NO Moiety Research Articles

A theoretical exploration of the effect and mechanism of CO on NO2 heterogeneous reduction over carbonaceous surfaces

A thorough understanding of the NO2 heterogeneous reduction reaction over a carbonaceous surfaces can help with the goal of providing useful information to aid in controlling NOx emissions. Multiple adsorption structures and reaction pathways on zigzag surfaces were obtained via density functional theory (DFT) calculation, revealing the effect and mechanism of the CO presence and its adsorption mode. Calculation results showed that the introduction of CO at the stage of CO/CO2 desorption accelerates the dissociation of CO2 from a zigzag surface. According to the theory of frontier molecular orbital, the CO presence promotes the transfer of electrons from the char surface to the CO2 moiety, decreasing the energy barrier of CO2 desorption. On the other hand, kinetic and thermodynamic analysis indicates that the introduction of CO during NO2 reduction facilitates the reduction of NO2 to NO, but has little influence on the reduction rate. In addition, the adsorption mode of CO shows little effect on the weak interaction between NO2 moiety and the char edge, but has a significant effect on the weak interaction between CO moiety and char edge. Thus, as the adsorption mode of CO changes, a significant difference in mechanisms can be observed at the stage of CO2 desorption rather than NO2 reduction. To sum up, these theoretical results reveal in detail the effect and mechanism of CO on NO2 heterogeneous reduction, which further explain previous experimental results.

Synthesis and in vitro characterization of the genotoxic, mutagenic and cell-transforming potential of nitrosylated heme

Data from epidemiological studies suggest that consumption of red and processed meat is a factor contributing to colorectal carcinogenesis. Red meat contains high amounts of heme, which in turn can be converted to its nitrosylated form, NO-heme, when adding nitrite-containing curing salt to meat. NO-heme might contribute to colorectal cancer formation by causing gene mutations and could thereby be responsible for the association of (processed) red meat consumption with intestinal cancer. Up to now, neither in vitro nor in vivo studies characterizing the mutagenic and cell transforming potential of NO-heme have been published due to the fact that the pure compound is not readily available. Therefore, in the present study, an already existing synthesis protocol was modified to yield, for the first time, purified NO-heme. Thereafter, newly synthesized NO-heme was chemically characterized and used in various in vitro approaches at dietary concentrations to determine whether it can lead to DNA damage and malignant cell transformation. While NO-heme led to a significant dose-dependent increase in the number of DNA strand breaks in the comet assay and was mutagenic in the HPRT assay, this compound tested negative in the Ames test and failed to induce malignant cell transformation in the BALB/c 3T3 cell transformation assay. Interestingly, the non-nitrosylated heme control showed similar effects, but was additionally able to induce malignant transformation in BALB/c 3T3 murine fibroblasts. Taken together, these results suggest that it is the heme molecule rather than the NO moiety which is involved in driving red meat-associated carcinogenesis.

Deconstruction - Reconstruction: Analysis of the Crucial Structural Elements of GluN2B-Selective, Negative Allosteric NMDA Receptor Modulators with 3-Benzazepine Scaffold.

