Electrochemical and conformational studies of microcystin-LR

The detection of microcystins in freshwater and in biological samples has b ecome increasingly important due to their toxicity and tumor-promoting natu re. This paper describes the electrochemical characterization of microcysti n-LR using cyclic voltammetry and anodic stripping voltammetry at different substrates of gold, platinum, glassy carbon and carbon pastes electrodes. Results of electrochemical oxidation reactions indicated that gold-catalyze d complexes were formed between mercury ions and microcystin at approximate ly 450 mV versus a silver/silver chloride reference electrode. The resultin g complex, that was also observed using copper, zinc, lead and gallium ions , was strongly dependent on the concentration of microcystins at picomolar levels with quantitation range of 10 pM-1 nM. The energetics of interaction of the metal ions with the cyclic peptide was studied using semi-empirical molecular orbital calculations. Stable conformation was obtained when the metal ions were localized within the cavity region of the microcystin. This is likely to provide a new approach to the possible mechanisms of detoxifi cation for this class of hepatotoxic peptides. It is also likely to result in the development of suitable electrochemical method of detection for othe r types of microcystin. (C) 2000 Elsevier Science B.V. All rights reserved.