An improved sol-gel process involving the use of hollow silica microspheres as a supporting additive was applied for the co-immobilization of whole cells of Escherichia coli with Chromobacterium violaceum ω-transaminase activity and Lodderomyces elongisporus with ketoreductase activity. The co-immobilized cells with two different biocatalytic activities could perform a cascade of reactions to convert racemic 4-phenylbutan-2-amine or heptan-2-amine into a nearly equimolar mixture of the corresponding enantiomerically pure R amine and S alcohol even in continuous-flow mode. The novel co-immobilized whole-cell system proved to be an easy-to-store and durable biocatalyst.
Effects of various additives on the lipase from Burkholderia cepacia (BcL) immobilized on mixed-function-grafted mesoporous silica gel support by hydrophobic adsorption and covalent attachment were investigated. Catalytic properties of the immobilized biocatalysts were characterized in kinetic resolution of racemic 1-phenylethanol (rac-1a) and 1-(thiophen-2-yl)ethan-1-ol (rac-1b). Screening of more than 40 additives showed significantly enhanced productivity of immobilized BcL with several additives such as PEGs, oleic acid and polyvinyl alcohol. Effects of substrate concentration and temperature between 0-100 °C on kinetic resolution of rac-1a were studied with the best adsorbed BcLs containing PEG 20 k or PVA 18-88 additives in continuous-flow packed-bed reactor. The optimum temperature of lipase activity for BcL co-immobilized with PEG 20k found at around 30 °C determined in the continuous-flow system increased remarkably to around 80 °C for BcL co-immobilized with PVA 18-88.
An efficient and easy-to-perform method was developed for immobilization of CaLB on mesoporous aminoalkyl polymer supports by bisepoxide activation. Polyacrylate resins (100-300 µm; 50 nm pores) with different aminoalkyl functional groups (ethylamine: EA and hexylamine: HA) were modified with bisepoxides differing in the length, rigidity and hydrophobicity of the units linking the two epoxy functions. After immobilization, the different CaLB preparations were evaluated using the lipase-catalyzed kinetic resolution (KR) of racemic 1-phenylethanol (rac-1) in batch mode and in a continuous-flow reactor as well. Catalytic activity, enantiomer selectivity, recyclability, and the mechanical and long-term stability of CaLB immobilized on the various supports were tested. The most active CaLB preparation (on HA-resin activated with 1,6-hexanediol diglycidyl ether-HDGE) retained 90% of its initial activity after 13 consecutive reaction cycles or after 12 month of storage at 4˝C. The specific rate (r flow ), enantiomer selectivity (E) and enantiomeric excess (ee) achievable with the best immobilized CaLB preparations were studied as a function of temperature in kinetic resolution of rac-1 performed in continuous-flow packed-bed bioreactors. The optimum temperature of the most active HA-HDGE CaLB in continuous-flow mode was 60˝C. Although CaLB immobilized on the glycerol diglycidyl ether (GDGE)-activated EA-resin was less active and less selective, a much higher optimum temperature (80˝C) was observed with this form in continuous-flow mode KR of rac-1.
The front cover picture shows a novel biocatalyst for cascade biotransformations comprising co‐immobilized cells with two different biocatalytic activities. A rational strategy based on an improved sol–gel process using hollow silica microspheres as a supporting additive was applied to co‐immobilize various whole cells with different biocatalytic activities directly after harvesting fermentations. Entrapment of Escherichia coli cells with Chromobacterium violaceum ω‐transaminase activity and Lodderomyces elongisporus cells with ketoreductase activity in presence of silica microspheres (depicted here as footballs) provided a biocatalyst with easy recovery, long‐term storability and good mechanical stability. The co‐immobilized whole‐cell biocatalyst could perform a reaction cascade converting racemic 4‐phenylbutan‐2‐amine or heptan‐2‐amine to a nearly equimolar mixture of enantiomerically pure (R)‐amine and the corresponding (S)‐alcohol even in continuous‐flow mode. More information can be found in the communication by G. Hornyánszky, L. Poppe, et al. on page 1845 in Issue 17, 2018 (DOI: 10.1002/cbic.201800286).
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