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

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 x 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 2136 with ZnTCPP, methyl viologen (MV2+), and ethylenediaminetetraacetic acid tetrasodium salt (EDTA-4Na) with light. When colloidal platinum was added as a catalyst, photoindueed hydrogen production was observed upon continuous irradiation of visible light. The estimated turnover number of photoinduced hydrogen evolution was 5.0 x 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.