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91.
Guchhait N Banerjee S Chakraborty A Nath D Patwari Naresh G Chowdhury M 《The Journal of chemical physics》2004,120(20):9514-9523
The hydrated clusters of tetrahydroisoquinoline have been investigated by laser-induced fluorescence (LIF), UV-UV hole burning, and IR-UV double-resonance spectroscopy in a seeded supersonic jet. Clusters of different sizes and isomeric structures have different 0-0 transitions (origins) in the LIF spectrum. UV-UV hole burning spectroscopy has been used to identify different cluster species and their vibrational modes. The structures of the clusters have been predicted by comparing the observed OH and NH frequencies in the IR-UV double-resonance spectra with the results calculated at different levels of sophistication. It is found that the water molecules form linear and six- and eight-membered cyclic H-bonded structures at the nitrogen center of 1:1, 1:2, and 1:3 clusters, respectively. 相似文献
92.
Nellutla S van Tol J Dalal NS Bi LH Kortz U Keita B Nadjo L Khitrov GA Marshall AG 《Inorganic chemistry》2005,44(26):9795-9806
The dimeric, pentacopper(II)-substituted tungstosilicate [Cu(5)(OH)(4)(H(2)O)(2)(A-alpha-SiW(9)O(33))(2)](10)(-) (1) has been characterized by single-crystal X-ray diffraction, elemental analysis, IR, electrochemistry, magnetic measurements, electron paramagnetic resonance (EPR), and mass spectrometry (MS). Magnetization and high-field EPR measurements reveal that the pentameric copper core {Cu(5)(OH)(4)(H(2)O)(2)}(6+) of 1 exhibits strong antiferromagnetic interactions (J(a) = -51 +/- 6 cm(-)(1), J(b) = -104 +/- 1 cm(-)(1), and J(c) = -55 +/- 3 cm(-)(1)) resulting in a spin S(T) = (1)/(2) ground state. EPR data show that the unpaired electron spin density is localized on the spin-frustrated apical Cu(2+) ion with g(zz) = 2.4073 +/- 0.0005, g(yy) = 2.0672 +/- 0.0005, g(xx) = 2.0240 +/- 0.0005, and A(zz) = -340 +/- 20 MHz (-0.0113 cm(-)(1)). 1 can therefore be considered as a model system for a five-spin, electronically coupled, spin-frustrated system. Polyanion 1, which is stable over a wide pH domain (pH 1-7), was characterized by cyclic voltammetry (CV) in a pH 5 medium. Its CV was constituted by an initial two-step reduction of the Cu(2+) centers to Cu(0) through Cu(+), followed at more negative potential by the redox processes of the W centers. Controlled potential coulometry of 1 allows for the reduction of the five Cu(2+) centers, as seen by consumption of 10.05 +/- 0.05 electrons per molecule. Polyanion 1 triggers efficiently the electrocatalytic reduction of nitrate and nitrite, and it also catalyzes the reduction of N(2)O. To our knowledge, this is the first example of N(2)O catalytic reduction by a polyoxoanion. Fourier transform ion cyclotron resonance MS was used to unambiguously assign the molecular weight of the solution-phase species 1 and the oxidation states of the Cu atoms in the central {Cu(5)(OH)(4)(H(2)O)(2)}(6+) core. Infrared (IR) multiphoton dissociation MS/MS of 1 showed evidence of a condensation process similar to bronze formation at low irradiation intensity. Higher IR intensity resulted in the formation of stable fragments consistent with those previously observed in the solution chemistry of polyoxoanions. 相似文献
93.
94.
Pankaj Bandhoria Vivek K. Gupta Musarat Amina Naresh K. Satti Prabhu Dutt Krishan A. Suri 《Journal of chemical crystallography》2006,36(2):153-159
6α,7α-epoxy-5α,17α,dihydroxy-1-oxo-22R-witha-2,24-dienolide (C28H38O6) was isolated from Withania somnifera leaves. The structure of the withanolide was established by spectral analysis and X-ray diffraction studies as withanone. The compound crystallizes in the orthorhombic space group P212121 with unit cell parameters: a = 9.191(10) Å, b = 12.858(6) Å, c = 21.400(16) Å, Z = 4. The crystal structure was solved by direct methods and refined to R = 0.0603 for 1742 observed reflections. There is positional disorder of the H atom in a hydroxy group (O5), resulting in two possible hydrogen-bond linkages. All the rings of the steroid skeleton are trans connected. Ring A exists in a half-chair conformation, ring B is intermediate between a half-chair and a sofa, ring C a distorted chair, and five-membered ring D is intermediate between a half-chair and an envelope. The δ-lactone ring E adopts a sofa conformation. The twist along the length of the steroid nucleus is negligible [C19–C10…C13–C18=1.8°]. Both the hydroxy groups are involved in hydrogen bonding. 相似文献
95.
