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