Excitation-energy migration in self-assembled cyclic zinc(II)-porphyrin arrays: a close mimicry of a natural light-harvesting system

The excitation-energy-hopping (EEH) times within two-dimensional cyclic zinc(II)-porphyrin arrays 5 and 6, which were prepared by intermolecular coordination and ring-closing metathesis reaction of olefins, were deduced by modeling the EEH process based on the anisotropy depolarization as well as the exciton-exciton annihilation dynamics. Assuming the number of energy-hopping sites N = 5 and 6, the two different experimental observables, that is, anisotropy depolarization and exciton-excition annihilation times, consistently give the EEH times of 8.0 +/- 0.5 and 5.3 +/- 0.6 ps through the 1,3-phenylene linkages of 5 and 6, respectively. Accordingly, the self-assembled cyclic porphyrin arrays have proven to be well-defined two-dimensional models for natural light-harvesting complexes.     

A recyclable catalyst for asymmetric transfer hydrogenation with a formic acid-triethylamine mixture in ionic liquid

A novel task-specific ionic ligand with an imidazolium salt moiety was synthesized, and its catalytic ability and recyclability for asymmetric transfer hydrogenation of acetophenone derivatives with a formic acid-triethylamine azeotropic mixture in an ionic liquid [bmim][PF6] was examined.     

Parallel vs. anti-parallel orientation in a curdlan/oligo(dA) complex as estimated by a FRET technique

We already found that beta-1,3-glucan polysaccharides form polymeric complexes with certain polynucleotides, but the parallel vs. anti-parallel orientation in those complexes had remained unsolved. In this paper, this controversial problem has been discussed for curdlan/oligo(dA) complexes utilizing two different energy transfer techniques. The first system consists of a combination of fluorescein-labeled curdlan and 3'-(or 5'-)tetramethyl-rhodamine (TAMRA)-labeled oligo(dA). The second system utilizes gold nanoparticles: that is, two curdlan chains were linked by a disulfide bond and after complexation with oligo(dA), the complex was immobilized on gold nanoparticles. In this system, TAMRA was attached to the 3'(or 5') end of oligo(dA) and the gold particle acted as a fluorescence quencher (energy acceptor). These experiments have led us to conclude that in the curdlan/oligo(dA) complex, parallel orientation is more favourable than anti-parallel orientation. These findings have enabled us to envision a clearer image for the complexation mode between beta-1,3-glucan polysaccharides and polynucleotides.     

Peroxotungstate immobilized on ionic liquid-modified silica as a heterogeneous epoxidation catalyst with hydrogen peroxide

Peroxotungstate immobilized on ionic liquid-modified SiO2 is capable of heterogeneously epoxidizing a wide range of olefins with the maintenance of the catalytic activity of homogeneous analogue. The epoxidation was immediately stopped by the removal of the catalyst, and no tungsten species could be found in the filtrate after the removal of the catalyst. These results can rule out any contribution to the observed catalysis from the tungsten species that leached into the reaction solution, and the observed catalysis is truly heterogeneous in nature. Furthermore, the catalyst was reusable without the loss of the catalytic performance.     

Wave propagation in saturated ground using the volume fractions

The purpose of this paper is to study the dynamic behavior of soft ground including a porous layer by considering the porosity change. In order to take the porosity change into account, the concept of the volume fraction, which has been proposed in continuum mechanics, is introduced. The constitutive equations presented by Bowen are applied to the analysis of the porous media. According to Bowen's theory, the porosity is considered as a variable called the volume fraction and has its own constitutive equation. The constitutive equation of the volume fraction has thermoelastic equation coefficients and is determined by the strains of the solid and the fluid. This means that the compressibilities of the solid and the fluid are considered. When the special condition is assumed, Bowen's theory can contain Biots's theory, which has been applied in earthquake engineering. The wave propagation in the ground including a porous layer, modeled by Bowen's theory, is studied and compared with that of Biot's theory. One-dimensional attenuation and surface amplitude are calculated. The effect of the volume fraction is discussed with respect to the compressibilities of the solid and the fluid.     

Catalyst design of hydrotalcite compounds for efficient oxidations

Various Mg-Al type hydrotalcites were examined as catalysts for the epoxidation of olefins and N-oxidation of pyridines using hydrogen peroxide. The catalytic activity of hydrotalcites increased with increasing the basicity of their surface. Adding cationic surfactants, e.g., n-dodecyltrimethylammonium bromide, to the above system remarkably accelerated the reaction rate. The hydrotalcites, into which were introduced both Ru and Co cations in the Brucite layers, were found to be good catalysts for the oxidation of various alcohols in the presence of molecular oxygen. Moreover, these hydrotalcites could smoothly catalyze also the oxygenation of diphenylmethane, fluorene, and xanthene at benzylic position with excellent yields. The hydrotalcite catalysts could be easily separated from the reaction mixture and reused with retention of their high catalytic performance for the above oxidations.     

