Verteilungskoeffizienten in gemischten Tensidsystemen

In der vorliegenden Arbeit wird eine Methode entwickelt, die es ermöglicht die Eignung von Tensiden für neuartige Trennprozesse zu evaluieren. Hierzu werden Tensid/ Wasser Phasengleichgewichte und Mizelle/ Wasser Verteilungskoeffizienten ermittelt, unter der Berücksichtigung des Einflusses von Alkoholen, pH Wert und Tensidmischungen. Basierend auf experimentellen und prädiktiven (COSMO-RS) Ergebnissen wird die Implementierung von Tensidsystemen anhand von Beispielen demonstriert.In this work the applicability of surfactants in novel separation processes is investigated. The surfactant/ water phase behavior and micelle/ water partition coefficients were determined, considering the influence of alcohols, the pH value and surfactant mixtures. Based on the experimental and predicted (COSMO-RS) results, the implementation of surfactant based systems is demonstrate

Partition coefficients of ionizable solutes in mixed nonionic/ionic micellar systems

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 DMW 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 DMW 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. © 2012 American Chemical Society

Extension of COSMO-RS for monoatomic electrolytes: modeling of liquid-liquid equilibria in presence of salts

COSMO-RS is a widely accepted method to calculate thermodynamic properties like partition coefficients, VLE-, and LLE-data. At present COSMO-RS cannot account for long-range ion-ion interactions. Further, the element specific COSMO-radii for cations like lithium or potassium have not been optimized. In this work an extension of COSMO-RS for monoatomic electrolytes is presented. Based on experimental mean ionic activity coefficients in aqueous solutions new element specific COSMO-radii for alkali metals were introduced. The new parameterization accounts for long-range ion-ion interactions and cation hydration as well as an element specific hydrogen bonding contribution for anions. In order to evaluate the new parameterization, mean ionic activity coefficients in mixed solvent systems were calculated and compared to experimental data. In addition, liquid-liquid equilibria in presence of electrolytes were calculated with the new parameterization. The influence of monoatomic electrolytes on immiscible aqueous organic systems can be accurately reproduced. Further, the salt induced phase separation of miscible aqueous organic system was successfully predicted

Recovery of sugars from aqueous solution by micellar enhanced ultrafiltration

The separation of hydrophilic substances, like sugars, from aqueous solutions is still a huge challenge. Within this work the extraction of sugars with micellar systems was performed by means of the micellar enhanced ultrafiltration (MEUF) and compared to the state of the art extraction based on organic solvents. Phenylboronic acid was used as carrier to solubilize sugars (arabinose, cellobiose, glucose, and sucrose) in different kind of micelles (formed by the cationic surfactant CTAB and the non-ionic/cationic surfactant mixture Triton X-100™/Aliquat 336™). It was shown that the partition coefficients of the sugars in micellar systems are higher than those achieved with organic solvents, especially using the cationic surfactant. Monosaccharides were recovered efficiently and with a high selectivity (up to 64% for the monosaccharides compared to 17% for the disaccharides). It was shown, that the recovery can be enhanced with increasing cationic surfactant content. Furthermore the equilibration time can be reduced significantly compared to the extraction with organic solvents. Thus, micellar enhanced ultrafiltration is a promising method for the recovery of sugars and other hydrophilic components from aqueous streams without any use of organic solvents

COSMO-RS for the prediction of the retention behavior in micellar liquid chromatography based on partition coefficients of non-dissociated and dissociated solutes

Several methods for the description of the retention behavior in micellar liquid chromatography (MLC) were described previously. Thereby, the most common are the linear solvation energy relationships (LSER). However, for the evaluation of the LSER, a number of experimental data are necessary. In this work, the retention data are predicted based on a single data point for a given solute/surfactant combination. The prediction of micelle/water partition coefficients with the COSMO-RS model was evaluated for the nonionic surfactant Brij 35 and the cationic CTAB for 21 solutes. The predicted partition coefficients along with the retention data of a single measurement were combined with a common retention model for the evaluation of partition coefficients. Thus, the description of the retention data based on a minimum of experimental data was realized in this work. The COSMO-RS model appears to be suitable for the flexible and qualitative prediction of the retention data, which is of special benefit, when a large number of solutes are studied. Furthermore, the introduced method is a promising alternative to describe the retention behavior of ionizable solutes, which is of great interest for e.g. pharmaceutical processes and analyses. To evaluate the method, lipophilicity profiles of several solutes were determined with MLC. While for the nonionic surfactant the lipophilicity is similar to the octanol/water system, a contrary phenomenon, namely a significant increase of the partition coefficient with progressive dissociation can be observed with the ionic surfactant. The MLC method proved to be an efficient method for the determination of micelle/water partition coefficients, excluding non-binding and " overbinding" solutes. The introduced COSMO-RS based approach for the estimation of the retention in MLC is especially promising for highly retarding solutes, since it is time and cost saving compared to the experimental determination

