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排序方式: 共有217条查询结果,搜索用时 15 毫秒
71.
Wieslaw Strek 《Molecular physics》2013,111(6):2005-2015
A quantum mechanical theory of the solvent effect on radiationless transitions is developed within the framework of a dynamic coupling model. This model allows us to describe the solvent effect on any mechanism of intramolecular radiationless transition, in polar as well as non-polar solvents. 相似文献
72.
Effects of the method of identification of the diffusion coefficient on accuracy of modeling bound water transfer in wood 总被引:2,自引:0,他引:2
An alternative approach to determining the bound water diffusion coefficient is proposed. It comprises a method for solving
the inverse diffusion problem, an improved algorithm for the bound-constrained optimization as well as an alternative submodel
for the diffusion coefficient’s dependency on the bound water content. Identification of the diffusion coefficient for Scots
pine wood (Pinus sylvestris L.) using the proposed inverse approach is presented. The accuracy of predicting the diffusion process with the use of the
coefficient values determined by traditional sorption methods as well as by the inverse modeling approach is quantified. The
similarity approach is used and the local and global relative errors are calculated. The results show that the inverse method
provides valuable data on the bound water diffusion coefficient as well as on the boundary condition. The results of the identification
can significantly improve the accuracy of mass transfer modeling as studied for drying processes in wood. 相似文献
73.
An observation of negative refraction in the naturally obtained composition of graphene and barium ferrite is reported. The capacitance and inductance measurements revealed the electric and magnetic resonances accompanied with the negative values of permittivity and permeability in the overlapped frequency range. According to the “left‐handed” media approach such a material is characterized by negative refraction. The derived values of the real part of refractive index are negative at the frequencies above 500 MHz.
74.
Abstract The liquid crystalline properties of 1-(alkylamino)-3-[(4″-hexyl-trans-cyclohexyl-4′-phenyl]-prop-1-en-3-one-s, from methyl to octadecyl, and their copper (II) complexes have been examined by optical, DSC, X-ray and EPR methods. The compounds are enantiotropic nematogens except those having the shortest and the longest terminal chains. Short chains promote the SA phase in both ligands and complexes, whereas long chains promote SC and crystal H phases for the ligands or SA and SC phases for the complexes. A partly bilayer smectic Ad phase is observed from ligands terminated with short non-polar substituents. Direct isotropisation from the crystal H phase for some of the compounds, as well as other phase transitions have been studied. The molecular shape of the complexes and the organization of their mesomorphic phases are discussed, based on the refractive indices and X-ray data. 相似文献
75.
Allyl ethers are widely used for the “temporary” protection of hydroxy groups in carbohydrates. The allyl group is conveniently removed by isomerization and subsequent cleavage of the labile prop-1-enyl group.2 The rearrangement of allyl ethers to prop-1-enyl ethers is readily achieved by treatment with potassium t-butoxide in dimethyl sulfoxide, using tris(tripheny1phosphine)rhodium chloride, palladium on activated charcoal and by an ene reaction with diethylazodicarboxylate. acidic conditions, ozonolysis followed by alkaline hydrolysis, reaction with alkaline permanganate solution, or treatment with mercuric chloride in the presence of mercuric oxide. The isomerization of allyl ethers to prop-1-enyl ethers can also be carried out in the presence of palladium on carbon or complex bis(benzonitrile)palladium(11) chloride. Bruce and Roshan-Ali' showed that derivatives of allyl phenyl ether are smoothly cleaved by this complex. This has made it possible to remove the protecting group in a one-pot operation. We have now investigated the effect of palladium catalysts on the isomerization and cleavage of the allyl group in carbohydrate derivatives. 相似文献
76.
Marek Chmielewski Izabela Fokt Jacek Grodner Grzegorz Grynkiewicz Wieslaw Szeja 《Journal of carbohydrate chemistry》2013,32(5):735-741
Abstract Benzylated glycals, unlike their acylated congeners which easily undergo allylic rearrangement, are frequently employed as reactive enol ether type substrates in a variety of electrophilic addition reactions.1–4 Although these compounds are considered to be readily available substrates, reported procedures for their syntheses involve some steps of limited efficiency, chromatographic separations or costly reagents,5–7 and experimental requirements not amenable for large scale preparations. In view of the recent applications of benzylated glycals to syntheses of O-glycosides,1,2 C-glycosyl compounds,3 and β-lactams,4 we have undertaken a study aimed at efficient one step benzylation procedures applicable to pyranoid 1-enitols as well as to their acylated derivatives. This goal was eventually achieved by employing a catalytic phase transfer alkylation system with 相似文献
77.
