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ESI Mass Spectra (esi + mass_spectrum)
Selected AbstractsNon-Covalent Aggregation of Discrete Metallo-Supramolecular Helicates into Higher Assemblies by Aromatic Pathways: Structural and Chemical Studies of New Aniline-Based Neutral Metal(II) DihelicatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2005Miguel Vázquez Abstract Neutral manganese(II), iron(II), cobalt(II), nickel(II), zinc(II) and cadmium(II) complexes with an N -tosyl-substituted N4 -donor Schiff base containing a 4,4'-methylenedianiline residue as spacer [H2La: N,N' -bis(2-tosylaminobenzylidene)-4,4'-methylenedianiline], and the zinc(II) complex with an analogous ligand [H2Lb: N,N' -bis(2-tosylaminobenzylidene)-4,4'-oxodianiline] have been prepared by an electrochemical procedure. FAB and ESI mass spectra of the complexes show peaks due to species corresponding to a general formula [M2(La,b)2 + H]+, thereby suggesting their dinuclear nature. A detailed study of the crystal packing in the unit cell of the zinc(II) complex with H2La shows that the helicates aggregate to form discrete prismatic moieties containing three molecules held together by ,,, and ,,, interactions. Moreover, the ZnII neutral dihelicate with H2Lb forms a 3D network in the solid state due to intermolecular ,-stacking interactions. 1H NMR studies of the diamagnetic compounds reported herein have been performed. Finally, the ligand H2La and its ZnII and CdII complexes have been studied by spectrophotometric and spectrofluorimetric techniques in order to get a better understanding of the formation mechanisms of the complexes and of the nature of their fluorescence emission. Emission studies show that the ZnII and CdII dihelicates with H2La display a green fluorescence in acetonitrile solution (, = 473 nm, , = 0.03 and , = 476 nm, , = 0.01, respectively). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Internal energy distribution of peptides in electrospray ionization : ESI and collision-induced dissociation spectra calculationJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 4 2008Alireza Pak Abstract The internal energy of ions and the timescale play fundamental roles in mass spectrometry. The main objective of this study is to estimate and compare the internal energy distributions of different ions (different nature, degree of freedom ,DOF' and fragmentations) produced in an electrospray source (ESI) of a triple-quadrupole instrument (Quattro I Micromass). These measurements were performed using both the Survival Yield method (as proposed by De Pauw) and the MassKinetics software (kinetic model introduced by Vékey). The internal energy calibration is the preliminary step for ESI and collision-induced dissociation (CID) spectra calculation. meta -Methyl-benzylpyridinium ion and four protonated peptides (YGGFL, LDIFSDF, LDIFSDFR and RLDIFSDF) were produced using an electrospray source. These ions were used as thermometer probe compounds. Cone voltages (Vc) were linearly correlated with the mean internal energy values ( The Orbitrap: a new mass spectrometerJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 4 2005Qizhi Hu Abstract Research areas such as proteomics and metabolomics are driving the demand for mass spectrometers that have high performance but modest power requirements, size, and cost. This paper describes such an instrument, the Orbitrap, based on a new type of mass analyzer invented by Makarov. The Orbitrap operates by radially trapping ions about a central spindle electrode. An outer barrel-like electrode is coaxial with the inner spindlelike electrode and mass/charge values are measured from the frequency of harmonic ion oscillations, along the axis of the electric field, undergone by the orbitally trapped ions. This axial frequency is independent of the energy and spatial spread of the ions. Ion frequencies are measured non-destructively by acquisition of time-domain image current transients, with subsequent fast Fourier transforms (FFTs) being used to obtain the mass spectra. In addition to describing the Orbitrap mass analyzer, this paper also describes a complete Orbitrap-based mass spectrometer, equipped with an electrospray ionization source (ESI). Ions are transferred from the ESI source through three stages of differential pumping using RF guide quadrupoles. The third quadrupole, pressurized to less than 10,3 Torr with collision gas, acts as an ion accumulator; ion/neutral