Intermittent simulated moving bed chromatography: 2. Separation of Tröger’s base enantiomers

The intermittent simulated moving bed (I-SMB) process is a modification of the conventional SMB process that has been recently analyzed theoretically [1]. Here, we present a comparative analysis of the two processes, each operated in a six column 1-2-2-1 configuration (one column in sections 1 and 4 and two columns in sections 2 and 3) and in a four-column 1-1-1-1 configuration. Experiments are carried out on a properly modified laboratory unit to separate racemic mixtures of the enantiomers of Tröger’s base in ethanol on ChiralPak AD at a total feed concentration of 1 g/L. Simulations are carried out for the same system using the equilibrium dispersive model and a bi-Langmuir isotherm, whose parameters have been preliminarily estimated from pulse and breakthrough experiments. Experiments and simulations are fully consistent and demonstrate that the four-column I-SMB process (but not the four-column SMB process) can separate the two enantiomers at very high purity and achieve a productivity twice as large as that of the six-column I-SMB and conventional SMB processes with the same solvent consumption.     

Interlayer water molecules in vanadium pentoxide hydrate. 8. Dynamic properties by quasi-elastic neutron scattering

The dynamics of water molecules in the layered vanadium pentoxide hydrate, V(2)O(5).nH(2)O, were studied by quasi-elastic neutron scattering (QENS) measurements. Heterogeneity of the dynamic properties was confirmed by alpha-relaxation model analysis. Translational diffusion of monolayer and double-layer water molecules is by site-to-site diffusion and is reduced relative to that of bulk water. Water molecules lose their mobility markedly and solidify with decreasing temperature. However, mobile water remains at 253 K. Rotational diffusion coefficients are unaffected by confinement and are very similar to the bulk values determined at temperatures in the range 253-298 K. The dynamic speed characterized by QENS is much faster than that expected from the data determined by deuterium NMR (DNMR) measurements at low temperatures.     

Pyridylazulenes: synthesis, color changes, and structure of the colored product

A facile method for the synthesis of 1- and 2-pyridylazulenes, and of 1,3-dipyridylazulenes, is described. Color and spectral changes of these pyridylazulenes upon the addition of either acid or metal ions were investigated in detail. The color changed from blue to red upon the addition of trifluoroacetic acid or soft metal ions, depending on the substitution patterns of the pyridyl group on the azulene skeleton. The structures of the protonated or coordinated products were examined on the basis of the spectral data. It was found that the protonation or coordination of metal ions occurred on the nitrogen atom of the pyridine ring, but not on the carbon atom of azulene ring. The transition intervals of several pyridylazulenes for use as pH indicators were also determined.     

Preparation and characterization of silica—polyimide composite membranes coated on porous tubes for CO2 separation

Silica-polyimide microcomposite membranes were prepared on γ-alumina-coated α-alumina support tubes, and their gas permeation properties were evaluated with He, N₂ and CO₂. Smoothing of the substrate surface and hybridization of silica and polyamic acid were both effective to form defect-free thin composite membranes. The CO₂ permeance of a membrane with a silica content of 68 wt% was one order of magnitude higher than that of a polyimide membrane having the same thickness. The permselectivity of CO₂ to N₂ was 30 at 30°C and 13 at 100°C. Contributions of the silica and polyimide phases to permeance of the composite membrane were analyzed with a two-phase permeation model. The effective thickness of the rate-controlling polyimide phase was less than one-tenth of the total thickness of the silica-polyimide membrane.     

Reactivity and Structural Properties of a Mechanochemically Treated Ag2O-V2O5 System in Relation to AgVO3 Polymorphs

Formation and chemical properties of amorphous AgVO₃, which was prepared by mechanochemical treatment of an Ag₂O-V₂O₅ mixture, and crystalline AgVO₃ were studied in relation to AgVO₃ polymorphs. A ball-milled sample of the mixture was assigned as a highly deformed β-AgVO₃ rather than the low density phase α-AgVO₃. Crystalline α-AgVO₃ and β-AgVO₃ were converted into deformed β-AgVO₃ by ball milling, which produced a clear change. δ-AgVO₃ is resistant to mechanical treatment and its structure was not markedly affected. The dissolved chemical species from the ball-milled sample precipitates to form α-AgVO₃ without a seeding crystal, but other polymorphs deposit if they are present; i.e., β-AgVO₃ and δ-AgVO₃ grow on the seeding crystal.     

