生物转化CO2到甲醇过程的辅酶再生：人工光合作用的探索

Bioconversion of CO2 to methanol involves formic acid, formaldehyde, and ethanol dehydrogenases. Although it has been reported that the three types of redox enzymes succeeded in synthesis of methanol in reactor, but the productivity and efficiency of the process, especially the cofactor regeneration problem has been not solved. Inspired by the natural photosynthesis system, this project propose a novel photochemical cofactor regeneration system incorporated with the bio-catalyzed methanol synthesis from CO2. Based on hollow nanofiber technology developed in our research group, the new system will introduce polyelectrolyte and graphene oxide as co-carrier material. These three dehydrogenase and coenzyme NAD(H) will be in situ encapsulated inside lumen chamber of the hollow nanofibers, while precise assembly of electron mediator and photosensitizer onto the outer of the materials will be realized through layer-by-layer (LbL) self-assembly mechanism, which is driven by their electrostatic interactions with polyelectrolytes, and their interactions with graphene oxide, both are presented on the outer surface of the hollow nanofiber as co-carrier materials. Through above approach, a coupled system of photochemical coenzyme regeneration and cascade redox reaction is biomimetically designed and integrated, with which, the challenge of coenzyme regeneration faced by bioconversion of CO2 can be solved. At the same, such LbL self-assembly will afford the integrated system enhanced electron transfer efficiency and an improved enzyme stability. Based on results from the current project, we expect that a new technology platform with the characteristic of artificial photosynthesis will be developed to serve next generation of multi-enzyme cascade reaction for synthesis of bio-based products.

生物转化CO2到甲醇涉及甲酸脱氢酶、甲醛脱氢酶和乙醇脱氢酶，虽然已有文献报道将这三种氧化还原酶放入反应器成功实现了甲醇的合成，但过程的产率、效率，尤其是辅酶再生的难题并没有解决。受自然界光合作用体系的启发，本项目设计一种新型的光化学辅酶再生-生物催化CO2合成甲醇体系。新体系利用本研究组已有的中空纳米纤维技术，以聚合电解质和氧化石墨烯作为共固定化载体材料，将三种脱氢酶和辅酶NAD(H)原位包埋在材料的中空腔室内；结合层层自组装的技术原理，依次将电子媒介和光敏剂分子通过与材料外壁上聚合电解质之间的静电力以及氧化石墨烯之间的π-π作用力，精确组装到材料的外表面，由此实现光化学辅酶再生-多酶级联反应体系的仿生设计与集成组装。不仅解决从CO2合成甲醇过程的辅酶再生难题，同时通过层层组装提高电子传递效率和酶系统稳定性，有望发展成为带有人工光合作用特征的新一代多酶级联催化合成生物基化学品的平台技术。

针对现有生物催化CO2合成甲醇体系所面临辅酶再生的难题，受自然界光合作用体系的启发，设计了多种具有人工光合作用系统（Artificial Photosynthesis System，APS）特征的光化学辅酶再生-多酶级联催化系统。主要开展了如下研究内容：1）在本研究组已有的中空纳米纤维技术的基础上，将聚合电解质和氧化石墨烯作为共固定化载体材料，将生物转化CO2到甲醇涉及三种氧化还原酶以及辅酶NAD(H)原位包埋在材料的中空腔室内；结合层层自组装的技术原理，依次将电子媒介光敏剂分子精确组装到材料的外表面，首次实现了光化学辅酶再生-多酶级联反应体系的仿生设计与集成组装；2）构建了基于二维TaS2纳米片，以及锑烯-黑磷复合纳米片的APS，不仅NADH再生率高达83.9%，而且实现了以水为电子供体的辅酶再生与光-酶耦联，促进了APS的发展；3）为了进一步提高电子传递效率，采用“bottom-up”自下而上化学合成法，分别构建了“仿绿色植物叶绿体”和“仿光合细菌绿小体”的APS，将目前APS中“分子间”或“材料间”的电子传递界面，进一步变为“分子内”的传递，催化NADH的再生率高达91%。上述研究成果不仅解决从CO2合成甲醇过程的辅酶再生难题，通过深入研究光-酶偶联过程中影响电子传递的主要规律，对于促进APS的发展和应用具有重要的意义。本项目共发表期刊论文14篇，其中4篇发表在IF>10的期刊上，包括Adv Func Materials, ACS Catalysis、J Material Chem A (2篇)，远远超出预期研究目标。项目负责人受邀担任生物化工领域的重要期刊Biochem Eng J、J Chromatography A的编委。