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1.
Yang Cai Zhenzhen Mo Nalaka S. Rannulu Bing Guan Srinivasan Kannupal Bruce C. Gibb Richard B. Cole 《Journal of mass spectrometry : JMS》2010,45(3):235-240
Electrospray‐generated precursor ions usually follow the ‘even‐electron rule’ and yield ‘closed shell’ fragment ions. We characterize an exception to the ‘even‐electron rule.’ In negative ion electrospray mass spectrometry (ES‐MS), 2‐(ethoxymethoxy)‐3‐hydroxyphenol (2‐hydroxyl protected pyrogallol) easily formed a deprotonated molecular ion (M‐H)? at m/z 183. Upon low‐energy collision induced decomposition (CID), the m/z 183 precursor yielded a radical ion at m/z 124 as the base peak. The radical anion at m/z 124 was still the major fragment at all tested collision energies between 0 and 50 eV (Elab). Supported by computational studies, the appearance of the radical anion at m/z 124 as the major product ion can be attributed to the combination of a low reverse activation barrier and resonance stabilization of the product ions. Furthermore, our data lead to the proposal of a novel alternative radical formation pathway in the protection group removal of pyrogallol. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
2.
Unusual odd-electron fragments from even-electron protonated prodiginine precursors using positive-ion electrospray tandem mass spectrometry 总被引:1,自引:0,他引:1
Chen K Rannulu NS Cai Y Lane P Liebl AL Rees BB Corre C Challis GL Cole RB 《Journal of the American Society for Mass Spectrometry》2008,19(12):1856-1866
Reports of anticancer and immunosuppressive properties have spurred recent interest in the bacterially produced prodiginines. We use electrospray tandem mass spectrometry (ES-MS/MS) to investigate prodigiosin, undecylprodiginine, and streptorubin B (butyl-meta-cycloheptylprodiginine) and to explore their fragmentation pathways to explain the unusual methyl radical loss and consecutive fragment ions that dominate low-energy collision-induced dissociation (CID) mass spectra. The competition between the formation of even-electron ions and radical ions is examined in detail. Theoretical calculations are used to optimize the structures and calculate the energies of both reactants and products using the Gaussian 03 program. Results indicate that protonation occurs on the nitrogen atom that initially held no hydrogen, thus allowing formation of a pseudo-seven-membered ring that constitutes the most stable ground state [M + H](+) structure. From this precursor, experimental data show that methyl radical loss has the lowest apparent threshold but, alternatively, even-electron fragment ions can be formed by loss of a methanol molecule. Computational modeling indicates that methyl radical loss is the more endothermic process in this competition, but the lower apparent threshold associated with methyl radical loss points to a lower kinetic barrier. Additionally, this characteristic and unusual loss of methyl radical (in combination with weaker methanol loss) from each prodiginine is useful for performing constant neutral loss scans to quickly and efficiently identify all prodiginines in a complex biological mixture without any clean-up or purification. The feasibility of this approach has been proven through the identification of a new, low-abundance prodigiosin analog arising from Hahella chejuensis. 相似文献
3.
A. Alatas A.H. Said H. Sinn C.N. Kodituwakku B. Reinhart M.-L. Saboungi 《Journal of Physics and Chemistry of Solids》2005,66(12):2230-2234
The dynamical structure factors of supercooled-liquid and hot-solid silicon are measured by inelastic X-ray scattering at the same temperature, 1620 K. Two significant changes in the averaged longitudinal sound velocities and in the longitudinal modulus are observed. First, we observe a different longitudinal modulus in the polycrystalline hot-solid silicon compared to the extrapolated value obtained from the single-crystal measurement. This reduction of the modulus may be a precursor of the semiconductor-to-metal transition. Second, the increase in the longitudinal modulus in the liquid upon supercooling is consistent with an increase in the degree of the directional bonding. 相似文献
4.
Misharin AS Moskovets E Gamage CM Doroshenko VM Vilkov AN 《Rapid communications in mass spectrometry : RCM》2008,22(8):1175-1180
This study presents the first practical demonstration of an operational tripole ion guide. The transmission was measured for both the tripole and quadrupole ion guides at 1 Torr pressure. It was found that the quadrupole provides 2.5-3 times better ion transmission efficiency. Two different electric schemes for driving the tripole were tested. Similar transmission characteristics were obtained in both cases. A brief analysis of the tripole performance and ways to improve it is presented. 相似文献
5.
