Stability Of CH Research Articles

Thermochemistry and Reaction Kinetics of Secondary Ethyl Radical of Methyl Ethyl Sulfide, CH<sub>3</sub>SCH•CH<sub>3</sub>, with <sup>3</sup>O<sub>2</sub> to CH<sub>2</sub>SCH(OO•)CH<sub>3</sub>

The quantum Rice-Ramsperger-Kassel (QRRK) theory is used to analyze the reaction between the activated CH₃S CH•CH₃ and molecular oxygen to account for further reaction and collisional and deactivation. hydroxyl radicals initiate the oxidation of Methyl ethyl sulfide (CH₃SCH₂CH₃) and MES (methylthioethane) under combustion conditions. The CBS-QB3 and G3MP2B3 composite and M062X/6-311+G(2d, p) DFT methods was used to study the thermochemical properties of reactants, products and transition states. These thermochemical properties are used for the calculations for kinetic and thermochemical parameters. Under high pressure and low temperature, isomerization and stabilization of the CH₃SCH(OO•)CH₃ adduct is of importance. Under atmospheric pressure and at temperatures between above 600 ~ 800 K reactions of the chemically activated peroxy adduct become important relative to stabilization. The reaction between CH₃SCH•CH₃ and O₂ forms an energized peroxy adduct CH₃SCH(OO•)CH₃ with a calculated well depth of 30.2 kcal/mol at the CBS-QB3 level of theory. Kinetic parameters are calculated using the thermochemical properties of products, reactants and transition states obtained using under CBS-QB3 method of calculation. At temperature below 500 K, Stabilization of CH₃SCH(OO•)CH₃ adduct is of importance. Temperature of 500-900 K, is optimal for intramolecular hydrogen shift and the isomerization of CH₃SCH(OO•)CH₃ adduct. At temperature above 800 K, all of the subsequent reaction paths are of importance. For a reaction to move forward under pressure 1-4 atm, the recommended optimal temperature is between 600-800 K. A new pathway for the CH₃SCH(OO•)CH₃ adduct is observed, the attachment of peroxyl oxygen radical to sulfur followed by carbon-sulfur bond dissociation and formation of oxygen-sulfur and oxygen-carbon double bonds.

Multifunctional core-shell-like nanoarchitectures for hybrid supercapacitors with high capacity and long-term cycling durability

Transition metal oxide/hydroxide with multifunctional hierarchical nanostructures has attracted widespread attention in supercapacitors (SCs) because of their large accessible surface area, high electrochemical activity and superior redox chemistry. Herein, core-shell-like copper (Cu) hydroxide nanotube arrays grafted nickel aluminum layered double hydroxide nanosheets were facilely synthesized on porous Cu foam (CH NTAs@NiAl LDH NSs) for use as an efficient battery-type electrode in hybrid SCs. With the synergistic effects of NiAl LDH NSs on well-adhered CH NTAs/CF, the core-shell-like composite (prepared for 24 h) delivered a maximum areal capacity of 334.3 μAh/cm2 at a current density of 3 mA/cm2 in 2 M KOH electrolyte, which is comparatively higher than other samples synthesized at different growth times. Moreover, the core-shell-like CH NTAs@NiAl LDH NSs-24 demonstrated an outstanding cycling stability of 134.3% after 10,000 cycles. Utilizing high capacity and stability of CH NTAs@NiAl LDH NSs-24, a pouch-type hybrid SC was further assembled with core-shell-like composite as a positive electrode and reduced graphene oxide as a negative electrode with a filter paper as a separator in aqueous alkaline electrolyte. The hybrid SC showed a high areal capacity of 250 μAh/cm2 at 2 mA/cm2 with maximum areal energy and power densities of 181.9 μWh/cm2 and 24,991.5 μW/cm2, respectively. Successfully harvesting the solar energy via solar cell panel and subsequently delivering the stored energy to switching and proximity applications also demonstrated the real-time applicability of our hybrid SCs.

