Characterization of the O-4 phosphorylated and O-5 substituted Kdo reducing end group and sequencing of the core oligosaccharide of Aeromonas salmonicida ssp salmonicida lipopolysaccharide using tandem mass spectrometry

The molecular structure of the wild strain of the lipopolysaccharide core of Aeromonas salmonicida, ssp salmonicida has been sequenced using tandem mass spectrometry. The core oligosaccharide was determined to contain an O-4 phosphorylated and O-5 substituted Kdo reducing group, and its structure is proposed as the follows: [structure: see text] After the core oligosaccharide of LPS was released from the lipid A portion by conventional treatment with 1% acetic acid, we demonstrated the existence of a homogeneous mixture composed mainly of the native core oligosaccharide containing the Kdo with its O-4 phosphate group intact, and a degraded core oligosaccharide mixture, which eliminated the O-4 phosphate group with extreme facility. The precise molecular structure and glycone sequence of the homogeneous mixture of phosphorylated and dephosphorylated core oligosaccharides was determined by electrospray ionization (ESI) mass spectrometry and tandem mass spectrometric analysis. CID-MS/MS of the homogeneous mixture of permethylated core oligosaccharides afforded a series of diagnostic product ions which confirmed the established sequence of the glycones to be determined. Matrix-assisted laser desorption/ionization (MALDI) tandem mass spectrometry reconfirmed the molecular structure of the dephosphorylated homogeneous permethylated mixture of the core oligosaccharides containing the diastereomeric 4,8- and 4,7-anhydro-alpha-keto acids.     

Characterization and de novo sequencing of snow crab tropomyosin enzymatic peptides by both electrospary ionization and matrix‐assisted laser desorption ionization QqToF tandem mass spectrometry

The protein tropomyosin (TM) is a known major allergen present in shellfish causing frequent food allergies. TM is also an occupational allergen generated in the working environment of snow crab (Chionoecetes opilio) processing plants. The TM protein was purified from both claw and leg meats of snow crab and analyzed by electrospray ionization and matrix‐assisted laser desorption/ionization (MALDI) using hybrid quadruple time‐of‐flight tandem mass spectrometry (QqToF‐MS). The native polypeptide molecular weight of TM was determined to be 32 733 Da. The protein was further characterized using the ‘bottom‐up’ MS approach. A peptide mass fingerprinting was obtained by two different enzymatic digestions and de novo sequencing of the most abundant peptides performed. Any post‐translational modifications were identified by searching their calculated and predicted molecular weights in precursor ion spectra. The immunological reactivity of snow crab extract was evaluated using specific antibodies and allergenic reactivity assessed with serum of allergic patients. Subsequently, a signature peptide for TM was identified and evaluated in terms of identity and homology using the basic local alignment search tool (BLAST). The identification of a signature peptide for the allergen TM using MALDI‐QqToF‐MS will be critical for the sensitive and specific quantification of this highly allergenic protein in the work place. Copyright © 2010 John Wiley & Sons, Ltd.     

Control of the oscillator strength of the exciton in a single InGaN-GaN quantum dot

We report direct evidence for the control of the oscillator strength of the exciton state in a single quantum dot by the application of a vertical electric field. This is achieved through the study of the radiative lifetime of a single InGaN-GaN quantum dot in a p-i-n diode structure. Our results are in good quantitative agreement with theoretical predictions from an atomistic tight-binding model. Furthermore, the increase of the overlap between the electron and hole wave functions due to the applied field is shown experimentally to increase the attractive Coulomb interaction leading to a change in the sign of the biexcitonic binding energy.     

Instabilités de l'écoulement produisant le bruit de fenteFlow instabilities producing the slot-tone

The nature of the instability governing the self-sustained tones produced by a low Mach number plane jet impinging on a slotted plate, known as slot-tone, is identified experimentally. For a given Reynolds number, the natural shear-layer and the jet column mode frequencies of the free jet delimit the values of the measured slot-tone operating frequencies. The oscillations at lower frequencies are the result of the amplification of the jet column mode, and those at higher frequencies correspond to the shear layer instabilities. To cite this article: A. Billon et al., C. R. Mecanique 332 (2004).     

Tandem mass spectrometric analysis of novel diquaternary ammonium gemini surfactants and their bromide adducts in electrospray-positive ion mode ionization

Gemini surfactants are cationic lipids which are utilized for both in vitro and in vivo gene delivery. Structurally, they are comprised of two hydrophobic tail regions with polar head termini that are attached to one another through a spacer region. Structural elucidation and characterization of 29 novel diquaternary ammonium gemini surfactant molecules were achieved using a quadrupole time-of-flight mass spectrometer (QqToF-MS) and a quadrupole-hexapole-quadrupole mass spectrometer (QhQ-MS). The tested compounds were categorized into four distinct structural families based upon the composition of the spacer region. Single stage (MS), tandem stage (MS/MS) and quasimulti-stage (quasi MS(3)) mass spectrometric analysis allowed for confirmation of each gemini surfactant's molecular composition and structure through the identification of common and unique product ions. Identification of similarities in the gemini surfactants' fragmentation behaviour resulted in the production of a universal fragmentation pathway that can assist in the future MS/MS analysis of novel quaternary ammonium gemini surfactants, with unique product ions being indicative of specific structural elements. Furthermore, evidence for the association of agemini surfactant with bromine counter ion was confirmed during MS analysis of tested gemini surfactants regardless of their chemical composition; previously, evidence for bromine and gemini surfactant association was only observed with compounds bearing short alkyl spacer regions. MS/MS analysis of the bromine adducts was also confirmatory to the molecular structure.Understanding the ionization and fragmentation behaviour of gemini surfactants, including bromine adducts, will allow for future qualitative and quantitative identification of these novel drug delivery agents within biological samples.     

