Access to Optically Active 3‐Substituted Piperidines by Ring Expansion of Prolinols and Derivatives

The ring expansion of prolinols via an aziridinium intermediate gives C3‐substituted piperidines in good yields and enantiomeric excess, the substituent at the C3 position being derived from the most reactive nucleophile in the reaction mixture. Depending on the nucleophile, the reaction proceeds under thermodynamic or kinetic control. The regioselectivity of attack of nucleophiles on the aziridinium intermediate depends on the nature of the substituents on the nitrogen atom and the C4 position of the starting prolinols.     

Water‐Stable Zirconium‐Based Metal–Organic Framework Material with High‐Surface Area and Gas‐Storage Capacities

We designed, synthesized, and characterized a new Zr‐based metal–organic framework material, NU‐1100 , with a pore volume of 1.53 ccg^?1 and Brunauer–Emmett–Teller (BET) surface area of 4020 m²g^?1; to our knowledge, currently the highest published for Zr‐based MOFs. CH₄/CO₂/H₂ adsorption isotherms were obtained over a broad range of pressures and temperatures and are in excellent agreement with the computational predictions. The total hydrogen adsorption at 65 bar and 77 K is 0.092 g g^?1, which corresponds to 43 g L^?1. The volumetric and gravimetric methane‐storage capacities at 65 bar and 298 K are approximately 180 v_STP/v and 0.27 g g^?1, respectively.     

Li8Si8, Li10Si9, and Li12Si10: Assemblies of Lithium-Silicon Aromatic Units

We report the global minima structures of Li₈Si₈, Li₁₀Si₉, and Li₁₂Si₁₀ systems, in which silicon moieties maintain structural and chemical bonding characteristics similar to those of their building blocks: the aromatic clusters T_d−Li₄Si₄ and C_2v−Li₆Si₅. Electron counting rules, chemical bonding analysis, and magnetic response properties verify the silicon unit‘s aromaticity persistence. This study demonstrates the feasibility of assembling silicon-based nanostructures from aromatics clusters as building blocks.     

Magnetic microsphere-based methods to study the interaction of teicoplanin with peptides and bacteria

Teicoplanin (teic) from Actinoplanes teichomyceticus is a glycopeptide antibiotic used to treat many Gram-positive bacterial infections. Glycopeptide antibiotics inhibit bacterial growth by binding to carboxy-terminal d-Ala-d-Ala intermediates in the peptidoglycan of the cell wall of Gram-positive bacteria. In this paper we report the derivatization of magnetic microspheres with teic (teic-microspheres). Fluorescence-based techniques have been developed to analyze the binding properties of the microspheres to two d-Ala-d-Ala terminus peptides. The dissociation constant for the binding of carboxyfluorescein-labeled d-Ala-d-Ala-d-Ala to teic on microspheres was established via fluorimetry and flow cytometry and was determined to be 0.5 × 10⁻⁶ and 3.0 × 10⁻⁶ mol L⁻¹, respectively. The feasibility of utilizing microparticles with fluorescence methods to detect low levels (the limit of bacterial detection was determined to be 30 colon-forming units; cfu) of Gram-positive bacteria has been demonstrated. A simple microfluidic experiment is reported to demonstrate the possibility of developing microsphere-based affinity assays to study peptide–antibiotic interaction.     

Girard-P derivative of 2-pyridinecarboxaldehyde as analytical reagent. Spectrophotometric determination of copper

The synthesis, characteristics, properties, and reactions with metallic ions of pycolinaldehyde derivatives of Girard-P reagent have been studied. The reagents form complexes with Cu(II), Ni(II), Co(II), Hg(II) and (I), Zn(II), Cd(II), and Fe(III), and (II), which exhibit a good sensibility but whose spectra have the absorption maxima located in the ultraviolet zone. The spectrum of copper complex in the presence of ascorbic acid shows another absorption band at the visible region and this makes the spectrophotometric determination of copper very selective. The influence of the different experimental parameters on the formation of copper complex without ascorbic acid and with this compound was studied, and the optimum conditions for the determination of copper were established. The precision of the procedure, expressed in terms of relative standard deviation, was 1.1%. The method has been tested on “white metal E-8” samples.     

Measurement of the generalized polarizabilities of the proton in virtual Compton scattering at Q2=0.92 and 1.76 GeV2

We report a virtual Compton scattering study of the proton at low c.m. energies. We have determined the structure functions P(LL)-P(TT)/epsilon and P(LT), and the electric and magnetic generalized polarizabilities (GPs) alpha(E)(Q2) and beta(M)(Q2) at momentum transfer Q(2)=0.92 and 1.76 GeV2. The electric GP shows a strong falloff with Q2, and its global behavior does not follow a simple dipole form. The magnetic GP shows a rise and then a falloff; this can be interpreted as the dominance of a long-distance diamagnetic pion cloud at low Q2, compensated at higher Q2 by a paramagnetic contribution from piN intermediate states.     

Enhanced fusion-evaporation cross sections in neutron-rich 132Sn on 64Ni

Evaporation residue cross sections have been measured with neutron-rich radioactive 132Sn beams on 64Ni in the vicinity of the Coulomb barrier. The average beam intensity was 2 x 10(4) particles per second and the smallest cross section measured was less than 5 mb. Large sub-barrier fusion enhancement was observed. Coupled-channel calculations taking into account inelastic excitation significantly underpredict the measured cross sections below the barrier. The presence of several neutron transfer channels with large positive Q values suggests that multinucleon transfer may play an important role in enhancing the fusion of 132Sn and 64Ni.     

Transverse asymmetry AT' from the quasielastic 3He(e,e') process and the neutron magnetic form factor

We have measured the transverse asymmetry A(T') in 3He(e,e(')) quasielastic scattering in Hall A at Jefferson Laboratory with high precision for Q2 values from 0.1 to 0.6 (GeV/c)(2). The neutron magnetic form factor G(n)(M) was extracted based on Faddeev calculations for Q2 = 0.1 and 0.2 (GeV/c)(2) with an experimental uncertainty of less than 2%.     

Novel microscopic mechanism of intermixing during growth on soft metallic substrates

Generic computer simulations using empiric interatomic potentials suggest a new, collective mechanism that could be responsible for mixing at heteroepitaxial interfaces. Even if single adsorbate atoms diffuse by hopping on the substrate surface and do not mix at the terraces, two-dimensional islands formed by nucleation may become unstable above a certain critical size and explode upwards forming clusters of several atomic layers. This process is accompanied by strong distortions of the underlying atomic layers, and on soft materials it can result in surface etching and incorporation of substrate atoms into the islands.