F i g u r e 1 ) .

F o r simple nitrosa

t i o n reactions, t h e n , the rate of n i t r o s a t i o n d e p e n d s o n t h e concentrations of t h e v a r i o u s n i t r o s a t i n g species a n d o n t h e c o n c e n t r a t i o n of free a m i n e , b o t h of w h i c h are affected b y p H .

Ascorbic Acid Oxidation I n a n a e r o b i c systems, a s c o r b i c a c i d / a s c o r b a t e reacts w i t h a l l o f t h e n i t r o s a t i n g agents s h o w n i n S c h e m e 1.

T h e s e reactions are g e n e r a l l y

faster t h a n the reactions b e t w e e n amines or a m i d e s a n d t h e r e s p e c t i v e n i t r o s a t i n g agents, a n d a s c o r b i c a c i d has b e e n s h o w n to b e a n effective i n v i t r o i n h i b i t o r of a m i n e n i t r o s a t i o n v i a c o m p e t i t i o n for these agents ( 1 7 , 2 4 ) . T h e s e results h a v e b e e n e x t e n d e d to m o r e p r a c t i c a l areas s u c h as t h e p r e v e n t i o n of n i t r o s a m i n e f o r m a t i o n i n foods a n d i n v i v o

(20,

21,22). I n p r i n c i p l e , t h e n , ascorbic a c i d appears to h a v e c o n s i d e r a b l e i m p o r tance as a n i n h i b i t o r of i n v i v o n i t r o s a t i o n of i n g e s t e d or b i o s y n t h e s i z e d amines v i a endogenous n i t r i t e .

H o w e v e r , this p o t e n t i a l is f a r

from

realized. T h e reaction conditions actually encountered i n l i v i n g organisms are c o m p l e x a n d v a r i e d a n d — p e r h a p s m o r e i m p o r t a n t l y — t h e i n v i t r o interactions a m o n g a s c o r b i c a c i d , n i t r i t e , a n d amines are not s t r a i g h t forward. T h e e q u i l i b r i a s h o w n i n S c h e m e 1, for e x a m p l e , g i v e rise to b o t h polar

(H N0 \

N 0

c a n be i n t e r c e p t e d b y a s c o r b i c a c i d to f o r m n o n - n i t r o s a t i n g N O .

2

3

2

NO ) +

2

and nonpolar

(N 0 ) 2

I n the presence of o x y g e n , h o w e v e r , N 0 2

v i a N O a n d N 0 , as s h o w n i n S c h e m e 2 2

3

3

n i t r o s a t i n g agents.

and N 0 2

4

The

can be regenerated

(23,24).

I n h i b i t i o n of n i t r o s a t i o n i n this system, t h e n , w i l l be effective at best o n l y u n t i l the ascorbate has b e e n c o n v e r t e d to d e h y d r o a s c o r b a t e . T h e a m i n e - n i t r i t e reactions i n p h y s i o l o g i c a l systems m a y be f u r t h e r obscured b y carbonyl (25)

or p s e u d o h a l o g e n

(19)

catalysts, b y

con

stituents of gastric j u i c e or i n t e s t i n a l fluids, or b y m u l t i p h a s i c i n t e r a c t i o n s


574

ASCORBIC

ACID

i n l i p i d - c o n t a i n i n g m i c e l l e s s u c h as those f o u n d i n t h e s m a l l intestine (26).

N i t r o s a t i o n s of a m i n e s w i t h l o n g a l k y l c h a i n s ( n > 6 ) are e n h a n c e d

b y m i c e l l e f o r m a t i o n (27).

T h e m e c h a n i s m s of these reactions are not

k n o w n b u t , d e p e n d i n g o n w h e t h e r t h e n i t r o s a t i o n occurs o n the surface or i n t h e i n t e r i o r of the m i c e l l e s , p o l a r a n d / o r n o n p o l a r n i t r o s a t i n g agents m a y be involved.


2.0


24.

Ascorbic Acid &• Nitrosation of Dialkyl Amines

KIM E T AL.

575

d e h y d r o a s c o r b a t e -f- N O

t

h

ascorbate

N 0

| HN0 ->N 0 2

2

2

N O ^ ^| N0 3

N 0

* ^

2

2

4

amine Downloaded by UNIV OF MISSOURI COLUMBIA on October 7, 2013 | http://pubs.acs.org Publication Date: June 1, 1982 | doi: 10.1021/ba-1982-0200.ch024

A . nitrosamine Scheme 2.