Sung Hwan Yoon Chaminda M. Gamage Kent J. Gillig Vicki H. Wysocki 《Journal of the American Society for Mass Spectrometry》2009,20(6):957-964
The implementation of surface-induced dissociation (SID) to study the fast dissociation kinetics (sub-microsecond dissociation)
of peptides in a MALDI TOF instrument has been reported previously. Silicon nanoparticle assisted laser desorption/ionization
(SPALDI) now allows the study of small molecule dissociation kinetics for ions formed with low initial source internal energy
and without MALDI matrix interference. The dissociation kinetics of N(CH3)4+ and N(CD3)4+ were chosen for investigation because the dissociation mechanisms of N(CH3)4+ have been studied extensively, providing well-characterized systems to investigate by collision with a surface. With changes
in laboratory collision energy, changes in fragmentation timescale and dominant fragment ions were observed, verifying that
these ions dissociate via unimolecular decay. At lower collision energies, methyl radical (CH3) loss with a sub-microsecond dissociation rate is dominant, but consecutive H loss after CH3 loss becomes dominant at higher collision energies. These observations are consistent with the known dissociation pathways.
The dissociation rate of CH3 loss from N(CH3)4+ formed by SPALDI and dissociated by an SID lab collision energy of 15 eV corresponds to log k = 8.1, a value achieved by
laser desorption ionization (LDI) and SID at 5 eV. The results obtained with SPALDI SID and LDI SID confirm that (1) the dissociation
follows unimolecular decay as predicted by RRKM calculations; (2) the SPALDI process deposits less initial energy than LDI,
which has advantages for kinetics studies; and (3) fluorinated self-assembled monolayers convert about 18% of laboratory collision
energy into internal energy. SID TOF experiments combined with SPALDI and peak shape analysis enable the measurement of dissociation
rates for fast dissociation of small molecules. 相似文献
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8.
Mulders N West JT Chan MH Kodituwakku CN Burns CA Lurio LB 《Physical review letters》2008,101(16):165303
X-ray diffraction experiments show that solid 4He grown in aerogel is highly polycrystalline, with an hcp crystal structure (as in bulk) and a crystallite size of approximately 100 nm. In contrast to the expectation that the highly disordered solid will have a large supersolid fraction, torsional oscillator measurements show a behavior that is strikingly similar to high purity crystals grown from the superfluid phase. The low temperature supersolid fraction is only approximately 3 x 10(-4), and the onset temperature is approximately 100 mK. 相似文献
9.
Vilkov AN Gamage CM Misharin AS Doroshenko VM Tolmachev DA Tarasova IA Kharybin ON Novoselov KP Gorshkov MV 《Journal of the American Society for Mass Spectrometry》2007,18(8):1552-1558
A new Fourier transform ion cyclotron resonance mass spectrometer based on a permanent magnet with an atmospheric pressure ionization source was designed and constructed. A mass resolving power (full-width-at-half-maximum) of up to 80,000 in the electron ionization mode and 25,000 in the electrospray mode was obtained. Also, a mass measurement accuracy at low-ppm level has been demonstrated for peptide mixtures in a mass range of up to 1200 m/z in the isotopically resolved mass spectra. 相似文献
10.
J. P. Hill D. S. Coburn Y.‐J. Kim T. Gog D. M. Casa C. N. Kodituwakku H. Sinn 《Journal of synchrotron radiation》2007,14(4):361-365
The design and commissioning of an inelastic X‐ray scattering instrument at CMC‐XOR at the Advanced Photon Source is reported. The instrument features a 2 m vertical‐scattering arm with a novel counterweight design to reduce the twisting moment as the arm is moved in the scattering plane. A Ge(733) spherical analyzer was fabricated and an overall resolution of 118 meV (FWHM) was obtained with a Si(444) monochromator and a Si(111) pre‐monochromator. Early results from a representative cuprate, La2CuO4, are reported. 相似文献