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排序方式: 共有117条查询结果,搜索用时 187 毫秒
91.
Associating polymers have been prepared by radical copolymerization in water of acrylamide with a micelleforming cationic polymerizable surfactant. To estimate the locus of initiation, the polymerizations were carried out in the presence of initiators and radical inhibitors of various solubilities (water-soluble or oil-soluble), and the decay of inhibitor concentration has been monitored by electron spin resonance spectroscopy. Conversion–time curves simultaneously determined. The experimental data have been interpreted by taking into account the concentration and lifetime of the different radical species (primary radicals, oligoradicals, inhibitors), their partitioning between the micelles and the aqueous continuous phase, and the dynamics of the micellar system. Analysis of the data provided some insight into the copolymerization mechanism of these micellar systems. 相似文献
92.
Mihailo Lj. Mihailović Ljubinka Lorenc Milan Dabović Ivan Juranić Ernest Wenkert Jean-Marie Bernassau Muppala S. Raju Andrew T. McPhail Richard W. Miller 《Tetrahedron letters》1979,20(51):4917-4920
The stereochemistries and conformations of the cyclopropane ring containing compounds derived from (E-3α- and (E)-3β-hydroxy-5,10-seco-1(10)-cholesten-5-one tosylates have been determined by X-ray methods and the results correlated with 13C nmr chemical shift data. 相似文献
93.
Khandelwal A Lukacova V Kroll DM Raha S Comez D Balaz S 《The journal of physical chemistry. A》2005,109(29):6387-6391
The linear response (LR) approximation and similar approaches belong to practical methods for estimation of ligand-receptor binding affinities. The approaches correlate experimental binding affinities with the changes upon binding of the ligand electrostatic and van der Waals energies and of solvation characteristics. These attributes are expressed as ensemble averages that are obtained by conformational sampling of the protein-ligand complex and of the free ligand by molecular dynamics or Monte Carlo simulations. We observed that outliers in the LR correlations occasionally exhibit major conformational changes of the complex during sampling. We treated the situation as a multimode binding case, for which the observed association constant is the sum of the partial association constants of individual states/modes. The resulting nonlinear expression for the binding affinities contains all the LR variables for individual modes that are scaled by the same two to four adjustable parameters as in the one-mode LR equation. The multimode method was applied to inhibitors of a matrix metalloproteinase, where this treatment improved the explained variance in experimental activity from 75% for the unimode case to about 85%. The predictive ability scaled accordingly, as verified by extensive cross-validations. 相似文献
94.
The addition of a small amount of monomer strongly decreased the clouding temperature of nonionic emulsifier (Tween 20). The clouding temperature of the Tween 20 aqueous solution was independent of emulsifier concentration but it strongly varied in the presence of monomer. The decreased cloud temperature was attributed to the penetration of monomer molecules into the interfacial layer that increased the flocculation of microdroplets (monomer-swollen micelles). The surface tension of homogenized ((mini)emulsion) butyl acrylate aqueous emulsion was much smaller than that estimated at or above CMC of Tween 20. The polymerization rate vs. conversion curve of the (mini)emulsion deviates from the three rate intervals typical for the emulsion polymerisation. The shape of the rate-conversion curve reminds more the four rate intervals curve. Interval 2 is overlapped with the initial maximal rate and rate shoulder at higher conversion. The initial maximal polymerization rate (Rp,max,1) is attributed to the abrupt increase in polymer particles, the polymerization under monomer saturated condition and emulsifier containing peroxide groups (Twperoxid 20). The rate of emulsion polymerization of BA initiated by ammonium peroxodisulphate (APS) is ca. by one order of magnitude larger than that of blank polymerization (without APS). The second maximal rate (rate shoulder) can result from the gel effect. The more pronounced increase in Rp,max,1 with Tw 20 concentration supports the presence of peroxide groups. The slight dependence of Rp,max,2 on [Tw 20] for both APS and DBP (dibenzoyl peroxide) is discussed in terms of the depressed radical entry rate into the close packed surface later of polymer particles. The low activation energy is attributed to the decreased barrier for entering radicals into the polymer particles with increasing temperature. This is more pronounced with the accumulation of covalently bound emulsifier moieties (resulting from Twperoxid 20) at the particle surface. The ratio of the final number of polymer particles to the initial number of monomer droplets (Np/Ndrop) promotes the partial monomer droplet nucleation. The dye approach indicates that the degree of depletion of monomer droplets decreases from the classical emulsion polymerization to the polymerization in pre-homogenized emulsions and the emulsion polymerization with a prolonged-emulsification interval. 相似文献
95.
