Beyerane derivatives and a sesquiterpene dimer from Japanese Cypress (Chamaecyparis obtusa)

In the course of studies on biological active constituents from woody plants, we previously reported the isolation of many lignan derivatives as neurite outgrowth-promoting compounds from an ethyl acetate soluble fraction of Japanese Cypress (Chamaecyparis obtusa). Further chemical investigation on the residual parts of the ethyl acetate soluble fraction of a methanol extract of Japanese Cypress resulted in the isolation of four new beyerene type derivatives and a novel sesquiterpene dimer formed between cryptomeridiol and hinokiic acid. Their structures were elucidated as 18-O-(Z)-p-coumaroylbeyer-15-ene-18-ol (1), 18-O-(E)-p-coumaroylbeyer-15-ene-18-ol (2), 18-O-(E)-p-coumaroylbeyer-15-ene-11beta,18-diol (3), 18-O-(Z)-p-coumaroylbeyer-15-ene-11beta,18-diol (4) and ent-cryptomeridiol-4-yl-hinokiiate (5) by (1)H-NMR, (13)C-NMR, 2D-NMR, and HR-MS spectral analysis.     

Electronic structure of six-coordinate iron(III) monoazaporphyrins

The electronic structures of six-coordinate iron(III) octaethylmonoazaporphyrins, [Fe(MAzP)L 2] (+/-) ( 1), have been examined by means of (1)H NMR and EPR spectroscopy to reveal the effect of meso-nitrogen in the porphyrin ring. The complexes carrying axial ligands with strong field strengths such as 1-MeIm, DMAP, CN (-), and (t)BuNC adopt the low-spin state with the (d xy ) (2)(d xz , d yz ) (3) ground state in a wide temperature range where the (1)H NMR and EPR spectra are taken. In contrast, the complexes with much weaker axial ligands, such as 4-CNPy and 3,5-Cl 2Py, exhibit the spin transition from the mainly S = 3/2 at 298 K to the S = 1/2 with the (d xy ) (2)(d xz , d yz ) (3) ground state at 4 K. Only the THF complex has maintained the S = 3/2 throughout the temperature range examined. Thus, the electronic structures of 1 resemble those of the corresponding iron(III) octaethylporphyrins, [Fe(OEP)L 2] (+/-) ( 2). A couple of differences have been observed, however, in the electronic structures of 1 and 2. One of the differences is the electronic ground state in low-spin bis( (t)BuNC) complexes. While [Fe(OEP)( (t)BuNC) 2] (+) adopts the (d xz , d yz ) (4)(d xy ) (1) ground state, like most of the bis( (t)BuNC) complexes reported previously, [Fe(MAzP)( (t)BuNC) 2] (+) has shown the (d xy ) (2)(d xz , d yz ) (3) ground state. Another difference is the spin state of the bis(3,5-Cl 2Py) complexes. While [Fe(OEP)(3,5-Cl 2Py) 2] (+) has maintained the mixed S = 3/2 and 5/2 spin state from 298 to 4 K, [Fe(MAzP)(3,5-Cl 2Py) 2] (+) has shown the spin transition mentioned above. These differences have been ascribed to the narrower N4 cavity and the presence of lower-lying pi* orbital in MAzP as compared with OEP.     

Dependence of the conduction of a single biphenyl dithiol molecule on the dihedral angle between the phenyl rings and its application to a nanorectifier

The transport properties of a biphenyl dithiol (BPD) molecule sandwiched between two gold electrodes are studied using the nonequilibrium Green's function method based on the density functional theory. In particular, their dependence on the dihedral angle (phi=90 degrees -180 degrees ) between two phenyl rings is investigated. While the dihedral-angle dependence of the density of states projected on the BPD molecular orbitals is small, the transport properties change dramatically with phi. The transmission at the Fermi energy exhibits a minimum at phi=90.0 degrees and greatly increases with phi. The ratio of the maximum obtained at phi=180 degrees to the minimum exceeds 100. As an application of this characteristic transport behavior, a BPD molecule functionalized with NH(2) and NO(2) groups is considered. It is found that this molecule works as a nanorectifier.     

