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931.
Brouillette Y Lisowski V Fulcrand P Martinez J 《The Journal of organic chemistry》2007,72(7):2662-2665
A series of 10 optically pure 3,4-dihydro-1H-thieno[3,2-e][1,4]diazepine-2,5-dione derivatives has been synthesized in 41-75% yields on treatment of 1H-thieno[3,2-d][1,3]oxazine-2,4-dione with different natural alpha-amino acids. 相似文献
932.
Jeong SD Hong SJ Park KJ Ham S Sessler JL Lynch V Lee CH 《The Journal of organic chemistry》2007,72(16):6232-6240
New core-modified, meso-alkylidenyl porphyrinoids bearing multiple exocyclic double bonds were synthesized and characterized. The synthesis was accomplished using a typical "3 + 1"-type condensation approach. Stable exocyclic tautomers bearing double bonds at the meso positions, as well the corresponding endocyclic tautomers, were isolated in the case of both thiabenziporphyrin and thiapyriporphyrin products prepared in the course of this study. On the other hand, only the exocyclic tautomer was isolated in the case of the congeneric oxapyriporphyrin and oxabenziporphyrin. Expanded analogues of the exocyclic forms of oxabenziporphyrin and thiabenziporphyrin were also isolated as minor products. A single-crystal X-ray diffraction analysis of the expanded thiabenziporphyrin (20) revealed that all four pyrrole rings displayed an inverted geometry, presumably reflecting the strong hydrogen-bonding extant between the pyrrole N-H proton and the carbonyl group of the malonate moiety in the solid state. On the other hand, the expanded oxabenziporphyrin (14) was found to possess a severely distorted geometry with only one pyrrole ring being inverted. Careful analysis of the structure revealed that the solid-state geometry of the expanded macrocycles correlates well with the internal angle defined by the 2- and 5 substituents and the centers of the furan (14) or thiophene (20) subunits. 相似文献
933.
Hnyk D Brain PT Rankin DW Robertson HE Smart BA Banks RE Murtagh V 《Dalton transactions (Cambridge, England : 2003)》2007,(2):265-271
The structure of N-fluorobis(trifluoromethylsulfonyl)imide, prepared by a relatively safe and easy method, has been determined by gas-phase electron diffraction (GED), employing the SARACEN method, with flexible restraints based on the MP2/6-311G* structure, and by X-ray crystallography at 150 K. The strongly electron-withdrawing CF(3) and SO(2)CF(3) groups make the C-S and N-S distances long, averaging 187.7(3) and 171.7(3) pm, respectively, in the gas phase. The gas consists of two conformers, one (75%) with a CF(3) group on each side of the SNS plane, one anti-periplanar and one syn-periplanar to the further N-S bond (ap, sp), and the other with both CF(3) groups on the same side, i.e. denoted ap, ap. These conformers have very different SNS angles, 126.9(9) degrees and 117.1(17) degrees respectively. In the crystal all molecules have the ap, sp conformation, with parameters similar to those found for this conformer in the gas phase. 相似文献
934.
Direct activation of unprotected thioimidoyl furanosides yielded in only one step and few minutes a panel of rare uridine 5'-diphospho-furanoses. Diastereoselectivity of the reaction was tightly connected with reaction time, temperature, and nature of the furanosyl donor. This approach was totally selective since no ring expansion from the initial five-membered ring to the more stable pyranose form was observed. 相似文献
935.
The zero-mean process
is said to be almost periodically correlated whenever its shifted covariance kernel is almost periodic in t uniformly with respect to . Then it admits a Fourier–Bohr decomposition: . This paper deals with the estimation of the spectral covariance a(λ,τ) from a discrete time observation of the process , when jitter and delay phenomena are present in conjunction with periodic sampling. Under mixing conditions, we establish
the consistency and the asymptotic normality of empirical estimators as the sampling time step tends to 0 and the sampling
period tends to infinity.
相似文献
936.
E. D. Éidel’man 《Physics of the Solid State》2000,42(1):1-3
It is shown that an analog of Thomson waves, existing in an ideal fluid, is possible in metals and semiconductors. Possibility of observation of such waves is discussed. 相似文献
937.
Analytic approaches are developed for integrating the nondiagonalizable Whitham equations for the generation and propagation
of nonlinear modulated finite-amplitude waves in dissipationless dispersive media. Natural matching conditions for these equations
are stated in a general form analogous to the Gurevich-Pitaevskii conditions for the averaged Korteweg-de Vries equations.
