Discrete series characters and two-structures

Let be a connected semisimple real Lie group with compact Cartan subgroup. Harish-Chandra gave formulas for discrete series characters which are completely explicit except for certain interger constants appearing in the numerators. The main result of this paper is a new formula for these constants using two-structures. The new formula avoids endoscopy and stable discrete series entirely, expressing (unaveraged) discrete series constants directly in terms of (unaveraged) discrete series constants corresponding to two-structures of noncompact type.

     

Determination of the molecular structure of diacetylene from high-resolution FTIR spectroscopy

The high-resolution infrared absorption spectra of eight²H or¹³C substituted isotopomers of diacetylene have been recorded, and the bands corresponding to thev ₄ fundamental andv ₆ combination of the major isotopomer have been analyzed using a Loomis-Wood-type program. Effective ground-state rotational constants have been obtained from ground-state combination differences. A number ofr ₀,r _s,r _m , and (r _m )_corr structures have been calculated from the available data and are compared to those obtained by ab initio methods. The (r _m )_corr structure, which is a reliable near-equilibrium structure of diacetylene, isr _C–H=106.131(13) pm;r _C–C=137.081(16) pm;r _C-C=120.964(14). (r _m )_corr structures of the related molecules cyanogen, cyanoacetylene, and cyanodiacetylene have been calculated, and near-equilibrium structures of triacetylene and dicyanoacetylene have been predicted.     

Avidin self-associates with boric acid gel suspensions: an affinity boron carrier that might be developed for boron neutron-capture therapy

It has been shown in preliminary studies that the antibacterial protein avidin self-associates with the boric acid gel polymer, and avidin-coated gel particles in the micrometer and submicrometer size ranges are of interest for boron neutron-capture therapy (BNCT), which is neutron-induced fission of boron-10 to produce intense alpha radiation for tumor destruction. The gel particles carry large amounts of boron-10 and are theoretically able effect a meaningful tissue dosing through BNCT. A gross precipitation of gel particles occurs within 46 min of mixing when the avidin/colloid ratio is about 0.34 g avidin/g colloid. This is a minimum time if gel and avidin concentrations are in the low microgram/milliliter range, but at higher proportions of avidin the time delay to precipitation increases significantly; i.e., the colloid surface becomes blocked, inhibiting lattice formation. The avidin-coated gel particles eventually cross-link, forming a solid matrix and precipitating on a timescale measured on the order of an hour. At shorter exposure times rapid agglutination-like reactions were observed with biotinylated bovine albumin, suggesting that two-stage pretargeting of specific tissues should be possible with biotinylated antitumor antibodies. However, for BNCT to be practical, avidin's interaction with the gel needs to be strengthened, and all aryl-B(OH)(2) groups on the particle surfaces must be blocked, or else the particles will interact strongly and nonspecifically with each other and with the carbohydrate groups present on most cell surfaces. Glyceric acid delays the precipitation of the particle suspensions while most simple and complex carbohydrates accelerate it.     

Electrochemical control of solid phase micro-extraction: conducting polymer coated film material applicable for preconcentration/analysis of neutral species

Exploitation of the physical, chemical and electrically conductive properties of poly(3-dodecylthiophene) (P3DDT) for the preconcentration and release in solid phase microextraction (SPME) of organometallic arsenobetaine (AsB) from aqueous media was investigated. Hydrophobic interactions between this neutral arsenic species and an undoped polythiophene (no applied potential) with n-substituted alkyl groups (n=12) in the three position were used for the diffusion-controlled preconcentration. After absorption into the polymer matrix, the chemical properties of this conductive polymer were changed by applying an external potential. This potential provides a sufficient driving force for desorption of the analyte from the extraction phase into an aqueous solution for subsequent analysis. The applied positive potential oxidizes the polymer to its charged hydrophilic state, which releases the neutral analyte. The concentration and speciation of the analyte from the sample matrix was analyzed by HPLC coupled to an ICP-MS. The diffusion-controlled uptake was fast (equilibrium attained within minutes) and did not require pretreatment of the analyte. The electrochemically-controlled release of the analyte is also very rapid (within minutes). This conducting polymer film system, therefore, can offer analytical applications for the convenient preconcentration and subsequent analysis of neutral environmental species.     

