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Knock-on synthesis of tritopic calix[4]pyrrole host for enhanced anion interactions

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Abstract

Interactions of anionic guests with a tritopic peripherally functionalized conjugated calix[4]pyrrole host (1) prepared using a regioselective synthetic method is reported. The regioselectivity of synthesis relies on selective N-alkylation of the calix[4]pyrrole caused by peripheral substitution of one pyrrole group with subsequent N-alkylation at the opposing pyrrole group termed by us ‘knock-on’ regioselectivity. The resulting host molecule exhibits anion interactions with common chloride and nitrate anions enhanced by an order of magnitude over the parent conjugated calix[4]pyrrole. Combined analysis of 1H NMR and UV-vis spectroscopic titration data enabled an evaluation of binding strengths of anions with the host KA in a binding model where the salt dissociation process is also incorporated in the form of its dissociation constant Kd. Anions could be classified as two types based on their interactions with 1: Type A anions (chloride, nitrate, perchlorate, hydrogensulphate) associate as 1 : 1 complexes through hydrogen bonding while interactions involving Type B anions (acetate, fluoride, dihydrogenphosphate) are complicated by host deprotonation and/or countercation association. Hosts based on rim-functionalized calix[4]pyrroles such as 1 represent a promising new family of chromophores for estimation of biologically relevant anions or other species.

Graphical abstract: Knock-on synthesis of tritopic calix[4]pyrrole host for enhanced anion interactions

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Publication details

The article was received on 04 Jun 2019, accepted on 22 Jul 2019 and first published on 23 Jul 2019


Article type: Paper
DOI: 10.1039/C9DT02365H
Dalton Trans., 2019, Advance Article

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    Knock-on synthesis of tritopic calix[4]pyrrole host for enhanced anion interactions

    M. K. Chahal, J. Labuta, V. Březina, P. A. Karr, Y. Matsushita, W. A. Webre, D. T. Payne, K. Ariga, F. D'Souza and J. P. Hill, Dalton Trans., 2019, Advance Article , DOI: 10.1039/C9DT02365H

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