pH-Controlled Nanoparticle Catalysts for Highly Selective Tandem Henry Reaction from Mixtures

Abstract

Nature has a remarkable ability to perform selective transformation of complex biological mixtures into desired products using enzymatic catalysts. We report the preparation of nanoparticle catalysts through molecular imprinting within crosslinked micelles. These catalysts were highly selective for their targeted substrates and could selectively hydrolyze less reactive acetals over more reactive ones even under basic conditions. Their catalytic activity and selectivity were tunable through rational postmodification of the active site. These properties enabled the nanoparticle catalysts to produce the desired β-nitro alcohol from a four-component acetal mixture in a tandem deprotection/Henry reaction that required incompatible acidic and basic catalysts in the two steps.

Tunable Artificial Enzyme–Cofactor Complex for Selective Hydrolysis of Acetals

“…Syntheses of substrates 3a−c/f, 35 3d, 53 surfactant 4, 54 cross-linker 5, 16 surface ligand 6, 16 7, 55 and 13 35 were reported previously. Syntheses of substrates 3e 56 and 3g 57 were adapted from the known procedures.…”

“…A key feature of the system is the facile tuning of catalytic activity by easy "plug-and-play" switching of the acid cofactor, which could not be achieved if the acid groups are covalently attached to the active site. 35 In addition, both the number of acid cofactors and the depth of the active site impacted the catalysis strongly. The artificial enzyme−cofactor complex was able to distinguish subtle structural features of the substrates and even hydrolyze less reactive acetals over more reactive onesa feature frequently seen in enzymatic catalysis but rare in chemical catalysis.…”

“…Close proximity of the reactive group and the catalytic group allowed weak carboxylic acids to work as well as much stronger sulfonic acids in certain constructs. A key feature of the system is the facile tuning of catalytic activity by easy “plug-and-play” switching of the acid cofactor, which could not be achieved if the acid groups are covalently attached to the active site . In addition, both the number of acid cofactors and the depth of the active site impacted the catalysis strongly.…”

Tandem Aldol Reaction from Acetal Mixtures by an Artificial Enzyme with Site-Isolated Acid and Base Functionalities

“…To convert the imprinted pockets of MINP into enzyme-like catalytic active sites, we need to install specific functional groups at the desired positions. Previous methods of functionalization require complicated synthesis of specially designed templates and/or functional monomers. ,− A quick, high-yielding, one-step postfunctionalization is ideal, especially if different types of catalytic groups can be introduced at the desired locations. We, thus, designed template 1a with the following considerations.…”

Molecularly Imprinted Synthetic Glucosidase for the Hydrolysis of Cellulose in Aqueous and Nonaqueous Solutions

“…The addition, removal, and shift of a single methyl (or methylene) group in the guest can be distinguished by the so-called molecularly imprinted nanoparticles (MINPs). Catalytic groups can be installed inside the imprinted pockets to afford highly selective, enzyme-mimetic catalysts. − …”