Laser desorption ionization using time-of-flight mass spectrometer afforded with quadrupole ion trap was used to study As2Ch3 (Ch = S, Se, and Te) bulk chalcogenide materials. The main goal of the study is the identification of species present in the plasma originating from the interaction of laser pulses with solid state material. The generated clusters in both positive and negative ion mode are identified as 10 unary (Sp+/– and Asm+/–) and 34 binary (AsmSp+/–) species for As2S3 glass, 2 unary (Seq+/–) and 26 binary (AsmSeq+/–) species for As2Se3 glass, 7 unary (Ter+/–) and 23 binary (AsmTer+/–) species for As2Te3 material. The fragmentation of chalcogenide materials was diminished using some polymers and in this way 45 new, higher mass clusters have been detected. This novel approach opens a new possibility for laser desorption ionization mass spectrometry analysis of chalcogenides as well as other materials.
Negative mode proteome analysis offers access to unique portions of the proteome and several acidic post-translational modifications; however, traditional collision-based fragmentation methods fail to reliably provide sequence information for peptide anions. Negative electron transfer dissociation (NETD), on the other hand, can sequence precursor anions in a high-throughput manner. Similar to other ion–ion methods, NETD is most efficient with peptides of higher charge state because of the increased electrostatic interaction between reacting molecules. Here we demonstrate that NETD performance for lower charge state precursors can be improved by altering the reagent cation. Specifically, the recombination energy of the NETD reaction—largely dictated by the ionization energy (IE) of the reagent cation—can affect the extent of fragmentation. We compare the NETD reagent cations of C16H10●+ (IE?=?7.9 eV) and SF5●+ (IE?=?9.6 eV) on a set of standard peptides, concluding that SF5●+ yields greater sequence ion generation. Subsequent proteome-scale nLC-MS/MS experiments comparing C16H10●+ and SF5●+ further supported this outcome: analyses using SF5●+ yielded 4637 peptide spectral matches (PSMs) and 2900 unique peptides, whereas C16H10●+ produced 3563 PSMs and 2231 peptides. The substantive gain in identification power with SF5●+ was largely driven by improved identification of doubly deprotonated precursors, indicating that increased NETD recombination energy can increase product ion yield for low charge density precursors. This work demonstrates that SF5●+ is a viable, if not favorable, reagent cation for NETD, and provides improved fragmentation over the commonly used fluoranthene reagent.
Peptide cation-radical fragment ions of the z-type, [●AXAR+], [●AXAK+], and [●XAR+], where X = A, C, D, E, F, G, H, K, L, M, N, P, Y, and W, were generated by electron transfer dissociation of peptide dications and investigated by MS3-near-ultraviolet photodissociation (UVPD) at 355 nm. Laser-pulse dependence measurements indicated that the ion populations were homogeneous for most X residues except phenylalanine. UVPD resulted in dissociations of backbone CO─NH bonds that were accompanied by hydrogen atom transfer, producing fragment ions of the [yn]+ type. Compared with collision-induced dissociation, UVPD yielded less side-chain dissociations even for residues that are sensitive to radical-induced side-chain bond cleavages. The backbone dissociations are triggered by transitions to second (B) excited electronic states in the peptide ion R-CH●-CONH- chromophores that are resonant with the 355-nm photon energy. Electron promotion increases the polarity of the B excited states, R-CH+-C●(O–)NH-, and steers the reaction to proceed by transfer of protons from proximate acidic Cα and amide nitrogen positions.
