Takahashi Kosuke, Sato Taisei, Yamazaki Hirosato, Yagi Masayuki
Department of Materials Science and Technology, Faculty of Engineering & Center for Transdisciplinary Research, Niigata University, 8050 Ikarashi-2, Niigata 950-2181, Japan.
Department of Materials Science and Technology, Faculty of Engineering & Center for Transdisciplinary Research, Niigata University, 8050 Ikarashi-2, Niigata 950-2181, Japan; PRESTO (Precursory Research for Embryonic Science and Technology), Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
J Photochem Photobiol B. 2015 Nov;152(Pt A):119-26. doi: 10.1016/j.jphotobiol.2015.04.004. Epub 2015 Apr 16.
Heterogeneous water oxidation catalyses were studied as a synthetic model of oxygen evolving complex (OEC) in photosynthesis using mica adsorbing various manganese species. Distribution of manganese species formed in the oxidative dimerization reaction of Mn(II)(terpy)2 (terpy=2,2':6',2″-terpyridine) (1') with various oxidants in water was revealed. 1' was stoichiometrically oxidized to form di-μ-oxo dinuclear manganese complex, (OH2)(terpy)Mn(III)(μ-O)2Mn(IV)(terpy)(OH2) (1) by KMnO4 as an oxidant. When Oxone and Ce(IV) oxidants were used, the further oxidation of 1 to (OH2)(terpy)Mn(IV)(μ-O)2Mn(IV)(terpy)(OH2) (2) was observed after the oxidative dimerization reaction of 1'. The mica adsorbates with various composition of 1', 1 and 2 were prepared by adding mica suspension to the various oxidant-treated solutions followed by filtration. The heterogeneous water oxidation catalysis by the mica adsorbates was examined using a Ce(IV) oxidant. The observed catalytic activity of the mica adsorbates corresponded to a content of 1 (1ads) adsorbed on mica for KMnO4- and Oxone-treated systems, indicating that 1' (1'ads) and 2 (2ads) adsorbed on mica do not work for the catalysis. The kinetic analysis suggested that 1ads works for the catalysis through cooperation with adjacent 1ads or 2ads, meaning that 2ads assists the cooperative catalysis by 1ads though 2ads is not able to work for the catalysis alone. For the Ce(IV)-treated system, O2 evolution was hardly observed although the sufficient amount of 1ads was contained in the mica adsorbates. This was explained by the impeded penetration of Ce(IV) ions (as an oxidant for water oxidation) into mica by Ce(3+) cations (generated in oxidative dimerization of 1') co-adsorbed with 1ads.
利用吸附了各种锰物种的云母，对非均相水氧化催化剂进行了研究，作为光合作用中析氧复合物（OEC）的合成模型。揭示了Mn(II)(terpy)2（terpy = 2,2':6',2″-三联吡啶）（1'）与水中各种氧化剂在氧化二聚反应中形成的锰物种分布。1'被化学计量氧化，以高锰酸钾作为氧化剂形成二-μ-氧代双核锰配合物(OH2)(terpy)Mn(III)(μ-O)2Mn(IV)(terpy)(OH2)（1）。当使用过硫酸氢钾复合盐和Ce(IV)氧化剂时，在1'的氧化二聚反应后观察到1进一步氧化为(OH2)(terpy)Mn(IV)(μ-O)2Mn(IV)(terpy)(OH2)（2）。通过将云母悬浮液加入到各种氧化剂处理的溶液中，然后过滤，制备了具有不同1'、1和2组成的云母吸附物。使用Ce(IV)氧化剂研究了云母吸附物的非均相水氧化催化作用。对于高锰酸钾和过硫酸氢钾复合盐处理的体系，观察到的云母吸附物的催化活性与吸附在云母上的1（1ads）含量相对应，这表明吸附在云母上的1'（1'ads）和2（2ads）对催化作用无效。动力学分析表明，1ads通过与相邻的1ads或2ads协同作用来进行催化，这意味着2ads虽然不能单独进行催化，但能协助1ads的协同催化。对于Ce(IV)处理的体系，尽管云母吸附物中含有足够量的1ads，但几乎观察不到氧气的析出。这可以解释为，与1ads共吸附的Ce(3+)阳离子阻碍了Ce(IV)离子（作为水氧化的氧化剂）渗透到云母中。
