Synthesis of functional polyolefins using cationic bisphosphine monoxide-palladium complexes

The copolymerization of ethylene with polar vinyl monomers, such as vinyl acetate, acrylonitrile, vinyl ethers, and allyl monomers, was accomplished using cationic palladium complexes ligated by a bisphosphine monoxide (BPMO). The copolymers formed by these catalysts have highly linear microstructures and a random distribution of polar functional groups throughout the polymer chain. Our data demonstrate that cationic palladium complexes can exhibit good activity for polymerizations of polar monomers, in contrast to cationic α-diimine palladium complexes (Brookhart-type) that are not applicable to industrially relevant polar monomers beyond acrylates. Additionally, the studies reported here point out that phosphine-sulfonate ligated palladium complexes are no longer the singular family of catalysts that can promote the reaction of ethylene with many polar vinyl monomers to form linear functional polyolefins.     

One-pot aromatic amination based on carbon–nitrogen coupling reaction between aryl halides and azido compounds

An efficient copper-mediated C–N coupling reaction between various aryl halides and azido compounds to produce the corresponding aromatic primary amines was established. The present amination is apparently involved in both the reduction of an azido functionality to the corresponding primary amino group and its cross-coupling reaction with aryl halides in a one-pot manner. The present amination could be applied to the synthesis of procaine, a local anesthetic drug. A mechanistic study indicated that 2-aminoethanol could work as a major hydrogen donor and the reaction would proceed without the formation of the intermediary aryl azide.     

A geometrical characterization of strongly regular graphs

We give a necessary and sufficient condition of a Euclidean representation of a simple graph to be spherical. Moreover we show a characterization of strongly regular graphs from the view point of Euclidean representations of a graph. From this characterization, we define a natural generalized concept of a strongly regular graph closely related to Euclidean designs and codes.     

Expression of heme oxygenase-1 due to intracellular reactive oxygen species induced by ultrasound

The present study was undertaken to elucidate the mechanism by which ultrasound induces the expression of heme oxygenase-1 (HO-1). When human lymphoma U937 cells were exposed to a 1 MHz continuous wave for 1 min, HO-1 expression examined by real-time quantitative polymerase chain reaction and immunoblotting was observed at intensities above the cavitational threshold. No induction of HO-1 expression was observed in the cells exposed for 1 min to 42 degrees C, a temperature higher than that during sonication. When a potent antioxidant, N-acetyl-l-cysteine, was added to the culture medium before or after sonication, the induction was attenuated, indicating that reactive oxygen species (ROS) are involved. However, the addition of catalase did not affect the induction, and no HO-1 was observed on the addition of pre-sonicated medium, suggesting that hydrogen peroxide due to the recombination of hydroxyl radicals generated extracellularly was not involved. The addition of free radical scavengers, glutathion-monoethyl ester, dimethyl sulfoxide and D(-)-mannitol, suppressed the induction. A decrease in mitochondrial membrane potential and the generation of superoxide were also observed in the sonicated cells, suggesting that mitochondria were the source of intracellularly generated ROS. These results indicate that superoxide secondarily generated from damaged mitochondria, not hydroxyl radicals generated in medium directly by sonication, give rise to intracellular oxidative stress inducing HO-1 expression.     

Theoretical studies of phosphorescence spectra of tris(2,2'-bipyridine) transition metal compounds

