Chelation of Vanadium( IV ) by a Natural and Edible Biopolymer Poly( γ ‐glutamic acid) in Aqueous Solution: Structure and Binding Constant of Complex

The naturally occurring edible biopolymer poly( γ ‐glutamic acid) ( γ ‐PGA) is shown to be an efficient chelating agent of vanadium( IV ). The structure of poly( γ ‐glutamic acid)oxovanadium( IV ) (VO‐ γ ‐PGA) complex in solution has been analyzed by electron spin resonance and UV‐visible absorption spectra. The equatorial coordination sphere of vanadium( IV ) is proposed to be [2 × carboxylate (2O)–VO–(OH 2 ) 2 ]. The binding isotherm is determined for suspensions of γ ‐PGA in vanadium( IV ) oxide sulfate (VS) solutions of different concentrations, and the data have been adjusted to fit the modified Langmuir equation. The maximum amount of vanadium bound per gram of γ ‐PGA is estimated to be 141 mmol · g −1 with a binding constant of 22 L · g −1 at pH 3.