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26 The Radiation Chemistry of Anhydrous Solid State Glycine, Alanine, and Downloaded by UNIV OF TEXAS AT DALLAS on July 11, 2016 | http://pubs.acs.org Publication Date: January 1, 1968 | doi: 10.1021/ba-1968-0081.ch026
Glycine Salts 1
W. CARL GOTTSCHALL, JR. and BERT M. TOLBERT University of Colorado, Boulder, Colo. The radiation chemistry of glycine and alanine as well as the alkali metal salts of glycine has been investigated in the anhydrous solid state. Results of cesium-137 gamma irradiation indicate CO is the chief gaseous product with larger amounts of NH being released upon dissolution of the samples. Similarity of yields indicates little difference in decomposition mechanism and good agreement with the general mechanism postulated by Tolbert. G(CO ) values were glycine, 1.02; alanine, 0.89; sodium glycinate, 0.43; potassium glycinate, 0.54; rubidium glycinate, 0.91. Other products and their G values were for glycine G(H ) = 0.1; G(NH ) = 4.3, G(CH NH ) = 1; G ( - M ) = 6 and for alanine G(H ) = 0.5; G(NH ) = 3.3; G(CH CH NH ) = 2; G ( - M ) = 5. 2
3
2
2
3
3
2
2
3
3
2
2
TkyTuch w o r k has b e e n d o n e o n t h e i r r a d i a t i o n of a m i n o acids i n s o l u t i o n ™*
(8, 9, 10, 11, 16, 21) b u t little i n f o r m a t i o n c a n b e f o u n d o n s o l i d
state w o r k (1, 18)
despite the a d v a n t a g e
of a v o i d i n g i n d i r e c t effects.
E P R investigations of i r r a d i a t e d g l y c i n e (4, 6, 12, 22) a n d alanine
(17)
offer i n d e p e n d e n t results of a p h y s i c a l nature w h i c h correlate w i t h the c h e m i c a l results of this i n v e s t i g a t i o n .
T h e qualitative a n d quantitative
effects of a l k a l i m e t a l cations i n the c r y s t a l l i n e m a t r i x also are h e l p f u l i n d e t e r m i n i n g the m e c h a n i s m of i r r a d i a t i o n p r o d u c e d d e c o m p o s i t i o n . Experimental M a t e r i a l s . T h e best grade c o m m e r c i a l g l y c i n e a n d alanine f r o m t h e California Corporation for Biochemical Research were recrystallized 1
Present address: University of Denver, Denver, Colo. 80210. 374 Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
26.
GOTTSCHALL, JR. AND TOLBERT
Glycine, Alanine, and Glycine Salts 375
t w i c e — f i r s t f r o m g l a c i a l acetic a c i d a n d t h e n f r o m e t h y l a l c o h o l w a t e r . A n a l i q u o t of l a b e l e d a m i n o a c i d - l - C f r o m N u c l e a r C h i c a g o C o r p o r a t i o n ( c a l c u l a t e d to y i e l d a m i n o a c i d of specific a c t i v i t y s u c h that the a c i d or salts f o r m e d f r o m i t w o u l d h a v e a specific a c t i v i t y of a p p r o x i m a t e l y o n e t e n t h of a m i c r o c u r i e p e r m i l l i g r a m ) w a s p i p e t t e d i n t o t h e s o l u t i o n i m m e d i a t e l y p r i o r to the p r e p a r a t i o n s . T h e a m i n o acids w e r e t h e n p r e c i p i t a t e d or salts p r e p a r e d b y a d d i n g the a p p r o p r i a t e a l k a l i m e t a l h y d r o x i d e or carbonate a n d subsequent c r y s t a l l i z a t i o n . C r y s t a l s o b t a i n e d w e r e r e c r y s t a l l i z e d a n d d r i e d i n a v a c u u m desiccator over M g C 1 0 . Specific a c t i v i t y of each c o m p o u n d w a s c h e c k e d b y c o m b u s t i o n i n a m o d i f i e d P r e g l f u r n a c e f o l l o w e d b y assay of the C 0 with a Cary V i b r a t i n g Reed Electrometer. S o d i u m a n d p o t a s s i u m h y d r o x i d e s w e r e B a k e r A n a l y t i c a l Reagent. R u b i d i u m carbonate w a s F i s h e r Scientific C o m p a n y " p u r i f i e d . " Apparatus. T h e i r r a d i a t i o n s w e r e p e r f o r m e d i n the U n i v e r s i t y of C o l o r a d o cesium-137 g a m m a source at 2 2 ° C . T h e source w a s c a l i b r a t e d at 2.78 ± 0.02 X 1 0 e.v./gm./hr. b y a F r i c k e dosimeter at 2 2 ° C . u s i n g G ( F e ) = 15.6. M a s s Spectra w e r e r u n o n a C o n s o l i d a t e d E l e c t r o d y n a m i c s C o r p o r a t i o n M a s s Sepectrometer T y p e 21-103C to d e t e r m i n e H y i e l d s as w e l l as y i e l d s f r o m " d r y " analyses f o r c o m p a r i s o n w i t h y i e l d s o b t a i n e d after d i s s o l u t i o n of the i r r a d i a t e d c o m p o u n d . S a m p l e tubes w e r e b r o k e n d i r e c t l y i n the gas s a m p l i n g system to y i e l d " d r y " analyses results. 1 4
