Relative thermodynamic stabilities of 2-substituted 4-methylene-1,3-dioxolanes and 4-methyl-1,3-dioxoles

The relative thermodynamic stabilities of 24 pairs of carbon-carbon double-bondexo-endo isomeric 2-substituted 4-methylene-1,3-dioxolanes (a) and 4-methyl-1,3-dioxoles (b) have been determined by base-catalyzed chemical equilibration in DMSO solution. In all cases, theendo isomer (b) is the favored species at thermodynamic equilibrium. A single alkyl substitutent on C-2 gives only a negligible contribution to the relative stability of the isomeric forms, but the presence of two alkyl groups on C-2 increases the relative stability of theendo isomer by 2–3 kL mol^–1. A still higher effect in favor of theendo isomer is produced by introduction of a single alkoxy group on C-2; this effect is further slightly accentuated by 2,2-dialkoxy substitution at C-2. The origin of the favorable effect of 2-alkoxy substitution on the relative stability of theendo isomer is not clear, but it seems to arise from an unexpected stability of theendo isomer rather than from an enhanced destabilization of theexo form.     

Influence of the pore structure of MCM-41 and SBA-15 silica fibers on atomic layer chemical vapor deposition of cobalt carbonyl

Mesoporous high surface area MCM-41 and SBA-15 type silica materials with fibrous morphology were synthesized and used as support materials for the ALCVD (atomic layer chemical vapor deposition) preparation of Co/MCM-41 and Co/SBA-15 catalysts. Co/MCM-41 and Co/SBA-15 catalysts were prepared by deposition of Co2(CO)8 from the gas phase onto the surfaces of preheated support materials in a fluidized bed reactor. For both silica materials, two different kinds of preparation methods, direct deposition and a pulse deposition method, were used. Pure silica supports as well as supported cobalt catalysts were characterized by various spectroscopic (IR) and analytical (X-ray diffraction, Brunauer-Emmett-Teller, elemental analysis) methods. MCM-41 and SBA-15 fibers showed considerable ability to adsorb Co2(CO)8 from the gas phase. For MCM-41 and SBA-15 silicas, cobalt loadings of 13.7 and 12.1 wt % were obtained using the direct deposition method. The cobalt loadings increased to 23.0 and 20.7 wt % for MCM-41 and SBA-15 silicas, respectively, when the pulse deposition method was used. The reduction behavior of silica-supported cobalt catalysts was found to depend on the catalyst preparation method and on the mesoporous structure of the support material. Almost identical reduction properties of SBA-15-supported catalysts prepared by different deposition methods are explained by the structural properties of the mesoporous support and, in particular, by the chemical structure of the inner surfaces and walls of the mesopores. Pulse O2/H2 chemisorption experiments showed catalytically promising redox properties and surface stability of the prepared MCM-41- and SBA-15-supported cobalt catalysts.     

Wettability conversion on the liquid flame spray generated superhydrophobic TiO2 nanoparticle coating on paper and board by photocatalytic decomposition of spontaneously accumulated carbonaceous overlayer

Titanium dioxide (TiO₂) is a photoactive material with various interesting and useful properties. One of those is the perfect wettability of TiO₂ surface after ultraviolet (UV) illumination. Wettability of a solid surface plays an important role in the field of printing, coating, and adhesion among others. Here we report on a superhydrophobic and photoactive liquid flame spray (LFS) generated TiO₂ nanoparticle coating that can be applied on web-like materials such as paper and board in one-step roll-to-roll process. The LFS TiO₂ nanoparticle coated paper and board were superhydrophobic instantly after the coating procedure because of spontaneously accumulated carbonaceous overlayer on TiO₂, and thus there was no need for any type of separate hydrophobization treatment. The highly photoactive LFS TiO₂ nanoparticle coating could be converted steplessly from superhydrophobic to superhydrophilic by UV-illumination, and the coating gave strong response to natural daylight illumination even in the shade. The superhydrophobic LFS TiO₂ coated surface can be used as an intelligent substrate, where photo-generated hydrophilic patterns guide the fluid setting and figure formation. Our study reveals that the wettability changes on the LFS TiO₂ surface were primarily caused by the photocatalytic removal of the carbonaceous material from TiO₂ during the UV-illumination and spontaneous accumulation of the carbonaceous material on the surface of the metal oxide during storage in the dark. The latter mechanism was found to be a temperature activated process which could be significantly speeded up by heat treatment. If other mechanisms such as surface oxidization, increment of hydroxyl groups, or charge separation played a role in the wetting phenomena on TiO₂, their effect was rather secondary as the removal and accumulation of the carbonaceous material dominated the wettability changes on the surface. Our study gives valuable information on the complex issue of photo-induced wettability changes on TiO₂.     

