Ruthenium-catalysed linear-selective allylic alkylation of allyl acetates

The regioselectivity in the ruthenium-catalysed allylic alkylation of mono substituted allyl acetates with the malonate anion was highly controlled by Ru3(CO)12 with 2-(diphenylphosphino)benzoic acid, and the linear-type alkylated product was obtained.     

RISM-SCF study of the free-energy profile of the Menshutkin-type reaction NH3+CH3Cl→NH3CH3++Cl− in aqueous solution

The free-energy profile for the Menshutkin-type reaction NH₃ + CH₃Cl → NH₃CH₃ ⁺ + Cl⁻ in aqueous solution is studied using the RISM-SCF method. The effect of electron correlation on the free-energy profile is estimated by the RISM-MP2 method at the HF optimized geometries along the reaction coordinate. Solvation was found to have a large influence on the vibrational frequencies at the reactant, transition state and product; these vibrational frequencies are utilized to calculate the zero-point energy correction of the free-energy profile. The computed barrier height and reaction exothermicity are in reasonable agreement with those of experiment and previous calculations. The change of solvation structure along the reaction path is represented by radial distribution functions between solute-solvent atomic sites. The mechanisms of the reaction are discussed from the view points of solute electronic and solvation structures. Received: 26 June 1998/Accepted: 28 August 1998 / Published online: 2 November 1998     

Strong binding between acidic guests and fluorescein modified -γ-Cyclodextrin via hydrogen bonding

-Cyclodextrin with appended fluorescein (1) has been prepared as a sensor and a charge-changeable receptor for detecting organic compounds including terpenoids, carboxylic acids and bile acids. Compound1 has cationic, neutral and anionic forms depending on the pH of the solutions. The anionic form of1 at about neutral pH exhibits the highest sensing ability for carboxylic acids and bile acids, while at alkaline pH it detects hardly any of the guests examined. The high sensitivity and selectivity of the anionic form of1 at around neutral pH for acidic guests seems to be caused by the hydrogen bond between the phenoxide anion moiety of fluorescein and acidic guests. The neutral form of1 exhibits little sensing ability for all the guests, but the cationic form shows comparatively higher sensing ability for the guests examined.     

κ-型卡拉胶/聚乙烯吡咯烷酮共混水凝胶的辐射制备及性质研究

采用辐射技术制备了κ-型卡拉胶 ( KC) /聚乙烯基吡咯烷酮 ( PVP)共混水凝胶 ,研究了共混凝胶内 KC含量、PVP的分子量和辐照剂量等对 KC/ PVP共混水凝胶性质的影响 .实验发现 ,KC与高分子量的 PVP( k-90 )共混后在一定剂量范围内辐照可得到高强度、高溶胀行为的 KC/ PVP共混水凝胶 ,随着共混凝胶内KC含量的增加 ,凝胶强度及溶胀性能均显著提高 .分析表明 ,KC与高分子量的 PVP共混后 ,在较低剂量下 KC的降解被抑制 ,从而获得一种由物理交联的 KC和化学交联的 PVP形成的互穿网络 ( IPN)凝胶 .     

Semi-synthesis of an artificial scandium(iii) enzyme with a β-helical bio-nanotube

We have succeeded in preparing semi-synthesized proteins bound to Sc(3+) ion which can promote an epoxide ring-opening reaction. The Sc(3+) binding site was created on the surface of [(gp5βf)(3)](2) (N. Yokoi et al., Small, 2010, 6, 1873) by introducing a cysteine residue for conjugation of a bpy moiety using a thiol-maleimide coupling reaction. Three cysteine mutants [(gp5βf_X)(3)](2) (X = G18C, L47C, N51C) were prepared to introduce a bpy in different positions because it had been reported that Sc(3+) ion can serve as a Lewis-acid catalyst for an epoxide ring-opening reaction upon binding of epoxide to bpy and two -ROH groups. G18C_bpy with Sc(3+) can accelerate the rate of catalysis of the epoxide ring-opening reaction and has the highest rate of conversion among the three mutants. The value is more than 20 times higher than that of the mixtures of [(gp5βf)(3)](2)/2,2'-bipyridine and l-threonine/2,2'-bipyridine. The elevated activity was obtained by the cooperative effect of stabilizing the Sc(3+) coordination and accumulation of substrates on the protein surface. Thus, we expect that the semi-synthetic approach can provide insights into new rational design of artificial metalloenzymes.     