4
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1 4
2
1 9
3 +
2
T h e gas c h r o m a t o g r a p h also u s e d to d e t e r m i n e " d r y " analysis y i e l d s was P e r k i n E l m e r F r a c t o m e t e r M o d e l 154. A s i m p l e d e v i c e w a s c o n structed of T y g o n t u b i n g a n d brass connectors to p e r m i t breakage a g a i n of the i r r a d i a t e d capillaries d i r e c t l y i n t h e carrier stream. Procedure. C a p i l l a r y t u b i n g of 2 ± k m m . i n t e r n a l d i a m e t e r a n d a thickness of 200 ± 100 m i c r o m e t e r s w a s d r a w n o u t of b o r o s i l i c a t e glass t u b i n g . Segments of 10 ± 2 c m . l e n g t h w e r e sealed at one e n d a n d l a b e l e d . F u n n e l s of s i m i l a r t u b i n g w e r e u s e d to l o a d 15 ± 10 m g . of sample into each t u b e ; i n the case of h y g r o s c o p i c salts l o a d i n g w a s per f o r m e d i n a d r y b o x . Samples r e p o r t e d i n this p a p e r w e r e a l l e v a c u a t e d to 1 0 - 2 0 m i c r o n s of m e r c u r y b e f o r e b e i n g sealed. Samples sealed i n a i r w e r e o b s e r v e d to give h i g h e r d e c o m p o s i t i o n values. x
Samples w e r e i r r a d i a t e d at least i n d u p l i c a t e to t o t a l doses of 20, 40, 80, a n d 160 megarads. H o p e f u l l y to i m p r o v e consistency of data, a l l samples w e r e a l l o w e d to r e m a i n at least 2 days i n a —15 ° C . freezer f o r d i s s i p a t i o n of short l i v e d free r a d i c a l s b e f o r e analyses w e r e c o n d u c t e d . N o d a t a w a s o b t a i n e d o n r a d i c a l content at t i m e of analysis. T h e apparatus u s e d is s h o w n i n F i g u r e 1. T w e n t y m l . of IN N a O H was p l a c e d i n crusher t u b e " a " a n d t h e n a sample tube. T h e stopper w a s put i n p l a c e a n d the b u b b l e r t u b e " b " l o w e r e d to the b o t t o m of the crusher tube. N i t r o g e n gas w a s u s e d to p u r g e the s o l u t i o n a n d t h e n t h e sample t u b e w a s c r u s h e d u n d e r the N a O H w i t h c r u s h i n g r o d " c . " O x y g e n c o n t a i n i n g 5 % C 0 w a s s w e p t t h r o u g h the s o l u t i o n f o r several m i n u t e s and then into a n e v a c u a t e d i o n i z a t i o n c h a m b e r . T e n m l . of 3 5 % per c h l o r i c a c i d w a s a d d e d d r o p w i s e to the a l k a l i n e s o l u t i o n f r o m t h e d r o p p i n g f u n n e l "e." C 0 released w a s swept a l o n g w i t h t h e 0 - C 0 gas i n t o the i o n i z a t i o n c h a m b e r . A f t e r the c h a m b e r r e a c h e d a t m o s p h e r i c 2
1 4
2
2
Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
2
376
RADIATION CHEMISTRY
1
pressure, the v a l v e w a s c l o s e d a n d the voltage generated i n the i o n i z a t i o n chamber was measured w i t h a C a r y V i b r a t i n g Reed Electrometer (14). T h e C o n w a y m i c r o d i f f u s i o n m e t h o d (2) w a s e m p l o y e d to d e t e r m i n e the amounts of a m m o n i a a n d amines r e s u l t i n g f r o m i r r a d i a t i o n of d u p l i cate samples a n d subsequent d i s s o l u t i o n i n 0 . 0 0 6 N H S 0 . T h e R u s s e l l p r o c e d u r e (15) f o r a q u a n t i t a t i v e c o l o r i m e t r i c d e t e r m i n a t i o n w a s e m p l o y e d w i t h the readings m a d e at 628 m/x o n a B e c k m a n Spectro photometer.