For the first time ever it is demonstrated in this work that, in spontaneous conditions and following the imposition of an electric field, mutual penetration of components of WO3 and Me2(WO4)3 occurs at heterophase interfaces WO3|Me2(WO4)3 where Me = In, Eu, or Sc. Tungstic oxide WO3 is pulled onto the inner surface of ceramic Me2(WO4)3 and, in turn, components of Me2(WO4)3 penetrate onto the surface of grains of ceramic WO3, which is confirmed by the method of x-ray—fluorescence analysis. Data concerning the conductivity and transport numbers of Eu2(WO4)3 and a composite on its basis, which was manufactured as a result the electrosurface transport of WO3, are obtained for the first time ever. With allowance made for the data on the O2? character of the ionic conduction in MeWO4 and Eu2(WO4)3 it is concluded that the type of ionic carriers in tungstates (Men+)2/n[WO4] makes no impact on the mechanism of spontaneous and field-induced processes that are developing at the (Men+)2/n[WO4]|WO3 interfaces. 相似文献
Systematic laser desorption/ionization (LDI) experiments of fullerene-C60 on a wide range of target plate materials were conducted to gain insight into the initial ion formation in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The positive and negative ion signal intensities of precursor, fragment, and cluster ions were monitored, varying both the laser fluence (0–3.53 Jcm?2) and the ion extraction delay time (0–950 ns). The resulting species-specific ion signal intensities are an indication for the ionization mechanisms that contribute to LDI and the time frames in which they operate, providing insight in the (MA)LDI primary ionization. An increasing electrical resistivity of the target plate material increases the fullerene-C60 precursor and fragment anion signal intensity. Inconel 625 and Ti90/Al6/V4, both highly electrically resistive, provide the highest anion signal intensities, exceeding the cation signal intensity by a factor ~1.4 for the latter. We present a mechanism based on transient electrical field strength reduction to explain this trend. Fullerene-C60 cluster anion formation is negligible, which could be due to the high extraction potential. Cluster cations, however, are readily formed, although for high laser fluences, the preferred channel is formation of precursor and fragment cations. Ion signal intensity depends greatly on the choice of substrate material, and careful substrate selection could, therefore, allow for more sensitive (MA)LDI measurements.
In order to find single source precursors (SSP), the structures, relative stabilities, and IR spectra of small asymmetric clusters (HFInN3)n (n = 1–6) are systematically investigated by means of the density functional theory at the B3LYP level. The obtained geometries show that the frameworks of clusters (HFInN3)n (n = 2–6) prefer to be 2n-membered ring with alternating indium and α-nitrogen atoms. The averaged binding energies reveal that all of asymmetric clusters (HFInN3)n (n = 1–6) can continue to gain energy as the cluster size n increasing. The second-order difference of energy (Δ2E) and the HOMO-LUMO energy gap (Egap) as a function of the cluster size n both exhibit a pronounced even-odd alternation phenomenon. The influences of cluster size n and temperature T on the thermodynamic properties of clusters are discussed. Judged by enthalpies and Gibbs free energies, the formations of the most stable clusters (HFInN3)n (n = 2–6) from the monomer are thermodynamically favorable in the range of 200–800 K. 相似文献
Bacteriochlorophyll a (BChl a), a photosynthetic pigment performing the same functions of chlorophylls in plants, features a bacteriochlorin macrocycle ring (18 π electrons) with two reduced pyrrole rings along with a hydrophobic terpenoid side chain (i.e., the phytol residue). Chlorophylls analysis by matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) is not so straightforward since pheophytinization (i.e., release of the central metal ion) and cleavage of the phytol–ester linkage are invariably observed by employing protonating matrices such as 2,5-dihydroxybenzoic acid, sinapinic acid, and α-cyano-4-hydroxycinnamic acid. Using BChl a from Rhodobacter sphaeroides R26 strain as a model system, different electron-transfer (ET) secondary reaction matrices, leading to the formation of almost stable radical ions in both positive ([M]+?) and negative ([M]??) ionization modes at m/z 910.55, were evaluated. Compared with ET matrices such as trans-2-[3-(4-t-butyl-phenyl)-2-methyl-2-propenylidene]malononitrile (DCTB), 2,2':5',2''-terthiophene (TER), anthracene (ANT), and 9,10-diphenylanthracene (DP-ANT), 1,5-diaminonaphthalene (DAN) was found to provide the highest ionization yield with a negligible fragmentation. DAN also displayed excellent ionization properties for two metal ion-substituted bacteriochlorophylls, (i.e., Zn- and Cu-BChl a at m/z 950.49 and 949.49), respectively. MALDI MS/MS of both radical charged molecular species provide complementary information, thus making analyte identification more straightforward.
