Effect of molecular dynamics and modulated structure on H NMR spectrum studied in [Mg(H2O)6][SiF6]

The spectrum of magnetic resonance is typically affected by a modulated structure in an incommensurate phase, resulting in the broadened spectrum characterized by ‘edge singularities’. We demonstrate that the modulated structure in the crystal where molecular motion exists is responsible for the narrowing of the spectrum in the fast motional region by means of the simulation of ²H NMR spectrum of [Mg(H₂O)₆][SiF₆]. The program developed by combining the theories of phase solitons in the incommensurate phase and motional change of ²H NMR spectrum was used for the simulation. We obtained a good agreement between the theoretical ²H NMR spectrum and experimental one for [Mg(H₂O)₆][SiF₆].     

Structural disorder and diffusional pathway of oxide ions in a doped Pr2NiO4-based mixed conductor

MEM nuclear density analysis from neutron diffraction data measured in situ at 1015.6 degrees C has indicated the two-dimensional network of curved O2-O3-O2 oxide-ion diffusion paths on the (Pr,La)-O layer in a K2NiF4-type structured oxide-ionic and electronic mixed conductor (Pr0.9La0.1)2(Ni0.74Cu0.21Ga0.05)O4+delta.     

Synthesis and isomerization of conjugated oligomers containing azoimidazole unit

The Suzuki (for O1 – O3 ) and Stille (for O4 ) coupling polymerization of 2‐(phenylazo)imidazole bearing the benzyl protecting group at the 1‐position gave conjugated oligomers. The transformation from the neutral imidazole in the conjugated oligomer O2 , consisted of the alternating 2,5‐didecyl‐1,4‐phenylene unit, to the cationic imidazolium salt O2S was performed. Depending on the chemical structure of coupling partners, the absorption maximum of conjugated oligomers showed red shift or blue shift from that of the model compound M with the benzene ring at the 4,5‐positions. The absorption maximum wavelength of the cationic conjugated oligomer O2S showed a blue shift from that of the neutral conjugated oligomer O2 . The trans‐to‐cis photoisomerization of the azoimidazole unit in conjugated oligomers was observed by irradiating the light at 436 nm, and the conversion degree to the cis structure had a rough correlation with the maximum absorption wavelength of materials. The trans‐to‐cis photoisomerization in the film state was sluggish. On the other hand, the cis‐to‐trans thermal isomerization of the azoimidazole unit was confirmed and the absorbance returned to the initial state before the photoisomerization. The trans‐to‐cis photoisomerization of the cationic conjugated oligomer O2S required large energy, and the prolonged light irradiation might decompose the azoimidazole unit. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Asymmetric cyclization of 2-alkenylphenols. A comparative study on the use of palladium(II) and titanium(IV) complexes

The oxidative cyclization of 2-(3-pentenyl)phenol catalyzed by [(η³-pinene)PdOAc]₂ gives optically active (+)-2-vinylchroman (25% e.e.), while (−)-2-(1-hydroxyethyl)chroman (56% e.e.) is formed as a single diastereomer upon treatment with t-BuOOH in the presence of Ti(OⁱPr)₄ and -(+)-diethyl tartrate. 2-(2-Butenyl)phenol also undergoes the Ti-promoted asymmetric cyclization to give (2S,1′R)-(−)-2-(1-hydroxyethyl)-2,3-dihydrobenzofuran (29% e.e.).     

Crystal structures and topochemical polymerizations of 7,7,8,8-tetrakis(alkoxycarbonyl)quinodimethanes

Highly conjugated monomers, 7,7,8,8-tetrakis(alkoxycarbonyl)quinodimethanes (methoxy (1a), ethoxy (1b), isopropoxy (1c), benzyloxy (1d), chloroethoxy (1e), and bromoethoxy (1f)), were synthesized. Recrystallizations of 1a, 1c, 1e, and 1f yielded two crystal forms (prisms (1a-A) and needles (1a-B), needles (1c-A) and plates (1c-B), prisms (1e-A) and plates (1e-B), and prisms (1f-A) and needles (1f-B)), which have different molecular packing modes by X-ray crystal structure analysis, indicating that the crystals are polymorphic. In the photopolymerizations of these monomer crystals in the solid state, 1a-A, 1e-A, and 1f-A polymerized topochemically to give crystalline polymers. For their thermal polymerizations in the solid state, in addition to 1a-A, 1e-A, and 1f-A, 1e-B and 1f-B polymerized, but polymers formed from the 1e-B and 1f-B were amorphous. The packing of quinodimethane molecules in the crystals was defined by four kinds of parameters, stacking distance (d(s)), the distance between the reacting exomethylene carbon atoms (d(cc)), the angles formed between the stacking axis and longer axis of the monomer molecule (theta(1)), and the shorter axis of the monomer molecule (theta(2)), and then the polymerization reactivity of these quinodimethanes in the solid state was discussed on the basis of these parameters.     

