A lattice Monte Carlo simulation of the FePt alloy using a first-principles renormalized four-body interaction

Although a lattice Monte Carlo method provides an effective, simple, and fast way to study thermodynamic properties of substitutional alloys, it cannot treat by itself the off-lattice effects, such as thermal vibrations and local distortions. Therefore, even if the interaction among atoms at lattice points is calculated accurately by means of first-principles calculations, the lattice Monte Carlo simulation overestimates the order-disorder phase transition temperature. In this paper, we treat this problem in the investigation of the FePt alloy, which has recently attracted considerable interest in its magnetic properties. We apply a simple version of the potential renormalization theory to determine the interaction among atoms, including partly the off-lattice effects by means of first-principles calculations. Then, we use the interaction to perform a lattice Monte Carlo simulation of the FePt alloy on a fcc lattice. From the results, we find that the transition temperature obtained after the present renormalization procedure becomes closer to the experimental value.     

Quantized hydration energies of ions and structure of hydration shell from the experimental gas-phase data

With previous data on alkali metal and halide ions included [Rais, J.; Okada, T. Anal. Sci. 2006, 22, 533], we analyzed rather broad data on ionic hydration from the point of view of gaseous cluster energetics. We have now added alkaline earth cations, Zn(2+), H(+), OH(-), Cu(+), Ag(+), Bi(+), Pb(+), and alkylammonium cations. The present analysis revealed the octa-coordinated nature of alkaline earth cations, which is not fully pronounced for Be(2+) and Zn(2+), existence of Eigen protonium complex, which is trigonally hydrated, and particular property of the first OH-, H(2)O cluster. Whereas these findings are generally in accordance with theoretical model calculation studies, we have foreseen in addition tetrahedral hydration for halide anions and Rb(+) and Cs(+), as well as for alkylammonium ions. The obtained picture of the quantized solvation of ions is mirrored in the ionization potentials of outer electrons of pertinent atoms. This is a second independent phenomenon, and together, they invoked a common pattern formation ("Aufbau") obeying tetra- and octa-coordinated principles.     

Dual emission from rhenium(I) complexes induced by an interligand aromatic interaction

A series of rhenium(I) diimine complexes cis,trans-[Re(dmb)(CO)(2)(PR(1)R(2)R(3))(PR(4)R(5)R(6))](+) (dmb=4,4'-dimethyl-2,2'-bipyridine, R(n)=phenyl or alkyl), each of which bears two phosphine ligands with various numbers of phenyl groups, has been synthesized by using the photochemical ligand-substitution reaction. Detailed studies of the structural features, not only in the crystal but also in solution, indicate that the number of phenyl groups is a crucial factor in controlling the rotational conformation of the phosphine ligands, which in turn determines the extent of the π-π interaction between the aromatic diimine ligand and the phenyl group(s). The π-π interaction strongly affected both electrochemical and photophysical properties: 1) the oxidation power of the Re complex became stronger, 2) the lifetime of the excited state became longer, and 3) the Stokes shift between the (1) MLCT absorption band and emission from the corresponding (3) MLCT excited state became smaller. In particular, the diphenyl and triphenyl phosphine had much greater influence on the properties than the monophenyl phosphine ligand. Dual emission was observed from the different rotational conformers of the complexes with an intermediate number of phenyl groups in the phosphine ligands.     

Unexpected chiral induction from achiral cationic polythiophene aggregates and its application to the sugar pattern recognition

The aggregates of a cationic polythiophene (PT1) formed in poor solvent in the presence of sugars showed the distinct circular dichroism activity, the intensity being well correlated with the specific optical rotation [α] of sugars: therefore, the present system is useful as a novel sugar structure reading-out method.     

Alcohol and proton transport in perfluorinated ionomer membranes for fuel cells

To clarify the transport mechanisms of alcohols and proton in perfluorosulfonated ionomer (PFSI) membranes for fuel cells, four membranes having different equivalent weight (EW) values were examined. Membranes were immersed in methanol, ethanol, and 2-propanol to prepare a total of 12 samples, and membrane swelling, mass (alcohol and proton) transports, and interactions between alcohols and proton were investigated systematically in the fully penetrated state. The membrane expansion fraction theta and alcohol content lambda increased with decreasing the EW value for all the samples. The self-diffusion coefficients (D's) of the alkyl group and of OH (including protons) were measured separately by the pulsed-gradient spin-echo (PGSE)-NMR method and the D's also increased with decreasing the EW value. These results implied that the alcohols penetrate into the hydrophilic regions of the PFSI membranes and diffuse through the space expanded by the alcohols. The ionic cluster regions formed by the alcohols resemble those induced by water in the water swollen membrane, where protons dissociated from sulfonic acid groups transport through the regions together with water molecules. The D values decreased with increasing the molecular weight of alcohols. This trend was supported by activation energies Ea estimated from the Arrhenius plots of D in the temperature range from 30 to -40 degrees C. The PGSE-NMR measurements also revealed that protons move faster than the alkyl groups in the membranes. The proton transport by the Grotthuss (hopping) mechanism was facilitated by the increase of the alcohol content and the decrease of the molecular weight. This result was also supported by the experimental results of proton conductivity kappa and mobility u(H(+)). Density functional theory (DFT) calculations of the interaction energy DeltaE(int) between proton and alcohol (including OH) showed that the /DeltaE(int)/ increases with increasing the molecular weight of alcohols, which is in a inverse relationship with the kappa and u(H(+)) values. The proton transport depends strongly on the DeltaE(int) in the membranes.     