The NMDA receptor plays a key role in the pathogenesis of neurodegenerative disorders including Alzheimer's and Huntington's disease, as well as depression and drug or alcohol dependence. Due to its participation in these pathologies, the development of selective modulators for this ion channel is a promising strategy for rational drug therapy. The prototypical negative allosteric modulator ifenprodil inhibits selectively GluN2B subunit containing NMDA receptors. It was conformationally restricted as 2-methyl-3-(4-phenylbutyl)-2,3,4,5-tetrahydro-1H-3-benzazepine-1,7-diol, which showed high GluN2B affinity and inhibitory activity. For a better understanding of the relevance of the functional groups and structural elements, the substituents of this 3-benzazepine were removed successively (deconstruction). Then, additional structural elements were introduced (reconstruction) with the aim to analyze, which additional modifications were tolerated by the GluN2B receptor. The GluN2B affinity was recorded in radioligand receptor binding studies with the radioligand [3H]ifenprodil. The activity of the ligands was determined in two-electrode voltage clamp experiments using Xenopus laevis oocytes transfected with cRNA encoding the GluN1-1a and GluN2B subunits of the NMDA receptor. Docking studies showed the crucial interactions with the NMDA receptor protein. The deconstruction approach showed that removal of the methyl moiety and the phenolic OH moiety in 7-positon resulted in almost the same GluN2B affinity as the parent 3-benzazepine. A considerably reduced GluN2B affinity was found for the 3-benzazepine without further substituents. However, removal of one or both OH moieties led to considerably reduced NMDA receptor inhibition. Introduction of a NO2 moiety or bioisosteric replacement of the phenol by a benzoxazolone resulted in comparable GluN2B affinity, but almost complete loss of inhibitory activity. An O-atom, a carbonyl moiety or a F-atom in the tetramethylene spacer led to 6-7-fold reduced ion channel inhibition. The results reveal an uncoupling of affinity and activity for the tested 3-benzazepines. Strong inhibition of [3H]ifenprodil binding by a test compound does not necessarily translate into strong inhibition of the ion flux through the NMDA receptor associated ion channel. 3-(4-Phenylbutyl)-2,3,4,5-tetrahydro-1H-3-benzazepine- 1,7-diol (WMS-1410) shows high GluN2B affinity and strong inhibition of the ion channel. Deconstruction by removal of one or both OH moieties reduced the inhibitory activity proving the importance of the OH groups for ion channel blockade. Reconstruction by introduction of various structural elements into the left benzene ring or into the tetramethylene spacer reduced the NMDA receptor inhibition. It can be concluded that these modifications are not able to translate binding into inhibition.

Tuning Inner-Sphere Electron Transfer in a Series of Copper/Nitrosoarene Adducts.

A series of copper/nitrosoarene complexes was created that mimics several steps in biomimetic O2 activation by copper(I). The reaction of the copper(I) complex of N,N,N',N'-tetramethypropylenediamine with a series of para-substituted nitrosobenzene derivatives leads to adducts in which the nitrosoarene (ArNO) is reduced by zero, one, or two electrons, akin to the isovalent species dioxygen, superoxide, and peroxide, respectively. The geometric and electronic structures of these adducts were characterized by means of X-ray diffraction, vibrational analysis, ultraviolet-visible spectroscopy, NMR, electrochemistry, and density functional theory (DFT) calculations. The bonding mode of the NO moiety depends on the oxidation state of the ArNO moiety: κN for ArNO, mononuclear η2-NO and dinuclear μ-η2:η1 for ArNO•-, and dinuclear μ-η2:η2 for ArNO2-. 15N isotopic labeling confirms the reduction state by measuring the NO stretching frequency (1392 cm-1 for κN-ArNO, 1226 cm-1 for η2-ArNO•-, 1133 cm-1 for dinuclear μ-η2:η1-ArNO•-, and 875 cm-1 for dinuclear μ-η2:η2 for ArNO2-). The 15N NMR signal disappears for the ArNO•- species, establishing a unique diagnostic for the radical state. Electrochemical studies indicate reduction waves that are consistent with one-electron reduction of the adducts and are compared with studies performed on Cu-O2 analogues. DFT calculations were undertaken to confirm our experimental findings, notably to establish the nature of the charge-transfer transitions responsible for the intense green color of the complexes. In fine, this family of complexes is unique in that it walks through three redox states of the ArNO moiety while keeping the metal and its supporting ligand the same. This work provides snapshots of the reactivity of the toxic nitrosoarene molecules with the biologically relevant Cu(I) ion.

