title: Design of protonated polyazamacrocycles based on phenanthroline motifs for selective uptake of aromatic carboxylate anions and herbicides.
abstract: 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.
authors.affiliation: Departamento Química, CICECO and Secção Autónoma de Ciências da Saúde, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Carla
authors.initials: C
authors.lastname: Cruz
authors.forename: Vânia
authors.initials: V
authors.lastname: Calisto
authors.forename: Rita
authors.initials: R
authors.lastname: Delgado
authors.forename: Vítor
authors.initials: V
authors.lastname: Félix