Interaction of [RuIII(edta)(H2O)]– with amino acids in aqueous solution. Equilibrium, kinetic and protease inhibition studies

The interaction of [RuIII(edta)(H2O)]–(edta = ethylenediaminetetraacetate) with amino acids, viz. glycine, L-cysteine and S-methylcysteine, was investigated potentiometrically and kinetically. The concentration distribution of various complex species was evaluated as a function of pH. Kinetic data obtained as a function of [amino acid], temperature (5.0 to 45.0 °C) and pressure at a fixed pH of 6.0, reveal that the formation of [RuIII (edta)(Am)]–(Am = amino acid) occurs via a rapid amino acid concentration dependent complex-formation reaction of [RuIII(edta)(H2O)]–, followed by a slow amino acid concentration independent ring-closure step. The kinetic data and activation parameters are interpreted in terms of an associative interchange mechanism and discussed in reference to data reported for closely related systems in the literature. Enzyme inhibition studies revealed that [RuIII(edta)(H2O)]– effectively inhibits the cysteine protease activity in papain and bromalein enzymes.