Theoretical study on rate constants for the reactions of CF3CH2NH2 (TFEA) with the hydroxyl radical at 298 K and atmospheric pressure

Theoretical investigations are carried out on reaction mechanism of the reactions of CF₃CH₂NH₂ (TFEA) with the OH radical by means of ab initio and DFT methods. The electronic structure information on the potential energy surface for each reaction is obtained at MPWB1K/6-31+G(d,p) level and energetic information is further refined by calculating the energy of the species with a Gaussian-2 method, G2(MP2). The existence of transition states on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate (IRC) calculation. Our calculation indicates that the H abstraction from –NH₂ group is the dominant reaction channel because of lower energy barrier. The rate constants of the reaction calculated using canonical transition state theory (CTST) utilizing the ab initio data. The agreement between the theoretical and experimental rate constants is good at the measured temperature. From the comparison with CH₃CH₂NH₂, it is shown that the fluorine substution decreases the reactivity of the C-H bond.     

Reaction mechanism of CH3M≡MCH3 (M=C, Si, Ge) with C2H4: [2+1] or [2+2] cycloaddition?

The mechanism of the cycloaddition reaction CH₃M≡MCH₃ (M=C, Si, Ge) with C₂H₄ has been studied at the CCSD(T)/6-311++G(d,p)//MP2/6-311++G(d,p) level. Vibrational analysis and intrinsic reaction coordinate (IRC), calculated at the same level, have been applied to validate the connection of the stationary points. The breakage and formation of the chemical bonds of the titled reactions are discussed by the topological analysis of electron density. The calculated results show that, of the three titled reactions, the CH₃Si≡SiCH₃+C₂H₄ reaction has the highest reaction activity because it has the lowest energy barriers and the products with the lowest energy. The CH₃C≡CCH₃+C₂H₄ reaction occurs only with difficulty since it has the highest energy barriers. The reaction mechanisms of the title reactions are similar. A three-membered-ring is initially formed, and then it changed to a four-membered-ring structure. This means that these reactions involve a [2+1] cycloaddition as the initial step, instead of a direct [2+2] cycloaddition.     

Carbon nanotube functionalization with carboxylic derivatives: a DFT study

Chemical functionalization of a single-walled carbon nanotube (CNT) with different carboxylic derivatives including –COOX (X?=?H, CH₃, CH₂NH₂, CH₃Ph, CH₂NO₂, and CH₂CN) has been theoretically investigated in terms of geometric, energetic, and electronic properties. Reaction energies have been calculated to be in the range of ?0.23 to ?7.07 eV. The results reveal that the reaction energy is increased by increasing the electron withdrawing character of the functional groups so that the relative magnitude order is ?CH₂NO₂?>?CH₂CN?>?H?>?CH₂Ph?>?CH₃?>?CH₂NH₂. The chemical functionalization leads to an increase in HOMO/LUMO energy gap of CNT by about 0.32 to 0.35 eV (except for ?H). LUMO, HOMO, and Fermi level of the CNT are shifted to lower energies especially in the case of ?CH₂NO₂ and _?CH₂CN functional groups. Therefore, it leads to an increment in work function of the tube, impeding the field electron emission.     

Kinetic and mechanistic studies on the ruthenium induced activation of methylamine to oxidation

When aqueous solutions containing [Ru(NH₂CH₃)₆]²⁺ are exposed to oxygen [Ru(NH₂CH₃)₅(OH]²⁺ is produced as an identifiable intermediate as a result of the slow replacement of co-ordinated methylamine by water, and the subsequent rapid oxidation of this ruthenium(II) aquo complex. The [Ru(NH₂CH₃)₅(OH)]²⁺ ion then undergoes another slow reaction, probably the replacement of another methylamine ligand by water. All subsequent reactions leading to Ru(CN)₃·3H₂O are rapid. Rate data are reported, and a mechanism involving β-elimination from co-ordinated methylamine is postulated.     