Combined NMR and quantum chemical studies on the interaction between trehalose and dienes relevant to the antioxidant function of trehalose

In a previous study (Oku, K.; Watanabe, H.; Kubota, M.; Fukuda, S.; Kurimoto, M.; Tujisaka, Y.; Komori, M.; Inoue, Y.; Sakurai, M. J. Am. Chem. Soc. 2003, 125, 12739), we investigated the mechanism of the antioxidant function of trehalose against unsaturated fatty acids (UFAs) and revealed that the key factor relevant to the function is the formation of OH...pi and CH...O hydrogen bonds between trehalose and the cis double bonds of the UFA. Here, we investigate whether such intriguing interactions also occur between this sugar and cis double bonds in other unsaturated compounds. For this purpose, we selected various diene compounds (1,3-butadiene, 1,3-pentadiene, 1,4-pentadiene, and 2,5-heptadiene) as interaction partners. All NMR experiments performed, including 1H-1H NOESY measurements, indicated that trehalose selectively interacts with the cis-olefin proton pair in the above diene with a 1:1 stoichiometry, and the C-3 (C-3') and C-6' (C-6) sites of the sugar are responsible for the interaction. Similar interactions were not observed for the mixtures of the diene and other saccharides (neotrehalose, kojibiose, nigerose, maltose, isomaltose, sucrose, maltitol, and sorbitol). Quantum chemical calculations revealed that the OH-3 and OH-6 groups bind to the olefin double bonds of the diene through OH...pi and CH...O types of hydrogen bonds, respectively, and the stabilization energy of the resulting complex is 5-6 kcal mol(-1). These results strongly support the above NMR results. Finally, the activation energies were calculated for the hydrogen abstraction reactions from the activated methylene group of heptadiene. In particular, when the reaction was initiated by a methyl radical, the activation energy was only 10 kcal mol(-1) for the free heptadiene, but on complexation with trehalose it drastically increased to ca. 40 kcal mol(-1). This indicates that trehalose has a significant depression effect on the oxidation of the diene compounds. These results strongly support the antioxidant mechanism deduced in the previous study and indicate that the formation of unique multiple hydrogen bonds between trehalose and cis-olefin bonds is rather a general event not confined to the case of UFA.     

Conformation and location of membrane-bound salinomycin-sodium complex deduced from NMR in isotropic bicelles

An ionophore antibiotic salinomycin was studied in a membrane environment consisting of isotropic bicelles, a better model for biological membranes than micelles, and its conformation and topological orientation in bicelles was determined. 2D NMR measurements and restrained conformational search revealed that salinomycin-sodium salt in bicelles adopts an open conformation in which the orientation of the E-ring is significantly different from that in crystal and solution structures. This conformational alteration breaks an intramolecular hydrogen bond between 28-OH and 1-O, dislocates the ether oxygen of the E-ring from a coordinated position to the sodium ion observed in the crystal, and consequently weakens the complexation between salinomycin and the sodium ion. Paramagnetic relaxation experiments using doxyl-phospholipids reveal that salinomycin is embedded shallowly in bicelles, with both terminals being closer to the water interface and the olefin portion facing the bicelle interior. Measurements of intermolecular NOEs between salinomycin and phospholipids further supported this orientation. Weaker complexation with sodium ion and positional preference in the membrane polar region may facilitate the catch-and-release of metal ions at the polar/nonpolar interface of bilayers. On the basis of these findings, a model for salinomycin-assisted transport of metal ions across biological membranes is proposed.     

Enthalpy and interfacial free energy changes of water capillary condensed in mesoporous silica, MCM-41 and SBA-15

The effect of confinement on the solid-liquid phase transitions of water was studied by using DSC and FT-IR measurements. Enthalpy changes upon melting of frozen water in MCM-41 and SBA-15 were determined as a function of pore size and found to decrease with decreasing pore size. The melting point also decreased almost monotonically with a decrease in pore size. Analysis of the Gibbs-Thomson relation on the basis of the thermodynamic data showed that there were two stages of interfacial free energy change after the constant region, i.e., below a pore size of 6.0 nm: a gradual decrease down to 3.4 nm and another decrease after a small jump upward. This fact demonstrates that the simple Gibbs-Thomson relation, i.e., a linear relation between the melting point change and the inverse pore size, is limited to the range not far from the melting point of bulk water. FT-IR measurements suggest that the decrease in enthalpy change and interfacial free energy change with decreasing pore size reflect the similarity of the structures of both liquid and solid phases of water in smaller pores at lower temperatures.