• Kowol, Christian R.
• Keppler, Bernhard K.
• Jakusch, Tamas
• May, Nora V.
• Enyedy, Eva A.
• Kozma, Karoly
• Roller, Alexander
• Kiss, Tamas

Abstract

The stoichiometry and thermodynamic stability of vanadium(IV/V) and copper(II) complexes of pyridoxal thiosemicarbazone and pyridoxal-N-3, N-3-dimethylthiosemicarbazone have been determined by pH-potentiometry ((VO)-O-IV), EPR ((VO)-O-IV/Cu-II), UV-Vis (Cu-II, (VO)-O-IV and V-V) and V-51 NMR spectroscopy (V-V) in 30% (w/w) dimethyl sulfoxide/water solvent mixture. In all cases, mono-ligand complexes are formed in different protonation states. In addition, the proton-dissociation constants of the ligands were also determined by pH-potentiometry, UV-Vis and H-1 NMR spectroscopy. The solid state structures of the monoprotonated forms ((VO2)-O-V((LH)-H-1)x1.5H(2)O and (VO2)-O-V(L2(H))x0.8H(2)O) of the V-V complexes were characterized by single-crystal X-ray diffraction analysis. The mono-ligand complexes of Cu-II and V-V are dominant at physiological pH. With all investigated metal ions the pyridoxal moiety of the ligand causes an extra deprotonation step between pH 4 and 7 due to the non-coordinating pyridine-NH+. The pyridoxal-containing ligands form somewhat more stable complexes with both (VO)-O-IV and Cu-II ions than the reference compound salicylaldehyde thiosemicarbazone. Dimethylation of the terminal amino group resulted in the formation of V-V and Cu-II complexes with even higher stability. (C) 2017 Elsevier B.V. All rights reserved.

Topics

• compound
• x-ray diffraction
• copper
• electron spin resonance spectroscopy
• Nuclear Magnetic Resonance spectroscopy
• vanadium
• potentiometry