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排序方式: 共有321条查询结果,搜索用时 15 毫秒
311.
Effect of competing binding modes on retention in chromatography and capillary electrophoresis. A theoretical consideration
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A mathematical formalism has been developed to describe equilibrium in a system involving a single selector and a selectand molecule capable of binding to this selector by different modes. The generalization of this model to a multiselector system has also been considered. Applications of the developed equations in chromatography and CE are discussed. 相似文献
312.
Röger C Miloslavina Y Brunner D Holzwarth AR Würthner F 《Journal of the American Chemical Society》2008,130(18):5929-5939
The multichromophoric dyads 1, 2 and triad 3 have been synthesized by coupling of the appropriately functionalized chlorin derivative with naphthalene diimide dyes through esterification, and subsequent metalation of the chlorin center with zinc acetate. The self-assembly properties of naphthalene diimide (NDI)-zinc chlorin (ZnChl) dyads 1, 2 and triad 3 have been studied in nonpolar, aprotic solvents by UV-vis, CD, and steady-state emission spectroscopy, revealing formation of rod-like structures by noncovalent interactions of zinc chlorin units, while the appended naphthalene diimide dyes do not aggregate at the periphery of the rod antennae. In all these systems, photoexcitation of the enveloping naphthalene diimides at 540 and 620 nm, respectively, leads to highly efficient energy-transfer processes (FRET; phiET > or = 0.99) to the inner zinc chlorin backbone, as explored by time-resolved fluorescence spectroscopy on the picosecond time scale. The efficiencies of zinc chlorin rod aggregates for the harvesting of solar light are markedly increased from 26% for dyad 2 up to 63% for triad 3, compared to the LH capacity of the monochromophoric aggregates of model system ZnChl 6a. Thus, with the self-assembled zinc chlorin rod antenna based on triad 3, a highly efficient artificial LH system has been achieved. 相似文献
313.
Prof. Yuliya V. Rassukana Alona S. Cherednichenko Dr. Svitlana V. Shishkina Prof. Petro P. Onys'ko 《European journal of organic chemistry》2023,26(33):e202300607
A highly diastereoselective addition of nitromethane to the C=N bond of enantiomeric fluorine containing Ellman's aldimines, RFCH=NS(O)tert-Bu (RF=CF3, CF2Br, C2F5, HC2F4), has been successfully developed. The synthetic potential of the resulting β-nitrosulfinylamides was demonstrated through their conversion into optically active α-fluoroalkylated 1,3-nitroamines, 1,3-diamines, and 4-fluoroalkylated imidazolidin-2-ones. 相似文献
314.
Rudzevich Y Cao Y Rudzevich V Böhmer V 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(11):3346-3354
Tetra-urea calix[4]arenes substituted with four mono- or bisalkenyl residues have been converted into bis- or tetraloop compounds by intramolecular olefin metathesis, with use of a tetratosylurea calix[4]arene as template. The same strategy has now been used to synthesise trisloop compounds and bisloop compounds with adjacent loops, completing the series of the loop-containing tetra-urea derivatives. A tetra-urea calix[4]arene of the AABB type, where A stands for a bisalkenyl- and B for a monoalkenyl-substituted urea unit, was used as precursor for the three loops. It was easily synthesised from a tetraamino calix[4]arene in which two adjacent amino groups were Boc-protected. The ABCB-type precursor for the two adjacent loops was prepared through protection of two opposite amino functions with trityl groups. The capabilities of the novel macrocyclic tetra-ureas for the selective formation of hydrogen-bonded dimers were studied. 相似文献
315.
316.
Kosenkov D Gorb L Shishkin OV Sponer J Leszczynski J 《The journal of physical chemistry. B》2008,112(1):150-157
The tautomeric equilibrium and hydrogen bonding in nucleotide 2'-deoxyguanosine monophosphate that interacts with hydrated Mg2+ cation (4H2O.Mg[dGMP]) were studied at the MP2/cc-pVDZ//B3LYP/cc-pVDZ and B3LYP/aug-cc-pVTZ//B3LYP/cc-pVDZ levels of theory. The Mg2+ ion forms two inner-shell contacts with the nucleotide, similar to small phosphorylated molecules under physiological conditions. The presence of the phosphate group and the hydrated magnesium cation leads to a change in guanine tautomeric equilibrium of 4H2O.Mg[dGMP] in comparison to free guanine. The influence of the phosphate group and the magnesium cation on tautomeric equilibrium is larger in the anti conformation where the P=O-->Mg and Mg<--N7 coordinate bonds are formed. The canonical oxo form of guanine is more stable (by 6-8 kcal/mol) than the O6-hydroxo form in anti conformation. Thus, the interaction with Mg2+ ion is capable of further suppressing the likelihood of a spontaneous transient formation of the rare tautomer. In the syn conformation of 4H2O.Mg[dGMP], the interaction of the guanine nucleobase with the phosphate group and the magnesium cation is not as strong as in the anti conformation, and the relative stability of guanine tautomers is close to those in free guanine. 相似文献
317.
Omelchenko Irina V. Shishkin Oleg V. Gorb Leonid Hill Frances C. Leszczynski Jerzy 《Structural chemistry》2012,23(5):1585-1597
Structural Chemistry - Geometrical parameters, aromaticity, and conformational flexibility of the set of polysubstituted benzenes with different number and position of nitro and amino groups were... 相似文献
318.
Sviatenko L Gorb L Hovorun D Leszczynski J 《The journal of physical chemistry. A》2012,116(9):2333-2342
The computational analysis of multistep chemical interactions between 2'-deoxyadenosine and cis-2-butene-1,4-dial has been performed. The applied protocol includes generation of a multistep Gibbs free-energy reaction profile (PCM/M05-2X/6-311+G(d) level) for the transformations of the reagents to products, followed by evaluation of the rate constants, construction of the corresponding kinetic equations, and solving them. Such a procedure allows one to significantly extend the number of experimentally determined steps by addition of the ones computationally predicted. The primary products of the reaction are found to be four diastereomeric adducts characterized by virtually the same stability. The acid-catalyzed dehydration of these adducts leads to a more stable secondary product. Computational verification of UV and NMR spectra has also been performed. It has been revealed that simulated UV and NMR spectra of primary and secondary 2'-deoxyadenosine adducts of cis-2-butene-1,4-dial are in agreement with the experimental observations. 相似文献
319.
Bogdan A Rudzevich Y Vysotsky MO Böhmer V 《Chemical communications (Cambridge, England)》2006,(28):2941-2952
Calix[4]arenes bearing at their wide rim four urea residues easily form hydrogen bonded dimeric capsules. This has been used to preorganise alkenyl functions attached to these urea groups for their controlled connection via metathesis reaction. Multimacrocyclic tetraurea derivatives are thus obtained in excellent yields via heterodimers which are formed exclusively with tetratosylurea derivatives. Heterodimerisation of such bis- and tetraloop tetraureas leads analogously to multicatenanes, or to rotaxanes by stoppering. Huge macrocycles are detached from tetraloop derivatives by cleavage of the urea function. 相似文献
320.
Let S be a discrete semigroup, let β
S be the Stone-Čech compactification of S, and let T be a closed subsemigroup of β
S. We characterize ultrafilters from the smallest ideal K(T) of T and from its closure c
ℓ
K(T). We show that, for a large class of closed subsemigroups of β
S, c
ℓ
K(T) is not an ideal of T. This class includes the subsemigroups 0+⊂βℝ
d
and ℍ
κ
⊂β(⊕
κ
ℤ2). 相似文献