OXOVANADIUM(IV) AND AMINO-ACIDS .7. THE SYSTEM L-HISTIDINE PLUS VO2- A SELF-CONSISTENT POTENTIOMETRIC AND SPECTROSCOPIC STUDY( )

The equilibria in the system L-histidine + VO2+ in aqueous solution ha ve been studied in the pH range 2-13 by a combination of pH potentiome try and spectroscopy (ESR; visible absorption and circular dichroism); The results of the various methods are made Self-consistent, then rat ionalized assuming an equilibrium model including species (where HL de notes L-histidine) : MLH(2), MLH, MLH(-2), ML(2)H(4), ML(2)H(3), ML(2) H(2), ML(2)H, ML(2), ML(2)H(-1), M(2)L(2)H(-4) and several products of hydrolysis; formation constants, absorption and circular dichroism sp ectra are given for each species. Plausible isomeric structures for ea ch stoichiometry in solution are discussed.