Analysis of liquid structure without construction of any structure models by the X-ray scattering method.

A simple approach for determining a liquid structure using X-ray scattering data, in which a liquid structure is uniquely evaluated without construction of any plausible structure models, has been applied to liquid acetonitrile, acetone and cyclohexane. For a pair of molecules, a given point within a molecule is located at the origin with a given molecular orientation. The site of the given point of another molecule is defined by the polar coordinates and the molecular orientation is treated by three Eulerian angles. These parameters are optimized by a non-linear least-squares calculation applied to X-ray scattering data. The reliability of the method was examined by determining the liquid structure of polar acetonitrile and the obtained intermolecular interatomic distances are in good agreement with the previously reported values. The method was then successfully applied to the determination of the liquid structure of acetone and cyclohexane. Especially for nonpolar cyclohexane, the construction of a variety of plausible structural models is very difficult. It was revealed that acetone has an ordered liquid arrangement similar to that found in its crystal, although the intermolecular distances in liquid acetone are different from those in the crystal. On the other hand, the liquid structure of cyclohexane is disordered.     

Synthesis and morphology of polyethylene‐block‐poly(methyl methacrylate) through the combination of metallocene catalysis with living radical polymerization

Polyethylene‐block‐poly(methyl methacrylate) (PE‐b‐PMMA) was successfully synthesized through the combination of metallocene catalysis with living radical polymerization. Terminally hydroxylated polyethylene, prepared by ethylene/allyl alcohol copolymerization with a specific zirconium metallocene/methylaluminoxane/triethylaluminum catalyst system, was treated with 2‐bromoisobutyryl bromide to produce terminally esterified polyethylene (PE‐Br). With the resulting PE‐Br as an initiator for transition‐metal‐mediated living radical polymerization, methyl methacrylate polymerization was subsequently performed with CuBr or RuCl₂(PPh₃)₃ as a catalyst. Then, PE‐b‐PMMA block copolymers of different poly(methyl methacrylate) (PMMA) contents were prepared. Transmission electron microscopy of the obtained block copolymers revealed unique morphological features that depended on the content of the PMMA segment. The block copolymer possessing 75 wt % PMMA contained 50–100‐nm spherical polyethylene lamellae uniformly dispersed in the PMMA matrix. Moreover, the PE‐b‐PMMA block copolymers effectively compatibilized homopolyethylene and homo‐PMMA at a nanometer level. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3965–3973, 2003     

Function of vinyl copolymers with pendant porphyrin or metalloporphyrin dimers as photoredox catalyst

Photoredox catalytic functions of water-soluble vinyl copolymers with pendant porphyrin or metalloporphyrin dimers were investigated. With FRA-L-ascorbic acid in aqueous solution, a vinyl copolymer bearing Mg-porphyrin dimer linked with the shortest N,N′-methylenebisamide bridge was found to have a remarkable accelerating effect under illumination of visible light as compared with that bearing Mg-porphyrin monomer and other copolymers with longer dimer bridges as well as vinyl copolymers bearing porphyrin dimers and monomer. A copolymer bearing Zn-porphyrin dimer was much inferior to that bearing monomer. Copolymers with other metals such as Co(II), Ni(II), and Cu(II) were almost inert.     

Cobalt oxide supported gold nanoparticles as a stable and readily-prepared precursor for the in situ generation of cobalt carbonyl like species

A treatment of cobalt oxide supported gold nanoparticles (Au/Co₃O₄) under syngas atmosphere effectively generated a cobalt carbonyl-like active species in the reaction vessel. The preparation of Au/Co₃O₄ was quite simple and the in situ generated cobalt species could be used as a stable and easy handling alternative for dicobalt octacarbonyl without bothersome purification prior to use. The reactions, which are sensitive to the purity of the dicobalt octacarbonyl, such as the alkoxycarbonylation of epoxides and the Pauson-Khand reaction, smoothly progressed with Au/Co₃O₄.     

Synthesis, including asymmetric synthesis, of 1-substituted cyclopentenes from cyclobutanones with one-carbon ring-expansion by 1,2-carbon-carbon insertion of magnesium carbenoids

Treatment of 1-chlorovinyl p-tolyl sulfoxides, which were derived from cyclobutanones and chloromethyl p-tolyl sulfoxide, with lithium enolate of tert-butyl carboxylates, amides, lithium α-sulfonyl carbanions, and lithium α-carbanion of acetonitrile gave adducts in high to quantitative yields. The adducts were treated with Grignard regents, such as i-PrMgCl and EtMgCl in toluene to afford 1-substituted cyclopentenes in good to high yields with one-carbon ring-expansion via 1,2-carbon-carbon (1,2-CC) insertion reaction of the generated magnesium carbenoid intermediates. The magnesium carbenoid 1,2-CC insertion was found to be highly stereospecific. When optically pure chloromethyl p-tolyl sulfoxide was used in this procedure, optically active 1-substituted cyclopentenes were obtained in high optical purity.     

