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991.
Ignatyev I Montejo M Ortega PG González JJ 《Physical chemistry chemical physics : PCCP》2011,13(41):18507-18515
Activation barrier heights for the dehydration reaction of geminal carbinols and silanediols R'R″X(OH)(2) (X = C, Si) were estimated at the B3LYP and MP2 levels of theory employing Dunning's correlation-consistent triple-zeta basis sets. It was shown that the barrier height for carbon derivatives steadily decreases upon substitution by R groups, usually termed as electron-donating, such as alkyl and amino groups. Substitution by electron-withdrawing groups leads, however, only to small changes in barrier heights compared to that of methanediol. A similar tendency was also found for silicon derivatives, but high activation barriers of this reaction remain even for amino group substituted silanediols. Introduction of additional water molecules into the reactive space of carbinol dehydration drastically reduces barrier heights and brings the transition state energy for methanediol close to the experimental value. The difference between dehydration barrier heights for both methanediol and carbinols with electron-rich substituents becomes well-defined for dimeric species. The higher acidity of the hydroxyl group protons in molecules containing halogens and C==O groups brings about a noticeable growth in the dehydration barrier heights of these compounds. This difference in barrier heights for oligomeric species may be the reason for the stability of carbinols with electron-rich substituents. 相似文献
992.
González MG Rodríguez JD Rubio-Lago L García-Vela A Bañares L 《Physical chemistry chemical physics : PCCP》2011,13(36):16404-16415
The photodissociation of CH(3)I in the blue edge (217-230 nm) of the A-band has been studied using a combination of slice imaging and resonance enhanced multiphoton ionization (REMPI) detection of the CH(3) fragment in the vibrational ground state (ν = 0). The profiles of the CH(3) (ν = 0) kinetic energy distributions and the photofragment anisotropies are interpreted in terms of the contribution of the excited surfaces involved in the photodissociation process, as well as the probability of non-adiabatic curve crossing between the (3)Q(0) and (1)Q(1) states. In the studied region, unlike in the central part of the A-band where absorption to the (3)Q(0) state dominates, the I((2)P(J)), with J = 1/2, 3/2, in correlation with CH(3) (ν = 0) kinetic energy distributions show clearly two contributions of different anisotropy, signature of the competing adiabatic and non-adiabatic dynamics, whose ratio strongly depends on the photolysis wavelength. The experimental results are compared with multisurface wave packet calculations carried out using the available ab initio potential energy surfaces, transition moments, and non-adiabatic couplings, employing a reduced dimensionality model. A good qualitative agreement is found between experiment and theory and both show evidence of reverse (3)Q(0)←(1)Q(1) non-adiabatic dynamics at the bluest excitation wavelengths both in the fragment kinetic energy and angular distributions. 相似文献
993.
Marazzi M Sancho U Castaño O Frutos LM 《Physical chemistry chemical physics : PCCP》2011,13(17):7805-7811
The photochemistry and photophysics of a two-glycine minimal model is studied at the CASPT2//CASSCF level of theory. Different photoinduced processes are discussed, on the basis of the calculated minimum energy paths and the characterization of the electronic state crossings. Two main processes could provide UV-photostability to the hydrogen-bonded peptide system: (i) forward-backward photoinduced electron/proton transfer involving the H in the hydrogen bond, (ii) singlet-singlet energy transfer between two amino acids, providing ultrafast population of the low-energy n,π* state. 相似文献
994.
Moreno E Varughese T Spadafora C Arnold AE Coley PD Kursar TA Gerwick WH Cubilla-Rios L 《Natural product communications》2011,6(6):835-840
Chemical investigation of a new endophytic fungus, Mycosphaerella sp. nov. strain F2140, associated with the foliage of the plant Psychotria horizontalis (Rubiaceae) in Panama, resulted in the isolation of cercosporin (1) and a new cercosporin analog (3) as the major components. The structures of minor compounds in the extract were elucidated by detailed spectroscopic analysis as 2-(2-butyl)-6-ethyl-3-hydroxy-6-methylcyclohex-2-ene-1,5-dione (4), 3-(2-butyl)-6-ethyl-5-hydroxy-2-methoxy-6-methyl-cyclohex-2-enone (5), and an isomer of 5 (6). To study the influence of the hydroxy groups on the anti-parasitic activity of cercosporin, compound 1 was acetylated to obtain derivative 2. The isolated compounds 1- 6 were tested in vitro to determine their anti-parasitic activity against the causal agents of malaria (Plasmodium falciparum), leishmaniasis (Leishmania donovani), and Chagas disease (Trypanosoma cruzi). Cytotoxicity and potential anticancer activity of these compounds were evaluated using mammalian Vero cells and MCF7 cancer cell lines, respectively. Compounds 1 and 2 displayed high potency against L. donovani (IC50 0.46 and 0.64 microM), T. cruzi (IC50 1.08 and 0.78 microM), P. falciparum (IC50 1.03 and 2.99 microM), and MCF7 cancer cell lines (IC50 4.68 and 3.56 microM). Compounds 3-6 were not active in these assays at a concentration of 10 microg/mL. 相似文献
995.
