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161.
162.
Boris Mahltig Jean-François Gohy Sayed Antoun Robert Jérôme Manfred Stamm 《Colloid and polymer science》2002,280(6):495-502
This paper reports on the pH-dependent adsorption of weak the polyelectrolytic diblock copolymer poly(2-vinylpyridine)-block-poly(dimethylaminoethyl methacrylate), (PVP-b-PDMAEMA). Aqueous PVP-b-PDMAEMA solutions have been adsorbed on alkaline pretreated silicon substrates. Altogether two copolymers differing in block ratio and molecular weight were used for the investigations. While the electrical charge of both samples in solution was investigated by electrophoretic measurements, the adsorbed polymer layers were studied with ellipsometry and atomic force microscopy (AFM). Depending on pH the electrical charge of both blocks of the diblock copolymer varied. Three different regimes have been identified. Under acidic conditions at pH<5, both blocks are mainly positively charged. At medium pH between 5 and 8, only the PDMAEMA block is positively charged. At pH>8, both blocks are nearly uncharged and a polymer precipitation occurred in solution. Each of these pH regimes was characterized by a specific adsorption behaviour leading to two adsorption maxima at acidic and alkaline pH values, while at medium pH a plateau in the adsorbed amount was observed. Moreover, the structures of the polyelectrolytes formed on the substrate after adsorption were specific to each of the three pH regimes. 相似文献
163.
Andrea Schfer Manfred Hesse Max Viscontini Henning Paul Berthold Fischer 《Helvetica chimica acta》1995,78(7):1763-1776
The experimental conditions developed for the detection of rather stable radical cations in solution by electrospray-ionization mass spectrometry (ESI-MS) of a FeII complex of 2-amino-5,6,7,8-tetrahydro-5-methylpteridin-4 (3H)-one ( 1c ) are used to observe the formation of the more unstable radical cations formed from 2-amino-5,6,7,8-tetrahydropteridin-4(3H)-one ( 1a ) and tris(pentane-2,4-dionato)iron(III) ([FeIII(acac)3]; 4 ) and to monitor their oxidation to the corresponding p-quinonoid dihydropterin complexes. These results contribute to the understanding of the important role played by 6β-5,6,7,8-tetrahydro-L -biopterin ( 1b ; a homologue of 1a ) together with iron as constituent of some cofactors. The complexes obtained from 1a and iron may be considered, e.g. as a model of the cofactor of the phenylalanine hydroxylase. Moreover, we describe an improved synthesis of 1c . 相似文献
164.
Phase-transfer alkylation of the 2-oxocycloalkane-l-carbonitriles 1a and 1b with ethyl 4-bromo-3-methoxy-2-butenoate ( 2 ), followed by deprotection and base-catalyzed cyclization gave the annulated cyclopentenones 5a and 5b , respectively, in high overall yields (Scheme 1). Stereoselective catalytic hydrogenation of 5b followed by de-ethoxycarbonylation afforded 14-oxo-cis-bicyclo[10.3.0]pentadecane-l-carbonitrile ( 7 ). Treatment of 7 with LiN(i-Pr)2 in THF gave the known synthetic muscone precursor 8 (Scheme 2). The tricyclo[10.4.0.01,15]hexadecan-14-one ( 14 ) was prepared from 7 in 5 steps by a reaction sequence proceeding without affecting the chiral centres (Scheme 2). The structure of 14 was established by X-ray structure analysis (Figure). 相似文献
165.
Perfluoroorgano tin and lead compounds can be prepared in high yields from the reactions of (CH3)3SnOCOCF3 and (CH3)3Pb(OCOCF3) with perfluoroorgano cadmium complexes. (CH3)3SiOCOCF3 reacts with (CF3)2Cd complexes — probably via the intermediate (CH3)3SiCF3 and CF2 elimination — to form (CH3)3SiF and CF3CdOCOCF3 complexes. While the reaction of (CF3)2Cd·D with (CH3)3SnONO2 yields CF3NO as the only volatile product, (Rf)2Cd·D (Rf C2F5, iC3F7) forms RfCdONO2·D and (CH3)3SnRf. The preparations and properties of the partly new compounds as well as the n.m.r. spectra are described. 相似文献
166.
