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Infrared predissociation spectroscopy is carried out for the structure investigation of unprotonated cluster cations of protic molecules such as ammonia and methanol, which are generated through vacuum-ultraviolet one-photon ionization of their jet-cooled neutral clusters. The observed spectral features show that the cluster cations have the proton-transferred type structures, where a pair of a protonated cation and a neutral radical, NH4+...NH2 or CH3OH2+...OCH3, is formed. Theoretical calculations at the MP2 and B3LYP levels support the formation of the proton-transferred type structures for the cluster cations, and indicate that they are formed by proton-transfer following the photoionization of the neutral clusters. [ABSTRACT FROM AUTHOR]

An extension of Cohen’s nuclear Fukui function is presented in the spin-polarized framework of density-functional theory (SP-DFT). The resulting new nuclear Fukui function indices [uppercase_phi_synonym]Nα and [uppercase_phi_synonym]Sα are intended to be the natural descriptors for the responses of the nuclei to changes involving charge transfer at constant multiplicity and also the spin polarization at constant number of electrons. These generalized quantities allow us to gain new insights within a perturbative scheme based on DFT. Calculations of the electronic and nuclear SP-DFT quantities are presented within a Kohn-Sham framework of chemical reactivity for a sample of molecules, including H2O, H2CO, and some simple nitrenes (NX) and phosphinidenes (PX), with X=H, Li, F, Cl, OH, SH, NH2, and PH2. Results have been interpreted in terms of chemical bonding in the context of Berlin’s theorem, which provides a separation of the molecular space into binding and antibinding regions. [ABSTRACT FROM AUTHOR]

Nitrene‐transfer reactions are powerful synthetic tools for the direct incorporation of nitrogen atoms into organic molecules. The discovery of novel nitrene‐transfer reactions has been dominantly supported not only by improvements in transition‐metal catalysts but also by the employment of novel precursors of nitrenoids. Since pioneering work involving the use of organic azides and iminoiodinanes as practical synthetic tools for nitrogen‐containing compounds was reported, a new approach using various N‐heterocycles containing strain energy or a weak bond has emerged. In this review, we briefly summarize the history of nitrene‐transfer chemistry from the viewpoint of its precursors. In particular, the use of N‐heterocycles such as 2H‐azirines, 1,4,2‐dioxazol‐5‐ones, 1,2,4‐oxadiazol‐5‐ones, isoxazol‐5(4H)‐ones, and isoxazoles is comprehensively described, showing the recent remarkable progress in this chemistry. Rings open: This review summarizes transition‐metal‐catalyzed nitrene‐transfer reactions from the viewpoint of the development of nitrenoid species. The use of N‐heterocyclic compounds as novel precursors of nitrenoid species has been significantly broadened in recent years. Various types of ring‐opening and ring‐reconstructing reactions have been achieved. [ABSTRACT FROM AUTHOR]

The RhII-catalyzed oxyamination and diamination of alkenes generate 1,2-amino alcohols and 1,2-diamines, respectively, in good to excellent yields and with complete regiocontrol. In the case of diamination, the intramolecular reaction provides an efficient method for the preparation of pyrrolidines, and the intermolecular reaction produces vicinal amines with orthogonal protecting groups. These alkene difunctionalizations proceed by aziridination followed by nucleophilic ring opening induced by an Rh-bound nitrene generated in situ, details of which were uncovered by both experimental and theoretical studies. In particular, DFT calculations show that the nitrogen atom of the putative [Rh]2=NR metallanitrene intermediate is electrophilic and support an aziridine activation pathway by N ⋅⋅⋅N=[Rh]2 bond formation, in addition to the N ⋅⋅⋅[Rh]2=NR coordination mode. [ABSTRACT FROM AUTHOR]

Azidoformates are interesting potential nitrene precursors, but their direct photochemical activation can result in competitive formation of aziridination and allylic amination products. Herein, we show that visible-light-activated transition-metal complexes can be triplet sensitizers that selectively produce aziridines through the spin-selective photogeneration of triplet nitrenes from azidoformates. This approach enables the aziridination of a wide range of alkenes and the formal oxyamination of enol ethers using the alkene as the limiting reagent. Preparative-scale aziridinations can be easily achieved under continuous-flow conditions. [ABSTRACT FROM AUTHOR]

A facile and efficient one-pot synthesis of isoxazol-3(2 H)-ones has been developed starting from α-acyl cinnamides and tosyliminophenyliodinane catalyzed by copper(II) acetate [Cu(OAc)2] under very mild conditions involving a tandem aza-Michael addition and intramolecular cyclization sequence. [ABSTRACT FROM AUTHOR]

Irradiation of vinyl and aryl azides with visible light in the presence of Ru photocatalysts results in the formation of reactive nitrenes, which can undergo a variety of CN bond-forming reactions. The ability to use low-energy visible light instead of UV in the photochemical activation of azides avoids competitive photodecomposition processes that have long been a significant limitation on the synthetic use of these reactions. [ABSTRACT FROM AUTHOR]

