Quantum effect induced kinetic molecular sieving of hydrogen and deuterium in microporous materials

We report here our investigations using Monte Carlo and molecular dynamics (MD) simulations, as well as quasi-elastic neutron scattering experiments, to study the adsorption and diffusion of H₂ and D₂ in zeolite Rho. In the simulations, quantum effects are incorporated via the Feynman-Hibbs variational approach. At low temperatures, we observe a reversal of kinetic molecular sieving in which D₂ diffuses faster than H₂. Based on fits of bulk data, we suggest new set of potential parameters for hydrogen, with the Feynman-Hibbs variational approach used for quantum corrections. The transport properties obtained from MD simulations are in excellent agreement with the experimental results, with both showing significant quantum effects on the transport at low temperature. The MD simulation results on two different structures of zeolite Rho clearly demonstrate that the quantum effect is very sensitive to pore size. High transport flux selectivity is noted at low temperatures, suggesting feasibility of kinetic isotope separation.     

Cation-directed synthesis of tungstosilicates. 2. Synthesis, structure, and characterization of the open Wells-Dawson anion alpha-[{K(H2O)2}(Si2W18O66)]15- and its transiton-metal derivatives [{M(H2O)}(mu-H2O)2K(Si2W18O66)]13- and [{M(H2O)}(mu-H2O)2K{M(H2O)4}(Si2W18O66)]11-

The dimer alpha-[{K(H2O)2}(Si2W18O66)]15- (1), synthesized by reacting K10A-alpha-[SiW9O34] with two equivalents of H+ in aqueous solution, has been characterized by polarography and 183W NMR spectroscopy. Nine resonance signals have been observed with the tetrabutylammonium salt in dimethylformamide/acetonitrile solution, in agreement with the crystal structure of the anion which consists of two A-alpha-[SiW9O34]10- associated through two W-O-W junctions. This anion derives from the Wells-Dawson structure by breaking four W-O-W junctions. The pocket between the two-half-anions can be filled by several metal cations. Reaction of transition-metal cations with 1 leads to the formation of [{M(H2O)}(mu-H2O)2K(Si2W18O66)]13- (1M) (M = Co, Ni, Cu) and [{M(H2O)}(mu-H2O)2K{M(H2O)4}(Si2W18O66)]11- (1M2) (M = Mn, Co, Ni) complexes. One potassium is always included in the pocket with one or two transition metals. Because of the shift of the potassium cation to one side of the anion, the coordination modes of the two transition metals are different. Crystals of 1, 1M, and 1Co2 potassium salts are triclinic (P-1, Z = 2) and crystals of 1M2 potassium salts are monoclinic (P2(1)/n, Z = 4). The symmetry of 1Mand 1M2 complexes is C1 and they are present in the crystal as racemate inversion pairs.     

Cobalt-catalyzed versus uncatalyzed intramolecular Diels-Alder cycloadditions

The intramolecular [4+2] cycloadditions of dienynes was investigated using cobalt-based catalysts. Substrates without substitution on alkyne moiety were found to react under thermal activation. The use of a cobalt salt as catalyst made reactions cleaner by limiting the formation of byproducts. Cycloadditions with dienynes possessing a substituent on the alkyne pattern occurred only in presence of a cobalt catalyst which displayed a moderate to good activity depending on the substrate patterns.     

Rapid Screening of Serum-Free Media for the Growth of Adherent Vero Cells by Using a Small-Scale and Non-invasive Tool

The paper proposes a rapid screening method for a first step improvement of an animal component-free medium dedicated to the growth of the anchorage-dependent Vero cell line. A new, rapid, and non-invasive technique is presented to specifically monitor cultures of adherent cells in 96-well plates. The operating conditions of an image analyzer are adapted to take into account the decrease of cell size when the attached cell density increases. An experimental design is carried out to assess the influence of ten component groups in the original medium. Two groups including protein extracts, growth factor, insulin, glucose, and pyruvate show significant positive effects. The groups with vitamins and molecules related to nitrogenous bases display a less pronounced influence. The mixture of amino acids, B₁ vitamin, magnesium sulfate, and sodium phosphate as well as the couple sodium citrate and ferric chloride lead to a downward trend. The screening results are proved to be scalable in stirred cultures with cells on microcarriers. An improved serum-free medium, with some component groups being removed or added, can be rapidly formulated to reach respectively similar or 1.6 times higher cell density than in the original medium. The results from this global approach could be helpful to further focus experiments on identified medium components.     

Use of coated capillaries for the electrophoretic separation of stereoisomers of a growth hormone secretagogue

The diastereoisomeric separation of peptidomimetics of hexarelin, a strong growth hormone secretagogue, in CE has been studied. Highly sulfated‐γ‐CD was found to be an appropriate selector for the separation of the stereoisomers. However, non‐repeatable analyses were obtained on bare fused silica capillary due to the progressive adsorption of the analytes on the capillary wall. Two types of polyelectrolyte coating agents were tested to prevent this phenomenon. Coating with neutral polyethylene oxide was found to be efficient but resulted in a very long analysis time (about 40 min). Coating with cationic poly(diallyldimethylammonium) chloride was found both to prevent analyte adsorption, reduce analysis time and alter separation selectivity. EOF measurement revealed that the highly sulfated‐γ‐CDs were strongly adsorbed on the poly(diallyldimethylammonium) chloride coating surface yielding a stable strong cathodic EOF, which considerably reduced analysis time (about 12 min). Very good repeatability of analysis was obtained (RSD_{migration time}<1%).