Lehrstuhl Thermodynamik

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Aromatic volatile organic compounds absorption with phenyl-based deep eutectic solvents: a molecular thermodynamics and dynamics study
(2023-01-24) Yu, Gangqiang; Gajardo-Parra, Nicolás F.; Chen, Min; Chen, Biaohua; Sadowski, Gabriele; Held, Christoph
The suitability of phenyl-based deep eutectic solvents (DESs) as absorbents for toluene absorption was investigated by means of thermodynamic modeling and molecular dynamics (MD). The thermodynamic models perturbed-chain statistical associating fluid theory (PC-SAFT) and conductor-like screening model for real solvents (COSMO-RS) were used to predict the vapor–liquid equilibrium of DES–toluene systems. PC-SAFT yielded quantitative results even without using any binary fitting parameters. Among the five DESs studied in this work, [TEBAC][PhOH] consisting of triethyl benzyl ammonium chloride (TEBAC) and phenol (PhOH), was considered as the most suitable absorbent. Systems with [TEBAC][PhOH] had lowest equilibrium pressures of the considered DES–toluene mixtures, the best thermodynamic characteristics (i.e., Henry's law constant, excess enthalpy, Gibbs free energy of solvation of toluene), and the highest self-diffusion coefficient of toluene. The molecular-level mechanism was explored by MD simulations, indicating that [TEBAC][PhOH] has the strongest interaction of DES–toluene compared to the other DESs under study. This work provides guidance to rationally design novel DESs for efficient aromatic volatile organic compounds absorption.
Continuous phase separation of stable emulsions from biphasic whole-cell biocatalysis by catastrophic phase inversion
(2023-03-27) Janssen, Lisa; Sadowski, Gabriele; Brandenbusch, Christoph
The main bottleneck for the industrial implementation of highly promising multi-phase whole-cell biocatalytic processes is the formation of stable Pickering-type emulsions, hindering efficient downstream processing. Especially for the crucial step of phase separation, state-of-the-art processes require time-consuming and costly process steps (excessive centrifugation/use of de-emulsifiers). In contrast, using the phenomenon of catastrophic phase inversion (CPI), efficient phase separation can be achieved by addition of an excess dispersed phase within minutes. To show applicability of CPI as an innovative process step, a fully automated lab-scale prototype was designed and constructed within this work. A simple mixer-settler set-up enabled a continuous phase separation using CPI termed applied catastrophic phase inversion (ACPI). Test runs were conducted using emulsions from biphasic whole-cell biocatalysis (Escherichia coli JM101 and Pseudomonas putida KT2440 cells). Solvents used included n-heptane, ethyl oleate or 1-octanol as organic phase. These investigations revealed ideal process settings for a stable ACPI process (e.g., flow/stirring rates and volumetric phase ratios between organic and water phase). The knowledge of the CPI point is most crucial, as only the inverted state of emulsion is successfully destabilized.
