Bioactive water powders for catalysis in biphasic systems

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The use of biocatalysts in chemical synthesis holds enormous potential for a wide range of industries as they can increase the economic efficiency as well as the environmental friendliness of syntheses. However, a major drawback is their requirement of aqueous environment to be active. Thus, compounds with low solubility or stability in water, which are the majority of organic compounds in synthesis, can be hardly involved. This project aims to widen the scope of biocatalyzed syntheses by introducing bioactive water powders as novel, cheap and easy-to-handle tools to enable enzyme application in organic reaction media. The enzymes are to be "encapsulated" in small particles within their aqueous phase. This is achieved by hydrophobic silica particles that form a stable shell around the enzyme solution. It has already been demonstrated that such particles form stable emulsions (Pickering emulsions) in organic solvents and allow a considerable improvement of the activity of the biocatalysts, especially for sensitive enzymes. However, since an organic phase is still required to obtain the emulsion, negative effects on enzyme stability during the production process and resulting inactivation of the catalysts could not be avoided. In addition, the formation of the emulsions in the organic-aqueous environment cannot be standardized. To solve these problems, employment of dry water powders (DWPs), i.e. particle-stabilized water phases produced in air, for enzyme encapsulation prior to their subjection to organic solvents is suggested in this project. Such a use of DWPs has never been described before. Thus, a thorough fundamental study on the required material properties and the effects of the approach on enzymes and their catalytic efficiency will be performed. In close collaboration of material scientists and enzyme technologists at Jilin University (China) and TU Dresden (Germany), respectively, the system will be developed towards synthetic applicability in an iterative process and benchmarked against existing alternative approaches. The best variants will be loaded with different, industrially relevant enzymes and evaluated for synthetic performance. Among others, this will include recently described (pseudo)ephedrine dehydrogenases catalysing the asymmetric synthesis of various enantiomerically pure alpha-hydroxyketones.