Computational investigation of O2 reduction and diffusion on 25% Sr-doped LaMnO3 cathodes in solid oxide fuel cells

The oxygen reduction reaction (ORR) and diffusion mechanisms on 25% Sr-doped LaMnO(3) (LSM) cathode materials as well as their kinetic behavior have been studied by using spin-polarized density functional theory (DFT) calculations. Bader charge and frequency analyses were carried out to identify the oxidation state of adsorbed oxygen species. DFT and molecular dynamics (MD) results show that the fast O(2) adsorption/reduction process via superoxide and peroxide intermediates is energetically favorable on the Mn site rather than on the Sr site. Furthermore, the higher adsorption energies on the Mn site of the (110) surface compared to those on the (100) surface imply that the former is more efficient for O(2) reduction. Significantly, we predict that oxygen vacancies enhance O(2) reduction kinetics and that the O-ion migration through the bulk is dominant over that on the surface of the LSM cathode.

Anthracyclines disrupt telomere maintenance by telomerase through inducing PinX1 ubiquitination and degradation

Telomere maintenance is essential for cancer growth. Induction of telomere dysfunction, for example, by inhibition of telomeric proteins or telomerase, has been shown to strongly enhance cancer cells' sensitivity to chemotherapies. However, it is not clear whether modulations of telomere maintenance constitute cancer cellular responses to chemotherapies. Furthermore, the manner in which anti-cancer drugs affect telomere function remains unknown. In this study, we show that anthracyclines, a class of anti-cancer drugs widely used in clinical cancer treatments, have an active role in triggering telomere dysfunction specifically in telomerase-positive cancer cells. Anthracyclines interrupt telomere maintenance by telomerase through the downregulation of PinX1, a protein factor responsible for targeting telomerase onto telomeres, thereby inhibiting telomerase association with telomeres. We further demonstrate that anthracyclines downregulate PinX1 by inducing this protein degradation through the ubiquitin-proteasome-dependent pathway. Our data not only reveal a novel action for anthracyclines as telomerase functional inhibitors but also provide a clue for the development of novel anti-cancer drugs based on telomerase/telomere targeting, which is actively investigated by many current studies.

Thermal decomposition of ethanol. 4. Ab initio chemical kinetics for reactions of H atoms with CH3CH2O and CH3CHOH radicals

The potential energy surfaces of H-atom reactions with CH(3)CH(2)O and CH(3)CHOH, two major radicals in the decomposition and oxidation of ethanol, have been studied at the CCSD(T)/6-311+G(3df,2p) level of theory with geometric optimization carried out at the BH&HLYP/6-311+G(3df,2p) level. The direct hydrogen abstraction channels and the indirect association/decomposition channels from the chemically activated ethanol molecule have been considered for both reactions. The rate constants for both reactions have been calculated at 100-3000 K and 10(-4) Torr to 10(3) atm Ar pressure by microcanonical VTST/RRKM theory with master equation solution for all accessible product channels. The results show that the major product channel of the CH(3)CH(2)O + H reaction is CH(3) + CH(2)OH under atmospheric pressure conditions. Only at high pressure and low temperature, the rate constant for CH(3)CH(2)OH formation by collisonal deactivation becomes dominant. For CH(3)CHOH + H, there are three major product channels; at high temperatures, CH(3)+CH(2)OH production predominates at low pressures (P < 100 Torr), while the formation of CH(3)CH(2)OH by collisional deactivation becomes competitive at high pressures and low temperatures (T < 500 K). At high temperatures, the direct hydrogen abstraction reaction producing CH(2)CHOH + H(2) becomes dominant. Rate constants for all accessible product channels in both systems have been predicted and tabulated for modeling applications. The predicted value for CH(3)CHOH + H at 295 K and 1 Torr pressure agrees closely with available experimental data. For practical modeling applications, the rate constants for the thermal unimolecular decomposition of ethanol giving key accessible products have been predicted; those for the two major product channels taking place by dehydration and C-C breaking agree closely with available literature data.