Extremely low vapor‐pressure data as access to PC‐SAFT parameter estimation for ionic liquids and modeling of precursor solubility in ionic liquids
(2021-01-25) Bülow, Mark; Greive, Moritz; Zaitsau, Dzmitry H.; Verevkin, Sergey P.; Held, Christoph
Precursor solubility is a crucial factor in industrial applications, dominating the outcome of reactions and purification steps. The outcome and success of thermodynamic modelling of this industrially important property with equations of states, such as Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), vastly depends on the quality of the pure-component parameters. The pure-component parameters for low-volatile compounds such as ionic liquids (ILs) have been commonly estimated using mixture properties, e. g. the osmotic pressure of aqueous solutions. This leads to parameters that depend on the solvent, and transferability to other mixtures often causes poor modeling results. Mixture-independent experimental properties would be a more suitable basis for the parameter estimation offering a way to universal parameter sets. Model parameters for ILs are available in the literature [10.1016/j.fluid.2012.05.029], but they were estimated using pure-IL density data. The present work focuses on a step towards a more universal estimation strategy that includes new experimental vapor-pressure data of the pure IL. ILs exhibit an almost negligible vapor pressure in magnitude of usually 10−5 Pa even at elevated temperatures. In this work, such vapor-pressure data of a series of 1-ethyl-3-methyl-imidazolium-based [C2mim]-ILs with various IL-anions (e. g. tetrafluoroborate [BF4]−, hexafluorophosphate [PF6]−, bis(trifluoromethylsulfonyl)imide [NTf2]−) were experimentally determined and subsequently used for PC-SAFT parameter estimation. The so-determined parameters were used to predict experimental molecular precursor solubility in ILs and infinitely diluted activity coefficients of various solvents in ILs. The parameters were further compared to modeling results using classical parametrization methods (use of liquid-density data only for the molecular PC-SAFT and the ion-based electrolyte PC-SAFT). As a result, the modeled precursor solubilities using the new approach are much more precise than using the classical parametrization methods, and required binary parameters were found to be much smaller (if needed). In sum, including the pure-component vapor-pressure data of ILs opens the door towards parameter estimation that is not biased by mixture data. This procedure might be suitable also for polymers and for all kind of ionic species but needs extension to ion-specific parametrization in the long term.
Activity-based models to predict kinetics of levulinic acid esterification
(2022-10-20) Klinksiek, Marcel; Baco, Sindi; Leveneur, Sébastien; Legros, Julien; Held, Christoph
The solvent is of prime importance in biomass conversion as it influences dissolution, reaction kinetics, catalyst activity and thermodynamic equilibrium of the reaction system. So far, activity-based models were developed to predict kinetics and equilibria, but the influence of the catalyst on kinetics has not been succesfully predicted by thermodynamic models. In this work, the thermodynamic model ePC-SAFT advanced was used to predict the activities of the reactants and of the catalyst at various conditions (temperature, reactant concentrations, γ-valerolactone GVL cosolvent addition, catalyst concentration) for the homogeneously acid-catalyzed esterification of levulinic acid (LA) with ethanol. Different kinetic models were applied, and it was found that the catalyst influence on kinetics could be predicted correctly by simultaneously solving the dissociation equilibrium of H2SO4 catalyst along the reaction coordinate and by relating reaction kinetics to proton activity. ePC-SAFT advanced model parameters were only fitted to reaction-independent phase equilibrium data. The key reaction properties were determined by applying ePC-SAFT advanced to one experimental kinetic curve for a set of temperatures, yielding the reaction enthalpy at standard state urn:x-wiley:14394235:media:cphc202200729:cphc202200729-math-0001 , activation energy urn:x-wiley:14394235:media:cphc202200729:cphc202200729-math-0002 and the intrinsic reaction rate constant k=0.011 s−1 at 323 K, which is independent of catalyst concentration. The new procedure allowed an a-priori identification of the effects of catalyst, solvent and reactant concentration on LA esterification.
Verallgemeinerte thermodynamische Beschreibung regenerativer Gaskreisprozesse
(VDI Verlag Düsseldorf, 1990) Kühl, Hans-Detlev; Schulz, Siegfried; Hapke, Jobst
Model-based optimization of multi-stage nanofiltration using the solution-diffusion–electromigration model
(2023-08-04) Hubach, Tobias; Schlüter, Stefan; Held, Christoph
Nanofiltration is well suited to separate monovalent ions from multivalent ions, such as the separation of Li+ and Mg2+ from seawater, a potential lithium source for the production of lithium-ion batteries. To the best of our knowledge, there is no existing work on the optimization of a multi-stage membrane plant that differentiates between different ions and that is based on a validated transport model. This study presents a method for modeling predefined membrane interconnections using discretization along the membrane length and across the membrane thickness. The solution-diffusion–electromigration model was used as the transport model in a fundamental membrane flowsheet, and the model was employed to optimize a given flowsheet with a flexible objective function. The methodology was evaluated for three distinct separation tasks, and optimized operating points were found. These show that permeances and feed concentrations might cause negative rejections and positive rejections (especially for bivalent ions) depending on the ions’ properties and fluxes, thereby allowing for a favorable separation between the ions of different valence at optimized conditions. In an application-based case study for the separation of Li+ and Mg2+ from seawater, the method showed that under optimal conditions, the mol-based ratio of Mg2+/Li+ can be reduced from 2383 to 2.8 in three membrane stages.
