D. Pogocki, K. Bobrowski
Mar 1, 2014
Citations
2
Influential Citations
6
Citations
Journal
Israel Journal of Chemistry
Abstract
The participation of neighboring amino and carboxyl groups in thiazolidyne-4-carboxylic acid (thiaproline) and its two derivatives, thiazolidyne-2-carboxylic acid and thiazolidyne-2,4-dicarboxylic acid, is demonstrated during .OH-radical-induced oxidation in aqueous solutions. The reaction of .OH radicals with these compounds does not lead to the expected one-electron oxidized sulfur-centered radical cations and subsequently to the intermolecularly (S∴S)-bonded dimeric radical cations (even at very high concentration of thiaprolines (>50 mM)), but rather to the elimination of CO2 with the parallel formation of αN radicals. The latter radicals formed in thiaproline and thiazolidyne-2,4-dicarboxylic acid subsequently undergo β-fragmentation of the CS bond, leading to the thiyl radicals (RS.). The αN and RS. radicals were probed and quantified by one-electron reduction of p-nitroacetophenone (PNAP) and by one-electron oxidation of the monoanion of ascorbic acid (AH−), respectively. The calculated stabilization enthalpies of the αN radicals show that the loss of CO2 is thermodynamically a favorable process. The Gibbs free energies of β-fragmentation processes in thiaproline and thiazolidyne-2,4-dicarboxylic acid are equal to −3.7 and −10.2 kJ mol−1, respectively, showing that at room temperature both are exergonic. A general .OH-radical-induced oxidation mechanism of thiaproline derivatives in aqueous solutions is proposed.