Ab initio chemical kinetic study on the reactions of ClO with C2H2 and C2H4

The mechanisms for the reactions of ClO with C(2)H(2) and C(2)H(4) have been investigated at the CCSD(T)/CBS level of theory. The results show that in both systems, the interaction between the Cl atom of the ClO radical and the triple and double bonds of C(2)H(2) and C(2)H(4) forms prereaction van der Waals complexes with the O-Cl bond pointing perpendicularly toward the π-bonds, both with 2.1 kcal/mol binding energies. The mechanism is similar to those of the HO-C(2)H(2)/C(2)H(4) systems. The rate constants for the low energy channels have been predicted by statistical theory. For the reaction of ClO and C(2)H(2), the main channels are the production of CH(2)CO + Cl (k(1a)) and CHCO + HCl (k(1b)), with k(1a) = 1.19 × 10(-15)T(1.18) exp(-5814/T) and k(1b) = 6.94 × 10(-21) × T(2.60) exp(-6587/T) cm(3) molecule(-1) s(-1). For the ClO + C(2)H(4) reaction, the main pathway leads to C(2)H(4)O + Cl (k(2a)) with the predicted rate constant k(2a) = 2.13 × 10(-17)T(1.52) exp(-3849/T) in the temperature range of 300-3000 K. These rate constants are pressure-independent below 100 atm.

Ab initio chemical kinetic study on Cl + ClO and related reverse processes

The reaction of ClO with Cl and its related reverse processes have been studied theoretically by ab initio quantum chemical and statistical mechanical calculations. The geometric parameters of the reactants, products, and transition states are optimized by both UMPW1PW91 and unrestricted coupled-cluster single and double excitation (UCCSD) methods with the 6-311+G(3df) basis set. The potential energy surface has been further refined (with triple excitations, T) at the UCCSD(T)/6-311+G(3df) level of theory. The results show that Cl(2) and O ((3)P) can be produced by chlorine atom abstraction via a tight transition state, while ClOCl ((1)A(1)) and ClClO ((1)A') can be formed by barrierless association processes with exothermicities of 31.8 and 16.0 kcal/mol, respectively. In principle the O ((1)D) atom can be generated with a large endothermicity of 56.9 kcal/mol; on the other hand, its barrierless reaction with Cl(2) can readily form ClClO ((1)A'), which fragments rapidly to give ClO + Cl. The rate constants of both forward and reverse processes have been predicted at 150-2000 K by the microcanonical variational transition state theory (VTST)/Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The predicted rate constants are in good agreement with available experimental data within reported errors.

A characterization of local LOINC mapping for laboratory tests in three large institutions

OBJECTIVES

We characterized the use of laboratory LOINC® codes in three large institutions, focused on the following questions: 1) How many local codes had been voluntarily mapped to LOINC codes by each institution? 2) Could additional mappings be found by expert manual review for any local codes that were not initially mapped to LOINC codes by the local institution? and 3) Are there any common characteristics of unmapped local codes that might explain why some local codes were not mapped to LOINC codes by the local institution?

METHODS

With Institutional Review Board (IRB) approval, we obtained deidentified data from three large institutions. We calculated the percentage of local codes that have been mapped to LOINC by personnel at each of the institutions. We also analyzed a sample of unmapped local codes to determine whether any additional LOINC mappings could be made and identify common characteristics that might explain why some local codes did not have mappings.

RESULTS

Concept type coverage and concept token coverage (volume of instance data covered) of local codes mapped to LOINC codes were 0.44/0.59, 0.78/0.78 and 0.79/0.88 for ARUP, Intermountain, and Regenstrief, respectively. After additional expert manual mapping, the results showed mapping rates of 0.63/0.72, 0.83/0.80 and 0.88/0.90, respectively. After excluding local codes which were not useful for inter-institutional data exchange, the mapping rates became 0.73/0.79, 0.90/0.99 and 0.93/0.997, respectively.

CONCLUSIONS

Local codes for two institutions could be mapped to LOINC codes with 99% or better concept token coverage, but mapping for a third institution (a reference laboratory) only achieved 79% concept token coverage. Our research supports the conclusions of others that not all local codes should be assigned LOINC codes. There should also be public discussions to develop more precise rules for when LOINC codes should be assigned.

