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101.
Chitta RK Rempel DL Gross ML 《Journal of the American Society for Mass Spectrometry》2005,16(7):1031-1038
The dimerization of gramicidin, a 15-residue membrane peptide, in solution can be viewed as a model for protein-protein interactions. We reported previously that the dimer can be observed when electrosprayed from organic solvents and that the abundances of the dimer depends on the dielectric constant of the solvent. Here, we report an effort to determine an affinity constant for the dimerization of gramicidin by using gas-phase abundance. Two issues affecting the determination are the electrospray-induced dissociation of the dimer and discrimination in the electrospray of the dimer compared with the monomer. Other methods developed for the purpose of determining affinity from mass spectral abundance do not address the dissociation of the complex in the gas phase or can not be applied for cases of low affinity constant, K(a). We present a mathematical model that uses the ratio of the signal intensities of the dimer and the monomer during a titration. The model also incorporates the dissociation and an electrospray ionization-response factor of the dimer for extracting the affinity constant for the dimerization of gramicidin. The dimerization constants from the new method agree within a factor of two with values reported in the literature. 相似文献
102.
Gómez-Carrasco S González-Snchez L Aguado A Roncero O Alvariño JM Hernández ML Paniagua M 《The Journal of chemical physics》2004,121(10):4605-4618
A theoretical study of the F(2P) + OH(2Pi) --> HF(1Sigma+) + O(3P) reactive collisions is carried out on a new global potential energy surface (PES) of the ground 3A" adiabatic electronic state. The ab initio calculations are based on multireference configuration interaction calculations, using the aug-cc-pVTZ extended basis sets of Dunning et al. A functional representation of the PES shows no nominal barrier to reaction, contrary to previous results by others. Wave packet and quasiclassical trajectory calculations have been performed for this PES to study the F + OH(v = 0,j) reactive collision. The comparison was performed at fixed and constant values of the total angular momentum from 0 to 110 and relative translational energy up to 0.8 eV. The reaction presents a dynamical barrier, essentially due to the zero-point energy for the bending vibration near the saddle point. This determines two different reaction mechanisms. At energies higher than approximately 0.125 eV the reaction is direct, while below that value it is indirect and mediated by heavy-light-heavy resonances. Such resonances, also found in the simulations of the photodetachment spectrum of the triatomic anion, manifest themselves in the quasiclassical simulations, too, where they are associated to periodic orbits. 相似文献
103.
104.
T. ?kesson S. Almehed A. L. S. Angelis H. Atherton P. Aubry H. W. Bartels G. Beaudoin J. M. Beaulieu H. Beker O. Benary et al. 《Zeitschrift fur Physik C Particles and Fields》1991,49(3):355-366
Diffractive dissociation of nuclei (Be, Al, W) in collisions with 450 GeV/c protons,pApX, has been measured with the HELIOS spectrometer at the CERN Super Proton synchrotron. The dependence of the single-diffraction cross-section on the nuclear massA can be parametrized as SD mb×A
0.35±0.02, showing the peripheral nature of the process. The differential cross-section dSD=(3.8±0.3)mb ×A
0.35±0.02, is exponential with the slope parameter, increasing from 6.2±0.4 (GeV/c)–2 for beryllium to 7.9±0.5 (GeV/c)–2 for tungsten. The slope parameter also increases with increasing massM
X
of the diffractively produced state. The rapidity, multiplicity, and transverse-momentum distributions of the particles of the diffractively produced stateX show a longitudinal phase-space population and are remarkably insensitive to the nuclear mass. This, together with theA
1/3 dependence of SD, suggests that the dominant process of nuclear diffractive excitation is the dissociation of single nucleons.Deceased 相似文献
105.
A selective procedure is described for the determination of amitriptyline in plasma. The method involves extraction, separation of amitriptyline from its metabolites and subsequent oxidation by ceric sulphate in 5.4 M sulphuric acid. The oxidation product, anthraquinone, is determined by means of electron-capture gas chromatography. The metabolites were separated by a column chromatographic extraction technique. The choice of oxidation reagent, optimum conditions for the oxidation, and the electron-capture properties of anthraquinone are discussed. The method can be used to determine down to 2 ng of amitriptyline in a plasma sample; the relative standard deviation at the 50-ng level was 4.0% (n = 8). The levels of amitriptyline found in a series of plasma samples are compared with those obtained by gas chromatography with use of nitrogen-specific detection; the two techniques gave coincident results. 相似文献
106.
