Fig. 3: Ultrasound-controlled organocatalysis using (covalent)catalyst system in aqueous media.

a A schematic of catalyst availability from the (covalent)catalyst system via the application of ultrasound stimulus for hydrolysis reaction of active esters in aqueous buffer at pH = 7.0, b Reaction scheme for imidazole-functionalized alginate (Im-Alg), (c–e) FESEM image of alginate material before (c) and after (d, e) the application of ultrasound stimulus. Scale bar is 100 µm (for c, d), and 5 µm (for e). f–h Controlled conversion for hydrolysis reaction in aqueous buffer (pH = 7.0). f Hydrolysis of pNPA in the presence of Im-Alg (magenta diamond), Im-Alg and ultrasound stimulus applied at the start of reaction (blue triangle), at 30 min (navy blue circle) and none (black square). The line is to guide the eyes. g Reaction rate constants for pNPA hydrolysis at different condition involving (covalent) catalyst system. h Hydrolysis of DNPA in the presence of Im-Alg (magenta diamond), Im-Alg and ultrasound stimulus applied at the start of reaction (blue triangle) and none (black square), i Hydrolysis of p-NPB in the presence of Im-Alg (magenta diamond), Im-Alg and ultrasound stimulus applied at the start of reaction (blue triangle) and none (black square). Markers indicates the experimental data. Error bars are based on standard errors in duplicate runs.