Computational studies on metathetical and redox processes of HOCl in gas phase. III. Its self-reaction and interactions with HNOx (x = 1-3)

The gas-phase redox reactions of HOCl with its self and HNO(x) (x = 1-3) have been studied theoretically by ab initio quantum chemical and statistical mechanical theories. The structures of reactants, intermediate complexes, products, and transition states were optimized at the MPW1PW91/6-311+G(3df,2p) level of theory. The potential energy surface of each reaction was refined at the CCSD(T)/6-311+G(3df,2p) level of theory. The most favorable products are predicted to be ClClO + H(2)O and ClOCl + H(2)O for the HOCl self-reaction (A), H(2)O + Cl + NO for the HOCl + HNO reaction (B), H(2)O + ClNO(2) for the HOCl + HONO-t reaction (C), H(2)O + cis-ClONO for the HOCl + HONO-c reaction (D). For the HOCl + HONO(2) reaction (E), only one dehydration reaction channel was considered to produce H(2)O + ClONO(2). The rate constants of all above five reactions have been predicted at 300-3000 K by the VTST/RRKM theory. The calculation shows that the theoretical rate constants are within the upper limits of experimental results. In addition, we calculated the equilibrium constant for the Cl(2)O + H(2)O --> HOCl + HOCl reaction, which is also in reasonable agreement with experimental data within the error of the available experimental enthalpy change.

Computational studies on metathetical and redox processes of HOCl in the gas phase: (II) reactions with ClO(x) (x = 1-4)

The reactions of HOCl + ClO(x) (x = 1-4) have been studied theoretically by ab initio quantum chemical and statistical mechanical methods. The structures of reactants, intermediates, products, and transition states were optimized at the MPW1PW91/6-311+G(3df,2p) level of theory, and the potential energy surface of each reaction was refined at the G2M and CCSD(T)/6-311+G(3df,2p) levels of theory. The most favorable reaction channels are predicted to be Cl-abstraction in HOCl + ClO with a barrier of 18.5 kcal/mol and H abstraction in HOCl + OClO with a barrier of 23.9 kcal/mol. In the HOCl + ClO(3) reaction both processes can occur; the barriers of Cl and H abstraction are 16.4 and 17.1 kcal/mol, respectively. In the HOCl + ClO(4) reaction, the H abstraction transition state lies below that of the reactants by 1.4 kcal/mol. The rate constants for all low barrier channels have been calculated in the temperature range 200-3000 K by statistical theory. In addition, the rate constant for the reverse of the HOCl + ClO reaction, Cl(2)O + OH --> HOCl + ClO, has been predicted; the result is in good agreement with the bulk of available experimental data.

Fluorescence signals of quantum dots influenced by spatially controlled array structures

Fluorescence signals of quantum dots (QDs) influenced by different array structures of gold-coated silicon nanorods (SiNRs) were investigated via experimental observations and two-dimensional (2D) finite element method (FEM) simulations. On the densest gold-coated SiNRs array structure, the highest QD fluorescence quenching rates were observed and on the sparsest array structure, the highest QD fluorescence enhancement rates were observed. By developing a new technique which obtains the optical image of the array structures without losing information about the QD locations, we were able to further investigate how the QD fluorescence is influenced by spatially controlled array structures.

Dynamics of reactions O((1)D)+C(6)H(6) and C(6)D(6)

The reaction between O((1)D) and C(6)H(6) (or C(6)D(6)) was investigated with crossed-molecular-beam reactive scattering and time-resolved Fourier-transform infrared spectroscopy. From the crossed-molecular-beam experiments, four product channels were identified. The major channel is the formation of three fragments CO+C(5)H(5)+H; the channels for formation of C(5)H(6)+CO and C(6)H(5)O+H from O((1)D)+C(6)H(6) and OD+C(6)D(5) from O((1)D)+C(6)D(6) are minor. The angular distributions for the formation of CO and H indicate a mechanism involving a long-lived collision complex. Rotationally resolved infrared emission spectra of CO (1<or=upsilon<or=6) and OH (1<or=upsilon<or=3) were recorded with a step-scan Fourier-transform spectrometer. At the earliest applicable period (0-5 mus), CO shows a rotational distribution corresponding to a temperature of approximately 1480 K for upsilon=1 and 920-700 K for upsilon=2-6, indicating possible involvement of two reaction channels; the vibrational distribution of CO corresponds to a temperature of approximately 5800 K. OH shows a rotational distribution corresponding to a temperature of approximately 650 K for upsilon=1-3 and a vibrational temperature of approximately 4830 K. The branching ratio of [CO]/[OH]=2.1+/-0.4 for O((1)D)+C(6)H(6) and [CO]/[OD]>2.9 for O((1)D)+C(6)D(6) is consistent with the expectation for an abstraction reaction. The mechanism of the reaction may be understood from considering the energetics of the intermediate species and transition states calculated at the G2M(CC5) level of theory for the O((1)D)+C(6)H(6) reaction. The experimentally observed branching ratios and deuterium isotope effect are consistent with those predicted from calculations.

