title: Nitric oxide dioxygenation reaction by oxy-coboglobin models: in-situ low-temperature FTIR characterization of coordinated peroxynitrite.
abstract: The oxy-cobolglobin models of the general formula (NH(3))Co(Por)(O(2)) (Por = meso-tetra-phenyl and meso-tetra-p-tolylporphyrinato dianions) were constructed by sequential low temperature interaction of NH(3) and dioxygen with microporous layers of Co-porphyrins. At cryogenic temperatures small increments of NO were introduced into the cryostat and the following reactions were monitored by the FTIR and UV-visible spectroscopy during slow warming. Upon warming the layers from 80 to 120 K a set of new IR bands grows with correlating intensities along with the consumption of the ν(O(2)) band. Isotope labeling experiments with (18)O(2), (15)NO and N(18)O along with DFT calculations provides a basis for assigning them to the six-coordinate peroxynitrite complexes (NH(3))Co(Por)(OONO). Over the course of warming the layers from 140 to 170 K these complexes decompose and there are spectral features suggesting the formation of nitrogen dioxide NO(2). Upon keeping the layers at 180-210 K the bands of NO(2) gradually decrease in intensity and the set of new bands grows in the range of 1480, 1270, and 980 cm(-1). These bands have their isotopic counterparts when (15)NO, (18)O(2) and N(18)O are used in the experiments and certainly belong to the 6-coordinate nitrato complexes (NH(3))Co(Por)(η(1)-ONO(2)) demonstrating the ability of oxy coboglobin models to promote the nitric oxide dioxygenation (NOD) reaction similar to oxy-hemes. As in the case of Hb, Mb and model iron-porphyrins, the six-coordinate nitrato complexes are not stable at room temperature and dissociate to give nitrate anion and oxidized cationic complex Co(III)(Por)(NH(3))(1,2).
authors.affiliation: Molecule Structure Research Centre (MSRC) of the Scientific and Technological Centre of Organic and Pharmaceutical Chemistry NAS, 0014, Yerevan, Armenia. kurto@netsys.am
authors.forename: Tigran S
authors.initials: TS
authors.lastname: Kurtikyan
authors.forename: Shahane R
authors.initials: SR
authors.lastname: Eksuzyan
authors.forename: Vardan A
authors.initials: VA
authors.lastname: Hayrapetyan
authors.forename: Garik G
authors.initials: GG
authors.lastname: Martirosyan
authors.forename: Gohar S
authors.initials: GS
authors.lastname: Hovhannisyan
authors.forename: John A
authors.initials: JA
authors.lastname: Goodwin
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D003080:Cold Temperature; D009566:Nitrates / Q000737:chemistry; D009569:Nitric Oxide / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D030421:Peroxynitrous Acid / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods
chemical_list: D009566:Nitrates; D011166:Porphyrins; D030421:Peroxynitrous Acid; D009569:Nitric Oxide; D003035:Cobalt; D010100:Oxygen