Kinetic and Spectroscopic Behaviour of Proflavin Transients Studied by Pulse Radiolysis

Abstract

The semireduced transients of proflavin were studied in airfree acid aqueous solutions by a combined pulse radiolysis-computer optimization procedure. The main product, semiquinone (C-radical; 75%), formed with k=6.4 × 10⁹dm₃mol^-1s^-1 , decays by dimerisation (2k=2 × 10⁹dm³mol^-1s^-1) and dismutation (2k=0.5 x 10⁹dm³mol^-1s^-1). It possesses several absorption bands (ε₂₇₀ = 1900, ε₃₆₀ = 1530, ε₄₆₀ = 2250 and ε₅₃₀ = 200 m₂mol^-1 ). The second transient, R·-species (N-radical; 16.5%), is produced with k=1.4 × 10⁹dm³mol^-1s^-1 and decays preferentially by transformation into semiquinone with k = 2 × 10⁵s^-1; its absorption bands are: ε₂₉₅ = 2300, ε₃₈₀ = 1000, ε₄₄₀ = 5000 and ε₆₈₀ = 530m²mol^-1. Finally H-adducts on various positions of the aromatic ring (8.5%) are arising with k = 0.7 × 10⁹dm³mol^-1s^-1 , decay according to a pseudo first order reaction, k = 1.1 × 10⁴s^-1, and have absorption bands at ε₂₇₀ = 2100 and ε₄₃₅ = 1580m²mol^-1. The obtained results are of particular interest for the photochemical and photoelectrochemical solar energy utilization.