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A series of 5,5'-dicarboxamido-dipyrrolylmethanes have been synthesized and in some cases crystallographically characterized. Proton NMR titrations have revealed that these compounds, that contain only four neutral hydrogen bond donors and are acyclic, selectively bind anions in very competitive solvent media such as DMSO-d6/water mixtures.
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Vega et al. (2004) studied this question.
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