Research On Enzyme-Catalyzed Sequential Reduction of Carbon Dioxide

Enzyme-catalyzed reduction of CO2 will not only help to lessen greenhouse effect, but also to obtain valuable chemicals. The sequential reduction of CO2 to methanol under mild reaction conditions has been reported to be feasible by using sol-gel encapsulated or nanoparticle-attached dehydragenases as a biocatalyst, with reduced nicotinamide adenine dinuncleotide (NADH) as a cofactor. However, each enzymatic conversion in multi-step reaction and its influencing factors have not been well studied.

Here we put emphasis on the enzymatic synthesis of formaldehyde with formic acid or CO2 as a substrate, respectively, with a catalyst composing of one or two kinds of dehydrogenases. In the former, reactions were performed in a plastic tube containing formaldehyde dehydrogenase and NADH dissolved in phosphate buffer, and formaldehyde formed was examined by high performance liquid chromatography. The mole ratio of formic acid to NADH plays an important role in the promotion of reaction. The larger the ratio is, the higher the initial velocity and maximum conversion rate are. The yield of formaldehyde was up to 21.3% after reaction for one hour when formic acid was applied as a substrate. The conversion of CO2 to formaldehyde catalyzed by formate dehydrogenase and formaldehyde dehydrogenase with the assistance of NADH also showed a positive result in a preliminary study.

The work will provide a good guidance for further study on the membrane-attached dehydrogenases and their application in the conversion of carbon dioxide to formaldehyde or methanol.