Synthesis and DFT calculations of new ruthenium(II) nitrosyl complexes using cis-fac-dichlorotetrakis(dimethylsulfoxide)ruthenium(II) precursor and different oximes as sources of nitrosyl ligand

Three NO+-ruthenium(II) complexes were prepared by using cis-[RuCl2(DMSO)4] as precursor, P, and the compounds benzohydroxamic acid (BHA), 1′, anti-diphenylglyoxime (H2dpg), 2′, and dimethylglyoxime (H2dmg), 3′, as sources of NO moiety. The three complexes [RuCl2(DMSO)3(NO)]+(BA)−, 1, [RuCl2(DMSO)3(NO)]+(Hdpg)−, 2, and [RuCl2(DMSO)3(NO)]+(Hdmg)−, 3, were characterized by (FT-IR, NMR, UV-Vis) spectroscopy, thermogravimetry, and microanalysis. From FT-IR spectral data, two modes of coordination of DMSO to Ru atom through both S and O atoms were detected for 1 and 2. For 3, only S coordination was reported. Computational studies on the [RuCl2(DMSO)3(NO)]+ cationic parts, 1″, 2″ and 3″, of the investigated complexes 1, 2 and 3 were carried out by DFT. The molecular geometry and mode of attachment of Ru(II) with DMSO were performed with the B3LYP/LANL2DZ level of theory and basis set. Theoretical to the experimental agreement was achieved for analysis of IR data of the investigated complexes. Additional information about binding between the ruthenium atom and the DMSO ligand has been obtained by NBO analysis.

Poly (vinyl alcohol)/glutaraldehyde/Premna oblongifolia merr extract hydrogel for controlled-release and water absorption application

Fertilizer leaching and water slack are the most problems predominantly found in the agriculture practices. Many efforts have been done by promoting a medium for controlling fertilizer release and water retaining in vicinity of plant and soil. In this work, a biodegradable Premna Oblongifolia Merr (POM) extract/polyvinyl alcohol (PVA) composite based hydrogel for controlled-release and water absorption application has been prepared. The hydrogel composite was successfully synthesized through solution mixing of POM and PVA with an aid of crosslinking agent (glutaraldehyde) at optimum composition in volume ratio of 5:5:9, respectively. In particular, the fertilizer (Zinc nitrate) solution was incorporated into hydrogel matrix for controlled release study. The structural morphology of hydrogel composite was investigated by means of Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction. The water absorption capacity and fertilizer-controlled release behaviour of hydrogel composite were evaluated by gravimetric and atomic absorption spectroscopy techniques, respectively. The FTIR spectra showed the evidence of copolymerization of hydrogel precursors, indicated by the shifting of peak intensity and position of several functional groups (O-H, C-H sp3, C=O, C-N, C-O) as a result of interaction between POM extract and PVA moieties which predominantly occurs through intermolecular hydrogen bonding. In particular, the crosslinking of PVA and POM extract mediated by glutaraldehyde was evidenced by the appearance of new peak for -C-O-C moieties owing to the formation of hemiacetal bridges in between polymer backbones. The insertion of fertilizer into hydrogel matrix was sharpen the peaks of hydrogel moieties and led to new peak appearance at 1384 cm−1 (NO moieties), correspond to the interaction with zinc ions. The X-ray diffraction confirmed the modification of structural morphology of hydrogel with fertilizer insertion as indicated by the slight shift of interlayer distance of polymer matrices. The hydrogel composites showed the large water absorption capacity up to 550 % and could retained water in its matrix for almost 3 weeks. Absorption and released studies indicate that the micronutrient interacts chemically with a surface functional group of hydrogel. The released micronutrient should come from the second and the upper layer where it occurs only at high concentration. These results offer the promising applications for the controlled-release and water absorbent materials.

Sulfur: the heart of nitric oxide-dependent redox signalling.

Nitric oxide (NO), more benign than its more reactive and damaging related molecules, reactive oxygen species (ROS), is perfectly suited for duties as a redox signalling molecule. A key route for NO bioactivity is through S-nitrosation, the addition of an NO moiety to a protein Cys thiol (-SH). This redox-based, post-translational modification (PTM) can modify protein function analogous to more well established PTMs such as phosphorylation, for example by modulating enzyme activity, localization, or protein-protein interactions. At the heart of the underpinning chemistry associated with this PTM is sulfur. The emerging evidence suggests that S-nitrosation is integral to a myriad of plant biological processes embedded in both development and environmental relations. However, a role for S-nitrosation is perhaps most well established in plant-pathogen interactions.

Electronic processes in NO dimerization on Ag and Cu clusters: DFT and MRMP2 studies.

