3M Petrifilm Staph Express Count plate method for the enumeration of Staphylococcus aureus in selected types of meat, seafood, and poultry: collaborative study

The 3M Petrifilm Staph Express Count plate method was compared with AOAC Official Method 975.55 for the enumeration of Staphylococcus aureus in selected foods. Four foods--cooked, diced chicken; cured ham; smoked salmon; and pepperoni--were analyzed for S. aureus by 12 collaborating laboratories. For each food tested, the collaborators received 8 blind test samples consisting of a control sample, a low inoculation level, a medium inoculation level, and a medium inoculation level with background flora, each in duplicate. The mean log10 counts for the methods were comparable for all 4 foods. The repeatability and reproducibility variances of the 24 h Petrifilm Staph Express Count plate method were similar to those of the 72 h standard method.     

New polythiophenes bearing electron-acceptor phthalocyanine chromophores

Two new donor-acceptor copolymers comprising a polythiophene backbone, and bearing phthalocyanine chromophores on the side chains have been prepared. Preliminary photophysical characterization of these materials by FTIR photoinduced absorption indicates that electron transfer from the polythiophene to the phthalocyanine units takes place.     

Inexpensive device for measurements with ion-selective and pH electrodes

The design and construction of a simple device for measuring ionic concentrations (or pH) with ion-selective electrodes are described. The automated system includes a special electronic circuit with an operational amplifier, a signal conditioner and a personalcomputer. A digital multimeter can be used if automation is not required. The results obtained in tests with iodide-, chloride- and nitrate-selective electrodes and glass electrodes show very good agreement with those obtained with sophisticated commercial apparatus.     

Development and validation of an HPLC method for the determination of penicillin antibiotics residues in bovine muscle according to the European Union Decision 2002/657/EC

A high-performance liquid chromatographic method was developed for the determination of five penicillins: penicillin G (PENG), penicillin V (PENV), oxacillin (OX), cloxacillin (CLO), and dicloxacillin (DICLO), in bovine muscle. Samples were macerated with a mixture of H(2)O/CH(3)CN (1:1) and purified using RP-8 Adsorbex SPE cartridges after centrifugation, with mean recovery from spiked samples higher than 89%. The separation of the examined penicillins was achieved on an analytical column, an Inertsil C8 5 microm, 250x4 mm(2), at ambient temperature. The mobile phase consisted of 0.1% TFA/ACN 50:50 v/v delivered isocratically at a flow rate of 1.1 mL/min. Analytes were monitored at 240 nm. The procedure was validated according to the European Union Decision 2002/657/EC by means of selectivity, stability, decision limit, detection capability, accuracy, and precision. Method's LOQ values achieved were 54 microg/kg for PENG and DICLO, 46 microg/kg for PENV, 16 microg/kg for OX, and 43 microg/kg for DICLO. The detection capabilities (CC(beta)) were 73.6 microg/kg for PENG, 29.1 microg/kg for PENV, 350.6 microg/kg for OX, 379.9 microg/kg for CLO, and 355.8 microg/kg for DICLO. The method was applied to various samples from the local market. Two penicillins were identified by photodiode array (PDA) detection and quantified.     

Analysis of ochratoxin A in milk after direct immunoaffinity column clean-up by high-performance liquid chromatography with fluorescence detection

The present work describes a new analytical method for direct immunoaffinity column clean-up of ochratoxin A (OTA) in milk samples followed by determination of the toxin using high-performance liquid chromatography with fluorescence detection (HPLC-FD). Two different immunoaffinity cartridges (IAC) were investigated, and Ochraprep columns were chosen because they showed the best results. An average recovery of 89.8% and a mean RSD of 5.8% for artificially contaminated cow's milk in the range of 5-100 ng/L were attained. The calculated limit of detection (LOD) and limit of quantitation (LOQ) were as low as 0.5 and 5 ng/L, respectively. This new easy and fast method avoids a previous liquid-liquid extraction step and therefore the use of toxic chlorinated solvents. Chromatograms of the final extracts were clean and OTA could be easily detected at a retention time of 8.4 min without interferences. To assess the presence of the toxin in cow's milk eight samples of skimmed and four samples of whole milk were analysed and OTA was not detected over the established detection limit.     

