| 19197928 |
Cruz C, Calisto V, Delgado R, Felix V: Design of protonated polyazamacrocycles based on phenanthroline motifs for selective uptake of aromatic carboxylate anions and herbicides. Chemistry. 2009;15(13):3277-89.
Three novel large polyazamacrocycles containing two 1,10-phenanthroline units connected by different polyamine spacers have been synthesised and their protonated forms used as receptors for several aromatic carboxylate anions. The receptors bind to the anions in a 1:1 stoichiometry and exhibit remarkable binding selectivity (see figure). Analysis shows that molecular recognition is governed by pi-pi stacking interactions and multiple N--HO==C hydrogen bonds.Three novel large polyazamacrocycles 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-carboxylate (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--HO==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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