Periodically Arranged Arrays of Dendritic Pt Nanospheres Using Cage‐Type Mesoporous Silica as a Hard Template

Dendritic Pt nanospheres of 20 nm diameter are synthesized by using a highly concentrated surfactant assembly within the large‐sized cage‐type mesopores of mesoporous silica (LP‐FDU‐12). After diluting the surfactant solution with ethanol, the lower viscosity leads to an improved penetration inside the mesopores. After Pt deposition followed by template removal, the arrangement of the Pt nanospheres is a replication from that of the mesopores in the original LP‐FDU‐12 template. Although it is well known that ordered LLCs can form on flat substrates, the confined space inside the mesopores hinders surfactant self‐organization. Therefore, the Pt nanospheres possess a dendritic porous structure over the entire area. The distortion observed in some nanospheres is attributed to the close proximity existing between neighboring cage‐type mesopores. This new type of nanoporous metal with a hierarchical architecture holds potential to enhance substance diffusivity/accessibility for further improvement of catalytic activity.     

Simulation of Differential Phase Detection Method Combined with Astigmatic Method using a Half Mirror in an Optical Pick-up

In an error detection optical system for optical pick-ups using a parallel plane type half mirror, influence on the differential phase detection (DPD) signal by a coma aberration was simulated. The coma aberration deforms the spot profile on the photodetector and influences the DPD signal level characteristics and the offset characteristics with respect to the objective lens shift. In the 4-segment-type DPD, the coma aberration caused by a half mirror 2.75 mm thick hardly affects the DPD signal if the photodetector is not misaligned. On the other hand, the 2-segment-type DPD has a small offset variation with respect to the objective lens shift and a large variation of the DPD signal level against the misalignment of the photodetector in comparison with the 4-segment-type DPD when there is no coma aberration. In the presence of a coma aberration, however, these variations of the 2-segment-type DPD are suppressed by choosing a pair of elements without the coma apex part of the spot.     

Aryl- and alkenyllithium preparations and copper-catalyzed reaction between the derived magnesium reagents and the monoacetate of 4-cyclopentene-1,3-diol

[reaction: see text] Aryl- and alkenyllithiums, prepared by halogen-lithium exchange with lithium, exchange with n-(or t-)BuLi, stannane-lithium exchange with n-BuLi, and direct lithiation with n-BuLi, were transformed into magnesium reagents with MgCl2 and subjected to CuCN-catalyzed reaction with the title monoacetate. Except for the halogen-lithium exchange with n-BuLi, the other preparations of the lithium anions were found to be compatible with the CuCN-catalyzed reaction to afford S(N)2-type products efficiently.     

Complex amphiphilic networks derived from diamine‐terminated poly(ethylene glycol) and benzylic chloride‐functionalized hyperbranched fluoropolymers

Amphiphilic copolymer networks were prepared from hyperbranched fluoropolymer (HBFP*, M_n = 38 kDa, by atom transfer radical‐self condensing vinyl copolymerization) and linear diamine‐terminated poly(ethylene glycol) (DA‐PEG, M_n = 1,630 Da). Model studies found that the crosslinking mechanism occurred at ambient temperature as a result of reaction between DA‐PEG and the benzylic chlorides of HBFP*. These networks underwent covalent attachment to glass microscope slides derivatized with 3‐aminopropyltriethoxysilane, whereupon gel percent studies at various weight percentages of DA‐PEG to HBFP* found that curing could be achieved at lower temperatures and shortened time periods relative to the previously reported parent HBFP–PEG system. Thermogravimetric analysis revealed that the crosslinked materials gave no evident mass loss up to 250 °C. Differential scanning calorimetry of the complex amphiphilic networks showed a suppressed glass transition temperature, relative to that observed for neat HBFP*, and multiple melting DA‐PEG endotherm(s) near 30 °C. The films possessed a topographically‐complex surface with features that increased in tandem with an increase in the ratio of DA‐PEG to HBFP*, as detected by atomic force microscopy and quantified by increased rms roughness values. Internal reflection infrared imaging revealed a heterogeneous surface composition and confirmed that the domain sizes increased as the weight percent of DA‐PEG increased. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4782–4794, 2006     

Superconducting phase at 7.7 K in the HgxReO3 compound with a hexagonal bronze structure

We have successfully synthesized a new rhenium-based hexagonal bronze material, HgxReO3, which exhibits superconductivity with the transition temperature Tc=7.7 K at ambient pressure and 11.1 K at 4 GPa. This compound is a superconductor with the highest Tc among hexagonal bronzes. Moreover, it presents the novel crystallographic feature that (Hg2)2+ polycations, in contrast to monatomic cations in known hexagonal bronzes, are incorporated into open channels. There is evidence that conducting electrons tightly couple with Hg-related phonons. Our results inspire detailed studies on the role of the rattling phonon in the occurrence of superconductivity in the hexagonal bronzes.     