Experimentally observed NO dimerization on Cu and Ag surfaces is surprising because binding energy of NO dimer is very small in gas phase. MRMP2, MP2 to MP4, CCSD(T), and DFT studies of NO dimerization on Ag2 and Cu2 clusters disclosed that the CCSD(T) method could be applied to this reaction on Ag2 and Cu2 unlike NO dimerization in gas phase which exhibits significantly large nondynamical electron correlation effect. Charge-transfer (CT) from Ag2 and Cu2 to NO moieties plays important role in NN bond formation between two NO molecules. This CT considerably decreases nondynamical correlation effect. Also, the DFT method could be applied to this NO dimerization, if appropriate DFT functional is used; all pure functionals examined here and most of the hybrid functionals underestimated the activation barrier (Ea ), while only ωB97X provided Ea similar to CCSD(T)-calculated value. NO dimerization on similar Cu2 and Cu5 needs moderately larger Ea than those on Ag2 and Ag5 , because frontier orbital participating in the CT exists at lower energy in Cu2 and Cu5 than in Ag2 and Ag5 . The Ea decreases in the order Ag2 >> Ag38 > Ag7 ∼ Ag5 and the reaction energy (ΔE) is positive (endothermic) in Ag2 but significantly negative in Ag38 , Ag7 , and Ag5 , indicating that various Ag clusters could be effective for NO dimerization except for Ag2 . The decreasing order of Ea and increasing order of exothermicity are attributed to increasing order of the frontier orbital energy of Ag2 < Ag38 < Ag7 ∼ Ag5 . © 2018 Wiley Periodicals, Inc.

Models for potential dendritic nitric oxide donors: crystal structures of two 2-nitroanilino precursors and nitric oxide-release behavior of the nitrosated derivatives.

Two molecular precursors to dendrimeric materials that could serve as slow and sustained NO-releasing therapeutic agents have been synthesized and characterized. N1,N4-Bis(2-nitrophenyl)butane-1,4-diamine, C16H18N4O4, (I), crystallizes in a lattice with equal populations of two molecules of different conformations, both of which possess inversion symmetry through the central C-C bond. One molecule has exclusively anti conformations along the butyl chain, while the other has a gauche conformation of the substituents on the first C-C bond. N2,N2-Bis[2-(2-nitroanilino)ethyl]-N1-(2-nitrophenyl)ethane-1,2-diamine, C24H27N7O6, (II), crystallizes with one unique molecule in the asymmetric unit. Neighboring pairs of molecules are linked into dimers via N-H...O amine-nitro hydrogen bonds. The dimers are assembled into layers that stack in an A-B-A-B sequence such that the repeat distance in the stacking direction is over 46 Å. Molecular NO-release agents N1,N4-bis(2-nitrophenyl)-N1,N4-dinitrosobutane-1,4-diamine, C16H16N6O6, (III), and N1-(2-nitrophenyl)-N2,N2-bis{2-[(2-nitrophenyl)(nitroso)amino]ethyl}-N1-nitrosoethane-1,2-diamine, C24H24N10O9, (IV), were prepared via treatment of (I) and (II), respectively, with NaNO2 and acetic acid. The release of NO from solid-phase samples of (III) and (IV) suspended in phosphate buffer was monitored spectroscopically over a period of 21 days. Although (IV) released a greater amount of NO, as expected due to it having three NO moieties for every two in (III), the (IV):(III) ratio of the rate and extent of NO release was significantly less than 1.5:1, suggesting that some combination of electronic, chemical, and/or steric factors may be affecting the release process.

Nitro-functionalized Bis(pyrazolate) Metal-Organic Frameworks as Carbon Dioxide Capture Materials under Ambient Conditions.

