Design of Protonated Polyazamacrocycles Based on Phenanthroline Motifs for Selective Uptake of Aromatic Carboxylate Anions and Herbicides


Three novel large polyazatmacrocycles containing two 1,10-phenanthroline (phen) units connected by two polyamine spacers of different length, [32]phen(2)N(4), [30]phen(2)N(6) and Me(2)[34]phen(2)N(6), have been synthesised and their protonated forms used as receptors for binding studies with several aromatic carboxylate anions (benzoate (bzc(-)), 1-naphthalate (naphc(-)), 9-anthracenate (anthc(-)), pyrene-1-carboxylate (pyrc(-)), phthalate, (ph(2-)), isophthalate (iph(2-)), terephthalate (tph(2-)), 2,5-dihydroxy-1,4-benzenediacetate (dihyac(2-)) and, 1,3,5-benzenetricarboxylate (btc(3-))) and three herbicides (4-amino-3,5,6-trichloropyridine-2-carbox- ylate (ATCP(-)), dichlorophenoxyacetate (2,4-D(-)) and glyphosate (PMG(2-))) in water solution. The [30]phen(2)N(6) receptor was found to be the most suitable for binding the anions considered in a 1:1 stoichiometry. The three receptors exhibit a remarkable binding selectivity towards the extended aromatic anion pyrc(-) at low pH values. Their binding affinities for the monocarboxylate anions decrease with the extension of the aromatic system in the order pyrc(-) > anthc(-) > naphc(-) > bzc(-), which indicates the presence of pi-pi, stacking interactions in the molecular recognition of these anions. Molecular dynamics simulations carried out for the binding of {H(4)[30]phen(2)N(6)}(4+) and {H(6)Me(2)[34]phen(2)N(6)}(6+) with pyrc(-), anthc(-), naphc(-), iph(2-) and btc(3-) in water showed that these receptors adopt a folded conformation with the anion inserted between the two phen heads and that the molecular recognition is governed by pi-pi stacking interactions and multiple N-H center dot center dot center dot O=C hydrogen bonds. The binding free energies estimated theoretically are very similar to those found by potentiometric methods, which supports the proposed binding arrangement.



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Cruz, C; Calisto, V; Delgado, R; Felix, V

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The authors acknowledge the Fundacao para Ciencia e Tecnologia (FCT) with co-participation of European Community funds FEDER for financial support under projects PTDC/QUI/56569/2004 and PTDC/QUI/68582/2006. C.C. and V.C. thank the FCT for Ph. D. grants (SFRH/BD/19266/2004 and SFRH/BD/38075/2007, respectively).

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