Ion transfer of reduced Keggin-type heteropolymolybdate anions at the nitrobenzene/water interface and its relevance to their antitumoral activities

The transfer of two-electron reduced Keggin anions (alpha- and beta-[(PMo2M o10O40)-Mo-V-O-VI](5-) and alpha-[(SiMo2Mo10O40)-Mo-V-O-VI](6-)) across the nitrobenzene/water interface was studied by cyclic voltammetry. Based on m easurements of the ion-transfer potential at various pHs, ionic distributio n diagrams were prepared. It was found that the polyanion transfer was usua lly accompanied by the proton transfer. To confirm the validity of the dist ribution diagrams, the theoretical simulation of normal-pulse voltammograms was also performed. The ion-transfer potentials of some Keggin-type hetero polymolybdate anions at a physiological pH (7.0) showed an excellent correl ation with their antitumoral activities, suggesting a crucial role of their stability in the aqueous solution.