Reactions of nitrogen oxides with heme models. Characterization of NO and NO2 dissociation from Fe(TPP)(NO2)(NO) by flash photolysis and rapid dilution techniques: Fe(TPP)(NO2) as an unstable intermediate

Described are studies directed toward elucidating the controversial chemistry relating to the solution phase reactions of nitric oxide with the iron(II) porphyrin complex Fe(TPP)(NO) (1, TPP = meso-tetraphenylporphinato2-). The only reaction observable with clean NO is the formation of the diamagnetic dinitrosyl species Fe(TPP)(NO)2 (2), and this is seen only at low temperatures (K(1) < 3 M(-1) at ambient temperature). However, 1 does readily react reversibly with N2O3 in the presence of excess NO to give the nitro nitrosyl complex Fe(TPP)(NO2)(NO) (3), suggesting that previous claims that 1 promotes NO disproportionation to give 3 may have been compromised by traces of air in the nitric oxide sources. It is also noted that 3 undergoes reversible loss of NO to give the elusive nitro species Fe(TPP)(NO2) (4), which has been implicated as a powerful oxygen atom transfer agent in reactions with various substrates. Furthermore, in the presence of excess NO2, the latter undergoes oxidation to the stable nitrato analogue Fe(TPP)(NO3) (5). Owing to such reactivity of Fe(TPP)(NO2), flash photolysis and stopped-flow kinetics rather than static techniques were necessary for the accurate measurement of dissociation equilibria characteristic of Fe(TPP)(NO2)(NO) in 298 K toluene solution. Flash photolysis of 3 resulted in competitive NO2 and NO dissociation to give Fe(TPP)(NO) and Fe(TPP)(NO2), respectively. The rate constant for the reaction of 1 with N2O3 to generate Fe(TPP)(NO2)(NO) was determined to be 1.8 x 10(6) M(-1) s(-1), and that for the NO reaction with 4 was similarly determined to be 4.2 x 10(5) M(-1) s(-1). Stopped-flow rapid dilution techniques were used to determine the rate constant for NO dissociation from 3 as 2.6 s(-1). The rapid dilution experiments also demonstrated that Fe(TPP)(NO2) readily undergoes further oxidation to give Fe(TPP)(NO3). The mechanistic implications of these observations are discussed, and it is suggested that NO2 liberated spontaneously from Fe(P)(NO2) may play a role in an important oxidative process involving this elusive species.     

Adsorption-stress relationship in drying of silica/PVA suspensions

Mg-Al oxide obtained by thermal decomposition of NO(3)(-)-intercalated Mg-Al layered double hydroxide (NO(3)·Mg-Al LDH) was found to treat HNO(3), acting as both a neutralizer and fixative for NO(3)(-). The degree of NO(3)(-) removal increased with time, Mg-Al oxide quantity, and temperature. The NO(3)(-) removal could be represented by a first-order reaction. The apparent activation energy was 52.9 kJ mol(-1), confirming that NO(3)(-) removal by Mg-Al oxide proceeded under chemical reaction control. Furthermore, the adsorption of NO(3)(-) on Mg-Al oxide could be expressed by a Langmuir-type adsorption isotherm. The maximum adsorption amount and equilibrium adsorption constant were 3.8 mmol g(-1) and 1.33, respectively. The Gibbs free energy change was -18 kJ mol(-1), confirming that the uptake of NO(3)(-) from HNO(3) by Mg-Al oxide proceeded spontaneously.     

六水合硝酸镁增塑改性淀粉-聚乙烯醇复合膜的合成与性能

以六水合硝酸镁[Mg(NO₃)₂·6H₂O]为增塑剂, 采用流延法制备了增塑改性的淀粉-聚乙烯醇(PVA)复合膜, 并研究了改性后淀粉-PVA复合膜的性能. 研究结果表明, Mg(NO₃)₂·6H₂O与淀粉和PVA发生一定的相互作用, 破坏了淀粉和PVA中的结晶结构. 因此, Mg(NO₃)₂·6H₂O的加入可提高淀粉与PVA间的相容性, 改变了淀粉-PVA复合膜的力学性能, 使其拉伸强度下降, 断裂伸长率提高.     

