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941.
Clara C.S. Sousa M. Agostinha R. Matos Victor M.F. Morais 《The Journal of chemical thermodynamics》2009,41(12):1408-1412
In this work, we have determined the experimental standard (p° = 0.1 MPa) molar enthalpies of formation, in gas phase, of flavone and flavanone.These results were obtained by combining the standard molar enthalpies of formation in the condensed phase with the standard molar enthalpies of sublimation. The former values were derived from combustion experiments in oxygen, at T = 298.15 K, in a static bomb calorimeter. The values of the standard molar enthalpies of sublimation were obtained by Calvet microcalorimetry and corrected to T = 298.15 K.High-level density functional theory calculations using the B3LYP hybrid exchange–correlation energy functional with extended basis sets and more accurate correlated computational techniques of the MCCM/3 suite have been performed for the compounds.The obtained results, experimental and computational, for flavone and flavanone were compared with those obtained for chromone and chromanone, respectively. 相似文献
942.
M. Agostinha R. Matos Clara C.S. Sousa Victor M.F. Morais 《The Journal of chemical thermodynamics》2009,41(1):69-73
The standard (p° = 0.1 MPa) molar energies of combustion in oxygen, at T = 298.15 K, of 5-, 6- and 7-methoxy-α-tetralone were measured by static bomb calorimetry. The values of the standard molar enthalpies of sublimation were obtained by Calvet microcalorimetry and corrected to T = 298.15 K. Combining these results, the standard molar enthalpies of formation of the compounds, in the gas phase, at T = 298.15 K, have been calculated, 5-methoxy-α-tetralone -(244.8 ± 1.9) kJ · mol?1, 6-methoxy-α-tetralone ?(243.0 ± 2.8) kJ · mol?1 and 7-methoxy-α-tetralone ?(242.3 ± 2.6) kJ · mol?1.Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange–correlation energy functional with extended basis sets and more accurate correlated computational techniques of the MCCM/3 suite have been performed for the compounds. The agreement between experiment and theory gives confidence to estimate the enthalpy of formation of 8-methoxy-α-tetralone. Similar calculations were done for the 5-, 6-, 7- and 8-methoxy-β-tetralone, for which experimental work was not done. 相似文献
943.
944.
Victor Ryzhov Adrian K. Y. Lam Richard A. J. O’Hair 《Journal of the American Society for Mass Spectrometry》2009,20(6):985-995
In this work, we describe two different methods for generating protonated S-nitrosocysteine in the gas phase. The first method
involves a gas-phase reaction of protonated cysteine with t-butylnitrite, while the second method uses a solution-based transnitrosylation reaction of cysteine with S-nitrosoglutathione
followed by transfer of the resulting S-nitrosocysteine into the gas phase by electrospray ionization mass spectrometry (ESI-MS).
Independent of the way it was formed, protonated S-nitrosocysteine readily fragments via bond homolysis to form a long-lived
radical cation of cysteine (Cys•+), which fragments under collision-induced dissociation (CID) conditions via losses in the following relative abundance order:
•COOH ≫ CH2S > •CH2SH-H2S. Deuterium labeling experiments were performed to study the mechanisms leading to these pathways. DFT calculations were
also used to probe aspects of the fragmentation of protonated S-nitrosocysteine and the radical cation of cysteine. NO loss
is found to be the lowest energy channel for the former ion, while the initially formed distonic Cys•+ with a sulfur radical site undergoes proton and/or H atom transfer reactions that precede the losses of CH2S, •COOH, •CH2SH, and H2S. 相似文献
945.
Victor A. Mikhailov Helen J. Cooper 《Journal of the American Society for Mass Spectrometry》2009,20(5):763-771
Here, we show that to perform activated ion electron capture dissociation (AI-ECD) in a Fourier transform ion cyclotron resonance
(FT-ICR) mass spectrometer equipped with a CO2 laser, it is necessary to synchronize both infrared irradiation and electron capture dissociation with ion magnetron motion.
