Determination of antibiotics such as macrolides,ionophores and tiamulin in liquid manure by HPLC–MS/MS

A method for the analysis of several macrolide and ionophore antibiotics as well as tiamulin in liquid manure was developed. Reversed-phase liquid chromatography and atmospheric pressure chemical ionisation (APCI) tandem mass spectrometry was used for detection.High-performance liquid chromatographic (HPLC) separation of the antibiotics was achieved in 35 min. The analytes were extracted with ethyl acetate and the extracts were cleaned up by solid-phase extraction on a diol SPE cartridge. Recovery experiments with spiked liquid manure concentrations varying from 6 to 2,000 microg kg(-1) gave constant recovery rates. The recovery rates for the macrolides erythromycin, roxithromycin and oleandomycin were 75-94%, that for the ionophore salinomycin was 119%, while that for the pleuromutilin tiamulin was 123%, when using a macrolide internal standard. The relative standard deviation was found to be 15-36% and the limits of detection were 0.4-11.0 micro g kg(-1).The maximum concentrations found in manure samples were 43 micro g kg(-1) for tiamulin and 11 micro g kg(-1) for salinomycin.     

Statistical radical copolymerization of styrene and methyl methacrylate in a room temperature ionic liquid

Use of a room temperature ionic liquid as the medium for conventional free radical copolymerization of styrene and methyl methacrylate resulted in reactivity ratios that were significantly different from those obtained in conventional organic solvents or in bulk, demonstrating that polymerization in this alternative medium offers potential to create copolymers having new monomer sequences.     

Spreading of viscous droplets on a non viscous liquid

Some polymer melts (of high viscosity ) can wet completely the surface of a non miscible, simple liquid. We discuss here the laws of spreading for a macroscopic droplet of this type, when the internal friction of the droplet dominates. We predict a droplet radius increasing liket ^1/4 wheret is the spreading time, or equivalently a droplet curvature decreasing liket ^–1. The droplet should be surrounded by a precursor film, which is not discussed in the present note.     

A ruler for determining the position of proteins in membranes

Both the oxygen diffusion rate and the oxygen solubility vary with depth into the interior of biological membranes. The product of these two gradients generates a single gradient, a permeability gradient, which is a smooth continuous function of the distance from the center of the membrane. Using electron paramagnetic resonance and the spin-probe method, the relaxation gradient of oxygen, which is directly proportional to the permeability gradient, is the quantity that can be directly measured in membranes under physiological conditions. The gradient obtained provides a calibrated ruler for determining the membrane depth of residues either from loop regions of membrane-binding proteins or from the membrane-exposed residues of transmembrane proteins. We have determined the relaxation gradient of oxygen in zwitterionic and anionic phospholipid membranes by attaching a single nitroxide probe to a transmembrane alpha-helical polypeptide at specific residues. The peptide ruler was used to determine the depth of penetration of the calcium-binding loops of the C2 domain of cytosolic phospholipase A(2). The positions of selected residues of this membrane-binding protein that penetrate into the membrane, determined using this ruler, compared favorably with previous determinations using more complex methods. The relaxation gradient constrains the possible values of the membrane-dependent oxygen concentration and the oxygen diffusion gradients. The average oxygen diffusion coefficient is estimated to be at least 2-fold smaller in the membrane than that in water.     

Steps towards molecular parity violation in axially chiral molecules. I. Theory for allene and 1,3-difluoroallene

In view of exploring possibilities for an experimental investigation of molecular parity violation we report quantum-chemical calculations of the parity-conserving and parity-violating potentials in the framework of electroweak quantum chemistry in allene C3H4 and 1,3-difluoroallene C3H2F2, which is nonplanar and axially chiral in the electronic ground state but expected to be nearly planar and achiral in several electronically excited states. The parity-violating potentials Epv for allene and 1,3-difluoroallene calculated with the multiconfiguration linear-response (MC-LR) approach of Berger and Quack [J. Chem. Phys. 112, 3148 (2000)] show qualitatively similar behavior as a function of torsional angle tau with maximum values of about 0.5 pJ mol(-1) for C3H4 and 2 pJ mol(-1) for C3H2F2. However, in the latter case they are asymmetrically shifted around tau=90 degrees , with a nonzero value at the chiral equilibrium geometry resulting in a parity-violating energy difference between enantiomers DeltapvE=Epv(P)-Epv(M)=1.2 pJ mol(-1) (equivalent to about 10(-13) cm(-1)). The calculated barrier heights corresponding to the nonrigid (multiple, and in part chiral) transition states in 1,3-difluoroallene fall in the range of 180-200 kJ mol(-1). These high barriers result in hypothetical tunneling splittings much smaller than DeltapvE and thus parity violation dominates over tunneling for the stereomutation dynamics in 1,3-difluoroallene. Therefore, DeltapvE is predicted to be a spectroscopically measurable energy difference. Two of the lower excited electronic states of C3H2F2 (1A and 3A) are calculated to be planar or quasiplanar, allowing, in principle, for spectroscopic state selection of states of well-defined parity. The results are discussed in relation to possible schemes of measuring parity violation in chiral molecules.     

Pentakis(methoxycarbonyl)cyclopentadiene,a strong organic acid: Crystal and molecular structures of HC5(CO)2Me)5 and Li[C5(CO2Me)5](H2O)

Contrary to some previously depicted structures, the proton in HC₅(CO₂Me)₅ is bonded to two oxygens rather than to carbon; the lithium ion in Li[C₅(CO₂Me)₅] (H₂O) is tetrahedrally coordinated by two carbonyl oxygens from one C₅ anion, one from a second anion, and a water molecule.     

Microwave assisted, palladium catalyzed aminocarbonylations of heteroaromatic bromides using solid Mo(CO)6 as the carbon monoxide source

The direct conversion of a variety of heteroaromatic bromides into heteroaromatic amides is described. This reaction utilizes Mo(CO)₆ as the carbon monoxide source and is performed using microwave heating allowing for very short reaction times. This convenient methodology allows for the preparation of a variety of heteroaromatic amides useful in medicinal chemistry applications.     

Preparation and spectroscopic properties of 2-benzothiazolyl araldehyde hydrazones

Notwithstanding its tendency toward air oxidation in solution, 2-hydrazinobenzothiazole I reacted with aromatic aldehydes in ethanol to give the corresponding hydrazones III-XV in high yields and analytical purity. In related examples, acylation took place under similar conditions to produce hydrazides XVI-XX . The near-infrared bands of the absorption spectra of the araldehyde hydrazones have been associated with charge transfer and appeared to correlate with structural elements of the compounds in a way suggesting that the charge transfer was intermolecular.     

Synthesis and reactions of halogenated thiazole isocyanates

A synthesis of 2-chloro-4-(trifluoromethyl)-5-isocyanatothiazole and 2,5-dichloro-5-isocyanatothiazole is described via the “Curtius Rearrangement” performed under anhydrous conditions. The synthetic procedure described allows for the isolation, storage, and manipulation of these highly reactive isocyanates. A number of derivatives of the above isocyanates were prepared. These include: carbamates, thiocarbamates, ureas, amines, amidines, and amides.     

Synthetic analgesics: preparation of racemic 6,7-benzomorphans

A simple preparation of 2-carbomethoxy-2-azabicyclo[3.3.1]nonan-6-one ($\text{7}$ and its conversion to the racemic benzomorphans: $\text{9}$, $\text{10}$, $\text{14}$ are described.