ABSTRACT
New simple systems formed by a chain containing a squaramide function and a quaternised amine group attached to boehmite or silica-coated boehmite nanoparticles are able to discriminate anions in pure water.
ABSTRACT
The combination of squaramide units with tetraalkylammonium groups leads two hosts that bind distinctively dianions in water-ethanol mixtures. The formation of complexes of 2:1 stoichiometry with host was supported by ITC, fluorescence, and (1)H NMR data.
Subject(s)
Amines/chemistry , Cyclobutanes/chemistry , Anions/chemistry , Calorimetry , Dimerization , Erythrosine/chemistry , Magnetic Resonance Spectroscopy , Quaternary Ammonium Compounds/chemistry , Spectrometry, Fluorescence , ThermodynamicsABSTRACT
A rational design of a tripodal receptor for the molecular recognition of tricarboxylate salts in aqueous media, based on squaramide, has been performed using high-level DFT calculations (RI-BP86/SVP level of theory) in solution using the COSMO treatment, including some preliminary ab initio calculations at the higher RI-MP2/TZVP level of theory, comparing the ability of squaramide to bind carboxylate salts with two widely used guanidinium salts. The tripodal receptor has been synthesized using a new methodology that has been recently reported by some of us, and its capability of recognizing several mono-, di-, and tricarboxylate salts has been studied experimentally by means of microcalorimetry experiments in a very high competitive media, H(2)O:EtOH 1:3. These experiments give enthalpic and entropic data, which are unfortunately scarce in the literature of molecular recognition of anions. Finally, a fluorimetric ensemble of the receptor with fluorescein has been found to be useful for the fluorimetric determination of zinc citrate in a commercial toothpaste using competition assays.
Subject(s)
Cyclobutanes/chemical synthesis , Quaternary Ammonium Compounds/chemical synthesis , Tricarboxylic Acids/isolation & purification , Binding Sites , Cyclobutanes/chemistry , Models, Molecular , Molecular Structure , Quaternary Ammonium Compounds/chemistry , SolutionsABSTRACT
Secondary squaramides have considerable potential as hydrogen bond donors and acceptors. In CHCl(3) both, anti- and syn-squaramide rotamers are observed by NMR. The energetic barrier for anti/syn mutual interconversion determined by complete band shape analysis is approximately 63 kJ mol(-1). As in proline derivatives, a low rotational barrier is crucial for the design of foldable modules. In this paper, folding based on the low rotational barrier of squaramides is driven by donor atoms (N or O) located in the gamma position of an alkyl chain of a secondary squaramide. We demonstrate that the resulting minimal module exists as a folded conformer through the formation of a nine-membered ring stabilized by intramolecular hydrogen bonding. Molecular mechanics calculations and NMR studies support the existence of these folded conformers. The intramolecularly hydrogen bonded conformers are clearly visible even in CHCl(3)-EtOH mixtures. Folding occurs even in pure ethanol. As an indirect test, we studied the effectiveness of macrocyclization reactions in pure ethanol that require an effective templating effect to take place. The high yields obtained support the dominant role of a folded conformer even in this solvent.