The metal-organic frameworks (MOFs) M(BPZNO2 ) (M=Co, Cu, Zn; H2 BPZNO2 =3-nitro-4,4'-bipyrazole) were prepared through solvothermal routes and were fully investigated in the solid state. They showed good thermal stability both under a N2 atmosphere and in air, with decomposition temperatures peaking up to 663 K for Zn(BPZNO2 ). Their crystal structure is characterized by 3D networks with square (M=Co, Zn) or rhombic (M=Cu) channels decorated by polar NO2 groups. As revealed by N2 adsorption at 77 K, they are micro-mesoporous materials with BET specific surface areas ranging from 400 to 900 m2 g-1 . Remarkably, under the mild conditions of 298 K and 1.2 bar, Zn(BPZNO2 ) adsorbs 21.8 wt % CO2 (4.95 mmol g-1 ). It shows a Henry CO2 /N2 selectivity of 15 and an ideal adsorbed solution theory (IAST) selectivity of 12 at p=1 bar. As a CO2 adsorbent, this compound is the best-performing MOF to date among those bearing a nitro group as a unique chemical tag. High-resolution powder X-ray diffraction at 298 K and different CO2 loadings revealed, for the first time in a NO2 -functionalized MOF, the insurgence of primary host-guest interactions involving the C(3)-NO2 moiety of the framework and the oxygen atoms of carbon dioxide, as confirmed by Grand Canonical Monte Carlo simulations. This interaction mode is markedly different from that observed in NH2 -functionalized MOFs, for which the carbon atom of CO2 is involved.

Twisting of diarylnitroxides: An efficient tool for redox tuning

The electrochemical behavior of a new type of stable diarylnitroxide radicals with bulky substituent in the ortho-position of one of the phenyl rings is described. The presence of the substituent results in broken conjugation of one of the phenyl rings with the NO moiety (the other ring stays conjugated) giving rise to so called “twisted nitroxides”. New diphenylnitroxides with t-Bu and/or CF3 substituents were synthesized and are the first examples of diarylnitroxides which are extremely stable in solution and form both stable oxidized and reduced forms (oxoammonium cations and aminoxyl anions). These compounds exhibit fast ET kinetics and reversible electrochemical oxidation and reduction. Varying the torsion angle θ shifts Eox and Ered values in the opposite directions thus increasing the electrochemical potential gap, contrary to the traditional effects of substituents that commonly shift both potential values in the same direction. The electronic effect of the substituents in the ortho-position as well as the total electronic effect of both rings on the electrochemical potential values was estimated using the linear fit for the relationship between E1/2Ox+E1/2Red vs. the sum of Hammett constants (σp + σo·cosθ). The ρ value (the slope in the linear fit) is 0.501 indicating significant sensitivity of the potential values to the electronic effects and wide possibilities for tuning. The results obtained shed light on the efficient principles of molecular design for stable electroactive nitroxide-based materials.

Aminophenol based colorimetric chemosensor for naked-eye detection of biologically important fluoride and acetate ions in organo-aqueous medium: Effective and simple anion sensors

Three new novel colorimetric receptors (R1-R3) based on aminophenol have been designed and synthesized by simple Schiff base reaction and their anion sensing properties were examined, characterized by common spectroscopic techniques such as FT-IR, UV–visible, 1HNMR,13CNMR, ESI–MS and fluorescence. Receptors R1 and R2 bearing −OH group at ortho and para position acting as anion binding sites with NO2 moiety as an optical signaling unit. Receptors R1 and R2 elevated selective and sensitive ability towards F− and AcO− ions over the other competing anions in DMSO as well as in CH3CN. Receptors R1 and R2 showed high capability of sensing acetate and fluoride ions present in the form of sodium salts such as NaAcO and NaF in an aqueous medium. The color of both the receptors R1 and R2 solution changes from pale green to blue and pale yellow to peach color with the addition of sodium salts of acetate (NaAcO) and fluoride (NaF) with a bathochromic shift of 168 nm and 165 nm in the UV–vis absorption spectra of receptor R1 and 103 nm and 100 nm in case of receptor R2 due to ICT transition between the electron rich −OH and electron deficient NO2 moiety. Moreover, receptors R1-R2 showed noteworthy fluorescence enhancement, response towards F− and AcO− ion in DMSO. Compared to receptor R2, R1 shows a huge red shift towards F− and AcO− ions in organo-aqueous medium due to the presence of −OH proton at ortho position which effectively bind with both the anions. The binding constant and stoichiometry of the receptors-anions complex was calculated by using Benesi-Hildebrand (B–H) plot. The anion binding properties of receptor R1 via ICT mechanism was enlightened by UV–vis titration, 1HNMR studies.

