Highly photoluminescent nanocrystals based on a gold(I) complex and their electrophoretic patterning

The fabrication of nanocrystals (NCs) composed of the cationic Au(I) complex was demonstrated by the reprecipitation method in which the colloidal solution of the NCs showed brilliant green phosphorescence with a quantum yield of 83% in n-hexane. Characterization of the prepared NCs was performed by transmission electron microscopy observation and elemental analysis with energy-dispersive X-ray spectroscopy. The obtained Au(I) NCs were particles of random shapes with a diameter of 200-400 nm. The selected-area electron diffraction and X-ray diffraction measurements showed the characteristic diffraction patterns attributable to the crystal structure of the bulk crystal of the Au(I) complex. A similar method was performed with a different counteranion, leading to a colloidal solution of the microcrystals (MCs) with brilliant yellow phosphorescence and a quantum yield of 26% in n-hexane. Luminescence patterning of the NCs and MCs was also achieved successfully by electrophoretic deposition onto an indium tin oxide (ITO)-coated glass substrate, resulting in characteristic luminescence patterns on the ITO substrates with relatively high photoluminescence quantum yields.     

Activation of ultrathin oxide films for chemical reaction by interface defects

Periodic density functional theory calculations revealed strong enhancement of chemical reactivity by defects located at the oxide-metal interface for water dissociation on ultrathin MgO films deposited on Ag(100) substrate. Accumulation of charge density at the oxide-metal interface due to irregular interface defects influences the chemical reactivity of MgO films by changing the charge distribution at the oxide surface. Our results reveal the importance of buried interface defects in controlling chemical reactions on an ultrathin oxide film supported by a metal substrate.     

Dependence of single-molecule conductance on molecule junction symmetry

The symmetry of a molecule junction has been shown to play a significant role in determining the conductance of the molecule, but the details of how conductance changes with symmetry have heretofore been unknown. Herein, we investigate a naphthalenedithiol single-molecule system in which sulfur atoms from the molecule are anchored to two facing gold electrodes. In the studied system, the highest single-molecule conductance, for a molecule junction of 1,4-symmetry, is 110 times larger than the lowest single-molecule conductance, for a molecule junction of 2,7-symmetry. We demonstrate clearly that the measured dependence of molecule junction symmetry for single-molecule junctions agrees with theoretical predictions.     

Cu-mediated chemoselective trifluoromethylation of benzyl bromides using shelf-stable electrophilic trifluoromethylating reagents

Copper-mediated chemoselective trifluoromethylation at the benzylic position by the use of shelf-stable electrophilic trifluoromethylating reagents 3 in good to high yields under mild conditions is described for the first time. The generality of this trifluoromethylation for a wide variety of benzyl bromides facilitates the rapid creation of structural diversity of medicinal candidates in drug discovery.     

Pd(II)-catalyzed cascade reaction with 1,3-chirality transfer; stereoselective synthesis of chiral nonracemic 2,2'-THF-THF ring units

A Pd(II)-catalyzed cascade reaction of chiral nonracemic allylic alcohols possessing an internal mono- or diepoxide and a terminal alcohol provided a contiguous THF-THF ring unit stereospecifically. The cyclization takes place in a 5-exo-tet-5-exo-trig fashion with high chirality transfer through a syn-S(N)2' like process for the formation of the internal THF ring. Chiral bis- and tris-THF-THF ring units were effectively prepared from acyclic precursors by the Pd-catalyzed reaction.     

On the local asymptotic behavior of the likelihood function for Meixner Lévy processes under high-frequency sampling

We discuss the local asymptotic behavior of the likelihood function associated with all the four characterizing parameters (α,β,δ,μ) of the Meixner Lévy process under high-frequency sampling scheme. We derive the optimal rate of convergence for each parameter and the Fisher information matrix in a closed form. The skewness parameter β exhibits a slower rate alone, relative to the other three parameters free of sampling rate. An unusual aspect is that the Fisher information matrix is constantly singular for full joint estimation of the four parameters. This is a particular phenomenon in the regular high-frequency sampling setting and is of essentially different nature from low-frequency sampling. As soon as either α or δ is fixed, the Fisher information matrix becomes diagonal, implying that the corresponding maximum likelihood estimators are asymptotically orthogonal.     

On simulation of tempered stable random variates

Various simulation methods for tempered stable random variates with stability index greater than one are investigated with a view towards practical implementation, in particular cases of very small scale parameter, which correspond to increments of a tempered stable Lévy process with a very short stepsize. Methods under consideration are based on acceptance-rejection sampling, a Gaussian approximation of a small jump component, and infinite shot noise series representations. Numerical results are presented to discuss advantages, limitations and trade-off issues between approximation error and required computing effort. With a given computing budget, an approximative acceptance-rejection sampling technique Baeumer and Meerschaert (2009) [11] is both most efficient and handiest in the case of very small scale parameter and moreover, any desired level of accuracy may be attained with a small amount of additional computing effort.     

