Inversion of selectivity in anion recognition with conformationally blocked calix[4]pyrroles

[EN] Two calixpyrrole derivatives were synthesised. A p-dimethylaminobenzoyl group was electronically attached to a pyrrole ring, establishing an intramolecular hydrogen bond in a 1,3-alternate conformation. The formation of the H-bond was corroborated by IR, NMR, and X-ray measurements. NMR titration studies reveal that the H-bond is strong enough to block the conversion to a cone conformation, allowing them to only acquire a partial cone conformation. Affinity constants for several anions were calculated, and a noticeable increase was observed for tridentate tetrahedral anions, while the K-a of spheric or bidentate anions decreased. In the presence of several acids, the synthesised compounds can act as chemosensors by a double process: protonation of the amino group and coordination of the generated anion. In addition, a displacement approach gives rise to a proof of concept for sulphonate recognition.We thank the Spanish Government (DGICYT projects MAT2009-14564-C03) for support. R. G. thanks MEC for a pre-doctoral FPU fellowship. SCSIE and ICMOL (Universidad de Valencia) are gratefully acknowledged for all the equipment employed.Gotor Candel, RJ.; Costero Nieto, AM.; Gil Grau, S.; Parra Álvarez, M.; Ochando Gómez, LE.; Chulvi, K. (2012). Inversion of selectivity in anion recognition with conformationally blocked calix[4]pyrroles. Organic and Biomolecular Chemistry. 10(42):8445-8451. doi:10.1039/c2ob26309bS84458451104