Search results for "desorption"
showing 10 items of 340 documents
Characterization of heat-labile toxin-subunit B from Escherichia coli by liquid chromatography-electrospray ionization-mass spectrometry and matrix-a…
2012
The possibilities of characterizing the heat-labile enterotoxin (LT) of enterotoxigenic Escherichia coli (ETEC) by liquid chromatography electrospray mass spectrometry (LC/ESI-MS) and matrix-assisted laser desorption with time-of-flight mass spectrometry (MALDI-TOF-MS) were investigated. The B subunit from recombinant E. coli (expression in Pichia pastoris) can be detected by LC/ESI-MS expressed in P. pastoris and the charge envelope signals can be observed; LC/ESI-MS and MALDI-TOF-MS analysis allowed the acquisition of labile toxin subunit B (LTB) molecular weight and preliminary structural characterization of LTB toxin. MALDI-TOF analysis after reduction and alkylation of the protein evid…
Mass spectrometric studies of benzoxazine resorcarenes
2002
Eleven differently substituted 3,4-dihydro-2H-1,3-benzoxazine resorcarenes were studied by electrospray ionisation (ESI) and matrix-assisted laser desorption/ionisation (MALDI) mass spectrometry, using Fourier transform ion cyclotron resonance (FT-ICR) and time-of-flight (TOF) mass spectrometers, respectively. Under ESI conditions it was possible to transfer the intact resorcarenes from solution to the gas phase, yielding [M + H]+ and [M + 2H]+ ions as the main ions observed. Energy increase of the ions induced ready decomposition through successive eliminations of four CH2NR groups. Ion-molecule reactions showed that the ionising proton was situated somewhere inside the molecule and could …
Structural analysis of the O-specific polysaccharide isolated from Plesiomonas shigelloides O51 lipopolysaccharide.
2009
Plesiomonasshigelloides strain CNCTC 110/92 (O51) was identified as a new example of plesiomonads synthesising lipopolysaccharides (LPSs) that show preference for a non-aqueous surrounding during phenol/water extraction. Chemical analyses combined with (1)H and (13)C NMR spectroscopy, MALDI-TOF and ESI mass spectrometry showed that the repeating units of the O-specific polysaccharides isolated from phenol and water phase LPSs of P. shigelloides O51 have the same structure: -->4)-beta-D-GlcpNAc3NRA-(1-->4)-alpha-L-FucpAm3OAc-(1-->3)-alpha-D-QuipNAc-(1-->, containing the rare sugar constituent 2,3-diamino-2,3-dideoxyglucuronic acid (GlcpNAc3NRA), and substituents such as D-3-hydroxybutyric ac…
Structural analysis of the lipid A isolated from Hafnia alvei 32 and PCM 1192 lipopolysaccharides[S]
2010
Hafnia alvei, a Gram-negative bacterium, is an opportunistic pathogen associated with mixed hospital infections, bacteremia, septicemia, and respiratory diseases. The majority of clinical symptoms of diseases caused by this bacterium have a lipopolysaccharide (LPS, endotoxin)-related origin. The lipid A structure affects the biological activity of endotoxins predominantly. Thus, the structure of H. alvei lipid A was analyzed for the first time. The major form, asymmetrically hexa-acylated lipid A built of beta-D-GlcpN4P-(1-->6)-alpha-D-GlcpN1P substituted with (R)-14:0(3-OH) at N-2 and O-3, 14:0(3-(R)-O-12:0) at N-2', and 14:0(3-(R)-O-14:0) at O-3', was identified by ESI-MS(n) and MALDI-tim…
Comparative optical reflection and mass spectrometry analysis of thermodesorption of Langmuir-Blodgett films
1992
Abstract Thermodesorption of cadmium arachidate multilayers is studied by optical surface analysis and by mass spectrometry measurements. The optical reflection technique has been improved to discriminate signal contributions from desorption and light scattering. The scattering arises from film heterogeneities that are also observed by Nomarsky microscopy. The assessment of these heterogeneities is important to understand mass spectrometry data. Both the optical technique and mass spectrometry are sensitive to observing the multilayer phase transition at 110 °C and the desorption near 200 °C (at the heating rate applied). The mass spectrometry analysis yields detailed information on the des…
On the Adsorption Process in Polymer Brushes: A Monte Carlo Study
1996
The adsorption process of the single polymer chain in a polymer brush of varying surface coverages is studied by means of Monte Carlo simulations of the bond-fluctuation lattice model. Only the end monomers can adsorb at the grafting surface, whereas inner monomers interact repulsively with it. The brush builds up a steric hindrance which forces the penetrating polymer to stretch strongly and which is responsible for small adsorption probabilities at surface coverages close to the overlap density. The final step of the adsorption process is determined by a fluctuation of the end monomer around its average position, which is comparable to the initial step of the desorption process.
The influence of the “hot”-dimer adsorption mechanism on the kinetics of a monomer-dimer surface reaction
1993
“Hot” dimers are molecules which after adsorption dissociate and each of the remaining “hot” monomers fly apart up to a maximum distance R from the original adsorption site. The influence of the “hot”-dimer adsorption mechanism on relevant aspects of the bimolecular catalyzed reaction of the type A − (1/2)B2(“hot”) → AB is studied by means of the Monte-Carlo simulation technique. The temporal evolution of both the reactant's coverages as well as the rate of AB-production is evaluated and discussed. Due to the enhanced probability of “hot” species for encounters with other adsorbed particles, the rate of AB-production becomes faster when increasing R. This behavior may be relevant in the dyn…
Photodimers of cinnamic acid and related compounds. A stereochemical study by electron-impact and field desorption mass spectrometry
1974
The low energy (13 eV) electron-impact and field desorption mass spectra of some photodimers of cinnamic acid and related compounds containing the cyclobutane ring are reported and the fragmentation patterns analysed in order to obtain stereochemical information on the substituent position on the cyclobutane ring. Both symmetrical and asymmetrical splittings of the cyclobutane ring were detected, allowing characterisation of the head-to-head and head-to-tail structures of the title compounds. A ring opening rearrangement of the McLafferty type was also found.
Mechanical desorption of a single chain: unusual aspects of phase coexistence at a first-order transition.
2012
The phase transition occurring when a single polymer chain adsorbed at a planar solid surface is mechanically desorbed is analyzed in two statistical ensembles. In the force ensemble, a constant force applied to the nongrafted end of the chain (that is grafted at its other end) is used as a given external control variable. In the $z$-ensemble, the displacement $z$ of this nongrafted end from the surface is taken as the externally controlled variable. Basic thermodynamic parameters, such as the adsorption energy, exhibit a very different behavior as a function of these control parameters. In the thermodynamic limit of infinite chain length the desorption transition with the force as a contro…
On dewetting dynamics of solid films of hydrogen isotopes and its influence on tritium [Beta] spectroscopy
2000
The dewetting dynamics of solid films of hydrogen isotopes, quench-condensed on a graphite substrate, was measured at various temperatures below desorption by observing the stray light from the film. A schematic model describing the dewetting process by surface diffusion is presented, which agrees qualitatively with our data. The activation energies of different hydrogen isotopes for surface diffusion were determined. The time constant for dewetting of a quench-condensed T2 film at the working temperature of 1.86 K of the mainz neutrino mass experiment was extrapolated.