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Item type:Publication, Access status: without files , Modeling the solubility of CO₂ in aqueous methyl diethanolamine solutions with an electrolyte model based on COSMO-RS(2018-04-15); ; ; A new COSMO-RS based electrolyte model (COSMO-RS-ES) was applied to the prediction of the solubility of CO₂ in aqueous MDEA solutions. For this purpose, the model was combined with the Soave-Redlich-Kwong equation of state to describe the gas phase non-ideality. First, it was shown that the model can successfully describe the phase equilibria in the CO₂ + water, as well as in alkanolamine + water systems. Using a region specific interaction parameter for the amine, the accuracy of the model for the prediction of the phase equilibrium in alkanolamine + water systems was further improved. Additionally, a detailed investigation of different amine + water systems based on the calculation of the partial molar enthalpies and entropies provided valuable insights on the properties of the systems. The description of the ternary CO₂ + MDEA + H₂O system was successful after a readjustment of selected interaction energy equations of the model using few parameters. The model was then applied to the prediction of the species distribution as well as the prediction of the partial pressure of CO₂ at low gas loading.Publicationtype: Journal Article80 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of inorganic salts on the phase equilibrium of triton X-114 aqueous two-phase systems(American Chemical Society (ACS), 2016-03-17); ; ; ; In this work, we studied the liquid-liquid equilibrium of ternary systems containing nonionic surfactant Triton X-114, inorganic salts, and water. The salt impact of five different sodium salts (NaCl, NaBr, NaI, Na2SO4, and Na2HPO4) and four different chlorides (NaCl, KCl, LiCl, NH4Cl) was investigated. The influence of the inorganic additives was studied at 30 °C because at this temperature all prepared mixtures faced a separation above the cloud point temperature (CPT) in micellar (surfactant-rich) and aqueous (surfactant-lean) phase. The salting-out ability of the cations follows the series Na+ > K+ > NH4+ > Li+. We observed a more pronounced effect among the anions, where the salting-out effect decreased in the order HPO42- ≈ SO42- > Cl- > Br- > I-. All salts, except NaI, lead to an increase in the Triton X-114 concentration in the micellar phase and to a decrease of the surfactant fraction in the aqueous phase. Inorganic salts also distributed unevenly between both phases and, thus, accumulated in the aqueous phase. In the case of stronger salting-out kosmotropic anions (HPO42-, SO42-), the salt load of water in the aqueous phase was higher compared to the weaker agents Br- and I-.Publicationtype: Journal Article95 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Predicting solute partitioning in lipid bilayers: Free energies and partition coefficients from molecular dynamics simulations and COSMOmic(2014-07-28); ; ; ; Quantitative predictions of biomembrane/water partition coefficients are important, as they are a key property in pharmaceutical applications and toxicological studies. Molecular dynamics (MD) simulations are used to calculate free energy profiles for different solutes in lipid bilayers. How to calculate partition coefficients from these profiles is discussed in detail and different definitions of partition coefficients are compared. Importantly, it is shown that the calculated coefficients are in quantitative agreement with experimental results. Furthermore, we compare free energy profiles from MD simulations to profiles obtained by the recent method COSMOmic, which is an extension of the conductor-like screening model for realistic solvation to micelles and biomembranes. The free energy profiles from these molecular methods are in good agreement. Additionally, solute orientations calculated with MD and COSMOmic are compared and again a good agreement is found. Four different solutes are investigated in detail: 4-ethylphenol, propanol, 5-phenylvaleric acid, and dibenz[a,h]anthracene, whereby the latter belongs to the class of polycyclic aromatic hydrocarbons. The convergence of the free energy profiles from biased MD simulations is discussed and the results are shown to be comparable to equilibrium MD simulations. For 5-phenylvaleric acid the influence of the carboxyl group dihedral angle on free energy profiles is analyzed with MD simulations.Publicationtype: Journal ArticleScopus© Citations 53 26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Product recovery in surfactant-based separation processes : pervaporation of toluene from concentrated surfactant solutions(Elsevier, 2013-05-10); ; ; ; Aqueous micellar two-phase systems have been proposed for the cloud point extraction (CPE) of hazardous compounds or high valued products from aqueous solutions. The efficiency of the CPE strongly depends on the reuse of surfactant as well as the product recovery from the coacervate phase. In this work the membrane process pervaporation was successfully applied to remove contaminants from concentrated surfactant solutions. Experimental results show that a polyoctylmethylsiloxane membrane is the most suitable membrane to separate toluene from a 20. wt% Triton X-114 solution. Furthermore, it is demonstrated that trans-membrane fluxes decrease with increasing surfactant concentration. In case of toluene no correlation between concentration and depletion rate was observed. However, it was observed, that