Exact relationships between the hydrodynamic quantities on different sides of a dissipationless shock wave, an analog of the
shock adiabat in ordinary dissipative hydrodynamics and first proposed on the basis of physical considerations by Gurevich
and Meshcherkin, are obtained. The boundaries of a self similar, dissipationless shock wave are determined analytically as
a function of the density jump. Some specific examples are considered.
Zh. éksp. Teor. Fiz. 115, 1116–1136 (March 1999) 相似文献
938.
Vincent Thilliez 《manuscripta mathematica》1999,99(2):203-222
We give sufficient conditions of infinite determinacy (in the sense of Mather) with respect to right equivalence, in subrings
of C
∞ (ℝ
n
,0) defined by estimates on successive derivatives, such as rings of Gevrey germs. In this quantitative setting, a defect
(hidden in the classical C
∞ case) appears between the regularity of equivalent germs and the regularity of local diffeomorphisms of (ℝn,0) giving the equivalence. Our conditions yield precise estimates of this defect, related to some suitable Łojasiewicz exponents
of critical loci. We also show that the result is sharp in general.
Received: Received: 27 May 1998 相似文献
939.
Jifu Zhao Xinho Jin Yaping E Zai S. Zheng Yu J. Zhang Mohammad Athar Vincent A. DeLeo Hasan Mukhtar David R. Bickers Zhi Y. Wang 《Photochemistry and photobiology》1999,70(4):637-644
In previous studies, we showed that green tea and black tea extracts and their major polyphenolic constituents protect against UVB light-induced carcinogenesis in murine skin. All of these studies required chronic administration of tea extracts or specific constituents either topically or orally. However, it is not known whether acute or subchronic administration of black tea extracts or constituents can ameliorate UVB-induced early effects in skin. In the present study, cultured keratinocytes and mouse and human skin were employed to assess the effect of both oral and topical administration of standardized black tea extract (SBTE) and its two major polyphenolic subfractions namely BTF1 and BTF2 against UVB-induced photodamage. In SKH-1 hairless mice, topical application of SBTE (0.2 mg/cm2) prior to UVB exposure (180 mJ/cm2) resulted in 40% reduced incidence and 64% reduced severity of erythema and 50% reduction in skinfold thickness by day 6 when compared to nontreated UVB-exposed animals. The SBTE was also effective in protecting against UVB-induced erythema in human volunteers. Administration of SBTE 5 min after UVB irradiation was similarly effective in reducing UVB-induced inflammation in both murine and human skin. The major polyphenolic subfractions, BTF1 and BTF2, were also effective in protecting in mouse skin. The SBTE subfractions inhibited UVB-induced tyrosine phosphorylation of epidermal growth factor receptor (EGFR). The UVB irradiation of human epidermoid carcinoma cells resulted in 3.3-fold induction of tyrosine phosphorylation of EGFR. Pretreatment with BTF1 and BTF2 reduced tyrosine phosphorylation of EGFR by 53% and 31%, respectively. The UVB-mediated enhanced expression of the early response genes, c-fos and c-jun in human epidermal keratinocytes was reduced in a dose-dependent manner by SBTE. Topical application of SBTE was also effective in reducing accumulation of c-fos and p53 proteins by 82% and 78%, respectively, in UVB-exposed mouse skin. These data provide evidence that constituents of black tea can abrogate UVB-induced erythema and associated early events in murine and human skin. 相似文献
940.
Measurements of the masses of incorporated water and of the heats of hydration have been performed at 310 K, under air atmosphere saturated with water vapour, on three differently dehydrated samples of the Saccharomyces boulardii yeast in order to evaluate differences in physicochemical properties related to the following dehydration processes: cryodesiccation (or lyophilization) and thermodesiccation (spray drying and in-fluidized-bed heating).Thermogravimetric (TG) experiments have shown that the lyophilized yeast contains less residual water than heat-treated yeasts and that it incorporates more water and more rapidly. Isothermal water sorption of a spherical yeast cell has been represented by a two-parameter equation able to take account of a maximum of the hydration rate when this is taken as a function of time. On the other hand, isothermal DSC experiments have shown that hydration-heat values are higher for the heat-treated yeasts than for the lyophilized one. The TG and DSC results have been shown to be consistent with the idea that the physicochemical properties of a dehydrated yeast are related to cell-wall behaviour during desiccation.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献