Kinetic data needed to use alpha-AlW12O406- (alpha-2(1e)) as well-defined probe for investigating electron-transfer processes in water is evaluated using the extended Debye-Huckel equation. First, rate constants, as a function of ionic strength in water, are determined for electron self-exchange reactions between a series of AlW12O40n- ions (alpha and beta isomers of fully oxidized, one- and two-electron reduced ions). The kinetic data are plotted using the extended Debye-Huckel equation, in which the distance of closest contact is set equal to twice the hydrodynamic radius of a Keggin anion. In all cases. slopes of these plots give charge-product (z(1)z(2)) values within error of those anticipated based on the charges of the reacting ions. The aqueous solution chemistry of alpha-AlW12O405- (alpha-2(ox)) and alpha-AlW12O406- (alpha-2(1e)) is then fully defined, and the reduction potential of the alpha-2(ox)/alpha-2(1e) couple is determined. These studies provide the information needed to use alpha-2(1e) a powerful reducing agent, to obtain detailed information about the first steps in reduction of O-2 to H2O, a process of considerable importance to chemistry and biology. (c) 2006 Elsevier B.V. All rights reserved.