氧合血红素Fe—O2键性质新探索

Dioxygen (O2) is one of the most important diatomic molecules in the nature and life. In spite of a long history of study on the interactions of dioxygen with the oxygen-carrying and -storing heme complexes, there are a number of scientific debates concerning the geometric, electronic, and biophysical properties, many of which continue to the present time. These issues include the geometry of the bound dioxygen, the perplexing nature of the (diamagnetic) electronic structure, the dynamics of the Fe-O2 group in the heme environment, the relative orientation of the bound dioxygen with respect to the plane of the trans-histidine, and the unusual and intriguing features of M?ssbauer properties. The two important structures, [Fe(TpivPP)(1-MeIm)(O2)] and [Fe(TpivPP)(2-MeHIm)(O2)] are published decades ago, electronic and geometric structure analysis was prevented by limited data of poor quality and by high thermal motion of the structures. For instance, some of the structure-function relationships such as relative orientation of bound dioxygen and the proximal imidazole remains unexplored for lack of sufficient structural data. Herein, we propose two research strategies on the design and synthesis of new oxyheme models - hydrogen bonding (H-bonding) and covalent-bond axial ligand. H-bonding extensively exists in protein environment and is crucial for the oxyheme functions. Covalent-bond axial ligand could change the orientation, basicity of proximal histidine and thus charge donation to the iron, which finally tuning the Fe-O2 bond strength. These structural modification of oxyheme pocket could control and/or change the dioxygen motions and dynamic disorder. Therefore new insights to the electronic and geometric structures of the Fe-O2 bond are expected to gain. Since there have been contributions on synthetic chemistry of the models' preparation, these two strategies are practicable and promising. In addition, our previous experience on oxyhemes studies indicated that dioxygen motions are strongly related to the thermal situation. Hence the temperature-dependent single-crystal characterization, which will give vivo pictures on the dioxygen dynamic motions, is necessary. This project will shed lights on the studies of Fe-O2 bound nature, reveal new knowledge of oxyheme complexes, which will enrich the bioinorganic theories and are important for the biologically functional material research.

O2 是生命中最重要的双原子分子之一。但是氧合血红素Fe-O2键的本质问题却没有彻底解决。争论主要存在于Fe-O2键的电子结构、穆斯堡尔谱性质等方面。Fe-O2键本身的复杂性，使得难以依靠单一模型解决所有问题；本课题认为依靠不同模型，突出重点，获得多层次多角度的结构信息，再深入到产物电子结构，是更切实际的研究思路。因此依据蛋白环境，我们提出氢键与共轭键连接轴向配体两个模型策略。这两种策略可望抑制无序，排除干扰，提供新的Fe-O2 键空间形态，从而获得新的电子结构信息。两类模型在合成化学中有所体现，但是尚无氧合反应产物得到分离，以及空间与电子结构表征，因此是可行而紧迫的研究课题。基于已有的研究积累，我们同时强调多温度单晶表征，以观察随温度改变而发生的氧分子动态行为。本研究可以深入到Fe-O2键问题新的研究层面，收获新的信息，丰富生物无机理论，对于基于血红素模型的仿生材料也具有战略意义。

金属卟啉作为血红素的模型化合物，其合成与表征有力得推动着人们对血红素在自然与生命体中化学与生物功能的了解与认知。本课题的研究取得了以下几点重要成果。1）卡宾铁卟啉（血红素）电子结构的首次确定。2）合成与分离了首例 {FeNO}8模型化合物，是NO–与铁卟啉键合的首例单晶结构，填补了该领域的空白。3）通过NRVS波谱区分了Fe—N—O键的伸缩与弯曲振动；以及相差仅6cm-1、两种不同的弯曲振动；并首次定位了Fe—NIm键的伸缩振动。4）优化了氧合血红素模型化合物的单晶结构；在分子层面上首次揭示了氧与周边基团协同的动态行为；丰富了氧与亚铁血红素的配位模式。除此，我们还开发了若干种新型卟啉模型，并对其衍生物进行了深入表征，取得了阶段性成果。

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