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51.
Using an extension of the Langevin method, we calculate the fluctuations of a fluid about a stationary state held away from global thermal equilibrium by a temperature gradient or shear flow. In the former case, the Brillouin peaks in the light scattering spectrum acquire an asymmetry that is qualitatively similat to earlier results but different in detail. 相似文献
52.
Three types of highly filled polymers were studied by the molecular probe to evaluate the applicability of this technique to ageing studies. The probe was found efficient in characterizing the behaviour of a given composite under a given set of conditions, or the effect of the nature of the solid phase on the stability of the binder. Thus, the post-curing effect in composite containing NH,4CLO4 and Al was analysed in detail. ΔHa = 15·8 kcal/mole was found for this first-order reaction. In a second example, Fe2O3 was shown to decrease the post-curing effect leading to a very thermally stable material. Finally, the absence of aluminium resulted in a reduced hydrolytic stability of the binder. 相似文献
53.
The first enantiocontrolled total synthesis of the marine natural product oscillarin is described. The proposed structure and absolute configuration of oscillarin is thus confirmed, and a previously assigned structure of a subunit was shown to be incorrect. The X-ray structure of an oscillarin-thrombin complex was resolved at 2.0 A resolution, which validated its potent inhibitory activity against the enzyme with an IC(50) = 28 nM. Methodology was developed for the synthesis of enantiopure octahydroindole-2-carboxylic acids with usable functionality at C-6. The method consists of the halocarbocyclization of N-acyloxyiminium ions containing an olefinic tether in the presence of tin tetrachloride or tin tetrabromide. This N-acyloxyiminium ion aza-Prins carbocyclization proved to be general for the construction of octahydroindole and perhydroquinoline 2-carboxylic acids. Mechanistic rationales are based on an antiperiplanar attack of the terminal alkene on the iminium ion, leading to an incipient secondary carbocation which is trapped by halide via an equatorial attack. X-ray crystal structures of products corroborate the expected stereochemistry. 相似文献
54.
Rivière J Bergeron F Tremblay S Gasparutto D Cadet J Wagner JR 《Journal of the American Chemical Society》2004,126(21):6548-6549
Oxidation products of cytosine, including 5-hydroxycytosine and 5-hydroxyuracil, are highly susceptible to subsequent oxidation. Here, the oxidation products of 5-hydroxy-2'-deoxyuridine have been studied by NMR and MS analyses. The initial products were diastereomers of isodialuric acid nucleoside. These products subsequently decomposed into corresponding dialuric acid derivatives at neutral pH. The position of the carbonyl and hydroxyl groups, at C5 and C6 for isodialuric acid and at C6 and C5 for dialuric acid derivatives, respectively, was determined by 1H- and 13C NMR analyses. In addition, these analyses revealed that the carbonyl groups of both isodaluric and dialuric acid derivatives exist in their fully hydrated form in aqueous solution. Finally, the dialuric acid derivatives were observed to undergo subsequent decomposition into the corresponding 5-hydroxyhydantoin derivatives. Studies of a trinucleotide containing 5-hydroxyuracil suggest that the reactions described herein for the monomer can be extrapolated to DNA. 相似文献
55.
[reaction: see text] Five-membered N-Boc acyliminium ions derived from L-pyroglutamic acid harboring 4-butenyl and 4-butynyl tethers undergo Lewis acid-mediated halo and tandem Friedel-Crafts carbocyclization within minutes at -78 degrees C to give stereodefined 6-substituted octahydroindole and hexahydroindole 2-carboxylic acid methyl esters, respectively. The cyclic vinyl bromides are excellent substrates for Pd-catalyzed Suzuki-Miyaura, Heck, and Stille couplings. The method also provides access to enantiopure sp2- and sp3-arylated azabicyclics that are novel and versatile scaffolds for chemical diversification. 相似文献
56.
