Design of surfactants suitable for protein extraction by reversed micelles.

New surfactants have been synthesized for potential use in reversed micellar protein extraction operations. Preferential solubility of the surfactant in an aliphatic solvent such as hexane, heptane, or isooctane and the formation of reversed micelles accompanied with solubilization of significant quantities of water can be achieved by using strongly hydrophobic, twin alkyl chains as the hydrophobic moiety. Different surfactants having identical water-solubilizing capacities can have significantly different behavior in protein extractions, where extraction efficiency appears to be governed by the nature of the interfacial complex that forms between surfactants and proteins. Bulky surfactant chains provide a steric hindrance to the adsorption of the surfactant to the protein surface, thus inhibiting solvation of the protein/surfactant complex, and hence protein extraction. Under these conditions, a precipitate forms either in the bulk aqueous phase or at the interface. Surfactants that can form a close-packed complex with the protein are excellent protein-solubilizing agents. Dioleyl phosphoric acid (DOLPA) appears to be the best surfactant currently available for protein extraction.