LEPS Potential Research Articles

Polysaccharides from Lachnum sp. Inhibited colitis-associated colon tumorigenesis in mice by modulating fecal microbiota and metabolites

It is still uncertain whether the consumption of Lachnum sp. polysaccharides (LEP) alleviates colorectal cancer (CRC) through the gut microbiota. In this study, our efforts are focused on the influence of LEP on CRC, intestinal barrier and inflammation, and fecal microbiota and the metabolites, in azoxymethane (AOM)/dextran sodium sulfate (DSS)-induced CRC mice. Results showed that LEP inhibited CRC mouse colon shortening and weight loss, decreased tumor incidence, restored intestinal barrier integrity, and reduced excessive inflammation. LEP consumption significantly altered microbiota overall structure and community, with reduced pernicious bacteria (such as Parabacteroides, Escherichia_Shigella, Desulfovibrio and Helicobacter), and increased beneficial bacterium (such as Alistipes, Alloprevotella and Ruminiclostridium). Fecal-metabolome profile indicated that a total of 43 metabolites were clearly changed, with 10 down-regulated and 33 up-regulated metabolites. In addition, short-chain fatty acids (SCFAs), including acetic acid, propionic acid and n-butyric acid, were significantly increased after LEP administration. Moreover, a strong correlation between the fluctuant gut microbiota and metabolites was found. These findings provided not only deeper insights into the responsibility of LEP for CRC alleviation, and but also the potential of LEP as a promising candidate for CRC prevention and treatment.

Efficient evaluation of the accuracy of molecular quantum dynamics on an approximate analytical or interpolated ab initio potential energy surface

AbstractAb initio electronic structure methods have reached a satisfactory accuracy for the calculation of static properties, but remain too expensive for quantum dynamical calculations. Recently, an efficient semiclassical method was proposed to evaluate the accuracy of quantum dynamics on an approximate potential without having to perform the expensive quantum dynamics on the accurate potential. Here, this method is applied for the first time to evaluate the accuracy of quantum dynamics on an approximate analytical or interpolated potential in comparison to the quantum dynamics on an accurate potential obtained by an ab initio electronic structure method. Specifically, the vibrational dynamics of H2 on a Morse potential is compared with that on the full CI potential, and the photodissociation dynamics of CO2 on a LEPS potential with that on the excited 1Π surface computed at the EOM‐CCSD/aug‐cc‐pVDZ level of theory. Finally, the effect of discretization of a potential energy surface on the quantum dynamics is evaluated. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2426–2435, 2010

Application of the Moving Boundary Truncation Method to Reactive Scattering: H + H2, O + H2, O + HD

The moving boundary truncation (MBT) method is a time-dependent adaptive method that can significantly reduce the number of grid points needed to perform accurate wave packet propagation while maintaining stability. This work presents a more robust variation of the method. Significant improvements have been made that allow the MBT method to be applied to any potential energy surface and used with any propagation method. The new variation of MBT is applied to the collinear H + H(2) reaction (using a LEPS potential) to demonstrate the stability and accuracy. Reaction probabilities are calculated for the three-dimensional nonrotating O((3)P) + H(2) and O((3)P) + HD reactions to demonstrate that the MBT can be used with a variety of numerical propagation techniques.

A 2d model of the dynamic of the collision: i2-polymeric liquid surfaces of perfluorinatedpolyether (PFPE), polydimetilsiloxane (PDMS) and squalane

This paper presents two dimension classical trajectory calculations for the scattering of an I 2 molecule in the liquid polymeric surfaces of perfluorinatedpolyether (PFPE), polydimethyl-siloxane (PDMS) and squalane. The potential function describing the interaction of the gas molecule with the liquid surface is formulated as a modified LEPS potential. Each diatomic I 2 molecule and the I-surface potential are represented as a Morse function, with parameters adjusted from experimental data of scattering experiments. The surface was modeled as a typical effective mass with two harmonic vibrational degrees of freedom. This dynamics of the scattering process is in good agreement with experimental dynamical data. The experimentally observed inelastic scattering (IS) and the trapping and desorption (TD) processes were characterized and the determined I 2 vibrational temperatures showed good agreement with experimental values.

ADSORPTION AND DISSOCIATION OF O/O2 ON FLAT AND STEPPED PALLADIUM SURFACES

The 5-parameter Morse potential (5-MP) of an O – Pd system and the improved extended LEPS potential of an O 2– Pd system were constructed. The adsorption and dissociation of oxygen atoms and oxygen molecules on flat and stepped palladium single crystal surfaces were studied detailedly, and the data of adsorption sites, adsorption geometry, binding energy, eigenvibration, dissociative mechanism, etc. were obtained. Theoretical results show that the high-symmetry sites are the preferred adsorption sites for tilted adsorption of oxygen molecules, and the tilted angle depends on the number of atoms per unit surface area. Meanwhile, a variety of dissociation pathways are analyzed in detail related to the O 2– Pd (111) system. These results show that the adsorptive dissociation of oxygen molecules on the Pd (111) hollow site is precursor-mediated, on the Pd (111) bridge site is direct dissociation and on the Pd (111) top site is not only depended on the translational energy, but also depended on the vibrational energy. Moreover, the role of the step defect for oxygen atoms and oxygen molecules is also discussed related to flat surface. Theoretical results are in good agreement with the experimental results, and explain well the divergence [N. Salanov and V. N. Bibin, Surf. Sci.441 (1999) 399; P. D. Nolan, B. R. Lutz, P. L. Tanaka and C. B. Mullins, Surf. Sci.419 (1998) L107] related to the O 2 dissociation mechanism.