Enhanced Photoluminescence and Stability of CH3NH3PbBr3 Perovskite Nanocrystals with Protonated Melamine

AbstractThe surface of CH3NH3PbBr3 perovskite nanocrystals (PNCs) plays a critical role in determining their optical properties and stability. The introduction of capping ligands can enhance photoluminescence (PL), reduce non‐radiative recombination, and improve stability. Here, we report a facile synthesis of CH3NH3PbBr3 PNCs with strong and highly stable green PL using melamine (Mela) as a simple and low‐cost capping ligand. The resulting CH3NH3PbBr3/Mela PNCs have cubic phase crystal structure with an average particle size of 5.29±0.06 nm. The optical absorption and PL of the CH3NH3PbBr3/Mela PNCs with narrow bandwidth can be tuned within the visible region, and the PL quantum yield (QY) reached 52.3% compared to 0.4% the pristine CH3NH3PbBr3 PNCs. A synergistic effect between NH3+ and the electron‐rich nitrogen atoms together with p‐p stacking capacity, likely contributes to enhance the PL by effectively passivating of the trap states of PNCs. Furthermore, melamine‐capped PNCs show high stability in protic solvents as a result of the steric bulkiness of the triazine rings, owing to the planar structure together with hydrogen bonding of melamine, which prevents solvent molecules from reaching and reacting with the core of PNCs. This study demonstrates a simple and effective approach for stabilizing PNCs for potential applications such as solar cells and LEDs.

Structure and Spin State of Iron(II) Assembled Complexes Using 9,10-Bis(4-pyridyl)anthracene as Bridging Ligand

Assembled complexes, [Fe(NCX)2(bpanth)2]n (X = S, Se, BH3; bpanth = 9,10-bis(4-pyridyl)anthracene), were synthesized. The iron for the three complexes was in temperature-independent high spin state by 57Fe Mössbauer spectroscopy and magnetic susceptibility measurement. X-ray structural analysis revealed the interpenetrated structure of [Fe(NCS)2(bpanth)2]n. In the local structure around the iron atom, the coordinated pyridine planes were shown to be a parallel type, which is in accordance with the results investigated by density functional theory (DFT) calculation. This complex (X = S) has CH–π interactions between the H atom of coordinated pyridine and the neighboring anthracene of the other 2D grid. It was suggested that the interpenetrated structure was supported by the stabilization of CH–π interaction, and this intermolecular interaction forced the relatively unstable parallel structure. That is, the unstable local structure is compensated by the stabilization due to intermolecular interaction, which controlled the spin state as high spin state.

Microencapsulation of chlorthalidone by spray-drying of double emulsion and melt granulation coating

ABSTRACTChlorthalidone (CH) is indicated in the management of hypertension either alone or in combination with other antihypertensive drugs, but it displays poor solubility and stability limiting its use in the development of new pharmaceutical alternatives. Spray-drying of double emulsions (SDE) and melt granulation coating (MGC) technologies were used for enhancing the stability of CH by using Eudragit® L30D-55 (EUD), Opadry® II (OPA), or Kollicoat® IR (KIR) as wall materials. SDE and MGC microcapsules containing CH were evaluated for particle size, morphology, release profiles, accelerated storage, and thermo-oxidative stability. Both types of microcapsules showed higher solubility (>80% in 20 min), lower degradation (<2%) under accelerated storage condition, and lower thermo-oxidative degradation than pure CH. However, SDE microcapsules showed smaller particle sizes (<16 µm) than MGC microcapsules (>700 µm), which widens the opportunity of incorporating microcapsules to dosage forms requiring different particle sizes for achieving their functionality.

Study on the stability of CH3NH3PbI3films and the effect of post-modification by aluminum oxide in all-solid-state hybrid solar cells

Degradation of perovskite has been a big problem in all-solid-state perovskite solar cells, although many researchers mainly focus on the high efficiency of these solar cells. This paper studies the stability of CH3NH3PbI3 films and finds that CH3NH3PbI3 is sensitive to moisture. The degradation reaction is proposed according to UV-Vis spectra and XRD results. In order to improve the degradation of CH3NH3PbI3, we introduce aluminum oxide as a post-modification material into all-solid-state perovskite solar cells for the first time. UV-Vis spectra show that Al2O3 modification could maintain the absorption of CH3NH3PbI3 after degradation. XRD results reveal that Al2O3 could protect perovskite from degradation. Moreover, the device post-modified by Al2O3 has shown more brilliant stability than that without modification when exposed to moisture. EIS results and dark current illustrate that the modification increased interface resistance in the dark, indicating the restrained electron recombination process.