Parahalogenated phenols accelerate the photochemical release of nitrogen oxides from frozen solutions containing nitrate

The photolysis of nitrate anion (NO(3)(-)) contained in surface ice and snow can be a regionally significant source of gas-phase nitrogen oxides and affect the composition of the planetary boundary layer. In this study, the photochemical release of nitrogen oxides from frozen solutions containing NO(3)(-) in the presence of organic compounds was investigated. Gas-phase nitrogen oxides were quantified primarily by NO-O(3) chemiluminescence detection of NO and NO(y) (=NO + NO(2) + HONO + HNO(3) + ∑PAN + ∑AN ...) and cavity ring-down spectroscopy of NO(2) and total alkyl nitrates (∑AN). The photochemical production of gas-phase NO(y) was suppressed by the presence of formate, methanesulfonate, toluene, or phenol. In contrast, para-halogenated phenols (in the order of Cl > Br > F) promoted the conversion of NO(3)(-) to gas-phase NO(y), rationalized by acidification of the ice surface.     

Nafion/Au溶胶自组装微铂传感器的研究及其在心肌细胞中NO水平测定中的应用

制备了一种新型的Nafion/Au溶胶修饰微铂传感器(Au溶胶颗粒的直径为7～14nm),并将该传感器应用于心肌细胞中NO水平的研究.实验结果表明,自组装制备的Nafion/Au溶胶修饰微传感器对NO有较高的灵敏度和良好的选择性,在1.0×10^-7～4.0×10^-5mol/L浓度范围内,NO的催化氧化电流与其浓度呈良好线性关系,检测限为5.0×10^-8mol/L.探讨了该修饰微传感器对NO的催化机理,研究了在L-精氨酸和乙酰胆碱刺激下心肌细胞内的NO释放.     

Reaction of a superoxochromium(III) ion with nitrogen monoxide: kinetics and mechanism.

The kinetics of the rapid reaction between Cr(aq)OO(2+) and NO were determined by laser flash photolysis of Cr(aq)NO(2+) in O(2)-saturated acidic aqueous solutions, k = 7 x 10(8) M(-1) s(-1) at 25 degrees C. The reaction produces an intermediate, believed to be NO(2), which was scavenged with ([14]aneN(4))Ni(2+). With limiting NO, the Cr(aq)OO(2+)/NO reaction has a 1:1 stoichiometry and produces both free NO(3)(-) and a chromium nitrato complex, Cr(aq)ONO(2)(2+). In the presence of excess NO, the stoichiometry changes to [NO]/[Cr(aq)OO(2+)] = 3:1, and the reaction produces close to 3 mol of nitrite/mol of Cr(aq)OO(2+). An intermediate, identified as a nitritochromium(III) ion, Cr(aq)ONO(2+), is a precursor to a portion of free NO(2)(-). In the proposed mechanism, the initially produced peroxynitrito complex, Cr(aq)OONO(2+), undergoes O-O bond homolysis followed by some known and some novel chemistry of Cr(aq)O(2+) and NO(2). The reaction between Cr(aq)O(2+) and NO generates Cr(aq)ONO(2+), k > 10(4) M(-1) s(-1). Cr(aq)OO(2+) reacts with NO(2) with k = 2.3 x 10(8) M(-1) s(-1).     