An ion of m/z 110.06036 (ion formula [C6H8NO]+; error: 0.32 mDa) was observed in the collision induced dissociation tandem mass spectrometry experiments of protonated N-(3-aminophenyl)benzamide, which is a rearrangement product ion purportedly through nitrogen-oxygen (N–O) exchange. The N–O exchange rearrangement was confirmed by the MS/MS spectrum of protonated N-(3-aminophenyl)-O18-benzamide, where the rearranged ion, [C6H8NO18]+ of m/z 112 was available because of the presence of O18. Theoretical calculations using Density Functional Theory (DFT) at B3LYP/6-31 g(d) level suggest that an ion-neutral complex containing a water molecule and a nitrilium ion was formed via a transition state (TS-1), followed by the water molecule migrating to the anilide ring, eventually leading to the formation of the rearranged ion of m/z 110. The rearrangement can be generalized to other protonated amide compounds with electron-donating groups at the meta position, such as, –OH, –CH3, –OCH3, –NH(CH3)2, –NH-Ph, and –NHCOCH3, all of which show the corresponding rearranged ions in MS/MS spectra. However, the protonated amide compounds containing electron-withdrawing groups, including –Cl, –Br, –CN, –NO2, and –CF3, at the meta position did not display this type of rearrangement during dissociation. Additionally, effects of various acyl groups on the rearrangement were investigated. It was found that the rearrangement can be enhanced by substitution on the ring of the benzoyl with electron-withdrawing groups.
The anilide anion (m/z 92) generated directly from aniline, or indirectly as a fragmentation product of deprotonated acetanilide, captures CO2 readily to form the carbamate anion (m/z 136) in the collision cell, when CO2 is used as the collision gas in a tandem-quadrupole mass spectrometer. The gas-phase affinity of the anilide ion to CO2 is significantly higher than that of the phenoxide anion (m/z 93), which adds to CO2 only very sluggishly. Our results suggest that the efficacy of CO2 capture depends on the natural charge density on the nitrogen atom, and relative nucleophilicity of the anilide anion. Generally, conjugate bases generated from aniline derivatives with proton affinities (PA) less than 350 kcal/mol do not tend to add CO2 to form gaseous carbamate ions. For example, the anion generated from p-methoxyaniline (PA = 367 kcal/mol) reacts significantly faster than that obtained from p-nitroaniline (PA = 343 kcal/mol). Although deprotonated p-aminobenzoic acid adds very poorly because the negative charge is now located primarily on the carboxylate group, it reacts more efficiently with CO2 if the carboxyl group is esterified. Moreover, mixture of CO2 and He as the collision gas was found to afford more efficient adduct formation than CO2 alone, or as mixtures made with nitrogen or argon, because helium acts as an effective “cooling” gas and reduces the internal energy of reactant ions.
Infusion of NaCl solutions into an electrospray ionization (ESI) source produces [Na(n+1)Cln]+ and other gaseous clusters. The n?=?4, 13, 22 magic number species have cuboid ground state structures and exhibit elevated abundance in ESI mass spectra. Relatively few details are known regarding the mechanisms whereby these clusters undergo collision-induced dissociation (CID). The current study examines to what extent molecular dynamics (MD) simulations can be used to garner insights into the sequence of events taking place during CID. Experiments on singly charged clusters reveal that the loss of small neutrals is the dominant fragmentation pathway. MD simulations indicate that the clusters undergo extensive structural fluctuations prior to decomposition. Consistent with the experimentally observed behavior, most of the simulated dissociation events culminate in ejection of small neutrals ([NaCl]i, with i?=?1, 2, 3). The MD data reveal that the prevalence of these dissociation channels is linked to the presence of short-lived intermediates where a relatively compact core structure carries a small [NaCl]i protrusion. The latter can separate from the parent cluster via cleavage of a single Na-Cl contact. Fragmentation events of this type are kinetically favored over other dissociation channels that would require the quasi-simultaneous rupture of multiple electrostatic contacts. The CID behavior of NaCl cluster ions bears interesting analogies to that of collisionally activated protein complexes. Overall, it appears that MD simulations represent a valuable tool for deciphering the dissociation of noncovalently bound systems in the gas phase.
A detailed energy-resolved study of the fragmentation reactions of protonated histidine-containing peptides and their b2 ions has been undertaken. Density functional theory calculations were utilized to predict how the fragmentation reactions occur so that we might discern why the mass spectra demonstrated particular energy dependencies. We compare our results to the current literature and to synthetic b2 ion standards. We show that the position of the His residue does affect the identity of the subsequent b2 ion (diketopiperazine versus oxazolone versus lactam) and that energy-resolved CID can distinguish these isomeric products based on their fragmentation energetics. The histidine side chain facilitates every major transformation except trans-cis isomerization of the first amide bond, a necessary prerequisite to diketopiperazine b2 ion formation. Despite this lack of catalyzation, trans-cis isomerization is predicted to be facile. Concomitantly, the subsequent amide bond cleavage reaction is rate-limiting.
