Nitroxyl(NO-/HNO)血红素衍生物的分离与电子结构研究

Nitroxyl (NO-/HNO) is the one-electron-reduced form of nitrosyl (NO), both of which are significant in many biological systems. There is great interest in the coordination chemistry of nitroxyl (NO-/HNO) with hemes because of the role of these complexes as an important effector molecule in biology or as key intermediates in nitrite (NO2-) and nitric oxide (NO) reducing enzymes. Recently, we have isolated the first {FeNO}8 heme complex [Co(Cp)2][Fe(TFPPBr8)(NO)] and its {FeNO}7 precursor [Fe(TFPPBr8)(NO)] using the extremely electron-poor porphyrin. The single crystal structures were determined at 100 K which suggest a low-spin state of the iron(II) centers. We also reported an individual and clear NO- stretch at 1540 cm-1 for the first time. In this project, we propose two porphyrin model strategies to isolate the HNO heme complex. The first model is the porphyrin possessing the hydrogen bonding (H-bonding), e.g. the “hangman” porphyrin. The second model is the well-known “picket fence” porphyrin. Both porphyrin models have been reported to stabilize neutral or charged small molecules by the non-covalent bond interactions. The second crucial question in the area of nitroxyl (NO-/HNO) is the controversial electronic structure of the {FeNO}8 complex. Several different DFT predications of the Fe-N-O moiety have been reported. We propose to determine the electronic configurations by the combination of several physical methods which including multiple-temperature solid-state Mössbauer, EPR (electron paramagnetic resonance) and NRVS (nuclear resonance vibrational spectroscopy). We have finished some experimental measurements and the data processing is underway. This project shall push forward the understanding on the nature of the nitroxyl (NO-/HNO) ligand, shed lights on the studies of nitric oxide complexes and enrich the bioinorganic theories.

Nitroxyl是指NO-及其共轭酸HNO。Nitroxyl(NO-/HNO)是nitrosyl(NO)的还原产物，两者均是重要的内源无机小分子。在首例NO-血红素（也是首例{FeNO}8）的单晶由本小组近期分离表征之后，HNO血红素的晶体结构以及存在争议的{FeNO}8的电子结构即成为此领域亟待解决的核心问题。本小组利用结构对功能的主动作用，提出含氢键卟啉与栅栏卟啉两种模型策略来分离HNO衍生物。我们同时提出以穆斯堡尔谱、EPR、NRVS等物理手段对{FeNO}8的电子结构进行表征的实验方案。通过对上述核心问题的研究，实现了解nitroxyl(NO-/HNO)配体本质的科学目的。本小组在此领域已有一定积累，对{FeNO}8的电子结构已有阶段性成果完成。本课题将深化对生命体系中氮氧化合物的理解，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。

2017年，基于本小组获得的首例NO-血红素（也是首例{FeNO}8）的单晶，我们提出了针对Nitroxyl(NO-/HNO)与nitrosyl(NO)两个重要的内源无机小分子的研究课题，目的在于解决HNO配位衍生物的晶体结构以及存在争议的{FeNO}8的电子结构。在过去的几年间，本小组利用结构对功能的主动作用，在七个研究课题上取得了重要进展。第一，氯配位铁咔咯化合物的合成与表征；第二，一氧化氮配位铁咔咯化合物的合成与表征；第三，五配位氰基铁卟啉化合物的合成与性质研究；第四，卟啉化调节金纳米粒子的电化学性能研究；第五，五配位Fe(III)卟啉的合成及性质研究；第六，金属有机骨架材料的合成及其在催化中的应用；第七，氯配位铁新型咔咯化合物的合成与表征。