Nitrous oxide, ligand

Yamakura T, Harris RA Effects of gaseous anesthetics nitrous oxide and xenon on ligand-gated ion channels comparison with isoflurane and ethanol. Anesthesiology 93 1093-1101,2000... 

A new representative of a multicopper cluster in a protein is Cuz in nitrous oxide reductase. As was discussed above this enzyme contains a binuclear CuA centre as in COX. While the latter in addition has CuB in the form of a copper-heme group, N20 reductase has Cuz which is the site of dinitrogen formation from the substrate N20. Recently a central inorganic sulfide has been found as a ligand to copper and multiple forms of Cuz were detected in the enzyme from Paracoccus pantotrophus.134 More recently a tetranuclear copper cluster with X-S bridges was proposed as structure for Cuz..135... 

Several different homogeneous catalyst systems for the reduction of NO by CO have been described to date (183-185, 187, 189), and in all cases, the reduction follows (113) with nitrous oxide as the reduced N-containing product, this despite the fact that reduction to N2 is more favored thermodynamically. The reason for adherence to the stoichiometry of (113), rather than (114), for example, may relate to the fact that N20, once formed, is a very poor ligand. 

At the same time, N20 proved to be a poor ligand and quite an inert oxidant. It resulted in a low reaction rate and needs a high reaction temperature. The lack of catalysts that could provide an effective activation of N20 is the main factor limiting a widespread use of nitrous oxide in liquid-phase oxidations. The development of such catalysts is an important target in this field. 

Brown EC, York JT, Antholine WE, Ruiz E, Alvarez S, Tolman WB. [Cu3(mu-S)2. clusters supported by N-donor ligands progress toward a synthetic model of the catalytic site of nitrous oxide reductase. 1. Am. Chem. Soc. 2005 127 13752-13753. 

Nitrous oxide, N2O, is commonly used as a mild dental anesthetic and propellant for aerosols on atmospheric decomposition, it yields its innocuous parent gases and is therefore an environmentally acceptable substitute for chlorofluorocarbons. On the other hand, N2O contributes to the greenhouse effect and is increasing in the atmosphere. Nitric oxide, NO, is an effective coordinating ligand its function in this context is discussed in Chapter 13. It also has many biological functions, discussed in Chapter 16. 

A comparative study of the metal centers in cytochrome c oxidase from several bacterial sources, including Thermus thermophilus and P. denitrificans, using EPR and MCD spectroscopy has established that in both cases cytochrome a is liganded by two histidine oxidases and the Cua center is identical to that in bovine cytochrome c oxidase (105, 106). The properties of the cytochrome Os/Cub dimer have not been established to be identical, although ferrocytochrome 03 is high-spin ferrous, as expected. Recent studies of the MCD properties of the Cua center in cytochrome c oxidase and a copper center in nitrous oxide reductase (107,108) show that the two centers are virtually identical. The evidence from the EPR hyperfine structure of the copper center in nitrous oxide reductase suggests that the center in this enzyme is a mixed-valence Cu(I)/Cu(II) dimer, which raises the interesting prospect that the Cua center in cytochrome c oxidase is also a dimeric copper species. 

REACTIONS OF COORDINATED LIGANDS - dealing with the chemistry of molecules such as oxygen, nitric and nitrous oxide, carbon dioxide, oximes, and nitriles... 

Upon adsorption of C02 and of N20 on the Cr(II)-containing catalyst, CrA and CrB sites formed linear adducts, whereas Crc sites were inert. CrB was thought to form only complexes with one ligand, whereas CrA could form complexes with two ligands. The presence of further coordination sites (vacancies) on CrA was shown by the formation of dicarbonyls (CrA(CO)2) and CrA(C0)(C02). Nitrous oxide was found to bind to chromium at either end, giving rise to species clearly discernible from each other by their IR spectra. A summary of these findings, listing the characteristics of the various species, is shown in Table 3. 

Electronic reflectance spectra of the Co(II)-exchanged dehydrated Type A zeolite, Co(II)A, show that the cobalt ions enter the S-II positions, where they form complexes with nitrous oxide, cyclopropane, water, and ammonia. These molecules represent ligands of increasing bond strength and, with the exception of ammonia, form reversible complexes with Co(II)A. In the case of nitrous oxide and cyclopropane, these complexes have a C3y symmetry water and ammonia complexes are tetrahedral. On a long exposure to water and ammonia, the Co(II) ions become highly coordinated to these ligands. 

To summarize the present results, Co (II) ions can be introduced into the Type A molecular sieves into the S-II type positions, where they are stable and resist both oxidation and reduction. These ions bind nitrous oxide, cyclopropane, water, and ammonia as additional ligands, their spectra being simultaneously changed in a defined fashion. The spectrochemical series of these ligands is, in the order of increasing ligand strength,... 

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