The electronic structure, spectroscopic features, and (catalytic) reactivity of complexes with nitrogen-centered radical ligands are described. Complexes with aminyl ([M(.NR2)]), nitrene/imidyl ([M(.NR)]), and nitridyl radical ligands ([M(.N)]) are detectable and sometimes even isolable species, and despite their radical nature frequently reveal selective reactivity patterns towards a variety of organic substrates. A classification system for complexes with nitrogen-centered radical ligands based on their electronic structure leads to their description as one-electron-reduced Fischer-type systems, one-electron-oxidized Schrock-type systems, or systems with a (nearly) covalent MN π bond. Experimental data relevant for the assignment of the radical locus (i.e. metal or ligand) are discussed, and the application of complexes with nitrogen-centered radical ligands in the (catalytic) syntheses of nitrogen-containing organic molecules such as aziridines and amines is demonstrated with recent examples. This Review should contribute to a better understanding of the (catalytic) reactivity of nitrogen-centered radical ligands and the role they play in tuning the reactivity of coordination compounds. [ABSTRACT FROM AUTHOR]

Crime scene: NH bond activation. When ammonia gets in the crosshairs of [Al2O3].+, the reaction is not limited to a single hydrogen‐atom transfer, double hydrogen abstraction takes place as well and free nitrene is liberated at room temperature. These results are confirmed by mass spectrometric and theoretical investigations. [ABSTRACT FROM AUTHOR]

The electronic structures of phenylnitrenes with anionic p-donating substituents are investigated by using mass spectrometry and electronic structure calculations. Reactions of para-CH2--substituted phenylnitrene, formed by dissociative deprotonation of p-azidotoluene, with CS2 and NO indicate that it has a closed-shell singlet ground state, whereas reactions of p-oxidophenylnitrene formed by dissociative deprotonation of p-azidophenol indicate either a triplet ground state or a singlet with a small singlet-triplet splitting. The ground electronic state assignments based on ion reactivity are consistent with electronic structure calculations. The stability of the closed-shell singlet states in nitrenes is shown by Natural Resonance Theory to be very sensitive to the amount of deprotonated-imine character in the wave function, such that large changes in state energies can be achieved by small modifications of the electronic structure. [ABSTRACT FROM AUTHOR]

In this work, the properties of the synthesized high-nitrogen compounds 4,4',6,6'-tetra(azido)azo-1,3,5-triazine (TAAT) and 4,4',6,6'-tetra(azido)hydrazo-1,3,5-triazine (TAHT), and a set of designed bridged triazines with similar bridges were studied theoretically to facilitate further developments for the molecules of interests. The gas-phase heats of formation were predicted based on the isodesmic reactions by using the DFT-B3LYP/AUG-cc-PVDZ method. The estimates of the condensed-phase heats of formation and heats of sublimation were estimated in the framework of the Politzer approach. Calculation results show that the method gives a good estimation for enthalpies, in comparison with available experimental data for TAAT and TAHT. The crystal density has been computed using molecular packing calculations. The calculated detonation velocities and detonation pressures indicate that -NF2, -NO2, -N-N-, and -N-N(O)- groups are effective structural units for improving the detonation performance of the bridged triazines. The synthesized TAAT and TAHT are not preferred energetic materials due to their inferior detonation performance. The p→π conjugation effect between the triazine rings and bridges makes the molecule stable as a whole. The electrostatic behavior of the bridged triazines is characterized by an anomalous surface potential imbalance when incorporating the strongly electron-withdrawing -NF2 and -NO2 groups into the molecule. An analysis of the bond dissociation energies shows that all these derivatives have good thermal stability over RDX and HMX, and the -NH-NH- bridge is more helpful for improving the stability than -N-N(O)- and -N-N- bridges. Considering the detonation performance and thermal stability, three bridged triazines may be considered as the potential candidates of high-energy density materials (HEDMs). [ABSTRACT FROM AUTHOR]

The enthalpies for H-atom abstraction reactions by triplet imidogen as well as ethyl, alkoxycarbonyl, acyl, phenyl, and vinyl nitrenes were calculated using density functional theory calculations. These calculations show that H-atom abstraction reactions are only feasible for triplet imidogen, alkoxycarbonyl, and acyl nitrenes in solution. The calculated charges on the N-atoms (QNPA) in the nitrene correlate with the magnitude of the transition state barrier for the H-atom abstraction reactions from methanol as a model reactant. Electron-withdrawing substituents on these nitrenes make them less stable but do not affect the transition state barrier significantly. Thus, as the electron deficiency of the N-atom in the nitrenes is increased, the H-atom abstraction reaction becomes more feasible. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A polymeric precursor, polyhydridomethylsilazane, was pyrolysed in an active ammonia atmosphere at 873 K with subsequent pyrolysis in an inert nitrogen atmosphere at 1873 K, and the polymer-derived ceramic products were studied using a field emission scanning electron microscope, X-ray diffractometer and high-resolution transmission electron microscope. No nanoneedles were observed in the 873 K pyrolysed products, while beta-Si3N4 nanoneedles were obtained after pyrolysis at 1873 K. The as-received nanoneedles were about 100–200 nm in diameter, and the maximum length reached about 10 µm. There were no bulbs or droplets on the tips of the nanoneedles, and no catalysts were used during the pyrolysis of the polymeric precursor. [ABSTRACT FROM AUTHOR]

