A 1,3‐Capped Calix[4] Conjugate Possessing an Amine Moiety as an Anion Receptor: Reversible Anion Sensing Detected by Spectroscopy and Characterization of the Supramolecular Features by Microscopy

Abstract

A phenylenediamine-capped conjugate of calix[4]arene (Lamino ) was synthesized by reducing its precursor, Limino , with sodium borohydride in methanol. The Lamino sample binds to anions due to the more flexible and bent conformation of the capped aminophenolic binding core, compared to the precursor Limino . The Lamino sample showed selectivity towards H2 PO4 (-) by exhibiting a ratiometric increase in emission by about 11-fold with a detection limit of (1.2±0.2) μm ((116±20) ppb) over 15 anions studied, including other phosphates, such as P2 O7 (4-) , adenosine monophosphate (AMP(2-) ), adenosine diphosphate (ADP(2-) ), and adenosine triphosphate (ATP(2-) ). The Lamino sample shows an increase in the absorbance at λ=315 nm in the presence of H2 PO4 (-) , CO3 (2-) , HCO3 (-) , CH3 CO2 (-) , and F(-) . The (1) H NMR spectroscopic titration of Lamino with H2 PO4 (-) , F(-) , and CH3 CO2 (-) showed major changes in the phenylene-capped and salicyl moieties, and thereby, confirming the aminophenolic region as the binding core. However, the binding strength of these anions followed the trend H2 PO4 (-) >F(-) ≫CH3 CO2 (-) >HSO4 (-) . The heat changes observed by isothermal titration calorimetry support this trend. The Lamino sample showed reversible sensing towards H2 PO4 (-) and F(-) in the presence of Mg(2+) and Ca(2+) , respectively. NOESY studies of Lamino , in comparison with its anionic complexes, revealed that major conformational changes occurred in the capping region to facilitate the binding of anion. ESI-MS and the Job's method revealed 1:1 stoichiometry between Lamino and H2 PO4 (-) or F(-) . In the SEM micrographs of Lamino , the spherical particles are converted into spherical aggregates and further form large agglomerates and even branched sheets in the presence of anions, depending upon their binding strength.

Excited‐state proton transfer via higher excited state in 2‐mercaptobenzothiazole: Absorption, fluorescence, Raman spectroscopic study, and theoretical calculation

“…The fluorescence intensities as a function of pH show the emission bands at 288 and 336 nm become no obvious intensity change in CH 3 OH when pH increases, whereas in H 2 O at pH = 1.6, two bands with equivalent intensity and the 288 nm becomes strong; the 336 nm decreases and even becomes even weak with the increasing pH, as shown in Figure S4. The large pH increases the acidity of the thiazole‐N–H moiety upon deprotonation . Based on the above‐mentioned experiments, it can be concluded that the dimer breaks apart and is further deprotonated to form anion monomers in a basic solvent environment.…”

Biomedical Applications of Calixarenes: State of the Art and Perspectives

“…[22e] In addition, the recognition properties of CAs are due not only to the presence of cavities, because the modification of CA scaffolds with individual ligands to afford podand-like structures also plays asignificant role in molecular recognition. [33] Thus,t he variability of scaffolds,c onformations,a nd substitution patterns allows CAst ob ind aw ide range of guests,s uch as inorganic anions, [34] inorganic cations, [35] organic anions, [36] organic cations, [37] neutral organic molecules, [38] and biological macromolecules. [39] In addition to exhibiting recognition properties,C As are also important building blocks for the fabrication of supramolecular architectures,such as micelles,vesicles,nanofibers, tubes,c apsules,c ages,r otaxanes,c atenanes,s upramolecular polymers,s olid lipid nanoparticles,a nd liquid crystals.…”

Biomedizinische Anwendungen von Calixarenen: Stand der Wissenschaft und Perspektiven

“…[22e] Darüber hinaus sind die Erkennungseigenschaften der CAs nicht nur auf das Vorhandensein von Kavitäten zurückzuführen, da die Modifikation der CA-Gerüste mit individuellen Liganden zur Erzeugung podandenartiger Strukturen, auch eine signifikante Rolle bei der molekularen Erkennung spielt. [33] Die Va riabilitätv on Gerüststrukturen, Konformationen und Substitutionsmustern ermçglicht es CAs, ein breites Spektrum an Gaststrukturen zu binden, wie anorganische Anionen, [34] anorganische Kationen, [35] organische Anionen, [36] organische Kationen, [37] neutrale organische Moleküle [38] und biologische Makromoleküle. [39] CAsw eisen nicht nur Erkennungseigenschaften auf, sondern sind auch wichtige Bausteine fürdie Herstellung von supramolekularen Architekturen wie Mizellen, Vesikeln, Nanofasern, Rçhren, Kapseln, Käfigen, Rotaxanen, Catenanen, supramolekularen Polymeren, festen Lipidnanopartikeln und Flüssigkristallen.…”