Interaction of N-hydroxyacetamide with vanadate:: A density functional study

The interaction between N-hydroxyacetamide (HL) and vanadate (VO3-) has been theoretically studied using density functional theory. All possible tautomers and conformations of two complexes formed have been fully optimized and vibrational analysis performed. From reported experimental results these two complexes have been shown to be in equilibrium in acidic aqueous solution: VO2LH2O and VO2(HL)L. The pentacoordinated VO2LH2O species having an intramolecular proton transferred from the coordinating H2O ligand to the oxo group, is the most stable. Seemingly, the most stable hexacoordinated VO2(HL)L species also has an oxo group protonated. Based on the analysis of the dipole moments of the species, the solvent effects within the continuum model are unlikely to change the relative stabilities of the different tautomers and conformers. The experimental infra-red spectrum of the VO2LH2O species has been measured and compared directly to the calculated frequencies. The most important peaks have been assigned to the corresponding normal modes. From the Mulliken population analysis, it is shown that the net charge on the vanadium atom and the oxygens surrounding the metal center are similar in the two species. The different coordination numbers may explain the differences of the reported V-51 NMR chemical shifts exhibited by these two species. (C) 1998 Elsevier Science Inc. All rights reserved.