Time resolved FT EPR study of the decarboxylation following photo-induced electron transfer between α-amino acids and anthraquinone-2,6-disulfonic acid in aqueous solution

Abstract

Using laser photolysis of basic anaerobic aqueous solutions of α-glycine, L-α-alanine and α–aminoisobutyric acid containing anthraquinone-2,6-disulfonic acid the two spin-polarized (CIDEP) C^•R₁R₂NH₂ and NH₂C^•R₁COO⁻ radicals (R₁, R₂ = H or CH₃) and the radical anion of anthraquinone-2,6-disulfonic acid were detected by time resolved Fourier transform electron paramagnetic resonance (FT EPR) spectroscopy. The FT EPR results reveal that α-glycine, L-α-alanine and α-aminoisobutyric acid were oxidized by the spin-polarized photo-excited triplet of anthraquinone-2,6-disulfonic acid through a one-electron transfer followed by a rapid decarboxylation. In a competing reaction channel the quinone triplet decays by hydrogen transfer from α-glycine and α-alanine yielding the NH₂C^•R₁COO⁻ radical. The rate constants for the electron transfer reaction and of the decarboxylation reaction were determined.