pH-Responsive aqueous homogeneous metal/enzyme catalysis and heterogeneous recovery enabled by organic cages

Abstract

Leveraging the complementary strengths of homogeneous and heterogeneous catalysts is highly desirable but remains highly challenging. Here, we present RCC3 (a nitrogen-containing organic cage)-mediated pH-responsive aqueous homogeneous metal/enzyme catalysis and heterogeneous recovery. This concept was well demonstrated in a palladium nanoparticle (PdNP)-catalyzed transfer hydrogenation reaction, a Candida antarctica lipase B (CALB)-catalyzed hydrolysis reaction, as well as a cascade reaction combining the two. At pH ≤ 7.0, dissolved protonated RCC3 performed multiple roles in solution processes, including accelerating mass transfer, activating and stabilizing the metal/enzyme catalysts, leading to highly efficient homogeneous catalysis, while at pH ≥ 9.5, RCC3-encapsulated metal/enzyme colloids were formed and precipitated, enabling rapid and facile catalyst recovery. Molecular dynamics (MD) simulations provided deeper insights into the mechanisms of the RCC3-induced enzyme recovery, activation and stabilization.