Synthesis of functionalized oxacalix[4]arenes

Tetranitrooxacalix[4]arenes are generated in high yield by the room-temperature S(N)Ar reaction of 1,3-dihydroxybenzenes with 1,5-difluoro-2,4-dinitrobenzene. The reaction is tolerant to a range of functionality on the nucleophilic component, including hydroxyl-substitution at the 2- and 5-positions, which yields previously unknown 26,28- and 5,17-dihydroxyoxacalix[4]arenes.     

High-speed analysis of residual solvents by flow-modulation gas chromatography

High-speed gas chromatographic (GC) separation of residual solvents in pharmaceutical preparations, using a flow-modulation technique, is described. These volatile compounds are separated on a series-coupled (tandem) column ensemble consisting of a polyethylene glycol column and a trifluoropropylmethyl/dimethylpolysiloxane column. This column ensemble is operated in stop-flow mode to enhance, or "tune", the separation. A valve between the junction point of the tandem column ensemble and a source of carrier gas at a pressure above the GC inlet pressure is opened for intervals of 2-8 s. This stops or slightly reverses the flow of carrier gas in the first column. Stop-flow pulses are used to increase the separation of target analytes that overlap in the total ensemble chromatogram, compared to non-stop-flow, or conventional, operation. All 36 target compounds, based on ICH Classes I and II residual solvent lists, are resolved in 12 min using the stop-flow technique and a single chromatographic analysis.     

Convenient synthesis of 4H-1,2,4-triazole-3-thiols using di-2-pyridylthionocarbonate

We report here the convenient synthesis of 4H-1,2,4-triazole-3-thiols using di-2-pyridyl-thionocarbonate as the thiocarbonyl transfer reagent. This method is suitable for microplate parallel synthesis and produces samples in screening-ready condition. It uses two large sets of building-blocks: amines and hydrazides.     

"One-step" alkynylation of adamantyl iodide with silver(I) acetylides

[reaction: see text] Silver(I) acetylides allow one-step alkynylation of adamantyl iodide in yields ranging from 25 to 68%.     

A critical analysis of electrospray techniques for the determination of accelerated rates and mechanisms of chemical reactions in droplets

Electrospray and Electrosonic Spray Ionization Mass Spectrometry (ESI-MS and ESSI-MS) have been widely used to report evidence that many chemical reactions in micro- and nano-droplets are dramatically accelerated by factors of ∼10² to 10⁶ relative to macroscale bulk solutions. Despite electrospray''s relative simplicity to both generate and detect reaction products in charged droplets using mass spectrometry, substantial complexity exists in how the electrospray process itself impacts the interpretation of the mechanism of these observed accelerated rates. ESI and ESSI are both coupled multi-phase processes, in which analytes in small charged droplets are transferred and detected as gas-phase ions with a mass spectrometer. As such, quantitative examination is needed to evaluate the impact of multiple experimental factors on the magnitude and mechanisms of reaction acceleration. These include: (1) evaporative concentration of reactants as a function of droplet size and initial concentration, (2) competition from gas-phase chemistry and reactions on experimental surfaces, (3) differences in ionization efficiency and ion transmission and (4) droplet charge. We examine (1–4) using numerical models, new ESI/ESSI-MS experimental data, and prior literature to assess the limitations of these approaches and the experimental best practices required to robustly interpret acceleration factors in micro- and nano-droplets produced by ESI and ESSI.

The application of Electrospray and Electrosonic Spray Ionization Mass Spectrometry (ESI-MS and ESSI-MS) to study accelerated reaction kinetics in droplets is examined using numerical models, new experimental data, and prior literature.     

Rhenium(V)-catalyzed synthesis of 2-deoxy-alpha-glycosides

A mild method for the synthesis of 2-deoxysugars from the coupling of glycals with a range of nucleophiles is described. The method employs 1 mol % of an air- and moisture-tolerant rhenium-oxo complex [ReOCl3(SMe2)(Ph3PO)] as a catalyst for the formation of O-, N-, and S-alpha-glycosides. The catalytic system tolerates a number of commonly employed protecting groups, including isopropylidene acetals, alkyl and silyl ethers, acetates, and benzoates. Furthermore, the high-oxidation-state complex selectively catalyzes the coupling with the glycal acceptor in preference to oxidation of the glycals, alcohols, and even thiols.