Regulation of protein function by S-nitrosation and S-glutathionylation: processes and targets in cardiovascular pathophysiology.

Decades of chemical, biochemical and pathophysiological research have established the relevance of post-translational protein modifications induced by processes related to oxidative stress, with critical reflections on cellular signal transduction pathways. A great deal of the so-called 'redox regulation' of cell function is in fact mediated through reactions promoted by reactive oxygen and nitrogen species on more or less specific aminoacid residues in proteins, at various levels within the cell machinery. Modifications involving cysteine residues have received most attention, due to the critical roles they play in determining the structure/function correlates in proteins. The peculiar reactivity of these residues results in two major classes of modifications, with incorporation of NO moieties (S-nitrosation, leading to formation of protein S-nitrosothiols) or binding of low molecular weight thiols (S-thionylation, i.e. in particular S-glutathionylation, S-cysteinylglycinylation and S-cysteinylation). A wide array of proteins have been thus analyzed in detail as far as their susceptibility to either modification or both, and the resulting functional changes have been described in a number of experimental settings. The present review aims to provide an update of available knowledge in the field, with a special focus on the respective (sometimes competing and antagonistic) roles played by protein S-nitrosations and S-thionylations in biochemical and cellular processes specifically pertaining to pathogenesis of cardiovascular diseases.

Deconstruction – reconstruction approach to analyze the essential structural elements of tetrahydro-3-benzazepine-based antagonists of GluN2B subunit containing NMDA receptors

The role of the phenolic and benzylic OH moieties for the interaction of tetrahydro-3-benzazepine-1,7-diol 3d with GluN2B subunit containing NMDA receptors was analyzed by their stepwise removal. Elimination of trifluormethanesulfinate from 10 and 13 represent the key steps in the synthesis. Removal of phenolic OH moiety led to 5-fold reduced GluN2B affinity of 4d compared with 3d. Additional removal of the benzylic OH moiety (5d) resulted in further reduced GluN2B affinity but increased σ1 and σ2 affinities. Introduction of a NO2 (6d) or NH2 moiety (7d) decreased the GluN2B affinity. 3-Benzazepin-1-ol 4i with the N-phenylcyclohexyl side chain showed the highest GluN2B affinity of this series of compounds (Ki = 2.2 nM) and, moreover, high selectivity over the PCP binding site, σ1 and σ2 receptors. In docking studies 3-benzazepines (S)-4-7 adopt the same binding poses as ifenprodil and display the same crucial interactions. Unexpectedly, the high-affinity ligands (S)-4i, (S)-4j, and (S)-6i were not able to inhibit the glutamate/glycine evoked current in two-electrode voltage clamp measurements and the cytotoxic effects of glutamate/glycine on transfected cell lines.

Trimethylamine N-oxide stabilizes proteins via a distinct mechanism compared with betaine and glycine

We report experimental and computational studies investigating the effects of three osmolytes, trimethylamine N-oxide (TMAO), betaine, and glycine, on the hydrophobic collapse of an elastin-like polypeptide (ELP). All three osmolytes stabilize collapsed conformations of the ELP and reduce the lower critical solution temperature (LSCT) linearly with osmolyte concentration. As expected from conventional preferential solvation arguments, betaine and glycine both increase the surface tension at the air-water interface. TMAO, however, reduces the surface tension. Atomically detailed molecular dynamics (MD) simulations suggest that TMAO also slightly accumulates at the polymer-water interface, whereas glycine and betaine are strongly depleted. To investigate alternative mechanisms for osmolyte effects, we performed FTIR experiments that characterized the impact of each cosolvent on the bulk water structure. These experiments showed that TMAO red-shifts the OH stretch of the IR spectrum via a mechanism that was very sensitive to the protonation state of the NO moiety. Glycine also caused a red shift in the OH stretch region, whereas betaine minimally impacted this region. Thus, the effects of osmolytes on the OH spectrum appear uncorrelated with their effects upon hydrophobic collapse. Similarly, MD simulations suggested that TMAO disrupts the water structure to the least extent, whereas glycine exerts the greatest influence on the water structure. These results suggest that TMAO stabilizes collapsed conformations via a mechanism that is distinct from glycine and betaine. In particular, we propose that TMAO stabilizes proteins by acting as a surfactant for the heterogeneous surfaces of folded proteins.

