Pulse radiolysis study of one-electron reduction of safranine T

Abstract

The one-electron reduction of safranine T by hydrated electrons and various reducing organic radicals in aqueous solution has been studied by the technique of nanosecond pulse radiolysis. The absorption spectrum of the transient semireduced safranine formed in these reactions exhibited λ_max at 400 and 650 nm with molar absorption coefficient values of 6.88×10³ and 9.9×10³ d mol^-1 cm^-1 respectively and decayed obeying a second-order rate law with a bimolecular rate constant of 0.97×10⁹ d mol^-1 s^-1 at neutral pH. It has two pK_a values of 3.0 and 8.5. The rate constants for the formation of semireduced safranine species by the reactions of most of the reducing radicals with the dye were very high and nearly diffusion controlled. The one-electron reduction potential of safranine T was estimated to be -0.35±0.02 V vs. NHE at pH 5. Reaction of H atoms with SF⁺ at acidic pH was also studied. The results obtained have been discussed with respect to the possibilities of different modes of H-atom reactions with safranine T.

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