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排序方式: 共有427条查询结果,搜索用时 15 毫秒
321.
Jolanta Ignatowska 《Journal of fluorine chemistry》2007,128(9):997-1006
Sodium dithionite initiated addition of CF2Br2, CF3I and (CF3)2CFI to the terminal double bond of allylbenzenes and of (CF3)2CFI to allylpyridines in a MeCN/H2O system were investigated. The reactions of CF2Br2 with allylbenzenes gave comparable amounts of adducts, 1-(2,4-dibromo-4,4-difluorobutyl)benzenes, debrominated products,1-(4-bromo-4,4-difluorobutyl)benzenes, and dimeric compounds in total yields 40-66%. Treatment of the adducts with DBU resulted in double dehydrohalogenation affording 4-aryl-1,1-difluorobutadienes which undergo Diels-Alder condensation with nitrogen dienophiles to give N-heterocycles with difluoromethylene group in the ring. The reactions of CF3I and (CF3)2CFI with allylbenzenes gave the respective adducts, (4,4,4-trifluoro-2-iodobutyl)benzenes and 1-(4,5,5,5-tetrafluoro-4-(trifluoromethyl)-2-iodopentyl)benzenes as the main products. Dehydrohalogenation of these adducts resulted, respectively, in (4,4,4-trifluoro-but-1-enyl)benzenes and 4-aryl-1,1-bis(trifluoromethyl)butadienes in high yields. (CF3)2CFI reacted rapidly with allylpyridines to give mixtures from which, after treatment with DBU, 4-pyridyl-1,1-bis(trifluoromethyl)butadienes were isolated in a ca. 60% yield. 相似文献
322.
Azothia- and Azoxythiacrown Ethers as Ion Carriers. Part II. Anionic Response of Membrane Electrodes
Katarzyna Wygladacz Elzbieta Malinowska Jolanta Szcztygelska-Tao Jan F. Biernat 《Journal of inclusion phenomena and macrocyclic chemistry》2001,39(3-4):309-314
Ion-selective electrodes with plasticized poly(vinyl chloride) membranes containing 13-membered azothia- and azoxythiacrown ether complexes with silver, mercury or copper ions have been investigated. The potentiometric response towards various anions was studied. For membranes based on azothiacrown ether (B) complexes the following selectivity patterns were found:I- > SCN-, Br- > Cl- ClO4
- > salicylate, NO3
- (complex B with silver), I- > ClO4
- > SCN-, Br- > salicylate > Cl-, NO3
- (complex B with mercury) and SCN- > I- > Br- > ClO4
- > Cl- > salicylate > NO3
- (complex B with copper). For azoxythiacrown ether (A) only membranes containing its complex with mercury exhibited pronounced anion response and the selectivity pattern was similar to that observed for complex B with mercury. The origin of the anion response has been discussed. 相似文献
323.
The dissociation constants (p
s
K
a
) of 2,4-D acid were determined in methanol-water mixtures of 10.9 to 38.9 wt.% methanol content. The Yasuda-Shedlovsky procedure
was used to obtain the pK
a
value in zero-% methanol. The distribution of 2,4-D acid in twelve two-phase organic solvent + water systems and its dimerization
in the organic phase were investigated. Values of the distribution coefficient (D
HR), distribution constant (K
D
), and dimerization constant (K
dim) of 2,4-D were obtained. The influence of the structure and polarity of the investigated organic solvents, as well as that
of pH of the aqueous phase, on the physical chemistry of 2,4-D in the two-phase systems are described. 相似文献
324.
Krzysztof Marciniec Jolanta Bafeltowska Maria J. Maślankiewicz Ewa Buszman Stanisław Boryczka 《液相色谱法及相关技术杂志》2016,39(15):702-709
Reversed-phase high-performance liquid chromatography analyses were used for the determination of the retention factor (log k) of a set of quinolinesulfonamides. The analyses utilized a mixture of acetonitrile/water as the mobile phase. The log k values were linearly dependent on the concentration of acetonitrile and extrapolated to 100% water and gave the lipophilicity parameter log kw. The parameter log PHPLC was determined from log kw values using the calibration curve obtained for five standards. The log PHPLC parameters are discussed in terms of structure–lipophilicity relationships. Furthermore, the theoretical lipophilic parameters (log Pcalc) for all compounds were calculated using chemical programs (e.g., Advanced Chemistry Development (ACD/ logP), miLogP, AlogP, ClogP, and Pallas). The determined log PHPLC and calculated log Pcalc values were compared by linear regression analysis. 相似文献
325.
Let E be a Banach space, and let E* be its dual. For understanding the main results of this paper it is enough to consider E=
n
. A symmetric random vector X taking values in E is called pseudo-isotropic if all its one-dimensional projections have identical distributions up to a scale parameter, i.e., for every E* there exists a positive constant c() such that (, X) has the same distribution as c() X
0, where X
0 is a fixed nondegenerate symmetric random variable. The function c defines a quasi-norm on E*. Symmetric Gaussian random vectors and symmetric stable random vectors are the best known examples of pseudo-isotropic vectors. Another well known example is a family of elliptically contoured vectors which are defined as pseudo-isotropic with the quasi-norm c being a norm given by an inner product on E*. We show that if X and Y are independent, pseudo-isotropic and such that X+Y is also pseudo-isotropic, then either X and Y are both symmetric -stable, for some (0, 2], or they define the same quasi-norm c on E*. The result seems to be especially natural when restricted to elliptically contoured random vectors, namely: if X and Y are symmetric, elliptically contoured and such that X+Y is also elliptically contoured, then either X and Y are both symmetric Gaussian, or their densities have the same level curves. However, even in this simpler form, this theorem has not been proven earlier. Our proof is based upon investigation of the following functional equation:
which we solve in the class of real characteristic functions. 相似文献
326.