Osmolyte effect on enzymatic stability and reaction equilibrium of formate dehydrogenase
(2022-11-03) Gajardo-Parra, Nicolás F.; Akrofi-Mantey, Harold; Ascani, Moreno; Cea-Klapp, Esteban; Matias Garrido, José; Sadowski, Gabriele; Held, Christoph
Osmolytes are well-known biocatalyst stabilisers as they promote the folded state of proteins, and a stabilised biocatalyst might also improve reaction kinetics. In this work, the influence of four osmolytes (betaine, glycerol, trehalose, and trimethylamine N-oxide) on the activity and stability of Candida bondinii formate dehydrogenase cbFDH was studied experimentally and theoretically. Scanning differential fluorimetric studies were performed to assess the thermal stability of cbFDH, while UV detection was used to reveal changes in cbFDH activity and reaction equilibrium at osmolyte concentrations between 0.25 and 1 mol kg−1. The thermodynamic model ePC-SAFT advanced allowed predicting the effects of osmolyte on the reaction equilibrium by accounting for interactions involving osmolyte, products, substrates, and water. The results show that osmolytes at low concentrations were beneficial for both, thermal stability and cbFDH activity, while keeping the equilibrium yield at high level. Molecular dynamics simulations were used to describe the solvation around the cbFDH surface and the volume exclusion effect, proofing the beneficial effect of the osmolytes on cbFDH activity, especially at low concentrations of trimethylamine N-oxide and betaine. Different mechanisms of stabilisation (dependent on the osmolyte) show the importance of studying solvent–protein dynamics towards the design of optimised biocatalytic processes.
Prediction of pH in multiphase multicomponent systems with ePC-SAFT advanced
(2022-06-30) Ascani, Moreno; Pabsch, Daniel; Klinksiek, Marcel; Gajardo-Parra, Nicolás; Sadowski, Gabriele; Held, Christoph
Proton activity, which is usually expressed as a pH value, is among the most important properties in the design of chemical and biochemical processes as it determines the dissociation of species in aqueous mixtures. This article addresses the prediction of pH values in multiphase systems based on the IUPAC definition via proton activity. The required proton activity coefficients were predicted using the thermodynamic equation of state ePC-SAFT advanced. The developed framework considers reaction equilibria and phase equilibria (vapor–liquid and liquid–liquid) to predict pH in the equilibrated liquid phases.