I n a d d i t i o n to these aspects o f t h e a m i n e n i t r o s a t i o n r e a c t i o n , t h e reactions of a s c o r b i c a c i d w i t h v a r i o u s c o m p o n e n t s of the n i t r i t e e q u i l i b r i a i n v o l v e t r a n s f o r m a t i o n s that are also affected b y t h e presence o r absence of o x y g e n (1,23).

S o m e of these are s h o w n s c h e m a t i c a l l y i n S c h e m e 3.

I f a t t e n t i o n is t h e n focussed o n t h e reactions o f a s c o r b i c a c i d / a s c o r b a t e r a t h e r t h a n o n t h e n i t r o s a t i o n of a m i n e s , i t c a n b e seen t h a t t h e a m o u n t of a s c o r b i c a c i d o r ascorbate a v a i l a b l e f o r i n h i b i t i o n o f n i t r o s a t i o n c a n b e d i m i n i s h e d b y t h e presence of o x y g e n . T h e e x p e r i m e n t a l d e s t r u c t i o n of ascorbate b y v a r i o u s c o m b i n a t i o n s of n i t r i t e , a i r , a n d n i t r o g e n is s h o w n i n F i g u r e 2 (24,28).

I t is a p p a r e n t

f r o m these experiments n o t o n l y that ascorbate is sensitive to t h e presence of e i t h e r a i r or n i t r i t e b u t that t h e c o m b i n a t i o n of these t w o reactants c a n c o m p l e t e l y exhaust the a v a i l a b l e ascorbate as o p p o s e d t o t h e s t o i c h i o m e t r i c d e p l e t i o n o b s e r v e d w i t h n i t r i t e alone. V a r i a t i o n s i n p H , i n a d d i t i o n to affecting t h e e q u i l i b r i a a m o n g t h e n i t r o s a t i n g agents a n d t h e concentrations of free a n d p r o t o n a t e d a m i n e s , also affect t h e r e l a t i v e c o n c e n t r a t i o n s of i o n i z e d ( a s c o r b a t e ) a n d n o n i o n i z e d forms of a s c o r b i c a c i d . T h e reactions o f a s c o r b i c

acid/ascorbate

w i t h e a c h of t h e n i t r o s a t i n g reagents are therefore also p H - d e p e n d e n t , as i l l u s t r a t e d i n F i g u r e 3 (16). Computer

Modeling

T h e observations above, t a k e n together, suggest t h a t t h e reactions among amines, nitrite, a n d ascorbic a c i d under physiological conditions w o u l d b e e x p e c t e d to b e e x t r e m e l y c o m p l e x a n d t h a t k i n e t i c studies might be experimentally intractible even i n vitro.

A s u m m a r y of t h e

e q u i l i b r i a a n d reactions that m i g h t o c c u r i n a n a n a e r o b i c m o d e l system is s h o w n i n S c h e m e 4. T h e q u e s t i o n " H o w does a s c o r b i c a c i d affect


576

ASCORBIC

ACID

2-nitrosylascorbic acid


OH

ONO

0'

CHOH I CH OH

H 0 2

2

semiquinone 2

ascorbic a c i d

dehydroascorbic acid Scheme 3.

the rate of a m i n e or a m i d e n i t r o s a t i o n ? " does not h a v e a c l e a r l y s i m p l e answer. O u r c u r r e n t a p p r o a c h to the c o m p l e x i t y of this p r o b l e m has b e e n to d e v e l o p a c o m p u t e r m o d e l t h a t c a n , i n p r i n c i p l e , p r o v i d e g u i d e l i n e s for e x p e r i m e n t a l designs a n d i n s i g h t i n t o p r o p e r t i e s of the system t h a t m a y b e e x p e r i m e n t a l l y i m p r a c t i c a l or inaccessible

(29).