The near-IR spectrum of NO(X̃2Π)-He detected through excitation into the Ã-state continuum: A joint experimental and theoretical study.

We present the first measurement of a bound-state spectrum of the NO-He complex. The recorded spectrum is associated with the first overtone transition of the NO moiety. The IR absorption is detected by exciting the vibrationally excited complex to the Ã-state dissociation continuum. The resulting NO(A) fragment is subsequently ionized in the same laser pulse. We recorded two bands centered around the NO monomer rotational lines, Q11(0.5) and R11(0.5), consistent with an almost free rotation of the NO fragment within the complex. The origin of the spectrum is found at 3724.06 cm-1 blue shifted by 0.21 cm-1 from the corresponding NO monomer origin. The rotational structures of the spectrum are found to be in very good agreement with calculated spectra based on bound states derived from a set of high level ab initio potential energy surfaces [Kłos et al. J. Chem. Phys. 112, 2195 (2000)].

Theoretical kinetic investigation of thermal decomposition of nitropropane

The thermal decomposition of nitropropane (CH3CH2CH2NO2) has been investigated at the CBS-QB3 level of theory. The pyrolysis of CH3CH2CH2NO2 mainly includes the simple bond ruptures mechanism, hydrogen abstraction processes, isomerization and secondary reactions. As a result, for the simple bond ruptures mechanism, the formation of $${\text{CH}}_{3} {\text{CH}}_{2} {\text{CH}}_{2}^{\cdot} +\,^{\cdot}{\text{NO}}_{2}$$ products is dominant with the energy barrier of 49.77 kcal mol−1. The process of H atom on the β–CH2 abstracted by one O atom of NO2 moiety in CH3CH2CH2NO2(CH3CH2CH2NO2 → CH3CH=CH2 + HONO) needs to overcome lower energy barrier than that of the rate-determining step (one of H atom on the α-CH2 and γ-CH3 abstracted of reaction) of the other hydrogen abstraction reactions. Therefore, we predict that the corresponding alkenes and HONO are the main products in the hydrogen abstraction reaction of nitroparaffin. Besides, the channel of the CH3CH2CHO + HNO formations (CH3CH2C(α)H2NO2 → CH3CH2C(α)H2ONO → CH3CH2CHO + HNO), occurring through the H atom of C(α) abstracted by the N atom of NO2 moiety after the isomerization reaction from CH3CH2CH2NO2 to CH3CH2CH2ONO, is favorable in the isomerization secondary reactions. Rate constants and branching ratios are estimated by means of the conventional transition state theory with zero curvature tunneling over the temperature range of 400–1500 K. The calculation shows that the overall rate constant in the temperature of 400–1500 K is mainly dependent on the competitive channels of formations of CH3CH=CH2 + HONO and $${\text{CH}}_{3} {\text{CH}}_{2} {\text{CH}}_{2}^{\cdot} +\,^{\cdot}{\text{NO}}_{2}$$ The three-parameter expression for the total rate constant is fitted to be k total = 1.74 × 10−13 T 8.20exp(17038.7/T) (s−1) between 400 and 1500 K.

