Unifying Candida antarctica lipase B and nZVI in bioinspired polymer nanomicelles: a nanobiohybrid synergy for sustainable synthesis of acetaminophen

Abstract

Polymer micelles are tailored nanostructures with the unique ability to encapsulate hydrophobic molecules that have proven to be promising candidates for applications such as drug delivery. With an aim to utilize the robust nature of polymer micelles for catalysis, we have synthesized a novel amphiphilic polymer derived from biocompatible precursors, such as tyrosine and polyethylene glycol. The polymer subsequently self-assembles into nanomicelles. These nanomicelles were loaded with Candida antarctica lipase B (CALB) and zerovalent iron nanoparticles (nZVI). The final magnetic catalyst (nZVI-CALB@NM) served as a nanoreactor for a one-pot cascade reaction consisting of two sequential steps, i.e., hydrolysis and reduction in an aqueous medium. The cascade synthesis of p-aminophenol from a series of p-nitrophenyl esters of fatty acids with different chain lengths was attempted in one pot at 35 °C in an aqueous medium. The hydrolysis step was catalyzed by CALB and the reduction step was catalyzed by nZVI synergistically in the hydrophobic core of nanomicelles to achieve the final product in high yield. Further, to demonstrate the industrial application of the nanoreactors, we have carried out the synthesis of acetaminophen, which is a commercial bioactive molecule. The cascade synthesis of p-acetaminophen from p-nitrophenylacetate was achieved in a single pot within 30 min without an acid catalyst and organic solvent in excellent yield (>98%). Recycling studies demonstrated the possibility of utilizing the catalyst possessing magnetic properties for five successive cycles without any significant loss of activity. The main advantages of our system are the solubility of hydrophobic substrates in an aqueous medium and superior catalytic activity, leading to a significant reduction in the consumption of toxic solvents, reaction time, and temperature compared to those previously reported. The as-prepared nanoreactors will open up a new avenue for other chemoenzymatic reactions in the future by combining the enzyme and metal catalyst.