Experimental Methods and Prediction with COSMO-RS to Determine Partition Coefficients in Complex Surfactant Systems

Surfactant-based separation processes are a promising alternative to conventional organic solvent processes. A crucial parameter to describe the efficiency of such processes is the partition coefficient between the surfactant aggregates (micelles) and the aqueous bulk phase. In this work, several experimental methods to determine these partition coefficients (micellar liquid chromatography, micellar enhanced ultrafiltration, and cloud point extraction) are evaluated and compared. In addition, these results are compared to predictions with the thermodynamic model COSMO-RS. In particular, systems with the nonionic surfactant TritonX-100 are studied. The partition equilibria of various solutes (pyrene, naphthalene, phenanthrene, phenol, 3-methoxyphenol, and vanillin) and the influence of different additives (alcohols) are investigated. All experimental methods show very good reproducibility. Moreover, the results from different methods are in good agreement, supplementing one another concerning the temperature ranges. Notably, the COSMO-RS model is capable of predicting partition coefficients between micelles and water in the investigated temperature range and at different alcohol concentrations. The results demonstrate the potential of the model COSMO-RS to facilitate the selection of optimized process parameters for a given separation problem. By predicting partition equilibria in multicomponent systems, the selection of surfactant, temperature, and appropriate additives can be facilitated

Prediction of micelle/water and liposome/water partition coefficients based on molecular dynamics simulations, COSMO-RS, and COSMOmic

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. B2008, 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. © 2013 American Chemical Society

Estimation of LPC/water partition coefficients using molecular modeling and micellar liquid chromatography

Lysophosphatidylcholine (LPC) is a lipid based, micelle forming emulsifier and thus a potential solubilizer for hydrophobic components in pharmaceutical and food products. Since many components of interest are very hydrophobic, the determination of the partition equilibrium between the micelles and the aqueous bulk phase is challenging. In this work several methods (micellar liquid chromatography (MLC), molar solubilization ratio (MSR) and an indirect method, using an organic solvent phase) for the experimental determination of partition coefficients are compared. For the first time the emulsifier LPC was employed in the MLC. It is shown, that the partition coefficients between micelles and water can be determined with good agreement to literature data and between the different methods for solutes in a wide hydrophobicity range.Moreover, the experimental data are compared to a priori predictions based on the thermodynamic model COSMO-RS. The prediction assuming the pseudophase approach is compared to the prediction using COSMOmic, thus taking into account the anisotropic structure of the micelles, obtained from molecular dynamics all-atom simulations. Both methods agree well with the experimental data for the partition coefficients between LPC and water and between the anionic surfactant SDS and water. Using COSMOmic, beside the partition coefficient, the location of the solute within the micelle is predicted. It is shown, that the combination of experimental methods and models like COSMO-RS reveals a deeper understanding of the specific interactions, which is needed for an efficient use of emulsifiers in a variety of applications

Prediction of Micelle/Water and Liposome/Water Partition Coefficients Based on Molecular Dynamics Simulations, COSMO-RS, and COSMOmic

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. <i>J. Phys. Chem. B</i> <b>2008</b>, <i>112</i>, 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-<i>sn</i>-glycero-3-phosphocholine), SOPC (stearoyl-oleoylphosphatidylcholine), DMPC (1,2-dimyristoyl-<i>sn</i>-glycero-3-phosphocholine), and POPC (1-palmitoyl-2-oleoyl-<i>sn</i>-glycero-3-phosphocholine)) as well as mixed bilayers was calculated. Experimental partition coefficients (log <i>P</i>) 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