collisions slow the ions and cause them to pool in an axial potential well at the end of the quadrupole. Ion bunches are injected from this pool into the Orbitrap analyzer for mass analysis. The ion injection process is described in a simplified way, including a description of electrodynamic squeezing, field compensation for the effects of the ion injection slit, and criteria for orbital stability. Features of the Orbitrap at its present stage of development include high mass resolution (up to 150 000), large space charge capacity, high mass accuracy (2,5 ppm), a mass/charge range of at least 6000, and dynamic range greater than 10.3 Applications based on electrospray ionization are described, including characterization of transition-metal complexes, oligosaccharides, peptides, and proteins. Use is also made of the high-resolution capabilities of the Orbitrap to confirm the presence of metaclusters of serine octamers in ESI mass spectra and to perform H/D exchange experiments on these ions in the storage quadrupole. Copyright © 2005 John Wiley & Sons, Ltd. [source] Electrospray mass spectra of group 6 (Fischer) carbenes in the presence of electron-donor compoundsJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2003M. A. Sierra Abstract Fischer carbene complexes 1,7 are not ionized under standard electrospray ionization (ESI) conditions. We report here that unsaturated chromium and tungsten (Fischer) carbene complexes can be ionized in an electrospray ion source in the presence of electron-donor compounds such as hydroquinone (HQ) or tetrathiafulvalene (TTF). The addition of these compounds, which seem to act as electron transfer agents, permits the recording and study of their ESI mass spectra in the negative mode of detection. Both chromium and tungsten(0) carbene complexes undergo in the first fragmentation stage a double simultaneous decarbonylation process. Copyright © 2003 John Wiley & Sons, Ltd. [source] Electrospray and matrix-assisted laser desorption/ionization mass spectral characterization of linear single nylon-6 oligomersJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2001Lu Shan Abstract Synthetic nylon-6 single molecular mass oligomers were studied by matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) mass spectrometry. These oligomers, considered as model compounds for the study of nylon-6 polymers, gave good mass spectrometric results using both MALDI and ESI. In spite of the gentle nature of both techniques, the MALDI and ESI spectra showed evidence of end-group cleavage from the oligomer chains. MALDI-MS was found to give similar fragmentation patterns for all of the oligomer samples. An increase in doubly charged ion signals with increasing oligomer mass was observed in the ESI mass spectra, as was end-group fragmentation. Signals from oligomer clusters were observed in ESI-MS for the dimer, tetramer and hexamer, most likely due to non-covalent bonding among the low-mass oligomer molecules. Copyright © 2001 John Wiley & Sons, Ltd. [source] Redox reactions of copper(II) upon electrospray ionization in the presence of acridine ligands with an amide side chainJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2009Aura Tintaru Abstract The complexation of copper(II) to acridine derivatives has been studied by means of electrospray ionization (ESI) mass spectrometry. Under soft conditions of ionization, the ESI mass spectra of methanolic solutions of copper(II) chloride and the acridine ligands show abundant signals of the mononuclear complexes formed from the metal and ligand. Depending on the position of the N -benzoylamino substituent in the acridinic heterocycle, however, the copper atom involved in the complexation process adopts different oxidation states in the resulting cations. Hence, the metal is reduced to copper(I) in the monocationic complex with the compound substituted in position 2, whereas it keeps its divalent state in the monocation formed with the compound substituted in position 4. As a consequence, the regioisomers lead to monocations with different masses in the ESI spectra. In order to understand this unusual behavior of two isomeric compounds, additional experiments have been performed with quinoline as a model. Copyright © 2008 John Wiley & Sons, Ltd. [source] The use of acetone as a substitute for acetonitrile in analysis of peptides by liquid chromatography/electrospray ionization mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 1 2010Theodore