KINETIC STUDY OF Fe(II) AND Fe(III) COMPLEXES OF DOPAMINE, (-)3-(3,4-DIHYDROXYPHENYL)-L-ALANINE AT PHYSIOLOGICAL pH

The kinetics of complex formation of dopamine, (-)3-(3,4-dihydroxyphenyl)-L-alanine ( Levodopa or LD), with Fe(II) and Fe(III) has been studied spectrophotometrically. The reactions were carried out at a pH range of 3.0 to 9.2, at 25 ± 1oC.Complex formation was not observed below pH 4.0. These investigations showed that the Fe(II) and Fe(III) complexes have identical spectra, indicative of same oxidation state of iron in these complexes. Fe(III)-LD complexation was studied only in non-buffered media. The reaction was very fast, and hence was studied using stopped flow technique. This reaction shows a linear dependence on [LD]. While, in case of Fe(II) complexation, a saturation pathway is followed. Rate laws have been deduced.