Theoretical investigation of novel silsesquioxane-supported Phillips-type catalyst by density functional theory (DFT) method

In spite of great commercial importance of the Phillips CrO_x/SiO₂ catalyst and long term research efforts, the precise physicochemical nature of active sites and polymerization mechanisms still remains unclear. The difficulties in a clear mechanistic understanding of this catalyst mainly come from the complexity of the surface chemistry of the amorphous silica gel support. In this work, novel silsesquioxane-supported Phillips Cr catalysts are utilized as realistic models of the industrial catalyst for theoretical investigation using the density functional theory (DFT) method in order to elucidate the effects of surface chemistry of silica gel in terms of supporting of chromium compounds and fluorination of the silica surface on the catalytic properties of the Phillips catalyst. Both qualitative and quantitative aspects with respect to various electronic properties and thermodynamic characteristics of the model catalysts were achieved. The future prospects of a state-of-the-art catalyst design and mechanistic approaches for the heterogeneous SiO₂-supported Phillips catalyst has been demonstrated. The text was submitted by the authors in English.     

Heavy metal phosphate nanophases in silica: influence of radiolysis probed via f-electron state properties

We have assessed the feasibility of carrying out time- and wavelength-resolved laser-induced fluorescence measurements of radiation damage in glassy silica. The consequences of alpha decay of Es-253 in LaPO₄ nanophases embedded in silica were probed based on excitation of 5f states of Cm³⁺, Bk³⁺, and Es³⁺ ions. The recorded emission spectra and luminescence decays showed that alpha decay of Es-253 ejected Bk-249 decay daughter ions into the surrounding silica and created radiation damage within the LaPO₄ nanophases. This conclusion is consistent with predictions of an ion transport code commonly used to model ion implantation. Luminescence from the ⁶D_7/2 state of Cm³⁺was used as an internal standard. Ion-ion energy transfer dominated the dynamics of the observed emitting 5f states and strongly influenced the intensity of observed spectra. In appropriate sample materials, laser-induced fluorescence provides a powerful method for fundamental investigation of alpha-induced radiation damage in silica.     

Characterization of nanostructured hollow polymer spheres with small-angle neutron scattering (SANS)

Hollow polymer spheres synthesized from a vesicle-directed polymerization can be dried and redispersed in water using a variety of nonionic ethoxylated alcohol surfactants as stabilizers. The final dispersions consist of both polymer shells and surfactant micelles, which remain together in colloidal suspension for at least several months. Small-angle neutron scattering (SANS) is used to measure the polymer shell thickness (63 A) and core radius (560 A) of the surfactant-stabilized hollow polymer spheres in the presence of surfactant micelles. Characterization by SANS provides information about the surfactant bilayer and polymer shell thicknesses which were previously unattainable.     

Fluorocarbohydrates Part XXV. Synthesis and structure of 2-deoxy-2-fluorolactose and related compounds

Experimental details describing the addition of CF₃OF to hexa- -accetyl- -lactal (I) are presented. Four fluorinated disaccharides: trifluoromethyl 3,6-di- -acetyl-2-fluoro-4- -(2′,3′,4′,6′-tetra- -acetyl-β-D-galactopyranosyl)-β- -mannopyrinoside (V), trifluoromethyl 3,6-di- -acetyl-2-deoxy-2-fluoro-4- -(2′,3′,4′,6′-tetra- -acetyl-β-D-galactopyranosyl)-α- -glucopyranoside (VI), 3,6-di- -acetyl-2-deoxy-2-fluoro-4- -(2′,3′,4′,6′-tetra- -acetyl-β- -galactopyranosyl)-β- -mannopyranosyl fluoride (VII), and 3,6-di- -acetyl-2-deoxy-2-fluoro-4- -(2′,3′,4′,6′-tetra- -acetyl-β-D-galactopyranosyl)-α- -glucopyranosyl fluoride (VIII) were isolated from the product mixture. The profound changes in both the rate and the major products of the addition, compared to those reported for related monosaccharide glycals, are discussed in relation to the steric influence exerted by the presence of the non-reducing (galactoside-B) ring of the disacchride glycals. The configuration and the confirmation of the fluorinated portion of the adducts were assigned on the basis of ¹⁹F.m.r. spectroscopic parameters and the structural     

Steroids and sex hormones. Quassinoid bitter principles. I. 1-oxo-2-methoxy-4 alpha-methyl-17 beta-hydroxy-delta2-5 alpha-androstene as a model for the ring a structure of quassine]

Starting from 3-oxo-17β-hydroxy-Δ¹-5α-androstene (2b) the preparation of 1-oxo-2-methoxy-4α-methyl-17β-hydroxy-Δ²-5α-androstene (9), a compound with the ring A structure of quassine (1) is described. The key problem of the reaction sequence is shown to be the monomethylation at C(4).     