Photodegradation of polystyrene containing flame-retardants: wavelength sensitivity and efficiency of degradation

Wavelength dependence on the photodegradation of flame-retardant materials (Polystyrene (PSt) containing flame-retardants) was studied. The effects of nine flame-retardants containing bromine (Br) on the efficiency of photodegradation of the PSt were compared. Samples were irradiated at 23 °C in air with monochromatic radiation of wavelengths 260, 280, 300, 320, 340, 360 and 380 nm using the Okazaki Large Spectrograph (OLS). UV-visible and FTIR spectra were measured to identify photo-induced chemical structural changes in the PSt. The number of main-chain scissions and the changes in the molecular weight distribution were estimated from the results of GPC measurements. It was found that the photo-stability of PSt was reduced by the addition of flame-retardants. The most effective irradiation wavelength for main-chain scission was found to be 280 nm for each flame-retardant except one. The photo-stability of PSt containing flame-retardants appears to depend upon the chemical structure of the additive.     

Volume changes accompanying the stepwise complex formation in aqueous solutions for the case of Cu2+ and Zn2+ with the ligand bipyridine and phenanthroline

The volume changes for each step in the successive complex formation between the metal ions Cu²⁺ and Zn²⁺ with the ligand L, where L is bpy = 2,2-bipyridine and phen = 1,10-phenanthroline, in water have been determined at 25°C in the following way: Aqueous solution of M(NO₃)₂ has been taken as solvent and the densities of solutions have been measured at various ratio of [ligand]/[M²⁺]. The partial molar volumes V ₂ ⁰ have been calculated for the nitrates of the complex ions [ML]²⁺, [ML₂]²⁺, and [ML₃]²⁺. The volume change V is given as V=V ₂ ⁰ ([ML _n+1](NO₃)₂)–V ₂ ⁰ ([ML _n ](NO₃)₂)–V ₂ ⁰ (L). Volume changes of the first coordination of L to M²⁺ are larger than the other two steps and the third step coordination leads to small or even negative values of V.     

Pin1 and Par14 peptidyl prolyl isomerase inhibitors block cell proliferation

Disruption of the parvulin family peptidyl prolyl isomerase (PPIase) Pin1 gene delays reentry into the cell cycle when quiescent primary mouse embryo fibroblasts are stimulated with serum. Since Pin1 regulates cell cycle progression, a Pin1 inhibitor would be expected to block cell proliferation. To identify such inhibitors, we screened a chemical compound library for molecules that inhibited human Pin1 PPIase activity in vitro. We found a set of compounds that inhibited Pin1 PPIase activity in vitro with low microM IC50s and inhibited the growth of several cancer lines. Among the inhibitors, PiB, diethyl-1,3,6,8-tetrahydro-1,3,6,8-tetraoxobenzo[lmn] phenanthroline-2,7-diacetate ethyl 1,3,6,8-tetrahydro-1,3,6,8-tetraoxo-benzo[lmn] phenanthroline-(2H,7H)-diacetate, had the least nonspecific toxicity. These results suggest that Pin1 inhibitors could be used as a novel type of anticancer drug that acts by blocking cell cycle progression.     

Polymerization of vinyl ethers with transition‐metal catalysts: An examination of the stereoregularity of the formed polymers

The polymerization of isobutyl vinyl ether (IBVE) and tert‐butyl vinyl ether (TBVE) was carried out with metallocene and nonmetallocene catalysts, and the stereoregularity of the formed polymers was examined with ¹³C NMR spectroscopy. IBVE afforded polymers with 63–68% dyad isotacticity by polymerization with mixtures of metallocene catalysts and methyl aluminoxane as a cocatalyst in toluene as a solvent. However, TBVE yielded polymers with 47–52% dyad isotacticity (21–28% triad isotacticity) under the same conditions, the isotacticity being lower than that of poly(isobutyl vinyl ether) (PIBVE). Nonmetallocene catalysts, including Ti, Zr, and Hf complexes with two phenoxy imine chelate ligands, provided PIBVE and poly(tert‐butyl vinyl ether) with 63–68 and 45–51% dyad isotacticity, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3938–3943, 2002     

A novel acid promoted ring‐opening polymerization of a seven‐membered cyclic carbonate initiated with BCl3

Ring‐opening polymerization of a seven‐membered cyclic carbonate, 1,3‐dioxepan‐2‐one, was investigated with a novel initiator system, BCl₃‐HCl·Et₂O. Addition of HCl·Et₂O promoted the polymerization even at 0°C to produce the corresponding polycarbonate with controlled molecular weight and narrow polydispersity ratio (< 1.2).