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21.
The pigments Luteoskyrin (Ls) and Rugulosin (Rg) might adopt a priori two extreme conformations, a planar and an angular one. To determine the predominant conformation in solution, the nature of the lowest energy transition of the chromophores and the presence of intramolecular H-bonding have been investigated. The solvent effects on electronic absorption and CD spectra indicated the π-π* nature of the lowest energy transition. Treatments of the electronic absorption results according to McRae and Kosower relations, IR absorption and PMR spectra suggested the presence of strong intra-molecular H-bonds. From these results it was concluded that Ls and Rg adopted in a variety of solvents the most planar conformation. 相似文献
22.
Anionic polymerization of methyl methacrylate in THF and toluene at ?70° was studied by means of i.r. spectroscopy. The reaction mixtures show characteristic absorption at 1600–1750 cm?1 caused by the stretching vibrations of the propagating centre as well as by the groups obtained in side reactions (metal splitting, addition to a carbonyl group, cyclization). Sec-butyllithium is more effective in THF than n-butyllithium, ethyllithium and fluorenyllithium. When polymerizing in toluene, small amounts of a donor (THF or HMPT) cause formation of active centres similar to those in pure THF. The “living” ends of oligo-MMA form 1:1 complexes with electron acceptors such as trialkylaluminium and triethylboron. 相似文献
23.
A method for improving separations of peptides and other positively charged species in capillary zone electrophoresis with untreated capillaries using acidic buffers containing tetraalkylammonium cations is described. Tetramethylammonium and tetrabutylammonium cations dynamically modify the capillary surface, leading to a reversal in the direction of the electroosmotic flow. As a result, the adsorption of positively charged peptides and proteins is minimized, and resolution and peak capacity are improved as the migration of cationic analytes is counterbalanced by the electroosmotic flow. The combining effect of reversing electroosmotic flow and cyclodextrin inclusion complexation on separations of closely related peptides and a protein mixture, as well as tryptic digest of hemoglobin is demonstrated. 相似文献
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Nguyen Thanh Long Pham Ngoc Dinh Alain 《Mathematical Methods in the Applied Sciences》1993,16(4):281-295
We study the following initial and boundary value problem: In section 1, with u0 in L2(Ω), f continuous such that f(u) + ? non-decreasing for ? positive, we prove the existence of a unique solution on (0,T), for each T > 0. In section 2 it is proved that the unique soluition u belongs to L2(0, T; H ∩ H2) ∩ L∞(0, T; H) if we assume u0 in H and f in C1(?,?). Numerical results are given for these two cases. 相似文献
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Nguyen Quang Do Thong 《K-Theory》1993,7(5):429-441
The well-known formula of Riemann-Hurwitz gives the change of genuses in ann-fold covering of compact connected Riemann surfaces. In Iwasawa theory, there existp-adic analogues which give the change of certain ±-invariants in ap-extension ofCM number fields. Using functorial and arithmetical properties ofK
3, we extend such Riemann-Hurwitzp-adic formulas to non-CM fields, assuming some restrictive hypotheses on the capitulation ofK
2. 相似文献