COMMUNICATIONS TO THE EDITOR
3 k=l
461
3
a4, k ’ d k , n =
dk, n
k=l
initial solution A,C in a clear manner. We choose dl, 1 = 1 for the reason just pointed out and get
= 1
because of the structure of (1). Under this condition, the matrix D becomes
1
D
= (0
0
D =
!
di, 2 - as, 3 - (al,3 - a3,3 - a1,1)d1,2 a13 - a33 - a12 a32
dl, 1 (1 - dl,1)a3,3!1,3 a3, 3 - a3, 2
+
- (1 - 4,1 ) a 3 .a32 ~ - a1,2 - ( a 3 , ~ - al, 2 as, 3 - a3.2 a l , 3 - a3,3 - al, 2
7
+ a1 , d d ~1 + a3,Z 2
Here dl, 1 and d l , 2 are free selectable parameters. The physical condition that the elements of the new solution A and c should be positive limits the two parameters to ranges the limits of which depend upon the
dl, 2 1 - 3.4948d1, 2 2.4948d1, 2
ca. 100 ev/3.6 ev (Le., -28), where 3.6 ev is the excitation energy of the 3 B ~state u of b e n ~ e n e . ~The only reasonable inference from the
Identification of a Specific Mode of Oxidation in the Radiolysis of the Purine Bases in
Oxygenated Aqueous Solution
Sir: The pyrimidine and purine moieties represent major sites of chemical degradation in the radiolysis of nucleic acids in aqueous solutions containing molecular oxygen. Radiation chemical studies of representative pyrimidines such as cytosine, uracil, and thymine in dilute aqueous solution have shown that OH radicals formed in the radiation decomposition of water add preferentially to the 5,6 carbon-carbon double bond to form the hydroxypyrimidyl r a d i ~ a l . ’ > ~In - ~oxygenated solution, this radical is scavenged by oxygen and in subsequent steps yields the 5,6 glycol as a radiolysis product. Reaction stoichiometries in the radiolysis of the purines in oxygenated solution remain to be established.2*6 Adenine has received the most attention and is reported by Scholes and Weiss1,6to yield ammonia with G(NH3) = 0.5 (molecule/100 ev) on radiolysis with y-rays in dilute aqueous solution; they suggest that such deamination arises as a consequence of OH addition to the central 5 6 double bond.’ ConlayE& and Ponnamperuma, Lemmon, and CalvinEb have isolated organic products from the same system and find 8-hydroxyadenine and 3,4,5-triaminopyrimidinederivatives are produced with G values of several tenths. The latter products provide evidence for OH attack a t the 7,8 position of the imidazole ring. Such reaction is in accord with Pullmans’ molecular orbital calculationsg which indicate that the T,8 bond of the purine nucleus has the highest mobile bond order. However, since the yield for OH production in the radiation decomposition of water corresponds to G O H = 2.4 for y-rays,l0 it follows that no conclusions regarding the major locus of reaction of OH with the purine
240r------
2ooi I60
s3 z4
8ot b
c \ 0.02 M I
0
I
1
I
1
40
20
Time, min. Figure 1. Yields of isomerization of cis-stilbene in benzene as functions of concentration and time of @Co y irradiation a t a dose rate of -1.2 X 10’8 ev ml-1 min-1.
present results is that in radiation-sensitized cis -.t trans isomerization of stilbene in benzene solution a chain mechanism is involved. Further, if the suggestion of an ionic chain is accepted, the earlier described method of calculation2 leads to a chain length of ca. 2000 on the basis of G(c+t) 210.
-
(4)
Cf.N. J. Turro, J.C h m . Educ., 43,13 (1966).
DEPARTMENT O F CHEMISTRY AND THE ROBERT R. HENTZ K. SHIMA RADIATION LABORATORY UNIVERBITY OF NOTRE DAME MILTONBURTON NOTREDAME,INDIANA46556 RECEIVED SEPTEMBER 20, 1966
The Journal of Physical Chemistry
(1) G. Scholes, J. F. Ward, and J. Weiss, J. MoZ. Biol., 2, 379 (1960). (2) G. Hems, Radiation Res., 13,777 (1960). (3) B. Ekert and R. hionier, Nature, 188,309 (1960). (4) R. Latarjet, B. Ekert, and P. Demerseman, Radiation Res. Suppl., 3,247 (1963). (5) (a) A. Kamal and W. 31. Garrison, Nature, 206, 1315 (1965); (b) J. Holian and W. &.IGarrison, . Radiation Res., 27, 257 (1966). (6) G. Scholes, Progr. Biophys., 13,59 (1963). (7) We use here the notation in which the carbon-carbon double bond of both the purine and pyrimidine nuclei is referred to as the 5,6 position. (8) (a) J. J. Conlay, Nature, 197,555 (1963); (b) G. Ponnamperuma, R. M. Lemmon, and SI. Calvin, Radiation Res., 18,540 (1963). (9) B. Pullman and A. Pullman, “Comparative Effects of Radiation,” M. Burton, et al., Ed., John Wiley and Sons, Inc., New York, N. Y . , 1960. (10) E. Hayon, Trans. Faraday SOC., 61,734 (1965).
