Reaction Equilibrium of the ω-Transamination of (S)-Phenylethylamine: Experiments and ePC-SAFT Modeling

Abstract

This work focuses on the thermodynamic equilibrium of the ω-transaminase-catalyzed reaction of (S)phenylethylamine with cyclohexanone to acetophenone and cyclohexylamine in aqueous solution. For this purpose, the equilibrium concentrations of the reaction were experimentally investigated under varying reaction conditions. It was observed that the temperature (30 and 37 °C), the pH (between pH 7 and pH 9), as well as the initial reactant concentrations (between 5 and 50 mmol•kg −1 ) influenced the equilibrium position of the reaction. The position of the reaction equilibrium was moderately shifted toward the product side by either decreasing temperature or decreasing pH. In contrast, the initial ratio of the reactants showed only a marginal influence on the equilibrium position. Further experiments showed that increasing the initial reactant concentrations significantly shifted the equilibrium position to the reactant side. In order to explain these effects, the activity coefficients of the reacting agents were calculated and the activity-based thermodynamic equilibrium constant K th of the reaction was determined. For this purpose, the activity coefficients of the reacting agents were modeled at their respective experimental equilibrium concentrations using the equation of state electrolyte PC-SAFT (ePC-SAFT). The combination of the concentrations of the reacting agents at equilibrium and their respective activity coefficients provided the thermodynamically consistent equilibrium constant K th . Unexpectedly, the experimental K m values deviated by a factor of up to four from the thermodynamic equilibrium constant K th . The observed concentration dependency of the experimental K m values could be explained by the influence of concentration on activity coefficients. Further, these activity coefficients were found to be strongly temperature dependent, which is important for the determination of standard enthalpy of reactions, which in this work was found to be +7.7 ± 2.8 kJ•mol −1 . Using the so-determined K th and activity coefficients of the reacting agents (ePC-SAFT), the equilibrium concentrations of the reaction were predicted for varying initial reactant concentrations, which were found to be in good agreement with the experimental behavior. These results showed a non-negligible influence of the activity coefficients of the reacting agents on the equilibrium position and, thus, on the product yield. Experiments and ePC-SAFT predictions showed that the equilibrium position can only be described accurately by taking activity coefficients into account.

Extractivein situproduct removal for the application of naturally producedl-alanine as an amine donor in enzymatic metaraminol production

“…Additionally, thermodynamic modelling, such as conducted by for another transaminase reaction, could further improve the shown concept. 10 Conclusively, an operational window for simultaneous transamination and product extraction was defined within an economically and ecologically feasible framework.…”

“…6,7 Nonetheless, enzyme-catalyzed transamination often exhibit an unfavorable reaction equilibrium resulting in low product titers. 8,9 To overcome these limitations, intensive prediction studies have taken place and showed a mild shift of the equilibrium while adjusting the pH and temperature of the reaction 10 . Many other transaminase reactions make use of large amounts of the cheap, oil-based amine donor isopropylamine (IPA), producing acetone as the side product.…”

Jeffamine® ED‐600: a polyether amine donor for enzymatic transamination in organic solvent/solvent‐free medium with membrane‐assisted product extraction

“…The synthetic potential of amine transaminases (ATAs) for the synthesis of chiral amines is enormous, especially when the transamination is carried out in the asymmetric synthesis mode . Although research in both academia and industry has been extensively performed, general challenges including substrate/product inhibition, instability of the enzyme and unfavorable thermodynamic equilibrium need to be overcome. Such limitations imply that the process parameters (substrate concentration, biocatalyst performance and product yield, productivity) of ATA‐catalyzed processes are not completely industrially competitive yet, despite a few successful industrial applications …”

Odd–even effect for efficient bioreactions of chiral alcohols and boosted stability of the enzyme

“…S2 and Table S6, ESI †), as reported in previous publications. 16 To allow for an assessment of the impact of IL on the conversion, the IL-anion ([NTf 2 ] À ) was xed and the overall IL concentration in the mixture was held constant at 10 mmol per liter of aqueous buffered solvent. Reactants and enzyme were added to the aqueous buffer solution at a constant temperature (see Table S5, ESI † for starting concentrations).…”

“…Such "odd-even" effects have been mainly described for pure components, [16][17][18][19][20] e.g., involving shis in melting points for alkanes. And these effects have also been described in the literature for multi-component systems, 17,18 such as for partition coefficients of a salt in ternary systems including ILs.…”