the viscosity of the solution is highly influenced by toluene concentration and thus, effects the efficiency of the pervaporation process. To improve the pervaporation performance the influence of temperature and volumetric flow rate on the depletion rate was investigated. The toluene depletion from surfactant-rich solution increases from 30.2% to 55.1% after 200. min by optimising these parameters. The presented results show that the product recovery after the cloud point extraction can successfully be fulfilled by pervaporation. Compared to alternative separation methods no loss of surfactant or excessive foaming was observed in any of the experiments. © 2013.Publicationtype: Journal Article69 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Estimation of LPC/water partition coefficients using molecular modeling and micellar liquid chromatographyLysophosphatidylcholine (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.Publicationtype: Journal Article67 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Combination of COSMOmic and molecular dynamics simulations for the calculation of membrane-water partition coefficientsThe importance of membrane-water partition coefficients led to the recent extension of the conductor-like screening model for realistic solvation (COSMO-RS) to micelles and biomembranes termed COSMOmic. Compared to COSMO-RS, this new approach needs structural information to account for the anisotropy of colloidal systems. This information can be obtained from molecular dynamics (MD) simulations. In this work, we show that this combination of molecular methods can efficiently be used to predict partition coefficients with good agreement to experimental data and enables screening studies. However, there is a discrepancy between the amount of data generated by MD simulations and the structural information needed for COSMOmic. Therefore, a new scheme is presented to extract data from MD trajectories for COSMOmic calculations. In particular, we show how to calculate the system structure from MD, the influence of lipid conformers, the relation to the COSMOmic layer size, and the water/lipid ratio impact. For a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayer, 66 partition coefficients for various solutes were calculated. Further, 52 partition coefficients for a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer system were calculated. All these calculations were compared to experimental data. © 2013 Wiley Periodicals, Inc.Publicationtype: Journal Article78 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Partition coefficients of ionizable solutes in aqueous micellar two-phase systemsThe potential of micellar cloud point systems for extraction processes has been demonstrated for a broad range of different applications. The extraction is based on the phenomenon that aqueous non-ionic surfactant solutions split into two phases if the temperature is increased beyond a certain temperature, the so called cloud point temperature (CPT). Recently, aqueous micellar two-phase systems have been implemented in a counter current extraction. However, almost equally important for large scale applications is the recovery of the solute from micellar solutions, which remains a serious concern considering micellar cloud point systems as alternative to conventional solvents. In conventional solvent extraction processes the influence of the pH on the partitioning of ionizable solutes is an important parameter to control the extraction and back extraction efficiency. However, the partitioning of ionizable solutes such as organic acids and bases in micellar two-phase systems has not been studied so far. In this work the partitioning of various ionizable solutes including phenolic as well as pharmaceutical active compounds has been investigated. Lipophilicity profiles of all solutes were analyzed for the system Triton. X-114/water in a pH range between 2 and 12. Further, the influence of temperature, solute concentration, as well as different salt concentrations on the partitioning of charged solutes was investigated. Experimental results are verified by means of predicted values using the thermodynamic model COSMO-RS. The results reveal that COSMO-RS can be applied to predict the partitioning of ionizable solutes in micellar biphasic systems, when the phase behavior of the pure surfactant is known.Based on these data optimal strategies for large scale micellar extraction processes are proposed and validated by means of a continuous pilot plant micellar extraction column. © 2012.Publicationtype: Journal Article114 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Prediction of micelle/water and liposome/water partition coefficients based on molecular dynamics simulations, COSMO-RS, and COSMOmic(American Chemical Society (ACS), 2013-02-11); ; ; ; 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.Publicationtype: Journal Article127 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Partition coefficients of ionizable solutes in mixed nonionic/ionic micellar systems(American Chemical Society (ACS), 2012-12-13); ; ; 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.Publicationtype: Journal Article81 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , COSMO-RS for the prediction of the retention behavior in micellar liquid chromatography based on partition coefficients of non-dissociated and dissociated solutes(Science Direct, 2012-12-07); ; ; ; 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.Publicationtype: Journal ArticleScopus© Citations 8 60