We introduce the set of bicomplex numbers
which is a commutative ring with zero divisors defined by
where
We present the conjugates and the moduli associated with the bicomplex numbers. Then we study the bicomplex Schr?dinger equation
and found the continuity equations. The discrete symmetries of the system of equations describing the bicomplex Schr?dinger
equation are obtained. Finally, we study the bicomplex Born formulas under the discrete symmetries. We obtain the standard
Born’s formula for the class of bicomplex wave functions having a null hyperbolic angle. 相似文献
57.
We propose a model based on the properties of cascading lenses modulation transfer function (MTF) to reproduce the irradiance of a screen illuminated through a dense aerosol cloud. In this model, the aerosol cloud is broken into multiple thin layers considered as individual lenses. The screen irradiance generated by these individual layers is equivalent to the point-spread function (PSF) of each aerosol lens. Taking the Fourier transform of the PSF as a MTF, we cascade the lenses MTF to find the cloud MTF. The screen irradiance is found with the Fourier transform of this MTF. We show the derivation of the model and we compare the results with the Undique Monte Carlo simulator for four aerosols at three optical depths. The model is in agreement with the Monte Carlo for all the cases tested. 相似文献
58.
H. M. Srivastava J. -L. Lavoie Richard Tremblay 《Annali di Matematica Pura ed Applicata》1979,119(1):9-24
Summary An attempt is made here to present a systematic introduction to and several applications of a certain method of obtaining
Rodrigues type representations for a fairly wide variety of sequences of special functions. The main results, contained in
Theorems2 and3 below, are shown to apply not only to the Bessel polynomials, the classical orthogonal polynomials including, for instance,
Hermite, Jacobi (and, of course, Gegenbauer, Legendre, and Tchebycheff), and Laguerre polynomials, and to their various generalizations
studied in recent years, but also to such other special functions as the Bessel function and a certain class of generalized
hypergeometric functions.
Entrata in Redazione il 25 giugno 1977.
This work was partially supported by the National Research Council of Canada under grants A-7353 and A-4027. For a preliminary
report of this paper see Notices Amer. Math. Soc.,24 (1977), p. A-238, Abstract no. 77T-B43. 相似文献
59.
We have developed a luminogenic probe for tyrosine phosphorylation based on a short peptide sequence containing an iminodiacetate moiety near the site of phosphorylation. In response to kinase activity, the probe provides a strong luminescence enhancement, resulting from the increased ability of the probe to bind and sensitize Tb3+ and Eu3+ ions upon phosphorylation. 相似文献
60.
Fürstner A Nevado C Waser M Tremblay M Chevrier C Teplý F Aïssa C Moulin E Müller O 《Journal of the American Chemical Society》2007,129(29):9150-9161
A concise and convergent total synthesis of the highly cytotoxic marine natural products iejimalide A-D (1-4) is reported, which relies on an effective ring-closing metathesis (RCM) reaction of a cyclization precursor containing no less than 10 double bonds. Because of the exceptional sensitivity of this polyunsaturated intermediate and its immediate precursors toward acid, base, and even gentle warming, the assembly process hinged upon the judicious choice of protecting groups and the careful optimization of all individual transformations. As a consequence, particularly mild protocols for Stille as well as Suzuki reactions of elaborate coupling partners have been developed that hold considerable promise for applications in other complex settings. Moreover, a series of non-natural "iejimalide-like" compounds has been prepared, differing from the natural lead in the polar head groups linked to the macrolide's N-terminus. With the aid of these compounds it was possible to uncover the hitherto unknown effect of iejimalide and analogues on the actin cytoskeleton. Their capacity to depolymerize this microfilament network rivals that of the latrunculins which constitute the standard in the field. Structural modifications of the peptidic terminus in 2 are thereby well accommodated, without compromising the biological effects. The iejimalides hence constitute an important new class of probe molecules for chemical biology in addition to their role as promising lead structures for the development of novel anticancer agents. 相似文献