Schmuck Carsten, Rehm Thomas, Geiger Lars, Schäfer Mathias
Universität Würzburg, Institut für Organische Chemie, Am Hubland, 97074 Würzburg, Germany.
J Org Chem. 2007 Aug 3;72(16):6162-70. doi: 10.1021/jo070641d. Epub 2007 Jul 13.
We have synthesized a new class of flexible zwitterions 6a-e, in which a carboxylate is linked via an alkyl chain with variable length (one to five methylene groups) to a guanidiniocarbonylpyrrole cation. The self-association properties of these zwitterions were determined by NMR dilution studies in DMSO and by ESI-MS experiments. The stability and hence also the size of the aggregates formed via self-assembly is critically dependent on the length and therefore flexibility of the spacer. Whereas the smallest zwitterion 6a forms large aggregates already at low concentrations, the more flexible zwitterions only form small oligomers (6b) or dimers (6c-e) at much larger concentrations. The differences between the five zwitterions can be explained based on the different extent of intramolecular ion pairing within the monomers. Any intramolecular ion pairing, which becomes possible with increasing linker length, stabilizes the monomer and therefore destabilizes any oligomer.
我们合成了一类新型的柔性两性离子6a - e，其中羧酸盐通过可变长度（一至五个亚甲基）的烷基链与胍基羰基吡咯阳离子相连。这些两性离子的自缔合性质通过在二甲亚砜（DMSO）中的核磁共振（NMR）稀释研究和电喷雾电离质谱（ESI - MS）实验来确定。通过自组装形成的聚集体的稳定性以及因此其大小关键取决于间隔基的长度，进而取决于其柔性。最小的两性离子6a在低浓度时就形成大的聚集体，而更具柔性的两性离子只有在高得多的浓度下才形成小的低聚物（6b）或二聚体（6c - e）。这五种两性离子之间的差异可以基于单体分子内离子对的不同程度来解释。随着连接基长度增加而可能发生的任何分子内离子对会使单体稳定，从而使任何低聚物不稳定。
