New macrocycles derived from biphenyl for pH-switched solvent extraction
Abstract Four new fluorescent macrocyclic ligands derived from biphenyl are described. The new compounds have been used in liquid–liquid extraction experiments and the influence of pH has been studied in those ligands containing carboxylic groups. The results obtained for the latter ligands have been compared with those observed in the presence of an external acid.
Conformationally regulated fluorescent sensors. Study of the selectivity in Zn 2+ versus Cd 2+ sensing
Abstract The Zn 2+ and Cd 2+ complexing properties of four ligands containing a 4,4′-substituted biphenyl moiety are described. Ligands 1 and 3 , containing only one 1-aza-18-crown-6 cavity, lead to selective complexation of Cd 2+ versus Zn 2+ . Ligand 4 , with two crown cavities linked to a tetramethylbenzidine unit, is able to form 1:1 complexes with Zn 2+ and Cd 2+ , showing a higher complexing constant with Zn 2+ than with Cd 2+ , probably due to enthalpic factors. Several complementary experiments suggest that the 1:1 complexes formed by ligand 4 involve both crown cavities acting together to give rise to clamp structures. The formation of this type of zinc complex gives rise to red sh…
Solid–liquid extraction of ω-amino acids using ditopic receptors
Abstract Five heteroditopic ligands have been prepared to be used in solid–liquid extraction of ω-amino acids into DMSO solutions. The prepared ligands contain crown ethers as cation binding sites and thiourea or amide groups for anion recognition. The aliphatic zone of the 1H NMR spectra suggests that two different species related to the amino acid are present in solution. One of these species is the complexed zwitterionic form and the other seems to be free non-zwitterionic amino acid. The presence of these two species allows extraction efficiencies higher than 100%.
Colorimetric sensing of anions by a neutral biphenyl based amide receptor
A new colorimetric sensor for fluoride is described. Compound 1 shows an open structure and its behaviour is compared with that of two related closed compounds 2 and 3. In all cases, the red colour developed in the presence of fluoride can be related to deprotonation processes, however ligand 1 gives rise to a faster colour change than 2 or 3 because of its higher flexibility. Other halides as well as carboxylates have been studied and the stoichiometry and complexation constants for the corresponding ligands have been determined.
Bis(crown ethers) derived from biphenyl: extraction and electrochemical properties
Abstract Ligands derived from 4,4′-dinitrobiphenyl containing azacrown cavities in the 2,2′ position have been used in extraction and transport experiments. Control experiments with a system containing only one complexing cavity have demonstrated that the capability of forming a sandwich-type complex in the aforementioned ligand not only increases extraction but also the transport across a liquid membrane. Extraction studies have also shown that the complex present in the membrane has a 1:1 stoichiometry with regard to both ligands. Electrochemical studies have also been carried out. The ligand containing two complexing cavities is capable of giving rise to a 2:1 complex under electrochemic…