A cylindrical chemosorptive denuder in series with a glass fibre filter has been evaluated for sampling toluene diisocyanate (TDI) aerosols. The sampler is designed for measuring personal exposure to diisocyanates. Several denuder coatings and derivatising reagents were investigated. Dimethylpolysiloxane (SE-30) and 5% phenyl dimethylpolysiloxane (SE-54) with either dibutylamine (DBA) or dipentylamine (DPeA) as derivatising reagents yielded the lowest vapour breakthrough (the amount (%) of the vapour that passes through the denuder), close to values predicted by theory. Immobilisation of the SE-30 denuder coating by in-situ cross-linking yielded comparable results. With an SE-30/DBA-coated denuder operating within an airflow range of 100–500 mL min–1, the phase separation was shown to be consistent with theoretical predictions derived by use of the Gormley–Kennedy equation. This provides a means of calculating the vapour breakthrough and correcting experimentally obtained values with regard to vapour–particulate phase distribution, suggesting that the denuder can provide accurate phase-distribution measurements. The SE-30/DBA denuder can be used over a concentration range spanning nearly six orders of magnitude. Its capacity is sufficient to perform 15-min exposure measurements of a TDI aerosol with air concentrations as high as 1,700 g m–3, 40 times higher than the Swedish occupational exposure limit (OEL). At the other end of the range, the estimated limit of detection (LOD) was less than 2 ng m–3 for both the vapour and the aerosol phases when LC–ESI–MS–MS was used for chemical analysis.Electronic Supplementary Material Supplementary material for this article is available at 相似文献
107.
Summary Atmospheric precipitation and aerosol samples are characterized by a complex mixture of several organic compounds. A simple method for the simultaneous determination of the main compound classes by GC/MS is presented. In detail, seasonal variations of C8–C32 fatty acids in precipitation in a semirural area have been studied. Total fatty acids concentrations of 7–53 g/l were detected. Summer rain is characterized by high amounts of fatty acids >C20 and lower amounts of C11–C20 species. Two effects may be responsible: larger emission rates of fatty acids during vegetation periods and an increased influence of vapour phase due to higher temperatures during summer. CPI values showed no general trend; lower CPI values for winter rain could not be observed. This would be expected if anthropogenic sources play an important role. Monounsaturated fatty acids (C16:1, C18:1) were more abundant during winter than in summer. High concentrations of polyunsaturated fatty acids (C18:x) could be detected during summer. High relative concentrations of the potential oxidation products of the unsaturated species, nonanedioic acid and w-oxononanoic acid, are associated with relatively low concentrations of their precursors. 相似文献
108.
H. Spieler H. J. K?rner K. E. Rehm M. Richter H. P. Rother 《Zeitschrift für Physik A Hadrons and Nuclei》1976,53(5):241-250
The reactions120Sn+72 MeV18O and122Sn+74 MeV16O were investigated with time of-flightE-E-telescopes. Data are presented for all quasi-elastic reaction channels. The two neutron stripping and pickup reactions (18O,16O), (18O,20O) and (16O,18O) are analyzed in detail. It is shown that these heavy ion induced two neutron transfer reactions proceed with essentially the same type of selectivity as the corresponding light ion induced reactions. The differential cross sections for transfer reactions leaving the120, 122Sn nuclei in their 2+ first excited states are shown to be influenced by interference effects due to additional inelastic excitations. 相似文献
109.
I. Tserruya R. Schulé H. Schmidt-B?cking K. Bethge 《Zeitschrift für Physik A Hadrons and Nuclei》1976,89(1):233-241
TheK-shell ionization cross sections of Mn, Ni, Cu, Zn and Ge under32S bombardment have been measured in the energy range from 5 to 48 MeV. The cross sections are compared with available theories based on a direct Coulomb ionization mechanism and with the predictions of theK-vacancy sharing process. This last process can reasonably account for the measured cross sections at high bombarding energies. The energy shifts of theK
- andK
-lines and theK
/K
-intensity ratios have also been measured. This information is used to deduce the defect configuration of the atoms. The mechanisms responsible for the multiple vacancy production are discussed. 相似文献
110.
Wax obtained from the pyrolysis of polyethylene waste can contain inorganic contaminants and must be purified before application.We evaluated different filter aids(perlite,sand,and rice husk ash)for the filtration of a crude wax and a pyrolysis wax through a filter medium that was coated with nylon 6 nanofibers to improve filtration efficiency.We first examined the performance of the filter aids in improving crude wax filtration,with the filtration time,temperature,and pressure held constant at 1 h,170℃,and 2.5 bar,respectively.Oily wax was then produced by pyrolysis of high-density polyethylene(HDPE)waste in the temperature range 425-475℃.The best filter aid was perlite,which had a filtrate production rate of 5.47×10-5m3/h.The highest oily wax yield(87.8%)was achieved at a pyrolysis temperature of 425℃.The assembly comprising the filter medium coated with nylon 6 nanofibers plus perlite as a filter aid was most suitable for removing impurities from the oily wax generated by the HDPE pyrolysis as it achieved a purification efficiency of 99.9%. 相似文献