We report a comprehensive study of collision-induced dissociation (CID) and near-UV photodissociation (UVPD) of a series of tyrosine-containing peptide cation radicals of the hydrogen-rich and hydrogen-deficient types. Stable, long-lived, hydrogen-rich peptide cation radicals, such as [AAAYR + 2H]+● and several of its sequence and homology variants, were generated by electron transfer dissociation (ETD) of peptide-crown-ether complexes, and their CID-MS3 dissociations were found to be dramatically different from those upon ETD of the respective peptide dications. All of the hydrogen-rich peptide cation radicals contained major (77%–94%) fractions of species having radical chromophores created by ETD that underwent photodissociation at 355 nm. Analysis of the CID and UVPD spectra pointed to arginine guanidinium radicals as the major components of the hydrogen-rich peptide cation radical population. Hydrogen-deficient peptide cation radicals were generated by intramolecular electron transfer in CuII(2,2′:6′,2″-terpyridine) complexes and shown to contain chromophores absorbing at 355 nm and undergoing photodissociation. The CID and UVPD spectra showed major differences in fragmentation for [AAAYR]+● that diminished as the Tyr residue was moved along the peptide chain. UVPD was found to be superior to CID in localizing Cα-radical positions in peptide cation radical intermediates.
The structures of the Pd4(SBu)4(OAc)4 (I) and Pd6 (SBu)12 (II) palladium clusters are determined by the X-ray diffraction method. For cluster I: a = 8.650(2), b = 12.314(2), c = 17.659(4) Å, α = 78.03(3)°, β = 86.71(2)°, γ = 78.13(3)°, V = 1800.8(7) Å3, ρcalcd = 1.878 g/cm3, space group P\(\bar 1\), Z = 4, N = 3403, R = 0.0468; for structure II: a = 10.748(2), b = 12.840(3), c = 15.233(3) Å, α = 65.31(3)°, β = 70.10(3)°, γ = 72.91(3)°, V = 1767.4(6) Å3, ρ calcd = 1.605 g/cm3, space group P\(\bar 1\), Z = 1, N = 3498, R = 0.0729. In cluster I, four Pd atoms form a planar cycle. The neighboring Pd atoms are bound by two acetate or two mercaptide bridges (Pd…Pd 2.95–3.23 Å, Pd…Pd angles 87.15°–92.85°). In cluster II, the Pd atoms form a planar six-membered cycle with Pd···Pd distances of 3.09–3.14 Å, the PdPdPd angles being 118.95°–120.80°. The Pd atoms are linked in pairs by two mercaptide bridges. The formation of clusters I and II in solution is proved by IR spectroscopy and calorimetry. Analogous clusters are formed in solution upon the reaction of palladium(II) diacetate with thiophenol. 相似文献
The structures and properties of asymmetric heterocycles (HBrBN3)n (n = 1-4) are systematically studied at the B3LYP/6-31G* level. The molecules (HBrBN3)n (n = 2-4) have the core structures of a 2n-membered ring with alternating boron and α-nitrogen atoms. The relationships between geometrical parameters and oligomerization degree n are discussed. The calculated IR spectra have four main characteristic regions. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed. Thermodynamic analysis of the gas-phase oligomerizations shows that formation of the most stable heterocycles (HBrBN3)n (n = 2-4) is enthalpy driven in the range of 200-800 K. 相似文献
Oxidative desulfurization (ODS) of organic compounds containing sulfur element from a model oil was performed using tungsten oxide catalysts supported on mesoporous silica with cubic Ia3d mesostructure, well-defined mesopores (7.2 nm), high surface area (719 m2/g), and three-dimensional pore network (WOx/KIT-6). The prepared WOx/KIT-6 catalysts (5–20 wt% WOx) were characterized by X-ray diffraction analysis, N2 sorption measurements, electron microscopy, H2-temperature programmed reduction, Raman spectroscopy, and thermogravimetric analysis. Among the mesoporous catalysts, 10 wt% WOx/KIT-6 exhibited the best catalytic performance. Sulfur-containing organic compounds, such as dibenzothiophene, 4,6-dimethyldibenzothiophene, and benzothiophene, were completely (100 %) removed from the model oil over 10 wt% WOx/KIT-6 catalyst in 2 h. In addition, the catalyst could be reused several times with only slight decrease in catalytic activity. 相似文献
