Refractive index matching to develop transparent polyaphrons: Characterization of immobilized proteins

• We evaluate the adsorbed structure of four proteins at the oil/water interface.
• Refractive index matching shows proteins are unchanged upon adsorption to the CLA.
• Hydrophobic interactions increase adsorption rate due to the presence of a solvent core.
• Non-ionic surfactants show no interactions with proteins.
• Structural preservation due to bound water within the CLA structure.

Refractive index matching was used to create optically transparent polyaphrons to enable proteins adsorbed to the aphron surface to be characterized. Due to the significant light scattering created by polyaphrons, refractive index matching allowed for representative circular dichroism (CD) spectra and acceptable structural characterization. The method utilized n-hexane as the solvent phase, a mixture of glycerol and phosphate buffer (30% [w/v]) as the aqueous phase, and the non-ionic surfactants, Laureth-4 and Kolliphor P-188. Deconvolution of CD spectra revealed that the immobilized protein adapted its native conformation, showing that the adsorbed protein interacted only with the bound water layer (“soapy shell”) of the aphron. Isothermal calorimetry further demonstrated that non-ionic surfactant interactions were virtually non-existent, even at the high concentrations used (5% [w/v]), proving that non-ionic surfactants can preserve protein conformation.

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