Abstract
In this report, the bio-inspired photocatalytic regeneration of NADH employing graphitic carbon nitride photocatalysis with a diatom frustule structure was presented. The functional structure was constructed from green and sustainable diatomite (diatom earth) by an “incipient wetness impregnation” method. By using [Cp*Rh(bpy)H2O]2+ as an electron mediator, the NADH yield can reach nearly 100%, with the enzymatically active 1,4-NADH being the only product. Furthermore, even without an electron mediator, a direct electron transfer between graphitic carbon nitride and β-NAD+ was possible and NADH could still be regenerated. Diatom-based carbon nitride showed a substantial improvement in regeneration efficiency compared with mpg-C3N4 which has a higher specific surface area. This was ascribed to the diatom structure, with its enhanced light trapping and scattering promoting high photocatalytic efficiency. Furthermore, abundant species of diatoms in the earth offer more possibilities to construct an artificial photosynthetic system using diatom frustules with excellent light-to-energy conversion efficiency.
Highlights
Diatoms are unicellular photosynthetic organisms and can be found in nearly every aquatic habitat on earth
One factor that limits the practical application of enzymatic catalysis in organic reactions is the high cost of enzyme-speci c cofactors
We present here a novel visible light driven photocatalytic method imitating the function of Photosystem I (PSI) for the regeneration of 1,4-NADH from NAD+ by diatom frustule structured graphitic C3N4 (DE-g-C3N4 in short)
Summary
Diatoms are unicellular photosynthetic organisms and can be found in nearly every aquatic habitat on earth. Photosystem I (PSI), an integral membrane protein complex in photosynthesis, uses light energy to mediate electron transfer from plastocyanin to ferredoxin and to ferredoxin–NADP reductase, where the ultimate reduction of nicotinamide adenine dinucleotide phosphate (NADP) to NADPH occurs, storing the light energy in chemical “currency”, as NAD(P)H carries hydrogen in a biologically convertible form (Scheme 1). Involves the simultaneous presence of enzymes and substrates.[6] Non-enzymatic electrochemical and newly proposed photocatalytic methods in the recent years can serve the purpose of NADH regeneration.[7,8] those non-enzymatic methods usually have major drawbacks, i.e. a rare metalchelating electron mediator or toxic methylviologen are usually prerequisites for the known NADH regeneration routes.[9,10,11,12,13] In view of increasing environmental and sustainability considerations, seeking a green, sustainable, economic, and efficient regeneration method for NADH is indispensable. To the best of our knowledge, the work represents the rst report about mediator-less metal-free photocatalytic regeneration of NADH from b-NAD+ and describes – with the involvement of an electron mediator – the highest conversion yield up to now
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