Novel mechanistic aspects on the reaction between low spin Fe(II) Schiff base amino acid complexes and hydrogen peroxide-Spectrophotometric tracer of intraperoxo intermediate catalyzed reaction

The kinetics and mechanism of the reaction of hydrogen peroxide with some Fe(II) Schiff base complexes were investigated spectrophotometrically in aqueous solution at pH 8 and 35 °C under pseudo-first-order conditions. The used ligands were derived from salicylaldehyde or o-hydroxynaphthaldehyde and some amino acids (l-leucine, l-iso-leucine, l-serine, l-methionine and dl-tryptophan). It was found that the formation of the purple interaperoxo complex appears only above pH 7.5. The reaction consists of two steps. The first step involves reversible formation of the intraperoxo intermediate which renders irreversible at pH 8. The second step consists of inner-sphere electron transfer. The suggested scheme illustrated first-order kinetics at low [H2O2] and zero-order at high [H2O2]. Moreover, the activation parameters of the reaction were evaluated.