A new three-carbon synthon for efficient synthesis of benzannelated and 1-(2-arylethenyl) heterocycles

The novel three-carbon synthon 1-(1H-1,2, 3-benzotriazol-1-yl)-3-chloroacetone for the synthesis of benzothiazoles, pyrido[1,2-a]indoles, and styryl-substituted indolizines and imidazo[1,2-a]pyridines is reported. The proposed routes are a general and efficient approach for heterocyclizations followed by benzannelations or attachment of arylethenyl pharmacophores.     

Simplified electron ejection in Fourier transform ion cyclotron resonance mass spectrometry by suspended trapping

Suspended trapping is used to eject electrons in negative-ion Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometric experiments. In contrast to electron ejection by resonant excitation of the trapping motion, suspended trapping involves allowing the electrons to escape along the z-axis (perpendicular to the trap plates) while the trapping potential is briefly removed. The duration of this event is sufficiently short (～10 μs) so that ion losses are negligible; the overall effect is that of a ‘high-pass mass filter’. Suspended trapping is simpler to implement and more generally applicable to various cell geometries than resonant electron ejection. The effectiveness of the suspended trapping technique is not compromised by the anharmonicity of the potential well in ‘elongated’ ICR traps, but depends simply on the time it takes the electrons to escape the cell. Finally, a small, positive offset potential (～+0.25 V) applied to the trap plates during the suspended trapping event increases the efficiency of the ejection.     

Development of a universal Raman detector for microchromatography

Summary A detector for microchromatography in which Raman spectroscopy is used to identify the eluted species has been developed. The detector is designed to be applicable to a wide range of compounds without requiring the presence of a chromophore. Its use is illustrated in the analysis of nitro compounds on a 250 μm i.d. column. Raman spectra of each of the compounds could be identified as they passed the detector. The advatages of the use of fully deuterated solvents are demonstrated by the analysis of nitrobenzenes in methanol/water mobile phases. The detection limit for nitrobenzene using the Raman line at 1342 cm⁻¹ was 75ng.     

Shift to Pseudomonic acid B production in P. fluorescens NCIMB10586 by mutation of mupirocin tailoring genes mupO, mupU, mupV, and macpE

Mupirocin, a polyketide-derived antibiotic from Pseudomonas fluorescens NCIMB10586, is a mixture of pseudomonic acids (PA) that target isoleucyl-tRNA synthase. The mup gene cluster encodes both type I polyketide synthases and monofunctional enzymes that should play a role during the conversion of the product of the polyketide synthase into the active antibiotic (tailoring). By in-frame deletion analysis of selected tailoring open-reading frames we show that mupQ, mupS, mupT, and mupW are essential for mupirocin production, whereas mupO, mupU, mupV, and macpE are essential for production of PA-A but not PA-B. Therefore, PA-B is not simply produced by hydroxylation of PA-A but is either a precursor of PA-A or a shunt product. In the mupW mutant, a new metabolite lacking the tetrahydropyran ring is produced, implicating mupW in oxidation of the 16-methyl group.     

Simulation of the Adhesion of Particles to Surfaces

The removal of micrometer and submicrometer particles from dielectric and metal films represents a challenge in postchemical mechanical polishing cleaning. Proper modeling of the adhesive force between contaminant particles and these films is needed to develop optimal solutions to postchemical mechanical polishing cleaning. We have previously developed and experimentally validated a model to describe the adhesion between spherical particles and thin films. This simulation expands previous models to characterize the adhesive interaction between asymmetrical particles, characteristic of a polishing slurry, and various films. Our simulation accounts for the contact area between particles and substrates, as well as the morphology of the surfaces. Previous models fail to accurately describe the contact of asymmetrical particles interacting with surfaces. By properly accounting for nonideal and geometry and morphology, the simulation predicts a more accurate adhesive force than predictions based upon an ideal van der Waals model. The simulation is compared to experimental data taken for both semi-ideal particle-substrate systems (polystyrene latex spheres in contact with silicon films) and asymmetrical systems (alumina particles in contact with various films). Copyright 2001 Academic Press.     

Determination of radiostrontium in soil samples using a crown ether

A simple and rapid method has been developed for the separation and determination of total radiostrontium in soil. The method consists of three basic steps: oxalate precipitation to remove bulk potassium, chromatographic separation of strontium from most inactive and radioactive interferences utilizing a crown ether (Sr. Spec, EIChroM Industries, Il. USA) and oxalate precipitation of strontium to evaluate the chemical yield. Radiostrontium is then determined by liquid scintillation counting of the dissolved precipitate. When 10 g samples of soil are used, the sensitivity of the method is about 10 Bq/kg. The chemical yield is about 80%. The separation and determination of radiostrontium can be carried out in about 8 hours.     