Inhibition of reticulocyte iron uptake by NH4Cl and CH3NH2

The aim of this investigation was to test the hypothesis that elevation of intracellular pH would inhibit iron uptake by reticulocytes. The experiments were performed with rabbit reticulocytes and iron bound to rabbit transferrin. Incubation of the cells with NH₄Cl, (NH₄)₂CO₃, CH₃NH₂ and (CH₃)₂NH was used in an attempt to increase intracellular pH. These substances were all found to inhibit iron uptake by reticulocytes. The mechanism of action of NH₄Cl and CH₃NH₂ was investigated in detail. Similar results were found with both reagents. They inhibited iron uptake in a concentration-dependent manner, but produced a small increase in the cellular uptake of transferrin. The onset of action was rapid and the effect was reversible. There was no decrease in the number of transferrin-binding sites per cell and their apparent affinity for transferrin increased slightly, while the efficiency of iron removal from transferrin per binding site diminished greatly. The rate of transferrin release from reticulocytes was unaffected. NH₄Cl did not affect the rate of iron release from transferrin in a cell-free system. Incubation of reticulocytes with 10 mM NH₄Cl or CH₃NH₂ was found to produce an increase in intracellular pH of 0.05—0.15 pH units. The intracellular pH determined by used of the weak acid 5,5-dimethyl-oxazolidine-2,4-dione was significantly higher than that obtained with the weak base (CH₃)₂NH. By transmission electron microscopy it was shown that reticulocytes treated with NH₄Cl or CH₃NH₂ have enlarged intracellular vesicles. The results are considered to support the hypothesis that iron release from transferrin in reticulocytes occurs as a result of protonation of the transferrin within intracellular vesicles. According to this hypothesis, weak bases such as NH₃ and CH₃NH₂ inhibit iron release by neutralizing H⁺ within the vesicles.     

Surface chemistry induces mitochondria-mediated apoptosis of breast cancer cells via PTEN/PI3K/AKT signaling pathway

Tumor cell can be significantly influenced by various chemical groups of the extracellular matrix proteins. However, the underlying molecular mechanisms involved in the interaction between cancer cells and functional groups in the extracellular matrix remain unknown. Using chemically modified surfaces with biological functional groups (CH₃, NH₂, OH), it was found that hydrophobic surfaces modified with CH₃ and NH₂ suppressed cell proliferation and induced the number of apoptotic cells. Mitochondrial dysfunction, cytochrome c release, Bax upregulation, cleaved caspase-3 and PARP, and Bcl-2 downregulation indicated that hydrophobic surfaces with CH₃ and NH₂ triggered the activation of intrinsic apoptotic signaling pathway. Cells on the CH₃- and NH₂-modified hydrophobic surfaces showed downregulated expression and activation of integrin β1, with a subsequent decrease of focal adhesion kinase (FAK) activity. The RhoA/ROCK/PTEN signaling was then activated to inhibit the phosphorylation of PI3K and AKT, which are essential for cell proliferation. However, pretreatment of MDA-MB-231 cells with SF1670, a PTEN inhibitor, abolished the hydrophobic surface-induced activation of the intrinsic pathway. Taken together, the present results indicate that CH₃- and NH₂-modified hydrophobic surfaces induce mitochondria-mediated apoptosis by suppressing the PTEN/PI3K/AKT pathway, but not OH surfaces. These findings are helpful to understand the interaction between extracellular matrix and cancer cells, which might provide new insights into the mechanism potential intervention strategies for tumor prognosis.     

Theoretical study on the functionalization of BC2N nanotube with amino groups

Using density functional theory calculations, we investigated properties of a functionalized BC₂N nanotube with NH₃ and five other NH₂-X molecules in which one of the hydrogen atoms of NH₃ is substituted by X = ?CH₃, ?CH₂CH₃, ?COOH, ?CH₂COOH and ?CH₂CN functional groups. It was found that NH₃ can be preferentially adsorbed on top of the boron atom, with adsorption energy of ?12.0 kcal mol^?1. The trend of adsorption-energy change can be correlated with the trend of relative electron-withdrawing or -donating capability of the functional groups. The adsorption energies are calculated to be in the range of ?1.8 to ?14.2 kcal mol^?1, and their relative magnitude order is found as follows: H₂N(CH₂CH₃) > H₂N(CH₃) > NH₃ > H₂N(CH₂COOH) > H₂N(CH₂CN) > H₂N(COOH). Overall, the functionalization of BC₂N nanotube with the amino groups results in little change in its electronic properties. The preservation of electronic properties of BC₂N coupled with the enhancement of solubility renders their chemical modification with either NH₃ or amino functional groups to be a way for the purification of BC₂N nanotubes.     