New insight into selective catalytic reduction of nitrogen oxides by ammonia over H-form zeolites: a theoretical study

Density functional theory calculations were carried out to investigate the reaction mechanism of selective catalytic reduction of nitrogen oxides by ammonia in the presence of oxygen at the Br?nsted acid sites of H-form zeolites. The Br?nsted acid site of H-form zeolites was modeled by an aluminosilicate cluster containing five tetrahedral (Al, Si) atoms. A low-activation-energy pathway for the catalytic reduction of NO was proposed. It consists of two successive stages: first NH(2)NO is formed in gas phase, and then is decomposed into N(2) and H(2)O over H-form zeolites. In the first stage, the formation of NH(2)NO may occur via two routes: (1) NO is directly oxidized by O(2) to NO(2), and then NO(2) combines with NO to form N(2)O(3), which reacts with NH(3) to produce NH(2)NO; (2) when NO(2) exceeds NO in the content, NO(2) associates with itself to form N(2)O(4), and then N(2)O(4) reacts with NH(3) to produce NH(2)NO. The second stage was suggested to proceed with low activation energy via a series of synergic proton transfer steps catalyzed by H-form zeolites. The rate-determining step for the whole reduction of NO(x) is identified as the oxidation of NO to NO(2) with an activation barrier of 15.6 kcal mol(-1). This mechanism was found to account for many known experimental facts related to selective catalytic reduction of nitrogen oxides by ammonia over H-form zeolites.     

Microchip electrophoresis with amperometric detection for the study of the generation of nitric oxide by NONOate salts

Microchip electrophoresis (ME) with electrochemical detection was used to monitor nitric oxide (NO) production from diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA/NO) and 1-(hydroxyl-NNO-azoxy)-L-proline disodium salt (PROLI/NO). NO was generated through acid hydrolysis of these NONOate salts. The products of acid hydrolysis were introduced into a 5-cm separation channel using gated injection. The separation was accomplished using reverse polarity and a background electrolyte consisting of 10 mM boric acid and 2 mM tetradecyltrimethylammonium bromide, pH 11. Electrochemical detection was performed using an isolated potentiostat in an in-channel configuration. Potentials applied to the working electrode, typically higher than +1.0 V vs. Ag/AgCl, allowed the direct detection of nitrite, NO, DEA/NO, and PROLI/NO. Baseline resolution was achieved for the separation of PROLI/NO and NO while resolution between DEA/NO and NO was poor (1.0 ± 0.2). Nitrite was present in all samples tested.     

Synthesis, characterization, solid-state molecular structures, and deprotonation reactions of cationic alcohol complexes of osmium nitrosyl porphyrins

New alkoxide (OEP)Os(NO)(OR) (OEP = 2,3,7,8,12,13,17,18-octaethylporphyrinato dianion; R = ethyl, isopropyl, hexyl, cyclohexyl) compounds and alcohol [(OEP)Os(NO)(HOR)]+ complexes (R = methyl, ethyl, isopropyl, hexyl, cyclohexyl) have been prepared in high yields and have been fully characterized by IR, 1H NMR, and UV-vis spectroscopy, and by elemental analyses. The (OEP)Os(NO)(OEt) compound was characterized by single-crystal X-ray crystallography. The cationic aqua and alcohol [(OEP)Os(NO)(HOR)]+ complexes (R = ethyl, isopropyl, hexyl) complexes were also characterized by single-crystal X-ray crystallography, and the latter represent the first osmium alcohol structures to be reported. The electrophilic [(OEP)Os(NO)]+ cation in the [(OEP)Os(NO)(HOR)]+ complexes renders the coordinated alcohol ligands susceptible to deprotonation by pyridine to produce the corresponding alkoxide (OEP)Os(NO)(OR) derivatives. A one-pot reaction sequence for the preparation of new (OEP)Os(NO)(OR) complexes from (OEP)Os(NO)(OEt) was developed, which was based on (i) initial protonation of the ethoxide compound to give [(OEP)Os(NO)(HOEt)]+, (ii) alcohol substitution by ROH to give [(OEP)Os(NO)(HOR)]+, and (iii) deprotonation of the latter by pyridine to give (OEP)Os(NO)(OR).     