R. Keppel The recent worldwide shortage of acetonitrile has prompted interest in alternative solvents for liquid chromatography/mass spectrometry (LC/MS). In this work, acetone was substituted for acetonitrile in the separation of a peptide mixture by reversed-phase high-performance liquid chromatography (RP-HPLC) and in the positive electrospray ionization mass spectrometry (ESI-MS) of individual peptides. On both C12 and C18 stationary phases, the substitution of acetone for acetonitrile as the organic component of the mobile phase did not alter the gradient elution order of a five-peptide retention standard, but did increase peak width, shorten retention times, and increase peak tailing. Positive ESI mass spectra were obtained for angiotensin I, bradykinin, [Leu5]-enkephalin, and somatostatin 14 dissolved in both acetonitrile/water/formic acid (25%/75%/0.1%) and acetone/water/formic acid (25%/75%/0.1%). Under optimized ESI-MS conditions, the mass spectral response of [Leu5]-enkephalin was increased two-fold when the solvent contained acetone. The substitution of acetone for acetonitrile resulted in only slight changes in the responses of the remaining peptides. A higher capillary voltage was required for optimum response when acetone was used. Compared with acetonitrile/water/formic acid (50/50/0.1%), more interfering species below m/z,=,140 were found in the ESI-MS spectra of acetone/water/formic acid (50/50/0.1%). Copyright © 2009 John Wiley & Sons, Ltd. [source] Comparison of negative and positive ion electrospray ionization mass spectra of calmodulin and its complex with trifluoperazineRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 15 2005Stephen J. Watt The protein calmodulin (apoCaM) undergoes a conformational change when it binds calcium. This structure of the protein (Ca4CaM) is a dumbbell-shaped molecule that undergoes a further profound conformational change on binding of the antipsychotic drug trifluoperazine (TFP). Experimental conditions were developed to prepare samples of apoCaM, Ca4CaM and Ca4CaM/TFP that were substantially free of sodium. The effects of the conformational changes of calmodulin on the charge-state distributions observed in positive ion and negative ion electrospray ionization (ESI) mass spectra were examined. Conversion of apoCaM into Ca4CaM was concomitant with a change in the negative ion ESI mass spectrum whereby the 16, ion was the most abundant ion observed for the apo form and the 8, ion was the most abundant for the complex. In contrast, in the positive ion ESI mass spectra of apoCaM and Ca4CaM, the most abundant species in each case was the 8+ ion. When a complex of Ca4CaM with TFP was prepared, the most abundant species was the 5+ ion. This is consistent with a conformational change of Ca4CaM that rendered some basic sites inaccessible to ionization in the ESI process. Using the same Ca4CaM/TFP mixture, no complex with TFP was observed in negative ion ESI mass spectra. These observations are discussed in the context of the structural changes that are known to occur in calmodulin, and suggestions are made to explain the apparently conflicting data. The results reported here reflect on the validity of using differences in charge-state distributions observed in ESI mass spectra to assess conformational changes in proteins. Copyright © 2005 John Wiley & Sons, Ltd. [source] Cluster ions of diquat and paraquat in electrospray ionization mass spectra and their collision-induced dissociation spectraRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2003Boris L. Milman Cluster ions such as [Cat+X+nM]+ (n,=,0,4); [Cat-H+nM]+ (n,=,1,3); and [2(Cat-H)+X+nM]+ (n,=,0,2), where Cat, X, and M are the dication, anion, and neutral salt (CatX2), respectively, are observed in electrospray ionization (ESI) mass spectrometry of relatively concentrated solutions of diquat and paraquat. Collision-induced dissociation (CID) reactions of the clusters were observed by tandem mass spectrometry (MS/MS), including deprotonation to form [Cat-H]+, one-electron reduction of the dication to form Cat+., demethylation of the paraquat cation to form [Cat-CH3]+, and loss of neutral salt to produce smaller clusters. The difference in acidity and reduction power between diquat and paraquat, evaluated by thermodynamical estimates, can rationalize the different fractional yields of even-electron ([Cat-H]+ and its clusters) and odd-electron (mostly Cat+.) ions in ESI mass spectra of