Abstract: Batch tests using swine slurry as substrate were conducted to elucidate the impact on anaerobic digestion of different ratio of substrate (COD)/inoculum (VS). Soluble COD, volatile fatty acids (VFAs) concentration, and pH were periodically analyzed in order to completely understand possible inhibitions. In addition, ammonia concentration was also calculated at the start up and final stage of the test. The results showed that the same methane yield was achieved with the three experimental ratios (COD/VS of 1, 2 and 3), however methane production rates were clearly different. This later parameter decreased with increasing ratios. This behaviour was explained by the accumulation of VFAs (predominantly acetic (HAc) and propionic acid (HPr)), reflected on the soluble COD profile as well. The possible inhibition by free ammonia was null since the values calculated were far below the threshold concentration reported in literature. [Copyright &y& Elsevier]

B3LYP/6-31G* calculations for competing (2 + 3)-cycloaddition pathways for 2-nitropropene-1 (1) to Z-C, N-diarylnitrones (2a–e) suggest a concerted reaction mechanism. However, the results point to the strongly asymmetric nature of transition complexes. Increasing polarity of the reaction environment and presence of electron-donating substituents in the nitrone phenyl rings contribute to the higher asymmetry of these structures. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Nitro-substituted phenolic ethers were successfully selectively dealkylated. The directing effect of the nitro group is supported by the excellent regioselectivities and good yields. These reactions demonstrate that the complexation of AlCl3 with the phenolic nitro group is stronger than with the phenolic ether alone. The mechanism for the selective dealkylation directed by the nitro group is proposed. [ABSTRACT FROM AUTHOR]

Inducible nitric oxide synthase (iNOS) has previously been shown to contribute to atherosclerotic lesion formation and protein nitration. Micro attenuated total reflection (ATR)-Fourier transform infrared (FTIR) spectroscopic imaging was applied ex vivoto analyse lesions in atherosclerotic (ApoE−/−) mice. Histologies of cardiovascular tissue of ApoE−/−mice that contain the gene for iNOS and ApoE−/−mice without iNOS (ApoE−/−iNOS−/−mice) were examined. Spectroscopic imaging of the aortic root revealed that iNOS did not affect the composition of the tunica media; furthermore, irrespective of iNOS presence, lipid esters were found to form the atherosclerotic plaque. ApoE−/−mouse aortic root lesions exhibited a more bulky atheroma that extended into the medial layer; signals characteristic of triglycerides and free fatty acids were apparent here. In ApoE−/−iNOS−/−mouse specimens, lesions composed of free cholesterol were revealed. ATR-FTIR spectra of the intimal plaque from the two mouse strains showed higher lipid concentrations in ApoE−/−mice, indicating that iNOS contributes to lesion formation. The reduction of lesion prevalence in ApoE−/−iNOS−/−mice compared with ApoE−/−mice is consistent with previous data. Moreover, the analysis of the plaque region revealed a change in the spectral position of the amide I band, which may be indicative of protein nitration in the ApoE−/−mouse, correlating with a more ordered (β-sheet) structure, while a less ordered structure was apparent for the ApoE−/−iNOS−/−mouse, in which protein nitration is attenuated. These results indicate that micro ATR-FTIR spectroscopic imaging with high spatial resolution is a valuable tool for investigating differences in the structure and chemical composition of atherosclerotic lesions of ApoE−/−and ApoE−/−iNOS−/−mice fed a high-fat Western diet and can therefore be applied successfully to the study of mouse models of atherosclerosis. [ABSTRACT FROM AUTHOR]

The quinuclidinolysis of 4-nitrophenyl, 2,4-dinitrophenyl and 2,4,6-trinitrophenyl O-ethyl dithiocarbonates (1, 2, and 3, respectively) are studied kinetically at 25.0 °C, ionic strength 0.2 M; the two former in water and the latter in 44 wt% ethanol–water. The Brønsted plots (log kN vs. pKa of quinuclidinium ions) for the reactions of 1 and 2 are linear with slopes β = 0.94 and 0.76, respectively, and that of 3 shows a smooth curvature. From these results and other arguments it can be concluded that the quinuclidinolysis of dithiocarbonate 1 in water is stepwise, in contrast to those of dithiocarbonates 2 in water and 3 in aqueous ethanol, which are concerted. The kinetics and mechanistic effects of the leaving and electrophilic groups and the amine nature are discussed. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Restricted rotation in indol-3-yl-N-alkyl- and indol-3-yl-N,N-dialkyl-glyoxalylamides can in principle give the syn-periplanar and anti-periplanar rotamers. In asymmetrically disubstituted glyoxalylamides, steric effects lead to the occurrence of both rotamers, as observed by NMR spectroscopy. The predominant peak corresponds with the anti rotamer, in which the bulkier alkyl group is orientated trans to the amide carbonyl group. In monoalkylated glyoxalylamides, only one set of peaks is observed, consistent with the presence of only one rotamer. Crystal structures of 5-methoxyindole-3-yl-N-tert-butylglyoxalylamide, indole-3-yl-N-tert-butylglyoxalylamide, and indole-3-yl-N-isopropylglyoxalylamide reported here reveal a syn conformation held by an intramolecular N-H...O hydrogen bond. [ABSTRACT FROM AUTHOR]

