Microcystin-LR and chemically degraded microcystin-LR electrochemical oxidation

• Published in: Analyst (London) Vol. 137; no. 8; pp. 194 - 1912
• Main Authors: Lopes, Ilanna C, Santos, Paulina V. F, Diculescu, Victor C, Peixoto, Francisco M. P, Arajo, Mrio C. U, Tanaka, Auro A, Oliveira-Brett, Ana Maria
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 21.04.2012
• Subjects: Amino acids; Analytical chemistry; Chemistry; Chromatographic methods and physical methods associated with chromatography; Chromatography, High Pressure Liquid; Constituents; Degradation; Electrochemical methods; Electrochemical Techniques; Electrodes; Exact sciences and technology; Glassy carbon; Hydrogen-Ion Concentration; Microcystins - chemistry; Other chromatographic methods; Oxidation; Oxidation-Reduction; Voltammetry; Human; Electrochemical method; Differential impulse voltamperometry; HPLC chromatography; Carbon electrode; Electron transfer; Degradation; Cyclic voltammetry; Ultraviolet detector; Aminoacid; Animal; Cyanobacteria; pH; Bacteria; Oxidation; Peak; Diffusion; Degradation product; Room temperature; Square wave
• ISSN: 0003-2654; 1364-5528
• DOI: 10.1039/c2an16017j

Microcystins (MCs) are cyclic hepatotoxic heptapeptides produced by certain strains of freshwater cyanobacteria toxic for humans and animals. The electrochemical behaviour of microcystin-LR (MC-LR) at a glassy carbon electrode (GCE) was investigated using cyclic voltammetry (CV), square wave voltammetry (SWV) and differential pulse voltammetry (DPV). The oxidation of MC-LR is a diffusion-controlled irreversible and pH-independent process that occurs with the transfer of only one electron and does not involve the formation of any electroactive oxidation product. Upon incubation in different pH electrolytes, homogeneous degradation of MC-LR in solution was electrochemically detected by the appearance of a new oxidation peak at a lower potential. The electrochemical behaviour of chemically degraded MC-LR is an irreversible, pH-dependent process, and involves the formation of two redox products that undergo reversible oxidation. The formation of degradation products of MC-LR was confirmed by HPLC with UV detection at room temperature. Experiments were also carried out in solutions containing constituent MC-LR amino acids, which enabled the understanding of the MC-LR electron transfer reaction and degradation. An oxidation mechanism for MC-LR is proposed. The electrochemical oxidation of MC-LR at a GCE is an irreversible and pH-independent process. This hepatotoxin undergoes homogenous degradation in buffer solution in a time-dependent manner.