Role of Zr4+ cations in NO2 adsorption on Ce(1-x)Zr(x)O2 mixed oxides at ambient conditions

Mixed oxides Ce(1-x)Zr(x)O(2) prepared by slow coprecipitation in NaOH were tested for NO(2) adsorption in dynamic conditions at room temperature. The samples were characterized before and after exposure to NO(2) by XRD, N(2)-adsorption, thermal analysis, potentiometric titration, and FT-IR. Mixed oxides show a better NO(2) adsorption capacity than the parent materials (CeO(2) and Zr(OH)(4)). This effect is linked to the presence of reduced cerium and oxygen vacancies induced by the addition of Zr(4+) cations to the structure. The results indicate that NO(2) reacts with Ce(3+) to form nitrite and nitrate species on the surface. The NO retention increases with an increase in the Zr(OH)(4) content. A decrease in the density of -OH groups on the surface after the exposure to NO(2), suggests their involvement in reactive adsorption of NO and/or NO(2). From the structural point of view, no real difference was observed on the Ce(1-x)Zr(x)O(2) materials before and after exposure to NO(2).     

基于表面活性剂单分子层修饰碳糊电极的一氧化氮电化学传感器及其应用

报道了一种表面活性剂单分子层修饰碳糊电极,并用于NO的高灵敏电化学检测。研究表明,表面活性剂通过烷基链在电极表面形成的疏水性单分子层微环境对NO的电化学响应具有较好的促进作用。其中,阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)对NO的电化学氧化表现出最强的催化活性和增敏作用。在Nafion膜覆盖的CTAB修饰碳糊电极上,NO的安培响应与其浓度在3.6×10-8～1.8×10-5mol/L范围内呈良好的线性关系,检出限为1.8×10-8mol/L。该电极作为低成本、高灵敏的NO电化学传感器,被成功应用于大鼠肺组织细胞中NO释放的实时监测。     

Reactions of nitrogen oxides with heme models. Spectral and kinetic study of nitric oxide reactions with solid and solute Fe(III)(TPP)(NO3)

The reaction(s) of nitric oxide (nitrogen monoxide) gas with sublimed layers containing the nitrato iron(III) complex Fe(III)(TPP)(eta(2)-O(2)NO) (1, TPP = meso-tetraphenyl porphyrinate(2)(-)) leads to formation of several iron porphyrin species that are ligated by various nitrogen oxides. The eventual products of these low-temperature solid-state reactions are the nitrosyl complex Fe(TPP)(NO), the nitro-nitrosyl complex Fe(TPP)(NO(2))(NO), and 1 itself, and the relative final quantities of these were functions of the NO partial pressure. It is particularly notable that isotope labeling experiments show that the nitrato product is not simply unreacted 1 but is the result of a series of transformations taking place in the layered material. Thus, the nitrato complex formed from solid Fe(TPP)(eta(2)-O(2)NO) maintained under a (15)NO atmosphere was found to be the labeled analogue Fe(TPP)(eta(2)-O(2)(15)NO). The reactivities of the layered solids are compared to the behaviors of the same species in ambient temperature solutions. To interpret the reactions of the labeled nitrogen oxides, the potential exchange reactions between N(2)O(3) and (15)NO were examined, and complete isotope scrambling was observed between these species under the reaction conditions (T = 140 K). Overall it was concluded from isotope labeling experiments that the sequence of reactions is initiated by reaction of 1 with NO to give the nitrato nitrosyl complex Fe(TPP)(eta(1)-ONO(2))(NO) (2) as an intermediate. This is followed by a reaction in the presence of excess NO that is equivalent to the loss of the nitrate radical NO(3)(*)( )()to give Fe(TPP)(NO) as another transient species. A plausible pathway involving NO attack on the coordinated nitrate of 2 resulting in the release of N(2)O(4) concerted with electron transfer to the metal center is proposed.     

