UPMC Université Paris 06 and CNRS, UMR 7610, Chimie des Polymères, F-75005 Paris, France.
Langmuir. 2012 May 15;28(19):7535-41. doi: 10.1021/la300887p. Epub 2012 May 2.
The phenylurea moiety is a ubiquitous synthon in supramolecular chemistry because it contains strong complementary hydrogen bonding groups and is synthetically very accessible. Here we investigate the possibility to strengthen self-association by conformational preorganization of the phenylurea moiety. In fact, we show that it is possible to strongly enhance intermolecular interactions between hydrogen bonded aromatic bis-ureas by substitution at the ortho positions of the phenylurea groups. Ortho substituents enforce a noncoplanar conformation of the urea and phenyl moieties better suited for hydrogen bonding. Substitution by methyl groups is more efficient than with larger groups, probably because of reduced steric hindrance. These effects have been demonstrated in the case of two different supramolecular architectures, which points to the probable generality of the phenomenon. In addition, this study has led to the discovery of a new bis-urea able to form very stable self-assembled nanotubes in toluene up to high temperatures (boiling point) or low concentrations (10(-7) M) and in chloroform down to 3 × 10(-4) M.
苯并脲部分是超分子化学中无处不在的合成子，因为它含有强互补氢键基团，并且在合成上非常容易获得。在这里，我们研究了通过苯并脲部分的构象预组织来增强自组装的可能性。事实上，我们表明，通过在苯并脲基团的邻位取代，可以强烈增强氢键连接的芳香族双脲之间的分子间相互作用。邻位取代基迫使脲和苯基部分呈现出非共面构象，更适合氢键形成。用甲基取代比用较大的基团取代更有效，这可能是由于空间位阻的降低。在两种不同的超分子结构的情况下已经证明了这种效应，这表明这种现象可能具有普遍性。此外，这项研究发现了一种新的双脲，它能够在甲苯中形成非常稳定的自组装纳米管，在高温（沸点）或低浓度（10^-7 M）下，甚至在氯仿中在 3×10^-4 M 下也能形成。
