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Ákos Kuki Ghazaleh Shemirani Lajos Nagy Borbála Antal Miklós Zsuga Sándor Kéki 《Journal of the American Society for Mass Spectrometry》2013,24(7):1064-1071
A simple collision model for multiple collisions occurring in quadrupole type mass spectrometers was derived and tested with leucine enkaphalin a common mass spectrometric standard with well-characterized properties. Implementation of the collision model and Rice-Ramsperger-Kassel-Marcus (RRKM) algorithm into a spreadsheet software allowed a good fitting of the calculated data to the experimental survival yield (SY) versus collision energy curve. In addition, fitting also ensured to estimate the efficiencies of the kinetic to internal energy conversion for Leucine enkephalin in quadrupole-time-of-flight and triple quadrupole instruments. It was observed that the experimental SY versus collision energy curves for the leucine enkephalin can be described by the Rice-Ramsperger-Kassel (RRK) formalism by reducing the total degrees of freedom (DOF) to about one-fifth. Furthermore, this collision model with the RRK formalism was used to estimate the critical energy (E o ) of lithiated polyethers, including polyethylene glycol (PEG), polypropylene glycol (PPG), and polytetrahydrofurane (PTHF) with degrees of freedom similar to that of leucine enkephalin. Applying polyethers with similar DOF provided the elimination of the effect of DOF on the unimolecular reaction rate constant. The estimated value of E o for PEG showed a relatively good agreement with the value calculated by high-level quantum chemical calculations reported in the literature. Interestingly, it was also found that the E o values for the studied polyethers were similar. Figure
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Ákos Kuki Miklós Nagy Lajos Nagy Miklós Zsuga Sándor Kéki 《Journal of the American Society for Mass Spectrometry》2010,21(9):1561-1564
The complex formation in solution, and the gas-phase dissociation of a phenanthrolineterminated poly(ethylene glycol) with
Fe2+ ions were investigated. The size distribution of poly(ethylene glycol)-α-monomethyl-ω-5-[1,10]phenanthroline (mPEG_phen)
was determined by electrospray ionization mass spectrometry (ESI-MS). Based on the measured ligand size distribution of mPEG_phen
by ESI-MS, the 1:3 complex formation (Fe2+/mPEG_Phen) was computer-simulated as a pure random assembly process. The simulated distribution fits excellently to that
of the complex Fe(mPEG_phen)32+ determined from the ESI-MS intensities. In addition, the collision-induced dissociation (CID) of the Fe(mPEG_phen)32+ complex was also studied by tandem mass spectrometry (ESI-MS/MS) and by computer simulation, as well. The ESI-MS/MS intensity
distribution of the Fe(mPEG_phen)22+ formed from Fe(mPEG_phen)32+ by the loss of an mPEG_phen ligand under CID conditions fits quite well to the calculated one. 相似文献
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Direct analysis in real time mass spectrometry (DART‐MS) of highly non‐polar low molecular weight polyisobutylenes
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Lajos Nagy Tibor Nagy György Deák Ákos Kuki Borbála Antal Miklós Zsuga Sándor Kéki 《Journal of mass spectrometry : JMS》2015,50(9):1071-1078
Low molecular weight polyisobutylenes (PIB) with chlorine, olefin and succinic acid end‐groups were studied using direct analysis in real time mass spectrometry (DART‐MS). To facilitate the adduct ion formation under DART conditions, NH4Cl as an auxiliary reagent was deposited onto the PIB surface. It was found that chlorinated adduct ions of olefin and chlorine telechelic PIBs, i.e. [M + Cl]? up to m/z 1100, and the deprotonated polyisobutylene succinic acid [M? H]? were formed as observed in the negative ion mode. In the positive ion mode formation of [M + NH4]+, adduct ions were detected. In the tandem mass (MS/MS) spectra of [M + Cl]?, product ions were absent, suggesting a simple dissociation of the precursor [M + Cl]? into a Cl? ion and a neutral M without fragmentation of the PIB backbones. However, structurally important product ions were produced from the corresponding [M + NH4]+ ions, allowing us to obtain valuable information on the arm‐length distributions of the PIBs containing aromatic initiator moiety. In addition, a model was developed to interpret the oligomer distributions and the number average molecular weights observed in DART‐MS for PIBs and other polymers of low molecular weight. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Sambasivarao Kotha Enugurthi BrahmacharyAtsuo Kuki Kamil Lang Demetrios AnglosBakthan SingaramWilliam Chrisman 《Tetrahedron letters》1997,38(52):4290
