Theoretical study of NH3 , H2 S, and HCN adsorption enhancement on defective graphene-supported Cu19 clusters.

Recent studies have shown that graphene-supported metal clusters can enhance catalytic reactivity compared with corresponding metal clusters. In this study, the adsorptions of NH3 , H2 S, and HCN on Cu19 and defective graphene-supported Cu19 clusters are investigated using plane-wave density functional theory. The results reveal the three gas molecules can be adsorbed on three types of top sites of Cu atoms, respectively. The adsorption energies of the corresponding adsorption sites on the defective graphene-supported Cu19 clusters are all increased compared with those on the Cu19 clusters. The orbital-resolved, crystal orbital Hamilton population analysis demonstrates that the larger the integrated crystal orbital Hamilton population, the stronger the adsorption between the gas molecule and the bonded Cu atom. The center of antibonding states on the defective graphene-supported Cu19 is shifted upward relative to Fermi level compared to the corresponding one on pure Cu19 , which explains the enhanced adsorption energy on defective graphene-supported Cu19. In addition, the closer d-band center to the Fermi level on the defective graphene-supported Cu19 indicates a stronger adsorption capacity than on pure Cu19 .

Enhanced CO adsorption on α-graphyne-supported and defective graphene-supported Cu19 clusters and a modified induction energy model.

Ab initio molecular dynamics calculations were carried out to study the adsorption of CO on Cu19, α-graphyne-supported Cu19 and defective graphene-supported Cu19 clusters. The average adsorption energies on the three clusters are significantly increased by 68%, 104%, and 123% compared to the experimental value on the pristine Cu(110) surface. Furthermore, the α-graphyne-supported and defective graphene-supported Cu19 clusters exhibit greater adsorption strength than the pure Cu19 cluster, with 22% and 33% higher adsorption energies, respectively. The crystal orbital Hamilton population analysis shows that for the same type of adsorption site, the adsorption energy is linearly related to the bond interaction strength between the adsorbate and the substrate. We propose a modified induction energy model to predict the increase of chemisorption energy on α-graphyne-supported and defective graphene-supported Cu19 clusters based on the bare Cu19 cluster. The chemisorption energy enhancement predicted by the improved induction energy model has very good agreement with that calculated based on the ab initio molecular dynamics method and is more accurate than that predicted by the original induction energy model.

Theoretical dynamics studies of the CH3 + HBr → CH4 + Br reaction: integral cross sections, rate constants and microscopic mechanism.

Quantum and quasi-classical dynamics calculations have been performed for the reaction of HBr with CH3. The accurate ab initio-based potential energy surface function developed earlier for this reaction displays a potential well corresponding to a reactant complex and a submerged potential barrier. The integral cross sections were calculated on this potential energy surface using both a six-degree-of-freedom reduced dimensional quantum dynamics and the quasi-classical trajectory method and very good agreement was found between the two approaches. The cross sections were found to diverge when the collision energy decreases, indicating that the reactant attraction is responsible for the dynamics at low collision energy. The quantum mechanical and the quasi-classical rate constants also agree very well and almost exactly reproduce the experimental results at low temperatures up to 540 K. The negative activation energy observed experimentally is confirmed by the calculations and is a consequence of the long-range attraction between the reactants. From the classical trajectories mechanistic details have been extracted. It is found that at very low collision energy, the reacting system crosses the potential barrier because the forces within the complex guide them, although some 30% is reflected from the product side of the barrier. When the collision energy increases, the system does not follow the most favorable path and the reactants are, with increasing probability, reflected from the repulsive walls of the nonreactive parts of the reactants, providing a picture beyond the decreasing excitation function.

Atomic-Level Mechanism, Solvent Effect, and Potential of the Mean Force of the F- + CH3CH2Cl SN2 Reaction in Aqueous Solution.