Ozonation of ranitidine: Effect of experimental parameters and identification of transformation products

This study focuses on the effect of experimental parameters on the removal of ranitidine (RAN) during ozonation and the identification of the formed transformation products (TPs). The influence of pH value, the initial concentrations, the inorganic and the organic matter on RAN's removal were evaluated. Results indicated high reactivity of RAN with molecular aqueous ozone. Initial ozone concentration and pH were proven the major process parameters. Alkaline pH values promoted degradation and overall mineralization. Dissolved organic matter reacts competitively to RAN with the oxidants (ozone and/or radicals), influencing the target compound's removal. The presence of inorganic ions in the matrix did not seem to affect RAN ozonation. A total of eleven TPs were identified and structurally elucidated, with the complementary use of both Reversed Phase (RP) and Hydrophilic Interaction Liquid Chromatography (HILIC) quadrupole time of flight tandem mass spectrometry (Q-ToF-MS/MS). Most of the TPs (TP-304, TP-315b, TP-299b, TP-333, TP-283) were generated by the attack of ozone at the double bond or the adjacent secondary amine, with the abstraction of NO2 moiety, forming TPs with an aldehyde group and an imine bond. Oxidized derivatives with a carboxylic group (TP-315a, TP-331a, TP-331b, TP-299a) were also formed. RAN S-oxide was identified as an ozonation TP (TP-330) and its structure was confirmed through the analysis of a reference standard. TP-214 was also produced during ozonation, through the CN bond rupture adjacent to the NO2 moiety. HILIC was used complementary to RP, either for the separation and identification of TPs with isomeric structures that may have been co-eluted in RPLC or for the detection of new TPs that were not eluted in the RP chromatographic system. Retention time prediction was used as a supporting tool for the identification of TPs and results were in accordance with the experimental ones in both RP and HILIC.

Cu–Ln compounds based on nitronyl nitroxide radicals: synthesis, structure, and magnetic and fluorescence properties

Three series of nitronyl nitroxide radical 3d–4f compounds, namely, [Ln(hfac)3Cu(hfac)2NIT-5Br-3Py]n (LnIII = La (1), Pr (2)), [Ln(hfac)3Cu(hfac)2NIT-5Br-3Py] (LnIII = Gd (3), Tb (4), Dy (5)) and [Ln(hfac)3Cu(hfac)2(NIT-5Br-3Py)2]n (LnIII = Gd (6), Tb (7), Dy (8); NIT-5Br-3Py = 2-(5-bromo-3-pyridyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetonate) have been successfully obtained. Single crystal X-ray crystallographic analysis reveals that complexes 1 and 2 consist of 1D chains built up by Ln(hfac)3 units bridged by the radical ligands through their NO moieties and the additional Cu ions are coordinated to the nitrogen atoms of the radicals. Complexes 3–5 are rare hetero-binuclear Cu–Ln compounds bridged by the nitronyl nitroxide radicals while complexes 6–8 possess one-dimensional chain structures with a repeating [Cu–Rad–Ln–Rad] sequence. DC magnetic studies show ferromagnetic interaction between the LnIII ion and the coordinated NO group in compounds 3–8. Tb–Cu derivatives (complexes 4 and 7) display frequency dependent ac magnetic susceptibilities, indicating slow magnetic relaxation behavior. The room-temperature photoluminescence spectra of complexes 4 and 7 exhibit strong characteristic emissions in the visible region.

Transnitrosylation products of the dipeptide cysteinyl-cysteine: an examination by tandem mass spectrometry and density functional theory.

The fragmentation pathways of protonated mono- and di-nitrosylated derivatives from the dipeptide Cys-Cys obtained by electrospray were examined. Protonated mononitrosylated dipeptide upon loss of ˙NO formed a radical cation, which in turn shows two fragment ions, one from the loss of HS˙ and the other from a neutral loss giving a radical cation of formula C2H5NS˙(+). Protonated dinitrosylated dipeptide dissociated by losing both ˙NO molecules, forming a cyclic structure with a vicinal disulfide bridge whose major dissociation channel was the loss of CO. After CO loss, two pathways were observed (loss of NH3 and C2H3NS) which were preceded by proton exchange occurring between one β-carbon and the nitrogen atom. DFT calculations did not show significant differences in the energies involved for the loss of the NO radical from either of the cysteine residues of the protonated di-nitrosylated dipeptide. Upon loss of the first NO radical, the thiyl radical afforded the vicinal disulfide product with a small barrier through radical substitution of the remaining NO moiety. The calculated relative energy barriers for the different channels are in good agreement with experimental observations. Structures of the ions obtained after dissociation are suggested on the basis of the proposed mechanisms.