An-Najah Staff

Kinetic oxidation of L-cysteine by [Fe(Fz)2] 1-  complex was carried out in acidic medium under  pseudo rate conditions. The molar ratios between iron(III), iron(II) and Ferrozine (HFz)  complexes in absence and presence of L-cysteine were individually determined using job's  method. The formation of [Fe2+-Fz] at lmax = 562nm was spectrophotometrically followed  during this kinetic study. The reaction is found to be first-order with respect to iron(III) and  L-cysteine, second-order with respect to HFz-1  ligand and reversed second-order with respect to  hydrogen ion concentrations. The salts effect was determined and no radical species have been  detected. The kobs rose when the temperature was increased which empowered the activation  parameters of the rate-determining step calculations. A reaction mechanism and rate law  derivation are proposed with a pre-equilibrium of an adduct formation between L-cysteine and  [Fe3+-Fz] complex.