Radical versus Nucleophilic Mechanism of Formaldehyde Polymerization Catalyzed by (WO(3))(3) Clusters on Reduced or Stoichiometric TiO(2)(110)

(WO(3))(3) clusters deposited on the (110) rutile TiO(2) surface are excellent catalysts for the formaldehyde (CH(2)O) polymerization reaction (J. Phys. Chem. C2010, 114, 17017). The present B3LYP study unravels the possible paths of this catalyzed reaction. According to the stoichiometry of the r-TiO(2) surface, the (WO(3))(3) clusters can be neutral, singly charged, or doubly charged. We find that only neutral (WO(3))(3) and anionic (WO(3))(3)(-) clusters are reactive toward CH(2)O molecules. In both cases it is possible to determine more than one mechanism on the basis of a nucleophilic attack of the formaldehyde O atom to the W ions of the cluster. The reaction proceeds through successive attacks of other CH(2)O molecules and the formation of acetal and polyacetal intermediates, which inhibits the chain propagation. Only in the case of the anionic (WO(3))(3)(-) catalyst is a totally different reaction path possible at low temperatures. This path involves the formation of radical species where the unpaired electron is localized on the organic moiety bound to the cluster. The polymer chain propagation follows a radical mechanism with low activation barriers. Thus, a cluster's electron charging speeds up the formaldehyde polymerization at low temperatures. On the basis of these unexpected results, we conclude that electron-rich supports and low working temperatures are the keys to kinetic control of the reaction favoring a fast radical chain propagation mechanism.     

Interactions in general continua with microstructure

This paper studies the behavior of the one dimensional Broadwell model of a discrete three velocity gas on a bounded domain 0 x 1 with specularly reflective boundary condition at x = 0, 1. For smooth initial data we show that the initial boundary value problem possesses a unique smooth solution which tends as t to a free state consisting of traveling waves f _1e (x – ct), f _2e (x + ct), f _3e (x) where each f _ie is 2-periodic. The convergence is in the weak* topology of an appropriate Orlicz-Banach state space. No smallness assumptions are made on the data.In memory of Ronald J. DiPerna     

Two Theories of Complex Bodies, one Lagrangean, the other Kinetic, Have a Common Ground

I have found in previous works that most special models proposed to represent bodies with some type of microstructure can be classified easily under the general umbrella of a theory where each element of the continuum is thought of as a Lagrangian system. To study phenomena in ‘kinetic’ continua I proposed an apparently different approach; the outcome is again a set of evolution equations. They mimic equations familiar in continua with affine microstructure: a Cauchy’s equation and an equation of balance of tensor moment of momentum, with the addition, however, of an equation of balance for a ‘Reynolds’ tensor’, an equation which, in a sense, shifts the boundary between kinetic and thermal properties of matter. I will show that there is no contrast between the two approaches. The latter one is based on an adequate and appropriately justified expression of the kinetic energy of the continuum, comprising the trace of the quoted Reynolds’ tensor and thus importing into the mechanical energy a term usually accounted by additional heat.     

Influence of steric interactions and random side chain variations on the mesomorphic properties of bowlic mesogens

The effect of structural variations on the mesomorphic nature of columnar liquid crystals of general structure I is studied. X-ray crystal structure analyses of compounds la and 2a reveal the columnar organization of the macrocyclic cores in the solid state. The up and down asymmetry of the cores is resolved in an alternating sequence of up-up and down-down intermolecular contacts. Specific interactions between the R substituents are present, which influence the stacking distance between the cores in the down-down intermolecular contacts. Statistical incorporation of different side chains on the same macrocyclic core produces, when the difference in length between the alkyl chains is appropriate, random mixtures having wide mesomorphic ranges. The increase of disorder associated with the statistical side chain distribution on the core and with the structural heterogeneity of each component of the mixture have the effect of depressing mainly the crystal-mesophase transition temperature.     

On surface biaxiality

We propose the following: on the boundary of a nematic liquid crystal, the function which describes the molecular orientation is subject to a further symmetry condition, besides that reflecting apolarity. This additional symmetry delimits a class of biaxial states; within that class we study a model problem for a thin layer in which the anchoring energy prevails over the elastic energy in the presence of an electric field. We show that, when the anchoring and electric energies favour uniaxial states with optic axes at right angles, the equilibrium configuration migrates from one state to the other, traversing a whole family of biaxial states as the strength of the electric field increases.     

Kinetic evidence for the unusual path in the hydrolysis of amides. pH-rate profile for N-trifluoroacetylindole

The first complete pH-rate profile (H_O-4 ÷ pH 12) for an amide is reported. Hydration of carbonyl moiety is suggested to be the first step of the reaction between H_O-4 ÷ pH 6.     

Probabilistic analysis of the subset-sum problem

Two linear time algorithms are shown to solve the n-object SUBSET-SUM problem with probability approaching 1 as n gets large, for a uniform instance distribution. Precise evaluations of the probabilities involved are given.     

Isocyanide insertion reaction in alkylcomplexes of iron: A dihaptoiminoacyl derivative of iron (II)

The dihaptoiminoacyl complex [Fe(CO)₂ (PMe₃)₂(η²CMeNCMe₃)]⁺ I^? was obtained by reaction of [Fe(CO)₂(PMe₃)₂ MeI] and tertbutylisocyanide. The structure of the complex was determined by an X-ray structure analysis.     

Oxide ultra-thin films on metals: new materials for the design of supported metal catalysts

Ultrathin oxide films on metals offer new opportunities for the design of supported nanoclusters with potential use in catalysis. This requires a characterization at the atomistic level of the structure and composition of the thin film, of its morphology and defect structure. A proper selection of metal/oxide interface, film thickness, lattice mismatch, etc. makes it possible to prepare collections of supported metal particles with novel properties. This critical review describes some illustrative examples, emphasizes the role of the interplay between theory and experiment, and relates some recent findings related to the possibility to control the charge state of a supported nanoparticle on an ultrathin oxide film (211 references).