The melting properties of D-α-glucose, D-β-fructose, D-sucrose, D-α-galactose, and D-α-xylose and their solubility in water: a revision
(2021-12-28) Chua, Yeong Zen; Do, Hoang Tam Joseph; Kumar, Aarti; Hallermann, Moritz; Zaitsau, Dzmitry; Schick, Christoph; Held, Christoph
Saccharides are still commonly isolated from biological feedstock by crystallization from aqueous solutions. Precise thermodynamic data on solubility are essential to optimize the downstream crystallization process. Solubility modeling, in turn, requires knowledge of melting properties. In the first part of this work, following our previous work on amino acids and peptides, D-α-glucose, D-β-fructose, D-sucrose, D-α-galactose, and D-α-xylose were investigated with Fast Scanning Calorimetry (FSC) in a wide scanning rate range (2000 K·s−1 to 10000 K·s−1). Using the experimental melting properties of saccharides from FSC allowed successfully modeling aqueous solubility for D-sucrose and D-α-galactose with the equation of state PC-SAFT. This provides cross-validation of the measurement methods to determine accurate experimental melting properties with FSC. Unexpectedly, the experimental FSC melting temperatures, extrapolated to zero scanning rates for thermal lag correction, were higher than results determined with DSC and available literature data. To clarify this inconsistency, FSC measurements towards low scanning rates from 10000 K·s−1 to 1 K·s−1 (D-α-glucose, D-β-fructose, D-sucrose) overlapping with the scanning rates of DSC and literature data were combined. At scanning rates below 1000 K·s−1, the melting properties followed a consistent non-linear trend, observed in both the FSC and the literature data. In order to understand the non-linear decrease of apparent melting temperatures with decreasing heating rate, the endothermic peaks were investigated in terms of isoconversional kinetics. The activation energies in the non-linear dependency region are in the range of 300
Prediction of salting-out in liquid-liquid two-phase systems with ePC-SAFT: effect of the Born term and of a concentration-dependent dielectric constant
(2021-03-26) Ascani, Moreno; Held, Christoph
Knowledge on phase equilibria is of crucial importance in designing industrial processes. However, modeling phase equilibria in liquid-liquid two-phase systems (LLTPS) containing electrolytes is still a challenge for electrolyte thermodynamic models and modeling still requires a lot of experimental input data. Further, modeling electrolyte solutions requires accounting for different physical effects in the electrolyte theory, especially the change of the dielectric properties of the medium at different compositions and the related change of solvation free energy of the dissolved ions. In a previous work, the Born term was altered by combining it with a concentration-dependent dielectric constant within the framework of electrolyte Perturbed-Chain Statistical Associating Fluid Theory (ePC-SAFT), and hence called ‘ePC-SAFT advanced’. In the present work, ePC-SAFT advanced was validated against liquid-liquid equilibria (LLE) of LLTPS water+organic solvents+alkali halides as well as aqueous two-phase systems containing the phase formers poly (propylene glycol) and an ionic liquid. All the ePC-SAFT parameters were used as published in the literature, and each binary interaction parameter between ion-solvent was set to zero. ePC-SAFT advanced allowed quantitatively predicting the salt effect on LLTPS without adjusting binary interaction parameters, while classical ePC-SAFT or meaningless mixing rules for the dielectric constant term failed in predicting the phase behavior of the LLTPS.
Performance improvements in Stirling cycle machines by a modified appendix gap geometry
(2021-09-20) Sauer, Jan; Kühl, Hans-Detlev
In this contribution, the optimization potential of the seal geometry in Stirling machines is explored both numerically and analytically, leading to a significant reduction of the related losses which are often referred to as appendix gap losses. These are induced by the narrow gap between the displacer and the cylinder and have mostly been underestimated so far. A recent experimental investigation revealed large optimization potentials by reduction of the seal and cylinder wall diameter near the seal, resulting in reduced appendix gap losses and further indirect positive effects. In this work, these experimental findings could be reproduced by a one-dimensional differential simulation model at a fully satisfyingaccuracy. Furthermore, these investigations reveal that the optimum geometry is largely machine-dependent. To provide an easily applicable design rule for this optimum geometry, a refined analytical model for the mass flow at the top of the gap is derived, which is based on a phasor analysis and a linearized mass balance that also accounts for changes in the spatial mean gas temperature in the gap. The optimum design predicted by this model is very close to numerical optimization results and sufficiently accurate under practical aspects. Furthermore, this model contributes to a better theoretical understanding of the loss mechanisms in the gap.