Molecular orbital studies of the stability of CH+5 and BH5

Molecular orbital studies of the stability of CH+5 and BH5

Kinetics and Stability of CH4–CO2 Mixed Gas Hydrates during Formation and Long‐Term Storage

The formation of CH4-CO2 mixed gas hydrates was observed by measuring the change of vapor-phase composition using gas chromatography and Raman spectroscopy. Preferential consumption of carbon dioxide molecules was found during hydrate formation, which agreed well with thermodynamic calculations. Both Raman spectroscopic analysis and the thermodynamic calculation indicated that the kinetics of this mixed gas hydrate system was controlled by the competition of both molecules to be enclathrated into the hydrate cages. However, the methane molecules were preferentially crystallized in the early stages of hydrate formation when the initial methane concentration was much less than that of carbon dioxide. According to the Roman spectra, pure methane hydrates first formed under this condition. This unique phenomenon suggested that methane molecules play important roles in the hydrate formation process. These mixed gas hydrates were stored at atmospheric pressure and 190 K for over two months to examine the stability of the encaged gases. During storage, CO2 was preferentially released. According to our thermodynamic analysis, this CO2 release was due to the instability of CO2 in the hydrate structure under the storage conditions.

Sampling and stability of methyl bromide on activated charcoal

Monitoring methyl bromide (CH 3 Br) emission into the atmosphere following soil fumigations requires sensitive and reproducible sampling methods. The factors affecting the sampling efficiency and stability of CH 3 Br on activated charcoal sampling tubes were identified and evaluated in this study. The number of tubes required for accurate sampling using activated coconut and petroleum charcoal tubes was determined for various sampling flow rates and sampling intervals. Breakthrough of CH 3 Br on both types of tubes increased with increasing flow rates and sampling intervals. CH 3 Br hydrolyzed rapidly on moist charcoal, and the reaction was enhanced by temperature. At 40 °C and 21% moisture content, the half-lives of degradation were only 11 h on coconut charcoal and 17 h on petroleum charcoal. The rapid hydrolysis of CH 3 Br on charcoal was caused by the high pH of the charcoal. To prevent degradation of CH 3 Br bromide, charcoal samples should be always kept at low temperature and under dry conditions during transport and storage. Correction for loss due to degradation during sampling may be necessary if samples are taken from atmospheres with high temperature and humidity.

Monte Carlo and molecular orbital study of carbon-centered radicals in water: Solvent effects on the conformation and stability of CH(OH)CN, CH(OH) 2 and CH(CN) 2

Monte Carlo simulations and MO calculations were carried out for three carbon-centered radicals, CH(OH)CN, CH(OH) 2 and CH(CN) 2, in H 2O, and the relative stability of these radicals was examined in connection with the substitution pattern. The solvation free energy changes along the OH rotation were calculated for CH(OH)CN and CH(OH) 2 by statistical perturbation theory, and the energy minimum conformations of these radicals were determined. The solvation free energy differences among the three radicals were calculated by the mutation technique, and merostabilization energy of CH(OH)CN in water was calculated to be −17.52 kcal mol −1, which is much larger than that in the gas phase. The electronic structures of these radicals in the H 2O solution were calculated by ab initio ROHF MIDI-4 ∗ MO method including the solvent H 2O molecules represented by point charge approximation. The calculated charge and spin populations indicated that the large stabilization energy of CH(OH)CN in H 2O was caused by a strong interaction between the OH group of CH(OH)CN and H 2O, and this effect was found only in CH(OH)CN which is substituted asymmetrically by electron-donor and electron-acceptor groups.

Reversible Displacement of Chemisorbed n-Alkanethiol Molecules on Au(111) Surface: An Atomic Force Microscopy Study

Atomic force microscopy has been used to study the structure and the stability of CH[sub 3](CH[sub 2])[sub 9]SH and CH[sub 3](CH[sub 2])[sub 17]SH molecules self-assembled on a Au(111) surface as a function of the load applied by the tip. Atomic resolution images taken during a loading and unloading cycle have revealed two sudden transitions corresponding to changes of the periodicity from a ([radical] 3 x [radical] 3)R30[degrees] (due to thiol layers) to a (1 x 1) due to Au(111), and back to the ([radical] 3 x [radical] 3)R30[degrees] of thiol layers. These results represent the first observation that under high load, self-assembled n-alkanethiol molecules on Au(111) can be reversibly displaced on the substrate surface by a sharp tip during the scan. 16 refs., 3 figs.