Switchable water absorption of paper via liquid flame spray nanoparticle coating

Surface wetting/anti-wetting and liquid absorption are relevant properties of many porous solids including paper and other cellulose-based materials. Here we demonstrate how surface wetting by water and water absorption of commercially available kraft paper can be altered by thin nanoparticle coatings fabricated by liquid flame spray in facile and continuous one-step process. Surface wettability and absorption properties of paper increased with silica and decreased with titania (TiO₂) nanoparticle coatings. Moreover, the water-repellent (superhydrophobic) TiO₂ nanoparticle coated paper could be switched to superhydrophilic and water absorbing by ultraviolet illumination. The experiments revealed that although surface wetting and liquid absorption of nanoparticle coated paper are strongly related to each other, they are two distinct phenomena which do not necessarily correlate. We propose wetting regimes on the nanoparticle coated paper samples on the basis of the experimental observations.     

Terahertz absorption spectra of commonly used antimalarial drugs

Optical Review - Terahertz (THz) spectra from the pure forms [i.e. the active pharmaceutical ingredients (APIs)] of four commonly used antimalarial drugs are reported. The well-defined spectral...     

1,3,5,7‐Tetraselena‐2,4,6,8(2,5)‐tetrathiophenaoctaphane

The novel title tetraselenacalix[4]arene, C₁₆H₈S₄Se₄ or [(C₄H₂S)Se]₄, has a centrosymmetric cyclic molecular structure with approximate C_2h molecular symmetry. The four thienyl rings are joined together by Se bridges and exhibit a syn–syn–anti–anti arrangement around the mol­ecule. The lattice consists of skewed stacks of mol­ecules, with chalcogen–chalcogen close contacts binding the stacks together, forming a two‐dimensional network of mol­ecules.     

One-pot synthesis of 3,4-disubstituted 1H-pyrroles from 2-tropanones

3,4-Disubstituted pyrroles (2, 3) were prepared from 6/7-carboxyethyl-3-phenyl-3-tropen-2-ones (1) regioselectively and with high yields by using tosylmethyl isocyanide (TosMIC). This procedure enables the synthesis of pyrroles substituted with two distinct groups: a phenyl group and a substituted pyrrolidine analogue. The crystal structure of product 2a was determined, and the analogous derivatives were identified by (1)H and (13)C NMR spectroscopy.     

Optical and electrical experiments at some transition-metal oxide foil-electrolyte interfaces2

Metal oxide layers formed from transition-metal foils oxidized by heating in air have been examined for their photoelectrolytic response. The metals examined are Y, Ti, Zr, Hf, V, Nb, Ta, Mo, W, and Pt. Weak photoeffects are observed for oxide layers of all of these metals. Sizable light-dependent oxygen gas evolution rates are found in Ti and also in W oxides. The spectral dependence of the oxygen response in these compounds is investigated, and interpretation is given of these experiments.     

Higher Weierstrass points on

We study the arithmetic properties of higher Weierstrass points on modular curves for primes . In particular, for , we obtain a relationship between the reductions modulo of the collection of -Weierstrass points on and the supersingular locus in characteristic .