The system l-malic acid+oxovanadium(IV); a potentiometric and spectroscopic study

Abstract

The equilibria in the system l-malic acid+oxovanadium(IV) in aqueous solution for 1 < pH < 12 have been studied by a combination of potentiometric and spectroscopic methods [electron paramagnetic resonance (EPR), visible absorption and circular dichroism (CD)]. The results of the various methods are made self-consistent in the region 1 ⪷ pH ⪷ 7, then rationalized assuming an equilibrium model including species MLH −2, MLH −1, ML, MLH, ML 2H −2, ML 2H −1, ML 2, ML 2H, ML 2H 2 (where H 2L denotes l-malic acid and M is VO 2+) and several hydrolysis products; their formation constants are given. Some other species were also detected in the region 7 ⪷ pH ⪷ 12.