Spectral and cyclic voltammetric studies of glyceryl guaiacolate drug in pure form and in situ chelation with some different transition metals

An equimolar series of binary complexes of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) with guaifenesin (glyceryl guaiacolate) (H2L or Gf) have been synthesized. The Gf ligand is deprotonated and coordinated to the metal ion with both oxygen's donor atoms with 1:1 (metal:Gf) ratio and it is determined by micro-analytical technique. The resulting metal chelates of Gf were characterized using the conductivity measurements, FT-IR, Laser Raman, electronic solid reactance, magnetic susceptibility calculation, 1H NMR, TGA and ESR spectral studies. The conductivity measurements confirm that all the metal complexes were non-electrolytic in DMSO except for chromium and iron(III) complexes have an electrolytic behavior. Based on spectral and analytical data octahedral geometry is assigned to the Cr(III), Mn(II), Fe(III), Co(II) and Ni(II) complexes with four coordinated water molecules, but the copper and zinc(II) complexes have square planner molecular geometry with two coordinated water molecules. The general molecular formula of the solid Gf complexes has been found as [M(Gf)(H2O)n]·x·yH2O, where M = Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II), n = 2 or 4, x = Cl− for (Fe and Cr(III) complexes) and y = 3 for (Cr(III) and Ni(II) complexes). The electrochemical reduction of Gf and its complexes were realized on a platinum wire electrode in Britton-Robinson (BR) buffer using the cyclic voltammetric (CV) technique. The effect of functional groups on reduction potential of the Gf was investigated. A general electrochemical reduction mechanism of the compounds is suggested.