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排序方式: 共有140条查询结果,搜索用时 11 毫秒
51.
Nikolay O. Mchedlov‐Petrossyan Natalya A. Vodolazkaya Anna G. Yakubovskaya Aleksey V. Grigorovich Vera I. Alekseeva Lyubov P. Savvina 《Journal of Physical Organic Chemistry》2007,20(5):332-344
The peculiarities of the structure of the fluorescent dye N,N'‐di‐n‐octadecylrhodamine advantage its using as an interfacial acid–base probe in aqueous micellar solution of colloidal surfactants. Two long hydrocarbon tails of the dye provide similar orientation of both cation and zwitterion on the micelle/water interface, with the ionizing group COOH exposed to the Stern region in all the systems studied. Further, the charge type of the acid–base couple, A+B±, ensures similar values of the ‘intrinsic’ contribution, pK, to the ‘apparent’ pK value in micelles of different surfactants. This makes the indicator suitable for determination of electrical surface potentials, Ψ. The pKs have been obtained in cationic, anionic, zwitterionic, and nonionic surfactant systems, at various salt background. In total 17 systems were studied. At bulk counterion concentration of ca. 0.05 M, the pK values vary from 2.14 ± 0.07 in n–C18H37N(CH3)Cl– micelles to 5.48 ± 0.06 in n–C16H33OSONa+ micelles. The Ψ values, corresponding to the Stern region of micelles, have been evaluated as Ψ = 59.16 pK–pK for T = 298.15 K. The pK parameter was equated to the average value of 4.23 in nonionic surfactants (4.12–4.32, depending on the surfactant type). For cetyltrimethylammonium bromide and sodium n‐dodecylsulfate micelles, the Ψ values (±(7–11) mV) appeared to be +118 mV and at bulk Br? concentration 0.019 M and ?76 mV at bulk Na+ concentration 0.020 M, respectively. This satisfactorily agrees with the theoretical values +111 and ?84 mV, estimated using the Oshima, Healy, and White equation for these well‐defined colloidal systems. Finally, not only absorption, but also fluorescence spectra display the same response to changes in bulk pH. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
52.
It has been shown in a number of recent papers that Graver bases methods enable to solve linear and nonlinear integer programming problems in variable dimension in polynomial time, resulting in a variety of applications in operations research and statistics. In this article we continue this line of investigation and show that Graver bases also enable to minimize quadratic and higher degree polynomial functions which lie in suitable cones. These cones always include all separable convex polynomials and typically more. 相似文献
53.
A method for simultaneous covalent immobilization of glucose oxidase and peroxidase with previously oxidized carbohydrate
residues to urea derivative of regenerated acetylcellulose granules is described. The effect of immobilization on the catalytic
properties of the separately immobilized enzymes are studied. The immobilized enzymes manifested no change in their pH and
temperature optima and slight increase ofK
m
x compared to data for the soluble enzymes. A column packed with simultaneously immobilized enzymes is used for manual glucose
determination in blood sera. The results are in high correlation with those obtained by the Beckman Glucose Analyzer method
(r = 0.976). The method is economic (the enzyme-carrier conjugate may be used more than 300 times), easy to perform, and less
time consuming than the manual methods utilizing soluble enzymes. The established manual method can be proposed for emergency
clinical analysis and smaller clinical laboratories. 相似文献
54.
G. B. Shul'pin A. E. Shilov G. V. Nizova A. K. Yatsimirskii S. A. Deiko P. Lederer 《Russian Chemical Bulletin》1986,35(10):2177-2179
Conclusion Heating a solution of PtCl6
2– ions and toluene in CF3CO2H-H2O leads to the formation of a platinum(IV) -tolyl complex which decomposes in the presence of free toluene to give 3,3-, 4,4-, 3,4-, 2,3- and 2,4-ditolyls.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2377–2380, October, 1986.This study was carried out in the framework of the Cooperation Program of Catalysis Scientists at the academies of sciences of the Socialist countries. 相似文献
55.