T h e rate e q u a t i o n f o r the f o r m a t i o n of a n i t r o s a m i n e f r o m a g i v e n a m i n e is set u p as i n E q u a t i o n 1. M a k i n g steady state a s s u m p t i o n s f o r d[R NNO] 2

dt

— fc [ R N H ] [ N 0 ] + fc 4

2

2

3

7

[B*NH][NO ] +

(1)

nitrous a n h y d r i d e a n d n i t r o s o n i u m i o n a l l o w s t h e expression of the a b o v e e q u a t i o n i n terms of the concentrations of v a r i o u s reagents a n d the rate a n d e q u i l i b r i u m constants i n S c h e m e 4. T h e rate constants or e q u i l i b r i u m constants f o r most of the i n d i v i d u a l steps i n S c h e m e 4 are a v a i l a b l e f r o m


KIM

ET

AL.

Ascorbic Acid ir "Nitrosation of Dialkyl Amines

577


24.

Scheme 4.

Reaction scheme for nitrosation in the presence of ascorbic acid.



578

ASCORBIC

ACID

PH Figure 3. Effect of pH on the reactions of ascorbic acid and ascorbate anion with various nitrosating species. (Reproduced, with permission, from Ref. 16.)

the l i t e r a t u r e (1,16,18,30-34).

A r b i t r a r y i n i t i a l c o n c e n t r a t i o n s of t h e

v a r i o u s reagents c a n t h e n b e e n t e r e d i n t o the c o m p u t e r a n d i n i t i a l rates u n d e r t h a t set of c o n d i t i o n s w i l l b e c a l c u l a t e d a n d p r i n t e d out. S i n c e a l l of t h e i n t e r a c t i o n s a m o n g the c o m p o n e n t s are c o n s i d e r e d , a n y p e r t u r b a t i o n of one b y t h e other w i l l a u t o m a t i c a l l y be i n c l u d e d . I f t h e p H is c h a n g e d , for e x a m p l e , t h e n the a m i n e / a m m o n i u m - i o n a n d a s c o r b i c a c i d / ascorbate c o n c e n t r a t i o n s w i l l b e a p p r o p r i a t e l y a d j u s t e d . F o r s i m p l e n i t r o s a t i o n reactions (i.e., [ascorbic a c i d ] = 0 )

there is

good quantitative agreement between calculated a n d observed

initial

rates as s h o w n for m o r p h o l i n e - » N - n i t r o s o m o r p h o l i n e i n F i g u r e 4. W h e n a s c o r b i c a c i d / a s c o r b a t e is a d d e d to t h e system, t h e g e n e r a l b e h a v i o r of t h e c a l c u l a t e d i n i t i a l rates is consistent w i t h t h a t i n t u i t i v e l y e x p e c t e d , t h a t is, t h e i n i t i a l rates are r e d u c e d w i t h i n c r e a s i n g a s c o r b i c a c i d , a n d the effect is p H d e p e n d e n t as s h o w n i n T a b l e I . T h e v e r s a t i l i t y of t h e c o m p u t e r c a n also b e seen i n F i g u r e 5 i n w h i c h c a l c u l a t e d p H profiles are p l o t t e d f o r different i n i t i a l c o n c e n t r a t i o n s of a s c o r b i c a c i d / ascorbate. A s e x p e c t e d , t h e greater t h e a s c o r b i c a c i d / a s c o r b a t e


concen-

KIM

ET

AL.

Ascorbic Acid ir Nitrosation of Dialkyl Amines

579


24.

Figure 5. Initial rate profiles for the nitrosation of morpholine in the presence of various concentrations of ascorbic acid, 10 m M morpholine, 10 mM nitrite, 0°C: a, [Asc] = 0; b, [Asc] = 0.01 m M ; c, [Asc] = 0.1 mM.


580

ASCORBIC

Table I.

[Asc]/[Nitrite]

2 3 4 5


8

99%

The Amount of Ascorbic A c i d Required for Reduction in Initial Rate* pH

ACID

2.9 0.33 0.05 0.02

System: lOmM morpholine, lOmAf nitrite, 0°C.

