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1.
Ab initio calculations showed that the tetrachlorodibenzo-para-dioxin radical cations (TCDD RCs) with a planar structure have two steady states with asymmetric dioxin cycles. The activation barriers between these states are up to 2 kcal/mole, so that the RCs may be regarded as being structurally nonrigid within the dioxin cycle. The 2,3,7,8-TCDD RC is more stable than the 1,4,6,9-TCDD RC, the energy difference being 5.2 kcal/mole. The adiabatic ionization potential of 2,3,7,8-TCDD (7.54 eV) is 0.1 eV smaller than the corresponding potential of 1,4,6,9-TCDD. These factors account for the increased hemoproteide affinity and hence increased biological activity of 2,3,7,8-TCDD. 相似文献
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Maria G. Semenova Larisa E. Belyakova Anna S. Antipova Yu. N. Polikarpov Lida Klouda Anna Markovic Michael M. Il'in 《Colloids and surfaces. B, Biointerfaces》2003,31(1-4):47-54
We report on the effect of commercially important polysaccharides (maltodextrins with variable dextrose equivalent (Paselli SA-2, MD-6 and MD-10) on the surface activity at the air–water interface of small-molecule surfactants (sms), possessing different hydrophobic–lipophilic balance ((SSL (Na+), the main component is a sodium salt of stearol–lactoyl lactic acid, and PGE (080), polyglycerol ester of C18 fatty acid), and widely used in food products. A marked change of the surface activity of sms was found in the presence of maltodextrins by tensiometry. The combined data of laser multiangle light scattering and mixing calorimetry have suggested that this result is governed by specific complex formation between maltodextrins and sms in aqueous medium. Measurements have been made of the molar mass, the second virial coefficient and the enthalpy of intermolecular interactions in aqueous solutions. The implication of a degree of polymerization of maltodextrins in this phenomenon was shown. The interrelation between the molecular parameters of the formed complexes and their surface activity at the air–water interface has been revealed and discussed. 相似文献
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We study applications of asymptotic methods of nonlinear mechanics and the method of Fokker-Planck-Kolmogorov equations to
stochastic oscillations in quasilinear oscillating systems with random perturbations.
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Translated from Neliniini Kolyvannya, Vol. 10, No. 4, pp. 510–518, October–December, 2007. 相似文献
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P. N. Lavrenko I. P. Kolomiets O. V. Ratnikova L. V. Vinogradova 《Polymer Science Series A》2006,48(9):981-988
For C60 fullerene-containing poly(2-vinylpyridines) synthesized by anionic polymerization, the molecular mass and hydrodynamic size of macromolecules in solutions have been determined by molecular hydrodynamics (translational diffusion and viscometry) and electrooptics in dilute benzene and THF solutions. Under the same conditions in the molecular mass range (9.8–123) × 103, the hydrodynamic behavior of linear poly(2-vinylpyridines) and their molecular-mass dependences have been examined and the conformational characteristics of macromolecules have been established. The branching of macromolecules has been characterized by comparing the properties of star-shaped fullerene-containing and linear poly(2-vinylpyridines). With consideration of the hydrodynamic data interpreted within the framework of regular star model, it is inferred that on average three to four linear polymer chains with a molecular mass of (8 ± 3) × 103 for each chain are attached to a fullerene core of C60 in molecules of fullerene-containing poly(2-vinylpyridines). The specific Kerr constant of fullerene-containing poly(2-vinylpyridines) in dilute benzene solution is ?(14 ± 1) × 10?12 cm5/[g (300 V)2]. As evidenced by the electrooptical data, the incorporation of fullerene into the polymer weakens self-association of macromolecules in solution. 相似文献
9.
It is shown that 2,2-difluoro-3-hydroxymethylbenzo-1,4-oxathianes are formed together with 3-trifluoromethylbenzo-1,4-oxathianes whenortho-(-trifluoromethyl--chloroethylthio)phenols are boiled with excess aqueous alkali. The mechanism of the reaction is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1457–1459, August, 1994. 相似文献
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Alexander S GolubevNatalia N Sergeeva Lothar HennigAlexey F Kolomiets Klaus Burger 《Tetrahedron》2003,59(9):1389-1394
An efficient synthesis of trifluoromethyl-containing 2,3-allenols via carbonyl-yne reaction of 3,3,3-trifluoropyruvates with acetylenes is described. In the presence of MgBr2·Et2O the reaction of methyl trifluoropyruvate with hex-1-yne proceeds diastereoselectively. Trifluoromethyl-substituted 2,3-allenols can be stereoselectively transformed into trifluoromethyl-substituted 2,5-dihydrofurans on treatment with AgNO3. 相似文献