Energy exchange network of inter‐residue interactions within a thermally fluctuating protein molecule: A computational study

Protein function is regulated not only by the structure but also by physical dynamics and thermal fluctuations. We have developed the computer program, CURrent calculation for proteins (CURP), for the flow analysis of physical quantities within thermally fluctuating protein media. The CURP program was used to calculate the energy flow within the third PDZ domain of the neuronal protein PSD‐95, and the results were used to illustrate the energy exchange network of inter‐residue interactions based on atomistic molecular dynamics simulations. The removal of the α3 helix is known to decrease ligand affinity by 21‐fold without changing the overall protein structure; nevertheless, we demonstrated that the helix constitutes an essential part of the network graph. © 2015 Wiley Periodicals, Inc.     

Structure,energy and solute segregation behaviour of [110] symmetric tilt grain boundaries in yttria-stabilized cubic zirconia

Yttria-stabilized cubic zirconia bicrystals with [110] symmetric tilt grain boundaries are systematically fabricated by the diffusion bonding method. It is revealed that the grain-boundary atomistic structures, excess energies and solute segregation behaviours are strongly dependent on the macroscopic geometries of the boundaries. High-resolution transmission electron microscopy combined with lattice statics calculations suggests that the grain-boundary structures are characterized by the accumulation of coordination-deficient cation sites at their cores, whose densities have a clear correlation with excess energies and amounts of solute segregation. The orientation dependence of grain-boundary properties in cubic zirconia can thus be linked and understood via local grain-boundary atomistic structures with the characteristic miscoordinated cation sites.     

Unified approach to catechin hetero-oligomers: first total synthesis of trimer EZ-EG-CA isolated from Ziziphus jujuba

A catechin hetero-trimer isolated from Ziziphus jujuba has been synthesized. Among three constituent monomers, (-)-epiafzelechin and (-)-epigallocatechin were prepared by de novo synthesis. Trimer formation relied on the unified approach to oligomers based on the bromo-capping and the orthogonal activation, reaching the reported structure of the natural product.     

Pyrene‐Based Y‐shaped Solid‐State Blue Emitters: Synthesis,Characterization, and Photoluminescence

A series of pyrene‐based Y‐shaped blue emitters, namely, 7‐tert‐butyl‐1,3‐diarylpyrenes 4 were synthesized by the Suzuki cross‐coupling reaction of 7‐tert‐butyl‐1,3‐dibromopyrene with a variety of p‐substituted phenylboronic acids in good to excellent yields. These compounds were fully characterized by X‐ray crystallography, UV/Vis absorption and fluorescence spectroscopy, DFT calculations, thermogravimetric analysis, and differential scanning calorimetry. Single‐crystal X‐ray analysis revealed that the Y‐shaped arylpyrenes exhibited a low degree of π stacking owing to the steric effect of the bulky tert‐butyl group in the pyrene ring at the 7‐position, and thus, the intermolecular π–π interactions were effectively suppressed in the solid state. Despite the significantly twisted nonplanar structures, these molecules still displayed efficient intramolecular charge‐transfer emissions with clear solvatochromic shifts on increasing solvent polarity. An intriguing fact is that all of these molecules show highly blue emissions with excellent quantum yields in the solid state. Additionally, the two compounds containing the strongest electron‐accepting groups, CN ( 4d ) and CHO ( 4f ), possess high thermal stability, which, together with their excellent solid‐state fluorescence efficiency, makes them promising potential blue emitters in organic light‐emitting device applications.     

First-principles supercell calculations for simulating a shallow donor state in Si

We present first-principles simulations of As-doped Si carried out using several cubic supercells of up to 10 648 atoms. The 1s As donor level in each supercell splits into three states, which have A₁, T₂, and E symmetries, respectively. The 1s(A₁) wavefunction is well converged in the largest cell, and its spread is close to those of the effective-mass theories. However, the calculated binding energies are smaller than experimental values. This discrepancy would be due to the self-interaction error within the approximated exchange-correlation density functional used in this calculation. Therefore, we also show perturbative calculations based on an impurity potential without the self-interaction error to estimate the binding energies of the 1s(A₁) donor state. The estimated binding energy in the largest supercell agrees well with the experimental value.