No abstract

Inspired by natural photosynthesis, photocatalytic NADH regeneration has drawn increasing interest in the recent decade as it provides a perfect approach for NAD+ reduction into NADH, which can be further consumed by oxidordeuctase for enzymatic redox reactions. However, two issues still remain unsolved in this procedure. First, the photocatalytic efficiency in NAD+ hydrogenation requires further improvement. Second, the rhodium electron mediator [Cp*Rh­(bpy)­H2O]2+ (M), which is always required for selective 1,4-NADH regeneration, is difficult to recover because of its good solubility in aqueous solution. Given the high price of M, it is highly wasteful and inefficient if it only spends once. Here, we report a Cp*Rh­(bpy)Cl implanted conjugated microporous polymer DTS/Rh@CMPs which can be employed as a highly effective visible light photocatalysts for in situ NADH regeneration without using additional M. In addition, the insertion of Rh complex into a polymer skeleton, as demonstrated in UV–vis, fluorescence, photocurrent and electrochemical impedance, dramatically improves the light absorption capacity and the electron separation and transfer efficiency. Compared with that of DTS@CMP-1 with M, an enhanced reaction yield of 33% was determined in DTS/Rh@CMP-1 suggesting that intramolecular electron transfer has a better activity than that of intermolecular electron transfer in photocatalytic NAD+ reduction. Moreover, as the Rh complex is rooted firmly in a polymer framework, negligible Rh loss and conversion decrease in NADH regeneration are observed. When the DTS/Rh@CMP-1 was coupled with yeast alcohol dehydrogenase (YADH, from Saccharomyces cerevisiae), 1.36 mM of methanol was accumulated, implying an excellent biocompatibility of DTS/Rh@CMP-1 and a high feasibility of photobiocatalysis for formaldehyde hydrogenation.

The design of a highly efficient polymer photocatalyst is an essential prerequisite for photo-biocatalysis in a polymer−enzyme coupled system, which offers an important platform for the synthesis of pharmaceuticals and fine chemicals. However, current polymers still suffer drawbacks of poor water wettability, low visible light absorption, and high recombination rate of photoinduced electron/hole pairs, which severely limit their application in photo-biocatalysis. Herein, we demonstrate a polymer/polymer double-shell hollow nanostructure (PCN@ PDBTS-HN) via a facile two-step polymerization with polymeric carbon nitride (PCN) and poly-dibenzothiophene sulfone (PDBTS) as internal and external shells, respectively. The covalent connection of those two polymer layers ensures the spontaneous electron transfer from PDBTS to PCN, as reflected in X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and fluorescence spectra, which could effectively accelerate the charge separation and migration. Thanks to its improved light-harvesting, increased hydrophilicity, and enhanced redox capacity, the obtained PCN@PDBTS-HN demonstrates an excellent catalytic efficiency in visible-light-promoted NADH regeneration with a conversion of 85.4% being achieved in 40 min (turnover frequency of 0.859 mmol g −1 h −1 ). This value is 1.4 and 2.6 times higher than that of pristine PCN and PDBTS, respectively, indicating an essential role of Z-scheme heterojunction in improving the catalytic efficiency. In addition, PCN@PDBTS-HN also displays excellent photocatalytic selectivity for 1,4-NADH regeneration, remarkable photostability, and good biocompatibility. A total amount of 2.12 mM methanol and 8.39 mM L-glutamate was accumulated in the polymer/alcohol dehydrogenase (YADH) and polymer/glutamate dehydrogenase (GDH) coupled system, respectively, implying high flexibility of fine chemical production via the photo-biocatalytic approach.