Reaction of hydrated electrons with safranine T (SF⁺), a phenazine dye useful as sensitizer in photogalvanic cell and the transient semireduced species formed by this reaction have been studied in SDS micellar medium using the technique of pulse radiolysis. Thee_aq⁻ reaction with SF⁺ in the micellar environment was only marginally slower (5.1 × 10⁹ dm³ mol⁻¹ s⁻¹) as compared to that in homogeneous aqueous medium (2.2 × 10¹⁰ dm³ mol⁻¹ s⁻¹) explicable on the basis of our finding that although a large fraction of the dye gets localized near the micelle Stern layer where the molecule experiences a dielectric.constant of ≈40, a small but significant concentration of the dye exists in the aqueous bulk as charge pair complex with the anionic surfactant monomer (association constant for the formation of the complex being 2.8 × 10⁴ dm³ mol⁻¹). The transient semireduced absorption band observed in the micellar medium showed a red shift of ≈ 50 nm and also the decay of the transient, which was very fast with 2k = 1 × 10⁹ dm³ mol⁻¹ s⁻¹ in aqueous medium, was stable in the SDS micellar medium over a few tens of milliseconds suggesting that the radical is incorporated deeper than the parent molecule in the SDS micelle. The effect of this stability on the photogalvanic conversion needs to be examined.

The pulse radiolysis technique has been employed to investigate the reaction of DNA-minor-groove ligand bisbenzimidazole Hoechst 33258 with pyrimidine and purine nucleotide-derived radicals. Formation of an N-centred Hoechst-33258 radical is observed. Bimolecular rate constants and the yields of Hoechst-33258 radical have been evaluated. While the rate constant for the reaction of pyrimidine-derived radicals with Hoechst-33258 remained the same (1–2) × 10⁹ dm³ mol⁻¹ s⁻¹, the yields of the Hoechst-33258 radical varied from 25% (5′-cytidine monophosphate) to 75% (5′-guanosine monophosphate) under anoxic conditions. The rate constant values for the reaction of purine-derived radicals with Hoechst-33258, under oxic and anoxic conditions, remained the same whereas with pyrimidine-derived radicals, the rate constant value under oxic conditions was about two orders of magnitude lower than under anoxic conditions. The difference in the yields of Hoechst-33258 radical with various nucleotide-derived radicals suggest the formation of different types of radicals and that the reaction mainly occurs by electron transfer from Hoechst-33258 to the nucleotide radicals.

Radiation chemical reactions of^•OH, O^•−, N₃^•and e_aq^t- witho- and m-hydroxycinnamic acids were studied. The second-orderrateconstantsforthereaction of^•OH with ortho and meta isomers in buffer solution at pH7 are 3.9±0.2 × 10⁹ and 4.4 ± 0.3 × 10⁹ dm³ mol^-1 s^-1 respectively. At pH 3 the rate with the ortho isomer was halved (1.6 ± 0.4 × 10⁹ dm³ mol^-1 s^-1) but it was unaffected in the case of meta isomer (k = 4.2±0.6 × 10⁹dm³mol^-1 s^-1). The rate constant in the reaction of N₃^• with the ortho isomer is lower by an order of magnitude (k = 4.9 ± 0.4 × 10⁸ dm³ mol^-1s^-1). The rates of the reaction of e_aq^t- with ortho and meta isomers were found to be diffusion controlled. The transient absorption spectrum measured in the^•OH witho-hydroxycinnamic acid exhibited an absorption maximum at 360 nm and in meta isomer the spectrum was blue-shifted (330 nm) with a shoulder at 390 nm. A peak at 420 nm was observed in the reaction of O^bb−with theo-isomer whereas the meta isomer has a maximum at 390 and a broad shoulder at 450 nm. In the reaction of the absorption peaks were centred at 370–380 nm in both the isomers. The underlying reaction mechanism is discussed.