Peter Segl’a Jozef Miklovič Dušan Mikloš Viera Mrázová Lenka Krupková Daniela Hudecová Zuzana Ondrušová Jozef Švorec Ján Moncol Milan Melník 《Transition Metal Chemistry》2009,34(1):15-22
The synthesis and characterization of six new 2-methylthionicotinate (2-MeSnic) copper(II) monomeric complexes [Cu(2-MeSnic)2L2] (L is furo[3,2-c]pyridine—fpy, 2-methylfuro[3,2-c]pyridine—Mefpy, 2,3-dimethylfuro[3,2-c]pyridine—Me2fpy or benzo[4,5]furo[3,2-c]pyridine—Bfp), [Cu(2-MeSnic)2(fpy)2(H2O)], as well as [Cu(2-MeSnic)2(CF3Phfpy)2(H2O)2] (CF3Phfpy is 2-(3-trifluoromethylphenyl)furo[3,2-c]pyridine) are reported. The characterizations were based on elemental analysis,
infrared, electronic and EPR spectra. The crystal structure of one of the complexes has been determined. The CuII atoms of [Cu(2-MeSnic)2(fpy)2(H2O)] are six-coordinated in a highly distorted tetragonal–bipyramidal arrangement by two nitrogen atoms, one from each fpy,
in trans-positions, by three oxygen atoms of the carboxyl groups of 2-MeSnic ligands (one monodentate, one asymmetrically bidentate),
one axial position being occupied by the oxygen of a water molecule. The antimicrobial effects have been tested on various
strains of bacteria, yeasts and filamentous fungi. A comparison of the IC50 and MIC values has shown a decrease of inhibition activities of tested compounds in the order: [Cu(2-MeSnic)2(Bfp)2] > Bfp > [Cu(2-MeSnic)2(CF3Phfpy)2(H2O)2] > [Cu(2-MeSnic)2(Me2fpy)2] > CF3Phfpy > [Cu(2-MeSnic)2(Mefpy)2] > Me2fpy > [Cu(2-MeSnic)2(fpy)2(H2O)] > [Cu(2-MeSnic)2(H2O)]2 > Mefpy > fpy = 2-MeSnicH = CuSO4.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
96.
Viera Zemanová Marián Slodi?ka 《Journal of Computational and Applied Mathematics》2010,234(7):2062-2068
We study a recovery problem for an unknown boundary data at the boundary part in static electromagnetism. Our computational area is a bounded domain Ω⊂Rn with a Lipschitz continuous boundary. The problem for determining the coefficient λ is considered. This coefficient represents one of the ferromagnetic material characteristics occupying this domain. The existence and uniqueness of a weak solution are proved and a numerical method for its recovery is supported by numerical experiments. 相似文献
97.
Victor Hugo Catricala Fernandes Natalie de Barros Viera Luiza Beatriz Lima Zanini Aline de Fátima Silva Paula Pio de Oliveira Salem Marisi Gomes Soares Karen de Jesus Nicácio Ana Claudia Chagas de Paula Luciano Sindra Virtuoso Tiago Branquinho Oliveira Eliane de Oliveira Silva Danielle Ferreira Dias Daniela Aparecida Chagas-Paula 《Photochemistry and photobiology》2020,96(1):14-20
There is some evidence in the literature of the photocyclization reaction of Tagitinin C ( 1 ) to Tagitinin F ( 2 ). Compound 2 has high pharmacological potential, but it is not easy to obtain, while compound 1 is easily obtained from a widespread plant, Tithonia diversifolia. Among different reaction conditions monitored, one was found that allowed the cyclization of 1 into 2 in <15 min in a photo-dependent reaction. Scaling-up the photocyclization of the pure compound 1 into 2 demonstrated 100% yield, and the isolation of 2 from a UV-irradiated extract was eight-fold higher than the quantity isolated from the non-UV-irradiated extract. We were also able to better understand the process of photoconversion and determine methods to isolate and quantify these compounds, which are known for their important antitumoral activities among other important pharmacological properties. 相似文献
98.
Rate constants for the esterification of eleven 2-[(carboxymethyl)sulfanyl]-4-oxo-4-arylbutanoic acids with diphenyldiazomethane in ethanol at 30 °C were determined, and correlated with substituent constants using classical Hammett and related methods. Statistically valid results for the para-substituted compounds were obtained by the Swain–Lupton approach. The compounds studied had significant conformational mobility due to seven rotatable bonds in their backbone. Going beyond the classical Hammett approach, we established a relatively fast procedure to find the optimal conformations that can be used in linear free-energy relationships, combining molecular dynamics with semiempirical calculations, and calculations using a higher level of theory (DFT and MP2). Fair correlations were observed with frontier orbitals, allowing inclusion of ortho-substituted derivatives and clarifying artifact-like data, as perceived by the Hammett-type approach. 相似文献
99.
Ignacio Viera Eduardo Manta Lucía González Graciela Mahler 《Tetrahedron: Asymmetry》2010,21(5):631-635
Novel α,α-disubstituted epoxy esters were prepared in enantiopure form by hydrolytic kinetic resolution (HKR) of the corresponding racemic mixtures using chiral salenCo(III) as catalyst. The methodology provides a convenient route to enantioenriched β,γ-epoxy esters 2a, 2c and 2d. 相似文献
100.
L'udmila Černáková Viera Chrástová Petra Volfová Anna Zahoranová 《Macromolecular Symposia》2002,179(1):305-314
Polystyrene/poly(butyl acrylate) dispersion with N-methylol groups were prepared through two - steps semi continuous emulsion polymerization, where N-methylol acrylamide (NMA) was used as a functional monomer. A high content of insoluble portions depending on the NMA dosing during polymerization was found in films casted from such dispersions. The crosslinking reactions between methylol groups during polymerization were assumed. Attenuated total reflectance Fourier transform infrared spectroscopy was used to study changes in films prepared from the functionalized and unfunctionalized dispersions. Comparison of the spectra of as-dried films and heat- treated films suggests the occurrence of post-polymerization crosslinking. 相似文献