STRIPS bijels could potentially be used as reaction media for biphasic enzymatic reactions of hydrophobic substrates by enabling rapid interphase mass transfer. This method enables continuous fabrication of bijels in diverse formats (nanoparticle, fiber, and membrane), potentially enabling various applications in biphasic chemical processes (Fig. Although the first examples of bijels were produced by arresting thermally quenched mixtures of oil and water, a recent study has demonstrated that bijels can be continuously produced using a wide variety of oil and nanoparticles by solvent transfer-induced phase separation (STRIPS). The size of the biphasic domains in bijels can be systematically varied, even below the micrometer scale, by changing the size and concentration of nanoparticles 30. Unlike typical emulsions, the structures in bijels do not undergo coarsening over time due to the rigidity provided by the interfacially jammed nanoparticle layers. The bijel is a structurally stable biphasic bicontinuous emulsion generated by jamming nanoparticles at the interface between immiscible liquids during spinodal decomposition 28, 29. Recently, a new class of biphasic liquid mixture known as bicontinuous interfacially jammed emulsion gel (bijel) has been introduced. However, these emulsion-based systems do not offer the possibility of performing reactive separation continuously because the dispersed phase remain isolated, making it challenging to add or remove agents to/from the dispersed phase. Particle-stabilized Pickering emulsions offer great potential to enable reactive separation of biphasic reactions using enzymes 23, 24, 25, 26, 27. Surfactants at the interface also form barriers to interphase mass transfer, reducing the efficacy of the enzymatic process. Although the interfacial area could be increased by energy-intensive emulsification, the addition of surfactants 11, or the use of sponge phases 12, 13 and microemulsions 14, 15, 16, these approaches may not be favored because enzymes can be undesirably deactivated by shear stress 17, 18, 19 or surfactants, resulting in inefficient conversion 20, 21, 22. However, slow mass transfer due to the limited interfacial area between two immiscible liquid phases significantly limits efficient conversion 8, 9, 10. To enable catalytic conversion of such a hydrophobic substrate, a biphasic system consisting of water and organic solvent is required 5, 6, 7. When a substrate is hydrophobic and thus insoluble in water, its conversion via enzymatic reaction is significantly reduced because the enzyme is typically water soluble and the substrate is present at a very low concentration in the aqueous phase. Despite these advantages, application of enzymatic reactions are typically limited to the conversion of water-soluble chemicals 3, 4. This work also demonstrates that bijels can potentially be used as reaction media to enable continuous reactive separations.Įnzymes are highly efficient natural catalysts that accelerate various reactions with high activity and (stereo-)specificity under mild reaction conditions, making them attractive catalysts for the industry-scale conversion of chemicals 1, 2. Our results demonstrate that bijels are powerful biphasic reaction media to accelerate enzymatic reactions with various hydrophobic reagents. The bijel system gives a four-fold increase in the initial reaction rate in comparison to a stirred biphasic medium. Using lipase-catalyzed hydrolysis of tributyrin as a model reaction in a batch mode, we show that bijels can be used as media to enable enzymatic reaction. In this study, to expedite the enzymatic conversion of a hydrophobic substrate, we use a bicontinuous interfacially jammed emulsion gel (bijel) which provides large interfacial area between two immiscible liquids: oil and water. Although enzymes are efficient catalysts capable of converting various substrates into desired products with high specificity under mild conditions, their effectiveness as catalysts is substantially reduced when substrates are poorly water-soluble.
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