Wieslaw Gessner Arnold Brossi Judith L. Flippen-anderson Clifford George 《合成通讯》2013,43(12):1371-1377
The unsubstituted ketospirolactam 1 afforded on alkyla-tion the two C(9)-butylated ketolactams 2 and 3, with 3 being the more stabile epimer, and the C(9)-dibutylated ketolactam 4. Structure of alcohol 5 obtained from 3 was secured by X-ray analysis. 相似文献
78.
Katarzyna Kaahurska Pawel P. Ziemiaski Wieslaw J. Roth Barbara Gil 《Molecules (Basel, Switzerland)》2021,26(7)
We investigated the properties and catalytic activity of zeolites with MWW topology obtained by unprecedented liquid exfoliation of the MCM-56 zeolite into solutions of monolayers and isolation/reassembly of the dispersed layers by various methods, with optional purification by dialysis or ammonium exchange. The layers were recovered by flocculation with alcohol or ammonium nitrate and freeze-drying. Flocculation alone, even with ammonium nitrate, did not ensure removal of residual sodium cations resulting in catalysts with low activity. Dialysis of the solutions with dispersed monolayers proved to be efficient in removing sodium cations and preserving microporosity. The monolayers were also isolated as solids by freeze-drying. The highest BET area and pore volume obtained with the freeze-dried sample confirmed lyophilization efficiency in preserving layer structure. The applied test reaction, Friedel–Crafts alkylation of mesitylene, showed high benzyl alcohol conversion due to increased concentration of accessible acid centers caused by the presence of secondary mesoporosity. The applied treatments did not change the acid strength of the external acid sites, which are the most important ones for converting bulky organic molecules. Zeolite acidity was not degraded in the course of exfoliation into monolayers, showing the potential of such colloid dispersions for the formation of active catalysts. 相似文献
79.
Michal Nowak Wieslaw Tryniszewski Agata Sarniak Anna Wlodarczyk Piotr J. Nowak Dariusz Nowak 《Molecules (Basel, Switzerland)》2021,26(7)
Ascorbic acid (AA) has antioxidant properties. However, in the presence of Fe2+/Fe3+ ions and H2O2, it may behave as a pro-oxidant by accelerating and enhancing the formation of hydroxyl radicals (•OH). Therefore, in this study we evaluated the effect of AA at concentrations of 1 to 200 µmol/L on •OH-induced light emission (at a pH of 7.4 and temperature of 37 °C) from 92.6 µmol/L Fe2+—185.2 µmol/L EGTA (ethylene glycol-bis (β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid)—2.6 mmol/L H2O2, and 92.6 µmol/L Fe3+—185.2 µmol/L EGTA—2.6 mmol/L H2O2 systems. Dehydroascorbic acid (DHAA) at the same range of concentrations served as the reference compound. Light emission was measured with multitube luminometer (AutoLumat Plus LB 953) for 120 s after automatic injection of H2O2. AA at concentrations of 1 to 50 µmol/L and of 1 to 75 µmol/L completely inhibited light emission from Fe2+-EGTA-H2O2 and Fe3+-EGTA-H2O2, respectively. Concentrations of 100 and 200 µmol/L did not affect chemiluminescence of Fe3+-EGTA-H2O2 but tended to increase light emission from Fe2+-EGTA-H2O2. DHAA at concentrations of 1 to 100 µmol/L had no effect on chemiluminescence of both systems. These results indicate that AA at physiological concentrations exhibits strong antioxidant activity in the presence of chelated iron and H2O2. 相似文献
80.
A functional Menger system is a set of n-place functions containing n projections and closed under the so-called Menger's composition of n-place functions. We give the abstract characterization for subsets of these functional systems which contain functions having one common fixed point. 相似文献