Phosphorescence spectra of tris(2,2'-bipyridine) metal compounds, [M(bpy)3]n+, where M = Zn(II), Ru(II), Os(II), Rh(III), and Ir(III), were calculated using a harmonic oscillator approximation of adiabatic potential surfaces obtained by density functional theory (DFT). Using the Huang-Rhys (S) factors calculated by theoretical Franck-Condon analysis of T1 and S0 geometries, we successfully reproduced the emission spectra observed under various conditions by nonempirical calculations. The simulations of well-structured spectra of the Zn(II), Rh(III), and Ir(III) compounds confirmed that the emission originated from localized ligand-centered excited states with considerably distorted geometries of C2 symmetry. The spectrum simulation revealed that the phosphorescence state of [Ru(bpy)3]2+ was localized 3MLCT both in a solution and a glass matrix. Furthermore, a highly resolved phosphorescence spectrum observed for [Ru(bpy)3]2+ doped in a [Zn(bpy)3](ClO4)2 crystal was reproduced well using the geometry of the localized 3MLCT by assuming mode-specific broadening of low-frequency intramolecular vibrational modes. The deuterium effects of the electronic origins of the doped crystal observed by Riesen et al. were in excellent agreement with those predicted for the localized 3MLCT. However, the calculated satellite structures of the localized 3MLCT involving bpy-h8 in [Ru(bpy-h8)(3-x)(bpy-d8)x]2+ (x = 1,2) exhibited only the bpy-h8 vibrational modes, inconsistent with the simultaneous appearance of both bpy-h8 and bpy-h8 modes in the observed spectra. A simulation on the basis of the geometry of the delocalized 3MLCT was in reasonable agreement with an unresolved spectrum observed for a neat crystal of [Ru(bpy)3](PF6)2, which is inconsistent with the assignments of localized 3MLCT on the basis of the electronic origins. The inconsistency of the assignment on the basis of the adiabatic model is discussed in terms of vibronic coupling between the localized 3MLCT states. The 3MLCT state in [Os(bpy)3]2+ seems to vary with the environment: a fully localized 3MLCT in a solution, partially localized in a glass matrix, and delocalized in PF6 salts.     

Syntheses and X-ray crystal structures of zirconium(IV) and hafnium(IV) complexes containing monovacant wells-Dawson and Keggin polyoxotungstates

The syntheses and crystal structures of a series of zirconium(IV) and hafnium(IV) complexes with Dawson monovacant phosphotungstate [alpha2-P2W17O61](10-) and in situ-generated Keggin monovacant phosphotungstate [alpha-PW11O39](7-), which was obtained by a reaction of [alpha-PW12O40](3-) with Na2CO3, are described. K15H[Zr(alpha2-P2W17O61)2].25H2O (K-1), K16[Hf(alpha2-P2W17O61)2].19H2O (K-2), (Et2NH2)10[Zr(alpha-PW11O39)2].7H2O (Et2NH2-3), and (Et2NH2)10[Hf(alpha-PW11O39)2].2H2O (Et2NH2-4), being afforded by reactions in aqueous solutions of monolacunary Dawson and Keggin polyoxotungstates with ZrCl2O.8H2O and HfCl2O.8H2O followed by exchanging countercations, were obtained as analytically pure, homogeneous colorless crystals. Single-crystal X-ray structure analyses revealed that the Zr(IV) and Hf(IV) ions are in a square antiprismatic coordination environment with eight oxygen atoms, four of them being provided from each of the two monovacant polyanion ligands. Although the total molecular shapes and the 8-coordinate zirconium and hafnium centers of complexes 1-4 are identical, the bonding modes (bond lengths and bond angles) around the zirconium(IV) and hafnium(IV) centers were dependent on the monovacant structures of the polyanion ligands. Additionally, the characterization of complexes 1-4 was accomplished by elemental analysis, TG/DTA, FTIR, and solution (31P and 183W) NMR spectroscopy.     

Highly phosphorescent iridium complexes containing both tridentate bis(benzimidazolyl)-benzene or -pyridine and bidentate phenylpyridine: synthesis, photophysical properties, and theoretical study of Ir-bis(benzimidazolyl)benzene complex

