Selektive Vesikelbildung aus Calixarenen durch Selbstaggregation

Tanaka, Yasutaka; Miyachi, Masami; Kobuke, Yoshiaki

doi:10.1002/(sici)1521-3757(19990215)111:4<565::aid-ange565>3.0.co;2-2

Cited by 16 publications

(2 citation statements)

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“…Crystallisation of equimolar amounts of bis-pyridylmethyltetra-tert-butylcalix [4]arene (1) [14] and 1,4-diiodotetrafluorobenzene (2 a) or its 1,4-dibromo analogue 2 b by slow solvent diffusion (carbon tetrachloride/vaseline oil system) affords white crystalline solid, 3 a and 3 b, respectively, which are stable to air and moisture at room temperature. Microanalyses (C, H, N, I, Br) and 1 H/ 19 F-NMR spectra in the presence of 2,2,2-trifluoroethyl ether as internal standard (see Experimental Section) reveal that the calixarene (CA) and perfluorocarbon (PFC) components 1 and 2 are present in a 1:1 ratio in co-crystal 3.…”

Section: Resultsmentioning

confidence: 99%

“…[1] Calixarenes have frequently been used as versatile platforms for the covalent insertion of appendages which drive self-assembly processes by using weak forces such as hydrogen bonds, [2] co-ordination bonds, [3] and van der Waals interactions. [4] However, in most cases, calixarenes have been used as endo-receptors [5] (concave molecules), a role they are perfectly tailored to by the cone conformation they frequently adopt. A wide variety of metal cations (alkaline, alkaline earth, transition metal, lanthanide cations) have been complexed in the solid state and in solution and the ion has invariably been included in the calixarene cavity region.…”

Section: Introductionmentioning

confidence: 99%

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Attractive pi-pi interactions between two of the four outside cavity faces of 1,3-bis-pyridylmethylcalix[4]arene (1) and both faces of 1,4-diiodotetrafluorobenzene (2a) form infinite one-dimensional non-covalent ribbons where the two modules alternate. These ribbons are cross-linked by electron donor-acceptor interactions between picolyl nitrogen atoms of calixarene 1 in one chain and iodine atoms of perfluoroarene 2a in another chain and the two-dimensional supramolecular network 3a is formed. A similar behaviour is also shown by 1,4-dibromotetrafluorobenzene (2b). The halogen bonding and the attractive pi-pi interactions occur in directions which are nearly orthogonal each other. Diiodotetrafluorobenzene, being involved in both these interactions, appears to be a particularly interesting tecton. The ability of electron-poor arenes to elicit the exo-receptor potential of calixarene module by connecting their outside faces through pi-pi interactions may be developed as a new and general binding protocol in calixarene self-assembly processes.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Cyclodextrin Bilayer Vesicles

Ravoo

Darcy

2000

Angewandte Chemie

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Over the past decade, several groups have reported amphiphilic cyclodextrin derivatives that display a range of lyotropic and thermotropic mesophases. Amphiphilic cyclodextrins have been shown to form monolayers at the air ± water interface [1] and micelles in water. [2] Thermotropic liquid crystals of cyclodextrins were also described. [3] Amphiphilic cyclodextrins can be admixed in limited percentages to phospholipid monolayers [4] as well as liposomes, [5] and they can be dispersed as ªnanoparticlesº of pharmaceutical interest. [6] However, with few exceptions, these materials have poor water solubility. We have now prepared the first examples of bilayer vesicles composed entirely of amphiphilic cyclodextrins. These vesicles combine the properties of liposomes and macrocyclic host molecules, and create new possibilities for the development of advanced host ± guest carrier and delivery systems. Some examples of vesicles composed of amphiphilic macrocycles such as calixarenes [7] and cryptands [8] were recently described.Heptakis(6-alkylthio)-b-cyclodextrins [3] display thermotropic mesophases and form monolayers at the air ± water interface, [1f,g, 3, 9] but are practically insoluble in water. The poor water solubility of these cyclodextrins most likely results from intramolecular hydrogen bonding of the secondary hydroxyl groups, as is the case for unmodified b-cyclodextrin. Attempts to ªbreakº this hydrogen-bond network by persubstitution of the secondary side by methyl and acetyl groups only slightly improved the water solubility. [9] However, we demonstrate herein that substitution of the secondary side with hydrophilic hydroxyethyl groups dramatically improves the water solubility (as observed previously for random and low-degree substitution of b-cyclodextrin [10] ), and provides cyclodextrins with pronounced amphiphilic character.Cyclodextrins 4 and 5 were obtained in a three-step synthesis from b-cyclodextrin. b-Cyclodextrin was per-brominated at the C 6 positions, [11] and the resulting heptakis(6bromo-6-deoxy)-b-cyclodextrin (1) yielded the 6-alkylthioethers 2 and 3 by reaction with potassium n-dodecylthiolate and n-hexadecylthiolate, respectively. [3] Subsequently, we developed an efficient modification of the hydroxyethylation process for b-cyclodextrin, [10] which uses ethylene carbonate as the alkylating agent. We found that 2 and 3 can be efficiently hydroxyethylated in tetra-N-methylurea (TMU) at 150 8C using an excess of ethylene carbonate and adding 10 % of K 2 CO 3 as base. [12] The elevated temperature is essential for rapid and extensive substitution. Cyclodextrin 4 was purified

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