Adsorption Behavior and Reaction Properties of NO and CO on Ir(111) and Rh(111)

Adsorption and reactions of NO over the clean and CO-preadsorbed Ir(111) and Rh(111) surfaces were investigated using infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD). Two NO adsorption states, indicative of hollow and atop sites, were present on Ir(111). Only NO adsorbed on hollow sites dissociated to N_a and O_a. The dissociated N_a desorbed as N₂ by recombination of N_a and by a disproportionation reaction between atop-NO and N_a. Preadsorbed CO inhibited atop-NO, whereas hollow-NO was not affected. Adsorbed CO reacted with O_a and desorbed as CO₂. NO adsorbed on the fcc-hollow, atop, and hcp-hollow sites in that order over Rh(111). The hcp-NO was inhibited by preadsorbed atop-CO, and fcc-NO and atop-NO were inhibited by CO preadsorbed on each type of the sites, indicating that NO and CO competitively adsorbed on Rh(111). From the Rh(111) surface-coadsorbed NO and CO, N₂ was produced by fcc-NO dissociation, and CO₂ was formed by reaction of adsorbed CO with O_a from dissociated fcc-NO.     

Ligand substitution,pH dependent deoxygenation,and linkage isomerization reactions of the 2,2'-bipyridinetetranitroruthenate dianion

The reaction of the [Ru(bpy)(NO(2))(4)](2-) (bpy = 2,2'-bipyridine) ion in aqueous solutions produces two different nitrosyl complexes, depending on the pH of the solution. At acidic pH, complex cis,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) was isolated. At neutral or basic pH, [Ru(bpy)(NO(2))(4)](2-) reacts to give cis,trans-Ru(bpy)(NO(2))(2)(NO)(OH). Both new complexes were fully characterized by elemental analysis and UV-vis, IR, (1)H NMR, and (15)N NMR spectroscopy. A single-crystal X-ray structure of cis,trans-Ru(bpy)(NO(2))(2)(NO)(OH) was also obtained. cis,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) isomerizes in acetone or water solution to give a mixture of the trans,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) and cis,cis-Ru(bpy)(ONO)(2)(NO(2))(NO) linkage isomers as determined by (1)H and (15)N NMR spectroscopy. A single-crystal X-ray structure of a solid solution of cis,cis-Ru(bpy)(ONO)(2)(NO(2))(NO)/trans,cis-Ru(bpy)(NO(2))(2)(ONO)(NO) was also obtained. This pair of isomers is the first crystallographically characterized compound with nitro, nitrito, and nitrosyl ligands. The kinetic studies of the Ru-NO(2) --> Ru-NO conversion reactions of [Ru(bpy)(NO(2))(4)](2)(-) in buffered solutions from pH 3 to pH 9 complement previous studies of the reverse reaction. The reactions are first order in [Ru(bpy)(NO(2))(4)](2-). At high pH, the reaction is independent of the concentration of H(+) while, at low pH, the reaction is first order in the concentration of H(+). The rate determining step of the high pH reaction involves breakage of the Ru-NO(2) bond while, at low pH, the mechanism involves a rapid reversible protonation of a NO(2) ligand followed by the rate determining loss of hydroxide to produce a nitrosyl ligand.     

CX_3NO(X=H,F,Cl)分子结构稳定性的Ab initio研究

CH_3NO(1)、CH_2FNO(2)、CHF_2NO(3)、CH_2ClNO(4)、CHCl_2NO(5)、CHCIFNO(6)、CF_3NO(7)和CCl_3NO(8)是一类重要的光化学分子,它们稳定性差、寿命短,实验研究其结构及稳定性较困难,仅CH_3NO、CF_3NO和CCl_3NO分子有理论研究,其余均未见报道,本文用ab initio方法在STO-3G水平上研究了上述分子结构稳定性,还用STO/     

氧化铈表面NO的热脱附性能

氧化铈表面ＮＯ的热脱附性能＊钟依均（浙江师范大学化学系，浙江金华３２１００４）罗孟飞黄宇增朱波袁贤鑫（杭州大学催化研究所，杭州３１００２８）关键词一氧化氮，热脱附，二氧化铈，表面反应ＣｅＯ２作为汽车尾气净化三效催化剂的助剂，由于其特殊的性能越来越引起...     