Chemosensitisation by manganese superoxide dismutase inhibition is caspase-9 dependent and involves extracellular signal-regulated kinase 1/2

Chemoresistance and therapeutic selectivity are major obstacles to successful chemotherapy of ovarian cancer. Manganese superoxide disumutase (MnSOD) is an important antioxidant enzyme responsible for the elimination of superoxide radicals. We reported here that MnSOD was significantly elevated in ovarian cancer cells and its overexpression was one of the mechanisms that increased resistance to apoptosis in cancer cells. Knockdown of MnSOD by small-interfering RNA (siRNA) led to an increase in superoxide generation and sensitisation of ovarian cancer cells to the two front-line anti-cancer agents doxorubicin and paclitaxel whose action involved free-radical generation. This synergistic effect was not observed in non-transformed ovarian surface epithelial cells. Furthermore, our results revealed that this combination at the cellular level augmented activation of caspase-3 and caspase-9, but not caspase-8, suggesting involvement of an intrinsic apoptotic pathway. Evaluation of signalling pathways showed that MnSOD siRNA enhanced doxorubicin- and paclitaxel-induced phosphorylation of extracellular signal-regulated kinase 1/2. Akt activation was not affected. These results identify a novel chemoresistance mechanism in ovarian cancer, and show that combination of drugs capable of suppressing MnSOD with conventional chemotherapeutic agents may provide a novel strategy with a superior therapeutic index and advantage for the treatment of refractory ovarian cancer.

Computational study on kinetics and mechanisms of unimolecular decomposition of succinic acid and its anhydride

The mechanisms and kinetics of unimolecular decomposition of succinic acid and its anhydride have been studied at the G2M(CC2) and microcanonical RRKM levels of theory. It was shown that the ZsgsZ conformer of succinic acid, with the Z-acid form and the gauche conformation around the central C-C bond, is its most stable conformer, whereas the lowest energy conformer with the E-acid form, ECGsZ, is only 3.1 kcal/mol higher in energy than the ZsgsZ. Three primary decomposition channels of succinic acid producing H2O + succinic anhydride with a barrier of 51.0 kcal/mol, H2O + OCC2H3COOH with a barrier of 75.7 kcal/mol and CO2 + C2H5COOH with a barrier of 71.9 kcal/mol were predicted. The dehydration process starting from the ECGCZ-conformer is found to be dominant, whereas the decarboxylation reaction starting from the ZsgsZ-conformer is only slightly less favorable. It was shown that the decomposition of succinic anhydride occurs via a concerted fragmentation mechanism (with a 69.6 kcal/mol barrier), leading to formation of CO + CO2 + C2H4 products. On the basis of the calculated potential energy surfaces of these reactions, the rate constants for unimolecular decomposition of succinic acid and its anhydride were predicted. In addition, the predicted rate constants for the unimolecular decomposition of C2H5COOH by decarboxylation (giving C2H6 + CO2) and dehydration (giving H3CCHCO + H2O) are in good agreement with available experimental data.

