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1.
Gottfried Mayer Vitali Vogel Bas G. G. Lohmeijer Jean‐Franois Gohy Jacomina A. Van Den Broek Winfried Haase Ulrich S. Schubert Dieter Schubert 《Journal of polymer science. Part A, Polymer chemistry》2004,42(17):4458-4465
Micelles prepared from amphiphilic block copolymers in which a poly(styrene) segment is connected to a poly(ethylene oxide) block via a bis‐(2,2′:6′,2″‐terpyridine‐ruthenium) complex have been intensely studied. In most cases, the micelle populations were found to be strongly heterogeneous in size because of massive micelle/micelle aggregation. In the study reported in this article we tried to improve the homogeneity of the micelle population. The variant preparation procedure developed, which is described here, was used to prepare two “protomer”‐type micelles: PS20‐[Ru]‐PEO70 and PS20‐[Ru]‐PEO375. The dropwise addition of water to a solution of the compounds in dimethylformamide was replaced by the controlled addition of water by a syringe pump. The resulting micelles were characterized by sedimentation velocity and sedimentation equilibrium analyses in an analytical ultracentrifuge and by transmission electron microscopy of negatively stained samples. Sedimentation analysis showed virtually unimodal size distributions, in contrast to the findings on micelles prepared previously. PS20‐[Ru]‐PEO70 micelles were found to have an average molar mass of 318,000 g/mol (corresponding to 53 protomers per micelle, which is distinctly less than after micelle preparation by the standard method) and an average hydrodynamic diameter (dh) of 18 nm. For PS20‐[Ru]‐PEO375 micelles, the corresponding values were M = 603,000 g/mol (31 protomers per micelle) and dh = 34 nm. The latter particles were found to be identical to the “equilibrium” micelles prepared in pure water. Both micelle types had a very narrow molar mass distribution but a much broader distribution of s values and thus of hydrodynamic diameters. This indicates a conformational heterogeneity that is stable on the time scale of sedimentation velocity analysis. The findings from electron microscopy were in disagreement with those from the sedimentation analysis both in average micelle diameter and in the width of the distributions, apparently because of imperfections in the staining procedure. The preparation procedure described also may be useful in micelle formation from other types of protomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4458–4465, 2004 相似文献
2.
Vitali Vogel Jean‐Franois Gohy Bas G. G. Lohmeijer Jacomina A. Van Den Broek Winfried Haase Ulrich S. Schubert Dieter Schubert 《Journal of polymer science. Part A, Polymer chemistry》2003,41(20):3159-3168
In aqueous solutions, amphiphilic block copolymers in which a polystyrene (PS) segment is connected to a poly(ethylene oxide) (PEO) block via a bis(2,2′:6′,2″‐ terpyridine ruthenium) complex can form micelles. Such micelles of the protomer type PS20‐[Ru]‐PEO70, according to the preparation procedure representing frozen micelles, were studied by sedimentation velocity and sedimentation equilibrium analysis in an analytical ultracentrifuge and by transmission electron microscopy, with different techniques applied for the sample preparation. The particles obtained were surprisingly multifarious in size. In ultracentrifugation experiments performed at relatively low salt concentrations, the distributions of the sedimentation coefficient s20,w showed a pronounced peak at 9.6 S and a broad, only partly separated second peak around 14 S. The molar mass of the particles at the peak was around 430,000 g/mol, corresponding to an aggregation number of approximately 85. The average hydrodynamic diameter of the particles in the peak fraction was approximately 13 nm. In electron micrographs of negatively stained samples, spheres of diameters between 10 and 25 nm were the most abundant particles, but larger ones with a wide size range were also visible. The latter particles apparently were composed of smaller ones. The data from both sedimentation analysis and electron microscopy showed that (1) the studied compound formed primary micelles of diameters around 20 nm and (2) the primary micelles had a tendency toward aggregation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3159–3168, 2003 相似文献
3.
[reaction: see text] The solid-supported synthesis followed by cyclization in solution of cyclic (alpha(2)beta)-tripeptides, potential peptide beta-turn mimetics, is described. The cyclization takes advantage of facilitating the rotation between trans- and cis-rotamers of two amide bonds. The method is amenable to combinatorial approaches as is illustrated by the synthesis of a small array of cyclic (alpha(2)beta)-tripeptides. 相似文献
4.
We consider the problem of interpolating scattered data in 3 by analmost geometrically smoothGC
2 surface, where almostGC
2 meansGC
2 except in a finite number of points (the vertices), where the surface isGC
1. A local method is proposed, based on employing so-called degenerate triangular Bernstein-Bézier patches. We give an analysis of quintic patches forGC
1 and patches of degree eleven for almostGC
2 interpolation. 相似文献
5.