Effects of molecular rovibrational states and surface topologies for molecule-surface interaction: chemisorption dynamics of D2 collision with rigid Ni surfaces

A quasiclassical and micro-canonical molecular dynamic simulation techniques have been applied for D2(v, j) + Ni-surface collision systems. Dissociative adsorptions of a D2 molecule on the rigid low index (100), (110) and (111), surfaces of the nickel are investigated to understand the effects of the different surfaces, impact sites and the initial rovibrational states of the molecule on molecule-surface collisions. Interactions between the molecule and the Ni surfaces are mimicked by a LEPS potential. Dissociative chemisorption probabilities of the D2(v, j) Molecule ( for the vibrational (v) = 0 and rotational (j) = 0,1, 3, 10, and for the v = 1, j = 0 states on different impact sites of the surfaces) are presented for the translation energies between 0.001 and 1.0 eV. The probabilities obtained at each collision site have unique behavior for the colliding molecule which is moving along the surface normal direction. It has been observed that at the low collision energies the indirect processes (steering effects) enhance the reactivity on the surfaces. The results are compared to the related studies in the literature.

Molecule–surface interaction: dissociative chemisorption of a D2 (v=0, j=0) molecule on rigid low index Ni surfaces

Abstract D2 + Ni-surface collision system has been studied by a quasiclassical molecular dynamic simulation method. Dissociative adsorption of a D2 molecule on rigid Ni(1 0 0), Ni(1 1 0) and Ni(1 1 1) surfaces are investigated. Interactions between the molecule and Ni surfaces were described by a LEPS potential. The contour plots of the LEPS function is presented as functions of the distances between the center of mass of the D2 and surface, and between the two deuterium atoms (D–D) for topologically different sites of the surfaces. Dissociative chemisorption probabilities of the D2 (v=0, j=0) molecule on various sites of the surfaces are presented for different translation energies between 0.001 and 1.0 eV. The probabilities obtained at each collision site have unique behavior. At low collision energies indirect processes enhance the reactivity. The results are compared with the available studies. The physical mechanisms underlying the results are discussed.

Dynamical simulations of the oxygen adsorption on the Ag(110) surface

The study of the adsorption of oxygen on silver surfaces is particularly important because it is a fundamental step in the catalytic partial oxidation of ethene. This gas-surface system is characterized by physisorption at low temperature, molecular and dissociative chemisorption at higher temperatures, and by the presence of a subsurface state. Starting from the results of recent molecular beam experiments, a theoretical study of the dynamical aspects of the process was initiated within the framework of a quasi classical trajectory approach. The reactive scattering of an O 2 beam on the (110) surface of Ag was simulated by using a LEPS potential which accounts for the electronic charge transfer from the metal surface to the incoming O 2 molecule. The dependence of the initial sticking coefficient of O 2 on its translational and rovibrational energies, on the incidence angles of the beam, and on the surface temperature was investigated.

Dynamics of the chemisorption of hydrogen on the Fe(001) surface

The binding energy curves of the H–Fe(001) system have been computed within a tight-binding approach in the extended Huckel approximation, and have been used to build a LEPS potential-energy surface for H2–Fe(001). The results indicate that the adsorption is exothermic with respect both to atomic and molecular hydrogen. The LEPS potential was then employed in stochastic quasi-classical trajectory calculations to study the dynamics of H2 adsorption. We have found that the dissociative adsorption probability Pa increases for increasing values of the collision and total energies, according to steep S-shaped curves; the H2 translational energy is more effective than the rovibrational component in overcoming the adsorption barrier; Pa decreases on increasing the polar angle of incidence, and a good trend is observed for normal energy scaling: Pa is significantly influenced by the corrugation of the (001) surface.

Quasiclassical Trajectory study of the reaction O( 3P) + HBr → OH + Br

Three-dimensional quasiclassical trajectory calculations were carried out for the reaction of oxygen atoms O( 3P) with hydrogen bromide molecules (HBr and DBr) for reaction temperatures of 200, 300 and 550 K, using a LEPS potential -energy surface. The calculated rate constants k O+HBr and k O+DBr and the kinetic isotope effect k O+HBr/ k O+DBr were found to be in very good agreement with experimental data. Calculations showed that vibrational energy is very effective for reaction, and that the major part of the energy released in the reaction appears as internal energy of the products. This is expected for a reaction of the type H + LH ' → HL + H ' (H and H ' are heavy atoms and L is a light atom) even though the potential-energy surface is repulsive. Above 95% of the OH is produced in the first vibrationally excited state, in very good agreement with experimental results. Reactant rotational energy is found to enhance the rate of reaction significantly.