Noncovalent ligand-to-ligand interactions alter sense of optical chirality in luminescent tris(β-diketonate) lanthanide(III) complexes containing a chiral bis(oxazolinyl) pyridine ligand

Highly luminescent tris[β-diketonate (HFA, 1,1,1,5,5,5-hexafluoropentane-2,4-dione)] europium(III) complexes containing a chiral bis(oxazolinyl) pyridine (pybox) ligand--[(Eu(III)(R)-Ph-pybox)(HFA)(3)], [(Eu(III)(R)-i-Pr-pybox)(HFA)(3)], and [(Eu(III)(R)-Me-Ph-pybox)(HFA)(3)])--exhibit strong circularly polarized luminescence (CPL) at the magnetic-dipole ((5)D(0) → (7)F(1)) transition, where the [(Eu(III)(R)-Ph-pybox)(HFA)(3)] complexes show virtually opposite CPL spectra as compared to those with the same chirality of [(Eu(III)(R)-i-Pr-pybox)(HFA)(3)] and [(Eu(III)(R)-Me-Ph-pybox)(HFA)(3)]. Similarly, the [(Tb(III)(R)-Ph-pybox)(HFA)(3)] complexes were found to exhibit CPL signals almost opposite to those of [(Tb(III)(R)-i-Pr-pybox)(HFA)(3)] and [(Tb(III)(R)-Me-Ph-pybox)(HFA)(3)] complexes with the same pybox chirality. Single-crystal X-ray structural analysis revealed ligand-ligand interactions between the pybox ligand and the HFA ligand in each lanthanide(III) complex: π-π stacking interactions in the Eu(III) and Tb(III) complexes with the Ph-pybox ligand, CH/F interactions in those with the i-Pr-pybox ligand, and CH/π interactions in those with the Me-Ph-pybox ligand. The ligand-ligand interactions between the achiral HFA ligands and the chiral pybox results in an asymmetric arrangement of three HFA ligands around the metal center. The metal center geometry varies depending on the types of ligand-ligand interaction.     

A risk assessment of human ether-a-go-go-related gene potassium channel inhibition by using lipophilicity and basicity for drug discovery

The blockade of human ether-a-go-go-related gene (hERG) potassium channels is widely regarded as the predominant cause of drug-induced QT prolongation. The correlation analysis between the inhibition of the hERG channel (hERG inhibition) and physicochemical properties was investigated by use of in-house quinolone antibiotics as model compounds. In order to establish a simple prediction model of hERG inhibition, we focused on the comprehensible physicochemical parameters such as lipophilicity (log P) and basicity (pK(a)). At first, the risk associated with increasing log P and pK(a) was examined by statistical analysis. It was demonstrated that the risk associated with increasing log P and pK(a) by one unit, respectively, almost identically increased. Consequently, equal attention should be paid to both parameters on hERG inhibition. Next, a prediction model of hERG inhibition which was represented by log P and pK(a) was investigated. As a result, we built the stepwise discriminant prediction model which took advantage of the risk judgment by zone classification. In conclusion, the impact of log P and pK(a) on hERG inhibition was clarified relatively and quantitatively. The quantitative risk assessment established based on both parameters, was considered to be a practical and useful tool in avoiding hERG inhibition and in the rational drug design for drug discovery, especially in lead optimization. Moreover, we also carried out a trend analysis using a different derivative and demonstrated that both parameters were equally significant for hERG inhibition.     

Hydrodynamic interpretation on the rotational diffusion of peroxylamine disulfonate solute dissolved in room temperature ionic liquids as studied by electron paramagnetic resonance spectroscopy

Rotational motion of a nitroxide radical, peroxylamine disulfonate (PADS), dissolved in room temperature ionic liquids (RTILs) was studied by analyzing electron paramagnetic resonance spectra of PADS in various RTILs. We determined physical properties of PADS such as the hyperfine coupling constant (A), the temperature dependence of anisotropic rotational correlation times (τ(∥) and τ(⊥)), and rotational anisotropy (N). We observed that the A values remain unchanged for various RTILs, which indicates negligible interaction between the N-O PADS group and the cation of RTIL. Large N values suggest strong interaction of the negative sulfonyl parts of PADS with the cations of RTILs. Most of the τ(∥), τ(⊥), and (τ(∥)τ(⊥))(1/2) values are within the range calculated on the basis of a hydrodynamic theory with stick and slip boundary conditions. It was deduced that this theory could not adequately explain the measured results in some RTILs with smaller BF(4) and PF(6) anions.