Home About us Contact
|
Home About us Contact | ||
|
|
||
Matrix-assisted Laser Desorption/ionization Time-of-flight (matrix-assisted + laser_ionization_time-of-flight)
Terms modified by Matrix-assisted Laser Desorption/ionization Time-of-flight Selected AbstractsStudy of human neutrophil peptides in saliva by matrix-assisted laser desorption/ionization time-of-flight mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2009Ming-Hui Yang Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry is used to rapidly characterize the human neutrophil peptides , HNP 1, 2, and 3 , in saliva. The saliva excreted from the parotid and sublingual/submandibular glands of 70 individuals were collected and examined using MALDI-TOF. The MALDI approach requires no sample pretreatment other than mixing the saliva-absorbing material with the matrix and drying under ambient conditions. Tissue paper was the best material for collecting the saliva samples because of its strong texture and high absorbance, and sinapinic acid was the best MALDI matrix for the analysis of the HNPs. HNPs were detected in almost all the samples collected from the parotid glands, with no obvious differences among age or gender. In contrast, the distribution of the HNPs in the samples collected from the sublingual/submandibular glands was age-dependent: no HNPs were detected for those collected from individuals younger than 30, but the HNPs were present in all of the samples collected from those older than 60 years. The increased probability of detecting saliva HNPs with age suggests that HNPs may function as a biomarker for aging. Copyright © 2009 John Wiley & Sons, Ltd. [source] Peptide products of the afp-6 gene of the nematode Ascaris suum have different biological actionsTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 5 2007Joanne Y. Yew Abstract Matrix-assisted laser desorption/ionization time-of-flight and tandem time-of-flight (MALDI-TOF and MALDI-TOF/TOF) mass spectrometry were used to sequence and localize three novel, related neuropeptides in the nervous system of the nematode Ascaris suum, AMRNALVRFamide (AF21), NGAPQPFVRFamide (AF22), and SGMRNALVRFamide (AF23). The amino acid sequences were used to clone a novel neuropeptide gene (afp-6) that encodes a precursor bearing a single copy of each of the peptides. In situ hybridization and immunocytochemistry revealed that both the transcript and the peptides are expressed in a single cell in the ventral ganglion. Pharmacological studies of intact nematodes injected with these peptides, as well as physiological studies of responses to them in muscle tissue, motor neurons, and the pharynx, reveal that these peptides have potent bioactivity in the locomotory and feeding systems. Further exploration of their effects may contribute to our understanding of neuropeptide modulation of behavior and also to the development of compounds with anthelmintic relevance. J. Comp. Neurol. 502:872,882, 2007. © 2007 Wiley-Liss, Inc. [source] Characterization of covalently inhibited extracellular lipase from Streptomyces rimosus by matrix-assisted laser desorption/ionization time-of-flight and matrix-assisted laser desorption/ionization quadrupole ion trap reflectron time-of-flight mass spectrometry: localization of the active site serine,JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 12 2004Martin Zehl Abstract A chemical modification approach combined with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry was used to identify the active site serine residue of an extracellular lipase from Streptomyces rimosus R6-554W. The lipase, purified from a high-level overexpressing strain, was covalently modified by incubation with 3,4-dichloroisocoumarin, a general mechanism-based serine protease inhibitor. MALDI time-of-flight (TOF) mass spectrometry was used to probe the nature of the intact inhibitor-modified lipase and to clarify the mechanism of lipase inhibition by 3,4-dichloroisocoumarin. The stoichiometry of the inhibition reaction revealed that specifically one molecule of inhibitor was bound to the lipase. The MALDI matrix 2,6-dihydroxyacetophenone facilitated the formation of highly abundant [M + 2H]2+ ions with good resolution compared to other matrices in a linear TOF instrument. This allowed the detection of two different inhibitor-modified lipase species. Exact localization of the modified amino acid residue was accomplished by tryptic digestion followed by low-energy collision-induced dissociation peptide sequencing of the detected 2-(carboxychloromethyl)benzoylated peptide by means of a MALDI quadrupole ion trap reflectron TOF instrument. The high sequence coverage obtained by this approach allowed the confirmation of the site specificity of the inhibition reaction and the unambiguous identification of the serine at position 10 as the nucleophilic amino acid residue in the active site of the enzyme. This result is in agreement with the previously obtained data from multiple sequence alignment of S. rimosus lipase with different esterases, which indicated that this enzyme exhibits a characteristic Gly-Asp-Ser-(Leu) motif located close to the N-terminus and is harboring the catalytically active serine residue. Therefore, this study experimentally proves the classification of the S. rimosus lipase as GDS(L) lipolytic enzyme. Copyright © 2004 John Wiley & Sons, Ltd. [source] Cyclic poly(pyridine ether)s by the polycondensation of 2,6-difluoropyridine with various diphenolsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2005Hans R. Kricheldorf Abstract The bistrimethylsilyl derivatives of six different diphenols were polycondensed with 2,6-difluoropyridine in N -methylpyrrolidone in the presence of K2CO3. On the basis of previous studies, the reaction conditions were optimized for almost quantitative conversions. The feed ratio was systematically varied to optimize the molecular weight. A 2 mol % excess of 2,6-difluoropyridine was needed to obtain maximum molecular weights. In the matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectra of the optimized polyethers, only cycles were found (detectable up to 5000 Da). Obviously, the relatively low molecular weights obtained under optimized conditions resulted from a limitation of the chain growth by cyclization, indicating a high cyclization tendency for poly(pyridine ether)s. The size exclusion chromatography measurements not only proved low molecular weights but also demonstrated the existence of bimodal mass distributions and high polydispersities. Protonation of the poly(pyridine ether)s required strong acids such as methane or trifluoromethane sulfonic acid. The solubilities of the neutral and protonated polyethers derived from bisphenol A were studied in various solvents. The MALDI-TOF mass spectra proved that protonation at 20,25 °C did not cause cleavage of ether bonds. