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EPR and 51V NMR studies of prospective anti-diabetic bis(3-hydroxy-4-pyridinonato) oxidovanadium(IV) complexes in aqueous solution and liposome suspensions

Abstract

We report EPR and 51V NMR characterization of vanadium(IV/V) species originated by bis(3-hydroxy-4-pyridinonato)oxidovanadium(IV) complexes in aqueous solution at pH 7.4, under aerobic conditions and along time. Since complexes possess variable hydrophilic/lipophilic balance and consequently different solubility in water we also performed a parallel study in POPC liposome suspensions. For the less soluble complexes we used DMSO as a co-solvent. We identified three groups of complexes with different solubility in water. Compounds 1 and 2 are soluble enough to produce 1.5 mM solutions in MOPS buffer. Compounds 3 and 4 exhibit intermediate solubility but studies in MOPS buffer and POPC liposomes demonstrate that solubilisation is considerably enhanced in liposome suspensions. Compounds 5 and 6 have low water solubility, which is not sufficiently enhanced in liposome suspensions thus constraining the use of DMSO as a co-solvent. Analysis of EPR spectra of bis(3-hydroxy-4-pyridinonato)oxidovanadium(IV) complexes shows that upon dissolution a single species is present in solution, [VOL2]. In the presence of air [VOL2] is oxidized to three species, [VO2L2]-, [VO2L] and V1 (H2VO4-) as characterized by the 51V NMR spectra. Addition of sodium ascorbate reduces the V(V) species to the original [VOL2] complex. The results demonstrate that the use of DMSO lowers the rate of oxidation of the [VOL2] complexes. For DMSO percentages higher than 10% two distinct EPR signals are observable and EPR Spin-Hamiltonian parameters confirm the presence of [VOL2] in two different solvation environments, which confirms the participation of DMSO in the first solvation sphere of the complex.

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Publication details

The article was received on 29 Nov 2017, accepted on 01 Feb 2018 and first published on 01 Feb 2018


Article type: Paper
DOI: 10.1039/C7NJ04678B
Citation: New J. Chem., 2018, Accepted Manuscript
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    EPR and 51V NMR studies of prospective anti-diabetic bis(3-hydroxy-4-pyridinonato) oxidovanadium(IV) complexes in aqueous solution and liposome suspensions

    S. Ferreira, A. Leite, T. Moniz, M. Andrade, L. M. P. F. Amaral, B. de Castro and M. Rangel, New J. Chem., 2018, Accepted Manuscript , DOI: 10.1039/C7NJ04678B

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