Iron, nitrosyl

These, and related, iron nitrosyl compounds have excited considerable interest because of their biological activity.Nitroprusside induces muscle relaxation and is therefore used to control high blood pressure. Roussin s black salt has antibacterial activity under conditions relevant to... 

The intrinsic kinetics of the reactions taking place in the scrubber, i.e. the reaction of NO with the iron chelate forming an iron nitrosyl complex (eq. 1) and the undesired oxidation reaction of the iron chelate (xanpla (eq. 2) wae deteimined in dedicated stirred cell contactors. Typical process conditions were T = 25-55 °C [Fe"(EDTA) "] = 1-100 mol/m [NO] = 1-1000 ppm pH = 5-8 and an oxygen level ranging between 1 and 20 vol%. 

CEC [Chisso Engineering Company] A process for removing oxides of nitrogen from flue-gases by scrubbing with an aqueous solution containing ferrous ion and ethylenediamine tetra-acetic acid (EDTA). An iron nitrosyl compound is formed. Developed by Chisso Engineering Company, Japan, and piloted in France and Japan. 

Based on the principle of microscopic reversibility one may conclude that the intermediate(s) in the off step will be the same as those generated during the k(m pathway, thus iron nitrosyl bond breakage (k 2)... 

Sodium nitroprusside (SNP), which is also known as Nipruss or Nipride to medical practitioners, was the first iron nitrosyl complex, prepared as far back as 1850 by Playfair [40]. The hypotensive property of SNP was first demonstrated by Johnson [41] in 1929. It was shown that application of a moderate dose of SNP reduces the blood pressure of a severely hypertensive patient without any side effect [42]. Since that time considerable research has been carried out to understand the mode of action of nitroprusside and its metabolic fate. SNP is now regarded as a potent vasodilator that causes muscle relaxation by releasing NO which activates the cytosolic isozyme of guanylyl cyclase [43-46]. 

Hydroxyurea reacts with oxy, deoxy and metHb in vitro to form iron nitrosyl hemoglobin (HbNO) and transfers NO to 2-6% of the iron heme groups [115]. Trapping studies using cyanide and carbon monoxide indicate that hydroxyurea oxidizes both oxy and deoxyHb to metHb and reduces metHb to deoxyHb specifically identifying the reaction of hydroxyurea and metHb as the critical reaction in the formation of HbNO from hydroxyurea [115]. Scheme 7.16 depicts the proposed mechanisms of N O and HbNO formation during the reaction of deoxy and metHb with hydroxyurea. Oxidation of hydroxyurea by metHb produces deoxyHb and the nitroxide radical (25,... 

Despite intense study of the chemical reactivity of the inorganic NO donor SNP with a number of electrophiles and nucleophiles (in particular thiols), the mechanism of NO release from this drug also remains incompletely understood. In biological systems, both enzymatic and non-enzymatic pathways appear to be involved [28]. Nitric oxide release is thought to be preceded by a one-electron reduction step followed by release of cyanide, and an inner-sphere charge transfer reaction between the ni-trosonium ion (NO+) and the ferrous iron (Fe2+). Upon addition of SNP to tissues, formation of iron nitrosyl complexes, which are in equilibrium with S-nitrosothiols, has been observed. A membrane-bound enzyme may be involved in the generation of NO from SNP in vascular tissue [35], but the exact nature of this reducing activity is unknown. 

A. R. Butler, F. W. Fhtney, D. L. H. Williams, NO, Nitrosonium Ions, Nitroxide Ions, Nitrosothiols and Iron-Nitrosyls in Biology A Chemist s Perspective , Trends Pharmacol. Sci. 1995, 16, 18-22. 

Iron nitrosyls coordination, 28 146, 148 nucleophilic attack, 28 153, 154 Iron oxide, 32 54-55 activation energy, 27 16, 17 in catalytic converter, 24 62 coatings containing, 40 103-105 CO conversion, 28 263 on silver, 27 14-17... 

In this paper, we present the results of the calculations of the excited-state energies and characters for nitrosyl ferrous and ferric heme complexes as a function of iron-nitrosyl distance. The calculated energy profiles are then used to identify the photoactive states for each complex. Similar calculations are also underway to characterize the photoactive states of Mn(II)N0 complexes (47). 

The ground- and excited-state electron distribution and energies, in each case, were calculated at five different iron-nitrosyl distances corresponding to successive displacement of NO in... 

The cyclodimerization of 1,3-butadiene and isoprene by zinc reduction of an iron nitrosyl complex dispersed in [BMIM]BF4 (and alternatively [BMIMJPFg) showed... 

Nitric oxide and iron nitrosyl complexes have been observed in the reduction of nitrite by bacterial nitrite reductases, which contain iron chlorin or iron isobac-terichlorin [151]. A specific nitric oxide reductase also exists to convert NO to nitrous oxide [9]. Iron complexes of chlorins, isobacteriochlorins, and porphyrins, as well as ruthenium and osmium polypyridines, and cobalt and nickel... 

