abstract
Two ditopic polyamine macrobicyclic compounds have been studied as receptors for the recognition of dicarboxylate anions of varying chain length in aqueous solution. One of the receptors consists of two tris(2-aminoethyl)amine-derived binding subunits separated by p-xylyl spacers, while the other is a heteroditopic compound, combining two different head units, a tren-derived and a 2,4,6-triethylbenzene-derived one, also separated by p-xylyl spacers. The acid base behavior of the compounds as well as their binding ability with oxalate (oxa(2-)), malonate (mal(2-)), succinate (suc(2-)), glutarate (glu(2-)), maleate (male(2-)) and fumarate (fum(2-)) anions were studied by potentiometry at 298.2 K in aqueous solution and at ionic strength 0.10 M in KTsO. NMR studies were also performed to obtain structural information in solution on the supermolecules formed by association of the protonated macrobicycles with the dicarboxylate substrates. The results revealed that both compounds are able to form stable associations with the dianionic substrates in competitive aqueous solution, with unprecedented selectivity for fum(2-) over other dicarboxylate competitors, including its cis isomer male(2-). In addition it was found that although the selectivity pattern is unaffected by the introduction of the 2,4,6-triethylbenzene head unit, the affinity toward dicarboxylates is significantly reduced. Therefore, the comparison between the binding behavior of these two receptors showed the effect of the increased rigidity and lipophilicity of the receptor with the 2,4,6-triethylbenzene head unit in the binding properties and the selectivity pattern.
keywords
ANION COORDINATION CHEMISTRY; MOLECULAR RECOGNITION; AQUEOUS-SOLUTION; SUBSTRATE COMPLEMENTARITY; POLYAMMONIUM RECEPTORS; SYNTHETIC RECEPTORS; CRYSTAL-STRUCTURE; BINDING; CONSTANTS; THERMODYNAMICS
subject category
Chemistry
authors
Mateus, P; Delgado, R; Brandao, P; Felix, V
our authors
Paula Cristina Ferreira da Silva Brandão
Assistant Researcher
Vítor Félix
Associate Professor with Aggregationacknowledgements
The NMR spectrometers are part of the National NMR Network and were purchased in the framework of the National Program for Scientific Re-equipment, Contract No. REDE/1517/RMN/2005, with funds from POCI 2010 (FEDER) and Fundacao pars a Ciencia e a Tecnologia (FCT). We also acknowledge M. C. Almeida for providing elemental analysis and ESI-MS data from the Elemental Analysis and Mass Spectrometry Service at the ITQB/IBET. P.M. thanks FCT for the grant (SFRH/BD/36159/2007).