Improved biocatalytic cascade conversion of CO2 to methanol by enzymes Co-immobilized in tailored siliceous mesostructured cellular foams

Abstract

CO₂ can be enzymatically reduced to methanol in a cascade reaction involving three enzymes: formate-, formaldehyde- and alcohol dehydrogenase (FateDH, FaldDH, ADH). We report an improvement in the yield of this reaction by co-immobilizing the three dehydrogenases in siliceous mesostructured cellular foams (MCF). This material consists of large mesopores suitable for the co-immobilization of these comparatively large enzymes. To improve the interaction between the enzymes and support, the host silica material was functionalized with mercaptopropyl groups (MCF-MP). The enzymes were fluorescently labelled to independently monitor their uptake and spatial distribution into the particle. The three dehydrogenases were co-immobilized using two sequential methods. In the first one, the enzymes were immobilized according to the reaction order (FateDH → FaldDH → ADH) and secondly in order of increasing enzyme size (FateDH → ADH → FaldDH). Two protein loadings were also tested: 50 and 150 mg_enzymes g_support⁻¹. We could observe a 4.5-fold higher methanol yield in comparison to enzymes free in solution when the enzymes were immobilized in order of size and with a loading of 50 mg_enzymes g_support⁻¹. The results of this work show that by using MCF-MP, a simple method of immobilization can be applied to significantly increase the activity of the enzymes for the cascade reaction.