Development of recombinant adeno-associated virus and adenovirus cocktail system for efficient hTERTC27 polypeptide-mediated cancer gene therapy

The low in vivo transduction efficiency of recombinant adeno-associated virus (rAAV) and the undesirably strong immunogenicity of adenovirus (rAdv) have limited their clinical utilization in cancer gene therapy. We have previously demonstrated that intratumoral injection of rAAV expressing a C-terminal polypeptide of human telomerase reverse transcriptase (rAAV-hTERTC27) effectively inhibits the growth of glioblastoma xenografts in nude mice. To further improve its efficacy, we combined rAAV-hTERTC27 with rAdv and investigated the efficiency of the cocktail vectors in vivo. At a nontherapeutic dose (1 x 10(8) plaque-forming units (PFUs)), rAdv-null and rAdv-hTERTC27 were equipotent in enhancing the therapeutic efficacy of rAAV-hTERTC27 (1.5 x 10(11) v.g.), and complete tumor regression was achieved in 25% of the treated animals. Importantly, the combination of rAAV-hTERTC27 and a therapeutic dose (2.5 x 10(9) PFU) of rAdv-hTERTC27 significantly augmented the therapeutic effects and led to a 38% complete tumor regression rate. In vivo optical imaging also showed that rAAV-luc/rAdv-luc cocktail vectors could synergistically enhance the early transient and latent sustained expression of luciferase, as compared to rAdv-luc and rAAV-luc alone. These findings suggest that the combination of rAAV-hTERTC27 and a therapeutic dose of rAdv-hTERTC27 is potentially a promising treatment for glioblastoma, and the rAAV/rAdv cocktail vector system warrants further development for cancer gene therapy.

Highly active nanocrystalline TiO(2) photoelectrodes

A simple method for the fabrication of highly photoactive nanocrystalline two-layer TiO(2) electrodes for solar cell applications is presented. Diluted titanium acetylacetonate has been used as a precursor for covering SnO(2):F (FTO) films with dense packed TiO(2) nanocrystallites. The nanoporous thick TiO(2) film follows the dense packed thin TiO(2) film as a second layer. For the latter, amorphous TiO(2) nanoparticles have been successfully synthesized by a sol-gel technique in an acidic environment with pH<1 and hydrothermal growth at a temperature of 200 °C. The acidic nanoparticle gel was neutralized by basic ammonia and a TiO(2) gel of pH 5 was obtained; this pH value is higher than the recently reported value of 3.1 (Park et al 2005 Adv. Mater. 17 2349-53). Highly interconnected, nanoporous, transparent and active TiO(2) films have been fabricated from the pH 5 gel. SEM, AFM and XRD analyses have been carried out for investigation of the crystal structure and the size of nanoparticles as well as the surface morphology of the films. Investigation of the photocurrent-voltage characteristics has shown improvement in cell performance along with the modification of the surface morphology, depending on pH of the TiO(2) gel. Increasing the pH of the gel from 2.1 to 5 enhanced the overall conversion efficiency of the dye-sensitized solar cells by approximately 30%. An energy conversion efficiency of 8.83% has been achieved for the cell (AM1.5, 100  mWcm(-2) simulated sunlight) compared to 6.61% efficiency in the absence of ammonia in the TiO(2) gel.

Photodissociation Dynamics of Phenol†

The photodissociation of phenol at 193 and 248 nm was studied using multimass ion-imaging techniques and step-scan time-resolved Fourier-transform spectroscopy. The major dissociation channels at 193 nm include cleavage of the OH bond, elimination of CO, and elimination of H(2)O. Only the former two channels are observed at 248 nm. The translational energy distribution shows that H-atom elimination occurs in both the electronically excited and ground states, but elimination of CO or H(2)O occurs in the electronic ground state. Rotationally resolved emission spectra of CO (1 <or= v <or= 4) in the spectral region of 1860-2330 cm(-1) were detected upon photolysis at 193 nm. After a correction for rotational quenching, CO (v <or= 4) shows a nascent rotational temperature of approximately 4600 K. The observed vibrational distribution of (v = 1)/(v = 2)/(v = 3)/(v = 4) = 64.3/22.2/9.1/4.4 corresponds to a vibrational temperature of 3350 +/- 20 K. An average rotational energy of 6.9 +/- 0.7 kcal mol(-1) and vibrational energy of 3.8 +/- 0.7 kcal mol(-1) are observed for the CO product. The dissociation channels, translational energy distributions of the photofragment, and vibrational and rotational energies of product CO are consistent with potential energy surfaces from quantum chemical calculations and the branching ratios from an RRKM calculation.

