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1.
Gabriela Ionita Petre Ionita Victor EM. Sahini Constantin Luca 《Journal of inclusion phenomena and macrocyclic chemistry》2001,39(3-4):269-271
The kinetics of oxidation of amino acids (Arg, His, Lys, Phe, Thr and Tyr), a dipeptide (Gly-His), and BSA (bovine serum albumin) by two persistent water soluble free radicals of the hydrazyl type has been studied.The rate decreases in the order Arg>Lys>Tyr>Thr>HisBSAPheGly-His with bothfree radicals. Addition to the reaction mixture of - and -cyclodextrin decreases the oxidation rate, probably due to amino acidencapsulation in the cyclodextrin cavity. -Cyclodextrin protects more efficiently against oxidation than -cyclodextrin. 相似文献
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We have used a variety of microscopic techniques to reveal the structure and motion of flux line arrangements, when the flux
lines in low T
c type II superconductors are caused to move by a transport current. Using small-angle neutron scattering by the flux line
lattice (FLL), we are able to demonstrate directly the alignment by motion of the nearest-neighbor FLL direction. This tends
to be parallel to the direction of flux line motion, as had been suspected from two-dimensional simulations. We also see the
destruction of the ordered FLL by plastic flow and the bending of flux lines. Another technique that our collaboration has
employed is the direct measurement of flux line motion, using the ultra-high-resolution spectroscopy of the neutron spin-echo
technique to observe the energy change of neutrons diffracted by moving flux lines. The muon spin rotation (μSR) technique gives the distribution of values of magnetic field within the FLL. We have recently succeeded in performing
μSR measurements while the FLL is moving. Such measurements give complementary information about the local speed and orientation
of the FLL motion. We conclude by discussing the possible application of this technique to thin film superconductors. 相似文献
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Two-photon sequential absorption spectroscopy has been used to selectively excite rotational structure in the B---X absorption transition of the 129I2 molecule up to within 2 cm−1 of the dissociation limit. Vibrational and rotational constants have been obtained for the B state levels with υ = 71–79. Le Roy's equations for long-range behaviour are expressed in mass-reduced form, and it is shown that these equations can be successfully used to combine the spectroscopic constants for 127I2 and 129I2 to give improved values of the long range constants for the B state. The improved values are only slightly different from those previously obtained by the same technique for 127I2 alone. 相似文献
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Aruna B. Wijeratne Sandra E. Spencer Jose Gracia Daniel W. Armstrong Kevin A. Schug 《Journal of the American Society for Mass Spectrometry》2009,20(11):2100-2105
The negative ion mode ESI mass spectral analysis of antimony(III)-D- and -L-tartrate (“tartar emetic”), in association with leucine enantiomeric isotopomers, revealed remarkable proton-assisted enantioselective
molecular recognition phenomena. The current study infers that recognition of amino acids by antimony(III)-D,L-tartrate complexes requires that the chiral selector associate a proton to become enantioselective. The dianionic selector
itself failed to show enantiomeric discrimination capacity. This observation was shown to be consistent both in solution-phase
targeting full scan and gas-phase targeting collision threshold dissociation (CTD) experiments. Importantly, this disparity
in enantioselective binding capacity between the dianionic and the protonated monoanionic representatives of antimony(III)-D- and-L-tartrates could only be clearly revealed by ESI-MS and tandem mass spectrometry experiments as described herein. This finding
urges a more in-depth study of mechanisms associated with exhibited enantiomeric resolving capacity of antimony tartrates
in HPLC and CE applications, as well as in former ESI-MS association studies. 相似文献
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E. M. Kithsiri Wijeratne 《Tetrahedron》2006,62(36):8439-8446
