Synthesis of Dendrimer-Like Star-Branched Poly(methyl methacrylate)s of Generations Consisting of Four Branched Polymer Chains at Each Junction by Iterative Methodology Involving Coupling and Transformation Reactions

A series of dendrimer-like star-branched poly(methyl methacrylate)s (PMMA)s of generations consisting of four branched segments at each junction have been successfully synthesized by developing an iterative methodology. It involves two reaction steps in each iterative reaction sequence, (a) a coupling reaction of the α-functionalized living anionic PMMA with four tert-butyldimethylsilyloxymethylphenyl (SMP) groups with benzy bromide (BnBr)-chain-functionalized PMMA and (b) a transformation of SMP group into BnBr functionality. By repeating the reaction sequence thrice, the above-mentioned dendrimer-like star-branched (PMMA)s of up to third-generation made up of 4, 20, and 84 PMMA segments and 16, 64, and 256 BnBr termini were synthesized by the first, second, and third iterative processes, respectively. The resulting polymers all were well-defined in branched architecture and precisely controlled in chain length.     

Kinetic solvent effects in the reactions of diphenyldiazomethane with electron acceptors. Correlation between electron affinities and the slopes of the plots of log k vs solvent basicity parameter, Dπ

Kinetic study of the reactions of diphenyldiazomethane with various electron acceptors were made in six aromatic solvents. Log k were correlated with the solvent basicity parameter, D_π, and the regression slopes were found to be a function of electron affinities.     

Two conformers of 10,11‐dihydro‐5H‐dibenzo[a,d]cyclo­heptene spiro‐linked with homobenzoquinone epoxide

The crystal structures of the two thermally equilibrated conformational isomers of the epoxide 1′,5′‐dimethyl­spiro[10,11‐dihydro‐5H‐dibenzo[a,d]cyclo­heptene‐5,8′‐4′‐oxatricyclo[5.1.0.0^3,5]octane]‐2′,6′‐dione, C₂₃H₂₀O₃, have been determined by X‐ray diffraction. In the tricyclic dione skeleton, the oxirane and cyclo­propane rings adopt an anti structure with respect to the conjunct quinone frame. The spiro‐linked 10,11‐dihydro‐5H‐dibenzo[a,d]cyclo­heptene ring of the major isomer has a fairly twisted boat form, folding opposite to the adjoining cyclo­propane methyl substituent, whereas the seven‐membered ring of the minor isomer has an almost ideal twist–boat form, inversely folding to the side of the relevant methyl group. The conformational structures of these isomers have been compared with those of the corresponding isomers of the unepoxidized homobenzoquinone.     

The simple solvent-free synthesis of 1H-quinazoline-2,4-diones using supercritical carbon dioxide and catalytic amount of base

Only supercritical carbon dioxide (scCO₂) as a reactant and a solvent, and catalytic amount of base (DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), DBN (1,5-diazabicyclo[4.3.0]non-5-ene), Dabco^® (1,4-diazabicyclo[2.2.2]octane), and triethylamine) afforded 1H-quinazoline-2,4-diones in good to excellent yields from 2-aminobenzonitriles. 6,7-Dimethoxy-1H-quinazoline-2,4-dione, which is a key intermediate of medicines (Prazosin, Bunazosin, and Doxazosin) was synthesized successfully in a 97% yield, using 0.1 equiv of DBU under scCO₂ (10 MPa) at 80 °C.     

EXAFS/FT-IR characterization of tetra-iridium carbonyl clusters bound to tris-(hydroxymethyl)phosphine grafted silica surface catalytically active for propene oxidation to acetone

Structure and catalytic activity of Ir₄(CO)₁₂ bound to tris-(hydroxymethyl)phosphine (THP) grafted silica (THP/SiO₂) was investigated by means of EXAFS, FT-IR and kinetic studies. It was found that Ir₄(CO)₁₂ was uniformly attached on THP/SiO₂ by substitution of CO by THP (Ir₄/THP/SiO₂). The tetra-iridium carbonyl cluster framework was remained during the substitution of THP ligands and two THP ligands coordinated to the iridium carbonyl clusters to form Ir₄(CO)₁₀(THP/SiO₂)₂. species. When Ir₄/THP/SiO₂ was evacuated at 373 K, bridge CO was desorbed and Debye-Waller factor of Ir---Ir contribution derived from EXAFS analysis was increased which suggested that the cluster framework was distorted by the evacuation at 373 K. The resulting sample evacuated at 373 K was an active catalyst for hydroformylation of ethene and partial oxidation of propene, while the Ir₄/THP/SiO₂ without evacuation exhibited poor catalytic activities. The propene oxidation reaction proceed on the Ir₄/THP/SiO₂ evacuated at 323–353 K under subatmospheric pressures to give acetone as a product in high selectivity. The ethene hydroformylation proceed on the evacuated Ir₄/THP/SiO₂ at lower temperatures compared with other conventional iridium catalysts. EXAFS characterization and kinetic studies suggested that the catalytic activities were associated with the structural distortion of the iridium cluster framework due to surface attachment by the bidentate phosphine substitution.     

Direct evidence for root growth of vertically aligned single-walled carbon nanotubes by microwave plasma chemical vapor deposition

The root growth mode of extremely dense and vertically aligned single-walled carbon nanotubes (SWNTs) synthesized by microwave plasma chemical vapor deposition was clarified by a new method, marker growth, which does not require transmission electron microscopy. SWNT layers were grown intermittently on a substrate, and a line between the layers was used as a marker to identify the growth mode. Micro-Raman spectroscopy revealed that the SWNT layers have the same diameter distribution.     

Photochemistry of Flavins in Micelles: Specific Effects of Anionic Surfactants on the Monomerization of Thymine Cyclobutane Dimers Photosensitized by Tetra-O-acyl Riboflavins*

It was found that tetra-o-acyl riboflavins efficiently photosensitize the monomerization of the cis, syn-cyclobutane dimers of 1,3-dimethylthymine and 1,3-dimethyluracil in aqueous solution in the presence of such anionic surfactants as sodium dodecyl sulfate and sodium hexadecyl sulfate at concentrations higher than their critical micelle concentration, while little monomerization of the dimers was photosensitized by the flavins in the absence of the surfactants and even in the presence of cationic and nonionic surfactants.     

An explicit time-domain finite element method for room acoustics simulations: Comparison of the performance with implicit methods

This paper presents the applicability of an explicit time-domain finite element method (TD-FEM) using a dispersion reduction technique called modified integration rules (MIR) on room acoustics simulations with a frequency-independent finite impedance boundary. First, a dispersion error analysis and a stability analysis are performed to derive the dispersion relation and the stability condition of the present explicit TD-FEM for three-dimensional room acoustics simulations with an infinite impedance boundary. Secondly, the accuracy and efficiency of the explicit TD-FEM are presented by comparing with implicit TD-FEM using MIR through room acoustics simulations in a rectangular room with infinite impedance boundaries. Thirdly, the stability condition of the explicit TD-FEM is investigated numerically in the case with finite impedance boundaries. Finally, the performance of the explicit TD-FEM in room acoustics simulations with finite impedance boundaries is demonstrated in a comparison with the implicit TD-FEM. Although the stability of the present explicit TD-FEM is dependent on the impedance values given at boundaries, the explicit TD-FEM is computationally more efficient than the implicit method from the perspective of computational time for acoustics simulations of a room with larger impedance values at boundaries.