Theoretical investigations on the synthesis mechanism of cyanuric acid from NH3 and CO2

In the synthesis of cyanuric acid from NH₃ and CO₂, urea and isocyanic acid OCNH are two pivotal intermediates. Based on density functional theory (DFT) calculations, the synthesis mechanism of cyanuric acid from NH₃ + CO₂ was investigated systematically. Urea can be synthesized from NH₃ and CO₂, and cyanuric acid can be obtained from urea or NH₃ + CO₂. In the stepwise mechanism of cyanuric acid from urea or NH₃ + CO₂, the energy barriers are relatively high, and the condition of high pressure and temperature does not decrease the energy barriers. Our theoretical model shows that cyanuric acid is actually acquired from OCNH via a one-step cycloaddition reaction.

Study on the photochemical reaction of HCN and its polymer products relating to primary chemical evolution

The photochemical reaction of HCN at 184.9 nm is studied in the gas phase. (CN)₂, H₂, CH₄, NH₃, N₂H₄, C₂H₆, and CH₃NH₂ are identified as gas phase products, and a reaction mechanism is proposed. HCN polymers^** are also obtained as solid reaction products, and their structure is investigated by Infrared Spectroscopy, UV-Visible Spectroscopy, Mass Spectrometry, and Amino acid Analysis. The process and nature of the formation of the polymers are discussed.     

Growth Engineering of CH3NH3PbI3 Structures for High‐Efficiency Solar Cells

Controlling the growth of perovskite crystals has been one of the interesting strategies to mold their fundamental properties and exploit their potential in the fabrication of high performance solar cells. Herein, the impact of chloride on the conversion of lead halide into CH₃NH₃PbI₃, morphology, and coverage of perovskite structures using modified two‐step approach is investigated systematically, which eventually dictates the overall performance of the resulting device. Structural and morphological characterization is thoroughly carried out by X‐ray diffraction and field emission scanning electron microscopy, respectively. Various spectroscopic techniques provide ample evidence that CH₃NH₃PbI₃ structures formed in the presence of chloride, in the lead halide precursor solution, exhibit desired properties, such as fewer defects. Moreover, the morphology of CH₃NH₃PbI₃ structures and surface coverage of the resulting layers are considerably different from those obtained in the absence of chloride. After gaining a rational understanding regarding the effect of chloride on the growth, morphology, and optical properties of CH₃NH₃PbI₃ structures, fabrication of devices revealing a power conversion efficiency of over 16% under standard AM 1.5 G illumination is realized. The fundamental understanding and high efficiency reported here distinguishes our results, particularly where chloride based precursors are involved.     