Physicochemical characterizations of polysilicon thin multilayer films have been studied after annealing. In-situ heavily boron-doped polysilicon (poly/Si) and nitrogen-doped silicon (NIDOS) films were deposited by low-pressure chemical vapor deposition (LPCVD) onto an oxidized monocrystalline silicon substrate. Secondary ion mass spectrometry (SIMS) profiles showed a boron diffusion reduction in the NIDOS layer. In addition, Fourier transform infrared spectroscopy (FTIR) analysis clearly showed an evolution of the absorption picks related to the nitrogen atom in the complex form leading to boron atom activation in the films. Therefore, this multilayer structure can be largely used for metal-oxide-semiconductor (MOS) devices. [ABSTRACT FROM AUTHOR]

The present work reports the first experimental thermochemical study of mono-N-oxides derived from quinoxaline, namely, 3-methoxycarbonyl-2-methyl-quinoxaline N-oxide and 3-ethoxycarbonyl-2-methyl-quinoxaline N-oxide. The values of the enthalpies of formation, in the condensed state, and of the enthalpies of sublimation, derived from static bomb calorimetry and Calvet microcalorimetry measurements, respectively, are combined to derive the standard molar enthalpies of formation in the gaseous phase for these two compounds. From the latter values, the first and second N&bond;O bond dissociation enthalpies for the corresponding di-N-oxides have been obtained. The gas-phase experimental results are also compared with calculated data obtained with a density functional theory approach. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The effect of chitosan (0.5% and 1%) added individually or in combination with nitrites (150ppm) on microbiological (Total Viable Counts, Lactic acid bacteria, Pseudomonas spp., Brochothrix thermosphacta, Enterobacteriaceae, yeasts and moulds), physicochemical-chemical (pH, chemical composition, lipid oxidation) and sensory properties of fresh pork sausages stored at 4°C for 28 days was investigated. Chitosan addition resulted in significant (p <0.05) inhibition of microbial growth, while nitrites did not seem to protect sausages from microbial spoilage. A gradual reduction of nitrites was observed till the end of storage, when nitrites were almost depleted in all nitrite containing samples. The rate of lipid oxidation in fresh pork sausages was significantly decreased (p <0.05) by addition of increasing levels of chitosan, while samples containing both chitosan and nitrites showed the lowest malondialdehyde (MDA) values, indicating a synergistic antioxidative effect. Consequently, the samples containing the combination of nitrites and chitosan at any level deteriorated less rapidly and were judged as more acceptable than all the other samples. [Copyright &y& Elsevier]

Abstract: A novel SiO2–NHC–Cu(I) 3b was developed and used as a highly efficient catalyst for [3+2] cycloaddition of organic azides and terminal alkynes. In the presence of SiO2–NHC–Cu(I) 3b (1mol %), the reactions of terminal alkynes with organic azides underwent smoothly to generate the corresponding regiospecific 1,4-disubstituted 1,2,3-triazoles in excellent yields under solvent-free reaction conditions at room temperature. Furthermore, catalyst 3b was quantitatively recovered from the reaction mixture by a simple filtration and reused for 10 cycles without loss of its activity. [Copyright &y& Elsevier]

Abstract: The reactions of [60] fullerene with excess fluoroalkanesulfonyl azides RfSO2N3 in o-dichlorobenzene under thermal or microwave irradiation condition afforded monoadduct opened [5,6]-bridged azafulleroids. While, similarly treatment of 2,2,2-trifluoroethyl azides CF3CH2N3 with C60 gave two monoadducts, i.e., opened [5,6]-bridged azafulleroids, closed [6,6]-bridged Aziridino-fullerene, and some multi-addition product. A general mechanism for these addition reactions was proposed. [Copyright &y& Elsevier]

Abstract: Introduction: In atherogenesis, dendritic cells, beside presenting antigens, may be sources of tumour necrosis factor (TNF)alpha and nitric oxide (NO), together with mast cells and smooth muscle cells. Material and Methods: We have looked at the expression of TNFalpha and inducible NO synthase (iNOs) by these cells by affinity cytochemistry in autoptical specimens from normal carotid arteries and not ruptured, hemorrhagic or calcified atheromata. Results: Round to dendritic, major histocompatibility complex class II molecules (MHC-II+) cells and avidin-labeled mast cells were rare in normal arteries and significantly more numerous in atheromata. Many MHC-II+ cells expressed S-100 antigen; while a few were positive for phalloidin; appreciable fractions of these cells were immunoreactive for TNFalpha and iNOs, both in control specimens and atheromata. The fraction of mast cells labeled for iNOs was significantly lower in atheromata than in controls. Phalloidin positive cells were the most abundant cell type in the normal intima and atheromata; the fractions of these cells labeled for TNFalpha and iNOs were significantly higher in atheromata than in controls. Very few of these cells were also labeled for MHC-II. Computerized image analysis confirmed that the amounts of iNOs and TNFalpha were higher in atheromata than in controls. The increase in TNFalpha in atheromata was also confirmed by western blot. Conclusions: Dendritic cells and mast cells can participate to the generation of TNFalpha and NO in the normal arterial wall and in atheromata, but myointimal cells are candidates as major sources of these molecules. [Copyright &y& Elsevier]