Ab initio kinetics for the unimolecular reaction C6H5OH --> CO + C5H6

The unimolecular decomposition of C(6)H(5)OH on its singlet-state potential energy surface has been studied at the G2M//B3LYP/6-311G(d,p) level of theory. The result shows that the most favorable reaction channel involves the isomerization and decomposition of phenol via 2,4-cyclohexadienone and other low-lying isomers prior to the fragmentation process, producing cyclo-C(5)H(6) + CO as major products, supporting the earlier assumption of the important role of the 2,4-cyclohexadienone intermediate. The rate constant predicted by the microcanonical RRKM theory in the temperature range 800-2000 K at 1 Torr--100 atm of Ar pressure for CO production agrees very well with available experimental data in the temperature range studied. The rate constants for the production of CO and the H atom by O-H dissociation at atmospheric Ar pressure can be represented by k(CO) = 8.62 x 10(15) T(-0.61) exp(-37,300/T) s(-1) and k(H) = 1.01 x 10(71) T(-15.92) exp(-62,800/T) s(-1). The latter process is strongly P-dependent above 1000 K; its high- and low-pressure limits are given.

Mechanisms of the reactions of W AND W+ with H2O: computational studies

The mechanism of the reactions of W and W(+) with the water molecule have been studied for several lower-lying electronic states of tungsten centers at the CCSD(T)/6-311G(d,p)+SDD and B3LYP/6-31G(d,p)+SDD levels of theory. It is shown that these reactions are essentially multistate processes, during which lower-lying electronic states of the systems cross several times. They start with the formation of initial prereaction M(H(2)O) complexes with M-H(2)O bonding energies of 9.6 and 48.2 kcal/mol for M = W and W(+), followed by insertion of the metal center into an O-H bond with 20.0 and 53.3 kcal/mol barriers for neutral and cationic systems, respectively. The overall process of M + H(2)O --> t-HM(OH) is calculated to be highly exothermic, 48.4 and 48.8 kcal/mol for M = W and W(+). From the HM(OH) intermediate the reaction may proceed via several different channels, among which the stepwise HM(OH) --> HMO + H --> (H)(2)MO and concerted HM(OH) --> (H)(2)MO pathways are more favorable and can compete (energetically) with each other. For the neutral system (M = W), the concerted process is the most favorable, whereas for the charged system (M = W(+)), the stepwise pathway is slightly more favorable. From the energetically most favorable intermediate (H)(2)MO the reactions proceed via H(2)-molecule formation with a 53.1 kcal/mol activation barrier for the neutral system. For the cationic system, H-H formation and dissociation is an almost barrierless process. The overall reaction of W and W(+) with the water molecule leading to H(2) + MO formation is found to be exothermic by 48.2 and 39.8 kcal/mol, respectively. In the gas phase with the collision-less conditions the reactions W((7)S) + H(2)O --> H(2) + WO((3)Sigma(+)), and W(+)((6)D) + H(2)O --> H(2) + WO(+)((4)Sigma(+)) are expected to proceed via a 10.4 and 5.1 kcal/mol overall energy barrier corresponding to the first O-H dissociation at the TS1. On the basis of these PESs, we predict kinetic rate constants for the reactions of W and W(+) with H(2)O.

High pressure fourier transform infrared spectroscopy of poly(dA)poly(dT), poly(dA) and poly(dT)

The effect of hydrostatic pressure upon the DNA duplex, poly(dA)poly(dT), and its component single strands, poly(dA) and poly(dT) has been studied by fourier-transform infrared spectroscopy (FT-IR). The spectral data indicate that at 28 degrees C and pressures up to 12 kbar (1200 MPa) all three polymers retain the B conformation. Pressure causes the band at 967 cm(-1), arising from water-deoxyribose interactions, to shift to higher frequencies, a result consistent with increased hydration at elevated pressures. A larger pressure-induced frequency shift in this band is observed in the single stranded polymers than in the double stranded molecule, suggesting that the effect of pressure on the hydration of single strands may be greater than upon a double stranded complex. A pressure-dependent hypochromicity in the bands attributed to base stacking indicates that pressure facilitates the base stacking in the three polymers, in agreement with previous assessments of the importance of stacking in the stabilization of DNA secondary structure at ambient and high pressures.