t r a t i o n , the l o w e r t h e i n i t i a l rate of n i t r o s a t i o n . A d d i t i o n a l l y , h o w e v e r , the m a x i m u m i n i t i a l rate shifts c o n c u r r e n t l y to l o w e r p H s . T h i s b e h a v i o r , p r e v i o u s l y u n r e p o r t e d , p r o b a b l y represents the d e c r e a s i n g c o n c e n t r a t i o n of ascorbate a n i o n r e l a t i v e to the less a c t i v e a s c o r b i c a c i d . Q u a n t i t a t i v e agreement b e t w e e n l i t e r a t u r e values ( 2 4 ) for n i t r o s a t i o n rates of m o r p h o l i n e i n the presence of a s c o r b i c a c i d , a n d those c a l c u l a t e d b y t h e c o m p u t e r m o d e l , are p o o r . T h e c a l c u l a t e d i n i t i a l rates are l o w e r t h a n the l i t e r a t u r e i n i t i a l rates, e v e n f o r a p r e s u m a b l y degassed

system

( F i g u r e 6 ) . R e c e n t experiments i n o u r laboratories s h o w that nitrosations i n the presence

of a s c o r b i c

a c i d are i n d e e d

( S c h e m e s 2, 3, a n d

4)

sensitive to o x y g e n ; that is, the d i s c r e p a n c i e s b e w e e n the e a r l i e r o b s e r v a tions ( 2 4 ) a n d the c a l c u l a t e d i n i t i a l rates m a y be b e c a u s e of i n c o m p l e t e d e g a s s i n g of the r e a c t i o n m i x t u r e s . W h e n m o r p h o l i n e is n i t r o s a t e d at p H 4 w i t h a d d e d ascorbic a c i d , the p r o d u c t i o n of N - n i t r o s o m o r p h o l i n e o v e r a 2-h p e r i o d is d r a m a t i c a l l y a l t e r e d b y t h e a m o u n t of o x y g e n present (Figure 7).

W h e n oxygen

is r i g o r o u s l y e x c l u d e d , the o b s e r v e d

and

c a l c u l a t e d i n i t i a l rates are i n g o o d agreement as s h o w n i n T a b l e I I . I n s u m m a r y , t h e g e n e r a l c o n c e p t , t h a t ascorbic a c i d c a n i n h i b i t or p r e v e n t the n i t r o s a t i o n of a m i n e s , is essentially t r u e . T h e specific effects, h o w e v e r , w h i c h c a n be e x p e c t e d i n a g i v e n system, d e p e n d o n a c o m p l e x set of interactions a m o n g p H , the n a t u r e of the a m i n e , t h e a m o u n t of

Table II.

Initial Reaction Rate of iV-Nitrosomorpholine Formation in the Presence of Ascorbic A c i d at p H 4 Initial Reaction Rate

[Asc]

Measured

0

1.3 X IO" 2.0 X 1 0 3.0 X 1 0 "

— 2.4 X 1 0 " (1.4-5.5) X 10"

8

1 1

3mM

(M/s) Calculated*

11

11

11

e

11

System: lOmM morpholine, lOmM N a N 0 in pH at 0°C, kept under N throughout the reaction. &4 measured in this work was used for the calculation. 95% confidence interval. a

2

6

0


2


24.

KIM E T AL.

0.2

Ascorbic Acid 6- Nitrosation of Dialkyl Amines

0.4

0.6 0.8 [Asc] / [Nitrite]

581

1.0

Figure 6. Effect of oxygen on the initial rates of nitrosation of morpholine in the presence of ascorbic acid, 10 m M morpholine, 10 m M nitrite, pH 4: a, air, 25°C; b, N bubbling, 2 5 ° C ; c, calculated anaerobic, 0°C. (Reproduced, with permission, from Ref. 24.) 2

o x y g e n present, a n d the presence or absence of catalysts. A l t h o u g h there has b e e n b o t h e x p e r i m e n t a l a n d t h e o r e t i c a l progress i n this area, there is s t i l l a n i n c o m p l e t e u n d e r s t a n d i n g of w h a t m i g h t a c t u a l l y be a n t i c i p a t e d for the effects of a s c o r b i c a c i d o n h u m a n i n v i v o n i t r o s a t i o n reactions.

Applications of Ascorbic Acid A s c o r b i c a c i d has b e e n s h o w n to i n h i b i t the f o r m a t i o n of IV-nitroso compounds both i n vitro and i n vivo.

A l t h o u g h a detailed literature

survey i n this area is b e y o n d the scope of this c h a p t e r , w e h a v e a set of

b r i e f descriptions

of

a g r o u p of representative

compiled

publications.

