Structural trends of 29Si–1H spin–spin coupling constants across double bond

The calculations of geminal and vicinal ²⁹Si–¹H spin–spin coupling constants across double bond in 15 alkenylmethylsilanes and alkenylchlorosilanes were carried out at the second‐order polarization propagator approach level in a good agreement with experiment. Two structural trends, namely, (i) the geometry of the coupling pathway and (ii) the effect of the electrowithdrawing substituent, have been interpreted in terms of the natural J‐coupling analysis within the framework of the natural bond orbital approach. Thus, the marked difference between cisoidal and transoidal ²⁹Si–¹H spin–spin coupling constants across double bond was accounted for the delocalization contributions including bonding and antibonding Si–C and C–H orbitals, whereas the chlorine effect was explained in terms of the steric contributions including bonding Si–Cl orbitals. Copyright © 2012 John Wiley & Sons, Ltd.     

The development and optimization of a modified single-drop microextraction method for organochlorine pesticides determination by gas chromatography-tandem mass spectrometry

We have developed a new method for single-drop microextraction (SDME) for the preconcentration of organochlorine pesticides (OCP) from complex matrices. It is based on the use of a silicone ring at the tip of the syringe. A 5 μL drop of n-hexane is applied to an aqueous extract containing the OCP and found to be adequate to preconcentrate the OCPs prior to analysis by GC in combination with tandem mass spectrometry. Fourteen OCP were determined using this technique in combination with programmable temperature vaporization. It is shown to have many advantages over traditional split/splitless injection. The effects of kind of organic solvent, exposure time, agitation and organic drop volume were optimized. Relative recoveries range from 59 to 117 %, with repeatabilities of <15 % (coefficient of variation) were achieved. The limits of detection range from 0.002 to 0.150 μg kg^?1. The method was applied to the preconcentration of OCPs in fresh strawberry, strawberry jam, and soil.

A new approach to the statistical treatment of 2D-maps in proteomics using fuzzy logic

A new approach to the statistical treatment of 2D-maps has been developed. This method is based on the use of fuzzy logic and allows to take into consideration the typical low reproducibility of 2D-maps. In this approach the signal corresponding to the presence of proteins on the 2D-maps is substituted with probability functions, centred on the signal itself. The standard deviation of the bidimensional gaussian probability function employed to blur the signal allows to assign different uncertainties to the two electrophoretic dimensions. The effect of changing the standard deviation and the digitalisation resolution are investigated.     

Multiplexed Determination of Amino‐Terminal Pro‐B‐Type Natriuretic Peptide and C‐Reactive Protein Cardiac Biomarkers in Human Serum at a Disposable Electrochemical Magnetoimmunosensor

A rapid magnetoimmunosensor for the simultaneous determination of two cardiac biomarkers, amino‐terminal pro‐B‐type natriuretic peptide (NT‐proBNP) and C‐reactive protein (CRP), in human serum is described. Specific capture antibodies were covalently immobilized onto carboxylic acid‐modified magnetic beads. The quantification of NT‐proBNP and CRP was performed by using indirect competitive and sandwich configurations, respectively, and horseradish peroxidase‐labeled tracers. The use of dual screen‐printed carbon electrodes allowed the achievement of simultaneous independent amperometric readout for each cardiac biomarker. The developed methodology showed very low limits of detection (0.47 ng mL^?1). An international standard for CRP serum spiked with NT‐proBNP was analyzed to evaluate the usefulness of the magnetoimmunosensor.     

Reversible Mechanical Switching of Magnetic Interactions in a Molecular Shuttle

An acid–base switchable molecular shuttle based on a [2]rotaxane, incorporating stable radical units in both the ring and dumbbell components, is reported. The [2]rotaxane comprises a dibenzo[24]crown-8 ring (DB24C8) interlocked with a dumbbell component that possesses a dialkylammonium (NH₂⁺) and a 4,4′-bipyridinium (BPY²⁺) recognition site. Deprotonation of the rotaxane NH₂⁺ centers effects a quantitative displacement of the DB24C8 macroring to the BPY²⁺ recognition site, a process that can be reversed by acid treatment. Interaction between stable 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radicals connected to the ring and dumbbell components could be switched between noncoupled (three-line electron paramagnetic resonance (EPR) spectrum) and coupled (five-line EPR spectrum) upon displacement of the spin-labelled DB24C8 macroring. The complete base- and acid-induced switching cycle of the EPR pattern was repeated six times without an appreciable loss of signal, highlighting the reversibility of the process. Hence, this molecular machine is capable of switching on/off magnetic interactions by chemically driven reversible mechanical effects. A system of this kind represents an initial step towards a new generation of nanoscale magnetic switches that may be of interest for a variety of applications.     

