Ionic strength dependence of formation constants: Complexation of histidine with molybdenum(VI)

The formation constants of species formed in the systems H(+)+Mo(VI)+histidine and H(+)+histidine have been determined in aqueous solution in the range 4 less than or equal to pH less than or equal to 8 at 25 degreesC and at ionic strengths ranging from 0.1 to 1.0 mol dm(-3) (NaClO(4)), using polarimetric, spectrophotometric, and potentiometric techniques. The composition of the complex was determined by the continuous variations method. It was shown that molybdenum(VI) forms a mononuclear 1:1 complex with histidine of the type MoO(3)L(-) at -log[H(+)] = 5.7. The dependence of the protonation of histidine and the stability constant of the complex on ionic strength is described by a Debye-Huckel type equation, and finally the results have been compared with data previously reported and interpreted.