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4781,4789, 2005 [source] Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry study on copolymers obtained by the alternating copolymerization of bis(,-lactone) and epoxide with potassium tert -butoxideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2005Chenxi Zhang Abstract Oligomer samples obtained by the anionic copolymerization of a bis(,-lactone), 2,8-dioxa-1-methylbicyclo[3.3.0]octane-3,7-dione (1), and glycidyl phenyl ether with potassium tert -butoxide have been analyzed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The MALDI-TOF mass spectra of these cooligomers show well-resolved signals that can be reliably assigned to linear, alternating cooligomers that have carboxylate chain ends or alkoxide chain ends and cyclic ones. The formation of these three series of cooligomers suggests that the polymerization process involves concomitant intermolecular transesterification and intramolecular back-biting. The intramolecular back-biting reaction causes the formation of cyclic cooligomers, whereas the intermolecular transesterification causes the reduction of the molecular weight and the transformation of the alkoxide active chain end into a carboxylate chain end. The MALDI-TOF mass spectrometry study has shown that an excess of monomer 1 enhances the selectivity of propagation by increasing the probability of the attack of the alkoxide chain end to 1. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2643,2649, 2005 [source] Mixed iridium(III) and ruthenium(II) polypyridyl complexes containing poly(,-caprolactone)-bipyridine macroligandsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2004Veronica Marin Abstract A hydroxy-functionalized bipyridine ligand was polymerized with ,-caprolactone utilizing the controlled ring-opening polymerization of ,-caprolactone in the presence of stannous octoate. The resulting poly(,-caprolactone)-containing bipyridine was characterized by 1H NMR and IR spectroscopy, and gel permeation chromatography, as well as matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, revealing the successful incorporation of the bipyridine ligand into the polymer chain. Coordination to iridium(III) and ruthenium(II) precursor complexes yielded two macroligand complexes, which were characterized by NMR, gel permeation chromatography, matrix-assisted laser desorption/ionization time-of-flight MS, cyclic voltammetry, and differential scanning calorimetry. In addition, both photophysical and electrochemical properties of the metal-containing polymers proved the formation of a trisruthenium(II) and a trisiridium(III) polypyridyl species, respectively. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4153,4160, 2004 [source] Characterization by mass spectrometry of an unknown polysiloxane sample used under uncontrolled medical conditions for cosmetic surgeryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 21 2008Cédric Schneider For a complete understanding of the raw material used for cosmetic surgery under uncontrolled medical conditions, an unknown sample of polydimethylsiloxanes has been investigated utilizing a combination of analytical techniques: pyrolysis/gas chromatography/mass spectrometry (Py/GC/MS), electrospray ionization (ESI)-MS, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF)MS, and liquid chromatography (LC)/MS. Among these techniques, the LC/APCI-MS coupling allowed the fastest and more effective analysis. In addition, the complexity of the mass spectra deduced from these LC/MS experiments was simplified compared to the mass spectra obtained by MALDI-TOF. In this work, we have demonstrated how the LC/APCI-MS coupling applied to polydimethylsiloxane samples permits the full characterization of samples where end groups of different nature can be present in very small quantities. Copyright © 2008 John Wiley & Sons, Ltd. [source] Negative ion dissociation of peptides containing hydroxyl side chainsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 2 2008Dan Pu The dissociation of deprotonated peptides containing hydroxyl side chains was studied by electrospray ionization coupled with Fourier transform ion cyclotron resonance (ESI-FTICR) via sustained off-resonance irradiation collision induced dissociation (SORI-CID). Dissociation under post-source decay (PSD) conditions was performed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF). This work included hexapeptides with one residue of serine, threonine, or tyrosine and five inert alanine residues. During SORI-CID and PSD, dissociation of [M,H], yielded c- and y-ions. Side-chain losses of formaldehyde (HCHO) from serine-containing peptides, acetaldehyde (CH3CHO) from threonine-containing peptides, and 4-methylene-2,5-cycohexadienone (C7H6O) from tyrosine-containing peptides were generally observed in the negative ion PSD and SORI-CID spectra. Side-chain loss occurs much less from tyrosine-containing peptides than from serine- and threonine-containing peptides. This is probably due to the bulky side chain of tyrosine, resulting in steric hindrance and poor geometry for dissociation reactions. Additionally, a selective cleavage leading to the elimination of the C-terminal residue from [M,H], was observed from the peptides with serine and threonine at the C-terminus. This cleavage does not occur in the dissociation of peptides with an amide group at the C-terminus or peptides with neutral or basic residues at the C-terminus. It also does not occur with tyrosine at the C-terminus. Both the C-terminal carboxylic acid group and the hydroxyl side chain of the C-terminal residue must play important roles in the mechanism of C-terminal residue loss. A mechanism involving both the C-terminal carboxylic acid group and a hydroxyl side chain of serine and threonine is proposed. Copyright © 2007 John Wiley & Sons, Ltd. [source] Porous polymer monolith for surface-enhanced laser desorption/ionization time-of-flight mass spectrometry of small moleculesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2004Dominic S. Peterson Porous poly(butyl methacrylate- co -ethylene dimethacrylate), poly(benzyl methacrylate- co -ethylene dimethacrylate), and poly(styrene- co -divinylbenzene) monoliths have been prepared on the top of standard sample plates used for matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry and the modified plates were used for laser desorption/ionization mass spectrometry (LDI-MS). The hydrophobic porous surface of these monoliths enables the transfer of sufficient energy to the analyte to induce desorption and ionization prior to TOFMS analysis. Both UV and thermally initiated polymerization using a mask or circular openings in a thin gasket have been used to define spot locations matching those of the MALDI plates. The desorption/ionization ability of the monolithic materials depends on the applied laser power, the solvent used for sample preparation, and the pore size of the monoliths. The monolithic matrices are very stable and can be used even after long storage times in a typical laboratory environment without observing any deterioration of their properties. The performance of the monolithic material is demonstrated with the mass analysis of several small molecules including drugs, explosives, and acid labile compounds. The macroporous spots also enable the archiving of samples. Copyright © 2004 John Wiley & Sons, Ltd. [source] Enhanced post-source decay and cross-ring fragmentation of oligosaccharides facilitated by conversion to amino derivativesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2004Jan Muzikar Post-source decay (PSD) fragmentation of chemically or enzymatically produced aminoglycans has been evaluated through matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Conversion of native glycans to their respective aminoglycan derivatives improved detection sensitivity of the usual fragments and promoted cross-ring fragmentation of linear oligosaccharides, facilitating linkage recognition. The cross-ring fragmentations for both dextrin and dextran oligosaccharides were not limited to the reducing-end glucose moiety, as they were extended throughout the entire molecule. When the amino group was generated for N-glycans derived from three different glycoproteins, an enhancement of PSD was observed, without a significant extent of cross-ring fragmentation. Copyright © 2004 John Wiley & Sons, Ltd. [source] Use of matrix clusters and trypsin autolysis fragments as mass calibrants in matrix-assisted laser desorption/ionization time-of-flight mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2002William A. Harris Trypsin autolysis fragments and matrix clusters are often observed as intense peaks in mass spectra of protein digests. It is demonstrated that these can be exploited to improve the mass calibration of a matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) spectrometer. Interpretation of some of the autolysis masses is complicated by the existence of disulfide bonds. Surprisingly large matrix clusters are often visible for ,-cyano-4-hydroxy-cinnamic acid. The fractional part of their masses differentiates them from protein digestion fragments. Copyright © 2002 John Wiley & Sons, Ltd. [source] Mass spectral studies on aryl-substituted N -carbamoyl/N -thiocarbamoyl narcotine and related compoundsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2002Shefali Aggarwal Positive ion mass spectral fragmentation of new N-carbamoyl/N-thiocarbamoyl derivatives of narcotine and compounds closely related to it are reported and discussed. The techniques used include electron impact (EI), fast-atom bombardment (FAB), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and electrospray ionization tandem mass spectrometry (ESI-MS/MS). Prominent peaks in the mass spectra of these compounds appear to involve C-C bond cleavage , to the amine nitrogen with loss of the 4,5-dimethoxy(1H)isobenzofuranone moiety from their molecular ions, along with another prominent peak at m/z 382. No molecular ion peaks of these compounds were recorded in EI, whereas intense [M,+,H]+ ion peaks were observed in FAB and ESI spectra. MALDI also yielded [M,+,H]+ ion peaks in good agreement with FAB and ESI studies. Copyright © 2002 John Wiley & Sons, Ltd. [source] Characterization of tetrathiofulvalene compounds using matrix-assisted laser desorption/ionization time-of-flight mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2001Shaoxiang Xiong Tetrathiofulvalene compounds are important components of charge-transfer complexes, which may be applied in various fields of scientific research and practical applications. Some of these compounds cannot be characterized by mass spectrometry. Here, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was used for the characterization of tetrathiofulvalenes. The samples could be easily desorbed and ionized to form singly charged ions, and mass spectra with isotopic resolution readily obtained. The mass spectrometric results for 26 compounds have shown that MALDI-TOF is more effective and convenient than other mass spectrometry methods, and resolves the problem of mass spectrometric characterization of tetrathiofulvalene compounds. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||