Influence of CH3 group of μ-N–C–S ligand on the properties of [Fe2(C4H5N2S)2(NO)4] complex

The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity

Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological and pathological events in biology. Metal coordination chemistry, especially with iron, is at the heart of many biological transformations involving NO. A series of heme proteins, nitric oxide synthases (NOS), soluble guanylate cyclase (sGC), and nitrophorins, are responsible for the biosynthesis, sensing, and transport of NO. Alternatively, NO can be generated from nitrite by heme- and copper-containing nitrite reductases (NIRs). The NO-bearing small molecules such as nitrosothiols and dinitrosyl iron complexes (DNICs) can serve as an alternative vehicle for NO storage and transport. Once NO is formed, the rich reaction chemistry of NO leads to a wide variety of biological activities including reduction of NO by heme or non-heme iron-containing NO reductases and protein post-translational modifications by DNICs. Much of our understanding of the reactivity of metal sites in biology with NO and the mechanisms of these transformations has come from the elucidation of the geometric and electronic structures and chemical reactivity of synthetic model systems, in synergy with biochemical and biophysical studies on the relevant proteins themselves. This review focuses on recent advancements from studies on proteins and model complexes that not only have improved our understanding of the biological roles of NO but also have provided foundations for biomedical research and for bio-inspired catalyst design in energy science.

Insight into the Electronic Structure of Biomimetic Dinitrosyliron Complexes (DNICs): Toward the Syntheses of Amido-Bridging Dinuclear DNICs

The ubiquitous function of nitric oxide (NO) guided the biological discovery of the natural dinitrosyliron unit (DNIU) [Fe(NO)2] as an intermediate/end product after Fe nitrosylation of nonheme cofactors. Because of the natural utilization of this cofactor for the biological storage and delivery of NO, a bioinorganic study of synthetic dinitrosyliron complexes (DNICs) has been extensively explored in the last 2 decades. The bioinorganic study of DNICs involved the development of synthetic methodology, spectroscopic discrimination, biological application of NO-delivery reactivity, and translational application to the (catalytic) transformation of small molecules. In this Forum Article, we aim to provide a systematic review of spectroscopic and computational insights into the bonding nature within the DNIU [Fe(NO)2] and the electronic structure of different types of DNICs, which highlights the synchronized advance in synthetic methodology and spectroscopic tools. With regard to the noninnocent nature of a NO ligand, spectroscopic and computational tools were utilized to provide qualitative/quantitative assignment of oxidation states of Fe and NO in DNICs with different redox levels and ligation modes as well as to probe the Fe-NO bonding interaction modulated by supporting ligands. Besides the strong antiferromagnetic coupling between high-spin Fe and paramagnetic NO ligands within the covalent DNIU [Fe(NO)2], in polynuclear DNICs, the effects of the Fe···Fe distance, nature of the bridging ligands, and type of bridging modes on the regulation of the magnetic coupling among paramagnetic DNIU [Fe(NO)2] are further reviewed. In the last part of this Forum Article, the sequential reaction of {Fe(NO)2}10 DNIC [(NO)2Fe(AMP)] (1-red) with NO(g), HBF4, and KC8 establishes a synthetic cycle, {Fe(NO)2}9-{Fe(NO)2}9 DNIC [(NO)2Fe(μ-dAMP)2Fe(NO)2] (1) → {Fe(NO)2}9 DNIC [(NO2)Fe(AMP)][BF4] (1-H) → {Fe(NO)2}10 DNIC 1-red → DNIC 1, for the transformation of NO into HNO/N2O. Of importance, the NO-induced transformation of {Fe(NO)2}10 DNIC 1-red and [(NO)2Fe(DTA)] (2-red; DTA = diethylenetriamine) unravels a synthetic strategy for preparation of the {Fe(NO)2}9-{Fe(NO)2}9 DNICs [(NO)2Fe(μ-NHR)2Fe(NO)2] containing amido-bridging ligands, which hold the potential to feature distinctive physical properties, chemical reactivities, and biological applications.

Comparative Analysis of Cytotoxic Activity of New Nitrosyl Iron-Sulfur Complexes in Human Tumor Cells In Vitro

We studied cytotoxic activity of new tetranitrosyl NO-generating binuclear iron-sulfur [Fe-S] complexes containing different ligands in the molecule against tumor cells in vitro. Cytotoxic activity of the most active complex with cysteamine (CysAm) was compared with that of antitumor drug cisplatin. Caspase activation and morphological changes in cells were visualized by fluorescence microscopy. Fluorescence of active caspases 3 and 7 and changes in nuclear DNA in cells in the presence of CyAm were detected by using fluorochrome-labeled inhibitor of caspases (FLICA) and Hoechst and propidium iodide reagents. Similar cytotoxic activities of CyAm and cisplatin were demonstrated in various human tumor cell lines of different histogenesis. Therefore, a new class of NO-donating [Fe-S] complexes can provide the base of potential drugs for chemotherapy with a new mechanism of action.

Nitrosyl iron complexes--synthesis, structure and biology

Nitrosyl complexes of iron are formed in living species in the presence of nitric oxide. They are considered a form in which NO can be stored and stabilized within a living cell. Upon entering a topic in bioinorganic chemistry the researcher faces a wide spectrum of issues concerning synthetic methods, the structure and chemical properties of the complex on the one hand, and its biological implications on the other. The aim of this review is to present the newest knowledge on nitrosyl iron complexes, summarizing the issues that are important for understanding the nature of nitrosyl iron complexes, their possible interactions, behavior in vitro and in vivo, handling of the preparations etc. in response to the growing interest in these compounds. Herein we focus mostly on the dinitrosyl iron complexes (DNICs) due to their prevailing occurrence in NO-treated biological samples. This article reviews recent knowledge on the structure, chemical properties and biological action of DNICs and some mononitrosyls of heme proteins. Synthetic methods are also briefly reviewed.

Synthesis, characterization and crystal structure of a dinuclear iron nitrosyl complex with 2-mercapto-1-[2-(4-pyridyl)-ethyl]-benzimidazolyl

A new dinuclear iron nitrosyl complex [Fe(2)(C(14)H(12)N(3)S)(2)(NO)(4)] (1) (C(14)H(12)N(3)S = 2-mercapto-1-[2-(4-pyridyl)-ethyl]-benzimidazolyl) has been obtained by the reaction of Fe(NO)(2)(CO)(2) with 2-mercapto-1-[2-(4-pyridyl)-ethyl]-benzimidazole in CH(3)OH under moderate condition. Complex 1 was characterized by IR, UV-vis, electrochemistry and single crystal X-ray diffraction. IR spectrum displays two strong characteristic NO stretching frequencies (nu(NO)) in solution and in solid state. Cyclic voltammetry shows one irreversible, two quasi-reversible and two reversible one-electron reductions and irreversible oxidizations. This result is consistent with the fact that complex 1 is very unstable and ready to lose NO in the air. As showing in the single crystal X-ray diffraction, complex 1 forms a "chair-shape" structure by the connections of two iron centers and S-C-N frames of benzimidazole. The dihedral angle of benzimidazole ring and 2Fe-2S plane is 73.6 degrees . The crystal data are the following: 1, monoclinic, space group P2(1)/c, a = 10.43940(10) A, b = 16.0900(2) A, c = 10.13240(10) A, alpha = 90 degrees , beta = 111.0940(10) degrees , gamma = 90 degrees , V = 1587.89(3) A(3), Z = 4.