Design of 3D-Printed Heterogeneous Reactor Systems To Overcome Incompatibility Hurdles when Combining Metal and Enzyme Catalysis in a One-Pot Process.

Combining chemo- and biocatalysis enables the design of novel economic and sustainable one-pot processes for the preparation of industrial chemicals, preferably proceeding in water. While a range of proofs-of-concept for the compatibility of such catalysts from these two different "worlds of catalysis" have recently been demonstrated, merging noncompatible chemo- and biocatalysts for joint applications within one reactor remained a challenge. A conceptual solution is compartmentalization of the catalytic moieties by heterogenization of critical catalyst components, thus "shielding" them from the complementary noncompatible catalyst, substrate or reagent. Exemplified for a one-pot process consisting of a metal-catalyzed Wacker oxidation and enzymatic reduction as noncompatible individual reactions steps, we demonstrate that making use of 3D printing of heterogeneous materials containing Cu as a critical metal component can overcome such incompatibility hurdles. The application of a 3D-printed Cu-ceramic device as metal catalyst component allows an efficient combination with the enzyme and the desired two-step transformation of styrene into the chiral alcohol product with high overall conversion and excellent enantioselectivity. This compartmentalization concept based on 3D printing of heterogenized metal catalysts represents a scalable methodology and opens up numerous perspectives to be used as a general tool also for other related chemoenzymatic research challenges.

Selective Coimmobilization of His-Tagged Enzymes on Yttrium-Stabilized Zirconia-Based Membranes for Continuous Asymmetric Bioreductions.

Scalability, process control, and modularity are some of the advantages that make flow biocatalysis a key-enabling technology for green and sustainable chemistry. In this context, rigid porous solid membranes hold the promise to expand the toolbox of flow biocatalysis due to their chemical stability and inertness. Yttrium-stabilized zirconia (YSZ) fulfills these properties; however, it has been scarcely exploited as a carrier for enzymes. Here, we discovered an unprecedented interaction between YSZ materials and His-tagged enzymes that enables the fabrication of multifunctional biocatalytic membranes for bioredox cascades. X-ray photoelectron spectroscopy suggests that enzyme immobilization is driven by coordination interactions between the imidazole groups of His-tags and both Zr and Y atoms. As model enzymes, we coimmobilized in-flow a thermophilic hydroxybutyryl-CoA dehydrogenase (TtHBDH-His) and a formate dehydrogenase (His-CbFDH) for the continuous asymmetric reduction of ethyl acetoacetate with in situ redox cofactor recycling. Fluorescence confocal microscopy deciphered the spatial organization of the two coimmobilized enzymes, pointing out the importance of the coimmobilization sequence. Finally, the coimmobilized system succeeded in situ, recycling the redox cofactor, maintaining the specific productivity using only 0.05 mM NADH, and accumulating a total enzyme turnover number of 4000 in 24 h. This work presents YSZ materials as ready-to-use carriers for the site-directed enzyme in-flow immobilization and the application of the resulting heterogeneous biocatalysts for continuous biomanufacturing.

Alkoxide-based precursors for direct drawing of metal oxide micro- and nanofibres.

The invention of electrospinning has solved the problem of producing micro- and nanoscaled metal oxide fibres in bulk quantities. However, until now no methods have been available for preparing a single nanofibre of a metal oxide. In this work, the direct drawing method was successfully applied to produce metal oxide (SnO2, TiO2, ZrO2, HfO2 and CeO2) fibres with a high aspect ratio (up to 10 000) and a diameter as small as 200 nm. The sol-gel processing includes consumption of precursors obtained from alkoxides by aqueous or non-aqueous polymerization. Shear thinning of the precursors enables pulling a material into a fibre. This rheological behaviour can be explained by sliding of particles owing to external forces. Transmission (propagation) of light along microscaled fibres and their excellent surface morphology suggest that metal oxide nanofibres can be directly drawn from sol precursors for use in integrated photonic systems.