This paper provides an integrated overview of the factors which control gelation in a family of dendritic gelators based on lysine building blocks. In particular, we establish that higher generation systems are more effective gelators, amide linkages in the dendron are better than carbamates, and long alkyl chain surface groups and a carboxylic acid at the focal point enhance gelation. The gels are best formed in relatively low polarity solvents with no hydrogen bond donor ability and limited hydrogen bond acceptor capacity. The dendrons with acid groups at the focal point can form two component gels with diaminododecane, and in this case, it is the lower generation dendrons which can avoid steric hindrance and form more effective gels. The stereochemistry of lysine is crucial in self-assembly, with opposite enantiomers disrupting each other's molecular recognition pathways. For the two-component system, stoichiometry is key, if too much diamine is present, dendron-stabilised microcrystals of the diamine begin to form. Interestingly, gelation still occurs in this case, and the systems with amides/alkyl chains are more effective gels, as a consequence of enhanced dendron–dendron intermolecular interactions allowing the microcrystals to form an interconnected network.
本文综合概述了控制基于赖
氨酸结构单元的树枝状凝胶剂系列凝胶化的各种因素。特别是,我们发现高世代体系是更有效的凝胶剂,树枝状结构中的酰胺连接比
氨基甲酸酯更好,长烷基链表面基团和焦点处的
羧酸能增强凝胶效果。凝胶最好在极性相对较低的溶剂中形成,这些溶剂没有氢键供体能力,而氢键受体能力有限。焦点上带有酸性基团的树枝状化合物可与二
氨基
十二烷形成双组分凝胶,在这种情况下,低代树枝状化合物可避免立体阻碍,形成更有效的凝胶。赖
氨酸的立体
化学在自组装中至关重要,相反的对映体会破坏彼此的分子识别途径。对于双组分系统来说,
化学计量是关键,如果二胺含量过高,二胺的树枝状稳定微晶就会开始形成。有趣的是,在这种情况下仍会发生凝胶化,而含有酰胺/烷基链的体系凝胶化效果更好,这是因为树枝膦-树枝膦分子间相互作用增强,使微晶形成相互连接的网络。