G. Le Bas C. de Rango N. Rysanek G. Tsoucaris 《Journal of inclusion phenomena and macrocyclic chemistry》1984,2(3-4):861-867
Studies of chiroptical properties need separation or at least enrichment of enantiomers. The separation is difficult with chiral conformers of molecules with very low barriers of internal rotation. However, in association with cyclodextrin, these labile molecules can exhibit a strong Cotton effect in solution: one chiral conformer is favoured by complexation. The cyclodextrins have the advantage to yield inclusion complex in solution as well as crystalline clathrates. Therefore, the absolute configuration of the guest can be obtained by determining the structure of the cyclodextrin. In this work, the first CD spectrum of 4-helicene is recorded and crystal structures of several clathrates of labile molecules are studied. 相似文献
6.
Valérie Bernat Catherine Ringard-Lefebvre Geneviève Le Bas Sylviane Lesieur 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):113-119
Interactions of α-cyclodextrin (α-CD) with dimyristoylphosphatidylcholine (DMPC) and Egg phosphatidylcholine (Egg-PC) were studied (i) by analyzing surface
pressure-area isotherms and surface tension of phospholipid monolayers formed at the interface between air and α-CD aqueous solutions and (ii) by X-ray diffraction performed on fully hydrated α-CD/phospholipid binary mixtures. The cyclodextrin molecules strongly interact with the two-dimension phospholipid assembly.
Their addition into the aqueous sub-phase leads to the removal of part of the phospholipids from the air-water interface:
the higher the α-CD concentration, the higher the phospholipid depletion. This should preferentially involve interactions between cyclodextrin
and the phosphatidylcholine head group as α-CD is water-soluble and not surface-active. At the three-dimension level, the bilayer packing of the phospholipid lamellar
phase appears not affected by the presence of cyclodextrin as shown by X-ray scattering at small angles whereas wide-angle
diffraction patterns reveal the formation of a crystalline phase organized in a pseudo-hexagonal lattice usually characteristic
of α-CD dimers. These results point out that α-CD should interact with bilayer-forming phospholipid molecules but likely according to a process that would preserve intact
at least a part of the multilamellar assembly. 相似文献
7.
Travaille AM Kaptijn L Verwer P Hulsken B Elemans JA Nolte RJ van Kempen H 《Journal of the American Chemical Society》2003,125(38):11571-11577
The lateral alignment of [012] habit-modified calcite crystals with respect to a carboxylic acid terminated self-assembled monolayer (SAM) of thiols has been determined. The crystals were grown from a Kitano solution (pH 5.6-6.0), and the samples were investigated with scanning electron microscopy, X-ray diffraction, and polarization microscopy. For the first time, a lattice match in one direction, which is the nearest neighbor direction of the SAM and the calcite <100> direction, has been experimentally shown. The experimental results are in good agreement with the theoretical models proposed in previous work, and it is expected that this method can be applied to similar systems where inorganic crystals nucleate with a preferred orientation to a SAM. 相似文献
8.
Oren?Regev Jean-Fran?ois?Gohy Bas?G.?G.?Lohmeijer Sunil?K.?Varshney Dominique?H.?W.?Hubert Peter?M.?Frederik Ulrich?S.?SchubertEmail author 《Colloid and polymer science》2004,282(4):407-411
Metallo-supramolecular diblock copolymers consisting of a polystyrene (PS) block connected to a poly(ethylene oxide) (PEO) block by a bis(terpyridine)ruthenium complex (PS20-[Ru]-PEO
y
) were used to prepare aqueous micelles. The length of the PS block was kept constant, while two PEOs of different molecular weight were used. The resulting hydrated micelles and aggregates were characterized by a combination of cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering measurements. The results were compared to those obtained for a covalent counterpart (PS22-b-PEO70). Cryogenic transmission electron microscopy allowed visualization of the PS core of the micelles. Moreover, the aggregates result from clustering of individual micelles. 相似文献
9.
Gohy JF Lohmeijer BG Schubert US 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(15):3472-3479
The formation of asymmetric bis-complexes, based on terpyridine ligands and ruthenium ions, is described as a powerful tool for the self-assembly of polymer blocks end-functionalized with terpyridine units. This is illustrated in this contribution for the synthesis of amphiphilic metallo-supramolecular block copolymers, which are further used to produce aqueous micelles. Finally, the reversibility of the supramolecular bond opens new avenues for the preparation and manipulation of these nano-objects. 相似文献
10.
Codée JD Stubba B Schiattarella M Overkleeft HS van Boeckel CA van Boom JH van der Marel GA 《Journal of the American Chemical Society》2005,127(11):3767-3773
A novel flexible assembly strategy is described for the modular synthesis of heparin and heparan sulfates. The reported strategy uses monomeric building blocks to construct the oligosaccharide chain to attain a maximum degree of flexibility. In the assembly, 1-hydroxyl glucosazido- and 1-thio uronic acid donors are combined in a sequential glycosylation protocol using sulfonium triflate activator systems. The key 1-thio uronic acids were obtained in an efficient manner from diacetone glucose employing a chemo- and regioselective oxidation of partially protected glucose and idose thioglycosides. 相似文献