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Chloroplast-inspired Artificial Photosynthetic Capsules for Efficient and Sustainable Enzymatic Hydrogenation Ziyi Cai, Jiafu Shi, Yizhou Wu, Yishan Zhang, Shaohua Zhang, and Zhongyi Jiang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04499 • Publication Date (Web): 24 Oct 2018 Downloaded from http://pubs.acs.org on October 28, 2018
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ACS Sustainable Chemistry & Engineering
Chloroplast-inspired
Artificial
Photosynthetic
Capsules for Efficient and Sustainable Enzymatic Hydrogenation Ziyi Caia,b, Jiafu Shib,c,d, *, Yizhou Wua,b, Yishan Zhanga,b, Shaohua Zhanga,b, Zhongyi Jianga,b,d,* a
Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical
Engineering and Technology, Tianjin University, 92 Weijin Road, Nankai District, Tianjin 300072, P. R. China b
Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), 92 Weijin
Road, Nankai District, Tianjin 300072, P. R. China c
School of Environmental Science and Engineering, Tianjin University, 92 Weijin Road, Nankai
District, Tianjin 300072, P. R. China d
State Key Laboratory of Bioreactor Engineering, East China University of Science and
Technology, 130 Meilong Road, Shanghai 200237, P. R. China *
Corresponding authors:
Jiafu Shi,
[email protected]; Zhongyi Jiang,
[email protected] KEYWORDS: Artificial photosynthesis; Chloroplast; Alginate capsule; Enzyme immobilization; Kinetic analysis
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ABSTRACT: Inspired by the structure and function of chloroplast, an artificial photosynthetic alginate (ALG) capsule bearing carboxymethylcellulose (CMC) matric, red phosphorus quantum dots@g-C3N4 (P/CN) tubular photocatalysts and alcohol dehydrogenase (ADH) is prepared for efficient and sustainable synthesis of methanol from formaldehyde. CMC liquid core resembles grana in chloroplast to afford favorable micro-environment for stabilizing ADH, whereas P/CN photocatalysts mimic thylakoid in chloroplast to supply nicotinamide adenine dinucleotide (NADH, the hydride donor) for triggering enzymatic hydrogenation. Moreover, P/CN photocatalysts reinforce the mechanical stability and, thereby, inhibit the swelling of ALG capsules, thus suppressing the leaching of P/CN photocatalysts and enzymes. The kinetic processes of photocatalytic regeneration and enzyme hydrogenation are investigated, respectively. The optimal coupling of photo-enzyme reactions enabled by the capsules achieves the efficient and sustainable production of methanol. Our study offers some guidance for rational construction of integrated and recyclable artificial photosynthetic systems towards a broad range of chemical/biochemical reactions.
INTRODUCTION Enzymes are one kind of bioactive macromolecules that can catalyze a broad range of reactions under ambient conditions with ultrahigh region-, stereo- and chemo-selectivity.1 Among various enzymes, dehydrogenases, which can accomplish the controlled and selective hydrogenation of carbon-oxygen bonds in the presence of hydride donors, have been applied to catalyze a series of important energy/environmental-related reactions, including selective hydrogenation of aldehyde to alcohol,2 controlled reduction of carbon dioxide,3,4 etc.
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ACS Sustainable Chemistry & Engineering
Currently, the hydrogenation reactions catalyzed by dehydrogenases primarily confront two technical bottlenecks, i.e., poor stabilities of enzymes against negative external stimuli5 and unsustainable supplement of hydride donors6. As for the first bottleneck, the conformation of free enzymes is prone to change under extreme pH, high temperature and other harsh conditions, which will lead to the denaturation and deactivation of enzymes.7 Enzyme immobilization offers a feasible and effective method to stabilize enzymes.8 Among various immobilization carriers, natural polymers with high hydrophilicity, including alginate (ALG),9,10 chitosan,11 etc., can retain high content of water in the polymer network, which offers appropriate chemical/physical micro-environment for preserving the enzyme conformation. However, the loose polymer networks as well as the weak interaction between enzyme and polymer often cause the leaching of enzyme from the carriers, leading to the undesirable reusability and recyclability. As for the second bottleneck, many hydrogenation reactions catalyzed by oxidoreductases require cofactors, e.g., nicotinamide adenine dinucleotide (NADH), nicotinamide adenine dinucleotide phosphate (NADPH), etc., as hydride donors.12 Particularly, nearly 80% of the oxidoreductaseinvolved reactions require NADH as the hydride donor.13 During the enzymatic hydrogenation reaction, NADH reduces the substrate(s) into product(s) catalyzed by enzymes, while itself is oxidized into NAD+. Given the high cost yet indispensable features of NADH, efficient regeneration of NADH is urgently required and can promote enzymatic hydrogenation for further practical application.14,15 Among the existing methods, photocatalysis for solar-driven NADH regeneration has become an attractive method due to its eco-friendly and sustainable solar energy.16 Several nanoscale photocatalysts, including dye-sensitized peptide nanotubes,17 dyesensitized graphene,18 cadmium sulfide quantum dots19 and nanostructured g-C3N4,20 etc., have been developed and exhibited high efficiency toward NADH regeneration. The enzymatic
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hydrogenation was also successfully coupled with photocatalytic regeneration of NADH, achieving the production of some target chemicals, like formate, methanol, etc.18,21-23 Nonetheless, in these cases, the nanoscale photocatalysts (10~100 nm) and enzymes (
