Discriminant analysis in the presence of interferences: Combined application of target factor analysis and a Bayesian soft-classifier

A method is described for performing discriminant analysis in the presence of interfering background signal. The method is based on performing target factor analysis on a data set comprised of contributions from analyte(s) and interfering components. A library of data from representative analyte classes is tested for possible contributing factors by performing oblique rotations of the principal factors to obtain the best match, in a least-squares sense, between test and predicted vectors. The degree of match between the test and predicted vectors is measured by the Pearson correlation coefficient, r, and the distribution of r for each class is determined. A Bayesian soft classifier is used to calculate the posterior probability based on the distributions of r for each class, which assist the analyst in assessing the presence of one or more analytes. The method is demonstrated by analyses performed on spectra obtained by laser induced breakdown spectroscopy (LIBS). Single and multiple bullet jacketing transfers to steel and porcelain substrates were analyzed to identify the jacketing materials. Additionally, the metal surrounding bullet holes was analyzed to identify the class of bullet jacketing that passed through a stainless steel plate. Of 36 single sample transfers, the copper jacketed (CJ) and non-jacketed (NJ) class on porcelain had an average posterior probability of the metal deposited on the substrate of 1.0. Metal jacketed (MJ) bullet transfers to steel and porcelain were not detected as successfully. Multiple transfers of CJ/NJ and CJ/MJ on the two substrates resulted in posterior probabilities that reflected the presence of both jacketing materials. The MJ/NJ transfers gave posterior probabilities that reflected the presence of the NJ material, but the MJ component was mistaken for CJ on steel, while non-zero probabilities were obtained for both CJ and MJ on porcelain. Jacketing transfer from a bullet to steel as the projectile passed through the steel also proved difficult to analyze. Over 50% of the samples left insufficient transfer to be identified. Transfer from NJ and CJ jacketing was successfully identified by posterior probabilities greater than 0.8.     

Probing the functional limits of the norepinephrine transporter with self-reporting, fluorescent stilbazolium dimers

A series of stilbazolium dimers were synthesized and investigated as sterically demanding ligands targeting the norepinephrine transporter (NET). The environmentally sensitive fluorescence of the dyes enables their use as self-reporting ligands; binding to and displacement from NET can be monitored by fluorescence microscopy.     

Spectral line parameters including temperature dependences of self- and air-broadening in the 2←0 band of CO at 2.3 μm

Temperature dependences of pressure-broadened half-width and pressure-induced shift coefficients along with accurate positions and intensities have been determined for transitions in the 2←0 band of ¹²C¹⁶O from analyzing high-resolution and high signal-to-noise spectra recorded with two different Fourier transform spectrometers. A total of 28 spectra, 16 self-broadened and 12 air-broadened, recorded using high-purity (≥99.5% ¹²C-enriched) CO samples and CO diluted with dry air (research grade) at different temperatures and pressures, were analyzed simultaneously to maximize the accuracy of the retrieved parameters. The sample temperatures ranged from 150 to 298 K and the total pressures varied between 5 and 700 Torr. A multispectrum nonlinear least squares spectrum fitting technique was used to adjust the rovibrational constants (G, B, D, etc.) and intensity parameters (including Herman–Wallis coefficients), rather than determining individual line positions and intensities. Self- and air-broadened Lorentz half-width coefficients, their temperature dependence exponents, self- and air-pressure-induced shift coefficients, their temperature dependences, self- and air- line mixing coefficients, their temperature dependences and speed dependence have been retrieved from the analysis. Speed-dependent line shapes with line mixing employing off-diagonal relaxation matrix element formalism were needed to minimize the fit residuals. This study presents a precise and complete set of spectral line parameters that consistently reproduce the spectrum of carbon monoxide over terrestrial atmospheric conditions.     

Identification of Acepromazine and Its Metabolites in Horse Plasma and Urine by LC–MS/MS and Accurate Mass Measurement

Acepromazine maleate (Sedalin^?) was administered orally to six thoroughbred horses at a dose of 0.15?mg?kg^?1. Urine and blood samples were collected up to 412?h post-administration. Plasma and urine were hydrolysed; plasma samples were then processed using liquid–liquid extraction and urine samples using solid-phase extraction. A sensitive tandem mass spectrometric method was developed in this study, achieving a lower limit of quantification for acepromazine of 10?pg?mL^?1 in plasma and 100?pg?mL^?1 in urine. Acepromazine, hydroxyethylpromazine, hydroxyacepromazine, hydroxyethylpromazine sulphoxide, hydroxyethylhydroxypromazine, dihydroxyacepromazine and dihydroxyhydroxyethylpromazine were detected in the post-administration samples. The parent drug and its metabolites were identified using a combination of UPLC–MS/MS and accurate mass measurement. Separation of the structural isomers hydroxyethylpromazine sulphoxide and hydroxyethylhydroxypromazine was another significant outcome of this work and demonstrated the advantages to be gained from investing in chromatographic method development.     

