Tohru Saitoh

Distribution of metal chelates between aqueous and surfactant phases separated from a micellar solution of a nonionic surfactant

A dilute micellar solution of poly(oxyethylene) 4-nonylphenyl ether with oxyethylene units 7.5 (PONPE-7.5) was separated into two phases (aqueous and surfactant phases) at room temperature. The partition constants of several chelating reagents and their metal chelates between the two phases were determined at 293 K and ionic strength 0.1 (NaClO4). The partition constants of the neutral metal chelates depend on the kind of metal ions and were considerably smaller than those expected from the regular solution theory. These facts suggested that the chelates were incorporated into a hydrocarbon environment in the surfactant phase, whereas the chelating reagents were distributed in the poly(oxyethylene) part of PONPE-7.5. A brief review was also presented on the analytical applications to the extraction of metal ions and organic compounds.

Volume constraint effect on solute partitioning to Triton X-100 micelles in water

On the basis of the simple two-phase model the partition constants (Kd) of various organic solutes and metal chelates between aqueous and Triton X-100 micellar phases are derived spectrophotometrically. The magnitude and the order of Kd are discussed in terms of molecular size, hydrophilicity and ion-association character of the solutes. The Kd values of neutral species increase almost linearly with their van der Waals molar volumes until the critical value near 110 ml mol–1 is reached. Above this critical volume, the constraint effect of the micelles gives rise to severe levelling off the partition constants at ca. 103.0 for bulky solutes. The Kd values of 2-(thiazol-2-ylazo)-4-tert-octylphenol, 2-(thiazol-2-ylazo)-4-methylphenol (HL) and the metal chelates of [FeIIL2] and [NiIIL2] are in a very narrow range of 102.83, 102.93, 103.06 and 103.16, respectively. The effects of micellar size are also examined using Brij-35 and Brij-58 surfactants.

Polymer‐induced phase separation in aqueous micellar solutions of octyl‐β‐D‐thioglucoside for extraction of membrane proteins

A water-soluble polymer such as polyethylene glycol (PEG), Dextran T-500 (Dx), or diethylaminoethyl-Dextran (DEAE-Dx) induced aqueous micellar solutions of octyl-beta-D-thioglucoside (OTG) to phase separation at 0 degrees C. One of the two phases thus formed is a surfactant-depleted aqueous solution (aqueous phase) of a water-soluble polymer and the other a concentrated OTG solution (surfactant-rich phase). In a combination of OTG with PEG or Dx, cytochrome P450 (P450) and cytochrome b(5) (b(5)) were well extracted into the surfactant-rich phase. The extraction yield of P450 was slightly greater than that of b(5). In contrast to PEG and Dx, DEAE-Dx markedly reduced the extraction of b(5), while that of P450 remained almost unchanged. DEAE-Dx served the dual functions of inducing the phase separation and preventing the extraction of b(5) into the surfactant-rich phase. This depressed extraction of b(5) was reversed by the addition of potassium phosphate. DEAE-Dx and potassium phosphate proved effective in controlling the extractability of b(5). The polymer-induced phase separation provides a new basis for highly efficient extraction of membrane proteins under mild conditions that should be acceptable for thermolabile membrane proteins under physiological conditions.