Dynamics Study of the HO(v‘=0) + O2(v‘ ‘) Branching Atmospheric Reaction. 1. Formation of Hydroperoxyl Radical

We report a theoretical study of the title four-atom atmospheric reaction for a range of translational energies 0.1 ≤ Etr/kcal mol-1 ≤ 40 and the range 13 ≤ v‘ ‘ ≤ 27 of vibrational quantum numbers of the oxygen molecule. All calculations have employed the quasiclassical trajectory method, and a realistic potential energy surface obtained by using the double many-body expansion (DMBE) method for ground-state HO3

Bioactivity, biocompatibility and antimicrobial properties of a chitosan-mineral composite for periodontal tissue regeneration

A composite membrane of the polymer, chitosan, and the silver-exchanged mineral phase, tobermorite, was prepared by solvent casting and characterised by scanning electron microscopy and Fourier transform infrared spectroscopy. The in vitro bioactivity, cytocompatibility and antimicrobial activity of the composite were evaluated with respect to its potential application as a guided tissue regeneration (GTR) membrane. The in vitro bioactivity was verified by the formation of hydroxyapatite on the surface of the membrane in simulated body fluid and its cytocompatibility was established using MG63 human osteosarcoma cells. The presence of silver ions conferred significant antimicrobial activity against S. aureus, P. aeruginosa and E. coli. The findings of this investigation have indicated that the chitosansilver-tobermorite composite is a prospective candidate for GTR applications

Free-standing polyelectrolyte membranes made of chitosan and alginate

Free-standing films have increasing applications in the biomedical field as drug delivery systems for wound healing and tissue engineering. Here, we prepared free-standing membranes by the layer-by-layer assembly of chitosan and alginate, two widely used biomaterials. Our aim was to produce a thick membrane and to study the permeation of model drugs and the adhesion of muscle cells. We first defined the optimal growth conditions in terms of pH and alginate concentration. The membranes could be easily detached from polystyrene or polypropylene substrate without any postprocessing step. The dry thickness was varied over a large range from 4 to 35 μm. A 2-fold swelling was observed by confocal microscopy when they were immersed in PBS. In addition, we quantified the permeation of model drugs (fluorescent dextrans) through the free-standing membrane, which depended on the dextran molecular weight. Finally, we showed that myoblast cells exhibited a preferential adhesion on the alginate-ending membrane as compared to the chitosan-ending membrane or to the substrate side.This work was financially supported by Foundation for Science and Technology (FCT) through the Scholarship SFRH/BD/64601/2009 granted to S.G.C. C.M. is indebted to Grenoble INP for financial support via a postdoctoral fellowship. This work was supported by the European Commission (FP7 Program) via a European Research Council starting grant (BIOMIM, GA 259370 to C.P.). C.P. is also grateful to Institut Universitaire de France and to Grenoble Institute of Technology for financial support. We thank Isabelle Paintrand for her technical help with the confocal apparatus and Patrick Chaudouet for his help with SEM imaging

Dynamics Study of the N(4S) + O2 Reaction and Its Reverse

We report quasiclassical trajectory calculations for the reaction N(4S) + O2 → NO + O by focusing on the rovibrational distributions of the NO product molecule at a collisional energy of 3 eV and the temperature dependence of the rate constant. The calculations employ the lowest adiabatic sheet of a recently reported (Varandas, A. J. C. J. Chem. Phys. 2003, 119, 2596) multisheeted double many-body expansion potential energy surface for the 2A‘ states of NO2, improved via a multiple energy-switching scheme to attain near-spectroscopic accuracy in the vicinity of the deep 2A1 minimum. For the quartet state, the calculations employ single-sheeted potentials from various sources, except for the rate constant where the results are taken from the literature. The rate constant for the reverse endothermic reaction is calculated by dividing the rate constant for the forward reaction by the equilibrium constant calculated using statistical mechanics. For both reactions, the agreement with the recommended rate constants is good. The vibrational distributions of NO are found to agree with previously reported theoretical estimates, which show fair agreement with the general trends observed from experiment