Ab Initio Chemical Kinetics for the OH + HNCN Reaction†

The kinetics and mechanism of the reaction of the cyanomidyl radical (HNCN) with the hydroxyl radical (OH) have been investigated by ab initio calculations with rate constants prediction. The single and triplet potential energy surfaces of this reaction have been calculated by single-point calculations at the CCSD(T)/6-311+G(3df,2p) level based on geometries optimized at the B3LYP/6-311+G(3df,2p) and CCSD/6-311++G(d,p) levels. The rate constants for various product channels in the temperature range of 300-3000 K are predicted by variational transition-state and Rice-Ramsperger-Kassel-Marcus (RRKM) theories. The predicted total rate constants can be represented by the expressions ktotal=2.66 x 10(+2)xT-4.50 exp(-239/T) in which T=300-1000 K and 1.38x10(-20)xT2.78 exp(1578/T) cm3 molecule(-1) s(-1) where T=1000-3000 K. The branching ratios of primary channels are predicted: k1 for forming singlet HON(H)CN accounts for 0.32-0.28, and k4 for forming singlet HONCNH accounts for 0.68-0.17 in the temperature range of 300-800 K. k2+k7 for producing H2O+NCN accounts for 0.55-0.99 in the high-temperature range of 800-3000 K. The branching ratios of k3 for producing HCN+HNO, k6 for producing H2N+NCO, k8 for forming 3HN(OH)CN, k9 for producing CNOH+3NH, and k5+k10 for producing NH2+NCO are negligible. The rate constants for key individual product channels are provided in a table for different temperature and pressure conditions.

Computational Study on the Mechanisms and Energetics of Trimethylindium Reactions with H2O and H2S

The reactions of trimethylindium (TMIn) with H2O and H2S are relevant to the chemical vapor deposition of indium oxide and indium sulfide thin films. The mechanisms and energetics of these reactions in the gas phase have been investigated by density functional theory and ab initio calculations using the CCSD(T)/[6-31G(d,p)+Lanl2dz]//B3LYP/[6-31G(d,p)+Lanl2dz] and CCSD(T)/[6-31G(d,p)+Lanl2dz] //MP2/[6-31G(d,p)+Lanl2dz] methods. The results of both methods are in good agreement for the optimized geometries and relative energies. When TMIn reacts with H2O and H2S, initial molecular complexes [(CH3)3In:OH2 (R1)] and [(CH3)3In:SH2 (R2)] are formed with 12.6 and 3.9 kcal/mol binding energies. Elimination of a CH4 molecule from each complex occurs with a similar energy barrier at TS1 (19.9 kcal/mol) and at TS3 (22.1 kcal/mol), respectively, giving stable intermediates (CH3)2InOH and (CH3)2InSH. The elimination of the second CH4 molecule from these intermediate products, however, has to overcome very high and much different barriers of 66.1 and 53.2 kcal/mol, respectively. In the case of DMIn with H2O and H2S reactions, formation of both InO and InS is exothermic by 3.1 and 30.8 kcal/mol respectively. On the basis of the predicted heats of formation of R1 and R2 at 0 K and -20.1 and 43.6 kcal/mol, the heats of formation of (CH3)2InOH, (CH3)2InSH, CH3InO, CH3InS, InO, and InS are estimated to be -20.6, 31.8, and 29.0 and 48.4, 35.5, and 58.5 kcal/mol, respectively. The values for InO and InS are in good agreement with available experimental data. A similar study on the reactions of (CH3)2In with H2O and H2S has been carried out; in these reactions CH3InOH and CH3InSH were found to be the key intermediate products.