Natalia urek Olena Karatsai Maria Jolanta Rdowicz Ireneusz Tomasz Kapusta 《Molecules (Basel, Switzerland)》2021,26(9)
Crataegus contains numerous health-promoting compounds that are also proposed to have anti-cancer properties. Herein, we aimed at a contemporaneous evaluation of the effects of polyphenol-rich extracts of berries, leaves, and flowers of six Crataegus species on the viability and invasive potential on the highly aggressive human glioblastoma U87MG cell line. The treatment with the extracts evoked cytotoxic effects, with the strongest in the berry extracts. All extracts not only promoted the apoptosis-related cleavage of poly (ADP-ribose) polymerase 1 (PARP1) but also substantially inhibited the activity of pro-survival kinases, focal adhesion kinase (FAK), and protein kinase B (PKB; also known as Akt), thus indicating the suppression of proliferative and invasive potentials of the examined glioblastoma cells. The qualitative and quantitative characterization of the extracts’ content was also performed and revealed that amongst 37 polyphenolic compounds identified in the examined Crataegus extracts, the majority (29) was detected in berries; the leaf and flower extracts, exerting milder cytotoxic effects, contained only 14 and 13 compounds, respectively. The highest polyphenol content was found in the berries of C. laevigata x rhipidophylla x monogyna, in which flavan-3-ols and phenolic acids predominated. Our results demonstrated that a high content of polyphenolic compounds correlated with the extract cytotoxicity, and especially berries were a valuable source of compounds with anti-cancer potential. This might be a promising option for the development of an effective therapeutic strategy against highly malignant glioblastomas in the future. 相似文献
327.
Marszalek J Pojman JA Page KA 《Langmuir : the ACS journal of surfaces and colloids》2008,24(23):13694-13700
Small-angle and ultrasmall-angle neutron scattering (SANS/USANS) measurements were used to determine the structural changes induced by photopolymerization of AOT/D2O/(dodecyl acrylate) inverse microemulsion systems. Scattering profiles were collected for the initial microemulsions and the films resulting from photopolymerization of the oil phase. The SANS data for the microemulsions were modeled as spherical, core-shell droplets. Upon polymerization, the clear mircoemulsions formed opaque films. From the SANS/USANS data of the films, it was apparent that this morphology was not preserved upon polymerization; however, it was clearly observed that the formulation of the microemulsion had a large impact on the structure within the films. The Guinier region in the USANS data (2.5 x 10(-5) A(-1) < or = Q < or = 5.3 x 10(-3) A(-1)) from the films indicates that very large structures are formed. Simultaneously, a well-defined peak (0.15 A(-1) < or = Q < or = 0.25 A(-1)) in the SANS data indicates that there are also much smaller structures formed. It is proposed that the low-Q scattering arises from aggregation of the nanometer-size water droplets in the microemulsion to form droplets large enough to scatter visible light, while the peak in the high-Q region results from bilayered structures formed by the surfactant. 相似文献
328.
Cu2+ complexes with peptides containing three histidine residues have very specific metal binding abilities and can mimic the structures of various multi-histidine metal binding sites in proteins. The main goal of the work concerns the investigations of coordination abilities of the group of N-terminally protected Ac-His-Arg-His-Gly-His-Gly, Ac-His-Gly-His-Arg-His-Gly, Ac-Gly-His-His-Arg-His-Gly and Ac-His-His-Gly-His-Arg-Gly, and their unprotected analogs His-Arg-His-Gly-His-Gly, His-Gly-His-Arg-His-Gly, Gly-His-His-Arg-His-Gly and His-His-Gly-His-Arg-Gly towards Cu2+ ions. Detailed spectroscopic (UV/Vis, CD and EPR) and potentiometric studies have been made. The stoichiometry and binding mode for each ligand–Cu2+ system were determined. 相似文献
329.
Selected amino acid standards are investigated on cellulose layers using organic-aqueous eluent systems modified with neutral and chaotropic salts: chlorides, iodides, nitrates, thiocyanates, perchlorates, and hexafluorophosphates at low concentrations ranging from 10 up to 80mM in whole mobile phase. The effect of salts used as the mobile phase modifier is analyzed by the comparison of densitograms, peak symmetry coefficient, and theoretical plate number. The efficiency of chromatographic systems modified with inorganic salts additives depends primarily on the kind of salt and organic solvent in the mobile phase. The best efficiency is obtained through the addition of ammonium thiocyanate to the mobile phase containing acetonitrile as an organic modifier. 相似文献
330.
Dr. Jolanta Nieszporek 《Chemphyschem》2023,24(4):e202200394
The influence of nicotinic acid (NC) on the kinetics and the mechanism of electroreduction of Zn2+ ions in the acetate buffer (pH=6.0) was investigated using electrochemical methods (EIS, CV, SWV and DC). It was shown that the anions of NC catalyze the electrode reaction (cap-pair effect) by adsorbing on the surface of the mercury electrode. The catalytic activity of NC is due to its ability to form active NC−Zn2+ complexes on the electrode surface, facilitating the electron transfer process. However, no evidence of the formation of such complexes in the solution was found using classical molecular dynamics. Moreover, it was proved that the electroreduction of Zn2+ ions in the presence of NC is a two-stage process. The first stage involves the transfer of the first electron, preceded by the partial loss of the hydration shell by the Zn2+ ions and formation of the active complex. Moreover, it was shown that in the range of lower concentrations, c≤1.10−2 mol.dm−3, the nicotinic acid shows weaker catalytic abilities than another form of vitamin B3 – nicotinamide. In the range of its higher concentrations, the nicotinic acid is a more effective catalyst for the electroreduction of Zn2+ ions. 相似文献