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2
To Sweep Gas
4
*- To aspirator
To ionization chamber
Figure
1.
Generation apparatus analyses
for C0
2
"wet"
(a)—thickwall crushing tube, (b)—bubbler tube, (c) —crushing rod, (d,f)—3-way valve, (e)—dropping funnel, (g)—gas flow indicator apparatus, and ( h ) — pressure regulator H i g h v o l t a g e electrophoresis at 50 v o l t s / c m . has b e e n s h o w n to separate amines a n d a m m o n i a f r o m their parent a m i n o a c i d (13) a n d was e m p l o y e d to p e r m i t c o l o r i m e t r i c d e t e r m i n a t i o n of a m m o n i a a n d the amines. T h e excess of a m m o n i a o b s e r v e d i n every case c o u p l e d w i t h factors of 10 a n d 100 h i g h e r sensitivity f o r a m m o n i a t h a n m e t h y l a m i n e or e t h y l a m i n e r e s p e c t i v e l y i n the p r o c e d u r e indicates that t h e m i c r o d i f f u s i o n results G ( N H + a m i n e s ) to a g o o d a p p r o x i m a t i o n are also the G ( N H ) values. G ( — M ) values w e r e d e t e r m i n e d b y isotopic d i l u t i o n u s i n g a m i n o acids r e c r y s t a l l i z e d as above, as w e l l as w i t h a n a u t o m a t i c a m i n o a c i d analyzer. ; i
3
Results F i g u r e 2 shows the m o l e % of the o r i g i n a l c o m p o u n d f o r C 0 a n d 2
NH
3
p r o d u c e d f r o m d u p l i c a t e radiolyses of g l y c i n e as a f u n c t i o n of dose.
Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
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26.
GOTTSCHALL, JR. AND TOLBERT
Figure 2.
377
Glycine, Alanine, and Glycine Salts
Yields of C0 irradiated 2
and NH glycine
3
for i n vacuo
F i g u r e 3 is the same p l o t for alanine. T h e curves are a l l i n i t i a l l y l i n e a r and
the G values w e r e c a l c u l a t e d f r o m this i n i t i a l l i n e a r p o r t i o n . L o w
d e v i a t i o n s o n the a m m o n i a curves at the highest a b s o r b e d dose
may
reflect h i g h d e c o m p o s i t i o n of o r i g i n a l a m i n o a c i d .
with
A m i n o acids
h i g h e r specific activities w e r e u s e d to d e t e r m i n e G ( C 0 ) 2
at l o w e r ab
s o r b e d doses. T h e s e values are s i g n i f i c a n t l y l o w e r as s h o w n i n F i g u r e 4. T h e p r o b l e m of i m p u r i t y i n t r o d u c e d b y the r a d i a t i o n d e c o m p o s i t i o n of the o r i g i n a l m a t e r i a l a n d its effect o n m e a s u r e d G values confronts a l l w o r k e r s i n this area. F o r consistency a n d since these values h a v e a m u c h m o r e r e l i a b l e a n a l y t i c a l basis, the h i g h dose values w i l l b e u s e d t h r o u g h out.
T h e results of interest are the r e l a t i v e G values i n any case since
absolute values are a c k n o w l e d g e d to d e p e n d o n dose. It s h o u l d b e stressed that the G ( H ) values i n this p a p e r arise f r o m 2
"dry"
analyses of the gases released f r o m the s o l i d w h i l e the other repre
sent " w e t " analyses of p r o d u c t released u p o n d i s s o l u t i o n . " D r y " results gave C 0
2
i n the largest y i e l d t h o u g h this c o r r e s p o n d e d to a G ( C 0 )
Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
2
of
378
RADIATION CHEMISTRY
1
o n l y 0.2 ±
0.1. W h e n the mass spectral " d r y " d a t a are n o r m a l i z e d to
G(C0 )
1 the G ( H ) v a l u e agrees a p p r o x i m a t e l y w i t h Bregers a n d
=
2
2
C O , C H , H 0 are also i n d i c a t e d as i n R e f e r e n c e 1 b u t i n less t h a n 1 0 % 4
of the C 0
2
2
yield.