The effect of hydrotreating VGO (FCC pretreatment) at different severities was examined with respect to FCC performance. Furthermore, the reaction mechanisms for conversion of the organic sulfur and nitrogen compounds found in the pretreated FCC feedstocks during FCC processing were studied. The studies were carried out under realistic conditions in a large pilot plant hydrotreating unit and in an FCC pilot plant operating with a circulating catalyst. It was found that the sulfur compounds in the FCC gasoline (i.e., thiophenes and benzothiophenes) were formed from recombination reactions between H 2S and olefins generated in the FCC unit. Similarly, the nitrogen compounds found in the FCC gasoline (i.e., anilines and indoles) were formed from recombination reactions between ammonia and olefins. These results show that the sulfur and nitrogen compounds in the FCC gasoline are mostly the same with only minor differences in the relative concentration of the individual compound. This phenomenon is not dependent on the feed charged to the FCC unit but is a result of equilibrium reactions between olefins, H 2S and ammonia, respectively, and the temperature in the FCC reactor. [ABSTRACT FROM AUTHOR]

Rice (Oryza sativa L.) blast disease caused by Magnaporthe grisea is one of the most destructive diseases in the rice-growing areas of the world. Silicon is an important nutritional element especially for rice. Two near-isogenic lines of rice with different resistance to blast disease, i.e. CO39 (susceptible) and C101LAC (Pi-1) (resistant), were selected to determine the effects of Si amendment on the severity and incidence of rice blast disease. The physiological and cytological mechanisms involved in the induced disease resistance by silicon were investigated. Exogenous Si application at a concentration of 2 mM reduced the disease index by 45% for CO39 and 56% for C101LAC (Pi-1). Si application alone did not change lignin content and the activities of defense-related enzymes including peroxidase (POD), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) in rice leaves of both isogenic lines. However, after inoculation with M. grisea, Si-treated rice plants significantly increased the activities of POD, PPO and PAL in leaves of both isogenic lines. Si and lignin content were also significantly increased in Si-treated inoculated seedlings. Environmental scanning electron microscope observations revealed that Si amendment resulted in higher Si deposit on dumbbell bodies in the rice leaves and silicon papilla accumulation on the guard cell of stoma. These results suggest that silicon-induced defense response and cell silicification of rice leaves altogether contribute to the silicon-induced rice resistance to blast disease. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the selective oxidation of ammonia into nitrogen over copper, silver and gold catalysts between room temperature and 400 C using different NH3/O2 ratios. The effect of addition of CeO x and Li2O on the activity and selectivity is also discussed. The results show that copper and silver are very active and selective toward N2. However the multicomponent catalysts: M/Li2O/CeO x /Al2O3 (M: Au, Ag, Cu) perform the best. On all three metal containing catalysts the activity and selectivity is influenced by the particle size and the interaction between metal particles and support. [Copyright &y& Elsevier]

[MoO2(acac)2] (acac=acetylacetonate) promotes the disproportionation of hydrazine in THF solutions. The active catalytic species, [MoVIO2]2+, are produced according to the reaction: [MoO2(C5H7O2)2]+2N2H4 →[MoO2]2+ +2C5H8N2 +2OH− +2H2O. The main product of the reduction of hydrazine is ammonia while 3,5-dimethylpyrazole (C5H8N2) was isolated as a side-product. A catalytic cycle was proposed and the probable reaction intermediate is a hydrazido-complex, [MoIV=NNH2(OH2)2]2+. The intermediate species, [MoVIO2NH3]2+ reacts with hydroxide ion leading to the complex cis-[MoVIO2(OH)2(NH3)], which was isolated and characterized. [Copyright &y& Elsevier]

The existence of a charge-transfer-to-solvent process when a KI contact ion pair (CIP) dissolved in supercritical water (SCW) is excited by UV light was confirmed by use of electronic structure calculations applied to molecular dynamics trajectories. We observed similar behavior with fluid density as that found for the KI-CIP in supercritical ammonia (SCA); nevertheless, there are some distinct features in the two supercritical solvents. First, the effect of the solvent field due to the molecules lying beyond the first solvation shell is very different in SCW compared with that observed in SCA; in SCW it actually has a destabilizing effect over the ground and excited states. Second, our results for the thermodynamic behavior of the CIP indicate that SCA is better solvent than SCW for this species. The differences found can be attributed to the solvent molecules surrounding the CIP and bridging the two ions; they shield more efficiently the ion pair from long-range solvent effects in SCA. The different behavior is partially attributed to a stronger solvent−solvent interaction in SCW than in SCA. [ABSTRACT FROM AUTHOR]

Abstract: The present study aimed to define the ability of erythropoietin (EPO) to mobilize hematopoietic stem cells (c-kit+/sca-1+/lin-1−; KSL-cells) and hematopoietic progenitor cells (CD34+ cells), including vascular endothelial growth factor receptor 2 expressing hematopoietic progenitor cells (CD34+/Flk-1+ cells). We also sought to determine the role of endothelial nitric oxide synthase (eNOS) in EPO-induced mobilization. Wild type (WT) and eNOS−/− mice were injected bi-weekly with recombinant erythropoietin (EPO, 1000U/kg, s.c.) for 14 days. EPO increased the number of KSL, CD34+, CD34+/Flk-1+ cells in circulating blood of wild type mice. These effects of EPO were abolished in eNOS−/− mice. Our results demonstrate that, EPO stimulates mobilization of hematopoietic stem and progenitor cells. This effect of EPO is critically dependent on activation of eNOS. [Copyright &y& Elsevier]

