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排序方式: 共有1391条查询结果,搜索用时 15 毫秒
991.
Emmanuel Gonzalez Robert Faure Emile-Jean Vincent Modesta Espada Jos Elguero 《Magnetic resonance in chemistry : MRC》1979,12(10):587-592
The 13C chemical shifts of 32 pyrazoles were measured in hexadeuterated dimethyl sulphoxide and in hexamethylphosphorotriamide. Substituent effects (methyl and amino groups on the pyrazolic carbons, and methyl, n-butyl and phenyl groups on the nitrogen) were calculated by multilinear regression analysis. The general problem of the 13C NMR study of annular tautomerism in azoles is discussed and illustrated by the 3(5)-aminopyrazole case. 相似文献
992.
993.
Gilles Nicollier Raffaele Tabacchi Jos Gavin Jos Luis Breton Antonio G. Gonzalez 《Helvetica chimica acta》1979,62(3):807-810
Triterpenoids from ‘Oakmoss’ (Evernia Prunastri (L .) ACH .) Seven triterpenoids have been isolated from ‘oakmoss’ (Evernia Prunastri (L .) ACH .) extracts by column chromatography and identified as friedelin ( 1 ), taraxerol ( 2 ), 29-nor-21 α-hopan-3,22-dione ( 3 ), moretenone ( 4 ), ursolic acid ( 5 ), lupeol ( 6 ) and lanosterol ( 7 ). 相似文献
994.
The spectral characteristics of biacetylmonoxime 2-picolyl-imine (BMPA) are reported in this paper. The acid-base behavior of BMPA is spectrophotometrically studied. 相似文献
995.
Suppose that a consistent one-step numerical method of orderr is applied to a smooth system of ordinary differential equations.Given any integer m 1, the method may be shown to be of orderr + m as an approximation to a certain modified equation. Ifthe method and the system have a particular qualitative propertythen it is important to determine whether the modified equationsinherit this property. In this article, a technique is introducedfor proving that the modified equations inherit qualitativeproperties from the method and the underlying system. The techniqueuses a straightforward contradiction argument applicable toarbitrary one-step methods and does not rely on the detailedstructure of associated power series expansions. Hence the conclusionsapply, but are not restricted, to the case of Runge-Kutte methods.The new approach unifies and extends results of this type thathave been derived by other means: results are presented forintegral preservation, reversibility, inheritance of fixed points.Hamiltonian problems and volume preservation. The techniquealso applies when the system has an integral that the methodpreserves not exactly, but to order greater than r. Finally,a negative result is obtained by considering a gradient systemand gradient numerical method possessing a global property thatis not shared by the associated modified equations. 相似文献
996.
Polyethyleneimine‐Coated Gold Nanoparticles: Straightforward Preparation of Efficient DNA Delivery Nanocarriers
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Dr. Mariano Ortega‐Muñoz Prof. M. Dolores Giron‐Gonzalez Prof. Rafael Salto‐Gonzalez Prof. Ana Belen Jodar‐Reyes Samantha E. De Jesus Prof. F. Javier Lopez‐Jaramillo Prof. Fernando Hernandez‐Mateo Prof. Francisco Santoyo‐Gonzalez 《化学:亚洲杂志》2016,11(23):3365-3375
A novel one‐pot method for the synthesis of polyethyleneimine (PEI)‐coated gold nanoparticles (AuPEI‐NPs) that combines the reductant–stabilizer properties of PEI with microwave irradiation starting from hydrogen tetrachloroaurate acid (HAuCl4) and branched PEI 25 kDa (b25kPEI) was explored. The method was straightforward, green, and low costing, for which the Au/PEI ratio (1:1 to 1:128 w/w) was a key parameter to modulate their capabilities as DNA delivery nanocarriers. Transfection assays in CHO‐k1 cells demonstrated that AuPEI‐NPs with 1:16 and 1:32 w/w ratios behaved as effective DNA gene vectors with improved transfection efficiencies (twofold) and significantly lower toxicity than unmodified b25kPEI and Lipofectamine 2000. The transfection mediated by these AuPEI‐NP–DNA polyplexes preferentially used the caveolae‐mediated route for intracellular internalization, as shown by studies performed by using specific internalization inhibitors as well as colocalization with markers of clathrin‐ and caveolae‐dependent pathways. The AuPEI‐NP polyplexes preferentially used the more efficient caveolae internalization pathway to promote transfection, a fact that supports their higher transfection efficiency relative to that of Lipofectamine 2000. In addition, intracellular trafficking of the AuPEI‐NPs was studied by transmission electron microscopy. 相似文献
997.
G. G. Trigo C. Avendao P. Ballesteros A. Gonzalez 《Journal of heterocyclic chemistry》1978,15(5):833-837
The conformations of a new series of compounds of the general structure N-alkylgranatanine-3-spiro-5′-hydantoin, synthesized in our laboratory from the corresponding 9-alkyl-9-azabieyclo-[3.3.1 ]nonan-3-ones, were studied by 1 H nmr spectroscopy at different pH values in some instances. We have assigned boat conformations for the spiropiperidines. 相似文献
998.
999.
Roberto Martínez Lucia Valle Marcos Gonzalez Claudia Romano 《Journal of heterocyclic chemistry》1997,34(3):1043-1045
Reaction of 4(7)-aminobenzimidazole with ethyl 2-alkylmalonates gave the novel 4,5,6,7-tetrahydro-5-alkyl-imidazo[1,5,4-ef][1,5]benzodiazepine-4,6-diones, and the 2-alkyl-4(7)-(2′-ethoxycarbonyl)acetamido-benzimidazoles. The structure of all the products was corroborated by ir, mass spectrometry and 1H-nmr. 相似文献
1000.
Polymer-supported N-alkyl-2-chloro pyridinium triflate was synthesized in one step from Wang resin. This reagent proved to be a very effective coupling reagent for the synthesis of esters or amides from carboxylic acids and alcohols or amines (primary and secondary). [reaction: see text] 相似文献