This requirement is essential for instruments in which the infrared laser is angled off-axis, such as the Thermo Finnigan
LTQ FT. Generally, the electron irradiation time required for proteins is much shorter (ms) than that required for peptides
(tens of ms), and the modulation of ECD, AI ECD, and infrared multiphoton dissociation (IRMPD) with ion magnetron motion is
more pronounced. We have optimized AI ECD for ubiquitin, cytochrome c, and myoglobin; however the results can be extended to other proteins. We demonstrate that pre-ECD and post-ECD activation
are physically different and display different kinetics. We also demonstrate how, by use of appropriate AI ECD time sequences
and normalization, the kinetics of protein gas-phase refolding can be deconvoluted from the diffusion of the ion cloud and
measured on the time scale longer than the period of ion magnetron motion. 相似文献
946.
Jeong‐Myeong Ha Victor Young 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(8):o388-o395
Four crystal structure determinations of 2,2,3,3,4,4‐hexafluoropentane‐1,5‐diol (HFPD), C5H6F6O2, were conducted on a single specimen by varying the temperature. Two polymorphs of HFPD were found to be enantiotropically related as phases (I) and (II), both in the space group P1. These structures contain closely related R44(20) sheets. A structure determination was completed on form (Ia) at 283 K. Form (Ia) was then supercooled below the phase transition temperature at 279 to 173 K to give form (Ib) for a second structure determination. Metastable form (Ib) was transformed by momentary warming and recooling to give form (II) for a third structure determination at 173 K. Form (II) transformed to form (Ic) upon warming to 283 K. Enantiotropic phase transitions between phases (I) and (II) were confirmed with X‐ray powder diffraction and differential scanning calorimetry. Form (Ia) was found as a twin by nonmerohedry by a reflection in (011). This twinning persists in all phases described. Additional twinning was found after the phase (I) to phase (II) transformation. These two additional twin components are related to the first pair by a 180° rotation about the (012) plane. This latter pair of twins persisted as the specimen was warmed back to form (Ic) at 283 K. 相似文献
947.
Paul Tongwa Tiffany L. Kinnibrugh Geetha R. Kicchaiahgari Victor N. Khrustalev Tatiana V. Timofeeva 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(4):o155-o159
The molecules of the title compounds, C16H15NOS2, (I), and C16H13Br2NOS2, (II), are E,E‐isomers and consist of an extensive conjugated system, which determines their molecular geometries. Compound (I) crystallizes in the monoclinic space group P21/c. It has one thiophene ring disordered over two positions, with a minor component contribution of 0.100 (3). Compound (II) crystallizes in the noncentrosymmetric orthorhombic space group Pca21 with two independent molecules in the unit cell. These molecules are related by a noncrystallographic pseudo‐inversion center and possess very similar geometries. The crystal packings of (I) and (II) have a topologically common structural motif, viz. stacks along the b axis, in which the molecules are bound by weak C—H...O hydrogen bonds. The noncentrosymmetric packing of (II) is governed by attractive intermolecular Br...Br and Br...N interactions, which are also responsible for the very high density of (II) (1.861 Mg m−3). 相似文献
948.
We introduce the formalism of differential conformal superalgebras, which we show leads to the “correct” automorphism group functor and accompanying descent theory in the conformal setting. As an application, we classify forms of N=2 and N=4 conformal superalgebras by means of Galois cohomology. 相似文献
949.
950.
Optimal location with equitable loads 总被引:1,自引:0,他引:1
Oded Berman Zvi Drezner Arie Tamir George O. Wesolowsky 《Annals of Operations Research》2009,167(1):307-325
The problem considered in this paper is to find p locations for p facilities such that the weights attracted to each facility will be as close as possible to one another. We model this problem
as minimizing the maximum among all the total weights attracted to the various facilities. We propose solution procedures
for the problem on a network, and for the special cases of the problem on a tree or on a path. The complexity of the problem
is analyzed, O(n) algorithms and an O(pn
3) dynamic programming algorithm are proposed for the problem on a path respectively for p=2 and p>2 facilities. Heuristic algorithms (two types of a steepest descent approach and tabu search) are proposed for its solution.
Extensive computational results are presented. 相似文献