Marita Hohmann Luise Krauth-Siegel K. Weidenhammer Wolfgang Schulze Manfred L. Ziegler 《无机化学与普通化学杂志》1981,481(10):95-106
Molecular and Crystal Structures of (CO)4W(μ-S-t-C4H9)2W(CO)4, η7-C7H7W(μ-SC6H4CH3)3W(CO)3 and η7-C7H7W(μ-S-n-C4H9)3W(CO)(μ-S-n-C4H9)2W(CO)4 The molecular structures of the two binuclear complexes (CO)4W(μ-S-t-C4H9)2W(CO)4 and η7-C7H7W(μ-SC6H4CH3)3W(CO)3 and of the tungsten cluster η7-C7H7W(μ-S-n-C4H9)3W(CO)-(μ-S-n-C4H9)2W(CO)4 respectively are described. In the nonlinear trinuclear cluster the central tungsten atom is connected to the two tungsten atoms by two and three μ-S-n-C4H9 bridges respectively and additionally by one W? W bond each. The coordination sphere of the W atoms is completed by a η7-C7H7 ring and four CO groups respectively; the central tungsten carries an additional CO group. 相似文献
167.
(Z)-2-Butenyl-dimethoxyborane adds smoothly to propanal and benzaldehyde to afford the homoallyl alcohols (R*,R*)- 1 and (R*,R*)- 2 , In contrast (E)-2-butenyl-dimethoxyborane leads to adducts having the (R*,S*)-configuration. Dimethoxy-(Z)-2-pentenylborane, dimethoxy-(Z)-(2-methyl-2-butenyl)borane and (2Z,4E)-or (2E,4Z)hexadienyl-dimethoxyborane, treated with propanal, give (R*,R*)- 3 , (R*,R*)- 4 , (E),(R*,S*)- 5 and (Z),(R*, R*)- 5 , respectively. A transition state model implying a pericyclic electron motion is in perfect agreement with the regio- and stereoselective outcome of these borane reactions. 相似文献
168.
Ring Enlargement by Lactonization of Methylated 1-(3′-Hydroxypropy1)-2-oxocyclododecane-1-carbonitriles The title compounds were prepared by Michael reaction of 2-oxocyclododecane-1-carbonitrile ( 1 ) and acrylaldehyde and its derivatives followed by NaBH4 reduction or methylation of the aldehyde group with [(CH3)2Ti(i-PrO)2] (Scheme 1). In all cases, the ring enlargement was performed with Bu4NF/THF to give different methylated derivatives of 12-cyano-15-pentadecanolide ( 13 ) in 95–99% yield. The Yields of the rearrangement products are not dependent on the positions and numbers of the CH3 groups in the side chain of 3 . The lactonization reaction is of unremarkable stereoselectivity. 相似文献
169.
Manfred Schlosser 《Angewandte Chemie (International ed. in English)》1974,13(11):701-706
Merits and drawbacks of known carbon-carbon linking procedures are outlined. Two novel methods are discussed in some detail: the copper-catalyzed alkylation of Grignard reagents and reactions with allylpotassium compounds. Both methods provide a very efficient access to saturated, unsaturated, as well as functionally substituted hydrocarbons and moreover permit an astonishing degree of regio- and stereoselective control of olefin synthesis. 相似文献
170.
During the examination of extracts from Oncinotis tenuiloba STAPF a new polyamine, N4-benzoylsperimidine ( 8 ), was isolated. For unambiguous structure elucidation, it was transformed into the diacetyl derivative 13 , and the three possible N-benzoyl-substituted isomers of spermidine 5, 8 , and 11 together with their peracetylated derivatives 12–14 , respectively, were synthesized and identified. 相似文献