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Item type:Publication, Access status: without files , Continuous Countercurrent Extractive Biocatalysis in Aqueous Surfactant Two-Phase Systems(2018-03); To evaluate the possibility of performing extractive biocatalysis in continuous mode, the hydrolysis of penicillin G in a micellar solution containing the nonionic surfactant Tergitol NP-7 was chosen as model system. While the product phenylacetic acid distributes into the micellar phase, 6-aminopenicillanic acid moves preferably into the aqueous phase. The yield in the continuous multi-step process was higher in comparison to equivalent batch systems. Overall, the results demonstrate the suitability of aqueous surfactant two-phase systems for continuous biocatalytic reactive extraction processes.Publicationtype: Journal Article145 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Mixed aqueous solutions of nonionic surfactants Brij 35/Triton X-100: Micellar properties, solutes' partitioning from micellar liquid chromatography and modelling with COSMOmicAqueous solutions of nonionic surfactants are of interest for bioprocesses, particularly as solubilizing agents for hydrophobic substances. To design such processes, the data on partition coefficients of solutes between micelles and their aqueous surrounding (Pmw) are of high value. An extended understanding of the partition behavior can be achieved from the structural information such as the micelle size and micelles composition. In this work, mixtures of nonionic surfactants Triton X-100 and Brij 35 were under study. The data on critical micelle concentrations showed partly non-ideal behavior of the solutions. The compositions of mixed micelles at different molar Brij 35/Triton X-100 ratios in the surfactant mixture were estimated from the data on self-diffusion coefficients (NMR diffusometry) and were calculated within the regular solution approach and predicted by Motomura's model. The change of the mixed micelle composition in dependence on the total surfactant concentration was observed. It has been found, that the average value of the mixed micelles radii is ∼4 nm. Whereas, the polydispersity indexes and the aggregation numbers increased with Triton X-100 fraction. Moreover, the Pmw values of different non-dissociated solutes (phenyl derivatives with various functional groups) were determined by means of micellar liquid chromatography (MLC) and were predicted using the thermodynamic model COSMOmic, an extension of COSMO-RS. In general, it has been proved that COSMOmic is able to predict Pmw in the mixed micellar system formed by nonionic surfactants. The obtained data show the possibility of modulating the partition behavior of solutes using the mixtures of nonionic surfactants. Apart from the hydrophobicity, the «surfactants – solute» specific interactions play an important role in the partition behavior of the investigated systems.Publicationtype: Journal Article171 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Kontinuierliche extraktive Biokatalyse in wässrigen tensidbasierten ZweiphasensystemenPublicationtype: Doctoral Thesis78 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Micellization and partition equilibria in mixed nonionic/Ionic micellar systems: predictions with molecular models(American Chemical Society (ACS), 2017-10-02); ; ; In practical applications, surfactant solutions are mostly used in mixtures of nonionic and ionic surfactants because they have improved characteristics compared to those of single surfactant solutions. By adjusting the composition of the micelles and the pH value, the solubilization of solutes can be enhanced. Nevertheless, the partitioning of solutes between nonionic/ionic mixed micelles and the aqueous phase is studied to a much lesser extent than for single surfactant solutions. Theoretical methods to predict partition equilibria in mixed micelles are of interest for screening studies. For those, the composition of the mixed micelle has to be known. Here we investigate mixtures of TX-114 (Triton X-114), Brij35 (C12E23), SDS (sodium dodecyl sulfate), and CTAB (cetyltrimethylammonium bromide). First, to investigate the surfactant compositions in the micelles, molecular dynamics (MD) self-assembly simulations were applied. Thereafter, the predictive COSMO-RS model, which applies the pseudophase approach, and its extension to anisotropic systems termed COSMOmic were compared for the prediction of partition equilibria in mixed micelles, where various molar ratios of the surfactants were considered. It could be demonstrated that both methods are applicable and lead to reasonable predictions for neutral molecules. However, taking into account the three-dimensional structure of the micelle is beneficial because the calculations with COSMOmic are in better agreement with experimental results. Because the partitioning behavior of ionizable molecules in mixed micelles is of particular interest, the partitioning of ionized isovanillin in mixed Brij35/CTAB micelles at different micelle compositions was calculated with COSMOmic. Using a thermodynamic cycle, the position-dependent pKa of isovanillin within the micelle is calculated on the basis of COSMOmic free energy profiles. As a result, the protolytic equilibrium of isovanillin within the micelles can be taken into account, which is crucial for the reliable prediction of partition coefficients.Publicationtype: Journal Article236 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Solute partitioning in micelles: combining molecular dynamics simulations, COSMOmic, and experiments(Soc., 2017-06-06); ; ; ; The partition equilibria of solutes between micelles and an aqueous phase is a key factor in many applications. Depending on the task, many micelle-solute combinations are possible. Therefore, theoretical methods to predict the partition behavior in micellar systems are needed. Here, two predictive methods are evaluated and compared. First, it is shown how molecular dynamics simulations (MD) with the umbrella sampling method can be used to calculate free energy profiles in micellar systems. The second applied method is an extension of the COSMO-RS theory to anisotropic systems termed COSMOmic. Both methods are compared by means of free energy profiles and experimental micelle/water