Observation of a stable methoxy intermediate on Cr(110)

Abstract Ultraviolet photoelectron spectroscopy (UPS) and work function changes are used to identify a stable methoxy intermediate, CH 3 O(ads), on Cr(110) at 90 K following low exposures of methanol, CH 3 OH(g). Higher methanol exposures at 90 K add subsequent layers of physisorbed methanol which desorb above 120 K. Methoxy dissociation into atomic fragments occurs between 250 and 400 K. The absence of a stable CO(ads) dissociation intermediate indicates that methyl group dehydrogenation is rate limiting on Cr(110). As was previously found on Fe(100) and Mo(100), the stability of CH 3 O(ads) over CO(ads) on Cr(110) is opposite of that proposed by Sexton based upon relative heats of adsorption. Consideration of the CH 3 O: metal and CO: metal bonding mechanisms leads to the proposition that substrate electronic properties, rather than steric or substrate morphological factors, are responsible for the anomalous methoxy stability on these surfaces.

Stable γ‐distonic oxonium ions: R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCHR′ĊH2CHR″ and their characteristic reaction

AbstractThe γ‐distonic radical ions R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}CHR′CH2ĊHR″ and their molecular ion counterparts R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^{{\rm + } \cdot } $\end{document}CHR′CH2CH2R″ have been studied by isotopic labelling and collision‐induced dissociation, applying a potential to the collision cell in order to separate activated from spontaneous decompositions. The stability of CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH(CH3)CH2ĊHCH3, C2H5\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH(CH3)CH2ĊHCH3, CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH(CH3)CH2ĊH2, CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH2CH2ĊHCH3 and C2H5\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH2CH2ĊHCH3, has been demonstrated and their characteristic decomposition, alcohol loss, identified. For all these γ‐distonic ions, the 1,4‐H abstraction leading to their molecular ion counterpart exhibits a primary isotope effect.

Identification and stability of CH 3, CH 2, and CH species on Co and Ni surfaces, a PES investigation

Identification and stability of CH 3, CH 2, and CH species on Co and Ni surfaces, a PES investigation

Identification and stability of CH 3, CH 2, and CH species on Co and Ni surfaces, a Pes investigation

CH 3, CH 2, CH, and C, adsorbed on polycrystalline Co or Ni, are idendified and characterized by XPS and UPS with respect to peak positions and temperature regimes of existence. The species are generated by adsorption and subsequent dissociation of CH 3Cl or CH 2Cl 2. Due to the early dissociation of the CC1 bond it is possible to study the CH n species and their stepwise dehydrogenation without interference. Constant and temperature independent peak positions over ranges of at least 50 K on Co and of about 40 K on Ni indicate that the peak maxima used for identification are generated by the respective single species and not by superimposition of two or more peaks of species drifting through the dehydrogenation.

Thermal stability of adsorbed CH3NCO on Cu{110} and Pt{110} from vibrational and photoelectron spectroscopies

Abstract The thermal stability of CH 3 NCO adsorbed on Cu{110} and Pt{110} is investigated using HREELS, TPD, and ARUPS. CH 3 NCO desorbs largely without fragmentation from Cu{110}, but on Pt{110} only about 20% of the adsorbed CH 3 NCO desorbs intact, with 80% decomposing on the surface at T > 200 K into CO(a), H(a), CH x (a), N(a) and NH y (a) fragments. The kinetics of the surface decomposition were characterised for 220 T K by HREELS and the activation energy for CH 3 NCO decomposition was found to vary strongly as a function of coverage.

The electronic structure and stability of CH +5 and CH −5

Geometry-optimized minimum basis set STO calculations are given for the CH − 5 and CH 5 − ions, together with double ζ-STO results at the computed minima, which give the lowest energies yet reported for the ions. An interpretation in terms of electron pairs is given for the relative stabilities of the various structures.