Ultrasensitive CE for heavy metal ions using the variations in the chemical structures formed from new octadentate fluorescent probes and cationic polymers

Novel fluorescent probes have been developed for the ultratrace detection of heavy metal ions by capillary electrophoresis using laser-induced fluorescence detection. Based on a molecular design, the probes are composed of an octadentate chelating moiety, a macrocyclic DOTA (tetraazacyclododecanetetraacetic acid) and an acyclic DTPA (diethylenetriaminepentaacetic acid) frame, a spacer and a fluorophore (fluorescein). These were chosen on the basis of their ability to form kinetically inert and highly emissive complexes, and to prevent a quenching effect even with heavy and paramagnetic metal ions. Addition of a cationic polymer, polybrene, in the separation buffer provided high resolution and simultaneous detection of Ca(2+), Mg(2+), Cu(2+), Zn(2+), Ni(2+), Co(2+), Mn(2+), Cd(2+) and Pb(2+). The direct fluorescence detection of these metal ions with high sensitivity at lower ppt levels, typically 2-7 × 10(-11) M (potentially sub-ppt), was successfully achieved. While separation of anionic compounds using a counter cation ("Ion Association (IA)" mode) is typically controlled by the ion association equilibrium constants, K(ass), it was found that differences in the mobilities, μ(ep(IAC)), of the ion association complexes formed between the probe complexes and counter cations are the driving forces for separation in this new method. This suggests that each of the polybrene-probe complexes has different chemical structures among metal ions, which were able to be determined by CD spectra in this investigation. This novel separation mode was termed the "Ion Association Complex (IAC)" mode, distinct from the IA mode.     

UV and IR spectroscopic studies of cold alkali metal ion-crown ether complexes in the gas phase

We report UV photodissociation (UVPD) and IR-UV double-resonance spectra of dibenzo-18-crown-6 (DB18C6) complexes with alkali metal ions (Li(+), Na(+), K(+), Rb(+), and Cs(+)) in a cold, 22-pole ion trap. All the complexes show a number of vibronically resolved UV bands in the 36,000-38,000 cm(-1) region. The Li(+) and Na(+) complexes each exhibit two stable conformations in the cold ion trap (as verified by IR-UV double resonance), whereas the K(+), Rb(+), and Cs(+) complexes exist in a single conformation. We analyze the structure of the conformers with the aid of density functional theory (DFT) calculations. In the Li(+) and Na(+) complexes, DB18C6 distorts the ether ring to fit the cavity size to the small diameter of Li(+) and Na(+). In the complexes with K(+), Rb(+), and Cs(+), DB18C6 adopts a boat-type (C(2v)) open conformation. The K(+) ion is captured in the cavity of the open conformer thanks to the optimum matching between the cavity size and the ion diameter. The Rb(+) and Cs(+) ions sit on top of the ether ring because they are too large to enter the cavity of the open conformer. According to time-dependent DFT calculations, complexes that are highly distorted to hold metal ions open the ether ring upon S(1)-S(0) excitation, and this is confirmed by extensive low-frequency progressions in the UVPD spectra.     

Structure of host-guest complexes between dibenzo-18-crown-6 and water, ammonia, methanol, and acetylene: evidence of molecular recognition on the complexation

Complexes of dibenzo-18-crown-6 (DB18C6, host) with water, ammonia, methanol, and acetylene (guest) in supersonic jets have been characterized by laser induced fluorescence (LIF), UV-UV hole-burning (UV-UV HB), and IR-UV double resonance (IR-UV DR) spectroscopy. Firstly, we reinvestigated the conformation of bare DB18C6 (species m1 and m2) and the structure of DB18C6-H(2)O (species a) [R. Kusaka, Y. Inokuchi, T. Ebata, Phys. Chem. Chem. Phys., 2008, 10, 6238] by measuring IR-UV DR spectra in the region of the methylene CH stretching vibrations. The IR spectral feature of the methylene CH stretch of DB18C6-H(2)O is clearly different from those of bare DB18C6 conformers, suggesting that DB18C6 changes its conformation when forming a complex with a water molecule. With the aid of Monte Carlo simulation for extensive conformational search and density functional calculations (M05-2X/6-31+G*), we reassigned species m1 and m2 to conformers having C(1) and C(2) symmetry, respectively. Also, we confirmed the DB18C6 part in species a of DB18C6-H(2)O to be "boat" conformation (C(2v)). Secondly, we identified nine, one, and two species for the DB18C6 complexes with ammonia, methanol, and acetylene, respectively, by the combination of LIF and UV-UV HB spectroscopy. From the IR spectroscopic measurement in the methylene CH stretching region, a similar conformational change was identified in the DB18C6-ammonia complexes, but not in the complexes with methanol or acetylene. The structures of all the complexes were determined by analyzing the electronic transition energies, exciton splitting, and IR spectra in the region of the OH, NH, and CH stretching vibrations. In DB18C6-ammonia complexes, an ammonia molecule is incorporated into the cavity of the boat conformation by forming "bifurcated" and "bidentate" hydrogen-bond (H-bond), similar to the case of the DB18C6-H(2)O complex. On the other hand, in the DB18C6-methanol and -acetylene complexes, methanol and acetylene molecules are simply attached to the C(1) and C(2) conformations, respectively. From the difference of the DB18C6 conformations depending on the type of the guest molecules, it is concluded that DB18C6 distinguishes water and ammonia from methanol and acetylene when it forms complexes, depending on whether guest molecules have an ability to form bidentate H-bonding.