Hiten Janardan Shah Naresh B. Kataria Gunta Subbaiah Chhagan N. Patel 《Chromatographia》2009,69(9-10):1055-1060
A rapid and specific liquid chromatographic–tandem mass spectrometric method is described for simultaneous analysis of valsartan (VAL) and hydrochlorothiazide (HCTZ) in human plasma. VAL and HCTZ were chromatographed on a C8 column with 75:15:10 (v/v) acetonitrile–methanol–0.001% aqueous ammonia as mobile phase. VAL and HCTZ were eluted at 0.69 min and 1.22 min, respectively, and, after electrospray ionization (ESI), detected in selected-reaction-monitoring mode. The precursor to product-ion transitions m/z 434.32 → 179.22 and m/z 295.85 → 204.86 were used to quantify VAL and HCTZ, respectively. Recovery by solid-phase extraction was >90% for both analytes and the internal standard. The method was suitable for application to a pharmacokinetic study after oral administration of tablet containing 160 mg VAL and 25 mg HCTZ to 18 healthy volunteers. 相似文献
96.
William P. Linak Jong-Ik Yoo Shirley J. Wasson Weiyan Zhu Jost O.L. Wendt Frank E. Huggins Yuanzhi Chen Naresh Shah Gerald P. Huffman M. Ian Gilmour 《Proceedings of the Combustion Institute》2007,31(2):1929-1937
Ultrafine coal fly-ash particles, defined here as those with diameters less than 0.5 μm, typically comprise less than 1% of the total fly-ash mass. These particles are formed primarily through ash vaporization, nucleation, and coagulation/condensation mechanisms, which lead to compositions notably different compared to other fine or coarse particle fractions formed by fragmentation. Whereas previous studies have focused on health effects of particulate matter with aerodynamic diameters less than 2.5 μm (PM2.5) (including both vaporization and fragmentation modes), this paper reports results of interdisciplinary research focused on both characterization and health effects of primary ultrafine coal ash aerosols alone. Ultrafine, fine, and coarse ash particles were segregated and collected from a coal burned in a 20 kW laboratory combustor and two additional coals burned in an externally heated drop tube furnace. Extracted samples from both combustors were characterized by transmission electron microscopy (TEM), wavelength dispersive X-ray fluorescence (WD-XRF) spectroscopy, Mossbauer spectroscopy, and X-ray absorption fine structure (XAFS) spectroscopy. Pulmonary inflammation was characterized by albumin concentrations in mouse lung lavage fluid after instillation of collected particles in saline solutions and a single direct inhalation exposure. Results indicate that coal ultrafine ash sometimes, but not always, contains significant amounts of carbon, probably soot originating from coal tar volatiles, depending on coal type and combustion device. Surprisingly, XAFS results revealed the presence of chromium and thiophenic sulfur in the ultrafine ash particles. Although the single direct inhalation study failed to reveal significant health effects, the instillation results suggested potential lung injury, the severity of which could be correlated with the carbon (soot) content of the ultrafines. Further, this increased toxicity is consistent with theories in which the presence of carbon mediates transition metal (i.e., Fe) complexes, as revealed in this work by TEM and XAFS spectroscopy, promoting reactive oxygen species, oxidation–reduction cycling, and oxidative stress. 相似文献
97.
For radiation having Gaussian quasiprobability functions, a general method of representation of density operators in terms of outer products of coherent states with nonsingular weight function and only two real variables of integration for every mode is given. It is shown that the representation simplifies, if minimum uncertainty states are used. 相似文献
98.
99.
A sequence (μ
n) of probability measures on the real line is said to converge vaguely to a measureμ if∫ fdμ
n →∫ fdμ for every continuous functionf withcompact support. In this paper one investigates problems analogous to the classical central limit problem under vague convergence.
Let ‖μ‖ denote the total mass ofμ andδ
0 denote the probability measure concentrated in the origin. For the theory of infinitesimal triangular arrays it is true in
the present context, as it is in the classical one, that all obtainable limit laws are limits of sequences of infinitely divisible
probability laws. However, unlike the classical situation, the class of infinitely divisible laws is not closed under vague
convergence. It is shown that for every probability measureμ there is a closed interval [0,λ], [0,e
−1] ⊂ [0,λ] ⊂ [0, 1], such thatβμ is attainable as a limit of infinitely divisible probability laws iffβ ε [0,λ]. In the independent identically distributed case, it is shown that if (x
1 + ... +x
n)/a
n, an → ∞, converges vaguely toμ with 0<‖μ‖<1, thenμ=‖μ‖δ
0. If furthermore the ratiosa
n+1/a
n are bounded above and below by positive numbers, thenL(x)=P[|X
1|>x] is a slowly varying function ofx. Conversely, ifL(x) is slowly varying, then for everyβ ε (0, 1) one can choosea
n → ∞ so that the limit measure=βδ
0.
To the memory of Shlomo Horowitz
This research was partially supported by the National Science Foundation. 相似文献
100.
S.William Pelletier Abdel-Monem M. Ateya Naresh V. Mody Haridutt K. Desai Lee C. Schramm 《Tetrahedron letters》1980,21(38):3647-3650
An efficient and simple method using alkaline ferricyanide for converting the NCH2CH2OH group-containing alkaloid derivatives into their “normal”- and “iso-type”-oxazolidine ring-containing alkaloids has been developed. This is the first one-step oxidation method which affords both types of oxazolidine rings simultaneously. 相似文献