New thermodynamic activity-based approach allows predicting the feasibility of glycolysis
(2021-03-17) Greinert, Thorsten; Vogel, Kristina; Maskow, Thomas; Held, Christoph
Thermodynamic feasibility analyses help evaluating the feasibility of metabolic pathways. This is an important information used to develop new biotechnological processes and to understand metabolic processes in cells. However, literature standard data are uncertain for most biochemical reactions yielding wrong statements concerning their feasibility. In this article we present activity-based equilibrium constants for all the ten glycolytic reactions, accompanied by the standard reaction data (standard Gibbs energy of reaction and standard enthalpy of reaction). We further developed a thermodynamic activity-based approach that allows to correctly determine the feasibility of glycolysis under different chosen conditions. The results show for the first time that the feasibility of glycolysis can be explained by thermodynamics only if (1) correct standard data are used and if (2) the conditions in the cell at non-equilibrium states are accounted for in the analyses. The results here will help to determine the feasibility of other metabolisms and to understand metabolic processes in cells in the future.
Partitioning of water-soluble vitamins in biodegradable aqueous two-phase systems
(2020-07-14) Wysoczanska, Kamila; Do, Hoang Tam; Sadowski, Gabriele; Macedo, Eugénia A.; Held, Christoph
Partition coefficients (K) of vitamins (riboflavin, nicotinic acid, nicotinamide, folic acid, cyanocobalamin) in aqueous two-phase systems (ATPS) composed by polyethylene glycol (PEG 4000, PEG 6000) and organic salt (sodium citrate and sodium tartrate) at T = 298.15 K and p = 1 bar have been studied. Data on liquid–liquid equilibria of the ATPS considered in this study have been taken from the literature (PEG-Na3Citrate) or measured in this work (PEG-Na2Tartrate) for PEG 4000 and PEG 6000 at T = 298.15 K and p = 1 bar. The experimental K values were validated by electrolyte perturbed-chain-statistical associating fluid theory predictions. The neutral cyanocobalamin has the highest K values among all studied vitamins at any ATPS studied in this work. This finding contrasted with expectations based on literature data which let assume that charged species have typically the highest K values in the considered ATPS. Thus, besides the typically strong charge–charge interactions especially specific forces (e.g., hydrogen bonding) explains the strong PEG-cyanocobalamin interaction resulting in the high K values.
In-silico screening of lipid-based drug delivery systems
(2020-11-23) Brinkmann, Joscha; Exner, Lara; Luebbert, Christian; Sadowski, Gabriele
Purpose: This work proposes an in-silico screening method for identifying promising formulation candidates in complex lipid-based drug delivery systems (LBDDS). Method: The approach is based on a minimum amount of experimental data for API solubilites in single excipients. Intermolecular interactions between APIs and excipients as well as between different excipients were accounted for by the Perturbed-Chain Statistical Associating Fluid Theory. The approach was applied to the in-silico screening of lipid-based formulations for ten model APIs (fenofibrate, ibuprofen, praziquantel, carbamazepine, cinnarizine, felodipine, naproxen, indomethacin, griseofulvin and glibenclamide) in mixtures of up to three out of nine excipients (tricaprylin, Capmul MCM, caprylic acid, Capryol™ 90, Lauroglycol™ FCC, Kolliphor TPGS, polyethylene glycol, carbitol and ethanol). Results: For eight out of the ten investigated model APIs, the solubilities in the final formulations could be enhanced by up to 100 times compared to the solubility in pure tricaprylin. Fenofibrate, ibuprofen, praziquantel, carbamazepine are recommended as type I formulations, whereas cinnarizine and felodipine showed a distinctive solubility gain in type II formulations. Increased solubility was found for naproxen and indomethacin in type IIIb and type IV formulations. The solubility of griseofulvin and glibenclamide could be slightly enhanced in type IIIb formulations. The experimental validation agreed very well with the screening results. Conclusion: The API solubility individually depends on the choice of excipients. The proposed in-silico-screening approach allows formulators to quickly determine most-appropriate types of lipid-based formulations for a given API with low experimental effort.