Poly(ethylene glycol)-lipase complexes that are highly active and enantioselective in ionic liquids

Lipase-catalyzed alcoholysis between vinyl acetate and 2-phenyl-1-propanol was investigated in dialkylimidazolium-based ionic liquids. Although native lipase powder exhibited very low activity in an ionic liquid, forming a poly(ethylene glycol)(PEG)-lipase complex improved the lipase activity in the ionic liquid. The activity of the PEG-lipase complex was higher in ionic liquids than in common organic solvents (n-hexane, isooctane and dimethylsulfoxide). Fluorescence measurements using 4-aminophthalimide revealed that the ionic liquids were more hydrophilic than the organic solvents used for non-aqueous enzymology. A kinetic study of lipase-catalyzed alcoholysis in an ionic liquid ([Bmim][PF6]) revealed that the Michaelis constant (Km) for 2-phenyl-1-propanol in the ionic liquid was half that in n-hexane, suggesting that the ionic liquid stabilized the enzyme-substrate complex. Finally, we carried out enantioselective alcoholysis of 1-phenylethanol in ionic liquids employing the PEG-lipase complex, and obtained high enantioselectivity, comparable to that in n-hexane.     

Liquid phase formation of alkyl- and perfluoro-phosphonic acid derived monolayers on magnesium alloy AZ31 and their chemical properties

Alkyl- and perfluoro-phosphonic acid derived SAMs were successfully formed on Mg alloy by liquid phase method for the first time. The chemical and anticorrosive properties of the prepared SAMs on magnesium alloys were characterized using contact angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and electrochemical measurements. Water contact angle measurements revealed that the maximum advancing/receding water contact angles of n-octyl (OP: CH(3)(CH(2))(7)PO(OH)(2)), n-dodecyl (DP: CH(3)(CH(2))(11)PO(OH)(2)), n-octadecyl (ODP: CH(3)(CH(2))(17)PO(OH)(2)) phosphonic acid, and 2-(perfluorohexyl)ethyl (PFEP: CF(3)(CF(2))(5)CH(2)CH(2)PO(OH)(2)) phosphonic acid were 105.1/64.7°, 108.3/69.6°, 111.9/75.2°, and 115.2/67.4° respectively. In the case of alkylphosphonic acid SAMs (OP, DP, and ODP), the advancing and receding water contact angles increased with an increase in the preparation time. The angle-resolved XPS (AR-XPS) data revealed that the film thicknesses of the OP, DP, ODP, PFEP on Mg alloy were estimated to be 0.8, 1.2, 1.7, and 1.1 nm, respectively. The XPS O 1s data support that the phosphonic acid derived SAM is covalently bound to the oxide or hydroxide surface of the Mg alloy in a monodenate or bidenate manner. Chemical stability of the alkyl- and perfluoro-phosphonic acid modified Mg alloy surfaces was investigated using aqueous solutions at pH=4.0, 7.0, and 10.0. The contact angles of OP, DP, and PFEP modified Mg surface decreased rapidly within the first 5 min after immersion in all the aqueous solutions and were less than 20°. On the other hand, the contact angles of the ODP modified Mg alloy after immersion in aqueous solutions at pH 4, 7 and 10 for 5 min were 45.1°, 89.3,° and 85.5°, respectively. The ODP modified Mg alloy had highest chemical stability in four types of the phosphonic acid derived SAMs used in this study, indicating that the molecular density of ODP on Mg alloy would be higher than those of OP, DP, PFEP on Mg alloy. The corrosion resistance of ODP modified Mg alloy was investigated by potentiodynamic polarization curve measurements. The ODP modified Mg alloy exhibits protective properties in a solution containing Cl(-) ions compared to unmodified Mg alloy.     

Measurements of Liquid-Phase Adsorption under High Pressure

Adsorption equilibria at about 1000 atm were measured for aqueous solutions of aromatic compounds. No significant difference between the isotherms at atmospheric pressure and at 1000 atm was found for nitrobenzene and ethylbenzene on activated carbon fiber. The decrease in the amount adsorbed due to the solubility increase with pressure and the increase in the amount adsorbed caused by compression of the adsorbed phase were considered to cancel each other. On the other hand, pressure had a marked effect on the adsorption of L-phenylalanine on a macroreticular adsorbent, resulting in a 1.5 to 2 times larger amount adsorbed at 1500 atm. The pressure effect was greater with larger amounts adsorbed. This implies that the molar volume of the adsorbed state is smaller than those of the pure state and dissolved state, and varies with the amount adsorbed.     

Mixed biopolymer systems based on starch

A binary mixture of starch-starch or starch with other biopolymers such as protein and non-starch polysaccharides could provide a new approach in producing starch-based food products. In the context of food processing, a specific adjustment in the rheological properties plays an important role in regulating production processing and optimizing the applicability, stability, and sensory of the final food products. This review examines various biopolymer mixtures based on starch and the influence of their interaction on physicochemical and rheological properties of the starch-based foods. It is evident that the physicochemical and rheological characteristics of the biopolymers mixture are highly dependent on the type of starch and other biopolymers that make them up mixing ratios, mixing procedure and presence of other food ingredients in the mixture. Understanding these properties will lead to improve the formulation of starch-based foods and minimize the need to resort to chemically modified starch.