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- Author or Editor: C. Gopinathan x
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Abstract
Hydrogen peroxide yields in air-saturated methanol-water mixtures with methanol: water volume ratios varying from 1
99 to 1000, produced by60Co gamma-irradiation boith at room temperature and at 77 K have been determined. At room temperature, G(H2O2) values are almost constant over the entire range of methanol: water ratios. However, for irradiations at 77 K, G(H2O2) values increase with increasing methanol concentration up to the volume ratio of 982.
Abstract
Using the pulse radiolysis technique, the oxidation of the biological protein bovine serum albumin (BSA) by the species N 3 . , CCl3O 2 . , OH and Br 2 .– has been studied in aqueous solution. The repair of the N 3 . oxidation by ascorbic acid and the effect of denaturing the protein on this repair has also been studied. The oxidation of Br 2 .– seems to follow a different course from that of the other oxidizing agents suggesting the possibility of positive hole mobility in this protein. The repair by ascorbic acid is found more effective in the case of denatured protein. The rate constants for the reaction of Br 2 – and N 3 . are lower, in general, in the case of the denatured protein as compared with the undenatured BSA both at pH 6.9 and pH 10.7, suggesting that the convoluted structure of the protein plays a part in the process.
Abstract
The use of beams of heavy ions such as carbon, neon and argon for radiation therapy has the advantage that they have a very sharp Bragg maximum. When the Bragg peak coincide with the tumour location, it is possible to deposit the bulk of the energy of the ion in the region occupied by the malignancy. However, the concentration of ions and free radicals will be very high in the Bragg peak region which has not received the attention it deserves. So mutual recombination of these species will be very high. It is therefore necessary to assess the extent of these radical-radical recombinations at very high LET values. Spur diffusion model calculations have been made for high energy argon ions using water as a medium. For comparison, calculations have been done for proton tracks. It has been shown that in the Bragg peak region of argon ions even very high concentrations of scavengers have very little effect on radical-radical interactions. The implication is that when LET values are very high, practically all the radicals undegro recombination with each other. In order to explain the observed lethality of high LET radiation, it is suggested that the hydrogen peroxide formed also contribute to the killing of cells. In addition, the decomposition of H2O2 will contribute oxygen. This may be one of the reasons why high LET radiation shows strong lethality to hypoxic cells.
Abstract
The triplet excited state of naphthalene (3N*) has been produced by irradiating solutions of naphthalene in mixtures of isopropanol-formamide, acetonitrile-formamide and N,N-dimethylformamide — formamide mixtures with 2 microsecond electron pulses. The yield and decay kinetics of the triplet have been studied over a wide range of compositions of the mixtures. An attempt has been made to explain the variation in the yields and decay rate constants on the basis of the micro properties of the solvent mixtures.
Abstract
Mixtures of methanol and isopropanol in a ratio (v/v) varying from 9
1 to 19 have been gamma-irradiated at 77 K and relative yields of trapped electrons have been measured. The reactivity of the trapped electrons towards acetone and uranyl nitrate has been studied at various methanol isopropanol ratios. On the basis of the results, an attempt has been made to assess the relative importance of the reaction of the electron with the solute prior to trapping with respect to the tunnelling reaction of the trapped electron with the solute.
Abstract
Trapped electron (e T – ) reactivity in methanol-isopropanol glasses irradiated at 77 K has been studied as a function of trap-depth, the variation in the trap depth being achieved by varying the methanol:isopropanol ratio. Benzyl chloride and carbon disulfide have been used as scavengers. In the case of the glasses containing benzyl chloride, the observed yield of the benzyl radical has been correlated with the trapping efficiency of the matrix. The data has been interpreted with the aim of assessing the relative importance of tunnelling in the scavenging of electrons in low temperature glassy matrices.
