Investigation on the Effect of Protein on the Properties of Bis(2-ethylhexyl) Sulfosuccinate/Isooctane Reverse Micelles

Abstract

The diameter of water-in-oil reverse micelles formed by sodium bis(2-ethylhexyl) sulfosuccinate (AOT) with water and with protein Bovine serum alumin (BSA) was investigated by dynamic light scattering (DLS) measurement of AOT/isooctane solution at 298.15 K. The diameter and viscosity of AOT reverse micelle increases with increasing ω0 (mole ratio of water to surfactant: ω0 = nw/ns). The viscosity of AOT/isooctane with water or BSA inside did not change with shear rate, exhibiting Newtonian behavior. For ω0 = 8.3, the diameter of AOT reverse micelles increases with increasing BSA concentration from 2 mg of BSA·mL−1 of H2O to 145 mg of BSA·mL−1 of H2O. The diameter of AOT reverse micelles increases only slightly with BSA inside compared with water inside at the same ω0. Incorporation of protein into the micelles does not affect their mean diameter significantly. The hydrodynamic diameter of BSA from 10 mg to 100 mg of BSA·mL−1 of H2O in 0.1 mol·L−1 AOT reverse micelles increased almost linearly with ω0 which confirmed that the diffusion coefficient was independent of ω0, indicating a spherical structure for the AOT reverse micelles. The localization of BSA is in the center part of the water pool without perturbation of the reverse micelles. For highly concentrated BSA from 50 mg to 145 mg·mL−1 of water, only when ω0 is higher than 5.6, the 0.1 mol·L−1 AOT reverse micelles can solubilize it.