KINETICS OF OXIDATION OF AMINO ACIDS BY SOME FREE STABLE HYDRAZYL RADICALSá

Gabriela Ionita,a Victor Em. Sahini,b Gheorghe Semenescua and Petre Ionitac
a University of Pitesti, Dept. of Physical Chemistry, Gh. Doja Street 41, 0300 Pitesti, Roumania
b University of Bucharest, Faculty of Chemistry, Bd. Carol I 13,  70346 Bucharest, Roumania
c Institute of Physical Chemistry, Spl. Independentei 202, Bucharest, Roumania
 

ABSTRACT

The kinetics of amino acids (Ser, Pro, Leu, Trp, Thr, Phe, Met, His) oxidation 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 isoelectric point of amino acids has been studied over the temperature range 298 - 318 K. The rate studies were made under pseudo-first order conditions with an excess of amino acid over the oxidant. The kinetics was followed by monitoring the disappearance of I and II, spectrophotometrically, at 520 nm and 514 nm, respectively. The activation parameters were determined from rate constant dependence on temperature. The amino acids with aromatic structure (His, Trp, Phe) were oxidised more rapidly than the others. A mechanistic pathway for amino acids oxidation was proposed and discussed, similarly with their enzymatic degradation, which have as final products a-keto-acids and ammonia. In this aim was followed a mechanistic and structural investigation grounded on isokinetic theory.