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991.
Temelso B Sherrill CD Merkle RC Freitas RA 《The journal of physical chemistry. A》2006,110(38):11160-11173
Symmetric and nonsymmetric hydrogen abstraction reactions are studied using state-of-the-art ab initio electronic structure methods. Second-order M?ller-Plesset perturbation theory (MP2) and the coupled-cluster singles, doubles, and perturbative triples [CCSD(T)] methods with large correlation consistent basis sets (cc-pVXZ, where X = D,T,Q) are used in determining the transition-state geometries, activation barriers, and thermodynamic properties of several representative hydrogen abstraction reactions. The importance of basis set, electron correlation, and choice of zeroth-order reference wave function in the accurate prediction of activation barriers and reaction enthalpies are also investigated. The ethynyl radical (*CCH), which has a very high affinity for hydrogen atoms, is studied as a prototype hydrogen abstraction agent. Our high-level quantum mechanical computations indicate that hydrogen abstraction using the ethynyl radical has an activation energy of less than 3 kcal mol(-1) for hydrogens bonded to an sp(2) or sp(3) carbon. These low activation barriers further corroborate previous studies suggesting that ethynyl-type radicals would make good tooltips for abstracting hydrogens from diamondoid surfaces during mechanosynthesis. Modeling the diamond C(111) surface with isobutane and treating the ethynyl radical as a tooltip, hydrogen abstraction in this reaction is predicted to be barrierless. 相似文献
992.
Ralph M. Kaufmann 《Letters in Mathematical Physics》2010,94(2):165-195
There are two approaches to constructing stringy multiplications for global quotients. The first one is given by first pulling back and then pushing forward. The second one is given by first pushing forward and then pulling back. The first approach has been used to define a global stringy extension of the functors K 0 and K top by Jarvis–Kaufmann–Kimura, A* by Abramovich–Graber–Vistoli, and H* by Chen–Ruan and Fantechi–Göttsche. The second approach has been applied by the author in the case of cyclic twisted sector and in particular for singularities with symmetries and for symmetric products. The second type of construction has also been discussed in the de Rham setting for Abelian quotients by Chen–Hu. We give a rigorous formulation of de Rham theory for any global quotient from both points of view. We also show that the pull–push formalism has a solution by the push–pull equations in the setting case of cyclic twisted sectors. In the general, not necessarily cyclic case, we introduce ring extensions and treat all the stringy extension of the functors mentioned above also from the second point of view. A first extension provides formal sections and a second extension fractional Euler classes. The formal sections allow us to give a pull–push solution while fractional Euler classes give a trivialization of the co-cycles of the pull–push formalism. The main tool is the formula for the obstruction bundle of Jarvis–Kaufmann–Kimura. This trivialization can be interpreted as defining the physics notion of twist fields. We end with an outlook on applications to singularities with symmetries aka. orbifold Landau–Ginzburg models. 相似文献
993.
994.
995.
Suwansa-Ard S Xiang Y Bash R Thavarungkul P Kanatharana P Wang J 《Electroanalysis》2008,20(3):308-312
A highly sensitive electrochemical DNA hybridization assay using Prussian blue (PB)-modified polymeric spheres as the oligonculeotide labeling tag is described. The sandwich assay relies on a secondary nucleic-acid probe functionalized with polystyrene beads loaded with numerous Prussian blue nanoparticles. The very strong catalytic activity of the captured PB 'artificial peroxidase' tag towards the reduction of hydrogen peroxide, along with the encapsulation of numerous catalytic particles onto polymeric beads, allows amperometric detection of the DNA target down to the 50 fM level (2.5 amol). Imaging and spectroscopic measurements are used to characterize the PB-tagged polystyrene beads. Such coupling of PB catalytic labels with polymeric carrier beads offers great promise for amplified transduction of different biomolecular interactions. 相似文献
996.
The dynamics of halide displacement from brominated poly(isobutylene-co-isoprene)(BIIR) by carboxylate nucleophiles are detailed and discussed in terms of a general reaction mechanism. The exomethylene allylic bromide isomer within BIIR is shown to undergo simultaneous SN2 alkylation of Bu4Nacetate and SN2′ rearrangement with Bu4NBr. The latter generates a Z-BrMe isomer that is more reactive toward esterification. Hence, overall polymer modification rates are auto-accelerating, as Bu4NBr liberated by esterification catalyzes allylic bromide rearrangement to a more reactive electrophile. This knowledge of reaction mechanisms is used to develop nucleophilic catalysis techniques involving iodide intermediates. 相似文献
997.
998.
Ralph G. Pearson 《International journal of quantum chemistry》2008,108(5):821-826
Equations are derived for the chemical potential and local hardness of the ground states of helium and the related two electron ions. With these properties it is possible to correct the energies of the simple single‐zeta wave functions to the nearly exact values. The calculations are simple for these simple systems. In principle, it is possible to extend this method to all atoms and molecules. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 相似文献
999.
Ralph deLaubenfels 《Semigroup Forum》2007,75(2):457-463
It is shown that, for any bounded, injective operator C, the class of injective, densely defined operators with dense range
and nonempty resolvent that generate bounded holomorphic C-regularized semigroups is closed under inversion, but, for any
n ∈ N, the class of injective, densely defined operators with dense range that generate bounded holomorphic n-times integrated
semigroups is very far from being closed under inversion: it is shown that, if both A and A-1 generate bounded holomorphic n-times integrated semigroups of sufficiently large angle θ, then they both generate strongly
continuous bounded holomorphic semigroups of angle θ. 相似文献
1000.