Metal atoms nitric oxide

Compounds of several different types might be formed by introduction of nitric oxide into complex ions. If the metal atom provides one of the electrons of the electron-pair bond, NO should assume the 02-like 82 structure. If both bond electrons come originally from NO (which then... 

Nitrogen oxides. Nitric oxide (NO) itself, has been shown to be a poor nitrosating agent (28), probably because it is unable to abstract an amino-H atom to generate the dialkyl-amino radical, which might then combine with further NO. However, the presence of even a small amount of air results in complete conversion, presumably via oxidation of NO to NO2. Nitrosation by NO is catalyzed by metal salts, such as Znl2, CuCl, and CUSO4. The metal catalyzed reaction is inhibited in acid or aqueous media (29). 

Nitric oxide binds in the end on position to ferrous hemes, with the nitrogen atom facing the iron (Scheidt and Piciulo, 1976 Jameson et d., 1981 Peng and Ibers, 1976). It binds more tightly to ferrous iron, but has a greater ability than CO to bind to iron in the ferric state, producing a diamagnetic complex. Ferrous-NO complexes are reasonably stable compared to ferrous-02 complexes, but in many cases they can be oxidized or reduced. Nitric oxide is much more likely than CO to react at a metal site rather than to bind reversibly. 

Condensation of metal atoms with nitric oxide may be accompanied... 

It is usually believed that NO inhibits enzymes by reacting with heme or nonheme iron or copper or via the S-nitrosilation or oxidation of sulfhydryl groups, although precise mechanisms are not always evident. By the use of ESR spectroscopy, Ichimori et al. [76] has showed that NO reacts with the sulfur atom coordinated to the xanthine oxidase molybdenum center, converting xanthine oxidase into a desulfo-type enzyme. Similarly, Sommer et al. [79] proposed that nitric oxide and superoxide inhibited calcineurin, one of the major serine and threonine phosphatases, by oxidation of metal ions or thiols. 

Although the net quantum yield of photodecomposition is found to be very small in the gas phase (typically 0.05), it has been found that in the presence of silver,16 mercury,16 oxygen,17 or nitric oxide,18 the quantum yield increases markedly. The two metals scavenge both atomic and molecular iodine, and the two gases scavenge alkyl radicals, thus suppressing both of the two possible inhibiting secondary steps. 

Owing to the extensive sharing of valence electrons over the metal and donor atoms in complexes of metals in low oxidation states, the zero oxidation state has little, if any, physical significance, and may be used for classifying purposes only. Outstanding examples are the complexes with nitric oxide which may be considered as NO+, NO- or NO, and consequently different oxidation states may be assigned to the same complex. 

These results have been discussed by Seel in Structure and Valence Theory of Inorganic Nitric Oxide Complexes (102). In such complexes, nitric oxide is covalently bonded to the metal atom as the positive ion NO+, it being assumed that an electron is transferred to the metal. This allows the isoelectronic groups NO+, CO, CN to be considered together and permits understanding of such known series as [Fen(CN)5NO]2, [Fen(CN)5CO]3-, and [Fen(CN)5CN]4-. 

Nitrous Oxide (N20). In contrast to nitric oxide, N20 is not readily reduced by hydrogen atoms. However, it is a good O-atom transfer reagent and spontaneously reacts with metal surfaces at elevated temperatures. Under alkaline conditions with a freshly formed platinum surface (Pt ), N20 induces a vol-tammetric reduction peak (Figure 11.8) 10... 

As in mononuclear nitrosyl complexes, it is convenient to separate the reactivity into two sections (1) reactions directly involving change at the NO, and (2) reactions of the metals that are enhanced by the presence of the nitrosyl ligand. The reaction of overwhelming importance that occurs with cluster coordinated nitric oxide is deoxygenation. Depending on the conditions this can ultimately sdeld NH, NH2, NCO, or simply N atoms coordinated to the cluster. 

These metals rip nitrogen atoms off the nitrogen oxide and nitric oxide. The leftover oxygen atoms form oxygen molecules, and the nitrogen atoms held by the metals combine to form harmless nitrogen. Figure 4.11 illustrates the process. 

Oxidation of copper metal by nitric acid. The copper atoms lose two electrons to form Cu2+ ions, which give a deep green color that becomes turquoise when diluted with water. 

---