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Hydrogels Composed of Organic Amphiphiles and α‐Cyclodextrin: Supramolecular Networks of Their Pseudorotaxanes in Aqueous Media
Author(s) -
Taira Toshiaki,
Suzaki Yuji,
Osakada Kohtaro
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200903315
Subject(s) - chemistry , supramolecular chemistry , crystallography , crystallinity , aqueous solution , cyclodextrin , proton nmr , rotaxane , stereochemistry , polymer chemistry , crystal structure , organic chemistry
Mixtures of N ‐alkyl pyridinium compounds [py‐ N ‐(CH 2 ) n OC 6 H 3 ‐3,5‐(OMe) 2 ] + (X − ) ( 1b Cl: n =10, X=Cl; 1c Br: n =12, X=Br) and α‐cyclodextrin (α‐CD) form supramolecular hydrogels in aqueous media. The concentrations of the two components influences the sol–gel transition temperature, which ranges from 7 to 67 °C. Washing the hydrogel with acetone or evaporation of water left the xerogel, and 13 C CP/MAS NMR measurements, powder X‐ray diffraction (XRD), and scanning electron microscopy (SEM) revealed that the xerogel of 1b Cl (or 1c Br) and α‐CD was composed of pseudorotaxanes with high crystallinity. 13 C{ 1 H} and 1 H NMR spectra of the gel revealed the detailed composition of the components. The gel from 1b Cl and α‐CD contains the corresponding [2]‐ and [3]pseudorotaxanes, [ 1b⋅ (α‐CD)]Br and [ 1b⋅ (α‐CD) 2 ]Br, while that from 1c Br and α‐CD consists mainly of [3]pseudorotaxane [ 1c⋅ (α‐CD) 2 ]Br. 2D ROESY 1 H NMR measurements suggested intermolecular contact of 3,5‐dimethoxyphenyl and pyridyl end groups of the axle component. The presence of the [3]pseudorotaxane is indispensable for gel formation. Thus, intermolecular interaction between the end groups of the axle component and that between α‐CDs of the [3]pseudorotaxane contribute to formation of the network. The supramolecular gels were transformed into sols by adding denaturing agents such as urea, C 6 H 3 ‐1,3,5‐(OH) 3 , and [py‐ N ‐ n Bu] + (Cl − ).