Five new isocoumarins, paraphaeosphaerins A-C and chaetochiversins A and B, biogenetically related to monocillin I and radicicol, have been isolated from solid agar cultures of Paraphaeosphaeria quadriseptata and Chaetomium chiversii, two fungal strains living in association with the Sonoran desert plants, Opuntia leptocaulis and Ephedra fasciculata, respectively. A new chroman-4-one, aposphaerin C, was also isolated from P. quadriseptata. Their structures and stereochemistry were elucidated using a combination of 1H and 13C homo- and hetero-nuclear 2D NMR techniques, 1H NMR analysis of Mosher's esters, and chemical correlations. 相似文献
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KM Clauwaert Van Bocxlaer JF HJ Major JA Claereboudt WE Lambert Van den Eeckhout EM Van Peteghem CH De Leenheer AP 《Rapid communications in mass spectrometry : RCM》1999,13(14):1540-1545
This paper describes the investigation of the potential of a quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOF) equipped with an atmospheric pressure ionisation interface for quantitative measurements of small molecules separated by reversed phase liquid chromatography. To this end, the detection limits and linear dynamic range in particular were studied in an LC/MS/MS experiment using 3,4-methylenedioxymethamphetamine standards and 3,4-methylenedioxyethylamphetamine for internal standardisation. In a second phase, the experiment was repeated with real biological extracts (whole blood, serum, and vitreous humour). A calibration for 3,4-methylenedioxymethamphetamine and its metabolite 3,4-methylenedioxyamphetamine was prepared in each of these matrices again using 3,4-methylenedioxyethylamphetamine as internal standard. The resulting quantitative data were compared with those obtained by liquid chromatography with fluorescence detection for the same extracts. The Q-TOF results revealed excellent sensitivity and a linear dynamic range of nearly four decades (2-10 000 pg on-column, r(2) = 0.9998, 1/x weighting). Furthermore, all the calibration curves prepared in biological material were superimposable, LC/MS/MS and LC-fluorescence, and the quantitative results for actual samples compared very favourably. It was concluded that the Q-TOF achieves a linear dynamic range for quantitative LC/MS/MS work exceeding that of fluorescence detection and at much better absolute sensitivity. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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The open-shell benzoylnitrene radical anion, readily generated by electron ionization of benzoylazide, undergoes unique chemical reactivity with radical reagents and Lewis acids in the gas phase. Reaction with nitric oxide, NO, proceeds by loss of N2 and formation of benzoate ion. This novel reaction is also observed to occur with phenylnitrene anion, forming phenoxide. Similar reactivity was observed in the reaction between benzoylnitrene radical anion and NO2, forming benzoate ion and nitrous oxide. Electronic structure calculations indicate that the reaction has a high-energy barrier that is overcome by the energy released by bond formation. Benzoylnitrene radical anion also transfers oxygen anion to NO and NO2 as well as to CS2 and SO2. In contrast, phenylnitrene anion reacts with carbon disulfide by C+ or CS+ abstraction, forming S- or S2-. Electronic structure calculations indicate that benzoylnitrene in the ground state resembles a slightly polarized benzoate anion, but with a free radical localized on the nitrogen. 相似文献
10.
The thermochemical properties of benzoylnitrene radical anion, C6H5CON-, were determined by using a combination of energy-resolved collision-induced dissociation (CID) and proton affinity bracketing. Benzoylnitrene radical anion dissociates upon CID to give NCO- and phenyl radical with a dissociation enthalpy of 0.85 +/- 0.09 eV, which is used to derive an enthalpy of formation of 33 +/- 9 kJ/mol for the nitrene radical anion. Bracketing studies with the anion indicate a proton affinity of 1453 +/- 10 kJ/mol, indicating that the acidity of benzamidyl radical, C6H5CONH, is between those of benzamide and benzoic acid. Combining the measurements gives an enthalpy of formation for benzamidyl radical of 110 +/- 14 kJ/mol and a homolytic N-H bond dissociation energy in benzamide of 429 +/- 14 kJ/mol. Additional thermochemical properties obtained include the electron affinity of benzamidyl radical, the hydrogen atom affinity of benzoylnitrene radical anion, and the oxygen anion affinity of benzonitrile. 相似文献