A novel constrained 7-amino-6,7-dihydro-8H-cyclopenta[g]quinoxaline-7-carboxylic acid derivative was prepared starting from 4,5-dimethyl-o-phenylenediamine. 相似文献
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Combinatorial approaches together with high-throughput screening have been used to develop highly selective stationary phases for chiral recognition. Libraries of potential chiral selectors have been prepared by the Ugi multicomponent condensation reactions and screened for their enantioselectivity using the reciprocal approach involving a chiral stationary phase with immobilized model target compound N-(3,5-dinitrobenzoyl)-alpha-l-leucine. The best candidates were identified from the library of phenyl amides of 2-oxo-azetidineacetic acid derivatives. This screening also enabled specification of the functionalities of the selector desired to achieve the highest level of chiral recognition. The substituents of the phenyl ring adjacent to the chiral center of the selector candidates exhibited the most profound effect on the chiral recognition. The best candidate was then synthesized on a larger scale, resolved into single enantiomers using preparative enantioselective HPLC, and attached to porous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) beads via an ester linkage to afford the desired stationary phase. Selectivities alpha as high as 3.2 were found for the separation of a variety of amino acid derivatives. 相似文献
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Formation of star‐shaped nanomicelles of polyisobutylene‐polystyrene (PIB‐PS) diblock copolymers in hexane solution is reported. The length of the polystyrene segments were varied in the Mn range of 4000‐13000 g/mol at approximately constant polyisobutylene segments length. The size and the size distribution of the nanomicelles were investigated by dynamic light scattering. Based on static light scattering measurements the mass‐average molecular mass of the micelles and the number of arms were also determined. The synthesized diblock‐copolymers were demonstrated to be capable of stabilizing the growing particles which were formed in the living anionic dispersion polymerization of styrene in hexane. 相似文献
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Singlet Excited States and the Light-Harvesting Function of Carotenoids in Bacterial Photosynthesis 总被引:3,自引:0,他引:3
Yasushi Koyama Michitaka Kuki Per Ola Andersson Tomas Gillbro 《Photochemistry and photobiology》1996,63(3):243-256
Abstract— The recent results of stationary-state and time-resolved absorption, fluorescence and Raman spectroscopies of some typical carotenoids are summarized. Theoretical analyses of carotenoid singlet states and of carotenoid-to-bacteriochlorophyll singlet-energy transfer are also included. On the bases of the energies, the lifetimes and other properties of singlet excited states of the carotenoids in solution and bound to the light-harvesting complexes, the energetics and the dynamics of the light-harvesting function in purple photosynthetic bacteria are discussed with emphasis on the 2Ag and Bu + states. 相似文献
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E. Kuki Y. Nakano O. Takayasu T. Takeuchi 《Journal of Radioanalytical and Nuclear Chemistry》1977,36(1):185-193
The detection of tritium and14C-ethylene on the surface of nickel sheet was carried out by means of autoradiography. Two autoradiographical methods were
used, the ordinary stripping-film method and the electron-microscope autoradiographical method. The ordinary autoradiographs
indicated that14C-ethylene accumulates at scratches on the surface of the sheet; however, tritium accumulates at grain boundaries and scratches.
Electron-microscope autoradiographs indicated that tritium accumulates on the step-edges of slip band of nickel. 相似文献