Iron, reaction with nitric oxide

Reactions of iron-polyaminocarboxylates with nitric oxide have already been covered, in Section 5.4.3.8 bi- and polynuclear complexes containing polyaminocarboxylate ligands will be found in Section 5.4.5.4 below. 

Wang X, Zhou M, Andrews L (2000) Reactions of iron atoms with nitric oxide and carbon monoxide in excess argon infrared spectra and density functional calculations of iron carbonyl nitrosyl complexes. J Phys Chem A 104 10104-10111... 

Water soluble iron porphyrins [Fem(TPPS)(H20) ]3-330 and [Fem(TMPy)(H20)2]5+ 331 332 (TPPS = maso-tetrakis(/ -sulfonatophenyl)porphyrin, TMPyP = / /e.vo-tetrakis(7V-methyl-4-pyridi-nium)porphyrin331 or maso-tetrakis (A -methyl-2-pyridinium)porphyrin332 dications) act as effective electrocatalysts for the reduction of nitrite to ammonia in aqueous electrolytes (Equation (64) Ei/2= 0.103 V vs. SCE at pH 7), with NH2OH or N20 also appearing as products depending on the reaction conditions. Nitric oxide then ligates to the iron(III) porphyrin to form a nitrosyl complex [Fen(P)(NO+)] (P = porphyrin) as intermediate. 

Interactions and reactions of iron porphyrins with dioxygen species,with nitric oxide (see Section 5.4.3.8), with nitrite and with nitrate, and also of complexes containing carbon-bonded ligands, have continued to attract considerable interest and be reviewed. 

Nitrite reductase (NAD(P)H) [EC 1.6.6.4] catalyzes the reaction of three NAD(P)H with nitrite to yield three NAD(P)+, NH4OH, and water. Cofactors for this enzyme include FAD, non-heme iron, and siroheme. (2) Nitrite reductase (cytochrome) [EC 1.7.2.1] is a copper-depen-dent system that catalyzes the reaction of nitric oxide with two ferricytochrome c and water to produce nitrite and two ferrocytochrome c. (3) Ferredoxin-nitrite reductase [EC 1.7.7.1], a heme- and iron-dependent enzyme, catalyzes the reaction of ammonia with three oxidized ferredoxin to produce nitrite and three reduced ferredoxin. (4) Nitrite reductase [EC 1.7.99.3] is a copper- and FAD-dependent enzyme that catalyzes the reaction of two nitric oxide with an acceptor substrate and two water to produce two nitrite and the reduced acceptor. 

Synthesis and reactions of nitric oxide (NO). l-NMMA inhibits nitric oxide synthase. NO complexes with the iron in hemoproteins (eg, guanylyl cyclase), resulting in the activation of cGMP synthesis and cGMP target proteins such as protein kinase G. Under conditions of oxidative stress, NO can react with superoxide to nitrate tyrosine. 

Traylor TG, Magde D, Marsters J, Jongeward K, Wu GZ, Walda K. Geminate processes in the reaction of nitric oxide with l-methylimidazole-iron(II) porphyrin complexes. Steric, solvent polarity, and viscosity effects. J Am Chem Soc 1993 115 4808. 

Several preparations of dicarbonyl dinitrosyl iron have been reported including treatment of [Fe3(CO)i2] or [Fe2(CO)9] with nitric oxide,86,87 acidification of a mixture of [HFe(CO)4]- and nitrite ion,88 reaction of iron pentacarbonyl with nitrosyl chloride89 and acidification of a mixture of [Fe(CO)3NO]- and nitrite ion90 as in equations (2) and (3). 

The most familiar complexes in this class are Roussin s red and black salts140 obtained as a mixture from the reaction of iron(III) sulfide with nitric oxide and an alkali metal sulfide.141 The dimeric and diamagnetic red salt, K2[Fe(NO)2S]2 gives rise to a series of stable esters [Fe(NO)2SR]2 (R = Me, Et, Ph etc.) which are also diamagnetic, dark red and soluble in organic solvents. Some preparative routes142 to the red salt and its esters are shown in Scheme 3. 

Ferrous salts readily combine in solution with nitric oxide to form nitroso derivatives, in which one molecule of nitric oxide is combined for each atom of ferrous iron. These substances, several of which are described in connection with their respective negative radicles (see pp. 93, 95, 105, 153, 161), readily dissociate in solution in accordance with the reversible reaction —... 

The reactions of nitric oxide with metal cluster compounds themselves are complicated by the possibility of metal—metal bond cleavage. In the next example, the tri-iron compound shows very different reactivity from its ruthenium and osmium analogs (26-28) ... 

The sequence of reactions involved in the overall reduction of nitric acid is complex, but direct measurements confirm that the acid has a high oxidation/reduction potential, -940 mV (SHE), a high exchange current density, and a high limiting diffusion current density (Ref 38). The cathodic polarization curves for dilute and concentrated nitric acid in Fig. 5.42 show these thermodynamic and kinetic properties. Their position relative to the anodic curves indicate that all four metals should be passivated by concentrated nitric acid, and this is observed. In fact, iron appears almost inert in concentrated nitric acid with a corrosion rate of about 25 pm/year (1 mpy) (Ref 8). Slight dilution causes a violent iron reaction with corrosion rates >25 x 1()6 pm/year (106 mpy). Nickel also corrodes rapidly in the dilute acid. In contrast, both chromium and titanium are easily passivated in dilute nitric acid and corrode with low corrosion rates. 

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