摘要
Conspectus Dinitrosyl iron complexes (DNICs) have been recognized as storage and transport agents of nitric oxide capable of selectively modifying crucial biological targets via its distinct redox forms (NO+, NO∗ and NO-) to initiate the signaling transduction pathways associated with versatile physiological and pathological responses. For decades, the molecular geometry and spectroscopic identification of {Fe(NO)2}9 DNICs ({Fe(NO)x}n where n is the sum of electrons in the Fe 3d orbitals and NO π∗ orbitals based on Enemark-Feltham notation) in biology were limited to tetrahedral (CN = 4) and EPR g-value ∼2.03, respectively, due to the inadequacy of structurally well-defined biomimetic DNICs as well as the corresponding spectroscopic library accessible in biological environments.The developed synthetic methodologies expand the scope of DNICs into nonclassical square pyramidal and trigonal bipyramidal (CN = 5) and octahedral (CN = 6) {Fe(NO)2}9 DNICs, as well as two/three accessible redox couples for mononuclear {Fe(NO)2}9/10 and dinuclear [{Fe(NO)2}9/10-{Fe(NO)2}9/10] DNICs with biologically relevant S/O/N ligation modes. The unprecedented molecular geometries and electronic states of structurally well-defined DNIC models provide the foundation to construct a spectroscopic library for uncovering the identity of DNICs in biological environments as well as to determine the electronic structures of the {Fe(NO)2} core in qualitative and quantitative fashions by a wide range of spectroscopic methods. On the basis of 15N NMR, electron paramagnetic resonance (EPR), IR, cyclic voltammetry (CV), superconducting quantum interference device (SQUID) magnetometry, UV-vis, single-crystal X-ray crystallography, and Fe/S K-edge X-ray absorption and Fe Kβ X-ray emission spectroscopies, the molecular geometry, ligation modes, nuclearity, and electronic states of the mononuclear {Fe(NO)2}9/10 and dinuclear [{Fe(NO)2}9/10-{Fe(NO)2}9/10] DNICs could be characterized and differentiated. In addition, Fe/S K-edge X-ray absorption spectroscopy of tetrahedral DNICs deduced the qualitative assignment of Fe/NO oxidation states of {Fe(NO)2}9 DNICs as a resonance hybrid of {FeII(∗NO)(NO-)}9 and {FeIII(NO-)2}9 electronic states; the quantitative NO oxidation states of [(PhS)3Fe(NO)]-, [(PhS)2Fe(NO)2]-, and [(PhO)2Fe(NO)2]- were further achieved by newly developed valence to core Fe Kβ X-ray emission spectroscopy as -0.58 ± 0.18, -0.77 ± 0.18, and -0.95 ± 0.18, respectively.The in-depth elaborations of electronic structures provide credible guidance to elucidate (a) the essential roles of DNICs modeling the degradation and repair of [Fe-S] clusters under the presence of NO, (b) transformation of DNIC into S-nitrosothiol (RSNO)/N-nitrosamine (R2NNO) and NO+/NO∗/NO-, (c) nitrite/nitrate activation producing NO regulated by redox shuttling of {Fe(NO)2}9 and {Fe(NO)2}10 DNICs, and (d) DNICs as H2S storage and cellular permeation pathway of DNIC/Roussin's red ester (RRE) for subsequent protein S-nitrosylation. The consolidated efforts on biomimetic synthesis, inorganic spectroscopy, chemical reactivity, and biological functions open avenues to the future designs of DNICs serving as stable inorganic NO+/NO∗/NO- donors for pharmaceutical applications.