Traube-Rule Interpretation of Protein Adsorption at the Liquid−Vapor Interface

Abstract

Pendant-drop tensiometry of aqueous-buffer solutions of purified human proteins spanning nearly 3 orders of magnitude in molecular weight (MW) reveals that reduction in liquid−vapor (LV) interfacial tension γlv followed a systematic progression in MW with the molar concentration required to reach a specified γlv value decreasing with increasing MW in a manner reminiscent of the Traube rule for linear hydrocarbon surfactants. Furthermore, the concentration dependence of interfacial tension (dγlv/d ln CB, where CB is bulk-solution concentration) is observed to be surprisingly invariant among this disparate group of proteins (i.e., approximately constant apparent Gibbs' surface excess Γ = −1/RT dγlv/d ln CB). These findings are interpreted through a model of protein adsorption predicated on the interfacial packing of spherical molecules with dimensions scaling as a function of MW. The Traube-rule-like ordering is rationalized as a natural outcome of an invariant partition coefficient that entrains a fixed fr...