Stabilization of Cu (III) in medium containing peptides: electrochemical studies and analytical applications

Author(s)

Denise Lowinsohn

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ)
• Defense date: 2003-05-05

Examining board members

Mauro Bertotti; Nina Coichev; Lauro Tatsuo Kubota

• Advisor: Mauro Bertotti

Abstract

The electrochemistry of Cu(II) in aqueous solutions containing triglycine, tetraglycine and pentaglycine had been investigated at glassy carbon surfaces. Experiments were carried out in the pH range between 7.0 and 10.0. A correlation between voltammetric waves and the nature of the Cu(II) species involved in the electrochemical steps was performed. Spectrophotometric and coulometric studies were also done to characterise Cu(II) and Cu(III) species in solution and prove the existence of a degradation step related to Cu(III) complexes. Rotating ring-disc voltammetry was employed to follow this chemical step coupled to the electrode reaction, at three different temperatures. Data show that Cu(III)/triglycine species degrade, with faster kinetics, when the results are compared with those obtained for tetraglycine and pentaglycine. An indirect amperometric method for the determination of sulfite in a flow injection configuration is described. The method is based on the amperometric measurement (OV vs Ag/AgCI (sat. NaCI)) of Cu(III) chemically generated by the sulfite induced autoxidation of Cu(II)/tetraglycine complex in the presence of traces of Ni(II) with a manifold that incorporates flow extraction of sulfite as SO2 through a PTFE membrane. The operational range was 2µmoIL-1 with a detection limit of 2µmolL-1 (S/N = 3). The repeatability for the determination (100 2µmolL-1) was evaluated to be 4.9% (n = 20) and the analytical frequency was 40h-1. Results for 3 wines and 2 juices samples showed excellent agreement with those obtained by using a recommended procedure for sulfite analysis. (AU)