초록
<P>Light-driven enzymatic catalysis is enabled by the productive coupling of a protein to a photosensitizer. Photosensitizers used in such hybrid systems are typically costly, toxic, and/or fragile, with limited chemical versatility. Carbon dots (CDs) are low-cost, nanosized light-harvesters that are attractive photosensitizers for biological systems as they are water-soluble, photostable, nontoxic, and their surface chemistry can be easily modified. We demonstrate here that CDs act as excellent light-absorbers in two semibiological photosynthetic systems utilizing either a fumarate reductase (FccA) for the solar-driven hydrogenation of fumarate to succinate or a hydrogenase (H<SUB>2</SUB>ase) for reduction of protons to H<SUB>2</SUB>. The tunable surface chemistry of the CDs was exploited to synthesize positively charged ammonium-terminated CDs (CD-NHMe<SUB>2</SUB><SUP>+</SUP>), which were capable of transferring photoexcited electrons directly to the negatively charged enzymes with high efficiency and stability. Enzyme-based turnover numbers of 6000 mol succinate (mol FccA)<SUP>−1</SUP> and 43,000 mol H<SUB>2</SUB> (mol H<SUB>2</SUB>ase)<SUP>−1</SUP> were reached after 24 h. Negatively charged carboxylate-terminated CDs (CD-CO<SUB>2</SUB><SUP>–</SUP>) displayed little or no activity, and the electrostatic interactions at the CD–enzyme interface were determined to be essential to the high photocatalytic activity observed with CD-NHMe<SUB>2</SUB><SUP>+</SUP>. The modular surface chemistry of CDs together with their photostability and aqueous solubility make CDs versatile photosensitizers for redox enzymes with great scope for their utilization in photobiocatalysis.</P><P><B>Graphic Abstract</B><BR><IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2016/jacsat.2016.138.issue-51/jacs.6b10146/production/images/medium/ja-2016-101462_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja6b10146'>ACS Electronic Supporting Info</A></P>