Dynamical valence fluctuation at the charge-density-wave phase boundary in iodide-bridged Pt compound [Pt(chxn)2I]I2

We synthesized a novel iodo-bridged linear chain platinum compound, having the quasi-two-dimensional charge-density-wave (CDW) ground state and the smallest band gap. In this compound, we discovered an anomalous valence state in the boundary region at which the CDW phase alternates in the crystal by means of ESR, X-ray diffuse scattering, STM, and electrical resistivity. This anomalous state can be explained by the fast fluctuation between Pt(IV)-I...Pt(II) and Pt(II)...I-Pt(IV) in the double well potential. This is the first observation of the dynamical fluctuation of the CDW phase among the quasi one-dimensional halogen-bridged complexes.     

An ESR spin-label study on molecular mobility in the interface between microphases of a diblock copolymer: effects of admixture of homopolymers that are miscible with one of the blocks

Molecular mobility in the interfacial region of a microphase-separated structure was studied in binary mixtures of AB-type diblock copolymers and homopolymers (miscible with only A) by the spin-label technique. In this study, we prepared (a) binary blends of polystyrene-block-poly(methyl acrylate) (PS-block-PMA) and homopolymer poly(cyclohexyl acrylate)'s having the number-averaged molecular weight (Mn) of 1000 (PCHA-S) and (b) having the Mn of 17300 (PCHA-L), and (c) binary mixtures of the PS-block-PMA and homopolymer PS with the Mn of 900 (PS-1). Emphasis was placed on effects of the molecular weight and the miscibility of added homopolymers on the mobility in the interfacial region of the microphase separation. Selective incorporation of the added PCHA-S, PCHA-L, and PS-1 into the PS phase of the PS-block-PMA was confirmed by modulated-temperature differential scanning calorimetry (MDSC) measurement as a decrease in the glass transition temperature of the PS phase. Moreover, the MDSC and small-angle X-ray scattering (SAXS) measurements suggested that the spatial distributions of the PCHA-S and PS-1 in the PS phase were relatively uniform because of their small Mn. On the other hand, the distribution of the PCHA-L in the PS phase was somewhat heterogeneous because of the large Mn of the PCHA-L. The spin-label at the junction point of the PS-block-PMA allowed us to estimate the mobility in the interfacial region of the microphase separation. Influence of the PCHA-S and PCHA-L on the mobility in the interfacial region was negligible even though the relatively uniform distribution of the PCHA-S in the PS phase was suggested by the SAXS and MDSC. More uniform distribution of the PS-1 than that of the PCHA-S in the PS phase was suggested by the SAXS, and the mobility in the interfacial region was slightly enhanced by the addition of the PS-1. However, the mobility was almost constant against an increase in the PS-1. The PS-1 was considered to be penetrated into the interfacial region and activated the mobility, but the fraction of the PS-1 in the interfacial region was constant irrespective of the blended amount of the PS-1. These results suggest that effects of homopolymers on the mobility in the interface are significantly related to their spatial distribution in the host phase.     

Oxidative dehydrogenation of ethane over Cr/ZSM-5 catalysts using CO2 as an oxidant

Highly active catalysts for oxidative dehydrogenation of ethane with CO2 were characterized by temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), Fourier transform infrared (FTIR) spectroscopy, and X-ray absorption fine-structure (XAFS) analysis. In the active catalysts, Cr/H-ZSM-5 (SiO2/Al2O3 > 190), Cr6+ = O, or possibly Cr5+ = O was the catalytic species on the zeolite support. In contrast, little Cr6+ (or Cr5+) was detected in the less-active catalysts. The Cr6+ (or Cr5+) species was reduced to an octahedral Cr3+ species by treatment with ethane at 773 K, and the reduced Cr species was reoxidized to the Cr6+ (or Cr5+) species by treatment with CO2 at 673-773 K. The Cr redox cycle played an important role in the catalyst's high activity.     

A Flexible Approach to Grandisine Alkaloids: Total Synthesis of Grandisines B,D, and F

This article describes in detail the first total synthesis of grandisine alkaloids, grandisines B, D, and F, which show affinity for the human δ‐opioid receptor. The key steps in this synthesis are construction of the isoquinuclidinone moiety of 2 by intramolecular imine formation and the tetracyclic ring system of 4 by stereoselective ring closure of the enolate of amine 8 generated by 1,4‐addition of ammonia to 9 . Synthesis of key intermediate 9 featured a highly stereoselective Brønsted acid mediated Morita–Baylis–Hillman (MBH) reaction via the N‐acyl iminium ion.     

