Kinetics of oxidation of amino acids by some free stable hydrazyl radicals

The kinetics of amino acids (Ser, Pro, Leu, Trp, Thr, Phe, Met, His) oxidat ion by sodium salts of 2-p-phenylsulfonic acid-2-phenyl-1-picrylhydrazyl (I ) and 2,2-di-p-phenylsulfonic acid-2-phenyl-1-picrylhydrazyl (II) at isoele ctric point of amino acids has been studied over the temperature range 298 - 318 K. The rate studies were made under pseudo-first order conditions wit h an excess of amino acid over the oxidant. The kinetics was followed by mo nitoring the disappearance of I and II, spectrophotometrically, at 520 nm a nd 514 nm, respectively. The activation parameters were determined from rat e constant dependence on temperature. The amino acids with aromatic structu re (His, Trp, Phe) were oxidised more rapidly than the others. A mechanisti c pathway for amino acids oxidation was proposed and discussed, similarly w ith their enzymatic degradation, which have as final products alpha-keto-ac ids and ammonia. In this aim was followed a mechanistic and structural inve stigation grounded on isokinetic theory.