The influence of oligo(ethylene glycol) side chains on the self-assembly of benzene-1,3,5-tricarboxamides in the solid state and in solution
作者:Patrick J. M. Stals、Jan F. Haveman、Rafael Martín-Rapún、Carel F. C. Fitié、Anja R. A. Palmans、E. W. Meijer
DOI:10.1039/b816418e
日期:——
Substituted benzene-1,3,5-tricarboxamides (BTAs) 1–4 comprising polar tetraethyleneglycol (tetraEG) and/or apolar (R)-3,7-dimethyloctyl side chains were synthesised and their self-assembly in the solid state and in solution was investigated. While BTA 1 (comprising 3 apolar side chains) shows helical columnar packing via threefold α-helical type intermolecular hydrogen bonding in the solid state and up to high dilutions in alkane solution (10−5 M), helical columnar order is only preserved for asymmetric BTA 2 (comprising 1 polar and 2 apolar side chains) in the solid state and in a concentrated alkane solution (10−2 M). The association constant Kass is reduced by a factor of 107 by introducing one polar tetraEG chain into the BTA. A further increase in the number of polar tetraEG chains attached to BTA core results in the complete loss of intermolecular hydrogen bond formation in the solid state and in solution. Moreover, for the polar BTAs 3–4, comprising 2 or 3 polar tetraEG chains, no self-assembly in water occurs because of the lack of hydrophobic shielding. We propose that tetraEG side chains interfere with the intermolecular hydrogen bonds, weakening the stacking behaviour of these asymmetric derivatives and drastically lowering the association constant due to competing intramolecular hydrogen bonding interactions. In contrast, one methoxyethyl unit does not affect the stability of the aggregation of BTAs (Kass = 3 × 107 M−1) showing that more than one EG unit is required to disrupt the self-assembly of BTAs.
合成了包含极性四乙烯乙二醇(tetraEG)和/或非极性(R)-3,7-二甲基八基侧链的取代苯-1,3,5-三羧酰胺(BTA)1–4,并研究了其在固态及溶液中的自组装行为。BTA 1(含有3个非极性侧链)在固态和高稀释度的烷烃溶液(10−5 M)中通过三重α螺旋类型的分子间氢键显示出螺旋柱状堆积,而不对称的BTA 2(含有1个极性和2个非极性侧链)仅在固态和浓缩的烷烃溶液(10−2 M)中保持螺旋柱状有序。引入一个极性tetraEG链到BTA中,结合常数Kass降低了107倍。进一步增加附加到BTA核心的极性tetraEG链的数量会导致固态和溶液中分子间氢键形成的完全丧失。此外,对于极性BTA 3–4(包含2或3个极性tetraEG链),由于缺乏疏水屏蔽,在水中不存在自组装现象。我们提出tetraEG侧链干扰分子间氢键,削弱这些不对称衍生物的堆积行为,并因为竞争的分子内氢键相互作用而显著降低结合常数。相比之下,一个甲氧乙基单位并不影响BTA聚集的稳定性(Kass = 3 × 107 M−1),这表明需要超过一个EG单位才能干扰BTA的自组装。