Dynamics Study of the OH + O2 Branching Atmospheric Reaction. 4. Influence of Vibrational Relaxation in Collisions Involving Highly Excited Species

The vibrational relaxation processes occurring during collisions of vibrationally excited O2 and OH are investigated using the quasiclassical trajectory method and a realistic double many-body expansion (DMBE I) potential energy surface for ground-state HO3. A salient feature is the observation of multiquanta deactivation processes for such high internal energies. It is also shown that the vibrational relaxation of colliding molecules is far less important than the reactive processes leading to formation of “odd-oxygen” (and hence ozone) under stratospheric local thermodynamic disequilibrium conditions

Unimolecular and Bimolecular Calculations for HN2

Using a recently reported double many-body expansion potential energy surface, quasi-classical, statistical mechanics, and quantum resonance calculations have been performed for the HN2 system by focusing on the determination of bimolecular (N + NH and H + N2) and unimolecular (decomposition of HN2) rate constants as well as the relevant equilibrium constants

Potential Energy Surface for Ground-State H2S via Scaling of the External Correlation, Comparison with Extrapolation to Complete Basis Set Limit, and Use in Reaction Dynamics

A global double many-body expansion potential energy surface is reported for the electronic ground state of H2S by fitting accurate ab initio energies calculated at the multireference configuration interaction level with the aug-cc-pVQZ basis set, after slightly correcting semiempirically the dynamical correlation by the double many-body expansion-scaled external correlation method. The function so obtained has been compared in detail with a potential energy surface of the same type recently reported ( Song, Y. Z. and Varandas, A. J. C. J. Chem. Phys. 2009, 130, 134317. ) by extrapolating the calculated raw energies to the complete basis set limit, eschewing any use of information alien to ab initio theory. The new potential energy surface is also used for studying the dynamics and kinetics of the S(1D) + H2/D2/HD reaction

Recalibrated Double Many-Body Expansion Potential Energy Surface and Dynamics Calculations for HN2

A single-sheeted double many-body expansion potential energy surface is reported for the lowest doublet state of HN2 by fitting additional multireference configuration interaction energies in the N···NH channel. A stratified analysis of the root-mean-squared error indicates an accuracy superior to that achieved for the previously reported form. Detailed dynamical tests are also performed for the N + NH reaction using both the quasi-classical trajectory method and the capture theory, and the results are compared with available empirical data. The vibrational resonances of the HN2 metastable radical are also calculated and compared with previous theoretical predictions

Nascent versus “Steady-State” Rovibrational Distributions in the Products of the O(3P) + O3(1A) Reaction

We report a trajectory simulation study of the O2(v‘,j‘) + O2(v‘‘,j‘‘) collisional process at a translational temperature of 1500 K with a view to compare the initial and final rovibrational distributions of the colliding species. As initial rotational and vibrational micropopulations we assume those calculated for the products of the forward title reaction. Rotational relaxation is found to occur to a larger extent than vibrational relaxation, a result that is in general agreement with experimental measurements for small and moderate delay times after the reaction O + O3 → O2(v‘,j‘) + O2(v‘‘,j‘‘) has occurred. Rather than a single rotational temperature reported from the experiments, the simulations predict two disparate rotational temperatures close to those characterizing the nascent micropopulation. An increase in temperature due to vibrational−translational and rotational−translational relaxation processes is also predicted

Dynamics Study of the OH + O2 Branching Atmospheric Reaction. 2. Influence of Reactants Internal Energy in HO2 and O3 Formation

The effect of reactants vibrational and rotational excitation on products (HO2 + O and O3 + H) formation is investigated for the title reaction by using the quasiclassical trajectory method and the realistic double many-body expansion (DMBE) potential energy surface for ground-state HO3. It is shown that it can be a potential source of ozone in the upper atmosphere