The crystal structures of compounds from the series [M(NH3)5Cl](NO3)2, (M = Ir, Rh, Ru) were described. The compounds crystallized in the tetragonal crystal system, space group I4, Z = 2. Crystal data for [Ir(NH3)5Cl](NO3)2(I): a = 7.6061(1) Å, b = 7.6061(1) Å, c = 10.4039(2) Å, V = 601.894(16) Å3, ρcalc = 2.410 g/cm3, R = 0.0087; [Rh(NH3)5Cl](NO3)2(II): a = 7.5858(5) Å, b = 7.5858(5) Å, c = 10.41357(7) Å, V = 599.24(7) Å3, ρcalc = 1.926 g/cm3, R = 0.0255; [Ru(NH3)5Cl](NO3)2(III): a = 7.5811(6) Å, b = 7.5811(6) Å, c = 10.5352(14) Å, V = 605.49(11) Å3, ρcalc = 1.896 g/cm3, R = 0.0266. The compounds were defined by IR spectroscopy and XRPA and thermal analyses. 相似文献
We investigate the tandem mass spectrometry of regiospecifically labeled, deprotonated sucrose analytes. We utilize density functional theory calculations to model the pertinent gas-phase fragmentation chemistry of the prevalent glycosidic bond cleavages (B1-Y1 and C1-Z1 reactions) and compare these predictions to infrared spectroscopy experiments on the resulting B1 and C1 product anions. For the C1 anions, barriers to interconversion of the pyranose [α-glucose-H]?, C1 anions to entropically favorable ring-open aldehyde-terminated forms were modest (41 kJ mol?1) consistent with the observation of a band assigned to a carbonyl stretch at ~?1680–1720 cm?1. For the B1 anions, our transition structure calculations predict the presence of both deprotonated 1,6-anhydroglucose and carbon 2-ketone ((4S,5S,6R)-4,5-dihydroxy-6-(hydroxymethyl)dihydro-2H-pyran-3(4H)-one) anion structures, with the latter predominating. This hypothesis is supported by our spectroscopic data which show diagnostic bands at 1600, 1674, and 1699 cm?1 (deprotonated carbon 2-ketone structures), and at ~?1541 cm?1 (both types of structure) and RRKM rate calculations. The deprotonated carbon 2-ketone structures are also the lowest energy product B1 anions.
The structures of palladium carbonylcarboxylate clusters [Pd2(CO)2(RCOO)2]n (n = 2, R = CH3, CH2Cl, CF3, n = 3, R = CMe3, CHMe2, n-C5H11) are studied in benzene and tetrahydrofuran solutions by IR and 1H and 13C NMR spectroscopy. The clusters in the solid state have a planar cyclic metal framework with pairs of the carbonyl and carboxylate ligands alternately coordinated on its sides. In solutions, compounds under consideration contain one-type carbonyl ligands and one-type carboxylate ligands; their structures are similar to thaso in the solid state. 相似文献
The heat capacities of Pb2V2O7 and Pb3(VO4)2 as a function of temperature in the range 350–965 K have been studied by the differential scanning calorimetry method. The CP = f(T) curve for Pb2V2O7 is described by the equation Cp = (230.76 ± 0.51) + (73.60 ± 0.50)×10-3T ? (18.38 ± 0.54)×105T-2 in the entire temperature range. For Pb3(VO4)2, there is a well-pronounced extreme point in the CP = f(T) curve at T = 371.5 K, which is caused by the existence of a structural phase transition. The thermodynamic properties of the oxide compounds have been calculated. 相似文献
A novel one-dimensional chain complex [Cd(NITpPy)2(N(CN)2)2)]n (NITpPy = 2-(4′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) has been synthesized and characterized structurally. It crystallizes in the triclinic space group P\(\bar 1\) with a = 7.1742(13), b = 9.4913(17), c = 13.208(2) Å, α = 71.020(2)°, β=87.308(2)°, γ = 70.503(2)°, V = 799.8(3) Å3, C28H32CdN12O4, Mr = 713.06, Z = 1, ρc = 1.48 g/cm3, μ(MoKα) = 0.736 mm?1, F(000) = 364, R = 0.0275 and wR = 0.0605 for 2702 observed reflections with I > 2σ(I). The crystal structure consists of infinite chains of [Cd(NITpPy)2(N(CN)2)2)] units linked by dicyanamide anions [N(CN)2]?. Each Cd2+ ion is six-coordinated with the geometry of a distorted octahedron. 相似文献