Favorskii rearrangement of α,β-epoxy ketones

Reactions of α,β-epoxy ketones with nucleophilic bases generally take one of two courses: (1) α-displacement followed by β-elimination of water or (2) Favorskii rearrangement via a cyclopropanone or zwitterion intermediate. Among the factors that appear to control these reactions, it is suspected that an α′-substituent effect may operate. Such an effect has been confirmed by observing the conversion of 3,5,5,6 - tetramethyl - 2,3 - epoxycyclohexanone (1) to the ring-contracted γ-lactone 3, together with other Favorskii rearrangement products, on treatment with refluxing methanolic potassium hydroxide. The α′-methyl substituted steroid 2 under similar reaction conditions was transformed into roughly equal amounts of 4, 5 and 4 (all rationalized by a Favorskii-like mechanism). In each case the analogous epoxy ketone lacking an α′-Me substituent failed to give any Favorskii products.     

Thermally responsive polymeric micellar nanoparticles self-assembled from cholesteryl end-capped random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide): synthesis, temperature-sensitivity, and morphologies

Cholesteryl end-capped thermally responsive amphiphilic polymers with two different hydrophobic/hydrophilic chain-length ratios were synthesized from the hydroxyl-terminated random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) and cholesteryl chloroformate. The hydroxyl-terminated precursor polymers with narrow molecular weight distributions were synthesized by free-radical polymerization using 2-hydroxyethanethiol as a chain-transfer agent. The aqueous solutions of the cholesteryl end-capped copolymers exhibited reversible phase transitions at temperatures slightly above human body temperature, with the lower critical solution temperature values being 37.7 and 38.2 degrees C, respectively. The critical micelle concentration values of the two cholesteryl end-capped polymers were 9 and 25 mg/L, respectively. Polymeric micellar nanoparticles were prepared from the amphiphilic polymers using a dialysis method as well as a direct dissolution method. Transmission electron microscope studies showed that the micellar nanoparticles existed in different morphologies, including spherical, star-like, and cuboid shapes. Pyrene as a model hydrophobic compound could be readily encapsulated in these polymeric nanoparticles, at loading levels of 1.0 and 0.8 mg/g for the two cholesteryl end-capped polymers, respectively. The temperature sensitivity and unusual morphology of these novel polymeric nanoparticles would make an interesting drug delivery system.     

Classical and quantum mechanical infrared echoes from resonantly coupled molecular vibrations

The nonlinear response function associated with the infrared vibrational echo is calculated for a quantum mechanical model of resonantly coupled, anharmonic oscillators at zero temperature. The classical mechanical response function is determined from the quantum response function by setting variant Planck's over 2pi-->0, permitting the comparison of the effects of resonant vibrational coupling among an arbitrary number of anharmonic oscillators on quantum and classical vibrational echoes. The quantum response function displays a time dependence that reflects both anharmonicity and resonant coupling, while the classical response function depends on anharmonicity only through a time-independent amplitude, and shows a time dependence controlled only by the resonant coupling. In addition, the classical response function grows without bound in time, a phenomenon associated with the nonlinearity of classical mechanics, and absent in quantum mechanics. This unbounded growth was previously identified in the response function for a system without resonant vibrational energy transfer, and is observed to persist in the presence of resonant coupling among vibrations. Quantitative agreement between classical and quantum response functions is limited to a time scale of duration inversely proportional to the anharmonicity.     

Molecular dynamics calculation of half-lives for thermal decay of Lennard-Jones clusters

Molecular dynamics has been used with a Lennard-Jones (6–12) potential in order to study the decay behavior of neutral Argon clusters containing between 12 and 14 atoms. The clusters were heated to temperatures well above their melting points and then tracked in time via molecular dynamics until evaporation of one or more atoms was observed. In each simulation, the mode of evaporation, energy released during evaporation, and cluster lifetime were recorded. Results from roughly 2000 simulation histories were combined in order to compute statistically significant values of cluster half-lives and decay energies. It was found that cluster half-life decreases with increasing energy and that for a given value of excess energy (defined asE=(E _tot ?E _gnd)/n), the 13 atom cluster is more stable against decay than clusters containing either 12 or 14 atoms. The dominant decay mechanism for all clusters was determined to be single atom emission.