writer：T. Komatsu, Rong-MinWang, P. A. Zunszain, S. Curry, E. Tsuchida
keywords：Biopolymer complexes, rHSA, Zn-protoporphyrin IX
source：期刊
specific source：J. Am. Chem. Soc., 2006, 128(50), 16297-16301
Issue time：2006年
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 (?T) 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  107 and 4.7  108 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 wellknown organic chromophore, tetrakis(1-methylpyridinium-4-yl)porphinatozinc(II) (ZnTMPyP4+), under the same conditions.