Quantum nature of the sign preference in ion-induced nucleation

Observed first in Wilson's pioneering experiments in the cloud chamber, the sign preference has remained a mystery for more than a century. We investigate the sign preference using a quantum approach and show that this puzzling phenomenon is essentially quantum in nature. It is shown that the effect of the chemical identity of the core ion is controlled by the electronic structure of the core ion through the influence on the intermolecular bonding energies during the initial steps of cluster formation. Our results demonstrate the superiority of the quantum approach and indicate fundamental problems of conventional ion-induced nucleation theories, in which the electronic structure of the core ion is either ignored or not treated rigorously.     

Mass Spectrometry,Review of the Basics: Electrospray,MALDI, and Commonly Used Mass Analyzers

Abstract

Mass spectrometry (MS) has progressed to become a powerful analytical tool for both quantitative and qualitative applications. The first mass spectrometer was constructed in 1912 and since then it has developed from only analyzing small inorganic molecules to biological macromolecules, practically with no mass limitations. Proteomics research, in particular, increasingly depends on MS technologies. The ability of mass spectrometry analyzing proteins and other biological extracts is due to the advances gained through the development of soft ionization techniques such as electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) that can transform biomolecules into ions. ESI can efficiently be interfaced with separation techniques enhancing its role in the life and health sciences. MALDI, however, has the advantage of producing singly charges ions of peptides and proteins, minimizing spectral complexity. Regardless of the ionization source, the sensitivity of a mass spectrometer is related to the mass analyzer where ion separation occurs. Both quadrupole and time of flight (ToF) mass analyzers are commonly used and they can be configured together as QToF tandem mass spectrometric instruments. Tandem mass spectrometry (MS/MS), as the name indicates, is the result of performing two or more sequential separations of ions usually coupling two or more mass analyzers. Coupling a quadrupole and time of flight resulted in the production of high-resolution mass spectrometers (i.e., Q-ToF). This article will historically introduce mass spectrometry and summarizes the advantages and disadvantages of ESI and MALDI along with quadrupole and ToF mass analyzers, including the technical marriage between the two analyzers. This article is educational in nature and intended for graduate students and senior biochemistry students as well as chemists and biochemists who are not familiar with mass spectrometry and would like to learn the basics; it is not intended for mass spectrometry experts.     

Rotating polarizer,compensator, and analyzer ellipsometry

In this paper we propose theoretically a set of ellipsometric configurations using a rotating polarizer, compensator, and analyzer at a speed ratio of N1ω：N2ω：N3ω. Different ellipsometric configurations can be obtained by giving different integral values to N1, N2, and N3. All configurations are applied to bulk c-Si and GaAs to calculate the real and imaginary parts of the refractive index of the samples. The accuracies of all ellipsometric configurations are investigated in the presence of a hypothetical noise and with small misalignments of the optical elements. Moreover, the uncertainties in the ellipsometric parameters as functions of the uncertainties of the Fourier coefficients are studied. The comparison among different configurations reveals that the rotating compensator–analyzer configuration corresponds to the minimum error in the calculated optical parameters.     

Photonic Patterns Printed in Chiral Nematic Mesoporous Resins

Chiral nematic mesoporous phenol‐formaldehyde resins, which were prepared using cellulose nanocrystals as a template, can be used as a substrate to produce latent photonic images. These resins undergo swelling, which changes their reflected color. By writing on the films with chemical inks, the density of methylol groups in the resin changes, subsequently affecting their degree of swelling and, consequently, their color. Writing on the films gives latent images that are revealed only upon swelling of the films. Using inkjet printing, it is possible to make higher resolution photonic patterns both as text and images that can be visualized by swelling and erased by drying. This novel approach to printing photonic patterns in resin films may be applied to anti‐counterfeit tags, signage, and decorative applications.     

Iodine assisted palladium catalyzed ring opening of bicyclic hydrazines with organoboronic acids: stereoselective synthesis of functionalized cyclopentenes and alkylidene cyclopentenes

A novel reactivity of organoboronic acids with bicyclic hydrazines leading to the stereoselective formation of trans-vicinal disubstituted cyclopentenes in good to excellent yield is discussed. The reaction of cyclopentadiene and fulvene derived azabicyclic alkenes with organoboronic acids afforded the trans-3,4-disubstituted cyclopentenes and alkylidene cyclopentenes in good to excellent yields. The products, having a broad range of substituents, are important intermediates in the synthesis of a number of pharmaceutically important molecules.