Novel mixed-ligand Ir(III) complexes, [Ir(L)(NwedgeC)X]n+ (L = N/\C/\N or N/\N/\N; X = Cl, Br, I, CN, CH3CN, or -CCPh; n = 0 or 1), were synthesized, where N/\CwedgeN = bis(N-methylbenzimidazolyl)benzene (Mebib) and bis(N-phenylbenzimidazolyl)benzene (Phbib), N/\N/\N = bis(N-methylbenzimidazolyl)pyridine (Mebip), and N/\C = phenylpyridine (ppy) derivatives. The X-ray crystal structures of [Ir(Phbib)(ppy)Cl] and [Ir(Mebib)(mppy)Cl] [mppy = 5-methyl-2-(2'-pyridyl)phenyl] indicate that the nitrogen atom of the ppy ligand is located trans to the coordinating carbon atom in Me- or Phbib, while the coordinating carbon atom in ppy occupies the trans position of Cl. [Ir(Mebip)(ppy)Cl]+ showed a quasireversible Ir(III/IV) oxidation wave at +1.05 V, while the Ir complexes, [Ir(Mebib)(ppy)Cl], were oxidized at +0.42 V versus Fc/Fc+. The introduction of an Ir-C bond in [Ir(Mebib)(ppy)Cl] induces a large potential shift of 0.63 V in a negative direction. Further, the oxidation potential of [Ir(Mebib)(Rppy)X] was altered by the substitution of R, R', and X groups. Compared to the oxidation potential, the first reduction potential revealed an almost constant value at -2.36 to -2.46 V for [Ir(L)(ppy)Cl] (L = Mebib and Phbib) and -1.52 V for [Ir(Mebip)(ppy)Cl. The UV-vis spectra of [Ir(Mebib)(R-ppy)X] show a clear singlet metal-to-ligand charge-transfer transition around 407 approximately 425 nm and a triplet metal-to-ligand charge-transfer transition at 498 approximately 523 nm. [Ir(Mebip)(ppy)Cl]+ emits at 610 nm with a luminescent quantum yield of Phi = 0.16 at room temperature. The phosphorescence of [Ir(Mebib)(ppy)X] was observed at 526 nm for X = CN and 555 nm for X = Cl with the high luminescent quantum yields, Phi = 0.77 approximately 0.86, at room temperature. [Ir(Phbib)(ppy)Cl] shows the emission at 559 nm with a luminescent quantum yield of Phi = 0.95, which is an unprecedentedly high value compared to those of other emissive metal complexes. Compared to the luminescent quantum yields of the Ir(ppy)2(L) derivatives and [Ir(Mebip)(ppy)Cl]+, the neutral Ir complexes, [Ir(L)(R-ppy)X] (L = Me- or Phbib), reveal very high quantum yields and large radiative rate constants (kr) ranging from 3.4 x 10(5) to 5.5 x 10(5) s(-1). The density functional theory calculation suggests that these Ir complexes possess dominantly metal-to-ligand charge-transfer and halide-to-ligand charge-transfer excited states. The mechanism for a high phosphorescence yield in [Ir(bib)(ppy)X] is discussed herein from the perspective of the theoretical consideration of radiative rate constants using perturbation theory and a one-center spin-orbit coupling approximation.     

Computing Raman and infrared wavenumbers of nanostructures: application to silicon nanowires

The characterization of nanostructures with spectroscopic methods is a fundamental tool in nanoscience. For novel nanostructures, the interpretation of spectral features is a challenging task. To address this issue, we present the “Symmetry‐Filtered Molecular Dynamics (SFMD)” method to calculate Raman and infrared wavenumbers from molecular dynamics (MD) simulations, employing only the symmetry of the atomic structure. Explicit and expensive calculations of the electric polarizability or the dipole moment are not required. Therefore, our method can be easily used with any standard MD software. On the basis of the density functional tight‐binding method for the MD simulations, we apply our method to bulk silicon and small‐diameter hydrogen‐passivated silicon nanowires. For bulk silicon, we study the wavenumber shift of the Raman peak with temperature and obtain results that are in good agreement with experiments. We further show that thermal lattice expansion is a minor effect (22%) and that temperature‐driven anharmonic effects (78%) are the main contributions to that wavenumber shift. By analyzing the bond lengths of different silicon nanowires, we found that surface stress manifests as a 0.37% shortening of bonds only in the outermost silicon layer. We further analyzed the diameter‐dependent wavenumber shift of a Raman peak in silicon nanowires. We found that the main contribution to the wavenumber shift comes from the phonon confinement effect and surface stress leads to an additional shift of 9–22%. Our results indicate that our method is able to produce quantitative results that can be compared with experiments. We propose our method to be used for the understanding of Raman and infrared spectra of novel bulk and nanostructures. Copyright © 2012 John Wiley & Sons, Ltd.     

Novel liquid crystal multistage circular polarization switch for three-dimensional laser pico projectors

Crosstalk is one of the most important factors affecting the image quality of polarization switching three-dimensional (3D) projectors. The variation in the phase difference of a polarization switch owing to dispersion degrades crosstalk performance. We propose a novel multistage circular polarization switch comprising liquid crystal devices using a ferroelectric liquid crystal (FLC) in-plane fast switch and a thick nematic liquid crystal (NLC) retarder. In this paper, we present a proof-of-concept model of a 3D laser pico projector using a scanning MEMS head in combination with the polarization switch. We also evaluate the crosstalk and 3D performance of the projector.