Biocatalysis in water-immiscible organic solvents: the use of immobilized living microorganisms

Simultaneous enzymatic activity modulation and rapid determination of enzyme kinetics by highly crystalline graphite dots

The research field in enzyme-based biotechnology urgently requires the discovery of new materials and methods with high-performance. Here we report that highly crystalline graphite dots (GDs) can modulate enzyme activities, and simultaneously allow for real-time measurements on enzyme kinetics in combination with mass spectrometry (MS). A well-defined modulation of lipolytic activities from inhibition to enhancement can be realized by selectively coupling lipase enzymes with GDs containing specific functional groups on the surface. As a unique feature of our approach, GDs in the enzyme reaction can simultaneously serve as a versatile matrix for rapid and sensitive detection of the residual enzyme substrate, the intermediate or final product of lipolytic digestion using MS technology. Therefore, enzyme kinetic data can be collected in a real-time, high-throughput format. This work provides a new platform for enzymological research in hybrid bio-catalytic processes with advanced nanotechnology.

Biocatalysis in multi-phase reaction mixtures containing organic liquids

A wide range of enzymes and whole microbial cells will act as catalysts in reaction mixtures that contain 2 or more phases, one of which is an organic liquid (either a reactant or including water-immiscible organic solvents). These "biphasic" systems have a variety of structures, knowledge of which aids predictions about biocatalyst activity and stability. There is often a dilute aqueous solution phase (containing the biocatalyst), which may be emulsified with the organic phase, or "trapped" within catalyst particles; sometimes however there may only be traces of water adsorbed to the enzyme or cells. These reaction systems offer several advantages for industrial applications, notably the higher solubilities of many reactants of interest, and the ability of readily available hydrolytic enzymes to catalyse syntheses. The most non-polar organic liquids are least likely to inactivate biocatalysts, though many do remain active with relatively polar solvents. Modification of the biocatalyst may stabilise against inactivation, especially where this is due to direct contact with the phase interface. The mass transfer processes required in these systems remain poorly understood, particularly because the interfacial area is often unknown. Attractive continuous reactors may be operated using a packed bed of catalyst with a trapped aqueous phase.