Modeling of the adsorption behavior and the chromatographic band profiles of enantiomers : Behavior of methyl mandelate on immobilized cellulose

The adsorption isotherms of (−)- and (+)-methyl mandelate from a hexane-isopropanol (90:10) solution were measured on a chromatographic column packed with 4-methylcellulose tribenzoate coated on silica. These isotherms are accounted for by a bi-Langmuir isotherm model, the two Langmuir terms having widely different initial slopes and saturation capacities, but each term having the same saturation capacity for the two enantiomers. The competitive isotherms were also measured. They are in excellent agreement with the prediction of a competitive bi-Langmuir model based on the single-component isotherms. The individual band profiles are in agreement with the profiles calculated from these isotherms. Thus, a simplified competitive isotherm can be used to model a separation on a chiral stationary phase the recognition mechanism of which is not well identified and the adsorption behavior of which is certainly not ideal.     

Base-assisted intramolecular 6-acetoxypyranone-acetylene [5+2] cycloaddition. Synthesis and reactivity of novel oxa-tricyclo[5.3.1.0]undecenones

The synthesis of 3,11-dioxatricyclo[5.3.1.0^1,5]undeca-5,9-dien-8-ones is reported from suitable 5-substituted furfuryl alcohols bearing an acetylenic side-chain. Successive peracid-mediated oxidative rearrangement of furan carbinols and base-assisted intramolecular 1,3-dipolar cycloaddition afforded oxygen-bridged tricyclo-undecane derivatives. Stereoselective transformations of cycloadducts are also discussed.     

Size fractionation of aquatic colloids and particles by cross-flow filtration: analysis by scanning electron and atomic force microscopy

The suitability of the combined application of environmental scanning electron microscopy (ESEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) for the evaluation of the ability of cross-flow filtration (CFF) to perform adequate size fractionation of freshwater colloids and particles was examined. ESEM and SEM imaging provided reference images of the CFF-generated fractions and, in estimating the experimental cut-off diameter of the membrane, provided evidence that separation was not consistent with nominal pore sizes of the membranes. However, analysis of the images showed that size distribution of CFF-generated fractions and the estimated cut-off diameter of the membranes were dependent on the advantages and limitations of the two imaging techniques. With both ESEM and SEM, best estimates of size cut-offs were lower than the nominal pore size of the membrane in the case of 0.45 μm membranes, but roughly accurate in the case of 0.1 μm pore size membranes. The results also suggested that the effectiveness of CFF may benefit from a pre-separation step using a minimally perturbing technique such as split thin-flow fractionation. AFM demonstrated the presence of colloids smaller than 50 nm in all fractions including the retentates, showing that CFF fractionation is not fully quantitative and not based on size alone. The results indicate that previous studies investigating trace element partitioning using CFF may need re-evaluation as the importance of particles and large colloids may be over-estimated.     

Syntheses and Structures of Trilithium Cyclotriphosphazenates Equipped with 2‐Halo‐aryl Substituents

Hexakis (2‐halo‐anilino) cyclotriphosphazenes (2‐X‐C₆H₄NH)₆P₃N₃ {X = F ( 1d ), Cl ( 1e ), Br ( 1f )} were prepared by refluxing mixtures of hexachloro cyclotriphosphazene, 2‐haloaniline and triethylamine in toluene and characterized by single crystal X‐ray diffraction. 1d , 1e and 1f were reacted with ⁿBuLi in thf. Reactions were monitored with ³¹P NMR. Addition of three equivalents of ⁿBuLi yields lithium complexes of trianionic phosphazenates [{(thf)₂Li}₃{(2‐X‐C₆H₄N)₃(2‐X‐C₆H₄NH)₃P₃N₃}] {X= F ( 2d ), Cl ( 2e ) and Br ( 2f )}. 2d , 2e and 2f were structurally characterized by X‐ray diffraction, which reveals monomeric cis‐metalated phosphazenates featuring central P₃N₃ ring systems of chair conformation. Lithium ions reside in three N(eq)‐P‐N(endo) chelation sites at one face of the P₃N₃ ring system. Li…X distances are rather long (> 3Å) indicating no Li‐X interactions.     

Electrodeposited copolymer electrolyte into nanostructured titania electrodes for 3D Li-ion microbatteries

The electrochemical synthesis of a copolymer electrolyte (PEO-PMMA) into titania nanotubes is described and studied. Compared with the electrochemical systems based on solid electrolytes deposited by top-down techniques, the copolymer/titania nanotube material reveals high electrochemical performance, opening new perspectives for the fabrication of 3D all-solid-state microbatteries.     

Synthesis of green organogelators with a sulfide linkage via solvent-free Michael addition: soft templates for the preparation of size-controlled gold nanoparticles

Green organogelators with a sulfide linkage and free amino groups were synthesized via phase transfer catalysis using a N-benzylcinchonidinium bromide catalyst. Their self-assemblies in various common solvents were examined. These compounds exhibit high gelation ability especially in aromatic and highly polar solvents with a low critical gelation of 0.1 wt %. The organogels were analyzed by ¹H nuclear magnetic resonance (¹H NMR) and Fourier transfer-infrared spectroscopies (FT-IR), and their phase transition temperatures were determined by differential scanning calorimetry. The homogeneity of the gel networks was examined by field emission scanning electron microscopy and transmission electron microscopy (TEM). A lamellar structure was also confirmed by X-ray diffraction analysis. The organogels were employed as soft-templates for the in situ generation of stable gold nanoparticles dispersed in the gel matrix, and the resulting GNP dispersions were studied by ¹H NMR and UV–vis absorption. Transmission electron microscopy showed that GNPs assemble into a thin membrane-like structure.