Nitrosyl complexes spectroscopy

Surface nitrosyl complexes of TMI have been thoroughly investigated by the computational spectroscopy [22,23,32,33,36,49], and their molecular structure has been ascertained by a remarkable agreement between the theory and experiment of both vibrational (oscillation frequencies and intensities) and magnetic (g and A tensors) parameters. The calculated pNO values for the examined mononitrosyls along with the experimental frequencies are listed in Table 2.6. Analogous collation of the IR data for dinitrosyl species is shown in Table 2.7. 

The Fe(II)-NO complexes of porphyrins 66-68) and heme proteins 24, 49, 53, 69-76) have been studied in detail by EPR spectroscopy, which allows facile differentiation between five-coordinate heme—NO and six-coordinate heme—NO(L) centers. However, only a few reports of the Mossbauer spectra of such complexes have been published 68, 77-82), and the only Fe(III)-NO species that have been studied by Mossbauer spectroscopy include the isoelectronic nitroprusside ion, [FeCCNlsCNO)] (7S), the five-coordinate complexes [TPPFe(NO)]+ 68) and [OEPFe(NO)]+ 82), and two reports of the nitro, nitrosyl complexes of iron(III) tetraphenylporphjrrins, where the ligand L is NO2 82, 83). 

Iron-sulfur-nitrosyl complexes (continued) from tetranuclear precursors, 32 343 tellurium analogs, 32 350 tetrairon complexes, N NMR spectroscopy, 32 365 x-ray crystallography [Fe(NO)(S2CNR2)2 and related clusters, 32 359-361... 

Nuclear quadrupole resonance spectroscopy, see also specific compounds cyclophosphazenes, 21 93 of subvalent compounds, 29 298, 308-309 transition metal nitrosyl complexes, 34 313-314... 

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. 

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. 

Effects of cytokines on the formation of nitric oxide by human islets as determined by EPR spectroscopy. Human islets were treated for 18 hr with 75 U/ml lL-1, 3.5 nM TNF-a, and 750 U/ml IFN-y, the islets were then isolated, and EPR spectroscopy was performed as described previously (Corbett et al., 1993b). Cytokine induced nitric oxide formation is demonstrated by the genetation of an EPR detectable g = 2.04 iton-nitrosyl complex which is prevented by 0.5 mM NMMA. Reproduced with permission from Proc. Nall. Acad. Set. U S.A. (Corbett et al., 1993b). 

When oxidized NiR was put in contact with NO, the FenNO + intermediate was directly observed by FTIR spectroscopy (vnc> = 1910 cm-1) (52). This agrees with similar values of the stretching frequency measured for related ferri-hemes (24). The high values (compared to the ferro-hemes), together with the short N O distances (1.63 1.65 A) are consistent with a multiple bond, and indeed support the FeIINO + description, as generally accepted for NP and other classical nitrosyl complexes. 

During the last decade, the fascinating phenomena of the photochromic effect became a hot problem of molecular structure and spectroscopy due to its promising application in the design of new memory storage systems at the molecular level. This phenomenon has been discovered and studied in several nitrosyl complexes of transition metal ions [1-6]. At low temperatures, the most extensively studied sodium nitroprusside Na2[Fe(CN)5(NO)] 2H2Q (SNP) demonstrates two excited... 

Formation of the N02 complex 36 (Scheme 1) upon addition of NaN02 to [(l)FeBr]Br in methanol is immediate. The product has been fully characterized by IR, NMR, UV/Vis spectroscopies and other methods. Attempts to obtain single crystals of 36, however, revealed a remarkable transformation into the nitrosyl complex (Fe(NO) 7 by slow hydrolysis. Complex 36 is diamagnetic with well-resolved NMR spectra which, similar to the spectra of the carbonyl and (Fe(NO) 6 complexes, indicate a C2V symmetrical cation in solution. The cyclic voltammogram (DMSO solution) has one quasi-reversible one-electron redox wave at —0.07 Vas the only feature, which we assign to the Fen/Fem couple of the mononuclear complex. Addition of water to methanol solutions of 36 (in sub-stoichiometric or stoichiometric amounts) under anaerobic conditions leads to the formation of the... 

Reactions of NO were also studied with the synthetic heme protein discussed earlier, namely the recombinant human serum albumin (rHSA) with eight incorporated TPPFe derivatives bearing a covalently linked axial base, were also investigated. The UV-vis absorption spectrum of the phosphate buffer solution at physiological pH showed absorption band maxima at 425 and 546 nm upon the addition of NO to form the nitrosyl species, which was also formed when the six-coordinate CO-adducts were reacted with NO gas. EPR spectroscopy revealed that the albumin-incorporated iron(II) porphyrin formed six-coordinate nitrosyl complexes. It was observed that the proximal imidazole moiety does not dissociate from the central iron when NO binds to the trans position. The NO-binding affinity P1 /2no was 1.7 X 10 torr at pH 7.3 and 298 K, significantly lower than that of the porphyrin complex itself, and was interpreted as arising from the decreased association rate constant (kon(NO), 8.9 x 10 M s" -1.5 x 10 M s ). Since NO-association is diffusion controlled, incorporation of the synthetic heme into the albumin matrix appears to restrict NO access to the central iron(II). ... 

No N nuclear quadrupole resonance (NQR) studies have been reported for transition metal nitrosyl complexes. This technique is expected to show interesting differences between linear and bent nitro-syls since the values of the quadrupole coupling constant and the asymmetry parameter depend on the relative populations of the nitrogen s,p, py, andpz orbitals. NQR spectroscopy has been used to study organic and inorganic nitroso compounds, and it is found that both... 

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