Odd–even effect for efficient bioreactions of chiral alcohols and boosted stability of the enzyme
(2020-07-29) Bülow, Mark; Schmitz, Alexa; Mahmoudi, Termeh; Schmidt, Dana; Junglas, Fabian; Janiak, Christoph; Held, Christoph
We describe a holistic approach for achieving a nearly quantitative conversion for an enzymatic reaction while simultaneously increasing the long-term stability of the enzyme. The approach provided chemical control of bioreactions by utilizing newly synthesized tetrahydrothiophene-based ionic liquids (THT ILs). We showcased its power by using THT-ILs as additives at a low concentration (only 10 mmol L−1) in the alcohol dehydrogenase (ADH)-catalyzed synthesis of methylated 1-phenylethanol (Me-PE). We discovered an “odd–even” effect of the IL-cation chain length: Me-PE displayed beneficial interactions with THT ILs having odd-numbered chain lengths and deleterious interactions with those having even-numbered chain lengths. An intermolecular thermodynamic simulation of the bulk phase and critical micelle concentration investigations of the local surroundings of the THT-ILs proved the occurrence of these interactions, and these two methods confirmed the odd–even effect from different perspectives. Additionally, storing the ADH enzyme in pure THT IL at room temperature allowed for a boosted long-term stability of the enzyme (500 times greater than that in aqueous buffer) without the need for freezing.
Amorphous-amorphous phase separation in API/polymer formulations
(2017-02-15) Luebbert, Christian; Huxoll, Fabian; Sadowski, Gabriele
The long-term stability of pharmaceutical formulations of poorly-soluble drugs in polymers determines their bioavailability and therapeutic applicability. However, these formulations do not only often tend to crystallize during storage, but also tend to undergo unwanted amorphous-amorphous phase separations (APS). Whereas the crystallization behavior of APIs in polymers has been measured and modeled during the last years, the APS phenomenon is still poorly understood. In this study, the crystallization behavior, APS, and glass-transition temperatures formulations of ibuprofen and felodipine in polymeric PLGA excipients exhibiting different ratios of lactic acid and glycolic acid monomers in the PLGA chain were investigated by means of hot-stage microscopy and DSC. APS and recrystallization was observed in ibuprofen/PLGA formulations, while only recrystallization occurred in felodipine/PLGA formulations. Based on a successful modeling of the crystallization behavior using the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), the occurrence of APS was predicted in agreement with experimental findings.
Experimental investigation of displacer seal geometry effects in Stirling cycle machines
(2019-11-05) Sauer, Jan; Kühl, Hans-Detlev
This contribution deals with an experimental investigation of the optimization potential of Stirling engines and similar regenerative machines by an enhanced design of the cylinder liner and the seal. The latter is mounted at the bottom end of the gap surrounding pistons and displacers that separate cylinder volumes at different temperature levels. The thermal loss associated with this gap may amount to more than 10% of the heat input into these machines. Mostly, its design is reduced to an estimation of the optimum width by analytical models, which usually do not account for further relevant optimization parameters, such as a step in the cylinder wall. However, a recently developed, enhanced analytical model predicts that this loss may be significantly reduced by such a step. In this work, this design was realized and investigated experimentally according to this prediction by modification of the cylinder liner and the seal of an extensively tested laboratory-scale machine. The results confirm that such a design actually reduces the thermal loss substantially, presumably by reducing the cyclic mass flows through the open end of the gap. Additionally, it even improves the net power output due to a reduced volumetric displacement by the piston or displacer, resulting in smaller flow losses and thermal regenerator losses, whereas the pressure amplitude remains virtually unchanged, contrary to initial expectations. This has led to the remarkable conclusion that the design of most Stirling engines is possibly suboptimal in this respect and may be improved a posteriori by a minor modification; i.e., a reduction of the effective displacer seal diameter.
