Liposomes and micelles find various applications as potential solubilizers in extraction processes or in drug delivery systems. Thermodynamic and transport processes governing the interactions of different kinds of solutes in liposomes or micelles can be analyzed regarding the free energy profiles of the solutes in the system. However, free energy profiles in heterogeneous systems such as micelles are experimentally almost not accessible. Therefore, the development of predictive methods is desirable. Molecular dynamics (MD) simulations reliably simulate the structure and dynamics of lipid membranes and micelles, whereas COSMO-RS accurately reproduces solvation free energies in different solvents. For the first time, free energy profiles in micellar systems, as well as mixed lipid bilayers, are investigated, taking advantage of both methods: MD simulations and COSMO-RS, referred to as COSMOmic (Klamt, A.; Huniar, U.; Spycher, S.; Keldenich, J. COSMOmic: A Mechanistic Approach to the Calculation of Membrane-Water Partition Coefficients and Internal Distributions within Membranes and Micelles. J. Phys. Chem. B 2008, 112, 12148-12157). All-atom molecular dynamics simulations of the system SDS/water and CTAB/water have been applied in order to retrieve representative micelle structures for further analysis with COSMOmic. For the system CTAB/water, different surfactant concentrations were considered, which results in different micelle sizes. Free energy profiles of more than 200 solutes were predicted and validated by means of experimental partition coefficients. To our knowledge, these are the first quantitative predictions of micelle/water partition coefficients, which are based on whole free energy profiles from molecular methods. Further, the partitioning in lipid bilayer systems containing different hydrophobic tail groups (DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine), SOPC (stearoyl-oleoylphosphatidylcholine), DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine), and POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine)) as well as mixed bilayers was calculated. Experimental partition coefficients (log P) were reproduced with a root-mean-square error (RMSE) of 0.62. To determine the influence of cholesterol as an important component of cellular membranes, free energy profiles in the presence of cholesterol were calculated and shown to be in good agreement with experimental data.

Surfactant solutions in practical applications usually are mixtures of ionic and nonionic surfactants. Because of synergistic effects, the solubilization of hydrophobic compounds can be enhanced while decreasing the needed amount of surfactant at the same time. In this work, the influence of the composition of Brij 35/CTAB and Brij 35/SDS mixed micelles on the partition coefficient log D(MW) of various acids and bases over the entire pH range was investigated. Two experimental methods (MLC, micellar liquid chromatography; MEUF, micellar enhanced ultrafiltration) are evaluated for the determination of partition coefficients in mixed-micelle systems. Although MLC stands out because of its automation and easy handling, MEUF is applicable to a broader log D(MW) range. It is shown that the partitioning can be influenced dramatically by the two investigated parameters. By adjusting the pH value and the composition of the micelles, we can tailor the partition behavior of solutes for virtually any application. The thermodynamic model COSMO-RS gives valuable predictions of the partition coefficients if the composition of the micelle is available. Different approaches for the description of the micellar composition are evaluated in this work. On the basis of the cmc value of the single surfactants and the mixture only, it is shown that the regular solution approximation gives reasonable micellar compositions. The partition coefficients between water and the mixed micelles are predicted with the COSMO-RS model, in good agreement with the experimental data. Moreover, the micellar composition can be evaluated by fitting the prediction to the experimentally determined partition coefficients.

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Aqueous nonionic surfactant solutions split into two phases if the temperature is increased beyond a certain temperature, the so‐called cloud point temperature. Presently many different types of nonionic surfactants are produced commercially, out of these numerous have been considered as potential solvent for the cloud point extraction. In this work the crucial thermophysical properties of nonionic surfactants are investigated to determine the potential of surfactant systems for extraction processes. Phase equilibria of the binary system Triton X‐114/water and the ternary system Triton X‐114/water/phenol were measured. Based on these data the cloud point extraction was implemented in a continuous stirred extraction column. It was found, that increasing temperature within the column reduces the loss of surfactant and leads to an increasing enrichment factor. This work demonstrates that surfactant/water systems represent a suitable alternative to conventional solvents and can effectively be processed in continuous extraction columns.