Water-in-Silicone Oil Emulsion Stabilizing Surfactants Formed From Native Albumin and α,ω-Triethoxysilylpropyl-Polydimethylsiloxane

Contact with hydrophobic silicones frequently leads to protein denaturation. However, it is demonstrated that albumin in water-in-silicone oil emulsions retains its native structure in the presence of a functional, triethoxysilyl-terminated silicone polymer, TES-PDMS. Both HSA and TES-PDMS were essential for the formation of stable water-in-silicone oil emulsions: attempts to generate stable emulsions using independently either the protein or the functionalized silicone as a surfactant failed. Confocal microscopy indicated that the human serum albumin (HSA) preferentially adsorbed at the oil/water interface, even in the presence of another protein (glucose oxidase). A variety of experiments demonstrated that the hydrolysis of the Si-OEt groups on the functional silicone occurred only to a limited extent, consistent with the absence of a covalent linkage between the silicone and protein, or of cross-linked silicones at the interface. The fluorescence spectra of HSA extracted from the emulsions, front-faced fluorescence experiments on the HSA/silicone emulsion itself, and HSA/salicylate binding studies all demonstrated that the stability of the water/oil interface decreased as the protein began to unfold: unfolding of the protein in the emulsion was slower than in aqueous solution. The experimental evidence indicated that the interaction between HSA and TES-PDMS is not associated with either homomolecular (HSA/HSA; TES-PDMS/TES-PDMS) interactions or with covalent linkage between two the polymers. Rather, the data is consistent with the direct binding of unhydrolyzed Si(OEt) 3 groups to native HSA. The nature of these interactions is discussed.