The mechanical and leaching stability of enzymes adsorbed on macroporous carriers is an important issue for the technical applicability of such biocatalysts. Both can considerably benefit from the deposition of silicone coating on the carrier surface. The coating of the immobilized lipase Novozyme 435 (NZ435), as a model enzyme preparation, with different silicone loadings was studied in detail by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), as well as by energy‐dispersive X‐ray spectroscopy (EDX) and BET isotherms, and offers explanations and prerequisites for its stabilizing effects. The deposition of silicone on the poly(methyl methacrylate) (PMMA) carrier was found to form an interpenetrating network composite rather than the anticipated core‐shell structure. The silicone precursors homogeneously wet the carrier surface including all inner pores and gradually fill the complete carrier. In parallel, the surface area of NZ435 decreases from an initial value of 89 m2g−1to 0.2 m2g−1after silicone loading. A visible layer of silicone on the outer surface of the carrier was only observed at a silicone concentration of 54 % w/w and more. Maximum leaching stability corresponds to the formation of this layer. The mechanical stability increases with the amount of deposited silicone. It can be expected that stabilization against leaching and/or mechanical stress by formation of silicone composites can easily be transferred to a whole range of alternative biocatalytic systems. This should considerably advance their general technical applicability and overall implementation of biocatalysts in chemical synthesis.

No abstract

Composite particles of the commercial lipase preparation NZ435 and silicone (silcoat-NZ435) have recently been described as promising biocatalysts for synthetic use. In this study, their actual potential for enhanced performance in industrial applications was evaluated, focusing on scenarios where carrier disintegration and catalyst leaching constitute key limitations. All three investigated model reactions, the syntheses of myristyl myristate, poly(ethylene glycol) 400-coconut fatty acid monoester and ethylene oxide and propylene oxide co-A C H T U N G T R E N N U N G polymer (EO/PO)-oleic acid diester, were considerably improved in terms of the maximal number of reaction cycles performed with the same batch of catalyst, and consequently in terms of the obtainable product amount. The total turnover numbers (TTN) increased by a factor up to 50, making the realization of this type of reactions in an industrial process more feasible. The utility of silcoat-NZ435 for stereoselective transformations was demonstrated with the enantioselective acylation of 1-phenylethanol with vinyl butyrate, in which full retention of the excellent stereoselectivity of native NZ435 was observed. Moreover, it was demonstrated for the first time that the methodology by which silcoat-catalysts are obtained can be successfully transferred to alternative carriers and enzymes (e.g., protease, esterase and laccase), opening a broad field for the implementation and advancement of biocatalysis in industrial processes.

Dynamic kinetic resolution (DKR) of racemic starting material is a promising route to optically pure (S)-benzoin (2-hydroxy-1,2-di(phenyl)ethanone) and various symmetrical and unsymmetrical derivatives thereof. Here, this route was advanced towards technical scale synthesis using the basic (rac)-benzoin as model system. The reaction employed stereoselective transesterification of (S)-benzoin with lipase TL® from Pseudomonas stutzeri and racemization of (R)-benzoin with Metal-TUD-1, a metal-associated acidic meso-porous silicate, in pure organic solvent. Enzyme performance was improved by immobilization on Accurel MP1001 (yielding Acc-LipTL), and Zr-TUD-1 (Si/Zr = 25) was identified as most effective racemization catalyst. Compatibility in solvent and temperature dependency enabled performance in only one pot. DKR in toluene at 50 °C yielded conversions above 98% and an ee of >97% in only five hours. Stability of Acc-LipTL was further improved with polyethylene imine and the reaction system was then reused in five cycles, retaining a conversion of >99% and a product-ee of >98%. On a semi-preparative scale, the isolated yield of enantiopure (S)-benzoin butyrate was >98%. Thus, the system provides a good basis for synthesis of enantiopure benzoin, and potentially a broader range of aromatic α-hydroxy ketones

No abstract

Scalable preparation of silCoat-biocatalysts by use of a fluidized-bed reactorSilCoat-biocatalysts are immobilized enzyme preparations with an outstanding robustness against leaching and mechanical stress and therefore promising tools for technical synthesis. They consist of a composite material made from a solid enzyme carrier and silicone. In this study, a method has been found to enable provision of these catalysts in large scale. It makes use of easily scalable fluidized-bed technology and, in contrast to the original method, works in almost complete absence of organic solvent. Thus, it is both a fast and safe method. When the Pt-catalyst required for silicone formation is cast on the solid enzyme carrier before coating, resulting composites resemble the original preparations in morphology, catalytic activity, and stability against leaching and mechanical forces. Only the maximum total content of silicone in the composites lies about 10% w/w lower resulting in an overall leaching stability below the theoretical maximum. When the Pt-catalyst is mixed with cooled siloxane solution before coating, surficial coating of the enzyme carriers is achieved, which provides maximum leaching stability at very low silicone consumption. Thus, the technology offers the possibility to produce both composite and for the first time also core-shell silCoat-particles, and optimize leaching stability over mechanical strength according to process requirements.

No abstract

The inside cover picture shows a scanning electron microscope image of a particle of the biocatalyst Novozym 435, a lipase immobilized on a macroporous carrier. A silicone coating can aid the mechanical and leaching stability of catalyst while retaining its activity, as demonstrated by Thum, Ansorge-Schumacher et al. in their paper on page 455 ff. Inside CoverLars O. Wiemann, RenØ Nieguth, Marrit Eckstein, Matthias Naumann, Oliver Thum*, and Marion B. Ansorge-Schumacher* The inside cover picture shows a scanning electron microscope image of a particle of the biocatalyst Novozym 435, a lipase immobilized on a macroporous carrier. A silicone coating can aid the mechanical and leaching stability of catalyst while retaining its activity, as demonstrated by Thum, Ansorge-Schumacher et al. in their paper on page 455 ff. Inside CoverLars O. Wiemann, RenØ Nieguth, Marrit Eckstein, Matthias Naumann, Oliver Thum*, and Marion B. Ansorge-Schumacher* The inside cover picture shows a scanning electron microscope image of a particle of the biocatalyst Novozym 435, a lipase immobilized on a macroporous carrier. A silicone coating can aid the mechanical and leaching stability of catalyst while retaining its activity, as demonstrated by Thum, Ansorge-Schumacher et al. in their paper on page 455 ff.