The cationic dinitrosyl iron complexes family with thiocarbamide derivatives: Synthesis, structure and properties in the solid state

Synthesis of a tetranitrosyl iron complex with unique structure and properties as an inhibitor of phosphodiesterases

A novel neutral tetranitrosyl iron complex {[Fe(H2O)4]2+[FeR2(NO)2]22-}·4H2O (1) with R = 5-(3-pyridyl)-4H-1,2,4-triazole-3-thiolyls (C7H5N4S), which is a supramolecular ensemble, has been synthesized and studied. As follows from X-ray diffraction analysis, this is an octahedral Fe2+complex (Lewis acid) with two monoanionic dinitrosyl groups [FeR2(NO)2]- (Lewis base) and 4 water molecules as the ligands. As follows from Mössbauer spectra, the coordinating Fe2+ ion is in a low-spin state S = 0, and the dinitrosyl Fe+ ion is in a low-spin state S = 1/2. According to the data of EPR spectroscopy, mass-spectrometry and amperometry, complex 1 in solution forms dinitrosyl particles of [Fe(C7H6N4S-H)2(NO)2]- composition, which are responsible for NO generation. In addition, complex 1 was shown to be a 5-6 times more efficient phosphodiesterase (PDE) inhibitor at 5 × 10-5 M and 10-4 M concentrations than its thioligand. Probable binding sites of the [FeR2(NO)2]- ligand for the bovine PDE1B model have been determined by molecular docking and quantum-chemical calculations.

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.

Cytoprotective Effects of Dinitrosyl Iron Complexes on Viability of Human Fibroblasts and Cardiomyocytes

Nitric oxide (NO) is an important signaling molecule that plays a key role in maintaining vascular homeostasis. Dinitrosyl iron complexes (DNICs) generating NO are widely used to treat cardiovascular diseases. However, the involvement of DNICs in the metabolic processes of the cell, their protective properties in doxorubicin-induced toxicity remain to be clarified. Here, we found that novel class of mononuclear DNICs with functional sulfur-containing ligands enhanced the cell viability of human lung fibroblasts and rat cardiomyocytes. Moreover, DNICs demonstrated remarkable protection against doxorubicin-induced toxicity in fibroblasts and in rat cardiomyocytes (H9c2 cells). Data revealed that the DNICs compounds modulate the mitochondria function by decreasing the mitochondrial membrane potential (ΔΨm). Results of flow cytometry showed that DNICs were not affected the proliferation, growth of fibroblasts. In addition, this study showed that DNICs did not affect glutathione levels and the formation of reactive oxygen species in cells. Moreover, results indicated that DNICs maintained the ATP equilibrium in cells. Taken together, these findings show that DNICs have protective properties in vitro. It was further suggested that DNICs may be uncouplers of oxidative phosphorylation in mitochondria and protective mechanism is mainly provided by the leakage of excess charge through the mitochondrial membrane. It is assumed that the DNICs have the therapeutic potential for treating cardiovascular diseases and for decreasing of chemotherapy-induced cardiotoxicity in cancer survivors.