Stereoselective Synthesis of the Urinary Metabolite N-Acetyl-S-(3,4-dihydroxybutyl)cysteine

On exposure to the potential carcinogen 1,3-butadiene, the major urinary metabolite in humans is N-acetyl-S-(3,4-dihydroxybutyl)cysteine. A novel, stereoselective synthesis of this cysteine–butadiene metabolite has been developed that is suitable for the production of either diastereomer for use in occupational exposure analysis. L-Cysteine and 4-bromo-1-butene are coupled via an S_N2 reaction to give the core structure. A Sharpless asymmetric dihydroxylation using the dihydroquinidine (DHQD) ligand provided the terminal 1,2-diol with the 3-hydroxyl group in the R configuration.

Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental resource.     

Characterization of an Electron Ionization Source Trap Operating in the Presence of a Magnetic Field Through Computer Simulation

We explore the feasibility of conducting electron ionization (EI) in a radio-frequency (rf) ion source trap for mass spectrometry applications. Electrons are radially injected into a compact linear ion trap in the presence of a magnetic field used essentially to lengthen the path of the electrons in the trap. The device can either be used as a stand-alone mass spectrometer or can be coupled to a mass analyzer. The applied parallel magnetic field and the oscillating rf electric field produced by the trap give rise to a set of coupled Mathieu equations of motion. Via numerical simulations, electron trajectories are studied under varying intensities of the magnetic field in order to determine the conditions that enhance ion production. Likewise, the dynamic behavior of the ions are investigated in the proposed EI source trap and the fast Fourier transform FFT formalism is used to obtain the frequency spectrum from the numerical simulations to study the motional frequencies of the ions which include combinations of the low-frequency secular and the high-frequency micromotion with magnetron and cyclotron frequencies. The dependence of these motional frequencies on the trapping conditions is examined and particularly, the limits of applying a radial magnetic field to the EI ion trap are characterized.

In Situ Spectroscopy of Calcium Fluoride Anchored Metal–Organic Framework Thin Films during Gas Sorption

Surface-mounted metal–organic frameworks (SURMOFs) show promising behavior for a manifold of applications. As MOF thin films are often unsuitable for conventional characterization techniques, understanding their advantageous properties over their bulk counterparts presents a great analytical challenge. In this work, we demonstrate that MOFs can be grown on calcium fluoride (CaF₂) windows after proper functionalization. As CaF₂ is optically (in the IR and UV/Vis range of the spectrum) transparent, this makes it possible to study SURMOFs using conventional spectroscopic tools typically used during catalysis or gas sorption. Hence, we have measured HKUST-1 during the adsorption of CO and NO. We show that no copper oxide impurities are observed and also confirm that SURMOFs grown by a layer-by-layer (LbL) approach possess Cu⁺ species in paddlewheel confirmation, but 1.9 times less than in bulk HKUST-1. The developed methodology paves the way for studying the interaction of any adsorbed gases with thin films, not limited to MOFs, low temperatures, or these specific probe molecules, pushing the boundaries of our current understanding of functional porous materials.     

Muridienin-1 and -2: The missing links in the biogenetic precursors of acetogenins of annonaceae

Isolation of Δ^n,n+4 diunsaturated γ-lactone derivatives of lacceroic and ghedoic acids, allows us to confirm the biogenetic pathway of the bioactive acetogenins of Annonaceae.     

Study of PET Surfaces After Laser or Plasma Treatment: Surface Modifications and Adhesion Properties Towards Al Deposition

The modifications induced on poly (ethylene terephthalate) (PET) by an excimer laser radiation or a low pressure plasma as well as their ability to improve Al–PET adhesion were investigated. For this purpose, surface roughness, chemical composition, surface wettability, and adhesion properties of PET were studied depending on the process parameters. Both treatments can significantly enhance the adhesion but the surface change responsible for the improvement was different for each pretreatment.     

Multiple quantum well structures and high-power lasers of gaas- algaas grown by metalorganic vapor phase epitaxy (MOVPE)1

GaAs/AlGaAs GRIN-SCH type multiple quantum well lasers with four wells of 11 nm GaAs, grown in an MOVPE chimney reactor, exhibit an output power as high as 110 mW/facet (CW, 30°C; 5 μm stripe) and 1.3 W/facet (pulsed, 30°C; 53 μm stripe) until catastrophic optical damage occurs. 2000 hours life tests conducted at 60°C and 15 mW CW show no noticeable degradation for the 5 μm stripe laser with a reflective coating on both facets. Raman spectroscopy on similar multiple quantum well structures with 65 GaAs wells is used to ascertain that the wells have minimum residual aluminum- content.     

Estimating extreme bivariate quantile regions

When simultaneously monitoring two possibly dependent, positive risks one is often interested in quantile regions with very small probability p. These extreme quantile regions contain hardly any or no data and therefore statistical inference is difficult. In particular when we want to protect ourselves against a calamity that has not yet occurred, we need to deal with probabilities p?<?1/n, with n the sample size. We consider quantile regions of the form {(x, y)?∈?(0, ∞?)²: f(x, y)?≤?β}, where f, the joint density, is decreasing in both coordinates. Such a region has the property that it consists of the less likely points and hence that its complement is as small as possible. Using extreme value theory, we construct a natural, semiparametric estimator of such a quantile region and prove a refined form of consistency. A detailed simulation study shows the very good statistical performance of the estimated quantile regions. We also apply the method to find extreme risk regions for bivariate insurance claims.     

Effective electrically tunable infrared reflectors based on polymer stabilised cholesteric liquid crystals

Electrically tunable infrared (IR) reflectors based on polymer stabilised cholesteric liquid crystals (PSCLC) have been fabricated. The influence of polymerisation time on bandwidth broadening and response time of the IR reflector was investigated. Such IR reflector can reflect broad band of infrared light from 725 to 1435 nm upon application of a DC electric field, while remaining predominantly transparent in the visible region, with the transmittance in the region of 400–700 nm being above 90%. Bandwidth broadening was induced using low operational power with acceptable switching speeds. Model tests reveal that this IR reflector can effectively control the indoor temperature. The distinct properties of such IR reflector make it a good candidate for smart windows of automobiles and buildings to control interior temperature and save energy.     

A form of regular variation and its application to the domain of attraction of the double exponential distribution

Probability Theory and Related Fields -