CYCLIC VOLTAMMETRIC CHARACTERIZATION OF RATE CONSTANTS FOR CONFORMATIONAL CHANGE IN AN ELECTRON-TRANSFER SQUARE SCHEME INVOLVING A COPPER(II) (I) MACROCYCLIC TETRATHIAETHER COMPLEX/

With a glassy-carbon ultramicroelectrode and appropriate circuitry, cy clic voltammograms have been generated for solutions containing the Cu (II/I)([14]aneS4) system at scan rates up to 60 kV s-1 in 80% methanol (w/w) at 25-degrees-C. These rapid-scan voltammograms provide direct evidence for the existence of metastable intermediates of both the Cu( I)L and the Cu(II)L species in conformance with our previously propose d square scheme mechanism. On the basis of the experimental data, esti mates have been made for all the specific homogeneous and heterogeneou s rate constants associated with this square scheme. The values of the se constants have then been further refined using digital simulation. The resulting simulated voltammograms are shown to correlate reasonabl y well with the experimental observations at even the most rapid scan rates achieved. The availability of the specific rate constant values representing Cu(I)L and Cu(II)L conformational interconversions makes it possible to predict the conditions under which conformational chang e of the Cu(I)L species should become rate limiting, resulting in the appearance of gated electron-transfer behavior in homogeneous cross re actions.