Analysis of atomic arrangement in magnetic Fe–Pt nanoparticles

The order parameter S of Fe–Pt nanoparticles is estimated from X-ray diffraction (XRD) patterns. The total intensity of a diffraction peak is obtained by Rietveld analysis as well as simply integrating the intensity. The Rietveld analysis is found to provide a plausible value of S even for a sample showing an XRD pattern with broad and overlapped peaks. Another order parameter Q, which is obtained from Mössbauer spectra, is introduced, and it is confirmed that Q is equivalent to the probability of Fe atoms being in the L1₀-type atomic arrangement. The coercivity of Fe–Pt nanoparticles is directly proportional to Q, while it vanishes at S=0.4, indicating that the magnetic property of Fe–Pt nanoparticles has a closer relationship to Q than S.     

(+)-Phorboxazole A synthetic studies. A highly convergent, second generation total synthesis of (+)-phorboxazole A

[structure: see text] A second generation total synthesis of the potent antitumor agent (+)-phorboxazole A (1) has been achieved. The cornerstone of this approach comprises a more convergent strategy, involving late-stage Stille union of a fully elaborated C(1-28) macrocycle with a C(29-46) side chain. The second generation synthesis entails the longest linear sequence of 24 steps, with an overall yield of 4.2%.     

Preparation of polymethyl methacrylate with well-controlled stereoregularity by anionic polymerization in an ionic liquid solvent

This study investigates the effect of ionic liquids (ILs) on the anionic polymerization of methyl methacrylate (MMA). Polymethyl methacrylate (PMMA), an isotactic polymer, is prepared by anionic polymerization at a high reaction temperature with an IL that acts as both solvent and additive. The most plausible reaction mechanism is determined using ¹H NMR and Fourier-transform infrared spectroscopy. The electrostatic interaction between MMA and the IL increases the apparent steric hindrance in MMA, resulting in the isotactic PMMA.     

Structure–function relationships of the supramolecular assembly of the bacterial photosynthetic antenna complexes in lipid membranes

Appropriate experimental platforms are required to clarify the structure–function relationships of membrane protein assemblies. In photosynthetic bacteria, light-harvesting complex 2 and light-harvesting/reaction center core complex play key roles in capturing and transferring light energy and facilitating subsequent charge separation. These photosynthetic apparatuses form a supramolecular assembly in the photosynthetic membrane. However, the mechanism through which this assembly influences the efficiency of energy conversion remains to be clarified. We review our recent studies that were conducted to evaluate the structure–function relationship of the supramolecular assembly of photosynthetic antenna complexes in various lipid bilayer systems, as well as the construction of novel systems of planar lipid membranes for use as experimental platforms.     

Photorefractive effect in the relaxor ferroelectric material 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3

The photorefractive effect in a nominally undoped 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 single crystal is measured. We report what is, to our knowledge, the first observation of the photorefractive effect in Pb-based relaxor ferroelectric crystals. The crystal is grown by the flux solution method. Then it is cut into a 2 mm x 4 mm x 8 mm piece and electrically poled along the [111] direction. The coupling constant of the two-wave mixing is 17 cm(-1), and the normalized time constant under 1-W/cm(2) illumination is 12 s at a wave-length of 476 nm. The effective trap density is calculated as 5 x 10(16) cm(-3) from the Debye screening length under the assumption of Kukhtarev's band-transport model. The dominant carrier is identified to be holes from the direction of two-wave mixing energy transfer.     

Role of Arg123 in Light‐driven Anion Pump Mechanisms of pharaonis Halorhodopsin†

Halorhodopsin (HR) acts as a light‐driven chloride pump which transports a chloride ion from the extracellular (EC) to the cytoplasmic space during a photocycle reaction that includes some photointermediates initiated by illumination. To understand the chloride uptake mechanisms, we focused on a basic residue Arg123 of HR from Natronomonas pharaonis (NpHR), which is the only basic residue located in the EC half ion channel. By the measurements of the visible absorption spectra in the dark and the light‐induced inward current through the membrane, it was shown that the chloride binding and transport ability of NpHR completely disappeared by the change of arginine to glutamine. From flashphotolysis analysis, the photocycle of R123Q differed from that of wildtype NpHR completely. The response of the R123H mutant depended on pH. These facts imply that the positive charge at position 123 is essential for chloride binding in the ground state and for the chloride uptake under illumination. On the basis of the molecular structures of HR and the anion‐transportable mutants of bacteriorhodopsin, the effects of the positive charge and the conformational change of the Arg123 side chain as well as the chloride‐pumping mechanism are discussed.     

Synthesis of optically active tetrahydrozerumbone

Tetrahydrozerumbone 2, which has a powerful balmy fragrance, has a stereogenic carbon at C2 and can be easily prepared from zerumbone 1, which is one of the most important materials that displays an NMRDOS character. Reduction of 2 gave two diastereomers 3 and 4; their optically active (>99% ee) alcohols were obtained by lipase-catalyzed stereoselective transesterification of each racemic alcohol. The enantioselectivity of tetrahydrozerumbol does not entirely depend on the hydroxyl position but on the 2-methyl position. Compounds (R)-2 and (S)-2 were obtained by Dess–Martin oxidation of the corresponding alcohols. Interestingly, (R)-2 showed a strong balmy fragrance while (S)-2 had hardly any fragrance.     

Field-induced order-disorder transition in antiferromagnetic BaCo(2)V(2)O(8) driven by a softening of spinon excitation

High field magnetization and ESR measurements on the quasi-one-dimensional (1D) antiferromagnet BaCo(2)V(2)O(8) have been performed in magnetic fields up to 50 T along the chain. The experimental results are explained well in terms of a 1D S=1/2 antiferromagnetic XXZ model in longitudinal fields. We show that the quantum phase transition from the Néel ordered phase to the spin liquid one in the model is responsible for a peculiar order to disorder transition in BaCo(2)V(2)O(8).