Solventless polyester synthesis using a recyclable biocatalyst magnetic nanoarchitecture†

Improving enzyme activity and stability as well as preserving selectivity is a must for rendering biocatalysis an economically viable technology. These improvements can be achieved by immobilizing the biocatalyst on the surface of metal oxide magnetic nanoparticles. The aim of this work is to rational design Biocatalyst Magnetic Nanoarchitecture (BMN) consisting of spinel iron oxides nanoparticles having optimized morpho structural (i.e., particles size, shape and crystallinity), textural (i.e., high surface area) and magnetic properties. Candida antarctica lipase B (CaLB) was immobilized on the nanoparticles' surface investigating the optimal bioconjugation conditions and performing the biochemical characterizations to quantify protein concentration and to assess enzymatic activity. Once immobilized on the magnetic nanoparticles surface, CaLB was tested for an enzymatic polycondensation reaction to synthesize polyesters starting from renewable monomers such as the dimethyl ester of adipic acid and 1,8-octanediol. Conversion of monomers was >87% over three reaction cycles while the number average molecular weights of the products were between 4200 and 5600 Da with a dispersity <2. Efficient recycling of the enzyme upon magnetic separation was demonstrated for three reaction cycles.