作者:Hisako Sato、Emiko Nogami、Tomoko Yajima、Akihiko Yamagishi
DOI:10.1039/c3ra44070b
日期:——
Gel formation by low molecular mass gelators was investigated. The gelator was trans(RR)- or trans(SS)-N,N′-n-bromoalkanoyl-1,2-diaminocyclohexane (denoted as RR-CnBr or SS-CnBr, respectively; n = the number of carbon atoms in an alkanoyl group). When n was varied from 5 to 12, the gelators formed transparent or opaque or turbid gels in benzene except for n = 8. Focusing on the end effects, the gelation behavior of CnBr was compared with that of non-brominated counterparts (denoted as RR- or SS-Cn). From the vibrational circular dichroism (VCD) spectra of enantiomeric gelator/benzene-d6 gels, the signs of the coupled peaks around 1640 cm−1, which were assigned to the symmetric and asymmetric CO stretching vibrations from the higher to lower wavenumber, respectively, were opposite between SS-CnBr and SS-Cn (or between RR-CnBr and RR-Cn). On the other hand, the signs of the coupled peaks around 1550 cm−1 assigned to the NH stretching vibrations remained unaffected. The observed reversal of the signs in the CO couplet was rationalized in terms of the different modes of stacking in fibrils. In the case of Cn, for example, the molecules were stacked through anti-parallel double intermolecular hydrogen bonds using two pairs of >NH and >CO groups, while, in the case of CnBr, a single intermolecular hydrogen bond was formed with the remaining pair of >NH and >CO groups forming an intramolecular hydrogen bond. Single crystal X-ray analyses were performed for SS-C6Br and SS-C8Br. The results demonstrated that the length of the bromoalkanoyl chains drastically affected the packing modes in crystalline states.
低分子量凝胶剂的凝胶形成进行了研究。凝胶剂为trans(RR)-或trans(SS)-N,N'-n-溴烷酰基-1,2-二氨基环己烷(分别表示为RR-CnBr或SS-CnBr;n为烷酰基中碳原子的数量)。当n从5变化到12时,凝胶剂在苯中形成透明、浑浊或不透明的凝胶,除了n=8的情况。聚焦于端效应,将CnBr的凝胶化行为与没有溴化的对应物(表示为RR-或SS-Cn)进行了比较。从手性凝胶剂/苯-d6凝胶的振动圆二色性(VCD)光谱中,1640 cm−1附近的耦合峰的符号在SS-CnBr和SS-Cn(或RR-CnBr和RR-Cn)之间是相反的,这些峰分别被归因于对称和不对称CO伸缩振动,频率由高到低。而1550 cm−1附近的耦合峰对应的NH伸缩振动的符号则保持不变。CO双峰符号的观察到的逆转可以通过纤维中不同的堆叠方式来解释。例如,在Cn的情况下,分子通过反平行的双分子氢键堆叠,使用两对>NH和>CO基团;而在CnBr的情况下,形成了单个分子间氢键,剩余的那对>NH和>CO基团形成了分子内氢键。对SS-C6Br和SS-C8Br进行了单晶X射线分析。结果表明,溴烷酰基链的长度对晶体状态下的堆积方式产生了显著影响。