Abstract: Tranilast (N-[3′,4′-dimethoxycinnamonyl] anthranilic acid), an orally active anti-allergic drug, is reported to exert the anti-inflammatory effects, but the underlying mechanisms that could explain the anti-inflammatory actions of tranilast remain largely unknown. Here, we found that tranilast induces heme oxygenase-1 (HO-1) expression through the extracellular signal-regulated kinase-1/2 (ERK1/2) pathway in RAW264.7 macrophages. Tranilast suppressed cyclooxygenase-2 (COX-2) and inducible nitric oxide (NO) synthase (iNOS) expression, and thereby reduced COX-2-derived prostaglandin E2 (PGE2) and iNOS-derived NO production in lipopolysaccharide (LPS)-stimulated macrophages. Similarly, tranilast diminished tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) production. Interestingly, the effects of tranilast on LPS-induced PGE2, NO, TNF-α, and IL-1β production were partially reversed by the HO-1 inhibitor tin protoporphyrin, suggesting that tranilast-induced HO-1 expression is at least partly responsible for the resulting anti-inflammatory effects of the drug. Thus, HO-1 expression via ERK1/2 activation may be at least one of the possible mechanisms explaining the anti-inflammatory actions of tranilast. [Copyright &y& Elsevier]

Nitric oxide (NO) effects are often mediated via S-nitrosothiol (SNO) formation; SNO uptake has recently been shown to be mediated in some cell types via system L-type amino acid transporters (LAT- 1, 2). Inhaled NO therapy may exert some biological effects via SNO formation. We therefore sought to determine if pulmonary epithelial SNO uptake depended on LAT or peptide transporter 2 (PEPT2). Both LAT-1 and PEPT2 proteins were detected by immunoblot and immunocytochemistry in L2 cells and rat lung. We tested SNO uptake through the transporters by exposing rat alveolar epithelial cells (L2 and type II) to RSNOs: S-nitrosoglutathione, S-nitrosocysteinylglycine (SNO- Cys-Gly), S-nitrosocysteine (CSNO), and to NO donor diethylamine NONOate (DEA-NONOate). SNO was detected in cell lysates by ozone chemiluminescence. NO uptake was detected by fluorescence in alveolar epithelial cells loaded with 4-amino-5-methylamino-2',7'- difluorofluorescein (DAF-FM) diacetate cultured in submersion and exposed to RSNOs and DEA NONOate. Addition of L-Cys but not o-Cys to RSNOs or DEA NONOate increased SNO and DAF-FM signal that was inhibited by coincubation with LAT competitors. Incubation of cells with PEPT2 substrate SNO-Cys-Gly showed no increase in SNO or DAF-FM signal unless incubated with L-Cys. This was unaffected by PEPT2 inhibition. We conclude that RSNOs (thionitrites, S-nitrosothiols) and NO enter alveolar epithelial cells predominantly by S-nitrosation of L-Cys, which is then imported through LAT. [ABSTRACT FROM AUTHOR]

Time-resolved infrared (TRIR) spectroscopy, product studies, and computational methods were applied to the photolysis of sulfilimines derived from dibenzothiophene that were expected to release acetylnitrene, trifluoroacetylnitrene, mesylnitrene, and tosylnitrene. All three methods provided results for acetylnitrene consistent with literature precedent and analogous experiments with the benzoylnitrene precursor, i.e., that the ground-state multiplicity is singlet. In contrast, product studies clearly indicate triplet reactivity for trifluoroacetylnitrene, though TRIR experiments were more ambiguous. Product studies suggest that these sulfilimines are superior sources for sulfonylnitrenes, which have triplet grounds states, to the corresponding azides, and computational studies shed light on the electronic structure of the nitrenes. [ABSTRACT FROM AUTHOR]

Abstract: The toxic effects of triclosan (TCS) and nonylphenol (4-n-NP) on activated sludge heterotrophic and autotrophic microorganisms were evaluated. Toxicity experiments with specific oxygen uptake rate (SOUR) and ammonia uptake rate (AUR) revealed that TCS was much more toxic to heterotrophic and autotrophic microorganisms than 4-n-NP. In experiments with heterotrophic biomass, increase of sludge age (θ c) from 5 to 15 days resulted in a decrease of median effective concentrations (EC50) of TCS from 38.2 to 9.97mgl−1 and in an increase of EC50 values of 4-n-NP from 441 to 649mgl−1. In experiments with autotrophic biomass and sludge age of 15 days, significantly lower EC50 values were obtained for both compounds, indicating the higher sensitivity of nitrifiers to TCS and 4-n-NP. To compare toxicity of TCS and 4-n-NP towards single species and mixed wastewater cultures, experiments were performed using marine bacterium Vibrio fischeri. EC50 values of 0.22 and 3.51mgl−1 were estimated for TCS and 4-n-NP, respectively, indicating the higher sensitivity of this bioassay to toxicants. According to the levels of tested compounds commonly found in influent wastewater and the results of this study, there is a possible risk for deterioration of nitrification in activated sludge systems due to the presence of TCS. [Copyright &y& Elsevier]

