Anion Binding by Fluorescent Ureido-Hexahomotrioxacalix[3]arene Receptors: An NMR, Absorption and Emission Spectroscopic Study

Abstract

Fluorescent receptors (4a–4c) based on (thio)ureido-functionalized hexahomotrioxacalix[3]arenes were synthesised and obtained in the partial cone conformation in solution. Naphthyl or pyrenyl fluorogenic units were introduced at the lower rim of the calixarene skeleton via a butyl spacer. The binding of biologically and environmentally relevant anions was studied with NMR, UV–vis absorption, and fluorescence titrations. Fluorescence of the pyrenyl receptor 4c displays both monomer and excimer fluorescence. The thermodynamics of complexation was determined in acetonitrile and was entropy-driven. Computational studies were also performed to bring further insight into the binding process. The data showed that association constants increase with the anion basicity, and AcO−, BzO− and F− were the best bound anions for all receptors. Pyrenylurea 4c is a slightly better receptor than naphthylurea 4a, and both are more efficient than naphthyl thiourea 4b. In addition, ureas 4a and 4c were also tested as ditopic receptors in the recognition of alkylammonium salts.

Critical Analysis of Association Constants between Calixarenes and Nitroaromatic Compounds Obtained by Fluorescence. Implications for Explosives Sensing

“…400 nm) and excimer (ca. 500 nm) bands in dichloromethane arising from the pyrene moieties, as reported previously ( Figure 2 ) [ 21 ].…”

“…Recently, we reported the anion binding properties of fluorescent ureido-hexahomotrioxacalix[3]arene receptors 1 and 2 , obtained in the partial cone conformation [ 21 ]. Following this line of research, the potential of naphthyl ( 1 ) and pyrenyl ( 2 ) ureas as chemosensors to detect nitroaromatic explosives was explored by fluorescence titrations.…”

“…The naphthyl ( 1 ) and pyrenyl ( 2 ) ureido-hexahomotrioxacalix[3]arene compounds studied in this work were previously synthesised [ 21 ], as well as the naphthyl urea dihomooxacalix[4]arene 3 [ 20 ].…”

“…In the course of our recent studies on anion binding by fluorescent homooxacalixarenes [ 19 , 20 , 21 ], calixarene analogues in which the CH 2 bridges are partly or completely replaced by CH 2 OCH 2 groups [ 22 , 23 ], we have extended our research into the recognition of a different kind of analyte, namely nitroaromatic compounds, by hexahomotrioxacalix[3]arene-based receptors. These macrocyclic compounds, with an 18-membered ring and having only two basic conformations, have already been investigated to detect explosives.…”

ULYSSES: Química Semi-Empírica para Macrossistemas

“…A versatilidade da biblioteca está demonstrada em algumas publicações recentes. A ULYSSES foi utilizada para explicar observações experimentais que aparentavam ser contraditórias, nomeadamente a observação de entalpias e entropias de complexação positivas em calixarenos [35], resultado teoricamente inesperado pois envolve a formação de complexos por adição. Verificou-se, via solvatação explícita, que este resultado era causado por efeitos de solvente.…”