Direct drug analysis from oral fluid using medical swab touch spray mass spectrometry

Fourteen common drugs of abuse were identified in spiked oral fluid (ng mL⁻¹ levels), analyzed directly from medical swabs using touch spray mass spectrometry (TS-MS), exemplifying a rapid test for drug detection. Multiple stages of mass analysis (MS² and MS³) provided identification and detection limits sought by international forensic and toxicological societies, Δ⁹-THC and buprenorphine excluded. The measurements were made using a medical swab as both the sampling probe and means of ionization. The adaptation of medical swabs for TS-MS analysis allows non-invasive and direct sampling of neat oral fluid. Data acquisition was rapid, seconds per drug, and MS³ ensured reliable identification of illicit drugs. The reported data were acquired to investigate (i) ionization of common drugs from commercial swabs, (ii) ion intensity over spray duration, and (iii) dynamic range, all as initial steps in development of a quantitative method. The approach outlined is intended for point-of-care drug testing using oral fluid in clinical applications as well as in situ settings, viz. in forensic applications. The proof-of-concept results presented will require extension to other controlled substances and refinement in analytical procedures to meet clinical/legal requirements.     

Emission of volatile sesquiterpenes and monoterpenes in grapevine genotypes following Plasmopara viticola inoculation in vitro

The grapevine (Vitis vinifera) is one of the most widely cultivated fruit crops globally, and one of its most important diseases in terms of economic losses is downy mildew, caused by Plasmopara viticola. Several wild Vitis species have been found to be resistant to this pathogen and have been used in breeding programs to introduce resistance traits to susceptible cultivars. Plant defense is based on different mechanisms, and volatile organic compounds (VOCs) play a major role in the response to insects and pathogens. Although grapevine resistance mechanisms and the production of secondary metabolites have been widely characterized in resistant genotypes, the emission of VOCs has not yet been investigated following P. viticola inoculation. A Proton Transfer Reaction‐Time of Flight‐Mass Spectrometer (PTR‐ToF‐MS) was used to analyze the VOCs emitted by in vitro‐grown plants of grapevine genotypes with different levels of resistance. Downy mildew inoculation significantly increased the emission of monoterpenes and sesquiterpenes by the resistant SO4 and Kober 5BB genotypes, but not by the susceptible V. vinifera Pinot noir. Volatile terpenes were implicated in plant defense responses against pathogens, suggesting that they could play a major role in the resistance against downy mildew by direct toxicity or by inducing grapevine resistance. The grapevine genotypes differed in terms of the VOC emission pattern of both inoculated and uninoculated plants, indicating that PTR‐ToF‐MS could be used to screen hybrids with different levels of downy mildew resistance. Copyright © 2015 John Wiley & Sons, Ltd.     

Competitive Gold‐Promoted Meyer–Schuster and oxy‐Cope Rearrangements of 3‐Acyloxy‐1,5‐enynes: Selective Catalysis for the Synthesis of (+)‐(S)‐γ‐Ionone and (−)‐(2S,6 R)‐cis‐γ‐Irone

We report a simple, highly stereoselective synthesis of (+)‐(S)‐γ‐ionone and (‐)‐(2S,6R)‐cis‐γ‐irone, two characteristic and precious odorants; the latter compound is a constituent of the essential oil obtained from iris rhizomes. Of general interest in this approach are the photoisomerization of an endo trisubstituted cyclohexene double bond to an exo vinyl group and the installation of the enone side chain through a [(NHC)Au^I]‐catalyzed Meyer–Schuster‐like rearrangement. This required a careful investigation of the mechanism of the gold‐catalyzed reaction and a judicious selection of reaction conditions. In fact, it was found that the Meyer–Schuster reaction may compete with the oxy‐Cope rearrangement. Gold‐based catalytic systems can promote either reaction selectively. In the present system, the mononuclear gold complex [Au(IPr)Cl], in combination with the silver salt AgSbF₆ in 100:1 butan‐2‐one/H₂O, proved to efficiently promote the Meyer–Schuster rearrangement of propargylic benzoates, whereas the digold catalyst [{Au(IPr)}₂(μ‐OH)][BF₄] in anhydrous dichloromethane selectively promoted the oxy‐Cope rearrangement of propargylic alcohols.