resumo
A new polyamine macrobicyclic compound was synthesised through a [1+1] "tripod-tripod coupling" strategy and using a Schiff base condensation reaction, followed by sodium borohydride reduction. The resulting compound is a heteroditopic cage (btpN(7)) in which one of the head units is appropriate for the coordination of copper(II), whereas the other head is available for additional hydrogen-bonding and electrostatic interactions with substrates. The acid-base behaviour of the new compound, the stability constants of its complex with the Cu2+ ion and the association constants of the copper( II) cryptate with oxalate (oxa(2-)), malonate (mal(2-)), succinate (suc(2-)), maleate (male(2-)) and fumarate (fum(2-)) were determined by potentiometry at 298.2 K in aqueous solution and at an ionic strength of 0.10 mol dm(-3) in KNO3. These studies revealed a clear preference of the receptor [CuH(h)btpN(7)H(2)O]((2+h)+) for oxa(2-) over the other dicarboxylate substrates. This arises from co-operativity between metal-anion coordination and electrostatic and hydrogen-bonding interactions, in accordance with the ideal size of this dicarboxylate, which allow it to take full advantage of the potential binding sites of the receptor. A qualitative indicator-displacement study, in agreement with the potentiometric studies, demonstrated that the copper cryptate receptor can be used as a selective visual sensor for oxalate.
palavras-chave
ANION COORDINATION CHEMISTRY; DITOPIC POLYAMMONIUM MACROCYCLES; P-XYLYL SPACERS; MOLECULAR RECOGNITION; DICARBOXYLATE ANIONS; CARBOXYLATE ANIONS; AQUEOUS-SOLUTION; RECEPTOR MOLECULES; SELECTIVE BINDING; CRYSTAL-STRUCTURE
categoria
Chemistry
autores
Mateus, P; Delgado, R; Brandao, P; Felix, V
nossos autores
Paula Cristina Ferreira da Silva Brandão
Investigador Auxiliar
Vítor Félix
Professor Associado com Agregaçãoagradecimentos
The authors acknowledge the Fundacao para a Ciencia e a Tecnologia (FCT) and Programa Operacional Ciencia e Inovacao (POCTI), with co-participation of the European Community funds FEDER, for financial support under project PTDC/QUI/68582/2006. The NMR spectrometers are part of the National NMR Network (REDE/1517/RMN/2005) supported by POCTI 2010 and the 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 and Dr. Filipe de Oliveira for help with the EPR spectra simulations. Pedro Mateus thanks FCT for the grant (SFRH/BD/36159/2007).