Effects of metal ions on photoinduced electron transfer in zinc porphyrin-naphthalenediimide linked systems

Zinc porphyrin-naphthalenediimide (ZnP-NIm) dyads and zinc porphyrin-pyromellitdiimide-naphthalenediimide (ZnP-Im-NIm) triad have been employed to examine the effects of metal ions on photoinduced charge-separation (CS) and charge-recombination (CR) processes in the presence of metal ions (scandium triflate (Sc(OTf)(3)) or lutetium triflate (Lu(OTf)(3)), both of which can bind with the radical anion of NIm). Formation of the charge-separated states in the absence and in the presence of Sc(3+) was confirmed by the appearance of absorption bands due to ZnP(.) (+) and NIm(.) (-) in the absence of metal ions and of those due to ZnP(.) (+) and the NIm(.) (-)/Sc(3+) complex in the presence of Sc(3+) in the time-resolved transient absorption spectra of dyads and triad. The lifetimes of the charge-separated states in the presence of 1.0 x 10(-3) M Sc(3+) (14 micros for ZnP-NIm, 8.3 micros for ZnP-Im-NIm) are more than ten times longer than those in the absence of metal ions (1.3 micros for ZnP-NIm, 0.33 micros for ZnP-Im-NIm). In contrast, the rate constants of the CS step determined by the fluorescence lifetime measurements are the same, irrespective of the presence or absence of metal ions. This indicates that photoinduced electron transfer from (1)ZnP(*) to NIm in the presence of Sc(3+) occurs without involvement of the metal ion to produce ZnP(.) (+)-NIm(.) (-), followed by complexation with Sc(3+) to afford the ZnP(.) (+)-NIm(.) (-)/Sc(3+) complex. The one-electron reduction potential (E(red)) of the NIm moiety in the presence of a metal ion is shifted in a positive direction with increasing metal ion concentration, obeying the Nernst equation, whereas the one-electron oxidation potential of the ZnP moiety remains the same. The driving force dependence of the observed rate constants (k(ET)) of CS and CR processes in the absence and in the presence of metal ions is well evaluated in terms of the Marcus theory of electron transfer. In the presence of metal ions, the driving force of the CS process is the same as that in the absence of metal ions, whereas the driving force of the CR process decreases with increasing metal ion concentration. The reorganization energy of the CR process also decreases with increasing metal ion concentration, when the CR rate constant becomes independent of the metal ion concentration.     

Chemical constituents of Ligularia virgaurea and its diversity in southwestern Sichuan of China

Chemical constituents of root extract and the nucleotide sequences of the atpB-rbcL intergenic region and the internal transcribed spacers (ITSs) of the ribosomal RNA gene were studied for Ligularia virgaurea var. virgaurea collected in southwestern Sichuan Province of China. Eleven samples were collected. Four of them were found to contain four new furanoeremophilanes, virgaurenones A-D, as well as a new eremophilanolide, virgaurenolide A. The other samples contained different furanoeremophilanes and their derivatives including nor-type of compounds, two of which were new. Diversity was found to be present in the nucleotide sequences as well. The chemical composition was found to be correlated with the ITS variation but not with the geographic distribution of the samples.     

Ab initio prediction of protein-ligand binding structures by replica-exchange umbrella sampling simulations

We have developed a prediction method for the binding structures of ligands with proteins. Our method consists of three steps. First, replica-exchange umbrella sampling simulations are performed along the distance between a putative binding site of a protein and a ligand as the reaction coordinate. Second, we obtain the potential of mean force (PMF) of the unbiased system using the weighted histogram analysis method and determine the distance that corresponds to the global minimum of PMF. Third, structures that have this global-minimum distance and energy values around the average potential energy are collected and analyzed using the principal component analysis. We predict the binding structure as the global-minimum free energy state on the free energy landscapes along the two major principal component axes. As test cases, we applied our method to five protein-ligand complex systems. Starting from the configuration in which the protein and the ligand are far away from each other in each system, our method predicted the ligand binding structures in excellent agreement with the experimental data from Protein Data Bank.     

Measurements of the thickness distribution of thin films with a slit-beam-profile reflectometer

The thickness distribution of single-layer thin films is measured with a slit-beam-profile reflectometer. A convergent slit beam generated by a cylindrical lens is projected onto a specimen. A CCD chip with a pixel matrix of 512 x 480 is used to detect the intensity distribution of the reflected beam, which is passed through another cylindrical lens. By analyzing the picture taken by the CCD, we can obtain information about the angular reflectance at each reflecting point along the slit line, and the thickness or the refractive index at each point can be evaluated by mathematical fitting to a reflectance formula.