Y. Espinosa-Almeyda J.C. López-Realpozo R. Rodríguez-Ramos J. Bravo-Castillero R. Guinovart-Díaz H. Camacho-Montes F.J. Sabina 《International Journal of Solids and Structures》2011,48(10):1525-1533
Imperfect bonding between constituents is studied where displacements, electric and magnetic static potentials are considered to have a jump proportional to the normal component of the mechanical traction, electric displacement and magnetic flux. This condition may model various interface damages or the thin glue layer between two adjacent phases. They are termed as the mechanically compliant, dielectrically weakly capacitance and magnetically weakly inductance at the interface. It is shown that while the more imperfect the interface is, the overall properties become weaker, such as longitudinal shear stiffness, out-of-plane piezoelectric coupling, and magnetoelectric coupling. Out-of-plane piezomagnetic coupling, transverse dielectric permittivity and transverse dielectric permeability exhibit no influence by imperfect bonding. The imperfect interface proposed is mimicked by the springs, capacitors and inductances for the mechanical, electric and magnetic interaction between the phases and are highly sensitive to the interphase properties. The results are compared mainly with the self consistent model reported in the literature and good agreements are shown. 相似文献
996.
Luis M. Romeo Luis I. DíezIsabel Guedea Irene BoleaCarlos Lupiáñez Ana GonzálezJavier Pallarés Enrique Teruel 《Experimental Thermal and Fluid Science》2011,35(3):477-484
Oxyfuel combustion is a promising alternative for CO2 capture. While this has been proven in pulverized fuel (PF) burners, research in fluidized bed (FB) reactors is still scarce. Our work aims to increase the knowledge about this technology. To this purpose, a 95 kWth FB oxyfuel combustion test rig has been erected. Its main characteristics are described in this paper, giving detailed information on the subsystems: the FB reactor, the fuel and oxidant supplies, and ancillaries. Plant flexibility is emphasized. It allows to operate under different CO2/O2 ratios, and to recycle CO2 from the flue gases. Both the processes design and monitoring are supported by simulations that have been validated against experimental data, regarding fluid dynamics, combustion, and heat transfer. Finally, the performance of the facility has been tested both with coal alone and blended with biomass. CO2 concentrations over 90% (dry basis) in the flue gases have been obtained. Comparison of air and oxygen combustion tests and operational recommendations are discussed, confirming the feasibility of the FB oxyfuel technology for CO2 capture purposes. 相似文献
997.
Antonio Algaba Fernando Fernández-Sánchez Manuel Merino Alejandro J. Rodríguez-Luis 《Nonlinear dynamics》2011,63(3):455-476
Non-transversal T-points have been recently found in problems from many different fields: electronic circuits, pendula, and
laser problems. In this work, we study a model based on the construction of a Poincaré map that describes the behaviour of
curves of saddle-node and cusp bifurcations in the vicinity of such a non-transversal T-point. This model is also able to
predict, reproduce, and explain the numerical results previously obtained in Chua’s equation. 相似文献
998.
Arturo de Pablo Fernando Quirós Ana Rodríguez Juan Luis Vázquez 《Advances in Mathematics》2011,226(2):1378
We develop a theory of existence, uniqueness and regularity for the following porous medium equation with fractional diffusion, with m>m?=(N−1)/N, N?1 and f∈L1(RN). An L1-contraction semigroup is constructed and the continuous dependence on data and exponent is established. Nonnegative solutions are proved to be continuous and strictly positive for all x∈RN, t>0. 相似文献
999.
Luis Silvestre 《Advances in Mathematics》2011,226(2):2020
We prove that the Hamilton–Jacobi equation for an arbitrary Hamiltonian H (locally Lipschitz but not necessarily convex) and fractional diffusion of order one (critical) has classical C1,α solutions. The proof is achieved using a new Hölder estimate for solutions of advection–diffusion equations of order one with bounded vector fields that are not necessarily divergence free. 相似文献
1000.
In this paper we obtain, for a class of plane curves, extensions of the well-known relation of inflection points, double points and bitangencies established by Fabricius-Bjerre for closed curves. 相似文献