Add time:08/25/2019         Source:sciencedirect.com

The stoichiometry and thermodynamic stability of copper(II), vanadium(IV/V), iron(II)/(III) and gallium(III) complexes of salicylaldehyde semicarbazone (SSC, HL) and its 5-bromo derivative (Br-SSC, HL) have been determined by pH-potentiometry, UV–Vis spectrophotometry, EPR, 1H and 51V NMR spectroscopy in 30% (w/w) dimethyl sulfoxide/water solvent mixture. Proton dissociation processes and lipophilicity of the ligands were also studied in detail. Formation of mono-ligand complexes such as [ML], [MLH−1], [MLH−2] was found with copper(II), vanadium(IV/V), while bis-ligand species of iron(II)/(III) and gallium(III) such as [ML2], [ML2H−1] and [ML2H−2] were also detected, in which the ligands coordinate via monoanionic (O−,N1,O) or dianionic (O−,N1,O−) modes. The bromine substituent on the phenol ring has no significant impact on the stability and binding modes but provides a remarkably enhanced lipophilic character, which is advantageous for the bioactivity. The Ga(III)–salicylaldehyde semicarbazone species show unambiguously higher stability; whereas Cu(II) species have somewhat lower stability relative to the corresponding thiosemicarbazone analogues, however no decomposition of the Cu(II) complex was observed even at micromolar concentrations at physiological pH.

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