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Title
| - Synthesis and Self-Association Properties of FlexibleGuanidiniocarbonylpyrrole−Carboxylate Zwitterions in DMSO:Intra- versus Intermolecular Ion Pairing
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Abstract
| - We have synthesized a new class of flexible zwitterions 6a−e, in which a carboxylate is linked via analkyl 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 DMSOand 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 smallestzwitterion 6a forms large aggregates already at low concentrations, the more flexible zwitterions onlyform small oligomers (6b) or dimers (6c−e) at much larger concentrations. The differences between thefive zwitterions can be explained based on the different extent of intramolecular ion pairing within themonomers. Any intramolecular ion pairing, which becomes possible with increasing linker length, stabilizesthe monomer and therefore destabilizes any oligomer.
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