T h e N H results f r o m this " d r y " study, h o w e v e r , are 3
c o n s i d e r a b l y l o w e r w i t h G ( N H ) ^ 0.01. D e s p i t e t h e large uncertainties 3
it c a n b e c o n c l u d e d that extensive t r a p p i n g of gaseous p r o d u c t s a n d or unstable p r o d u c t s i n c h e m i c a l forms w h i c h c o u l d i n c l u d e r a d i c a l s , i m i n e s , H C O - f , etc., exist.
T h e s e p r o d u c t s s u b s e q u e n t l y react w h e n d i s s o l v e d
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i n w a t e r , to give the gaseous p r o d u c t s . T h e m a g n i t u d e of t h e q u a n t i t a t i v e uncertainties
p r e c l u d e s a r a t i o n a l c o m p a r i s o n of a n y significance
b a s e d o n these n u m b e r s a n d h e n c e t h e y w i l l n o t b e discussed. " D r y " h y d r o g e n y i e l d s w e r e , h o w e v e r , assumed to b e q u a n t i t a t i v e . ALANINE
3.0
X *NH
3
o =C0
2
X
2.5
/
^
x
2.0
1.5
1.0 -
0.5
-
/ x/ /X
J1 2
Figure 3.
x
1I 4 ENERGY
I 6 INPUT, -21 ev/gm, x 10
Yields of C0 irradiated
2
i L 8
and NH for i n vacuo alanine 3
Q u a n t i t a t i v e results f o r acetic a n d p r o p i o n i c acids a n d the a p p r o p r i a t e a keto acids w e r e n o t o b t a i n e d i n this study, b u t their presence w a s q u a l i t a t i v e l y i n d i c a t e d a n d m a t e r i a l b a l a n c e w a s u s e d to a p p r o x i m a t e their G v a l u e s u m as 5 f o r g l y c i n e a n d 4 f o r alanine.
Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
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26.
GOTTSCHALL, JR. AND TOLBERT
Glycine, Alanine,
Yields of C0 for i n vacuo glycine and alanine
Figure 4.
2
and Glycine Salts 379
irradiated
X—Alanine, G(COz) — 0.63 O—Glycine, G(CQ ) = 0.75 2
Table I.
Decomposition Products and G Values for In Vacuo Irradiated Glycine and Alanine Glycine Solid n
2
2
2
Aqueous a
y G(-M) G(H ) G(C0 ) G(NH,) G(RNH ) G ( S acids)
Alanine
-6 0.1 1.02 4.3 1 5
—
—
0.3 1 0.2
2.0 0.90 4.0 0.19 3.6
— —
e
a
Solid
Aqueous
d
— — —
1.7 0.24
—
-5 0.5 0.89 3.3 2 4 r
— l.i 0.59 4.5 0.17 3.0
This work. Ref. 1 normalized to G ( C 0 ) = 1. Breger reported values as Volume% with C0 = 55.8%. Ref. 8 Ref. 10. Ref. 16. Numbers deduced from material balance requirement. a
&
2
c
d
6
1
Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
2
380
RADIATION CHEMISTRY
1
A c o m p i l a t i o n of t h e results f r o m this s t u d y f o r the various p r o d u c t s of g l y c i n e a n d alanine g a m m a i r r a d i a t e d in vacuo are listed i n T a b l e I, a l o n g w i t h c o r r e s p o n d i n g a i r r a d i a t e d g l y c i n e values a n d aqueous solu t i o n y i e l d s as i n d i c a t e d . It is w o r t h n o t i n g that t h e a i r r a d i a t e d g l y c i n e values t a b u l a t e d result f r o m c o n v e r s i o n of Bregers r e p o r t e d v o l u m e % values a n d n o r m a l i z a t i o n to a G ( C 0 ) 2
v a l u e of 1. T h i s data of course
does n o t i n c l u d e gaseous p r o d u c t s t r a p p e d , a d s o r b e d , or r e s u l t i n g f r o m
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d i s s o l u t i o n of other species.
2.1
2
Figure 5.
4 6 ENERGY INPUT, ety/gm, x 10
8
Yields of CO for i n vacuo irradiated glycine salts £
• —rubidium glycinate O—potassium glycinate A—sodium glycinate
F i g u r e V shows t h e amounts of C 0 p r o d u c e d f r o m the a l k a l i m e t a l salts as a f u n c t i o n of dose. G ( C 0 ) values o b t a i n e d f o r these g l y c i n e salts a n d c o r r e c t e d f o r electron density are s o d i u m glycinate, 0.43; potas s i u m glycinate, 0.54; a n d r u b i d i u m g l y c i n a t e , 0.91. 2
2
Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
26.
