Fig. 2: pH-switchable catalytic systems.
From: Switchable aqueous catalytic systems for organic transformations
a Schematic representation of the pH-switchable VK2H peptide as artificial hydrolase. The peptide showed conformational transition from unfolded random coil to β-sheet via changing the pH from acidic to alkaline. (Inset: chemical structure of peptide VK2H). The fibril structure can catalyze the hydrolysis of pNPA, whereas the unfolded structure is catalytically inactive. Switching the catalytic activity can be controlled by altering the pH. Adopted with permission from ref. 39, copyright 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. b pH-switchable organocatalysis with amine-porphyrin hybrid in aqueous solution. Formation of J-aggregates, at acidic pH, suppressed the catalytic activity of Isoindoline moiety of the hybrid, whereas deaggregated state of the hybrid at higher pH resulted efficient aldol reaction. Adopted with permission from ref. 40, copyright 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. c A schematic of assembly behavior of polymer structure in aqueous solution at different pH (inset: the structure of the polymer), and aggregation-induced aldol reaction that catalyzed by proline moiety. Adopted with permission from ref. 51, copyright 2020 Elsevier B.V. d Schematic of pH-induced emulsion inversion for styrene hydrogenation. At acidic pH, the catalyst can efficiently convert the substrate to product, whereas the reaction is terminated at basic pH (inset: The structural description of silica microsphere with catalytically active center). Adopted with permission from ref. 62, copyright 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
