Relative hydrophilicities of <i>cis</i> and <i>trans</i> formamides.

Li, Yong-Sheng; Escobar, Luis; Zhu, Yu-Jie; Cohen, Yoram; Ballester, Pablo; Rebek, Julius; Yu, Yang · Proc Natl Acad Sci U S A · 2019

basic_science · Level V

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Abstract

Secondary formamides are widely encountered in biology and exist as mixtures of both <i>cis</i> and <i>trans</i> isomers. Here, we assess hydrophilicity differences between isomeric formamides through direct competition experiments. Formamides bearing long aliphatic chains were sequestered in a water-soluble molecular container having a hydrophobic cavity with an end open to the aqueous medium. NMR spectroscopic experiments reveal a modest preference (<1 kcal/mol) for aqueous solvation of the <i>trans</i> formamide terminals over the <i>cis</i> isomers. With diformamides, the supramolecular approach allows staging of intramolecular competition between short-lived species with subtle differences in hydrophobic properties.