A Hydrophobicity Scale of Heteropoly- and Isopolyanions Based on Voltammetric Studies of Their Transfer at the Nitrobenzene/Water Interface

Abstract

A hydrophobicity scale of heteropoly- and isopolyanions is proposed on the basis of voltammetric studies concerning their transfer at the nitrobenzene (NB)/water (W) interface. For polyanions of various size and ionic charge (z = −2 to −6), the standard ion-transfer potential (Δ_O^Wφ), which is related to the Gibbs free energy of the transfer as Δ_O^Wφ = −ΔG_tr^O→W/zF (F, the Faraday constant), depends linearly on the quantity |z|/n^2/3 (n, the number of oxygen atoms in the polyanion structure), which should be proportional to the surface charge density of the polyanion. The value of |z|/n^2/3 may provide a useful criterion for evaluating the hydrophobic (or hydrophilic) properties of polyanions, including the stability in solutions and extractability into organic solvents.