these pesticides. The [Cat+n,·,Solv]2+ doubly charged cluster ions, where n,,,2 and Solv is the solvent molecule (methanol and/or water), are only observed as very weak peaks in precursor ion CID spectra of the Cat2+ salt cation at low collision energy. The presence of an anion and a solvent molecule in a cluster is assumed to be related to existence of tight and loose ion pairs, respectively, in multiply charged droplets/ions formed by ESI. The results emphasize again the role of solution chemistry concepts such as acidity/basicity, redox power, and ion-pair formation, for ESI. Copyright © 2003 John Wiley & Sons, Ltd. [source] Determination of phenolic compounds in rose hip (Rosa canina) using liquid chromatography coupled to electrospray ionisation tandem mass spectrometry and diode-array detectionRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2002Erlend Hvattum Liquid chromatography coupled with negative and positive electrospray ionisation (ESI) tandem mass spectrometry (MS/MS) and diode-array detection (DAD) was used for determination of phenols in rose hip (Rosa canina) extract. ESI mass spectra of the chromatographically separated phenols gave the molecular weight of the compounds through prominent [M,,,H], ions for most of the compounds and M+ ions for the anthocyanins. Collision induced dissociation (CID) of the [M,,,H], (or M+) precursor ions yielded product ions which determined the molecular weight of the aglycones. In-source fragmentation followed by CID of the resulting deprotonated aglycone ([A,,,H],) provided product ions for the identification of the unconjugated phenols. The identification was based on comparison with product ion spectra of commercial standards. UV-diode-array spectra were used for identity confirmation. This combined approach allowed the identification in rose hip extract of an anthocyanin, i.e. cyanidin-3- O -glucoside, several glycosides of quercetin and glycosides of taxifolin and eriodictyol. Phloridzin was identified, and several conjugates of methyl gallate were also found, one of which was tentatively identified as methyl gallate-rutinoside. Catechin and quercetin were found as the aglycones in the extract. Copyright © 2002 John Wiley & Sons, Ltd. [source] A Combined ESI- and MALDI-MS(/MS) Study of Peripherally Persulfonylated Dendrimers: False Negative Results by MALDI-MS and Analysis of Defects,CHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2005Thorsten Felder Dipl.-Chem. Abstract Mass spectrometry, in particular MALDI-MS, has often been used as a valuable means to characterize dendritic molecules with respect to their molecular masses. Also, it is a valuable tool for analyzing potential defects in their structure which result from incomplete synthetic steps. This article presents a comparison of ESI and MALDI mass spectrometric experiments on dendrimers persulfonylated at their periphery. While the ESI mass spectra easily permit impurities and defects to be identified and thus provide evidence for sample purity, reactions with acidic matrices occur during the MALDI process. The resulting defects are identical to those expected from incomplete substitution. Thus, in these cases, MALDI-MS yields false negative results. With mass-selected, ESI-generated ions, collision experiments were performed in an FT-ICR mass spectrometer cell to provide detailed insight into the fragmentation patterns of the various dendrimers. Different fragmentation patterns are observed depending on the exact structure of the dendrimer. Also, the nature of the charge is important. The fragmentation reactions for protonated species differ much from those binding a sodium or potassium ion. These differences can be traced back to different sites for binding H+ versus Na+ or K+. Tandem MS experiments on mass-selected dendrimer ions with defects can be used to distinguish different types of defects. A concise structural assignment can thus be made on the basis of these experiments. Even mixtures of two isobaric defect variants with the same elemental composition can be identified. Massenspektrometrie, insbesondere MALDI-MS wurde oft als wertvolle Analysenmethode für die Charakterisierung von Dendrimeren hinsichtlich ihrer Molekülmasse, aber auch hinsichtlich einer Analyse potentieller Strukturdefekte eingesetzt, die aus unvollständig verlaufenden Synthesestufen resultieren. In diesem Artikel berichten wir über einen Vergleich von ESI- und MALDI-massenspektrometrischen Experimenten