56.
Lyubov N. Sobenina Denis N. Tomilin Maxim D. Gotsko Igor A. Ushakov Boris A. Trofimov 《Tetrahedron》2018,74(13):1565-1570
On the example of menthofuran, a naturally abundant compound, it has been shown for the first time that the furan ring can be readily cross-coupled with acylhaloacetylenes in the solid Al2O3 powder at room temperature to afford the corresponding 2-ethynyl derivatives in up to 88% yield. The reaction represents a ring closing/ring opening process that includes reversible formation of the intermediate cycloadducts further producing acetylene derivatives with elimination of HHal. 相似文献
57.
Scandale W Vomiero A Baricordi S Dalpiaz P Fiorini M Guidi V Mazzolari A Della Mea G Milan R Ambrosi G Bertucci B Burger WJ Zuccon P Cavoto G Luci C Santacesaria R Valente P Vallazza E Afonin AG Chesnokov YA Maisheev VA Yazynin IA Kovalenko AD Taratin AM Denisov AS Gavrikov YA Ivanov YM Lapina LP Malyarenko LG Skorobogatov VV Suvorov VM Vavilov SA Bolognini D Hasan S Mozzanica A Prest M 《Physical review letters》2008,101(16):164801
Beam deflection due to axial channeling in a silicon crystal bent along the 111 axis was observed with 400 GeV/c protons at the CERN Super Proton Synchrotron. The condition for doughnut scattering of protons by the atomic strings of the crystal was attained. Such a condition allowed one to observe a beam deflection of 50 murad with about 30% efficiency. The contribution of hyperchanneled states of protons to the observed beam deflection was less than 2% according to simulation results. 相似文献
58.
59.
A.?A.?TrifonovEmail author B.?G.?Shestakov D.?M.?Lyubov K.?A.?Lyssenko 《Russian Chemical Bulletin》2018,67(1):50-55
The reaction of equimolar amounts of ytterbocene (C5Me4H)2Yb(THF)2 and iminopyridine 2,6-Pri2C6H3N=CH(C5H4N) accompanied by the one-electron oxidation of the ytterbium ion produced the unique lanthanide complex (C5Me4H)2YbIII[2,6-Pri2-C6H3NCH(C5H4N)]–? with the iminopyridine radical-anionic ligand. The structure of the complex in the crystalline state was established by X-ray diffraction and its magnetic properties were studied in the temperature range of 1.8—300 K. 相似文献
60.
Light‐Harvesting Three‐Chromophore Systems Based on Biphenyl‐Bridged Periodic Mesoporous Organosilica 下载免费PDF全文
Dr. Lyubov Grösch Dr. Young Joo Lee Dr. Frank Hoffmann Prof. Dr. Michael Fröba 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):331-346
Three‐chromophore systems with light‐harvesting behavior were prepared, which are based on periodic mesoporous organosilica (PMO) with crystal‐like ordered structure. The organic bridges of biphenyl‐PMO in the pore walls act as donors and two types of dye are incorporated in the one‐dimensional channels. Consecutive two‐step‐Förster resonance energy transfer is observed from the biphenyl moieties to mediators (diethyl‐aminocoumarin or aminoacridone), followed by energy transfer from mediators to acceptors (dibenzothiacarbocyanine, indodicarbocyanine, sulforhodamine G). High energy‐transfer efficiencies ranging from 70 to 80 % are obtained for two‐step‐FRET, indicating that the mesochannel structure with one‐dimensional ordering provides spatial arrangement of chromophore pairs for an efficient direct energy transfer. The emission wavelength can be tuned by a choice of acceptor dye: 477 nm (diethylaminocoumarin), 519 nm (aminoacridone), 567 nm (sulforhodamine G), 630 nm (dibenzothiacarbocyanine), and 692 nm (indodicarbocyanine). 相似文献