Interaction of N-hydroxyacetamide with vanadate in aqueous solution

Abstract

The equilibria between aqueous vanadate and N-hydroxyacetamide (acetohydroxamic acid, HL, CH 3 CONHOH) have been studied at 25 ЊC in 0.15 mol dm Ϫ3 NaCl medium by combined potentiometric, spectrophotometric, 51 V and 17 O NMR methods. Complexes form in the range pH 3 to 11, and many of their formation constants have been determined. The neutral species HV(HL) and HV(HL) 2 predominate below pH 4.5 and with HL : V > 2 : 1, where V is an abbreviation for [H 2 VO 4 ] Ϫ . These notional formulae do not specify the possible co-ordination or loss of water molecules from the complex anions and the charges shown are the overall species charges rather than any algebraic sum. From pH 4.5 to 8.5 the main species are [V(HL) 2 ] Ϫ and, to a lesser extent, [V(HL)] Ϫ . Oxygen-17 NMR data strongly suggest that [V(HL) 2 ] Ϫ has octahedral co-ordination, with a cis-VO 2 ϩ unit and two bidentate L Ϫ ligands, one of which can lose another proton above pH 8.5 to form [VL(HL)] 2Ϫ . The species [V(HL)] Ϫ also deprotonates above pH 9. The minor oligomeric species [V 2 (HL) 3 ] nϪ and [V 2 (HL) 4 ] nϪ also form, at higher concentrations of V and HL.

Formation and structure in aqueous solution of complexes between vanadium(V) and aminohydroxamic acids that potentiates vanadium’s insulinomimetic activity: l-glutamic γ-hydroxamic and l-aspartic-β-hydroxamic acids

“…Besides, the species of the systems which prevail in the 5-7 pH range, VO 2 L À and VO 2 H 2 L 2 À , have very similar chemical shifts, as shown in Table 1. These shifts are also similar to the ones of V(V)-aha [11] and V(V)-b-alaha (13), shown in Table 1.…”

“…Since vanadium(V) ion does not exhibit any d-d transition in the visible spectrum, the color observed must be attributed to a strong oxygen to metal charge-transfer absorbance band in the ultraviolet [26,27] that extends into the visible range. This behavior was observed in our previous works about the vanadium(V) complexation by acetohydroxamic [11], b-alaninehydroxamic [13], glycinehydroxamic and a-aminohydroxamic acids [28]. In all these cases there is no consumption or release of protons, as observed now.…”

“…In previous papers, we have demonstrated how combined potentiometric, spectrophotometric and 51 V NMR methods allowed the identification of several species and determination of their formation constants in aqueous solution containing vanadium(V) and acetohydroxamic acid [11,12] and b-alaninehydroxamic acid [13]. In both systems, at least two vanadium-ligand 0020-1693/$ -see front matter Ó 2010 Elsevier B.V. All rights reserved.…”

Chemistry and Biochemistry of Insulin-Mimetic Vanadium and Zinc Complexes. Trial for Treatment of Diabetes Mellitus

“…The detailed speciations of vanadyloligopeptides, 16 vanadyl-acetohydroxamic acid, 17 oxovanadium(IV,V)-D-saccharic, and mucic acids, 18 vanadyl-1,2-dimethyl-3-hydroxy-4(1H)-pyridinone in the presence of oxalate, citrate, and phosphate, 19 and vanadyl-acetylactamides 20 have also been intensively investigated. IR spectroscopy is a very useful tool for analyzing the existence of functional groups in a molecule.…”

“…4c. The oxidation kinetics of bis(maltolato)-oxovanadium(IV) [VO(ma) 2 ] in MeOH, 52 the interaction of N-hydroxyacetoamide with oxovanadium(V) ion in aqueous solution, 17 the solution structure of ammonium (dipicolinato)-oxovanadate(V), 53 the chelation properties of vanadate to monoionized diols and carbohydrates, 54 and the complex-forming tendency of vanadate with -hydroxycarboxylic acids 55 have been examined in detail by means of 51 V NMR spectroscopy. Zinc(II) is also diamagnetic, and thus the measurement of 1 H NMR spectrum of zinc(II) complexes is possible.…”