Sparingly fluorinated maltoside-based surfactants for membrane-protein stabilization

Membrane proteins pose formidable challenges during in vitro investigations, as they require amphiphilic molecules for their solubilization, stabilization, and crystallization for structural characterization. Therefore, numerous, chemically diverse new amphiphiles have been developed for membrane-protein applications. Among these, both perfluorinated and hemifluorinated surfactants have long been known to stabilize membrane proteins, but the contribution of the fluorine content in the aliphatic chain has not yet been examined in detail. We have synthesized two new maltose-based fluorosurfactants bearing either a perfluoroethyl (F2H9) or a perfluorobutyl (F4H5) tip at the end of the chain and compared them with the common detergent dodecyl maltoside and a commercial highly fluorinated octyl maltoside derivative. We describe the physicochemical properties, aggregate morphologies, and micellization thermodynamics of these sparingly fluorinated surfactants as a function of the length of the fluorinated segment and evaluate their biochemical use for membrane-protein stabilization. Intriguingly, the surfactant carrying a perfluorobutyl (F4H5) tip trumps both nonfluorinated dodecyl maltoside and a more extensively fluorinated octyl maltoside derivative in conferring extraordinary long-term functional and colloidal stability to the model membrane protein bacteriorhodopsin.