Reaction of acylsilanes with α-sulfinyl carbanions: regioselective synthesis of silyl enol ethers

The reaction of acylsilanes with α-sulfinyl carbanions such as α-lithioalkyl sulfoxide is described. The reaction proceeds to give silyl enol ethers preferentially through the initial formation of the α-silyl alkoxide intermediates. In particular, the products derived from enolizable acylsilanes were the regio-defined silyl enol ethers that cannot be obtained by usual enolization of the corresponding unsymmetrical ketones with base.     

Control of thermoresponsive property of urea end‐functionalized poly(N‐isopropylacrylamide) based on the hydrogen bond‐assisted self‐assembly in water

The precise synthesis and variation in the thermoresponsive property based on the supramolecular assembly of a novel urea end‐functionalized poly(N‐isopropylacrylamide) (PNIPAM) were studied. A series of PNIPAMs with different diphenylurea groups at the chain end (X? Ph? NH? CO? NH? Ph? trz? PNIPAM: X = H, OCH₃, CH₃, NO₂, Cl, and CF₃) were synthesized by using a combination of the atom transfer radical polymerization and the copper(I)‐catalyzed azide‐alkyne cycloaddition. The cloud point of the obtained polymers depended on the hydrogen‐bonding ability of the introduced urea group. The ¹H NMR measurement suggested that the obtained PNIPAM assembled in water via the intermolecular hydrogen bonding by the terminal urea group. From the dynamic light scattering and transmission electron microscopy measurements, the aggregated nanoparticles of the resulting polymer were directly observed in water at a temperature below its cloud point. The hydrogen‐bonding property of the chain end urea group was concluded to be involved in the aggregation of the PNIPAM in water, leading to the variation in its cloud point. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6259–6268, 2009     

Hexa‐ and Dodecanuclear Polyoxomolybdate Cyclic Compounds: Application toward the Facile Synthesis of Nanoparticles and Film Electrodeposition

Two new compounds based on O₃PCH₂PO₃^4? ligands and {Mo^V₂O₄} dimeric units have been synthesized and structurally characterized. The dodecanuclear Mo^V polyoxomolybdate species in (NH₄)₁₈[(Mo^V₂O₄)₆(OH)₆(O₃PCH₂PO₃)₆]?33 H₂O ( 1 ) is a cyclohexane‐like ring in a chair conformation with pseudo S₆ symmetry. In the solid state, the wheels align side by side, thus delimiting large rectangular voids. The hexanuclear anion in Na₈[(Mo^V₂O₄)₃(O₃PCH₂PO₃)₃(CH₃AsO₃)]? 19 H₂O ( 2 ) has a triangular framework and encapsulates a methylarsenato ligand. ³¹P NMR spectroscopic analysis revealed the stability of 2 in various aqueous media, whereas the stability of 1 depends on the nature of the cations present in solution. It has been evidenced that the transformation of 1 into 2 occurs in the presence of CH₃AsO₃^2? ions. This behavior shows that 1 can be used as a new precursor for the synthesis of Mo^V/diphosphonate systems. The two complexes were very efficient both as reductants of Pt and Pd metallic salts and as capping agents for the resulting Pt⁰ and Pd⁰ nanoparticles. The size of the obtained nanoparticles depends both on the nature of the polyoxometalate (POM; i.e., 1 or 2 ) and on the [metallic salt]/[POM] ratio. In all cases, X‐ray photoelectron spectroscopy (XPS) measurements have revealed the presence of Mo^VI species that stabilize the nanoparticles and the absence of Mo^V moieties. Diffuse‐reflectance FTIR spectra of the Pt nanoparticles show that the capping Mo^VI POMs are identical for both systems and contain the diphosphonato ligand. The colloidal solutions do not show any precipitate and the nanoparticles remain well‐dispersed for several months. The electrochemical reduction of Mo^V species was studied for 2 . Cyclic voltammetry alone and electrochemical quartz crystal microbalance coupled with cyclic voltammetry show the deposition of a film on the electrode surface during this reduction.     

Adaptively secure revocable hierarchical IBE from k-linear assumption

Designs, Codes and Cryptography - Revocable identity-based encryption (RIBE) is an extension of IBE with an efficient key revocation mechanism. Revocable hierarchical IBE (RHIBE) is its further...     

Chemisorption-induced gap states at organic-metal interfaces: benzenethiol and benzeneselenol on metal surfaces

Valence electronic states of benzenethiol (C(6)H(5)SH) and benzeneselenol (C(6)H(5)SeH) in the gas, condensed, and chemisorbed phases were examined by ultraviolet photoemission spectroscopy, metastable atom electron spectroscopy, and first-principles calculations using density functional theory. C(6)H(5)SH is chemisorbed on Pt(111) and Au(111) substrates to form a thiolate (C(6)H(5)S), and C(6)H(5)SeH is bound on Pt(111) substrate to form a selenolate (C(6)H(5)Se). In all cases, chemisorption-induced gap states (CIGSs) appear just below the Fermi level (E(F)) of the substrate, yielding a metallic character around the anchor S and Se atoms. However, the local density at E(F) decreases considerably from the anchor atom to the benzene ring, because strong coupling between benzene π(1e(1g)) and S 3p(or Se 4p) in free molecules is apparently lifted upon chemisorption. In other words, thiolates and selenolates (especially C(6)H(5)S on Au(111)) act as poor mediators of the metal wave functions at E(F), which is closely related to electric conductance in the relevant metal-organic-metal junctions at zero bias.     

Photodecomposition of water with methane over titanium oxide photocatalysts modified with metal

Metal-loaded titanium oxide photocatalysts produced hydrogen in the photodecomposition of water vapor with methane in the flow reactor. Ag/TiO₂ has the highest activity in comparison with other metal-loaded catalysts. The experiment in the absence of methane indicated that methane could effectively function as a reducing reagent of water. The significant decrease in the hydrogen formation rate with the time on stream was observed under all reaction conditions. The recalcination and the hydrogen rereduction of the used catalyst led to the restoration of the activity of the hydrogen formation. The adsorption of products and/or reactants on the catalyst surface seemed to cause these deactivations of the hydrogen formation.     

Kinetic study of thermal Z to E isomerization reactions of azobenzene and 4-dimethylamino-4'-nitroazobenzene in ionic liquids [1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with R = butyl, pentyl, and hexyl

Thermal Z to E isomerization reactions of azobenzene and 4-dimethylamino-4'-nitroazobenzene were examined in three ionic liquids of general formula 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (R = butyl, pentyl, and hexyl). The first-order rate constants and activation energies for the reactions of azobenzene measured in these ionic liquids were consistent with those measured in ordinary organic solvents, which indicated that the slow isomerization through the inversion mechanism with a nonpolar transition state was little influenced by the solvent properties, such as the viscosity and dielectric constant, of ionic liquids. On the other hand, the rate constants and the corresponding frequency factors of the Arrhenius plot were significantly reduced for the isomerization of 4-dimethylamino-4'-nitroazobenzene in ionic liquids compared with those for the isomerization in ordinary organic molecular solvents with similar dielectric properties. Although these ionic liquids are viscous, the apparent viscosity dependence of the rate constant could not be explained either by the Kramers-Grote-Hynes model or by the Agmon-Hopfield model for solution reactions. It is proposed that the positive and the negative charge centers of a highly polar rotational transition state are stabilized by the surrounding anions and cations, respectively, and that the ions must be rearranged so as to form highly ordered solvation shells around the charge centers of the reactant in the transition state. This requirement for the orderly solvation in the transition state results in unusually small frequency factors of 10(4)-10(7) s(-1).