Correlation between Lewis Acid−Base Surface Interaction Components and Linear Solvation Energy Relationship Solvatochromic α and β Parameters

Abstract

In this paper, we report our unexpected finding about the correlation between Lewis acid−base surface interaction components and linear solvation energy relationship (LSER) solvatochromic parameters α and β. In 1987, van Oss, Chaudhury, and Good proposed to split the asymmetric acid−base parts of a bipolar system into separate surface tension components: Lewis acid (electron acceptor) γ+ and Lewis base (electron donor) γ-. It was assumed that the ratio of γ+ and γ- for water at 20 °C was to be 1.0. With that ratio as a reference, the base components, γ- for other liquids, biopolymers, polymers, and solids appeared to be overestimated. Recently, we unexpectedly found a correlation for liquids between γ+ and γ-, and α (solvent hydrogen-bond-donating ability) and β (solvent hydrogen-bond-accepting ability) introduced since 1976 by Taft and Kamlet. From that correlation, we obtained a more realistic ratio for the normalized α and β values for water at ambient temperature to be 1.8 instead of 1.0. Based on this new ratio, we calculated total surface tensions for related materials at 20 °C. They are generally unchanged as expected, despite the considerable, favorable change in the γ+ and γ- values in the direction of lowering the Lewis basicity. The predicability of solubility with interfacial tension is also unaffected. For example, the sign of those negative interfacial tensions that favor solubility remains the same. In addition, the implications of other LSER parameters, e.g. Π* and δH2, on surface properties will be briefly mentioned.