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Design of Protonated Polyazamacrocycles Based on Phenanthroline Motifs for Selective Uptake of Aromatic Carboxylate Anions and Herbicides
Author(s) -
Cruz Carla,
Calisto Vânia,
Delgado Rita,
Félix Vítor
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200800993
Subject(s) - carboxylate , chemistry , protonation , stacking , hydrogen bond , aromaticity , selectivity , stereochemistry , phenanthroline , crystallography , medicinal chemistry , organic chemistry , molecule , ion , catalysis
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 π–π stacking interactions and multiple NH⋅⋅⋅OC 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 π–π 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 π–π stacking interactions and multiple NH⋅⋅⋅OC hydrogen bonds. The binding free energies estimated theoretically are very similar to those found by potentiometric methods, which supports the proposed binding arrangement.