Electrochemical behaviour of hen-egg-white lysozyme at the polarised water/1, 2-dichloroethane interface

Abstract

The electrochemical behaviour of hen-egg-white lysozyme (HEWL) was studied at the polarized water/1,2-dichloroethane interface. The voltammetric ion-transfer response was found to be dependent on the pH and ionic strength of the aqueous phase solution and also on the nature of the organic phase electrolyte anion. The current-pH behaviour of HEWL was dominated by the charge of the biomolecule at each pH, as indicated by the close relationship between the experimental peak currents and the theoretical curve for HEWL based on its known acid-base chemistry. Three organic electrolyte anions of differing hydrophobicities were investigated (TFPB-, TPBCl- and TPB-) and it was found that the ion transfer voltammetric peaks occurred at successively higher potentials in the order of increasing hydrophobicity, Deltaphi(TPB) < Deltaphi(TPBCl) < Deltaphi(TPBF). The voltammetric response was time dependent during multi-cyclic voltammetry experiments, with the formation of a white film of precipitate at the interface. A pre-peak consistent with adsorption of the HEWL ion transfer product at the liquid/liquid interface was also observed. The results suggest that an adsorption or re-arrangement of HEWL molecules with time at the interface is taking place. A mechanism for the response on application of a triangular potential waveform with cyclic voltammetry is proposed based on an i-C-i mechanism. Our results indicate that HEWL is electroactive at the polarized liquid/liquid interface and that such electrochemical methods may provide an approach to the label-free detection and characterization of protein molecules.

Haemoglobin unfolding studies at the liquid–liquid interface

“…The ionic strength, I c , of the 0.15M HCl + 0.15M KCl electrolyte solution is higher (0.3M) than that of the 10mM HCl electrolyte solution (0.01M). Both pH and I c have a strong influence on the protein conformation [13] so changes in the voltammograms were expected. Scanlon et al investigated the impact of these two parameters separately on the CVs of lysozyme at the ITIES [13].…”

“…Both pH and I c have a strong influence on the protein conformation [13] so changes in the voltammograms were expected. Scanlon et al investigated the impact of these two parameters separately on the CVs of lysozyme at the ITIES [13]. An increase of the aqueous phase pH leads to an increase of the peak currents, whereas the peak currents decreased when the ionic strength of the solution increased.…”

“…The electrochemical behaviour of proteins [9][10][11][12][13][14][15] at the interface between two immiscible electrolyte solutions (ITIES) has been reported recently. Proteins adsorb at the interface and assist the transfer of anions from the organic phase electrolyte to the aqueous phase.…”

Studying the ion transfer across liquid interface of thin organic-film-modified electrodes in the presence of glucose oxidase

“…1. The adsorption of the enzyme is mainly driven by the lipophylic interactions of the enzyme with the organic solvent [26][27][28][29][30][31][32][33][35][36][37]. It is plausible to assume that the enzyme molecules are oriented at the liquid interface, with the negatively charged surface leaning toward the aqueous phase.…”

“…In recent years, there has been an increased attention in the study of proteins at L|L interfaces, mainly by means of the four-electrode configuration setup [26][27][28][29][30][31][32][33]. Of particular interest are electron-transfer reactions across the L|L interfaces involving redox-active enzymes.…”