mit an ihrer Peripherie persulfonylierten Dendrimeren. Während die ESI-Massenspektren eine einfache Identifizierung von Verunreinigungen und Defekten erlauben und damit eine Reinheitskontrolle ermöglichen, laufen während der Ionisierung mittels MALDI Reaktionen mit sauren Matrices ab, die genau solche Defekte erzeugen, wie man sie aus einer unvollständigen Synthese erwarten würde. MALDI-MS führt hier also zu einem falsch-negativen Ergebnis. Mit massenselektierten Ionen aus der Electrospray-Ionisierung wurden Stoßexperimente in einer FT-ICR-Zelle durchgeführt, um einen detaillierten Einblick in das Fragmentierungsmuster der verschiedenen Dendrimere zu erhalten. Man beobachtet unterschiedliche Fragmentierungsmuster in Abhängigkeit von der genauen Struktur der Dendrimere. Auch die Art der Ladung ist wichtig, da die Fragmentierungswege der protonierten Dendrimere sich deutlich von denen ihrer Na+ - und K+ -Addukte unterscheiden. Diese Unterschiede können auf unterschiedliche Bindungsstellen für H+gegenüber Na+oder K+zurückgeführt werden. Tandem MS-Experimente mit massenselektierten, strukturdefekten Dendrimer-Ionen erlauben eine genaue Unterscheidung verschiedener Typen von Defekten. Sie können daher für eine detaillierte Strukturaufklärung verwendet werden. Sogar Mischungen zweier isobarer Defektvarianten mit gleicher Elementarzusammensetzung werden zuverlässig identifiziert. [source] Fractionation of Methyl Cellulose According to Polarity , a Tool to Differentiate First and Second Order Heterogeneity of the Substituent DistributionMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2006Roland Adden Abstract Summary: A set of four MCs (DS 1.80,1.95) has been analyzed with regard to their substituent pattern in the glucosyl units and along the polymer chain. The average heterogeneity of methylation observed for the entire material was analyzed in more detail after fractionation according to polarity. All fractions obtained were analyzed with respect to their DS, monomer composition and deviation from a random distribution of these monomers in the polymer chains. By this approach, heterogeneity of first and second order could be differentiated. While for three of the MCs only a minor DS-gradient over the material was observed, a more pronounced heterogeneity of first order was obtained for MC 4. ESI mass spectrum of the undissolved residue of MC 2 after deuteromethylation and partial hydrolysis; DP 2 and 3 are shown in detail. Signals are assigned according to the number of CH3 -groups. [source] Comparison of negative and positive ion electrospray ionization mass spectra of calmodulin and its complex with trifluoperazineRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 15 2005Stephen J. Watt The protein calmodulin (apoCaM) undergoes a conformational change when it binds calcium. This structure of the protein (Ca4CaM) is a dumbbell-shaped molecule that undergoes a further profound conformational change on binding of the antipsychotic drug trifluoperazine (TFP). Experimental conditions were developed to prepare samples of apoCaM, Ca4CaM and Ca4CaM/TFP that were substantially free of sodium. The effects of the conformational changes of calmodulin on the charge-state distributions observed in positive ion and negative ion electrospray ionization (ESI) mass spectra were examined. Conversion of apoCaM into Ca4CaM was concomitant with a change in the negative ion ESI mass spectrum whereby the 16, ion was the most abundant ion observed for the apo form and the 8, ion was the most abundant for the complex. In contrast, in the positive ion ESI mass spectra of apoCaM and Ca4CaM, the most abundant species in each case was the 8+ ion. When a complex of Ca4CaM with TFP was prepared, the most abundant species was the 5+ ion. This is consistent with a conformational change of Ca4CaM that rendered some basic sites inaccessible to ionization in the ESI process. Using the same Ca4CaM/TFP mixture, no complex with TFP was observed in negative ion ESI mass spectra. These observations are discussed in the context of the structural changes that are known to occur in calmodulin, and suggestions are made to explain the apparently conflicting data. The results reported here reflect on the validity of using differences in charge-state distributions observed in ESI mass spectra to assess conformational changes in proteins. Copyright © 2005 John Wiley & Sons, Ltd. [source]
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