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.     

Relationship between the broad OH stretching band of methanol and hydrogen-bonding patterns in the liquid phase

The OH stretching (nu(OH)) band of methanol observed in condensed phase has been analyzed in terms of hydrogen-bonding patterns. Quantum chemical calculations for methanol clusters have revealed that broadening of the nu(OH) envelope is reasonably reproduced by considering nearest and next-nearest neighbor interactions through hydrogen bonding. Because the hydrogen bond formed between donor (D) and acceptor (A) is cooperatively strengthened or weakened by a newly formed hydrogen bond at D or A, we have proposed the following notation for hydrogen-bonding patterns of monohydric alcohols: a(D)DAd(A)a(A), where a is the number of protons accepted by D (a(D)) or A (a(A)), and d(A) is the number of protons donated by A. The indicator of the hydrogen-bond strength, which is given by M(OH) = a(D) + d(A) - a(A), is correlated well with the nu(OH) wavenumber of the methanol molecule D participating in the a(D)DAd(A)a(A) pattern. The correlation between M(OH) and the hydrogen-bonding energy of the a(D)DAd(A)a(A) pattern has also been deduced from the calculation results for the clusters. The nu(OH) bands of methanol measured in the CCl4 solution and pure liquid have been successfully analyzed by the method proposed here.     

Palladium-catalyzed sp(3) CH activation of simple alkyl groups: direct preparation of indoline derivatives from N-alkyl-2-bromoanilines

The sp3 C-H activation of a simple alkyl group catalyzed by palladium(0) provides a novel and convenient strategy for the synthesis of various indolines from simple precursors, such as N-alkyl-2-bromoanilines. This study demonstrates that assisting moieties in the substrate such as a pyridine or quaternary carbon are not always necessary for sp3 C-H activation.     

Molecular understanding of the UCST-type phase separation behavior of a stereocontrolled poly(N-isopropylacrylamide) in bis(2-methoxyethyl) ether

The upper critical solution temperature (UCST)-type phase separation of an isotactic-rich poly( N-isopropylacrylamide) (PNiPA) in bis(2-methoxyethyl) ether (diglyme) has been investigated by turbidity measurement and infrared (IR) spectroscopy. The IR spectra of stereocontrolled PNiPAs in various solvents have clearly indicated that the amide I bands do not directly reflect the tacticity of the polymer. The relative intensity of the amide I bands changes depending upon the molecular environment around the amide groups of PNiPA, which is influenced by the tacticity. During the UCST-type phase separation of the isotactic-rich PNiPA in diglyme, the amide I band at around 1625 cm (-1) changes. To link the IR spectral change with the molecular information, quantum chemical calculations have been carried out for NiPA n-mers ( n = 1-4) with an isotactic stereosequence. The result has suggested that the amide I band at around 1625 cm (-1) arises from a helical structure formed by the isotactic stereosequences in the PNiPA main chain with the aid of intramolecular CO...H-N hydrogen bonding. The experimental IR spectra have revealed that the helical structures are unfolded as the temperature rises. The folding and unfolding of the isotactic sequences in the main chain may induce the thermal change in the solubility of the isotactic rich PNiPA in diglyme, resulting in the UCST-type phase separation of the solution.     

Radioactive decay speedup at T=5 K: electron-capture decay rate of (7)Be encapsulated in C(60)

The electron-capture (EC) decay rate of (7)Be in C(60) at the temperature of liquid helium (T=5 K) was measured and compared with the rate in Be metal at T=293 K. We found that the half-life of (7)Be in endohedral C(60) ((7)Be@C(60)) at a temperature close to T=5 K is 52.47+/-0.04 d, a value that is 0.34% faster than that at T=293 K. In this environment, the half-life of (7)Be is nearly 1.5% faster than that inside Be metal at room temperature (T=293 K). We then interpreted our observations in terms of calculations of the electron density at the (7)Be nucleus position inside the C(60); further, we estimate theoretically the temperature dependence (at T=0 K and 293 K) of the electron density at the Be nucleus position in the stable center inside C(60). The theoretical estimates were almost in agreement with the experimental observations.     

Physical properties of proton conducting membranes based on a protic ionic liquid

We have investigated the physical properties of proton conducting polymer membranes based on a protic ionic liquid (IL). Properties such as ionic conductivity, melting point of the polymer phase, and glass transition temperature of the liquid phase are studied as a function of IL/polymer ratio and temperature. We observe an increased thermomechanical stability of the membrane with increasing polymer content. However, there is a concomitant decrease in the conductivity with increasing polymer content. This decrease is larger than what can be expected from the dilution of the conducting IL by the insulating polymer matrix. The origin of this decrease can be caused both by the morphology of the membrane and by interactions between the polymer matrix and the ionic liquid. We find a change in the glass transition temperature and in the temperature dependence of the conductivity with increasing polymer content. Both effects can be related to the physical confinement of the IL in the polymer membrane.     

Zipper-mode double C-H activation: palladium-catalyzed direct construction of highly-fused heterocyclic systems

Direct construction of fused aromatic ring systems by "zipper-mode" double C-H bond activation is described. Treatment of (Z)-3-bromo-N-(2-bromo-3-phenylprop-2-enyl)aniline derivatives with a catalytic amount of Pd(OAc)2 and PCy3.HBF4 in the presence of Cs2CO3 in dioxane affords 4,5-naphtho[3,2,1-cd]indole derivatives in good yields. Introduction of heterocycles such as benzofuran, benzothiophene, or indole moieties into the substrates leads to the efficient construction of highly fused heterocyclic aromatic ring systems via C-H bond activation of the heteroaromatic rings.     

Asymmetric hydrogenation of alpha-hydroxy ketones catalyzed by MsDPEN-Cp*Ir(III) complex

Asymmetric hydrogenation of a series of alpha-hydroxy aromatic ketones in methanol catalyzed by Cp*Ir(OTf)(MsDPEN) (MsDPEN = N-(methanesulfonyl)-1,2-diphenylethylenediamine) affords the 1-aryl-1,2-ethanediols in up to 99% ee. The reaction can be conducted with a substrate-to-catalyst molar ratio as high as 6000 under 10 atm of H2. 1-hydroxy-2-propanone is also hydrogenated with high enantioselectivity.     

Facile synthesis of fluoroalkenes by palladium-catalyzed reductive defluorination of allylic gem-difluorides

Chemo- and stereoselective synthesis of fluoroalkenes was achieved in excellent yields via Pd-catalyzed C-F bond activation. In this transformation, Et3N plays a crucial role to produce reactive hydride species such as Ph(EtO)SiH2 and Ph(EtO)2SiH by promoting dehydrogenative coupling. The reaction proceeds efficiently at 50 degrees C with a variety of substrates and is also useful for the synthesis of fluoroalkene peptidomimetics.