Analytical Sciences

Abstract − Analytical Sciences, 24(7), 901 (2008).

Electrochemical Aspects of the Reverse Micelle Extraction of Proteins
Toshiyuki OSAKAI and Aya SHINOHARA
Department of Chemistry, Graduate School of Science, Kobe University, Nada, Kobe 657-8501, Japan
The mechanism of the solvent extraction of cytochrome c (Cyt c) via reverse micelle formation was studied from an electrochemical point of view. Potentiometric measurements showed that the Galvani potential difference of the oil/water (O/W) interface played a crucial role in the spontaneous extraction of Cyt c with bis(2-ethylhexyl)sulfosuccinate (AOT). However, the dependence of the extraction efficiency on the concentration of an aqueous electrolyte (KCl) could be explained not by the effect of the interfacial potential, but by the change in the interfacial tension (γ). Electrocapillary measurements showed that the adsorption of AOT anions to the O/W interface resulted in a significant decrease of γ in a higher potential range, where reverse micelles were formed. The bottom level of γ in the higher potential range was increased with [KCl]. The lower extraction efficiency for higher [KCl]'s was elucidated by a “size exclusion effect”. This was also supported by water-content measurements by the Karl Fisher method.