Stability constants of mixed ligand complexes of vanadium(III) with cysteine and the amino acids serine, threonine, methionine and phenylalanine

The formation of the ternary complexes of Vanadium (III)-L-cysteine with the amino acids serine (HSer), threonine (HThr), methionine (HMet) and phenylalanine (HPhe) in aqueous solution was studied by means of emf(H) electromotive force measurements under the conditions: 3.0 M KCl and temperature (25.0 +/- 0.1) degrees C, in order to know the speciation of these systems: The data obtained through potentiometric measurements were analyzed using the computer program generalized)east squares LETAGROP, which indicate the formation of ternary complexes of the type [V(Cys)(HL)](+), V(Cys)(L) and the hydrolysis products [V(Cys)(L)(OH)](-) and [V(Cys)(L)(OH)(2)](2-), where L represents the amino acids studied (L = Ser, Thr, Met, Phe). The spectrophotometric studies indicate the presence of six-coordinated and heptacoordinatect complexes for the V(III)-H(2)Cys-HThr system. The Delta log K '' indicated that the ternary complexes are more stable than the binary ones. (C) 2016 Elsevier B.V. All rights reserved.