Predicting the solubility of pharmaceutical cocrystals in solvent/anti-solvent mixtures
(2016-05-07) Lange, Linda; Heisel, Stefan; Sadowski, Gabriele
In this work, the solubilities of pharmaceutical cocrystals in solvent/anti-solvent systems were predicted using PC-SAFT in order to increase the efficiency of cocrystal formation processes. Modeling results and experimental data were compared for the cocrystal system nicotinamide/succinic acid (2:1) in the solvent/anti-solvent mixtures ethanol/water, ethanol/acetonitrile and ethanol/ethyl acetate at 298.15 K and in the ethanol/ethyl acetate mixture also at 310.15 K. The solubility of the investigated cocrystal slightly increased when adding small amounts of anti-solvent to the solvent, but drastically decreased for high anti-solvent amounts. Furthermore, the solubilities of nicotinamide, succinic acid and the cocrystal in the considered solvent/anti-solvent mixtures showed strong deviations from ideal-solution behavior. However, by accounting for the thermodynamic non-ideality of the components, PC-SAFT is able to predict the solubilities in all above-mentioned solvent/anti-solvent systems in good agreement with the experimental data.
Catalytic low-temperature dehydration of fructose to 5-hydroxymethylfurfural using acidic deep eutectic solvents and polyoxometalate catalysts
(2019-10-09) Körner, Sam; Albert, Jakob; Held, Christoph
HMF synthesis typically requires high temperature and is carried out in aqueous solutions. In this work, the low-temperature dehydration of fructose to HMF in different deep eutectic solvents (DES) was investigated. We found a very active and selective reaction system consisting of the DES tetraethyl ammonium chloride as hydrogen bond acceptor (HBA) and levulinic acid as hydrogen bond donor (HBD) in a molar ratio of 1:2 leading to a maximum HMF yield of 68% after 120 h at 323 K. The DES still contained a low amount of water at the initial reaction, and water was also produced during the reaction. Considering the DES properties, neither the molar ratio in the DES nor the reaction temperature had a significant influence on the overall performance of the reaction system. However, the nature of the HBA as well as the acidity of the HBD play an important role for the maximum achievable HMF yield. This was validated by measured yields in a DES with different combinations of HBD (levulinic acid and lactic acid) and HBA (choline chloride and tetra-n-alkyl ammonium chlorides). Moreover, addition of vanadium containing catalysts, especially the polyoxometalate HPA-5 (H8PV5Mo7O40) leads to drastically increased reaction kinetics. Using HPA-5 and the DES tetraethyl ammonium chloride—levulinic acid we could reach a maximum HMF yield of 57% after only 5 h reaction time without decreasing the very high product selectivity.
Simultaneous prediction of cosolvent influence on reaction equilibrium and Michaelis constants of enzyme-catalyzed ketone reductions
(2019-04-04) Wangler, Anton; Hüser, Aline; Sadowski, Gabriele; Held, Christoph
Understanding and quantification of cosolvent influences on enzyme-catalyzed reactions are driven by a twofold interest. On the one hand, cosolvents can simulate the cellular environment for deeper understanding of in cellulo reaction conditions. On the other hand, cosolvents are applied in biotechnology to tune yield and kinetics of reactions. Further, cosolvents are even present inherently, for example, for reactions with cofactor regeneration or for enzymes that need cosolvents in a function of a stabilizer. As the experimental determination of yield and kinetics is costly and time consuming, this work aims at providing a thermodynamic predictive approach that might allow screening cosolvent influences on yield and Michaelis constants. Reactions investigated in this work are the reduction of butanone and 2-pentanone under the influence of 17 wt % of the cosolvent polyethylene glycol 6000, which is also often used as a crowder to simulate cellular environments. The considered reactions were catalyzed by a genetically modified alcohol dehydrogenase (ADH 270). Predictions of cosolvent influences are based on accounting for a cosolvent-induced change of molecular interactions among the reacting agents as well as between the reacting agents and the solvent. Such interactions were characterized by activity coefficients of the reacting agents that were predicted by means of electrolyte perturbed-chain statistical associating fluid theory. This allowed simultaneously predicting the cosolvent effects on yield and Michaelis constants for two-substrate reactions for the first time.

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