Irradiation of 2-(3-alkenyl)allenylphenyl azides in the presence of excess CuI furnished functionalized 2,3-cyclopentenylindoles in good yield with only trace amounts of competitive C−N-bonded regioisomeric products. These results represent a significant departure from the modest-to-nonexistent regioselectivity that attended thermal cyclization of these allenyl azide substrates. [ABSTRACT FROM AUTHOR]

Novel reactions that can selectively functionalize carbon–hydrogen bonds are of intense interest to the chemical community because they offer new strategic approaches for synthesis. A very promising ‘carbon–hydrogen functionalization’ method involves the insertion of metal carbenes and nitrenes into C–H bonds. This area has experienced considerable growth in the past decade, particularly in the area of enantioselective intermolecular reactions. Here we discuss several facets of these kinds of C–H functionalization reactions and provide a perspective on how this methodology has affected the synthesis of complex natural products and potential pharmaceutical agents. [ABSTRACT FROM AUTHOR]

Experimental and theoretical studies on the photodissociation of aromatic azides, spectral and photochemical characteristics of nitrenes, as well as the application of azides as a light-sensitive component of positive luminescent photography, are reviewed. [ABSTRACT FROM AUTHOR]

The article explores the research findings on the spectroscopy and kinetics of arylnitrenes. Focus is made on the experimental and theoretical findings of 1997-2005. Topics discussed include: the photochemistry of phenyl azide and the kinetics and spectroscopy of phenylnitrene; the kinetics and spectroscopy of substituted phenylnitrenes; and the photochemistry of polycyclic aryl azides.

We report here the first gold-catalyzed nitrene transfer reaction. A gold(I) compound, supported by 4,4′,4″- tri-tert-butyl-2,2′:6′,2″-terpyridine (tBu3tpy) as the ligand, efficiently catalyzes olefin aziridination with the use of the commercially available oxidant PhI(OAc)2 and sulfonamides. This system also mediates carbene insertion into benzene. [ABSTRACT FROM AUTHOR]

The thermal decomposition of formyl, acetyl, and benzoyl azides to the corresponding isocyanate and nitrogen has been treated theoretically using ab initio molecular orbital calculations at the Møller–Plesset type 2 (MP2)(full)/6-31G* level. The reaction is stimulated by elongation of N&bond;N bond and is followed until the formation of the isocyanate and expulsion of nitrogen. The decomposition of formyl azide proved to be a concerted one-step reaction without the formation of a nitrene intermediate. In contrast, the conversion of both acetyl and benzoyl azides to the corresponding isocyanate and nitrogen is a two-step reaction, and a nitrene intermediate is formed. One transition state is located and identified during the course of the conversion of formyl azide, but two transition states are located and identified during the course of the conversion of acetyl and benzoyl azides. The thermodynamic functions, ΔEr and ΔHr, of the studied reactions are calculated. The results predict that the ease of conversion of the acyl azide to the isocyanate and nitrogen goes in the order: formyl azide > acetyl azide > benzoyl azide. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [ABSTRACT FROM AUTHOR]

Abstract: We have studied the thermal decomposition of 1,3-benzenedisulfonyl azide (1,3-BDSA), and verified that sulfonyl nitrenes formed are able to cross-link polyolefins, including PP. The decomposition was studied with DSC, TGA, and the GC–MS analysis of gaseous products. Both the decomposition of pure 1,3-BDSA and 1,3-BDSA dissolved in a polyolefin were studied. Decomposition occurs by loss of nitrogen giving sulfonyl nitrenes. In the polyolefin nitrenes cross-links the carbon chains by C–H insertion. Cross-linking of PP was verified with SEC. SEC showed no signs of decomposition of PP. Decomposition in the polyolefin was a first order reaction with a half-life of 25.7s at 200°C. Hence, 1,3-BDSA is suited for processing with polyolefins. Decomposition of pure 1,3-BDSA is more complicated with unwanted products such as SO2 and benzene being formed, thereby emphasising the need for good blending when used in polyolefins. [Copyright &y& Elsevier]

Computations find that o-phenylene(halo)carbenonitrenes 2-XN, X = F, Cl, Br, have quinoidal singlet biradical ground states such as the parent o-phenylenecarbenonitrene (2-HN). Compared to the parent 2-HN, halogen substitution stabilizes the A″ states relative to the A′ ones. Halogen substitution also affects the barrier and exothermicity of the ring-opening reaction (to form unsaturated nitriles 4-XN, X = F, Cl, Br), but it has a smaller effect on the ring-closing reaction (to form benzo(aza)cyclobutadiene 3-XN, X = F, Cl, Br). Attempts to generate and observe the o-phenylene(halo)carbenonitrenes 2-XN, X = F, Cl, Br, using matrix isolation spectroscopy under conditions similar to those of the successful observation of 2-HN failed. Instead, the observed photoproducts were a mixture of 3-XN and 4-XN. In each case, the major product of the mixture appears to be the thermodynamically more stable one. In the case of X = Br, the observed mixture contains an additional component that is postulated to be Z-6-BrN. o-Phenylenechlorocarbenocarbene is also computed to have a quinoidal singlet biradical ground state and relatively stabilized A″ excited states. Attempts to generate the biscarbene under matrix isolation conditions led to the detection of benzochlorocyclobutadiene (3-ClC), small amounts of the ring-open product (dienediyne 4-ClC), and cycloalkyne 5-ClC. Computations suggest that the formation of 5-ClC implies the generation of Z-6-ClC, which is analogous to the formation of Z-6-BrN from 2-BrN. [ABSTRACT FROM AUTHOR]

