Enzyme catalysis, made tremendous progress over the last years in identification of new enzymes and new enzymatic reactivity’s as well as optimization of existing enzymes. However, the performance of the resulting processes is often still limited, e.g., in regard of productivity, realized product concentrations and the stability of the enzymes. Different topics (like limited specific activity, unfavourable kinetics or limited enzyme stability) can be addressed via enzyme engineering. On the other hand, there is also a long list of topics that are not addressable by enzyme engineering. Here typical examples are unfavourable reaction thermodynamics, selectivity in multistep reactions or low water solubility. These challenges can only be addressed through an adaption of the reaction system. The procedures of process intensification (PI) represent a good approach to reach most suitable systems. The general objective of PI is to achieve significant benefits in terms of capital and operating costs as well as product quality, waste, and process safety by applying innovative principles. The aim of the review is to show the current capabilities and future potentials of PI in enzyme catalysis focused on enzymes of the class of oxidoreductases. The focus of the paper is on alternative methods of energy input, innovative reactor concepts and reaction media with improved properties.@en

Light-driven biocatalytic processes are notoriously hampered by poor penetration of light into the turbid reaction media. In this study, wirelessly powered light-emitting diodes are found to represent an efficient and scalable approach for process intensification of the photobiosynthetic production of diesel alkanes from renewable fatty acids.

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Peroxygenases are very interesting catalysts for specific oxyfunctionalization chemistry. Instead of relying on complicated electron transport chains, they rely on simple hydrogen peroxide as the stoichiometric oxidant. Their poor robustness against H₂O₂ can be addressed via in situ generation of H₂O₂. Here we report that simple graphitic carbon nitride (g-C₃N₄) is a promising photocatalyst to drive peroxygenase-catalyzed hydroxylation reactions. The system has been characterized by outlining not only its scope but also its current limitations. In particular, spatial separation of the photocatalyst from the enzyme is shown as a solution to circumvent the undesired inactivation of the biocatalyst. Overall, very promising turnover numbers of the biocatalyst of more than 60.000 have been achieved.

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In general, hydrogen peroxide is a stable and relatively mild oxidant and it can be regarded as the ultimate "green" reagent because water and oxygen are the only by-products. Besides the direct application of H₂O₂ in chemical processes more and more enzymatic syntheses based on hydrogen peroxide were developed. Different types of reactions can be addressed by using a hydrogen-peroxide driven biocatalysis (e.g. hydroxylations, epoxidations, sulfoxidations, halogenations, Baeyer-Villiger oxidations, decarboxylations). H₂O₂-driven reactions can often be used to substitute NAD(P)H dependent reactions. Therefore, laborious cofactor regeneration systems can be avoided by using H₂O₂-dependent enzymes. The tremendous increase in the number of publications dealing with this type of reactions clearly demonstrates the progress in this area in recent years. The described innovations range from new enzymes and types of reaction to novel reaction engineering approaches. This review aims to give the scope of possible advantageous applications of peroxyzymes and a critical discussion of their current limitations. The versatile reactions, the ecological advantageous and the great progress in the discovery and engineering of novel enzymes make a technical use feasible.

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Photoenzymatic cascades can be used for selective oxygenation of C−H-Bonds under mild conditions circumventing the hydrogen peroxide mediated peroxygenase inactivation via in situ H₂O₂ generation. Here, we report the “on demand” production of hydrogen peroxide via methanol assisted reduction of molecular oxygen using UV-illuminated titanium dioxide (Aeroxide P25) combined with the enantioselective hydroxylation of ethylbenzene to (R)-1-phenylethanole catalyzed by the Unspecific Peroxygenase from Agrocybe Aegerita. For the application of the system it is important to understand the influence of the reaction parameters to be able to optimize the system. Therefore, we systematically investigated product formation and enzyme inactivation as well as ROS formation (H₂O₂, ^.OH and ^.O₂⁻) applying different light intensities and temperatures. As a result, Turnover Numbers up to 220 000, photonic efficiencies up to 13.6 % and production rates up to 0.9 mM h⁻¹ were achieved.

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Selective oxyfunctionalizations of inert C−H bonds can be achieved under mild conditions by using peroxygenases. This approach, however, suffers from the poor robustness of these enzymes in the presence of hydrogen peroxide as the stoichiometric oxidant. Herein, we demonstrate that inorganic photocatalysts such as gold–titanium dioxide efficiently provide H₂O₂ through the methanol-driven reductive activation of ambient oxygen in amounts that ensure that the enzyme remains highly active and stable. Using this approach, the stereoselective hydroxylation of ethylbenzene to (R)-1-phenylethanol was achieved with high enantioselectivity (>98 % ee) and excellent turnover numbers for the biocatalyst (>71 000).

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