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This review summarizes our current understanding of the geometric and electronic structures of ferrous and ferric heme-nitrosyls, which are of key importance for the biological functions and transformations of NO. In-depth correlations are made between these properties and the reactivities of these species. Here, a focus is put on the discoveries that have been made in the last 10 years, but previous findings are also included as necessary. Besides this, ferrous heme-nitroxyl complexes are also considered, which have become of increasing interest recently due to their roles as intermediates in NO and multiheme nitrite reductases, and because of the potential role of HNO as a signaling molecule in mammals. In recent years, computational methods have received more attention as a means of investigating enzyme reaction mechanisms, and some important findings from these theoretical studies are also highlighted in this chapter. [ABSTRACT FROM AUTHOR]

A comprehensive overview is presented of the biologically relevant coordination chemistry of nitrosyls and its biochemical consequences. Representative classes of metal nitrosyls are introduced along with the structural and bonding aspects that may have consequences for the biological functioning of these complexes. Next, the biological targets and functions of nitrogen (II) oxide are discussed. Up-to-date biochemical applications of metal nitrosyls are reviewed. [ABSTRACT FROM AUTHOR]

This review provides a historical introduction to nitrosyl complexes. In the 1960s and 1970s, the renaissance of coordination chemistry led to the detailed study of nitrosyl complexes, and the emerging of new spectroscopic and structural techniques were used to define the metrics of nitric oxide when coordinated to transition metals and established that unlike CO and CN-, NO adopted alternative geometries. The development of theoretical models to account for this geometric ambivalence was initially based on semiempirical molecular orbital calculations in the early 1970s. Subsequently more accurate and sophisticated calculations have deepened our understanding of the bonding in transition metal-nitrosyl complexes. The discovery in the 1980s of the key importance of these complexes as models for the biological functions and transformations of NO encouraged these studies. NO is produced in vivo by the nitric oxide synthase (NOS) family of enzymes and plays a key role in the nerve-signal transreduction, vasodilation, blood clotting, and immune response by white blood cells. In these biological processes, the coordination of nitric oxide to metal centres is crucial, and therefore, their detailed study is essential for an understanding of nitric oxide's functions at the molecular level. [ABSTRACT FROM AUTHOR]

Crystalline compounds (HO)(phz)M(COCl)·(CHCOCH)·(HO) ( n = 0−2, M = Mn ( 1), Fe ( 3)) were obtained in an acetone-water-tetrahydrofuran medium by the reaction of metal sulfates with chloranilic acid and phenazine (phz). The molecular and crystal structure of 1 was studied by X-ray diffraction at 300, 200, and 150 K. The crystal structure is composed of polymeric cationic [(HO)(phz)] and anionic [Mn(COCl)] layers having honeycomb structure and stacked in such a way that open-ended through-going channels accommodating HO and CHCOCH solvent molecules are formed; the HO cations in the crystal structure are disordered. Magnetic studies indicate antiferromagnetic coupling of Mn ions through chloranilate ligands; transition to a magnetically ordered state occurs at T = 5 K. According to powder X-ray diffraction data, complex 3 is isostructural with compound 1 but differs crucially from 1 in the electronic structure. According to Fe Mössbauer spectroscopy, complex 3 exists in delocalized mixed-valence Fe/Fe state and, as a consequence, shows ferromagnetic character of magnetic correlations and semiconductor type of electrical conductivity. These features were ascribed to the valence tautomerism Fe + (COCl) → Fe + (COCl)·, which was observed for the first time for iron in a honeycomb structure. [ABSTRACT FROM AUTHOR]

Many nitrogen oxides have long been referred to by their common names rather than by IUPAC recommended nomenclature. This practice has expanded with the discovery that nitrogen oxides serve as biological signaling agents. This commentary addresses the recent introduction of a new term for metal nitrosyl complexes upon reduction and suggests a community-based approach to changes in nomenclature rather than through spontaneous introduction in the literature. [ABSTRACT FROM AUTHOR]