An electrochemical strategy for running nitrogen-transfer reactions on chemically inert anode surfaces has been developed. The generation and trapping of highly reactive nitrene-transfer reagents can be accomplished under mild conditions on platinum electrodes. The key factor that accounts for the high levels of chemoselectivity in this process is the phenomenon of overpotential. We have found that molecules that are similar in terms of propensity toward oxidation can be differentiated on the basis of their affinity to a given electrode surface. Thereby, reactive species can be selectively generated in the presence of acceptor molecules of interest. Specifically, a wide range of structurally dissimilar olefins can be transformed into the corresponding aziridines in the presence of N-aminophthalimide. Likewise, nitrene generation in the presence of sulfoxides leads to their chemoselective transformation into the corresponding sulfoximines. In this paper we discuss the underlying mechanistic foundation of these reactions. [ABSTRACT FROM AUTHOR]

Abstract: Spin indices of some simple nitrenes (R-N) and phosphinidenes (R-P), in both lowest-lying singlet and triplet states, have been evaluated using density functional computations at the B3LYP/6-311+G(d,p) level. Relatively good correlations between the spin hardness, spin-philicity and spin-donicity, and the vertical singlet–triplet energy gaps have been established. A comparison with spin indices of related reactive intermediates such as carbenes, silylenes and germylenes allows their similarities and differences to be emphasized. [Copyright &y& Elsevier]

We report the first observation that the intermolecular triplet sensitization of alkyl azides leads to bimolecular reactivity, by forming triplet alkyl nitrenes. The intermolecular triplet-sensitized photolysis of 1-azidoadamantane with acetone, acetophenone and benzophenone leads to the formation of di-(adamantan-1-yl)-1,2-diazene as the major product via dimerization of triplet adamantan-1-yl nitrene. The triplet alkyl nitrene also abstracts a H-atom from the solvent to form adamantan-1-yl amine, adamantan-1-yl-benzyl amine and adamantan-1-yl benzylidene amine. The rates of the energy transfer from acetophenone and benzophenone to 1-azidodamantane are 1×108 and 5×106 M−1 s−1, respectively. Triplet-sensitized photolysis of benzyl azide with acetophenone gave methylene phenyl amine, dibenzyl amine and tribenzyl amine as the major products. Thus triplet benzyl nitrene abstracts a H-atom from the solvent to form dibenzyl amine and tribenzyl amine and rearranges to form methylene phenyl amine. The energy transfer rate between acetophenone and benzyl azide is diffusion controlled, or 2×109 M−1 s−1. Sensitized photolysis of benzyl azide with benzophenone yielded only benzylideneamine. Presumably, benzophenone abstracts a H-atom from benzyl azide and the resulting radical rearranges into benzylideneamine. The rate of the chemical quenching of benzophenone with benzyl azide is 5×107 M−1 s−1. [Copyright &y& Elsevier]

Ar matrix photolysis of 1- and 2-naphthyl azides 3 and 4 at 313 nm initially affords the singlet naphthyl nitrenes, [SUP1]1 and [SUP1]2. Relaxation to the corresponding lower energy, persistent triplet nitrenes [SUP3]1 and [SUP3]2 competes with cyclization to the azirines 15 and 18, which can also be formed photochemically from the triplet nitrenes. On prolonged irradiation, the azirines can be converted to the seven-membered cyclic ketenimines 10 and 13, respectively, as described earlier by Dunkin and Thomson. However, instead of the o-quinoid ketenimines 16 and 19, which are the expected primary ring-opening products of azirines 15 and 18, respectively, we observed their novel bond-shift isomers 17 and 20, which may be formally regarded as cyclic nitrile ylides. The existence of such ylidic heterocumulenes has been predicted previously, but this work provides the first experimental observation of such species. The factors which are responsible for the special stability of the ylidic species 17 and 20 are discussed. [ABSTRACT FROM AUTHOR]

We realized large photoinduced refractive index increases of poly(methyl methacrylate) (PMMA) films containing phenylazide (PAZ) through photochemical and thermal processes. The refractive index increase of the PMMA film containing 30 wt% PAZ through the processes is as much as 0.0161 with transparency in a wide visible region both before and after photoirradiation and with moderate thermal stability. These excellent performances suggest the applicability of PAZ doped PMMA films for optical devices. [ABSTRACT FROM AUTHOR]

The photolysis of o-azidobenzoic acid in solutions, adsorbed on silica gel, and in a crystalline state was studied by IR and UV spectroscopy and thin-layer chromatography. It was found that the photolysis resulted in the formation of 2,1-benzisoxazolone (the product of intramolecular cyclization of singlet nitrenes) and anthranilic acid and o,o"-dicarboxyazobenzene (the reaction products of triplet nitrenes). The formation of 2,1-benzisoxazolone is a reversible reaction because of the secondary photolysis to singlet nitrenes, which leads to an increase in their concentration in the system. [ABSTRACT FROM AUTHOR]