S o m e of these h a v e b e e n r e v i e w e d i n earlier articles ( 3 5 , 5 0 ) . F o r c o n v e n i e n c e w e have d i v i d e d the studies into those t h a t evaluate q u a n t i t a t i v e effects, t h a t is, i n v i t r o ( T a b l e

I I I ) , a n d those i n w h i c h

i n h i b i t i o n of n i t r o s a t i o n is i n f e r r e d f r o m the absence of a n e x p e c t e d t o x i c effect i n i n t a c t a n i m a l s ( T a b l e I V ) .

It is r e m a r k a b l e that ascorbic

is effective i n systems as different as b a c o n fat a n d gastric juice.


acid

582

ASCORBIC

Table III. Inhibition of Nitrosation Ascorbic A c i d In V i t r o Amine or Amide

—

by

Effect

Refer en

k i n e t i c s of r e a c t i o n of n i t r i t e w i t h ascorbate

(16)

b l o c k i n g of N - m e t h y l a n i l i n e n o t v e r y effective c o m p a r e d w i t h stronger bases a n d m e t h y l u r e a

(17)

Morpholine

b l o c k i n g effective i n m o d e l s y s t e m

(36)

Dimethylamine

both ascorbate a n d e r y t h o r b a t e were effective i n f r a n k f u r t e r s

(22)

Dimethylamine

b l o c k i n g effective i n food a n d m o d e l systems

(S7)

Piperazine

b l o c k i n g effective i n gastric j u i c e

(88)

Morpholine

m e c h a n i s m of b l o c k i n g i n presence of o x y g e n

(24)

S e c o n d a r y amines, methylurea


ACID

Dimethylamine

b l o c k i n g effective i n m o d e l food s y s tems, b l o c k i n g effective i n c u r i n g brines a n d m e a t slices

(39,40

b l o c k i n g effective o n l y w i t h large excess of ascorbate i n homogenized potato

(4D

f o r m a t i o n of n i t r o s o p y r r o l i d i n e i n bacon inhibited, ascorbyl palmitate more effective t h a n ascorbate

(42)

Piperazine, aminophenazone

b l o c k i n g n i t r o s a t i o n i n h u m a n gastric juice

(48)

Pyrrolidine

blocking i n commercial bacon

(44)

Pyrrolidine

blocking i n protein-based model system

(4B)

Dimethylamine

b l o c k i n g i n seafood

(46)

Methapyrilene

b l o c k i n g n i t r o s a t i o n under s i m u l a t e d gastric conditions

(47)

mechanism

(48)

i n h i b i t i n g f o r m a t i o n of a m u t a g e n i n n i t r o s a t e d fish

(49)

review

(50)

review

(35)

Methylurea

Proline

— — — —



24.

K I M ET AL.

Ascorbic Acid i? Nitrosation of Dialkyl Amines

20

60 80 100 time, min

40

583

120

Figure 7. Time course of nitrosomorpholine formation. The reaction system was kept under N unless stated otherwise, 10 m M morpholine, 10 m M nitrite, pH 4, 0°C, varying oxygen: a, without ascorbic acid; b, [Asc] = 1 m M ; c,d, [Asc] = 3 m M , degassing of the solution was done by bubbling N through pasteur pipet for 5 min; d,f, exposed to air 30 min after the reaction started; e,f, [Asc] = 3 m M , degassing of the solution was done by bubbling N through gas dispersion tube for 1 h. 2

2

2

Table I V . Inhibition of Nitrosation by Ascorbic A c i d In V i v o Amine or Amide

Effect

References

Aminopyrine

inhibits hepatotoxicity

{21)

Aminopyrine


{20,51)

Dimethylamine


{52)

Ethylurea

i n h i b i t s t r a n s p l a c e n t a l carcinogenesis

{53)

Morpholine, piperazine, methylurea

ascorbate i n h i b i t s l u n g a d e n o m a f o r m a t i o n b y b l o c k i n g n i t r o s a t i o n , some p a r a d o x i c a l effects w h e n ascorbate given w i t h preformed carcinogen

{54)

Aminopyrine

i n h i b i t s carcinogenesis

{55)

Morpholine

inhibits nitrosomorpholine formation a n d l i v e r t u m o r s , enhances fores t o m a c h carcinogenesis

(56)

inhibits nitrosation

{57)

Chlordiazepoxide


584

ASCORBIC ACID


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Effects of Ascorbic Acid on the Nitrosation of Dialkyl Amines

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