Models for studying the binding capacity of albumin to zinc by stripping voltammetry

Abstract

The complexation capacity of albumin to zinc was studied by different voltammetric methods. Cyclic voltammetry was used with a hanging mercury drop electrode (HMDE) to diagnose qualitatively the electrode mechanisms occuring at a mercury electrode and to evaluate the charge-transfer rate constant of the electrochemcial reaction of zinc in the presence of different concentrations of albumin. The conditional stability constant of the zinc-albumin complex was determined pseudo-polarographically by differential-pulse anodic stripping voltammetry (DP-ASV) with a Nafion-coated mercury film electrode (Nf-MFE). This electrode permits the determination of free (labile) zinc and rejection of the interfering adsorption of free albumin on the glassy coarbon surface. A mean conditional stability constant of log β′=6.10±0.16 was obtained by this method. DP-ASV was used to calculate β′ by titrating an albumin solution with ZN(II) and by Ruzic data treatment. In this instance a mean of log β′=5.49±0.28 was found with the HMDE and Nf-MFE. The results are compared and discussed.