Simplicity of vacuum modules over affine Lie superalgebras

We prove an explicit condition on the level k for the irreducibility of a vacuum module $V^k$ over a (non-twisted) affine Lie superalgebra, which was conjectured by M. Gorelik and V.G. Kac. An immediate consequence of this work is the simplicity conditions for the corresponding minimal W-algebras obtained via quantum reduction, in all cases except when the level k is a non-negative integer.     

Direct excitation of the forbidden clock transition in neutral 174Yb atoms confined to an optical lattice

We report direct single-laser excitation of the strictly forbidden (6s2)1S0 <--> (6s6p)3P0 clock transition in 174Yb atoms confined to a 1D optical lattice. A small (approximately 1.2 mT) static magnetic field was used to induce a nonzero electric dipole transition probability between the clock states at 578.42 nm. Narrow resonance linewidths of 20 Hz (FWHM) with high contrast were observed, demonstrating a resonance quality factor of 2.6 x 10(13). The previously unknown ac Stark shift-canceling (magic) wavelength was determined to be 759.35 +/- 0.02 nm. This method for using the metrologically superior even isotope can be easily implemented in current Yb and Sr lattice clocks and can create new clock possibilities in other alkaline-earth-like atoms such as Mg and Ca.     

Quantitative parameter-free prediction of simulated crystal-nucleation times

We present direct comparisons between simulated crystal-nucleation times and theoretical predictions using a model of aluminum, and demonstrate that a quantitative prediction can be made. All relevant thermodynamic properties of the system are known, making the agreement of our simulation data with nucleation theories free of any adjustable parameters. The role of transient nucleation is included in the classical nucleation theory approach, and shown to be necessary to understand the observed nucleation times. The calculations provide an explanation on why nucleation is difficult to observe in simulations at moderate undercoolings. Even when the simulations are significantly larger than the critical nucleus, and when simulation times are sufficiently long, at moderate undercoolings the small concentration of critical nuclei makes the probability of the nucleation low in molecular dynamics simulations.     

Reactive lyotropic polyimide oligomers

Amine-terminated and maleimide-terminated oligomers of molecular weight 1200–1800 based on 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl and 3,3′,4,4′-biphenylenetetracarboxylic dianhydride were synthesized and characterized for lyotropic liquid crystalline behavior. Several different synthetic procedures were evaluated and a one-step procedure in m-cresol was found to be the most effective for producing fully imidized materials. Lyotropic behavior was observed only for the as-prepared solutions in m-cresol and in dilutions of this solution. Oligomer thermal stability was excellent, onsets of decomposition were in excess of 550°C. © 1996 John Wiley & Sons, Inc.     

Synthetic studies on the ingenane diterpenes. An improved entry into a trans-intrabridgehead system

[reaction: see text] The efficient construction of an ingenol intermediate exhibiting "insideminus signoutside" intrabridgehead stereochemistry is reported. The sequence features the net conversion of a cis-intrabridgehead compound into a highly strained trans-species via palladium-mediated isomerization of an allylic epoxide followed by a low-temperature alkoxide-accelerated 1,5-hydrogen migration.     

Reversible Photoswitching in Poly(2-oxazoline) Nanoreactors

This contribution reports light responsive catalytic nanoreactors based on poly(2-oxazoline) diblock copolymers. The hydrophobic block of the copolymer is a random copolymer consisting of a spiropyran functionalized 2-oxazoline (SPOx) and 2-(but-3-yn-1-yl)-4,5-dihydrooxazole (ButynOx), while the hydrophilic block is based on 2-methyl-2-oxazoline (MeOx). The block copolymer is terminated with tris(2-aminoethyl) amine (TREN) that serves as catalyst in a Knoevenagel condensation. Four block copolymers with different ButynOx/SPOx and hydrophilic/hydrophobic ratios are synthesized and self-assembled through solvent exchange. Micelles and vesicles of various sizes are observed by TEM, which undergo morphological and size changes in response to irradiation with UV light. We hypothesize that these transformations in the nanostructures are caused by increases in the hydrophilicity of the hydrophobic block when spiropyran (SP) isomerizes to merocyanine (MC) in the presence of UV light. The reversible transition from micellar to vesicular nanoreactors resulted in increased reaction kinetics through improved substrate accessibility to the catalytic site, or termination of the catalytic reaction due to polymer precipitation. These nanoreactors present a promising platform towards photoregulating reaction outcomes based on changes in nanostructure morphology.     

Binary Mixtures of Liquid Crystalline Ester Bismaleimides

Abstract

A binary system consisting of a chlorohydroquinone-based ester bismaleimide (3-Cl), T _m = 238°C, and a methylhydroquinone-based ester bismaleimide (3-Me), T _m = 251°C, was investigated for the purpose of improving processability by widening the nematic phase range before polymerization. Calculations based on the Schroeder-van Laar equation predicted a system eutectic composition of 41% 3-Me monomer and a eutectic temperature of 202°C. Experiments found the eutectic composition at 35% 3-Me and the eutectic temperature at 218.5°C. Discrepancies between experimental results and theoretical predictions are likely due to error in measured heats of fusion either due to impurities in the samples or due to the reactive nature of the components being considered. Thermal cycling was also found to have a significant melting point depression effect. While significant depression of the system melting point was achieved, polymerization still occurred immediately after melting in all systems evaluated. All mixtures could be polymerized from the nematic phase to yield a solid which retained the nematic orientation of the starting polymer melt.     

N-Glycosylamine-mediated isotope labeling for mass spectrometry-based quantitative analysis of N-linked glycans

N-Linked glycosylation is a major protein modification involved in many essential cellular functions. Methods capable of quantitative glycan analysis are highly valuable and have been actively pursued. Here we describe a novel N-glycosylamine-based strategy for isotopic labeling of N-linked glycans for quantitative analysis by use of mass spectrometry (MS). This strategy relies on the primary amine group on the reducing end of freshly released N-linked glycans for labeling, and eliminates the need for the harsh labeling reaction conditions and/or tedious cleanup procedures required by existing methods. By using NHS-ester amine chemistry we used this strategy to label N-linked glycans from a monoclonal antibody with commercially available tandem mass tags (TMT). Only duplex experiments can be performed with currently available TMT reagents, because quantification is based on the intensity of intact labeled glycans. Under mild reaction conditions, greater than 95 % derivatization was achieved in 30 min and the labeled glycans, when kept at ?20 °C, were stable for more than 10 days. By performing glycan release, TMT labeling, and LC–MS analysis continuously in a single volatile aqueous buffer without cleanup steps, we were able to complete the entire analysis in less than 2 h. Quantification was highly accurate and the dynamic range was large. Compared with previously established methods, N-glycosylamine-mediated labeling has the advantages of experimental simplicity, efficient labeling, and preserving glycan integrity.

Fluorescence monitoring of a benzo[a]pyrene metabolite using a regenerable immunochemical-based fiber-optic sensor

Microscale regenerable biosensors are described and utilized to measure the natural fluorophor benzo[a]pyrene tetraol (BPT). The sensors combine laser-excited/fiber-optic remote sensing principles with a unique capillary tube delivery system to make repetitive, heterogeneous fluoroimmunoassay measurements. Two sensor configurations and modes of operation are described. Concentrations of BPT in the nanomolar range are easily measured with a reproducibility of 10% or better, depending on the sensor design, selective measurements can be made in ca. 20 min, then the sensor can be regenerated by delivering new reagents to the sensing chamber, without removing the sensor from the sample.