Photodissociation of nitrous oxide starting from excited bending levels

The photodissociation dynamics of N2O in the wavelength region of 203-205 nm was studied by velocity map ion imaging. A speed resolution of 0.8% was obtained using standard projection imaging and subpixel centroiding calculations. To investigate N2O dissociation starting from the excited bending levels in the ground electronic state, a supersonic molecular beam and an effusive beam were used. The photoabsorption transition probability from the first excited bending level in the wavelength region of 203-205 nm was estimated to be seven times greater than that from the ground vibrational level.     

Electrophoretic behavior of plasmid DNA in the presence of various intercalating dyes

In the present study, the electrophoretic behavior of linear, supercoiled and nicked circular plasmid DNA in the presence of various intercalating dyes was characterized using pGL3 plasmid DNA as a model. The enzymatic digestion of pGL3 plasmid DNA with HindIIIwas monitored by capillary electrophoresis coupled with laser-induced fluorescence detection (CE-LIF). Nicked circular plasmid DNA was found to be relatively sensitive to enzymes, and was almost digested into the linear conformer after 10-min incubation, indicating that nicked circular plasmid DNA has little chance of targeting and entering the cell nucleus. Partly digested plasmid DNA containing only linear and supercoiled conformers can be used as a standard to confirm the migration order of plasmid DNA. In methylcellulose (MC) solution with YO-PRO-1 or YOYO-1, linear plasmid DNA eluted first, followed by supercoiled and nicked plasmid DNA, and nicked plasmid DNA eluted as a broad peak. With SYBR Green 1, nicked plasmid DNA eluted first as three sharp peaks, followed by linear and supercoiled plasmid DNA. The nuclear plasmid DNA from two transfected cell lines was successfully analyzed using the present procedure. Similar results were obtained with an analysis time of seconds using microchip electrophoresis with laser-induced fluorescence detection (mu-CE-LIF). To our knowledge, these results represent the first reported analysis of nuclear plasmid DNA from transfection cells by CE-LIF or mu-CE-LIF without pre-preparation, suggesting that the present procedure is a promising alternative method for evaluating transfection efficiency of DNA delivery systems.     

Addition of benzenethiol to terminal alkynes catalyzed by hydrotris(3,5-dimethylpyrazolyl)borate-Rh(III) bis(thiolate) complex: Mechanistic studies with characterization of the key intermediate

The Rh(III)-thiolate complex [Tp^∗Rh(SPh)₂(MeCN)] (2; Tp^∗ = hydrotris(3,5-dimethylpyrazolyl)borate) readily undergoes substitution of MeCN by XyNC (Xy = 2,6-dimethylphenyl) to give the isocyanide complex [Tp^∗Rh(SPh)₂(XyNC)] (3), whereas reaction of 2 with terminal alkynes results in the formation of the rhodathiacyclobutene complex [Tp^∗Rh(SPh){η²-CHCR(SPh)}] (4; R = aryl, alkyl). Molecular structures of 3 and 4 (R = CH₂Ph) have been determined by single crystal X-ray diffraction. Complex 2 as well as [Tp^∗Rh(cyclooctene)(MeCN)] have been found to catalyze regioselective addition of benzenethiol to terminal alkynes RCCH at 50 °C to give R(PhS)CCH₂ in moderate to high yields. The above products are selectively formed when R = CH₂Ph and n-C₆H₁₃, while cis-RCHCHSPh and RC(SPh)₂CH₃ are also obtained as by-products when R = p-MeOC₆H₄. Catalytic cycle involving 2 and 4 is proposed based on the mechanistic studies using NMR measurement.     

Polycarbonate Crystallization by Vapor‐Grown Carbon Fiber with and without Magnetic Field

Polycarbonate (PC)/vapor‐grown carbon fiber (VGCF™) composite was prepared through melt compounding. It was unexpectedly found from differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD) that the crystallization of PC was substantially accelerated in the presence of the ordered graphite surface of VGCF™. To make an aligned structure of PC crystallization together with the orientation of VGCF™, a magnetic field of 2.4 T was applied to the composite under several temperature profiles. The WAXD pattern revealed that not only dispersed VGCF™ but also matrix PC crystallization was magnetically aligned through the optimization of processes. The evidence for PC crystallization by VGCF™ with and without magnetic force is described.

Optical micrograph (a) and WAXD pattern (b) of PC/VGCF™ (95:5 wt. ratio) composite which was treated under a magnetic field (vertical direction) of 2.4 T under an optimized heating profile.