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REACTIONS OF ALANINE WITH REDUCING SPECIESFORMED IN WATERRADIOLYSIS
that under those conditions the dissociation is less than 50Yc.
Conductance of Anthracene2-,2Na+ Several samples of anthracene2-,2Na+ were prepared, and their conductances were investigated. Unfortunately, the scatter is too great to allow a reliable determination of A, or l/Ao2Kdi,,; however, the very low conductance of these solutions proves the low degree of dissociation which we estimate at about lo-’ M . Our findings agree again with the qualitative observations of Hoijtink, et aL2* Apparently, A2-,2Na+ are contact agglomerates whereas A’,Na+ may be, to a large extent, a solvent-separated ion pair. See in this
connection ref. 13. Discussion of the disproportionation of 2A- into A2A which resembles ours was published by Shaten~tein’~ in 1964. See also ref. 13.
+
Acknowledgment. The financial support of this study by the U. S. Army Research Office (Durham), Grant DA-ARO (D)-31-124-G52 1, Texaco, Inc. , and the National Science Foundation is gratefully acknowledged.
(13) R. C. Roberts and M. Sawarc, J. Am. Chem. SOC.,in press. (14) A. I. Shatenstein, E. S. Petrov, and M. I. Belusova, “Organic Reactivity,” Vol. 1, Tartu State University, Estonia, U.S.S.R., 1964, p. 191.
Reactions of Alanine with the Reducing Species Formed in Water Radiolysis’
by Boyd M. Weeks, Sibyl A. Cole, and Warren M, Garrison Lawrence Radiation Laboratory, University of California, Berkeley, California (Received June 10,1966)
A detailed study has been made of the effects of pH and of added scavengers on the reactions of alanine with the reducing species formed in water radiolysis. A principal reaction of the RNH3+ + hydrated electron (eaq-) leads to degradation of the N-C linkage, e.g., eaqR “3. The rate of removal of g,- by such reaction is strongly dependent on the ionic form of the a-amino acid; /?-alanine is relatively less reactive toward eaq- under all conditions of pH. A suggested reaction scheme accounts both qualitatively and quantitatively for the observed effects of pH on product yields from oxygen-free solutions of alanine under y rays.
+
+
The principal actions of ionizing radiations on solutes in dilute aqueous solution are initiated by the radiation-induced step2
HzO -m+
HzOz,Hz, OH, H, eaq- H+
(1)
Subsequent reactions of these oxidizing and reducing species with the simpler amino acids such’ as glycine and alanine in oxygen-free solutions lead to both oxidative and reductive deamination with formation of the corresponding keto acid and fatty acid as major degradation products. The relative and absolute yields of both major and minor products from glycine and alanine are strongly dependent on the pH of the
irradiated solution. One pH-dependent reaction that must be considered is of course the conversion of eaqto H by the hydronium ion2 eaq-
+ H30++H + H 2 0
(2)
However, conversion of eaq- to H is not specific to the (1) This work waa done under the auspices of the U. S. Atomic Energy Commission. (2) E. J. Hart, Science, 146, 19 (1964). (3) (a) G. Stein and J. Weiss, J. Chem. SOC.,3256 (1949); (b) N. E. Sharpless, A. E. Blair, and C. R. Maxwell, Radiation Res., 2, 135 (1955); (c) B. M. Weeks and W. M. Garrison, ibid., 9, 291 (1958).
Volume 69,Number 18 December 1966
B. M. WEEKS,S. A. COLE, AND W. R4. GARRISON
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H30+ ion. Other proton donors are also effective; ammonium ion, for example, converts eaq- to H via4 eaq-
+ NH4++H + NH3
(3)
and the analogous reaction eaq-
+ RNHs+ +H + RNHz
(4)
might be expected to be of importance in the radiolysis of aqueous solutions of organic compounds containing the NH2 function. With the amines, a dissociative cleavage of the N-C bond may also be envisaged eaq-
+ RNH8+ +R + NHs
(5)
Some preliminary evidence on the role of reaction 5 in the radiolysis of the a-amino acids in aqueous solution has been described.6 We report here a detailed study of the several processes involved in the deamination of alanine in oxygen-free solution under y rays. Data on the glycine-water system have also been included for purposes of comparison.
Experimental Section Materials. Alanine and glycine (Nutritional Biochemicals) were recrystallized several times from water. The labeled alanine and glycine (C1400H) were purified chromatographically on Dowex 50 (hydrogen form). Hydrochloric acid in progressively increasing concentration (0 to 4 N ) was used as the eluting agent. The separated amino acid hydrochlorides were passed through Dowex 1 (acetate form) to remove chloride ion; the acetic acid was removed under vacuum, and the amino acids were then recrystallized from water. The detailed procedures have ?xen described. Water from a Barnstead still redistilled first from alkaline permanganate and then from sulfuric acid was used in the preparation of the solutions. The chloroacetic acid (Eastman) was redistilled in vacuo. All other chemicals were reagent grade and were used without further purification. The pH adjustments were made with sulfuric acid or sodium hydroxide. Irradiations. The Pyrex irradiation cells were cleaned in nitric acid-hydrogen peroxide solution and rinsed with triply distilled water. The samples (10ml.) were irradiated in cylindrical Pyrex cells with a total volume of -40 ml. The samples containing C14-labeled amino acid were irradiated at a volume of 1 ml. in a proportionately smaller cell. Samples were degassed by evacuation. The irradiations were made with COW y rays from a 200-curie source. The dose rate, -5 x 1016 e.v. g.-1 min.-’ over the period of this study, was determined by the Fricke dosimeter (G@‘e3+) = 15.5, €305 2180 at 24’). Energy deposition in The Journal of Physical Chemistry
solutions was taken to be proportional to the electron density. Analytical Procedures. Gaseous products volatile at -80’ were transferred to a gas buret by means of a Toepler pump. After the total volume was measured, a sample was withdrawn for mass spectrometric analysis. The system was designed so that the neutral and alkaline samples could be acidified to pH
