Photoinduced Hydrogen-Evolution System with an Antibody–Porphyrin Complex as a Photosensitizer

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Abstract
A complex between a monoclonal antibody for porphyrin and zinc–porphyrin was utilized to construct an energy conversion system. Monoclonal antibody 2B6 bound meso-tetrakis(4-carboxyphenyl)porphyrin zinc complex (ZnTCPP) with a dissociation constant of 2.1 × 10−8 M. Upon binding the antibody, the lifetime of the excited triplet state of ZnTCPP increased from 0.5 to 1.2 ms. A stable cationic radical of viologen was obtained by irradiating the solution containing the complex of 2B6 with ZnTCPP, methyl viologen (MV2+), and ethylenediaminetetraacetic acid tetrasodium salt (EDTA-4Na) with light. When colloidal platinum was added as a catalyst, photoinduced hydrogen production was observed upon continuous irradiation of visible light. The estimated turnover number of photoinduced hydrogen evolution was 5.0 × 10−3 s−1. The catalytic activity of the 2B6–ZnTCPP complex on the hydrogen evolution was compared with that of ZnTCPP alone and the complexes of ZnTCPP with fragments of antibody 2B6 (2B6-H and 2B6-L). The heavy chain of antibody 2B6 mainly contributed to the complex formation with ZnTCPP and the resultant hydrogen production, and the whole antibody–ZnTCPP complex led to the efficient hydrogen production.