In order to identify common and distinctive features in the catalytic behavior of natural and artificial nitrogen-fixation clusters, the kinetics of the catalytic reduction of C2H2 in the presence of Mg-Mo-cluster (1) was investigated and compared with the kinetics of acetylene reduction catalyzed by the cluster FeMoco (2) isolated from the enzyme nitrogenase we studied previously. The reactions were conducted in the presence of Zn/Hg and Eu/Hg as reducing agents and PhSH and C6F5SH as proton donors, i.e., under the same conditions as had been used in the case of 2. Both polynuclear Mg-Mo-complex and the europium amalgam-reduced FeMoco have multiple interdependent binding sites for substrates and/or inhibitors. Carbon monoxide inhibits the acetylene reduction much less efficiently in systems with cluster 1 than in systems with cluster 2, although the type of inhibition is mixed in both systems: CO binds to multiple sites of the cluster and affects both C2H2 complexation to the reduced cluster and decomposition of the catalyst-substrate complex to give the products. Unlike isolated FeMoco, the Mg-Mo-cluster efficiently catalyzes the reduction of molecular nitrogen. The reaction is greatly inhibited by acetylene, while no inhibiting effect of N2 is observed in acetylene reduction, as was found earlier for a system with the natural cluster as the catalyst.
为了确定天然和人工固氮团簇催化行为的共同和独特特征,我们研究了 Mg-Mo- 团簇(1)存在下催化还原
C2H2 的动力学,并将其与我们以前研究过的从氮酶中分离出来的 FeMoco 团簇(2)催化还原
乙炔的动力学进行了比较。反应是在以 Zn/Hg 和 Eu/Hg 为还原剂,以 PhSH 和 C6F5SH 为质子供体的条件下进行的,即与 2 的反应条件相同。在具有簇 1 的系统中,
一氧化碳抑制
乙炔还原的效率要比具有簇 2 的系统低得多,尽管在这两个系统中抑制的类型是混合的:
一氧化碳与簇的多个位点结合,既影响 与还原簇的络合,也影响催化剂-底物络合物分解生成产物。与孤立的 FeMoco 不同,Mg-Mo 团簇能有效催化分子氮的还原反应。该反应受到
乙炔的极大抑制,而在
乙炔还原过程中没有观察到 N2 的抑制作用,这与早先发现的以天然团簇为催化剂的体系相同。