Molybdenum(VI) complexes of a 2,2'-biphenyl-bridged bis(amidophenoxide): competition between metal-ligand and metal-amidophenoxide π bonding

The 2,2'-biphenyl-bridged bis(2-aminophenol) ligand 4,4'-di-tert-butyl-N,N'-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-2,2'-diaminobiphenyl ((t)BuClipH(4)) reacts with MoO(2)(acac)(2) to form ((t)BuClipH(2))MoO(2), where the diarylamines remain protonated and bind trans to the terminal oxo groups. This complex readily loses water on treatment with pyridine or 3,5-lutidine to form mono-oxo complexes ((t)BuClip)MoO(L), which exhibit predominantly a cis-β geometry with an aryloxide trans to the oxo group. Exchange of the pyridine ligands is rapid and takes place by a dissociative mechanism, which occurs with retention of stereochemistry at molybdenum. Oxo-free alkoxide complexes ((t)BuClip)Mo(OR)(2) are formed from ((t)BuClipH(2))MoO(2) and ROH. Treatment of NMo(O(t)Bu)(3) with (t)BuClipH(4) results in complete deprotonation of the bis(aminophenol) and formation of a dimolybdenum complex ((t)BuClip)Mo(μ-N)(μ-NH(2))Mo((t)BuClip) containing both a bridging nitride (Mo-N = 1.848 ?, Mo-N-Mo = 109.49°) and a bridging amide group. The strong π bonding of this bis(amidophenoxide) ligand allows the molybdenum center to interconvert readily among species forming three, two, one, or zero π bonds from multiply bonded ligands.     

Cu(II)-promoted methanolysis of N,N-dipicolylacetamide. multistep activation by decoupling of > ̈̈N-C═O resonance via Cu(II)-N binding, delivery of the Cu(II):((-)OCH3) nucleophile, and metal ion assistance of the departure of the leaving group

The methanolysis of the Cu(II) complex of N-acetyl-N,N-bis(2-picolyl)amine (2) was investigated by a kinetic study as a function of pH in methanol at 25 °C and computationally by DFT calculations. The active species is the basic form of the complex (3(-)), or (1:Cu(II))((-)OCH(3))(HOCH(3))), and the rate constant for its solvolysis is k(max) = 1.5 × 10(-4) s(-1). The mechanism involves Cu(II) binding to the amide N lone pair, decoupling it from >N-C═O resonance, concomitant with Cu(II):((-)OCH(3)) delivery to the adjacent >N-C═O unit, followed by Cu(II)-assisted departure of the N,N-bis(2-picolyl)amide from a tetrahedral intermediate.     

Systems biology and systems chemistry: new directions for drug discovery

Improvements in drug design have historically been centered around structure-based optimization of molecule specificity for a targeted protein, in an effort to reduce unintentional binding to other proteins and off-target effects. Although the "one-to-one" drug design strategy has been successful in impairing function of targets associated with a number of diseases, recent reports of drug promiscuity, which are a potential source of adverse reactions in patients, make a case to refine the drug design strategy such that it includes an awareness of multiple interactions from both ligand and protein perspectives. Polypharmacology and chemical biology studies are amassing interaction data at rapid rates, and the integration of such data into an interpretable model requires zooming our perspective out from the single ligand-target level to the larger network-wide level. We review some of the recent developments in systems-level research for drug design and discovery, and discuss the directions that some drug design efforts are heading toward.     

Pulsed hydrogen/deuterium exchange mass spectrometry for time‐resolved membrane protein folding studies

Kinetic folding experiments by pulsed hydrogen/deuterium exchange (HDX) mass spectrometry (MS) are a well‐established tool for water‐soluble proteins. To the best of our knowledge, the current study is the first that applies this approach to an integral membrane protein. The native state of bacteriorhodopsin (BR) comprises seven transmembrane helices and a covalently bound retinal cofactor. BR exposure to sodium dodecyl sulfate (SDS) induces partial unfolding and retinal loss. We employ a custom‐built three‐stage mixing device for pulsed‐HDX/MS investigations of BR refolding. The reaction is triggered by mixing SDS‐denatured protein with bicelles. After a variable folding time (10 ms to 24 h), the protein is exposed to excess D₂O buffer under rapid exchange conditions. The HDX pulse is terminated by acid quenching after 24 ms. Subsequent off‐line analysis is performed by size exclusion chromatography and electrospray MS. These measurements yield the number of protected backbone N–H sites as a function of folding time, reflecting the recovery of secondary structure. Our results indicate that much of the BR secondary structure is formed quite late during the reaction, on a time scale of 10 s and beyond. It is hoped that in the future it will be possible to extend the pulsed‐HDX/MS approach employed here to membrane proteins other than BR. Copyright © 2012 John Wiley & Sons, Ltd.