We investigate the bimolecular nucleophilic substitution (SN2) reaction of F- with CH3CH2Cl in aqueous solution using combined multilevel quantum mechanism (ML-QM) theories with molecular mechanics (MM). The synchronized, atomic-level structural and charge evolutions are analyzed along the reaction path. The potential mean force along the reaction path in water is calculated at high-accuracy CCSD(T)/aug-cc-pVTZ/MM level of theory with a free energy barrier of 16.8 kcal/mol and a free energy of reaction of -9.7 kcal/mol. The water solvent hinders the reactivity by raising its reaction barrier by 15.1 kcal/mol, of which 13.6 kcal/mol comes from solvent energy contribution and 1.5 kcal/mol comes from the polarization effect. This indicates that the water solvent plays an essential role on this reaction in aqueous solution. We also predict the potential mean force profile based on the gas-phase reaction path and the solvation free energies of the stationary points; the comparison between our calculated result at CCSD(T)/MM level shows an excellent agreement with the predicted one with the free energy barrier at 16.2 kcal/mol and the free energy of reaction at -8.3 kcal/mol.

Time-dependent quantum dynamics study of the F + C2H6 → HF + C2H5 reaction.

The reaction probabilities, integral cross sections, energy efficiency and rate constants are investigated for the F + C2H6 reaction using the quantum reaction dynamics, wave packet method. The ground-state integral cross section calculated using a six-degree-of-freedom approach is in very good agreement with the quasi-classical trajectory results. We find that the H-CH2CH3 stretching motion has the largest enhancement to reactivity, followed by the H-CH2-CH3 bending motion. However, the stretching motion between CH2 and CH3 slightly hinders the reactivity. The energy-form efficacy based on an equal amount of total energy shows that translational energy is more effective in enhancing the reactivity than vibrational energy of the H-CH2CH3 stretching motion at a relatively lower translational energy, while the reverse is true at a relatively high translational energy. An energy-shifting method is employed to calculate the full-dimensional rate constants. The quantum rate constants agree well with one of the two main experimental measurements, and the activation energy has an excellent agreement with the one calculated using canonical variational transition-state theory.

Using quantum dynamics to study the effect of energy efficiency on the reactivity of the OH + DBr reaction.

We report a time-dependent, full dimensional, wave-packet calculation for the reaction of OH + DBr to examine the effect of the energy efficiency on the reactivity. This study shows that the vibrational excitations of the OH and DBr enhance the reaction. However, the rotational excitations of OH and DBr both hinder the reaction. As a result, the vibrational energies of both the OH and DBr reactants are more efficient at promoting the reactivity than the translational energy, while the rotational energies of OH and DBr are less effective than the translational energy. By analyzing the state population of the vibrational and rotational states along the reaction pathway, we also developed an approach in order to explain the enhancement of the vibrational excitation and the hindrance of the rotational excitation of the reaction. We found that the initial-state selected vibrational excited states of OH and DBr are the dominant components, respectively, for surmounting the barrier. However, the initial-state selected rotational excited states of OH and DBr are no longer the dominant states for surmounting the transition state owing to their population changes in the van der Waals well. This quantitative analysis demonstrates the potential well in the entrance valley plays an important role in the energy efficiency with regards to the reactivity.

Catalytic Descriptors to Investigate Catalytic Power in the Reaction of Haloalkane Dehalogenase Enzyme with 1,2-Dichloroethane.

Enzymes play a fundamental role in many biological processes. We present a theoretical approach to investigate the catalytic power of the haloalkane dehalogenase reaction with 1,2-dichloroethane. By removing the three main active-site residues one by one from haloalkane dehalogenase, we found two reactive descriptors: one descriptor is the distance difference between the breaking bond and the forming bond, and the other is the charge difference between the transition state and the reactant complex. Both descriptors scale linearly with the reactive barriers, with the three-residue case having the smallest barrier and the zero-residue case having the largest. The results demonstrate that, as the number of residues increases, the catalytic power increases. The predicted free energy barriers using the two descriptors of this reaction in water are 23.1 and 24.2 kcal/mol, both larger than the ones with any residues, indicating that the water solvent hinders the reactivity. Both predicted barrier heights agree well with the calculated one at 25.2 kcal/mol using a quantum mechanics and molecular dynamics approach, and also agree well with the experimental result at 26.0 kcal/mol. This study shows that reactive descriptors can also be used to describe and predict the catalytic performance for enzyme catalysis.