The literature is rich with examples of metal-nitrosyl complexes, and it would be surprising if the generation of NO by the immune system did not result in the formation of many such adducts. Previous articles have presented summaries of metal proteins that form NO complexes (Butler et al., 1985 Henry et al., 1993), and more recently evidence has mounted that generation of NO by the immune system and by endothelial cells produces a variety of iron-nitrosyl complexes (Mulsch et al., 1993 Vanin et al., 1993 Lancaster et al., 1994). It is unclear which of the potential products will prove to be of physiological relevance, but because the enzymes that may be involved range from the central focus of oxidative cellular metabolism (LoBrutto et al., 1983) to the enzymes of DNA repair (Asahara et al., 1989), the list of potential targets is long and varied. 

In other S = J iron-nitrosyl complexes, such as the Cys2-Fe(II)-(NO)2 complex, delocalization of the electron in extended molecular orbitals results in reduced orbital angular momentum contributions from the iron d orbitals. In this complex, delocalization apparently reduces the association of the unpaired elec-... 

An S = I iron-nitrosyl complex could result from several possibilities, including Fe NO, in which S = 2 Fe is coupled to S = NO, and Fe +NO, in which the ferric ion is intermediate spin. All known S = iron-nitrosyl com-... 

Lancaster, J. R., Wemerfelmayer, G., and Wachter, H. (1994). Coinduction of nitric oxide synthesis and intracellular nonheme iron-nitrosyl complexes in murine cytokine-treated fibroblasts. Free Radical Biol. Med. 16, 869-870. 

Butler, A. R., Glidewell, C., Hyde, A. R., and Walton, J. C. (1985). Formation of paramagnetic mononuclear iron nitrosyl complexes from diamagnetic di- and tetranuclear iron-sulphur nitrosyls Characterization by EPR spectroscopy and study of thiolate and nitrosyl ligand exchange reactions. Polyhedron 4, 797-809. 

Corbett, j. A., Lancaster, J. R., Jr., Sweetland, M. A., and McDaniel, M. L. (1991). lnterleukin-1 beta-induced formation of EPR-detectable iron-nitrosyl complexes in islets of Langerhans. Role of nitric oxide in interleukin-1 beta-induced inhibition of insulin secretion. J. Biol. Chem. 266, 21351-21354. 

Jezowska-Trezebiatowska, B., and Jezierski, A. (1973). Electron spin resonance spectroscopy of iron nitrosyl complexes with organic ligands. J. Mol. Struct. 19, 635-640. 

Stadler, J., Bergonia, H. A., Di Silvio, M., Sweetland, M. A., Billiar, T. R., Simmons, R. L., and Lancaster, J. R., Jr. (1993). Nonheme iron-nitrosyl complex formation in rat hepatocytes Detection by electron paramagnetic resonance spectroscopy. Arch. Biochem. Biophys. 302, 4-11. 

Interleukin 1-induced formation of iron-nitrosyl complexes by rat islets. Rat islets were incubated fot 18 hr in the presence or absence of 5 U/ml lL-1, 0.5 mM NMMA, or lL-1 and NMMA. The islets were isolated and the fotmation of nitric oxide was examined by EPR spectroscopy as described previously (Corbett et al., 1991a). IL-1 induces the formation of a g = 2.04 featute that is characteristic of the fotmation of iton-nittosyl complexes, and NMMA ptevents the formation of this axial g = 2.04 iton-nittosyl feature. Also shown is the simultaneous formation of nitrite by the same islets used for EPR spectroscopy. Repnxluced with permission from ]. Biol. Chem. (Corbett et al., 1991a), from the American Society for Biochemistry and Molecular Biology. 

IL-1 also appears to inhibit insulin secretion by modulating the mitochondrial oxidative metabolism of purified P cells. Treatment of purified P cells for 18 hr with IL-1 results in nearly complete inhibition of the oxidation of [ CJ-D-glucose to C02 (Fig. 10). This inhibition is completely prevented by NMMA (Corbett et al., 1992b). Treatment of purified a cells with lL-1 has no effect on glucose oxidation, suggesting that the effects of IL-1 are specific to the endocrine P cell (Fig. 10). These findings are further supported by the observation that lL-1 induces iron-nitrosyl complex formation and the accumulation of cGMP in the... 

If jS-cell production of nitric oxide participates in IDDM, human islets must produce nitric oxide in response to cytokines. We have shown that a combination of cytokines (lL-1, IFN, and TNF) induce the formation of nitric oxide by isolated human islets (Corbett et al., 1993b). The formation of nitric oxide has been demonstrated by cytokine-induced cGMP accumulation, nitrite formation, and EPR-detectable iron-nitrosyl complex formation (Fig. 12), all of which were prevented by NMMA. The cytokine combination of IFN and lL-1 are required for nitrite production, while TTSIF potentiates IL-1 and IFN-induced nitrite formation by human islets. The cytokine combination of lL-1, TNF, and IFN also influences the physiological function of insulin secretion by human islets. Low concentrations of this cytokine combination slightly stimulate insulin secretion, while high concentrations inhibit insulin secretion, similar to the concentration-dependent effects of lL-1 on rat islet function. NMMA partially prevents the inhibitory effects of this cytokine combination on insulin secretion from human islets, suggesting that nitric oxide may participate in )3-cell dysfunction associated with IDDM. 

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