Electrooxidation of Nitric Oxide at a Glass Carbon Electrode Modified with Functionalized Single-walled Carbon Nanotube

The electrocatalytic oxidation of nitric oxide(NO) at a glass carbon electrode(GC) modified with functionalized single-walled carbon nanotubes(SWCNTs) was investigated by cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS).It was found that the SWCNT modified electrode could speed greatly up the electron transfer rate compared with the bare GC electrode.After the SWCNT was treated with alkali or mixed acids,the reaction rate and activation energy of NO electrooxidation were changed to different extent.Chemical modification of the SWCNT surface is one of the most powerful methods to change the sensitivity of NO electrooxidation reaction.The modified electrode with SWCNT obtained by the firstly alkali treatment and then the mixed acids treatment was the best one for NO electrooxidation,the result of CV was also confirmed by that of EIS.The anodic processes of NO were recognized more clearly by exploring the reaction mechanism of NO electrooxidation at the SWCNT modified electrode.     

Photoinduced NO release by visible light irradiation from pyrazine-bridged nitrosyl ruthenium complexes

The binuclear complex [RuII(NH3)5(pz)RuII(bpy)2(NO)](PF6)5 was prepared and characterized by elemental analysis, UV-vis, and IR spectroscopy. The complex UV-vis spectrum has presented bands at 242, 286, and 530 nm in acetate buffer solution at pH 4.5. The photochemical study by laser flash-photolysis at 532 nm showed the NO release account from the NO measured by a NO sensor. The quantum yield for NO release (0.025 +/- 0.004 mol einsten-1) was determined with a laser flash-photolysis apparatus (Continuum Q-switched Nd:YAG laser). The major irradiation product of the [RuII(NH3)5(pz)RuII(bpy)2(NO)]5+ complex besides nitric oxide is [RuIII(NH3)5(pz)RuII(bpy)2(H2O)]5+.     

A Gaseous Nitric Acid Analyzer for the Remote Atmosphere Based on the Scrubber Difference/NO-Ozone Chemiluminescence Method

An in situ nitric acid analyzer has been designed for sensing in the remote atmosphere. Its operation is based on measuring the concentration difference between the total odd nitrogen species (NO(y)) and HNO(3)-scrubbed NO(y). NO(y) was measured by an NO-ozone chemiluminescent detector equipped with a molybdenum converter. A temperature-controlled annular denuder coated with NaCl was used as a scrubber of gaseous HNO(3). The current detection limit of the HNO(3) analyzer was estimated to be 158 and 71 pptv (parts per trillion by volume) with an integration time of 2 and 10 min (2sigma), respectively. The analyzer was calibrated using standard gaseous HNO(3) to verify its performance. The HNO(3) concentrations measured by the scrubber difference and the NO-ozone chemiluminescence methods (SDCL method) were in agreement with those obtained by the denuder method within the experimental uncertainties (more than +/-4%). We conducted limited field observations of NO(y) and HNO(3) in the remote atmosphere using the newly designed SDCL method at Cape Hedo, Okinawa, Japan.     

Study on the nitric oxide generating effects from aristolochic acid in vitro

In this study, an in vitro nitric oxide (NO)-assay system based on the Griess reaction was used to investigate the (NO)-generating effects of aristolochic acid (AA) for the first time. AA was separated into its different components, aristolochic acid I (AAI) and aristolochic acid II (AAII), by preparative HPLC. AAI and AAII were incubated with human intestine bacteria (HIB) or rat intestine bacteria (RIB). A NO mixture generated from AAI and AAII by intestinal bacteria was observed and denitroso metabolites of AAI or AAII were detected in vitro by liquid chromatography/tandem mass spectrometry. Therefore, NO generation might be closely related to the metabolic process of AA in vitro. It suggested that one possible mechanism for the toxicity of AA may be due to the generation of NO from these compounds by intestinal bacteria.