Measurement of the solubility of metal complexes in supercritical carbon dioxide using a UV–vis spectrometer

A new apparatus based on the circulation method was developed to measure the solubility of metal complexes in supercritical carbon dioxide (scCO₂) at a wide range of temperatures and pressures. A UV–vis spectrometer, which was connected to a small saturation cell through optical fibers, was used to determine solubility. The solubilities of cobalt(III) acetylacetonate (Co(acac)₃) and chromium(III) acetylacetonate (Cr(acac)₃) in scCO₂ were measured to check the validity of both the apparatus and the method and to accumulate new solubility data. The solubility data for Cr(acac)₃ obtained in this study were in good agreement with the data reported in the literature.The measured solubilities of Co(acac)₃ and Cr(acac)₃ were also correlated with the empirical equation including the three adjustable parameters, based on the equation proposed by Chrastil. The parameters were determined by fitting the equation to the experimental data for each metal complex and the calculated results closely replicated the experimental data.     

Enantioseparation of nicotine alkaloids in cigarettes by CE using sulfated β‐CD as a chiral selector and a capillary coated with amino groups

Nicotine (NC) and its related compounds (cotinine (CN), nornicotine (NN), anatabine (AT) and anabasine (AB)) were simultaneously enantioseparated by CE using a capillary with amino groups and sulfated β‐CD as a chiral selector. The optimum running conditions were found to be 30 mM acetate buffer (pH 5.0) containing 8% sulfated β‐CD with an applied voltage of +15 kV at 30°C using direct detection at 260 nm. Using a capillary coated with amino groups, the EOF migrates toward the positive pole. However, when sulfated β‐CD was added to the BGE, it was found that the EOF migrated toward the negative pole due to ionic adsorption of sulfated β‐CD to amino groups on the capillary inner wall. All the cationic analytes migrated as anions, suggesting that they formed stable anionic complexes with sulfated β‐CD. With this system and a simple pretreatment with mini‐cartridges, NC alkaloids in five cigarette samples were enantioseparated. As a result, each of the compounds except for CN was detected. In the case of NC, only (S)‐NC was detected (more than 99.9%), but in the case of NN, AT and AB, the ratios of (S)‐isomer to total isomers were in the ranges 58–70, 81–85 and 59–65%, respectively. On the other hand, only NC was detected in cigarette smoke and the ratio of (S)‐ and (R)‐NCs was 96:4. The amounts of NC alkaloids in cigarettes suggest that the production of (R)‐NC resulted from racemization due to the high temperature/burning of the cigarette.     

Anionic alternating copolymerization behavior of bifunctional six‐membered lactone and glycidyl phenyl ether

A copolymerization of 10‐methyl‐2H,8H‐benzo‐[1,2‐b:5,4‐b′]bipyran‐2,8‐dione ( 1 ) and glycidyl phenyl ether (GPE) was studied. 1 was a bislactone designed as a bifunctional analogue of 3,4‐dihydrocoumarin (DHCM), of which anionic 1:1 alternating copolymerization with GPE has been reported by us, previously. This alternating nature was inherited by the present copolymerization of 1 and GPE, leading to an intriguing copolymerization behavior in contrast to the ordinary statistical copolymerizations of monofunctional monomers and bifunctional monomers usually controlled by the proportional dependence of the crosslinking density on the monomer feed ratio: (1) When the feed ratio [GPE]₀/[ 1 ]₀ was 1, the two monomers underwent the 1:1 alternating copolymerization. In this case, 1 behaved as a monofunctional monomer, that is, only one of the two lactones in 1 participated in the copolymerization allowing the other lactone moiety to be introduced into the side chain almost quantitatively. (2) Increasing the feed ratio [GPE]₀/[1]₀ to larger than 4 allowed almost all of the lactone moieties to participate in the copolymerization system to give the corresponding networked polymers efficiently. The compositions of the copolymers [GPE unit]/[ 1 ‐derived acyclic ester unit] were always biased to smaller values than the feed ratios [GPE]₀/[lactone moiety in 1 ]₀ by the intrinsic 1:1 alternating nature of the copolymerization. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3662–3668, 2009