Photochemistry of NH3, CH4 and PH3. Possible applications to the Jovian planets

Photolysis of NH₃ at 185 nm in the presence of a two-fold excess of CH₄ results in the loss of about 0.25 mole of CH₄ per mole of NH₃ decomposed (ΔCH₄/ΔNH₃). The loss arises from the abstraction of hydrogen atoms from CH₄ by photolytically generated hot hydrogen atoms, the presence of which is established by the constancy of ΔCH₄/ΔNH₃ between 298 and 156 K and by the quenching of the abstraction reaction when either H₂ or SF₆ is added. From the latter result, it can be concluded that NH₃ photolysis in the H₂-abundant atmosphere of Jupiter is not responsible for the presence of the carbon compounds observed there such as ethane, acetylene, and hydrogen cyanide, but may have had a role in the early atmosphere of Titan. Photolysis of PH₃ with a 206 nm light source gives P₂H₄, which in turn is converted to a red-brown solid (P₄?). The course of the photolysis is not changed appreciably when the temperature is lowered to 157 K except that the concentration of P₂H₄ increases. The presence of H₂ has no effect on the P₂H₄ yield. Photolysis of 9∶1 NH₃∶PH₃ gives a rate of decomposition of PH₃ that is comparable with that observed by the direct photolysis of PH₃. Comparable amounts of P₂H₄ and the red-brown solid are also observed. The mechanisms of these photochemical reactions together with their implications to the atmospheric chemistry of Jupiter are discussed. The structures of the compounds responsible for the wide array of colorse.g., brown, red and white, observed in the atmosphere of Jupiter have been the subject of extensive speculation. One theory suggests that these colors are due to organic materials formed by the action of either solar ultraviolet light or electric discharges on mixtures of CH₄, NH₃ and NH₄HS in the Jovian atmosphere (Ponnamperuma, 1976; Khareet al., 1978). An alternative hypothesis is that the colors are due to inorganic compounds resulting from the photolysis of NH₄HS and PH₃ (Lewis and Prinn, 1970; Prinn and Lewis, 1975). In this paper we will summarize our experiments which were designed to test some of these hypotheses.     

Use of chemical ionization for GC–MS metabolite profiling

Metabolite profiling is commonly performed by GC–MS of methoximated trimethylsilyl derivatives. The popularity of this technique owes much to the robust, library searchable spectra produced by electron ionization (EI). However, due to extensive fragmentation, EI spectra of trimethylsilyl derivatives are commonly dominated by trimethylsilyl fragments (e.g. m/z 73 and 147) and higher m/z fragment ions with structural information are at low abundance. Consequently different metabolites can have similar EI spectra, and this presents problems for identification of “unknowns” and the detection and deconvolution of overlapping peaks. The aim of this work is to explore use of positive chemical ionization (CI) as an adjunct to EI for GC–MS metabolite profiling. Two reagent gases differing in proton affinity (CH₄ and NH₃) were used to analyse 111 metabolite standards and extracts from plant samples. NH₃-CI mass spectra were simple and generally dominated by [MH]⁺ and/or the adduct [M+NH₄]⁺. For the 111 metabolite standards, m/z 73 and 147 were less than 3% of basepeak in NH₃-CI and less than 30% of basepeak in CH₄-CI. With CH₄-CI, [MH]⁺ was generally present but at lower relative abundance than for NH₃-CI. CH₄-CI spectra were commonly dominated by losses of CH₄ [M+1-16]⁺, 1–3 TMSOH [M+1-nx90]⁺, and combinations of CH₄ and TMSOH losses [M+1-nx90-16]⁺. CH₄-CI and NH₃-CI mass spectra are presented for 111 common metabolites, and CI is used with real samples to help identify overlapping peaks and aid identification via determination of the pseudomolecular ion with NH₃-CI and structural information with CH₄-CI.     

Use of chemical ionization for GC–MS metabolite profiling

Metabolite profiling is commonly performed by GC–MS of methoximated trimethylsilyl derivatives. The popularity of this technique owes much to the robust, library searchable spectra produced by electron ionization (EI). However, due to extensive fragmentation, EI spectra of trimethylsilyl derivatives are commonly dominated by trimethylsilyl fragments (e.g. m/z 73 and 147) and higher m/z fragment ions with structural information are at low abundance. Consequently different metabolites can have similar EI spectra, and this presents problems for identification of “unknowns” and the detection and deconvolution of overlapping peaks. The aim of this work is to explore use of positive chemical ionization (CI) as an adjunct to EI for GC–MS metabolite profiling. Two reagent gases differing in proton affinity (CH₄ and NH₃) were used to analyse 111 metabolite standards and extracts from plant samples. NH₃-CI mass spectra were simple and generally dominated by [MH]⁺ and/or the adduct [M+NH₄]⁺. For the 111 metabolite standards, m/z 73 and 147 were less than 3% of basepeak in NH₃-CI and less than 30% of basepeak in CH₄-CI. With CH₄-CI, [MH]⁺ was generally present but at lower relative abundance than for NH₃-CI. CH₄-CI spectra were commonly dominated by losses of CH₄ [M+1-16]⁺, 1–3 TMSOH [M+1-nx90]⁺, and combinations of CH₄ and TMSOH losses [M+1-nx90-16]⁺. CH₄-CI and NH₃-CI mass spectra are presented for 111 common metabolites, and CI is used with real samples to help identify overlapping peaks and aid identification via determination of the pseudomolecular ion with NH₃-CI and structural information with CH₄-CI.

