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171.
Bandyopadhyay P Janout V Zhang LH Regen SL 《Journal of the American Chemical Society》2001,123(31):7691-7696
A series of ion conductors have been synthesized in which the degree of facial hydrophilicity has been systematically varied. Specifically, conjugates have been prepared from cholic acid and spermine in which the hydrophilic face of each sterol bears methoxy (1), hydroxy (2), carbamate (3), or sulfate groups (4). The ability of these conjugates to promote the transport of Na(+) across phosphatidylcholine membranes of varying thickness has been investigated by (23)Na NMR spectroscopy. Examination of observed activities in three different phosphatidylcholine membranes has provided evidence for membrane-spanning dimers as the transport-active species. In the thinnest membranes investigated, made from 1,2-dimyristoleoyl-sn-glycero-3-phosphocholine (C14), Na(+)-transport activity was found to increase, substantially, with increasing facial hydrophilicity. In thicker membranes, made from 1,2-dioleoyl-sn-glycero-3-phosphocholine (C18), observed activities were found to decrease with increasing facial hydrophilicity; with a membrane of intermediate thickness, prepared from 1,2-dipalmitoleoyl-sn-glycero-3-phosphocholine (C16), ion-conducting activity increased and then decreased, with continuous increases in facial hydrophilicity. The possible origins for these variations in activity are briefly discussed. 相似文献
172.
173.
Janina Müttel Dieter Rautenbach Friedrich Regen Thomas Sasse 《Graphs and Combinatorics》2013,29(4):1067-1076
We prove lower bounds on the number of different cycle lengths of cubic Hamiltonian graphs that do not contain a fixed subdivision of a claw as an induced subgraph. 相似文献
174.
McCullough DH Grygorash R Regen SL 《Langmuir : the ACS journal of surfaces and colloids》2007,23(19):9606-9610
Langmuir-Blodgett deposition of a single monolayer of 1,2,4,5-tetrakis[(N-(perfluoroundecanoamidoethyl)-N,N-dimethylammonium)methyl]benzene tetrabromide (1) onto a thin film made from alternating layers of poly(diallydimethylammonium chloride) (PDADMA) and poly(4-styrenesulfonate) (PSS) ions affords a uniform fluorinated surface of low energy. An analogous surface that has been constructed by self-assembly shows the same critical surface tension of 16.5 dyn/cm. A comparison of Zisman plots for these two modified films, in combination with analysis by X-ray photoelectron spectroscopy, indicates that Langmuir-Blodgett deposition produces a higher quality and more densely packed fluorocarbon surface that is very hydrophobic. In sharp contrast, the use of a single-chain analog (i.e., N-(perfluoroundecanoamidoethyl)-N,N,N-trimethylammonium bromide) (2)) affords relatively high energy surfaces by Langmuir-Blodgett deposition and by self-assembly. 相似文献
175.
Drouin F Whitehorne TJ Schaper F 《Dalton transactions (Cambridge, England : 2003)》2011,40(6):1396-1400
The reaction of N,N'-dibenzyl-2-amino-4-imino-pent-2-ene, nacnac(Bn)H, with 1 or 2 equiv. of MgnBu? afforded the homoleptic complex nacnac(Bn)?Mg. The reaction of nacnac(Bn)H with Mg(N(SiMe?)?)? yielded nacnac(Bn)MgN(SiMe?)?, which reacted with tert-butanol to form nacnac(Bn)MgOtBu. The latter complex crystallizes as an alkoxide bridge dimer and is active in the ring-opening polymerisation of rac-lactide. Polymerisations at room temperature afforded atactic polylactide, while polymerisations at -17 and -26 °C afforded polylactide with a small isotactic bias (P(m) = 0.52, and 0.55, respectively). 相似文献
176.
Wang Y Stedronsky E Regen SL 《Langmuir : the ACS journal of surfaces and colloids》2008,24(12):6279-6284
The main barrier for gas permeation across ionically cross-linked Langmuir-Blodgett (LB) bilayers, made from a 5,11,17,23,29,35-hexakis[( N, N, N-trimethylamonium)-N-methyl-37,38,39,40,41,42-hexakis-n-hexamedecyloxy-calix[6]arene hexachloride (1) and poly(sodium 4-styrenesulfonate) (PSS), has been determined by measuring the effects of NaCl on the thickness of the PSS layer encased between the calixarene layers and the permeation characteristics of the resulting membrane. Specifically, the fact that NaCl increases the uptake of PSS by the LB film and increases the permeance of these membranes toward N2 and CO2 but not He provides compelling evidence that the main barrier for permeation is the calixarene layers and not the PSS layer that is encased between them. The effects of NaCl on ionic cross-linking, surface pressure, and surface viscosities are discussed. 相似文献