Interpolating classical partitions of the set of positive integers

The Ramanujan Journal - We construct an easily described family of partitions of the positive integers into n disjoint sets with essentially the same structure for every $$n \ge 2$$ . In a special...     

Robust, soluble pentacene ethers

We report the synthesis and characterization of a series of alkoxy-substituted silylethynylated pentacene derivatives (R = CH(2)CH(2), CHCH, CH(2)). All three compounds are easily prepared, soluble in common organic solvents, and stable both as solids and in solution. Two of the derivatives possess significant pi-face interactions in the crystal. Values for lambda(max) for these new pentacene derivatives range from 621 to 674 nm, and oxidation potentials lie between 109 and 301 mV versus ferrocene.     

Determination of multiple drugs of abuse in human urine using capillary electrophoresis with fluorescence detection

Methods for separation and determination of multiple drugs of abuse in biological fluids using capillary electrophoresis (CE) with native fluorescence and laser-induced fluorescence (LIF) detection are described herein. Using native fluorescence, normorphine, morphine, 6-acetyl morphine (6-AM), and codeine were analyzed by CE without any derivatization procedure and detected at an excitation wavelength of 245 nm with a cut-off emission filter of 320 nm, providing a rapid and simple analysis. The detection limits were in the range of 200 ng/mL. For a highly sensitive analysis, LIF detection was also examined using a two-step precolumn derivatization procedure. In this case, drugs extracted from human urine were first subjected to an N-demethylation reaction involving the use of 1-chloroethyl chloroformate (ACE-Cl) and then derivatized using fluorescein isothiocyanate isomer I (FITC) and analyzed by CE coupled to a LIF detector. Variables affecting this derivatization: yield of demethylation reaction, FITC concentration, reaction time and temperature, were studied. The estimated instrumental detection limits of the FITC derivatives were in the range of 50-100 pg/mL, using LIF detection with excitation and emission wavelengths of 488 nm and 520 nm, respectively. The linearity, reproducibility and reliability of the methods were evaluated. In addition, a comparison of the characteristics for both native fluorescence and LIF detections was also discussed.     

Separation of racemic sulfoxides and sulfinate esters on four derivatized cyclodextrin chiral stationary phases using capillary gas chromatography

The separation of 17 chiral sulfoxides and eight chiral sulfinate esters by gas chromatography (GC) on four derivatized cyclodextrin chiral stationary phases (CSPs) (Chiraldex G-TA, G-BP, G-PN, B-DM) is presented. Many of these compounds are structural isomers or part of a homologous series. Differences in enantioselectivity of the methyl phenyl sulfoxide isomers on the derivatized gamma cyclodextrin and the heptakis 2,6-di-O-methyl-beta-cyclodextrin (i.e. B-DM) CSPs are discussed. Under the conditions of this study, the molecular mass cut-off for the GC separation of these compounds was approximately 230. Compounds of higher molecular mass were not eluted from the CSPs at reasonable times and temperatures, but these higher molecular mass enantiomers can be separated by liquid chromatography and capillary electrophoresis. The enantiomeric separation and elution order of a sulfinate ester containing two stereogenic centers as well as 15 chiral sulfoxides is presented. The G-TA and B-DM CSPs generally gave opposite elution orders for most of the compounds studied.     

Alternative approaches to infrared multiphoton dissociation in an external ion reservoir

In this work we present variations on in-hexapole infrared multiphoton dissociation (IRMPD) for the characterization of modified oligonucleotides using an ESI-FTICR spectrometer. We demonstrate that IRMPD in the external ion reservoir provides a comprehensive series of fragments allowing thorough characterization of a wide range of oligonucleotides containing alternative backbones and 2′ substitutions. An alternative pulse sequence is presented that allows alternating MS and IRMPD MS/MS spectra to be acquired on a chromatographic timescale without loss in ionization duty cycle. Ions are excited to a larger cyclotron radius such that they “dodge” the IR laser beam that travels through the center of the trapped ion cell and impinges on the external ion reservoir creating IRMPD fragments that will be detected in the next scan. An alternative approach for directing IR radiation into the external ion reservoir using a hollow fiber waveguide as a photon conduit is presented. This approach offers a simple and robust alternative to the previously utilized on-axis scheme and may allow effective implementation with lower power lasers owing to the inherent increase in power density achieved by focusing the nascent laser beam into the hollow fiber waveguide.     

Measuring surface area of airborne titanium dioxide powder agglomerates: relationships between gas adsorption,diffusion and mobility-based methods

Inhalation toxicology studies generally use the Brunauer, Emmett, and Teller (BET) gas adsorption method to measure total surface area of particles whereas occupational exposures are more readily measured by real-time mobility-based surface areas or active surface area measured with diffusion charger-based instruments. Three surface area measurement methods were studied: filter-based inert gas adsorption (BET method), diffusion charging, and mobility-based methods. The goal of the project was to investigate and develop a correlation between the measurement methods. The experimental design consisted of measuring surface area in a series of five trials for each of two powder types, fine and ultrafine titanium dioxide with primary particle sizes of 440 and 20 nm, respectively, and two aerosol concentrations. Diffusion charger instruments tended to underestimate the total particle surface area measured by the BET, but were well correlated with mobility-based surface areas obtained from a scanning mobility particle sizer. Filter-based gas adsorption methods and diffusion charging methods provide different but valuable information on total and active surface areas of particles, respectively. Results indicate they should not be used as predictors of one another.     

Ionic liquid-alkane association in dilute solutions

Enthalpies and entropies of transfer were measured by gas chromatography for dilute solutions of a homologous series of eight even n-alkanes (from octane to docosane) into six different ionic liquids (ILs) (namely, 1-butyl-3-methylimidazolium chloride, bromide, iodide, triflate and hexafluorophosphate; plus N-butylmethylpyridinium bis {(trifluoromethyl) sulfonyl}-imide) over the 80–150 °C temperature range, all ILs being in the liquid state. Over a narrow concentration range, the entropic change may be consistent with a solvophobic association model of n-alkanes in ILs. A very simple model is proposed to account for the thermodynamic data. This approach can be used to approximate interionic distances and possible dielectric constants for ILs. Although the model may have some use in dilute alkane-IL solutions, more sophisticated models, particularly for the enthalpic contributions, are desirable.     

Zinc-catalyzed silylation of terminal alkynes.

A rapid and high-yielding silylation of terminal alkynes employing TMSOTf and catalytic quantities of Zn(OTf)2 has been developed. The reaction works well for a variety of substrates including reactive esters. Fifteen examples with yields of >90% are reported.