Ionization and fragmentation of neutral and acidic glycosphingolipids with a Q-TOF mass spectrometer fitted with a MALDI ion source

This paper reports the use of a quadrupole time-of-flight (Q-TOF) mass spectrometer fitted with a matrix-assisted laser desorption/ionization (MALDI) ion source for the analysis of neutral and acidic glycosphingolipids. All compounds gave strong [M + Na]+ ions with 2,5-dihydroxybenzoic acid as the matrix, with no loss of sensitivity with increasing mass as was observed from the corresponding ions produced by electrospray. Neutral glycosphingolipids showed negligible in-source fragmentation but sialylated compounds fragmented by loss of sialic acid. However, these losses were not accompanied by unfocused post-source-decay ions as observed with MALDI-reflectron-TOF instruments. The MS/MS spectra were almost identical to those obtained by electrospray. Fragmentation of all compounds was mainly by glycosidic cleavage to give ions, both with and without the ceramide moiety, which defined the carbohydrate chain sequence. Weak ions which defined the sphingosine chain length and abundant ions, produced by loss of the acyl chain, were present when this chain contained a 2-hydroxy group. The technique was applied to the identification of ceramide-trihexosides present in tissues from mice genetically modified to model one of the glycolipid storage diseases (Fabry disease).     

Halogen–Aromatic π Interactions Modulate Inhibitor Residence Times

Prolonged drug residence times may result in longer‐lasting drug efficacy, improved pharmacodynamic properties, and “kinetic selectivity” over off‐targets with high drug dissociation rates. However, few strategies have been elaborated to rationally modulate drug residence time and thereby to integrate this key property into the drug development process. Herein, we show that the interaction between a halogen moiety on an inhibitor and an aromatic residue in the target protein can significantly increase inhibitor residence time. By using the interaction of the serine/threonine kinase haspin with 5‐iodotubercidin (5‐iTU) derivatives as a model for an archetypal active‐state (type I) kinase–inhibitor binding mode, we demonstrate that inhibitor residence times markedly increase with the size and polarizability of the halogen atom. The halogen–aromatic π interactions in the haspin–inhibitor complexes were characterized by means of kinetic, thermodynamic, and structural measurements along with binding‐energy calculations.     

Chiral pool based synthesis of pyrrolidinium ionic liquids

Chiral ionic liquids show promising applications in various different fields. A series of pyrrolidinium-based chiral ionic liquids bearing a chiral cation, a chiral anion or both was prepared in good yields using an efficient, economic and simple pathway. The chirality was introduced using (l)-lactate and (l)-menthol derivatives. The resultant chiral compounds were characterized by both spectroscopy and polarimetry. We envision that these new chiral compounds can serve as effective reaction media and chiral catalysts for asymmetric reactions, which are presently being investigated in our lab.     

The intersection marker method for 3D interface tracking of deformable surfaces in finite volumes

Currently, the majority of computational fluid dynamics (CFD) codes use the finite volume method to spatially discretise the computational domain, sometimes as an array of cubic control volumes. The Finite volume method works well with single‐phase flow simulations, but two‐phase flow simulations are more challenging because of the need to track the surface interface traversing and deforming within the 3D grid. Surface area and volume fraction details of each interface cell must be accurately accounted for, in order to calculate for the momentum exchange and rates of heat and mass transfer across the interface. To attain a higher accuracy in two‐phase flow CFD calculations, the intersection marker (ISM) method is developed. The ISM method is a hybrid Lagrangian–Eulerian front‐tracking algorithm that can model an arbitrary 3D surface within an array of cubic control volumes. The ISM method has a cell‐by‐cell remeshing capability that is volume conservative and is suitable for the tracking of complex interface deformation in transient two‐phase CFD simulations. Copyright © 2015 John Wiley & Sons, Ltd.