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

Using laser photolysis of basic anaerobic aqueous solutions of alpha -glyci ne, l-alpha -alanine and alpha -aminoisobutyric acid containing anthraquino ne-2,6-disulfonic acid the two spin-polarized (CIDEP) (CR1R2NH2)-R-. and (N H2CR1COO-)-R-. radicals (R-1, R-2=H or CH3) and the radical anion of anthra quinone-2,6-disulfonic acid were detected by time resolved Fourier transfor m electron paramagnetic resonance (FT EPR) spectroscopy. The FT EPR results reveal that alpha -glycine, L-alpha -alanine and alpha -aminoisobutyric ac id were oxidized by the spin-polarized photo-excited triplet of anthraquino ne-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 alpha -glycine and alpha -alanine yielding the ( NH2CR1COO-)-R-. radical. The rate constants for the electron transfer react ion and of the decarboxylation reaction were determined.