title: Photosensitized reduction of water to hydrogen using human serum albumin complexed with zinc-protoporphyrin IX.
abstract: We present the photophysical properties of complexes of recombinant human serum albumin (rHSA) with Zn(II)-protoporphyrin IX (ZnPP) and their activities in the photosensitized reduction of water to hydrogen (H2) using methyl viologen (MV2+) as an electron relay. The ZnPP is bound in subdomain IB of wild-type rHSA [rHSA(wt] by an axial coordination of Tyr-161 and, in the rHSA(I142H/Y161L) mutant [rHSA(His], by a His-142 coordination. Both the rHSA(wt)-ZnPP and rHSA(His)-ZnPP complexes showed a long-lived photoexcited triplet state with lifetimes (tauT) of 11 and 2.5 ms, respectively. The accommodation of ZnPP into the protein matrix efficiently eliminated the collisional triplet self-quenching process. The addition of a water-soluble electron acceptor, MV2+, resulted in a significant decrease in the triplet lifetime. The transition absorption spectrum revealed the oxidative quenching of rHSA-3ZnPP* by MV2+. The quenching rate constant (kq) and backward electron transfer rate constant (kb) were determined to be 1.4 x 10(7) and 4.7 x 10(8) M(-1) s(-1) for rHSA(wt)-ZnPP. In the presence of the colloidal PVA-Pt as a catalyst and triethanolamine (TEOA) as a sacrificial electron donor, the photosensitized reduction of water to H2 takes place. The efficiency of the photoproduction of H2 was greater than that of the system using the well-known organic chromophore, tetrakis(1-methylpyridinium-4-yl)porphinatozinc(II) (ZnTMPyP4+), under the same conditions.
authors.affiliation: Advanced Research Institute for Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan. teruyuki@waseda.jp
authors.forename: Teruyuki
authors.initials: T
authors.lastname: Komatsu
authors.forename: Rong-Min
authors.initials: RM
authors.lastname: Wang
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Zunszain
authors.forename: Stephen
authors.initials: S
authors.lastname: Curry
authors.forename: Eishun
authors.initials: E
authors.lastname: Tsuchida
mesh_terms: D004583:Electrons; D006801:Humans; D006859:Hydrogen / Q000737:chemistry*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010777:Photochemistry; D017319:Photosensitizing Agents / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D011524:Protoporphyrins / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry; D012709:Serum Albumin / Q000737:chemistry*; D013057:Spectrum Analysis; D014867:Water / Q000737:chemistry*
chemical_list: D017319:Photosensitizing Agents; D011524:Protoporphyrins; D011994:Recombinant Proteins; D012709:Serum Albumin; D014867:Water; C017803:zinc protoporphyrin; D006859:Hydrogen; C028025:protoporphyrin IX