Electrochemical Characteristics of 4-oxo-4H-pyran-dicarboxylic Acid (Chelidonic Acid) and some of its Metal Complexes

A few novel metal complexes of chelidonic acid (chelH(2)), namely [Ca(chel)(H2O)(3)] (1), [Cu(chel)(H2O)(5)]2H(2)O (2) and [VO(chel)(H2O)(3)]2H(2)O (3) were prepared, identified by elemental analysis and characterized by electrochemical methods. IR-spectra and thermal stability in solid state are discussed as well. The electrochemical characteristics of the free chelidonic acid and its complexes 1-3 were studied by (cyclic) square-wave voltammetry, on static mercury drop electrode (SMDE) and paraffin-impregnated graphite electrode (PIGE), in aqueous media over a wide pH range. The reduction of chelidonic acid on SMDE is a kinetically controlled electrode reaction, occurring with the transfer of one electron and two protons for 1<pH<6, whereas in very alkaline media the electron transfer is pH independent, i.e. the mechanism of electro-reduction of chelH(2) is proposed. The experimental parameters of the electroanalytical procedure were optimized and the method was applied for the investigation of the metal ion coordination preferences toward chelidonic acid. For the direct determination of solid complexes 1-3, SW voltammetry of microparticles was used.