Interaction of the divalent lead cation with cyclosporin A: an experimental and theoretical study
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On the basis of extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Pb2+(aq) + 1·Sr2+(nb) ⇄ 1·Pb2+(nb) + Sr2+(aq) occurring in the two-phase water–nitrobenzene system (1 = cyclosporin A; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K ex (Pb2+, 1·Sr2+) = 0.1 ± 0.1. Further, the stability constant of the 1·Pb2+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β nb (1·Pb2+) = 9.2 ± 0.2. Finally, applying quantum chemical DFT calculations, the most probable structure of the proven 1·Pb2+ cationic complex species was derived. In the resulting complex, the “central” cation Pb2+ is bound by four bonding interactions to the corresponding four oxygen atoms of the parent cyclosporin A ligand. The interaction energy, E(int), of the considered 1·Pb2+ complex was found to be −1016.3 kJ/mol, confirming also the formation of this complex.
KeywordsDivalent lead cation Cyclosporin A Complexation Extraction and stability constants DFT calculations
This work was supported by the Grant Agency of Faculty of Environmental Sciences, Czech University of Life Sciences, Prague, Project No. 42900/1312/3114 entitled “Environmental Aspects of Sustainable Development of Society,” and by the Czech Ministry of Education, Youth, and Sports (Project MSMT No. 20/2015).
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