[The protective role of adiponectin in Con A-induced mouse liver injury].

OBJECTIVE: To evaluate the role of adiponectin in regulating tumor necrosis factor alpha (TNF alpha) production and preventing fulminant autoimmunological damage of hepatocytes following concanavalin A (Con A) injection into mice. METHODS: Three days after recombinant plasmids pAA-neo-mAd were injected into the mice via the tail veins, Con A was injected into the mice. Mice transfected with empty pAA-neo vector served as controls. The serum levels of alanine aminotransferase (ALT), TNF alpha and adiponectin were detected, and histological examination of livers was carried out at different time points after the Con A injection. All results were subjected to statistical analyses. RESULTS: Histological examinations showed that the damage in livers of mice with high serum adiponectin levels was milder than that of the controls. The serum levels of ALT and TNF alpha were both lower than those of the controls (P less than 0.01, respectively). Statistical analyses showed the serum levels of ALT was negatively related to the levels of adiponectin in the sera (r=-0.5034). CONCLUSION: Adiponectin is effective in protecting hepatocytes from Con A-induced immunological injury. The mechanism of this protective effect may be caused by inhibiting the synthesis and/or release of TNF alpha.

Present status of serum lipid levels in Beijing professional populations and its trend of changes over 15 years--a collaborative study of seven research and clinical laboratories in Beijing.

BACKGROUND: China's economy has been growing rapidly since 1980, which may have affected blood lipid levels. We carried out a study on serum lipid levels and prevalence of lipid abnormalities in Beijing professional populations in 2001-2002 and assessed the changing trends of lipid levels by comparing the results with that of a similar study in 1984-1986. METHODS: The study population included 31,068 government employees, medical and educational workers and scientific research personnel (male/female 6:4). All participants had physical examination and blood chemistry tests. Lipid parameters analyzed included total cholesterol, low- and high-density lipoprotein (LDL and HDL) cholesterol and triglyceride. RESULTS: Total cholesterol, LDL cholesterol and triglyceride concentrations increased significantly as compared with the 1984-1986 study, but the variations of lipid levels with age and sex remained unchanged. Age-adjusted prevalence of dyslipidemia and its distribution in different sexes and age groups were statistically analyzed. Comparing the results with the data of the US in the 1990s, total cholesterol concentration was lower by 16 mg/dl in men and 18 mg/dl in women, whereas LDL cholesterol concentration was lower by 20 mg/dl in men and 15 mg/dl in women. HDL cholesterol was significantly higher than the US in both genders. CONCLUSIONS: The mean levels of total cholesterol (LDL cholesterol ) increased rapidly in the 1980s, stabilized and descended slightly in 1990s. Coronary lipid risk level in Beijing professional populations is significantly lower than in the US.

[Study on phenotypic and genotypic characterization of clinical multidrug-resistant Escherichia coli isolates].

OBJECTIVE: To study the mechanisms on drug susceptibility and resistance of clinically multidrug-resistant Escherichia coli isolates, to provide information on related treatment. METHODS: The susceptibility of E. coli strains that isolated from different kinds of samples in the last 3 years on drugs was analyzed by agar dilution test, with strains that exhibiting resistances to cefotaxime, ciprofloxacin and amikacin simultaneously collected for further analysis. Resistant genes which mediate resistance to ß-lactamases, fluoroquinolone and aminoglycoside as well as phylogenic type were detected by PCR amplification while genetic relation was analyzed by PFGE. Transferability of resistant plasmids was identified by conjugation test. RESULTS: In total, 137 multidrug-resistant E. coli isolates were collected. Only 1% of the isolates exhibited resistance to both imipenem and meropenem while 4% of the strains were resistant to piperacillin/tazobactam. Most (85%) of the isolates were positive to ESBL and majority of them produced CTX-M. Target substitution and production of methylases were the main mechanisms causing resistance to fluoroquinolones and aminoglycosides respectively. CONCLUSION: The main source of clinical multidrug-resistance was collected from urine samples. Carbapenem and enzyme inhibitor-containing antibiotics seemed to be the available antibiotics that were sensitivity to the clinically multidrug-resistant E. coli isolates.