Nanoscale Designing of Iron-Sulfur Active Center in Nitrogenase towards Nano-biomimetic Enzyme

本研究的目的是通过揭示氮氧化酶中铁硫活性中心的功能和作用机制，建立纳米级仿生酶。为了实现这一研究目标，开发了两种方法；(1)为了通过气相反应高效地生成功能团簇，对激光汽化和分子束制备有机金属和分子团簇的工艺进行了改进。(2)将自组装单层膜在金衬底上的软着陆方法扩展到各种衬底上，并利用红外反射吸收光谱（IRAS）和程序升温解吸光谱对其特性进行了评价。功能团簇，如钒-苯的有机金属团簇，与裸金衬底相比，可以有效地软着陆在金衬底上的自组装单层上。研究了V（苯）_2夹层簇软着陆在不同链长正烷硫醇（C_n-SAM, n = 8、12、16、18和22）自组装单层上的吸附状态和热稳定性。红外光谱分析证实，V（苯）_2簇被分子吸附，并在所有的SAM基底上保持夹层结构。此外，支撑在SAM衬底上的簇具有分子轴偏离表面法线70-80°的取向。TPD谱的Arrhenius分析表明，支撑簇解吸的活化能随SAMs链长的增加而线性增加。对于最长链C_<22>-SAM，其活化能可达150 kJ/mol左右，在室温附近可明显抑制支撑簇的热脱附，优于覆盖碳氢分子的硅衬底。

The aim of this research has focused on the creation of nanoscale biomimetic enzyme by unveiling the function and mechanism of an iron-sulfur active center in nitrogenase enzyme. To achieve this research target, two methodologies have been developed ; (1) The production technique of organometallic and molecular clusters has been refined by laser vaporization and molecular beam in order to generate functional cluster efficiently through gas phase reactions. (2) The soft-landing method using self-assembled monolayer on a gold substrate was broadened toward various substrates, and their characteristics were evaluated by infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption spectroscopy.Functional clusters, such as organometallic cluster of vanadium-benzene, could be soft-landed efficiently onto the self-assembled monolayer on a gold substrate compared to a bare gold substrate. The adsorption state and thermal stability of V(benzene)_2 sandwich clusters soft-landed onto a self-assembled monolayer of different chain-length n-alkanethiols (C_n-SAM, n = 8, 12, 16, 18, and 22) were studied. The IRAS measurement confirmed that V(benzene)_2 clusters are molecularly adsorbed and maintain a sandwich structure on all of the SAM substrates. In addition, the clusters supported on the SAM substrates are oriented with their molecular axes tilted 70-80° off the surface normal. An Arrhenius analysis of the TPD spectra reveals that the activation energy for the desorption of the supported clusters increases linearly with the chain-length of the SAMs. For the longest chain C_<22>-SAM, the activation energy reaches around 150 kJ/mol, and the thermal desorption of the supported clusters can be considerably suppressed near room temperature, which is superior to a silicon substrate covered with hydrocarbon molecules.