Glued Langmuir-Blodgett bilayers having unusually high He/CO2 permeation selectivities

Single Langmuir-Blodgett bilayers derived from 5,11,17,23,29,35-hexakis[(N,N,N-trimethylammonium)-N-methyl-37,38,39,40,41,42-hexakis-n-hexamedecyloxy-calix[6]arene hexachloride (1), which have been ionically cross-linked (i.e., "glued together") with poly(acrylic acid), have been found to exhibit He/CO2 permeation selectivities as high as 150. This degree of selectivity, for a membrane that is less than 6 nm in thickness, is without precedent. In principle, materials of this type could lead the way to improved membranes for hydrogen purification.     

Viewing membrane-bound molecular umbrellas by parallax analyses

Fluorescence quenching measurements have been made for a series of di-walled and tetra-walled molecular umbrellas having moderate (i.e., hydroxyl-) and strong (i.e., sulfate-) facial hydrophilicity, using Cascade Blue as the fluorophore. Through the use of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphotempocholine, 1-palmitoyl-2-stearoyl-(5-DOXYL)-sn-glycero-3-phosphocholine, and 1-palmitoyl-2-stearoyl-(12-DOXYL)-sn-glycero-3-phosphocholine as fluorescence quenchers, evidence has been obtained for a membrane-bound state in which the umbrella molecules lie on the surface of the lipid bilayer. In the case of the sulfated molecular umbrellas, evidence has also been obtained for a subpopulation in which the fluorophore lies deeper within the membrane. Probable structures for the shallow-lying and deep-lying molecular umbrellas are discussed.     

Total synthesis of 7-deoxypancratistatin-1-carboxaldehyde and carboxylic acid via solvent-free intramolecular aziridine opening: phenanthrene to phenanthridone cyclization strategy

Solid-state silica-gel-catalyzed opening of aziridine 6 provided phenanthrene 7, whose oxidative cleavage, recyclization, and further elaboration furnished the C-1 aldehyde and carboxylic acid derivatives of 7-deoxypancratistatin for potential analogue synthesis.     

High resolution spectroscopy of and

Extensions in frequency coverage coupled with sensitive spectroscopic techniques have enabled high resolution measurements of pure rotational spectra of deuteromethane and its 13-C substituted counterpart up to J^′=7. The current work reveals a small inconsistency in previously reported frequency measurements of ¹²CH₃D at J^′=5.     

Voltammetric and electrochemical ESR studies of oxidation reactions mediated by tris(4-bromophenyl)amine in acetonitrile

The electrochemical oxidation of tris(4-bromophenyl)amine in the presence of 2,6-lutidine is examined in acetonitrile. Voltammetric and spectroscopic investigations suggest that the electrogenerated triaryl aminium radical cation oxidizes 2,6-lutidine in an EC' mechanism, and an equilibrium constant for this homogeneous electron transfer is estimated. The mediated oxidation of a protected phenyl selenoglycoside by this reaction mixture is studied by the use of electrochemical ESR, employing a tubular flow cell, and signal intensity data is found to be consistent with the proposed mechanism, allowing the determination of kinetic parameters by computational simulation. Products of the mediated glycoside oxidation are determined by proton NMR and mass spectrometry.     

Particle-in-cell modeling of relativistic laser–plasma interaction with the adjustable-damping,direct implicit method

Implicit particle-in-cell codes offer advantages over their explicit counterparts in that they suffer weaker stability constraints on the need to resolve the higher frequency modes of the system. This feature may prove particularly valuable for modeling the interaction of high-intensity laser pulses with overcritical plasmas, in the case where the electrostatic modes in the denser regions are of negligible influence on the physical processes under study. To this goal, we have developed the new two-dimensional electromagnetic code ELIXIRS (standing for ELectromagnetic Implicit X-dimensional Iterative Relativistic Solver) based on the relativistic extension of the so-called Direct Implicit Method [D. Hewett, A.B. Langdon, Electromagnetic direct implicit plasma simulation, J. Comput. Phys. 72 (1987) 121–155]. Dissipation-free propagation of light waves into vacuum is achieved by an adjustable-damping electromagnetic solver. In the high-density case where the Debye length is not resolved, satisfactory energy conservation is ensured by the use of high-order weight factors. In this paper, we first derive the electromagnetic direct implicit method as a simplified Newton scheme. Its linear properties are then investigated through numerically solving the relation dispersions obtained for both light and plasma waves, accounting for finite space and time steps. Finally, our code is successfully benchmarked against explicit particle-in-cell simulations for two kinds of physical problems: plasma expansion into vacuum and relativistic laser–plasma interaction. In both cases, we will demonstrate the robustness of the implicit solver for crude discretizations, as well as the gains in efficiency which can be realized over standard explicit simulations.     

THz measurements of propane

Propane is present in many planetary atmospheres, as confirmed by vibrational spectroscopy in the infrared wavelengths. As the simplest alkane with a permanent dipole moment, propane has a rotational spectrum. The relatively light atom framework causes the strongest rotational transitions to appear in the submillimeter wavelength range. This fact, as well as the small dipole moment, have prevented the molecule from being observed in the interstellar medium. Telescopes with high sensitivity at high altitude such as the Atacama Large Millimeter Array or above the Earth’s atmosphere like the Herschel Space Observatory are likely to be sensitive enough for detection of this species in the interstellar medium, planetary nebulae, hot cores and/or planetary atmospheres. We present the rotational spectra of propane in its ground and first two excited vibrational states, measured through 1.6 THz. The ground state submillimeter spectrum is approximated well by semi-rigid rotor. The submillimeter data has been combined with high resolution centimeter wavelength data to enable analysis of the equivalent dual-hindered rotor torsional substates using a simplified version of a symmetric two-top Hamiltonian. The same model has been applied to the torsionally excited states that experience more large-amplitude motion and require additional tunnelling parameters.     

Alumina-Assisted Basic Hydrolysis of Esters1

“Anhydrous hydroxide” formed by reaction of 2 equiv of potassium tert-butoxide with 1 equiv of water in dry ether serves as a useful reagent for hydrolyzing esters and tertiary amides at ambient temperatures.² During the course of our studies dealing with alumina as a support and as a catalyst for solid-liquid biphase reactions, we have discovered that potassium hydroxide crushed together with neutral alumina (reagent 1) provides the basis for an equally effective means for carrying out ester hydrolysis.^3,4 Moreover, isolation of the alcohol is readily accomplished by simple filtration and solvent evaporation.     

Submillimeter measurements of isotopes of nitric acid

The ground and low-lying vibrational states of nitric acid are observable with current instrumentation in the Earth’s thermal submillimeter atmospheric emission. Remote sensing continues to improve to higher sensitivity and future missions will allow these measurements with minimal integration time. Sensing of weaker spectral features will require signal averaging, and choices of spectral windows for these features will require knowledge of the higher vibrational states and rare isotopes of the strongly emitting species. Nearly comprehensive information on vibrational states and isotopically substituted species is now available from wide bandwidth scans of natural and isotopically enriched nitric acid. In this work, ground state rotational spectra of five isotopically substituted species of nitric acid are analyzed in the submillimeter spectral range. We present the Hamiltonian parameters necessary for prediction and identification of isotopic features across the nitric acid ground state rotational spectrum.