Efficient electrospray ionization from polymer microchannels using integrated hydrophobic membranes

A simple process for realizing stable and reliable electrospray ionization (ESI) tips in polymer microfluidic systems is described. The process is based on the addition of a thin hydrophobic membrane at the microchannel exit to constrain lateral dispersion of the Taylor cone formed during ESI. Using this approach, ESI chips are shown to exhibit well-defined Taylor cones at flow rates as low as 80 nL min(-1) through optical imaging. Furthermore, stable electrospray current has been measured for flow rates as low as 10 nL min(-1) over several hours of continuous operation. Characterization of the electrospray process by optical and electrical monitoring of fabricated ESI chips is reported, together with mass spectrometry validation using myoglobin as a model protein. The novel process offers the potential for low-cost, direct interfacing of disposable polymer microfluidic separation platforms to mass spectrometry.     

Determination of atrazine, its degradation products and metolachlor in runoff water and sediments using solid-phase extraction

In order to determine the fate of the herbicides atrazine (as well as some of its degradation products) and metolachlor in water and sediments, a method was developed to extract and analyse these compounds. The two matrices were separated completely by centrifugation followed by filtration using nylon filters (0.45 mum). Sediments were extracted with a mixture of methanol-0.1N hydrochloric acid (50:50, v/v) using a wrist-action shaker. Filtered water and extracts of sediments were adjusted to pH 4, then concentrated and purified onto two solid-phase extraction cartridges using in tandem C(18) bonded phase column atop sulfonic acid bonded column (SCX). Atrazine, deethylatrazine, deisopropylatrazine and metolachlor retained by the C(18) column were eluted with ethyl acetate. Chlorodiaminotriazine and hydroxyatrazine retained by the SCX column were eluted with a 50:50 (v/v) acetonitrile-0.1M Na(2) HPO(4) aqueous solution (pH 8.5). The extracts were quantified by high performance liquid chromatography with diode array detector (HPLC-DAD) and by gas chromatography with nitrogen-phosphorus detector (GC-NPD). Overall percent recoveries were about 75% and detection limits were between 0.05 and 0.15 microg/l., and 0.5 and 1.5 microg/kg for water and sediments, respectively.     

Effect of modified virtual orbitals on local Coulomb correlation holes in FCN

Local Coulomb correlation hole distribution functions may be used to assess the extent to which electron correlation effects are present in large scale SCF + CI wave functions. From a set of modified virtual orbitals, ordered according to their interaction with the SCF configuration, we have constructed a limited SCF + CI wave function with improved convergence characteristics with respect to that formed from the canonical virtual orbital set. These wave functions, of the same size yet with different energies, have been used to examine the range and depth of local Coulomb correlation holes in FCN. In all cases, the depth of the local Coulomb hole is no more than 10% or so of that of the corresponding Fermi hole, and the range Fermi correlation is generally less than that of Fermi correlation. This is particularly marked in the high density regions around the nuclei. The significance of our results is discussed in relation to a recent proposal for the incorporation of Coulomb correlation into the local exchange method.     

Novel fragmentation pathway for CID of (b<Subscript>n</Subscript>−1+Cat)<Superscript>+</Superscript> ions from model,metal cationized peptides

We report a new fragmentation pathway for the CID of (b3 - 1 + Cat)+ product ions derived from the model peptide AXAG, where X = beta-alanine, gamma-aminobutyric acid, epsilon-amino-n-caproic acid, or 4-aminomethylbenzoic acid. By changing the amino acid to the C-terminal side of the amino acid X, and incorporating 15N and 13C labeled residues at the same position, we conclude that the dissociation pathway most likely leads to a metal cationized nitrile. With respect to the various amino acids at position X, the putative nitrile product becomes more prominent, relative to the conventional (a3 - 1 + Cat)+ species, in the order beta-alanine < gamma-aminobutyric acid < epsilon-aminocaproic acid < 4-aminomethylbenzoic acid. The pathway is not observed for peptides with alpha-amino acids at position X. The product ion is observed most prominently during the CID of Li+ and Na+ cationized peptides, only to a small extent for Ag+ cationized peptides, and not at all from protonated analogues.