A theoretical study of surface reduction mechanisms of CeO(2)(111) and (110) by H(2)

Reaction mechanisms for the interactions between CeO(2)(111) and (110) surfaces are investigated using periodic density functional theory (DFT) calculations. Both standard DFT and DFT+U calculations to examine the effect of the localization of Ce 4f states on the redox chemistry of H(2)-CeO(2) interactions are described. For mechanistic studies, molecular and dissociative local minima are initially located by placing an H(2) molecule at various active sites of the CeO(2) surfaces. The binding energies of physisorbed species optimized using the DFT and DFT+U methods are very weak. The dissociative adsorption reactions producing hydroxylated surfaces are all exothermic; exothermicities at the DFT level range from 4.1 kcal mol(-1) for the (111) to 26.5 kcal mol(-1) for the (110) surface, while those at the DFT+U level are between 65.0 kcal mol(-1) for the (111) and 81.8 kcal mol(-1) for the (110) surface. Predicted vibrational frequencies of adsorbed OH and H(2)O species on the surfaces are in line with available experimental and theoretical results. Potential energy profiles are constructed by connecting molecularly adsorbed and dissociatively adsorbed intermediates on each CeO(2) surface with tight transition states using the nudged elastic band (NEB) method. It is found that the U correction method plays a significant role in energetics, especially for the intermediates of the exit channels and products that are partially reduced. The surface reduction reaction on CeO(2)(110) is energetically much more favorable. Accordingly, oxygen vacancies are more easily formed on the (110) surface than on the (111) surface.

Ab initio study of the ClO + NH2 reaction: prediction of the total rate constant and product branching ratios

The mechanism for ClO + NH2 has been investigated by ab initio molecular orbital and transition-state theory calculations. The species involved have been optimized at the B3LYP/6-311+G(3df,2p) level and their energies have been refined by single-point calculations with the modified Gaussian-2 method, G2M(CC2). Ten stable isomers have been located and a detailed potential energy diagram is provided. The rate constants and branching ratios for the low-lying energy channel products including HCl + HNO, Cl + NH2O, and HOCl + 3NH (X(3)Sigma(-)) are calculated. The result shows that formation of HCl + HNO is dominant below 1000 K; over 1000 K, Cl + NH2O products become dominant. However, the formation of HOCl + 3NH (X(3)Sigma(-)) is unimportant below 1500 K. The pressure-independent individual and total rate constants can be expressed as k1(HCl + HNO) = 4.7 x 10(-8)(T(-1.08)) exp(-129/T), k(2)(Cl + NH2O) = 1.7 x 10(-9)(T(-0.62)) exp(-24/T), k3(HOCl + NH) = 4.8 x 10(-29)(T5.11) exp(-1035/T), and k(total) = 5.0 x 10(-9)(T(-0.67)) exp(-1.2/T), respectively, with units of cm(3) molecule(-1) s(-1), in the temperature range of 200-2500 K.

Experimental and Theoretical Studies of Rate Coefficients for the Reaction O(3P) + C2H5OH at High Temperatures

Rate coefficients of the reaction O(3P)+C2H5OH in the temperature range 782-1410 K were determined using a diaphragmless shock tube. O atoms were generated by photolysis of SO2 at 193 nm with an ArF excimer laser; their concentrations were monitored via atomic resonance absorption. Our data in the range 886-1410 K are new. Combined with previous measurements at low temperature, rate coefficients determined for the temperature range 297-1410 K are represented by the following equation: k(T)=(2.89+/-0.09)x10(-16)T1.62 exp[-(1210+/-90)/T] cm3 molecule(-1) s(-1); listed errors represent one standard deviation in fitting. Theoretical calculations at the CCSD(T)/6-311+G(3df, 2p)//B3LYP/6-311+G(3df) level predict potential energies of various reaction paths. Rate coefficients are predicted with the canonical variational transition state (CVT) theory with the small curvature tunneling correction (SCT) method. Reaction paths associated with trans and gauche conformations are both identified. Predicted total rate coefficients, 1.60 x 10(-22)T3.50 exp(16/T) cm3 molecule(-1) s(-1) for the range 300-3000 K, agree satisfactorily with experimental observations. The branching ratios of three accessible reaction channels forming CH3CHOH+OH (1a), CH2CH2OH+OH (1b), and CH3CH2O+OH (1c) are predicted to vary distinctively with temperature. Below 500 K, reaction 1a is the predominant path; the branching ratios of reactions 1b,c become approximately 40% and approximately 11%, respectively, at 2000 K.