partition coefficients. A particular focus is on the partitioning of ionized solutes. As experimental data for partitioning in micelles especially for charged solutes is rare, partition coefficients were also determined experimentally. To get a general understanding of micelles examples of all micelle classes (classified by headgroup charge) are studied: nonionic Triton X-114 (TX114), zwitterionic miltefosine (HePC), anionic sodium dodecyl sulfate (SDS), and cationic cetyltrimethylammonium bromid (CTAB). The free energy profiles of neutral solutes obtained from MD simulations and COSMOmic are in an overall good agreement, and partition coefficients from both methods are in good agreement with experimental data. Depending on the system, the results for charged solutes show some deviations between the methods and experimental data.Publicationtype: Journal Article115 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of D-glucose as additive on thermodynamics and physical properties of aqueous surfactant two-phase systems for the continuous micellar extraction(Elsevier, 2017-03-06); ; ; Aqueous nonionic surfactants solutions can form two coexisting phases when heated beyond the so called cloud point temperature. Hence, these surfactants are potential solvents for extraction processes. In this work the effect of d-glucose on phase behavior of aqueous surfactant two-phase systems containing the nonionic surfactants Tergitol 15-S-7 or Triton X-114 was investigated in order to design micellar systems for liquid-liquid extraction. It was found that d-glucose can lead to an increased density difference if the surfactant-rich phase is the lighter one as well as an enhancement of the phase separation. Furthermore, the effect of d-glucose on the liquid-liquid equilibrium of aqueous Tergitol 15-S-7 solutions was studied. The partition behavior of three model solutes was determined and modeled with the combination of molecular dynamics simulations and the thermodynamic model COSMOmic. Based on these data an experiment in a continuous extraction column using an aqueous surfactant two-phase system containing d-glucose as additive was performed. The results demonstrate that sugars as additives can be used to tailor surfactant solutions in a beneficial way for separation processes.Publicationtype: Journal Article126 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Kontinuierliche extraktive Biokatalyse in wässrigen mizellaren ZweiphasensystemenPublicationtype: Journal Article116 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Molecular dynamics simulations of various micelles to predict micelle water partition equilibria with COSMOmic: Influence of micelle size and structure(2016-08-25); ; ; ; Due to the large number of different surfactant and solute molecules used in micellar solutions, it is important to have predictive models for micelle-water partition equilibrium. The relative new method COSMOmic, an extension of COSMO-RS, can predict thermodynamic data by taking the anisotropy of a system into account. For this purpose, it needs the structure of the system in atomistic resolution. In previous studies, atomic distributions were obtained from self-assembly molecular dynamics (MD) simulations. In this work MD simulations starting from pre-assembled micelles are used to receive atomic distributions. These simulations are more efficient than self-assembly simulations with respect to system size and simulation time and allow the detailed study of micelle size/structure influences on solute partitioning. For the first time a wide range of aggregation numbers for different types of surfactants are investigated. More than 90 different micelles structures were obtained for six different surfactants: SDS (sodium dodecyl sulfate), CTAB (cetyltrimetylammonium bromide), C12E10, Brij35 (C12E23), Triton X-114 and Triton X-100 with initial aggregation numbers between 20 and 160. These were investigated with respect to micelle size, micelle shape, surfactant concentration and simulation time. To examine the prediction quality of COSMOmic, experimental data was collected and 36 micelle-water partition coefficients for C12E10, Triton X-100 and Brij35 were measured. In total more than 370 experimental partition coefficients were used to validate the calculations. The results show that the calculations are in good agreement with the experimental data and that they are better than predictions from methods that do not take the micelle structure into account (pseudo phase approach). In this context, small spherical micelles are proven to be more efficient while larger more ellipsoidal micelles show a higher probability to result in outliers. Therefore, this article provides a guideline for the development of averaged atomic distributions as input for COSMOmic.Publicationtype: Journal Article88 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The role of phase behavior in the enzyme catalyzed synthesis of glycerol monolaurate(Royal Society of Chemistry (RSC), 2016-03-24); ; ; ; Partial glycerides such as monoacylglycerides (MAGs) are important functional ingredients with various applications in the cosmetics and food industry. Direct synthesis of high purity MAGs is commercially not feasible due to low selectivity and substrate miscibility problems. In this article, a selectivity increase in synthesis towards MAG with the addition of 5 wt% of the amphoteric surfactant cocamidopropyl betaine (CAPB) compared to a solvent free reaction is demonstrated. In comparison to tert-butanol, the addition of CAPB leads to similar MAG contents in the equilibrium state and furthermore CAPB does not need to be removed from the reaction, because it is an approved additive in cosmetic products. Additionally it acts as a solubilizer in the product mixture. By adding 5 wt% of CAPB to the enzymatic glycerolysis of TL, the selectivity towards ML could be increased by 17% compared to the solvent free reaction. Also in the enzymatic esterification of glycerol and lauric acid the addition of 5 wt% CAPB shows an increase in selectivity towards ML up to 9% compared to the solvent free esterification. The major function is a direct influence on the phase behavior of the reaction mixture.Publicationtype: Journal Article143 - 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 Article94