Conformational transition and mass transfer in extraction of proteins by AOT–alcohol–isooctane reverse micellar systems

We examined quantitatively the effect of alcohols on protein and reverse micellar structure. We used circular dichroism (CD) to compare the effects of various alcohols on the protein structure, and percolation phenomena to evaluate the effects of various alcohols on reverse micellar structure. Upon the addition of alcohols to the bulk aqueous phase, proteins were denatured significantly, depending on the alcohol species and concentration, suggesting that use of alcohol directly to the stripping solution is not effective in back-extraction processes of proteins. In the present study, a new method, a small amount of alcohol is added to the surfactant–organic solution to improve the back-extraction behaviors of proteins. Practically, in the back-extraction process, the alcohols suppressing the cluster formation of reverse micelles (high value of βt), remarkably improved the back-extraction behavior of proteins. In addition, the same alcohol molecules showed a positive effect on the rate and fraction of protein back-extraction. From a result of the CD measurement of the back-extracted proteins, it was known that the alcohols added to reverse micellar solution allowed the proteins to back-extract safely without causing structural changes. These results show that the values of βt, defined by the variation of percolation processes, and the back-extraction behaviors of proteins have a good relationship, suggesting that the back-extraction processes were controlled by the micellar–micellar and protein–micellar interactions.