     

Exploring the Limiting Open‐Circuit Voltage and the Voltage Loss Mechanism in Planar CH3NH3PbBr3 Perovskite Solar Cells

Perovskite solar cells based on CH₃NH₃PbBr₃ with a band gap of 2.3 eV are attracting intense research interests due to their high open‐circuit voltage (V_oc) potential, which is specifically relevant for the use in tandem configuration or spectral splitting. Many efforts have been performed to optimize the V_oc of CH₃NH₃PbBr₃ solar cells; however, the limiting V_oc (namely, radiative V_oc:V_oc,rad) and the corresponding ΔV_oc (the difference between V_oc,rad and V_oc) mechanism are still unknown. Here, the average V_oc of 1.50 V with the maximum value of 1.53 V at room temperature is achieved for a CH₃NH₃PbBr₃ solar cell. External quantum efficiency measurements with electroluminescence spectroscopy determine the V_oc,rad of CH₃NH₃PbBr₃ cells with 1.95 V and a ΔV_oc of 0.45 V at 295 K. When the temperature declines from 295 to 200 K, the obtained V_oc remains comparably stable in the vicinity of 1.5 V while the corresponding ΔV_oc values show a more significant increase. Our findings suggest that the V_oc of CH₃NH₃PbBr₃ cells is primarily limited by the interface losses induced by the charge extraction layer rather than by bulk dominated recombination losses. These findings are important for developing strategies how to further enhance the V_oc of CH₃NH₃PbBr₃‐based solar cells.     

Substitution reactions of metallic complexes of 2,2′,2″-triaminotriethylamine. XVI. Kinetics of the (oxalato)(2,2′,2″-triaminotriethylamine) cobalt(III) cation in dilute and concentrated acid

The main emphasis in the study has been the investigation of the kinetics of the stepwise reactions of [Co(tren)C₂O₄]⁺ ion [tren = 2,2’,2”-triaminotriethylamine, N(CH₂CH₂NH₂)₃] in both dilute and concentrated acids, as well as the characterization in solution of some new Co(III) tren complexes. The aquation reaction was conducted in 1.0 M HClO₄ solution under various conditions. Protonation of a carbonyl oxygen in the complex appeared to increase the lability of the Co—O moiety, leading to a unidentate oxalate ligand. The stepwise anation of [Co- (tren)C₂O₄]+ to [Co(tren)Cl₂]+ in concentrated HCl was also followed. Both systems react by a dissociative reaction mechanism.     

Occurrence of sym-homospermidine in extremely thermophilic bacteria

Triamines produced by an extreme thermophile, Thermus thermophilus, were isolated and their chemical structures were determined. It was found that two novel triamines, norspermidine (1,7-diamino-4-azaheptane, NH₂(CH₂)₃· NH(CH₂)₃NH₂) and sym-homospermidine (1,9-diamino-5-azanonane, NH₂(CH₂)₄NH· (CH₂)₄NH₂) are present in the thermophile cells in addition to spermidine (1,8-diamino-4-azaoctane, NH₂(CH₂)₃NH(CH₂)₄NH₂).     

The Amide Route in Imine Metathesis with Imidomolybdenum Catalysts: A Model DFT Study

Gradient-corrected density-functional computations (BP86/ECP1 level) confirm the viability of the recently proposed reaction pathway for imine metathesis with imidomolybdenum(VI) species [Mo(NR)₂L_x] (e.g., L_x = Cl₂, DME; R = tBu). In addition to a Chauvin-type [2+2] addition-elimination mechanism, model calculations for the [MoCl₂(NH)₂] + NH₃ + CH₂NH system corroborate the suspected involvement of amido intermediates such as [MoCl₂(NH)(NH₂)₂] and . Several catalytic cycles are characterised that differ in the stereochemistry of the ligands about Mo. The lowest computed rate-determining barriers are only a few kcal mol^-1 higher than that obtained for the Chauvin-type mechanism in the [MoCl₂(NH)₂] + CH₂NH system via , provided the necessary H-atom transfers are catalysed efficiently by traces of base.Electronic Supplementary Material available.     