A theoretical and numerical consideration of the longitudinal and transverse relaxations in the rotating frame

We previously derived a simple equation for solving time-dependent Bloch equations by a matrix operation. The purpose of this study was to present a theoretical and numerical consideration of the longitudinal (R_1ρ = 1/T_1ρ) and transverse relaxation rates in the rotating frame (R_2ρ = 1/T_2ρ), based on this method. First, we derived an equation describing the time evolution of the magnetization vector (M(t)) by expanding the matrix exponential into the eigenvalues and the corresponding eigenvectors using diagonalization. Second, we obtained the longitudinal magnetization vector in the rotating frame (M_1ρ(t)) by taking the inner product of M(t) and the eigenvector with the smallest eigenvalue in modulus, and then we obtained the transverse magnetization vector in the rotating frame (M_2ρ(t)) by subtracting M_1ρ(t) from M(t). For comparison, we also computed the spin-locked magnetization vector. We derived the exact solutions for R_1ρ and R_2ρ from the eigenvalues, and compared them with those obtained numerically from M_1ρ(t) and M_2ρ(t), respectively. There was excellent agreement between them. From the exact solutions for R_1ρ and R_2ρ, R_2ρ was found to be given by R_2ρ = (2R₂ + R₁)/2 − R_1ρ/2, where R₁ and R₂ denote the conventional longitudinal and transverse relaxation rates, respectively. We also derived M_1ρ(t) and M_2ρ(t) for bulk water protons, in which the effect of chemical exchange was taken into account using a 2-pool chemical exchange model, and we compared the R_1ρ and R_2ρ values obtained from the eigenvalues and those obtained numerically from M_1ρ(t) and M_2ρ(t). There was also excellent agreement between them. In conclusion, this study will be useful for better understanding of the longitudinal and transverse relaxations in the rotating frame and for analyzing the contrast mechanisms in T_1ρ- and T_2ρ-weighted MRI.     

Monohydride-Dichloro Rhodium(III) Complexes with Chiral Diphosphine Ligands as Catalysts for Asymmetric Hydrogenation of Olefinic Substrates

We report full details of the synthesis and characterization of monohydride-dichloro rhodium(III) complexes bearing chiral diphosphine ligands, such as (S)-BINAP, (S)-DM-SEGPHOS, and (S)-DTBM-SEGPHOS, producing cationic triply chloride bridged dinuclear rhodium(III) complexes ( 1 a : (S)-BINAP; 1 b : (S)-DM-SEGPHOS) and a neutral mononuclear monohydride-dichloro rhodium(III) complex ( 1 c : (S)-DTBM-SEGPHOS) in high yield and high purity. Their solid state structure and solution behavior were determined by crystallographic studies as well as full spectral data, including DOSY NMR spectroscopy. Among these three complexes, 1 c has a rigid pocket surrounded by two chloride atoms bound to the rhodium atom together with one tBu group of (S)-DTBM-SEGPHOS for fitting to simple olefins without any coordinating functional groups. Complex 1 c exhibited superior catalytic activity and enantioselectivity for asymmetric hydrogenation of exo-olefins and olefinic substrates. The catalytic activity of 1 c was compared with that of well-demonstrated dihydride species derived in situ from rhodium(I) precursors such as [Rh(cod)Cl]₂ and [Rh(cod)₂]⁺[BF₄]⁻ upon mixing with (S)-DTBM-SEGPHOS under dihydrogen.     

Kinetic Resolution of the Racemic 2‐Hydroxyalkanoates Using the Enantioselective Mixed‐Anhydride Method with Pivalic Anhydride and a Chiral Acyl‐Transfer Catalyst

A variety of optically active 2‐hydroxyalkanoates and the corresponding 2‐acyloxyalkanoates are produced by the kinetic resolution of racemic 2‐hydroxyalkanoates by using achiral 2,2‐diarylacetic acid with hindered carboxylic anhydrides as the coupling reagents. The combined use of diphenylacetic acid, pivalic anhydride, and (+)‐(R)‐benzotetramisole ((R)‐BTM) effectively produces (S)‐2‐hydroxyalkanoates and (R)‐2‐acyloxyalkanoates from the racemic 2‐hydroxyalkanoates (s‐values=47–202). This protocol directly provides the desired chiral 2‐hydroxyalkanoate derivatives from achiral diarylacetic acid and racemic secondary alcohols that do not include the sec‐phenethyl alcohol moiety by using the transacylation process to generate the mixed anhydrides from the acid components with bulky carboxylic anhydrides under the influence of the chiral acyl‐transfer catalyst. The transition state that provides the desired (R)‐2‐acyloxyalkanoate from (R)‐2‐hydroxyalkanoate included in the racemic mixture is disclosed by DFT calculations, and the structural features of the transition form are also discussed.     

Development of a non-destructive isotopic analysis method by gamma-ray emission measurement after negative muon irradiation

Journal of Radioanalytical and Nuclear Chemistry - Variations in isotopic abundance provide useful information for various scientific fields. Herein we performed a feasibility study by...