Mixed micelles containing sodium oleate: the effect of the chain length and the polar head group.

We have investigated the mixing behavior of binary mixtures of the alkylglucosides (CnG) octyl beta-D-glucoside and decyl D-glucoside in combination with sodium oleate (NaOl), and the amine oxide surfactants (AO) N,N-dimethyldodecylamine oxide, N,N-bis (2-hydroxyethyl)dodecylamine oxide, and 3-lauramidopropyl-N,N-dimethylamine oxide in combination with NaOl. From the equilibrium surface tension measurements, the critical micelle concentration (cmc) data were obtained as functions of the composition. Values of the cmc were analyzed according to both the regular solution model developed by Rubingh for mixed micelles and Maeda's formulation for ionic/nonionic mixed micelles. Two interaction parameters, beta and B1, were estimated from the regular solution model and Maeda's formulation, respectively. For NaOl/CnG mixed systems, a decrease in the hydrocarbon chain length of CnG resulted in a stronger interaction with NaOl from both beta and B1 values. For NaOl/AO mixed systems, the bulkiness of a polar head group of AO surfactants influenced the interaction between NaOl and AO. The dynamic surface tension measurements show that all surface tension values of surfactant solutions examined decreased with the time. We found that the time dependence of surface tension values for NaOl mixed systems was greatly influenced by the presence of NaOl rather than the other component.

New artificial host compounds containing galactose end groups for binding chiral organic amine guests: chiral discrimination and their complex structures.

New linear host (1) and cyclic hosts (2 and 3), which have galactopyranose skeletons as chiral origins and oxyethylenes skeletons as binding sites, were designed based on the structural features extracted from the fructo-oligosaccharide derivatives, having a large chiral discrimination ability, and were then synthesized. These hosts showed chiral discrimination toward chiral organic ammonium salts. For example, the chiral discrimination ability (the ratio of association constants: K(R)/K(S)) of host 1, which has the highest value among them, was K(R)/K(S) = 3 for Trp-O-(i)Pr(+) and K(R)/K(S) = 0.7 for 1-(1-naphthyl)ethylammonium (NEA(+)) at 298 K in CHCl(3). It was clarified that host 1 changed the conformation from a linear structure to the pseudo-ring structure by complexation with cations such as alkali metallic ions and chiral organic ammonium ions. The (1)H NMR induced shifts of host 1 by adding the NEA(+) guests showed that the host-guest complex structures are clearly different, depending upon the chirality of the guest; in the complex with (R)-NEA(+), the naphthyl group of the guest is located above the oxyethylene skeleton of the host and in the complex with (S)-NEA(+), and the naphthyl group is located between the edges of the pseudo-ring of the host. The clearly different structure of the complex of host 1 with NEA(+) may be caused by the dynamic molecular recognition, thus the induced-fitting mechanism.

Effects of micellar charge density on the coefficient of the Corrin-Harkins relation.

Effects of the micelle composition (ionic species fraction alpha(M)) on the coefficient of the Corrin-Harkins relation (k(CH)) of ionic/nonionic mixed micelles were examined in the case of dodecyldimethylamine oxide. Long alkyl chain amine oxides exist either in the nonionic or the cationic (protonated form) species depending on the pH of solutions and hence the control of the micelle composition near the critical micelle concentration (cmc) is possible by adjusting the pH of the solutions. On the basis of the cmc data from the surface tension measurements and the hydrogen ion titration curves, we evaluated the k(CH) values as a function of the micelle composition alpha(M) for the first time. The obtained k(CH) values were compared with the degree of the counterion binding, theta, in the solutions without added salt. The k(CH) values increased with alpha(M), and were approximately identical with theta for alpha(M)>0.4. In the range alpha(M)<0.4, it is likely that theta is greater than k(CH). An empirical relation proposed by D. G. Hall et al. ("Mixed Surfactant Systems," Am. Chem. Soc., Washington, D.C. 1992) on the relation between theta and the micelle composition was also compared with these experimental results. Experimental values, k(CH) and theta, followed the empirical relation for alpha(M)>0.4; however, both k(CH) and theta increased steeply in the range alpha(M) 0.25-0.3.