Modulation of starch nanoparticle surface characteristics for the facile construction of recyclable Pickering interfacial enzymatic catalysis

Abstract

In this work, maize starch (MS) was successively modified via an esterification reaction with acetic anhydride (AA) and phthalic anhydride (PTA). Combined with the gelatinization–precipitation process, the formed starch nanoparticles at an AA/PTA ratio of 2 (MS-AP (2)) and 3 (MS-AP (3)) had similar regular spheres but distinct surface characteristics. In order to enhance the activity of lipase B from Candida antarctica (CALB) in an organic solvent, we designed an oil-in-water (o/w) and a water-in-oil (w/o) Pickering interfacial catalytic system simultaneously by utilizing MS-AP (2) and MS-AP (3) as robust Pickering emulsion stabilizers. Impressively, during the esterification of 1-butanol and vinyl acetate, the specific activity of CALB in the o/w (0.0843 U μL⁻¹) or w/o (0.0724 U μL⁻¹) Pickering interfacial catalytic system was much higher than that of free enzymes in the monophasic (0.0198 U μL⁻¹) and biphasic (0.0282 U μL⁻¹) system. Moreover, after preliminarily elaborating mass transfer discrepancies between the o/w and w/o Pickering interfacial catalytic systems and calculating their mass transfer resistance, we clarified the effects of the location of these two phases on the catalytic capacity of the Pickering emulsion. Impressively, both Pickering interfacial catalytic systems exhibited high effectiveness in product separation. It was found that the w/o Pickering emulsion enabled the organic product to be facilely isolated through a simple decantation, while the o/w Pickering emulsion achieved similar results after adjusting the system temperature. The bio-based nanomaterials and simple protocol, in conjunction with the stability to simultaneously achieve high catalysis efficiency and excellent recyclability, makes us believe that this starch nanoparticle-based Pickering interfacial catalytic system is a promising system for meeting the requirements of green and sustainable chemistry.