A Comparative Study for Chelation of Iron(II) and Iron(III) with Active Component of Antiparkinsonian Drug Molecule

Syed Zafar Abbas Zaidi, Nasreen Fatima

Abstract


In the present study interaction of Fe(II) and Fe(III) with antiparkinsonian drug molecule, Levodopa (LD), is investigated using Potentiometry and Spectrophotometry. Fe(II) and Fe(III) both metals showed same spectra, which is an evidence of identical complex. Molar absorptivities of the complexes were found to be more than 100 M-1 cm-1, showed charge transfer spectra. Addition of an antioxidant, decolorized the initial intense color of the complex, which is evident of high oxidation state of iron in the complex. Catecholic ligands are strong reductants, thus chelate a metal ion in high oxidation state and show LMCT bands. These points confirm that, in the complex, iron has high oxidation state, regardless of initial source of metal.

Stoichiometry of the complex was explored by Mole Ratio, Slope Ratio and Job’s Plot methods showed consistency in results. Fe(II) and Fe(III) both form 1:3 metal to ligand ratio. Formation constant, found by different methods, are high and consistent. pK1= 6.42, pK2= 6.60 and pK3= 13.81 for Fe(III)-LD complex and pK2= 7.21 and pK3= 9.94, rather than pK1 which is unidentified, for Fe(II)-LD complex, were evaluated by Potentiometric data. Kinetics of complex formation showed the direct relationship in case of Fe(III)-LD, while in Fe(II)-LD complex the saturation pathway was observed. t1/2 for Fe(II) and Fe(III) complex with LD were calculated, indicative of very fast reaction in case of Fe(III)-LD having t1/2 = 0.917 ms. Kinetics results helps to originates mechanism of the reaction.


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