GOTTSCHALL, JR. AND TOLBERT
381
Glycine, Alanine, and Glycine Salts
Discussion A q u e o u s w o r k (8, 9,10,
has p e r m i t t e d d e d u c t i o n of p r i n
11, 16, 21)
c i p a l s t o i c h i o m e t r i c relationships as w e l l as a satisfactory r e a c t i o n q u e n c e for in vacuo
i r r a d i a t e d a m i n o acids.
se
C o m p a r i s o n of the results
f r o m aqueous a n d s o l i d state r a d i a t i o n c h e m i s t r y is not a s t r a i g h t f o r w a r d matter to be a n t i c i p a t e d a priori, h o w e v e r , since i n the aqueous w o r k o n l y a m i n e a n d c a r b o n d i o x i d e w e r e p o s t u l a t e d to result f r o m d i r e c t a c t i o n whereas N H , H , acids, a n d a d d i t i o n a l C 0 3
2
w e r e p r o d u c t s of secondary
2
reactions i n v o l v i n g aqueous species H ° , O H ° , a n d H 0 .
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2
It m i g h t b e
2
p o i n t e d out that effects o b s e r v e d i n this s t u d y m u s t represent a c o m b i n a t i o n of r a d i c a l degradations a n d p u r e d i r e c t r a d i a t i o n c h e m i s t r y effects. M o s t s o l i d a m i n o acids saturate w i t h free r a d i c a l s at doses of ^ (7)
10
whereas the results d i s c u s s e d result f r o m doses of 1 0 - 1 0 7
Garrison (3)
8
6
rads rads.
m o d i f i e d M a x w e l l ' s earlier scheme to i n c l u d e reactions of
the h y d r a t e d electron; the reactions of a n electron also c a n take p l a c e i n the s o l i d state. A s is seen f r o m T a b l e I, g a m m a y i e l d s of N H i n the 3
s o l i d state are i n f a i r agreement w i t h aqueous values. A s earlier n o t e d , the s o l i d state N H
3
values result f r o m " w e t " analyses a n d h e n c e one
c o n c l u d e s that regardless of p a t h w a y a n d p o s s i b l y d i f f e r i n g w a t e r u n s t a b l e intermediates the final d e c o m p o s i t i o n results are s u r p r i s i n g l y close.
Pre
cautions w e r e not t a k e n to e x c l u d e o x y g e n f r o m the " w e t " analyses a n d the d a t a of M a x w e l l et al. o b t a i n e d b y i r r a d i a t i o n of o x y g e n saturated aqueous solutions (10)
gave a G ( N H ) of 4.3 also. T h e C 0 3
y i e l d s are
2
seen to be s i m i l a r t h o u g h a m i n e y i e l d s differ significantly. Since a m i n e y i e l d s in aquo are extremely s m a l l , the r e l a t i v e i m p o r t a n c e of p r i m a r y effects, reflected b y this y i e l d , vs. secondary effects is o b v i o u s . T h e f o l l o w i n g m e c h a n i s t i c scheme is therefore p r o p o s e d b a s e d u p o n the ideas suggested b y G a r r i s o n ( 3 ) , Tolbert (19)
modified and supplemented
by
to e x p l a i n s o l i d state c o m p l e x i t i e s a n d consistent w i t h the
concepts i n t r o d u c e d b y S i n c l a i r a n d H a n n a RCHN H C0 — +
3
2
_
M M
M
M
(17).
— > ( R C H N H C 0 ) ° + e~ +
(I)
R C N H C 0 - + H°
(2)
+
—
+
>
3
3
2
2
fast (RCHN H C0 ) +
3
2
-> R C H N H
0 +
+
e~ + R C H N H C 0 - ~> N H 3
2
3
2
+ C0
(2)
2
+ RCHCOo"
3
H° + R C H N H C 0 - -> N H
3
4
+
(3a)
+ RCHC0 "
(3b)
2
-> H + R C N H C 0 " 2
RCHN H +
3
+
3
2
+ RCHN H C0 " -» RCH N H 3
2
2
+
3
+ RCN H C0 " +
3
2
Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
(4)
382
RADIATION CHEMISTRY
R C H C 0 - + R C H N H C 0 " -> R C H C 0 ' + R C N H C 0 " +
2
8
2
2
+
2
3
2
1
(5)
plus r a d i c a l c o m b i n a t i o n a n d d i s p r o p o r t i o n a t i o n reactions. Without
i n c l u s i o n of r a d i c a l c o m b i n a t i o n
a n d disproportionation
reactions m a t e r i a l b a l a n c e c a n n o t b e e m p l o y e d to v e r i f y or p r e d i c t G values.
