Abstract
A multicyclophane with a core based on tris(2-aminoethyl)amine (TREN) linked by amide spacers to three fragments of pillar[5]arene was synthesized. The choice of the tris-amide core allowed the multicyclophane to bind to anion guests. The presence of three terminal pillar[5]arene units provides the possibility of effectively binding the colorimetric probe N-phenyl-3-(phenylimino)-3H-phenothiazin-7-amine (PhTz). It was established that the multicyclophane complexed PhTz in chloroform with a 1:1 stoichiometry (lgKa = 5.2 ± 0.1), absorbing at 650 nm. The proposed structure of the complex was confirmed by 1H-NMR spectroscopy: the amide group linking the pillar[5]arene to the TREN core forms a hydrogen bond with the PhTz imino-group while the pillararenes surround PhTz. It was established that the PhTz:tris-pillar[5]arene complex could be used as a colorimetric probe for fluoride, acetate, and dihydrogen phosphate anions due to the anion binding with proton donating amide groups which displaced the PhTz probe. Dye displacement resulted in a color change from blue to pink, lowering the absorption band at 650 nm and increasing that at 533 nm.
Highlights
Creating supramolecular systems capable of anion detection is an important direction for modern chemistry
Alkyl groups and pyridinium fragments can enter into the pillar[5]arene cavity, while the pillar[n]arenes with the larger macrocycle size are still synthetically difficult to achieve [19]. This is the reason why we have proposed as an alternative approach to binding relatively large aromatic substrates to unify in one structure several pillar[5]arene fragments, which increase the effectivity of association with the aromatic substrate by multicenter interactions
We have developed an approach to synthesize a multicyclophane with a TREN core
Summary
Creating supramolecular systems capable of anion detection is an important direction for modern chemistry. Detecting inorganic anions allows the control of food quality [3]. The introduction of amide, hydroxyl, urea, and thiourea fragments into receptor structures allow for the formation of additional coordination sites for more effective and selective binding of anionic substrates by hydrogen bonds [4,5,6]. One of the most widespread approaches to constructing macrocycle-derived anion sensors is using a macrocyclic platform for spatial preorganization of proton donating groups, which provides conformity of the receptors spatial structure to the substrate [7]. The anion is bound by forming hydrogen bonds with spatially preorganized functional groups [8,9] and with macrocyclic fragments [10,11]
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