Studies on the oxidative degradation of nylons by nitrogen dioxide in supercritical carbon dioxide

Oxidative degradation of nylons was carried out using nitrogen dioxide (NO₂) as the oxidizing agent and supercritical carbon dioxide (scCO₂) as the reaction medium. Seven typical nylons were studied: three ring opening polymerization type nylons (nylon-6, -11 and -12) and four condensation co-polymerization type nylons (nylon-4/6; -6/6; -6/9 and -6/12). All the nylons decomposed in the NO₂/scCO₂ system under relatively mild conditions (140 °C, 1 h, and 10 MPa) and provided aliphatic α, ω-diacids such as succinic, glutaric and adipic acids in good yields. The product distribution of these α, ω-diacids strongly depended on the reaction conditions such as temperature, time and amount of NO₂, but not on the total pressure. Furthermore, the proportions of the products were affected by the type of nylon. A mechanism is proposed and a detailed discussion regarding the degradation of nylon in the NO₂/scCO₂ system is provided.     

Complex formations of silver(I) trifluoroacetate and trifluoromethanesulfonate with benzene and cyclohexene

An apparatus for measurements of equilibrium ligand vapor pressure has been applied in order to determine the stoichiometry of benzene and cyclohexene complexes of silver(I) trifluoroacetate (AgCF₃CO₂) and silver(I) trifluoromethanesulfonate (silver(I) triflate, AgCF₃SO₃) in the solid state. It has been found that the equilibrium leads the formation of such complexes as: (AgCF₃CO₂)₂(C₆H₆), (AgCF₃CO₂)₂(C₆H₁₀), (AgCF₃CO₂)₂(C₆H₁₀)₃, (AgCF₃SO₃)₂(C₆H₆), (AgCF₃SO₃)(C₆H₆), (AgCF₃SO₃)(C₆H₁₀) and (AgCF₃SO₃)(C₆H₁₀)₂. The temperature dependence of the gas-solid equilibrium ligand pressure has also been examined for these complexes, and the enthalpy and entropy changes according to the following complex dissociation reactions were estimated: (AgCF₃CO₂)L_m (s) AgCF₃CO₂ (s)+mL (g): and (AgCF₃SO₃)L_n (s) AgCF₃SO₃ (s)+nL (g), where L's are benzene and cyclohexene. On the basis of the thermodynamic data obtained, the effects of the counter anion as well as the ligand on the complex stability are discussed.     

Diffusion in a curved tube

The diffusion of particles in confining walls forming a tube is discussed. Such a transport phenomenon is observed in biological cells and porous media. We consider the case in which the tube is winding with curvature and torsion, and the thickness of the tube is sufficiently small compared with its curvature radius. We discuss how geometrical quantities appear in a quasi-one-dimensional diffusion equation.     

Characterization of the molecular species formed by interaction of acetonitrile and copper(I) chloride in the liquid and solid phase

Summary The equilibrium vapour pressure of the solid complex, CuCl·MeCN, was measured at several temperatures. The enthalpy and entropy changes according to the following complex formation were determined: CuCl(s)+ MeCN(g)CuCl·MeCN(s); H=–56.9 kJ mol^–1 and S=–150 J mol^–1 K ^–1, respectively. Vapour pressure osmometry shows that a monomer-dimer equilibrium of CuCl exists in the acetonitrile solution. The equilibrium constant was found to be 0.93±0.08. A gas chromatographic technique was employed to determine the monomeric species as [Cu(MeCN)₄]Cl.     

Swelling behavior of poly(sodium acrylate) gels crosslinked by aluminum ions

The cylindrical poly(sodium acrylate) gel (SA gel) was synthesized in the glass capillary using aluminum ions as the crosslinker. The swelling ratio of the gel was measured after the repeated exchange of solvent (distilled deionized water, about pH 5.8). The gel exhibited two relaxation processes; at first the gel swells rapidly as exchange of water (the swelling process), then shrinks very slowly (the shrinking process). In order to reveal the microscopic structural change (especially, the formation of hydrogen bonding) by water exchange, attenuated total refraction (ATR) Fourier transform infrared (FT-IR) spectroscopy was applied to the gels with different swelling ratio. The IR absorption peaks of the gel were assigned based on those of poly(sodium acrylate) aqueous solutions at different pH. On the swelling process, the carboxyl groups were gradually protonated, and the intermolecular hydrogen bonding started to form in the gel with maximum swelling ratio. On the shrinking process, the formation of hydrogen bonding gradually increased with long-time repeated water exchange which resulted in the shrinkage of the gel. Effects of the repeated water exchange on the swelling behavior were discussed in terms of the exchange of counter ions and the formation of hydrogen bonding.     

An Insertion or Deletion in the Extramembrane Loop Connecting Helices E and F of Archaerhodopsin-1 Affects in vitro Refolding and Slows the Photocycle

Abstract— Upon addition of retinal, archaeopsin-1 expressed in Escherichia coli (_ecaO-1002) regenerated the chromophore in dimyristoyl phosphatidylcholine (DMPC), 3-[(3-cholamidopropyl) dimethylammonio]-l-propanesulfonate (CHAPS) and sodium dodecyl sulfate(SDS) mixed micelles as efficiently as the same opsin prepared from halobacteria. Introduction of an insertion or a deletion of five amino acids into the surface loop connecting helices E and F changed the secondary and tertiary structures of _ecaO-1002 in SDS, and diminished regeneration of the chromophore. The effect of the insertion and deletion on the in vitro refolding was specific to archaeopsin because the same insertion introduced at the corresponding position of bacterioopsin (bO) did not affect chromophore regeneration. The photocycle of the regenerated _ecaR-1002 decreased in DMPC/CHAPS/SDS mixed micelles compared with that of aR-1 in the claret membrane, which was consistent with the reported behavior of bO. Unexpectedly, the insertion and deletion in loop EF perturbed the photocycle of the regenerated _ecaR-1002. The accumulation of long-lived N- and O-like intermediates suggested that the insertion and deletion slowed down the proton uptake steps at the cytoplasmic surface.     

Determination of copper(I)-ethylene complexes, [Cu(C2H4)]+ and [Cu(C2H4)2]+, with aid of EDTA titration of copper(I) and copper(II) ions

Summary Volumetric measurements of ethylene and simple EDTA titration of copper(I) and copper(II) ions confirm that [CuL]⁺ and [CuL₂]⁺ are formed when an aqueous solution of copper(II) is reduced by copper metal in the presence of ethylene, (L). The formation constants,K ₁=[CuL⁺]²[Cu²⁺]^–1[L]^–2 andK ₂=[CuL ₂ ⁺ ]^–1[L]^–1, have been estimated. The formation of [CuL]⁺ is accompanied by an enthalpy change, H, of –25 kJ mol^–1, and a positive entropy change, S, of 13 J mol^–1 K^–1.