Deng Wei, Yamaguchi Hiroyasu, Takashima Yoshinori, Harada Akira
Department of Macromolecular Science, Graduate School of Science, Osaka University, Machikaneyama, Toyonaka, Osaka, 560-0043, Japan.
Chem Asian J. 2008 Apr 7;3(4):687-95. doi: 10.1002/asia.200700378.
A methodology for preparing supramolecular hydrogels from guest-modified cyclodextrins (CDs) based on the host-guest and hydrogen-bonding interactions of CDs is presented. Four types of modified CDs were synthesized to understand better the gelation mechanism. The 2D ROESY NMR spectrum of beta-CD-AmTNB (Am=amino, TNB=trinitrobenzene) reveals that the TNB group was included in the beta-CD cavity. Pulsed field gradient NMR (PFG NMR) spectroscopy and AFM show that beta-CD-AmTNB formed a supramolecular polymer in aqueous solution through head-to-tail stacking. Although beta-CD-AmTNB did not produce a hydrogel due to insufficient growth of supramolecular polymers, beta-CD-CiAmTNB (Ci=cinnamoyl) formed supramolecular fibrils through host-guest interactions. Hydrogen bonds between the cross-linked fibrils resulted in the hydrogel, which displayed excellent chemical-responsive properties. Gel-to-sol transitions occurred by adding 1-adamantane carboxylic acid (AdCA) or urea. (1)H NMR and induced circular dichroism (ICD) spectra reveal that AdCA released the guest parts from the CD cavity and that urea acts as a denaturing agent to break the hydrogen bonds between CDs. The hydrogel was also destroyed by adding beta-CD, which acts as the competitive host to reduce the fibrils. Furthermore, the gel changed to a sol by adding methyl orange (MO) as a guest compound, but the gel reappeared upon addition of alpha-CD, which is a stronger host for MO.
本文提出了一种基于环糊精（CDs）的主客体相互作用和氢键相互作用，由客体修饰的环糊精制备超分子水凝胶的方法。合成了四种类型的修饰环糊精，以更好地理解凝胶化机制。β-环糊精-氨三硝基苯（Am = 氨基，TNB = 三硝基苯）的二维ROESY NMR谱表明，TNB基团包含在β-环糊精的空腔中。脉冲场梯度NMR（PFG NMR）光谱和原子力显微镜（AFM）表明，β-环糊精-氨三硝基苯在水溶液中通过头对头堆积形成了超分子聚合物。尽管由于超分子聚合物生长不足，β-环糊精-氨三硝基苯没有产生水凝胶，但β-环糊精-肉桂酰氨三硝基苯（Ci = 肉桂酰基）通过主客体相互作用形成了超分子原纤维。交联原纤维之间的氢键导致了水凝胶的形成，该水凝胶表现出优异的化学响应特性。通过添加1-金刚烷羧酸（AdCA）或尿素发生凝胶-溶胶转变。1H NMR和诱导圆二色性（ICD）光谱表明，AdCA从环糊精空腔中释放客体部分，尿素作为变性剂破坏环糊精之间的氢键。添加作为竞争性主体的β-环糊精也会破坏水凝胶，从而减少原纤维。此外，通过添加作为客体化合物的甲基橙（MO），凝胶转变为溶胶，但加入对MO亲和力更强的α-环糊精后，凝胶再次出现。