Effects of Nitrapyrin [2-Chloro-6-(Trichloromethyl) Pyridine] on the Obligate Methanotroph Methylosinus trichosporium OB3b

Nitrapyrin inhibited growth, CH₄ oxidation, and NH₄⁺ oxidation, but not the oxidation of CH₃OH, HCHO, or HCOONa, by Methylosinus trichosporium OB3b, suggesting that nitrapyrin acts against the methane monooxygenase enzyme system. The inhibition of CH₄ oxidation could be reversed by repeated washing of nitrapyrin-inhibited cells, indicating that its effect is bacteriostatic. The addition of Cu²⁺ did not release the inhibition. Methane oxidation was also inhibited by 6-chloro-2-picoline. These data suggest that the mode of action of nitrapyrin on M. trichosporium is different from that on chemoautotrophic NH₄⁺ oxidizers or methanogens.     

Deodorizing Mechanism of (–)-Epigallocatechin Gallate against Methyl Mercaptan

The deodorizing mechanism of (-)-epigallocatechin gallate (EGCg), the main constituent of a green tea extract, against methyl mercaptan (CH₃SH) was investigated. EGCg showed deodorizing activity against CH₃SH by a chemical reaction between EGCg and CH₃SH. The non-volatile reaction products were identified to be compounds introducing a methylthio and/or a methylsulfinyl group into the B ring of EGCg, and gaseous oxygen was necessary for deodorizing activity. From these results, it was assumed that the deodorizing mechanism of EGCg was due to the addition of a methylthio group to the ortho-quinone generated by atmospheric oxygen. It was also found that secondary compounds produced by the reaction between EGCg and CH₃SH had a stronger deodorizing activity than that of EGCg itself.     

Mechanism for the Coupled Photochemistry of Ammonia and Acetylene: Implications for Giant Planets,Comets and Interstellar Organic Synthesis

Laboratory studies provide a fundamental understanding of photochemical processes in planetary atmospheres. Photochemical reactions taking place on giant planets like Jupiter and possibly comets and the interstellar medium are the subject of this research. Reaction pathways are proposed for the coupled photochemistry of NH₃ (ammonia) and C₂H₂ (acetylene) within the context Jupiter’s atmosphere. We then extend the discussion to the Great Red Spot, Extra-Solar Giant Planets, Comets and Interstellar Organic Synthesis. Reaction rates in the form of quantum yields were measured for the decomposition of reactants and the formation of products and stable intermediates: HCN (hydrogen cyanide), CH₃CN (acetonitrile), CH₃CH = N-N = CHCH₃ (acetaldazine), CH₃CH = N-NH₂ (acetaldehyde hydrazone), C₂H₅NH₂ (ethylamine), CH₃NH₂ (methylamine) and C₂H₄ (ethene) in the photolysis of NH₃/C₂H₂ mixtures. Some of these compounds, formed in our investigation of pathways for HCN synthesis, were not encountered previously in observational, theoretical or laboratory photochemical studies. The quantum yields obtained allowed for the formulation of a reaction mechanism that attempts to explain the observed results under varying experimental conditions. In general, the results of this work are consistent with the initial observations of Ferris and Ishikawa (1988). However, their proposed reaction pathway which centers on the photolysis of CH₃CH = N-N = CHCH₃ does not explain all of the results obtained in this study. The formation of CH₃CH = N-N = CHCH₃ by a radical combination reaction of CH₃CH = N? was shown in this work to be inconsistent with other experiments where the CH₃CH = N? radical is thought to form but where no CH₃CH = N-N = CHCH₃ was detected. The importance of the role of H atom abstraction reactions was demonstrated and an alternative pathway for CH₃CH = N-N = CHCH₃ formation involving nucleophilic reaction between N₂H₄ and CH₃CH = NH is advanced.