Proton Electron Nuclear Double Resonance Study of Oxovanadium(IV) Complexes of D-Galacturonic and Polygalacturonic Acids

The 'H electron nuclear double resonance (ENDOR) spectra of the VO(IV)-D-galacturonic acid system in aqueous solution have been studied as a function of pH. Couplings between the paramagnetic ion and the protons of ligand or water molecules have been distinguished by comparative examination of the spectra recorded in water and D2O. Comparison of data with results available from potentiometric and other spectroscopic measurements allowed interpretation of the pH dependence of ENDOR spectra and the assignment of the main observed resonances, e.g. those due to methine protons on the carbon atoms bearing deprotonated carboxyl and/or hydroxyl groups co-ordinated to the metal ion.