Occurrence
of r a d i c a l reactions
to regenerate a m i n o acids is
c l e a r l y i m p l i e d , f o r example, since G ( — M ) d e t e r m i n e d =
—6 f o r g l y c i n e
w h i l e s u m m i n g a p p r o p r i a t e p r e c e d i n g reactions w o u l d l e a d to a v a l u e of Downloaded by UNIV OF TEXAS AT DALLAS on July 11, 2016 | http://pubs.acs.org Publication Date: January 1, 1968 | doi: 10.1021/ba-1968-0081.ch026
— 14.1.
A v a i l a b l e d a t a u n f o r t u n a t e l y cannot present a c o m p l e t e p i c t u r e
b u t this g o a l must a w a i t f u t u r e results. It has come to the authors' attention that d a t a c i t e d b y M a x w e l l i n d i c a t e that R e a c t i o n 5 does n o t o c c u r i n aqueous s o l u t i o n . D i s
(11)
p r o p o r t i o n a t i o n reactions NHXHCOOH + CH COOH -» NHCHCOOH + CH COOH
(6)
2 N H C H C O O H -> N H C H C O O H + N H C H C O O H
(7)
2
3
and 2
have b e e n
2
suggested
2
instead b u t these results m a y n o t d i s p r o v e t h e
p o s s i b i l i t y of R e a c t i o n 5 i n t h e s o l i d state. T h e results f o r the a l k a l i m e t a l salts f u r t h e r i n d i c a t e s i m i l a r i t y i n p r i n c i p a l d e c o m p o s i t i o n m e c h a n i s m s f o r these examples. of course d o n o t p r o v e the m e c h a n i s m .
T h e s e results
Note, however, the trend i n the
a l k a l i m e t a l salts t o w a r d greater d e c o m p o s i t i o n d e s c e n d i n g t h e p e r i o d i c column.
T h i s t r e n d corresponds to a m e t a l l i c i o n decrease i n electro
n e g a t i v i t y or charge density a n d suggests a c o r r e l a t i o n b e t w e e n r a d i a t i o n s t a b i l i t y a n d electron d e n s i t y o n t h e o x y g e n a t o m .
Such a correlation
a n d r e l a t i o n s h i p to t h e o r y of t h e p r i m a r y r a d i a t i o n event i n s o l i d state i r r a d i a t i o n s has b e e n treated i n a p r e v i o u s article ( 5 ) . T h e l o w e r G ( C 0 ) values at v e r y l o w r a d i a t i o n levels ( F i g u r e s 2, 3, 2
a n d 4 ) are difficult to e x p l a i n . D e c a r b o x y l a t i o n b y r a d i c a l - r a d i c a l reac tions suggested b y c o m p a r i s o n w i t h saturation of E P R signals is a possi bility.
R e c e n t w o r k b y T o l b e r t a n d K r i n k s (20)
on the decarboxylation
of p h e n y l a l a n i n e in vacuo a n d i n H S shows n o change i n G values a n d 2
does n o t i n d i c a t e s u c h a m e c h a n i s m . higher G ( C 0 ) 2
A n o t h e r possible e x p l a n a t i o n f o r
values at h i g h e r doses is r a d i a t i o n d e c a r b o x y l a t i o n of
i n t e r m e d i a t e species p r o d u c e d b y the r a d i a t i o n d e c o m p o s i t i o n process. Acknowledgments W . C a r l G o t t s c h a l l , Jr. w o u l d l i k e to a c k n o w l e d g e s u p p o r t f r o m a U n i v e r s i t y of C o l o r a d o F e l l o w s h i p , a D u P o n t T e a c h i n g F e l l o w s h i p , a n d a n N I H P r e d o c t o r a l F e l l o w s h i p i n successive years d u r i n g w h i c h t h e research w a s p e r f o r m e d .
Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
26.
GOTTSCHALL, JR. AND TOLBERT
Glycine, Alanine, and Glycine Salts 383
Downloaded by UNIV OF TEXAS AT DALLAS on July 11, 2016 | http://pubs.acs.org Publication Date: January 1, 1968 | doi: 10.1021/ba-1968-0081.ch026
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Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
