Urea‐, Squaramide‐, and Sulfonamide‐Based Anion Receptors: A Thermodynamic Study

Abstract

In this work, we compare the anion-binding capabilities of receptors 1-5, characterized by similar structures, but possessing different hydrogen-bond-donor moieties (urea, squaramide, and sulfonamide). The presence of chromophoric substituents on the receptor's skeleton allowed the determination of association constants by performing UV/Vis titrations with the investigated anions on solutions of the receptors in pure acetonitrile. Additional quantitative studies of the anion-binding properties of receptors 1-5 were performed by isothermal titration calorimetry (ITC). The experimental results indicated that 1 and 2 formed 1:1 hydrogen-bonded complexes with most of the anions investigated. In the case of receptors 3-5, the formation of the 1:1 adduct was observed only with anions of low basicity (i.e., chloride, bromide, iodide, and hydrogen sulfate). With more basic anions (i.e., acetate and dihydrogen phosphate), both spectrophotometric and ITC titrations accounted for the deprotonation of the sulfonamide group, involving the formation of the conjugated base of the receptor.

Nuclear Magnetic Resonance Spectroscopy Investigations of Naphthalene-Based 1,2,3-Triazole Systems for Anion Sensing

“…A number of colorimetric and fluorometric sensors have been developed to detect anions through a Brønsted acid-base reaction and/or hydrogen bond formation at the N-H and O-H moieties [18]. For ion recognition, complicated molecules with multistep syntheses are used to create highly conjugated systems with common scaffolds such as ureas, amides, and/or phenolic groups [19,20]. Photoinduced electron transfer (PET) [21,22], metal-to-ligand charge transfer (MLCT) [22,23]; excimer/exciplex formation [23], intramolecular charge transfer (ICT) [24]; and excited state intra/intermolecular proton transfer (ESPT) [25,26] are some of the signaling mechanisms by which the anions are detected.…”

Thermodynamics of Complexation between Thiourea-based Receptor and Acetate in Water/Acetonitrile Mixture

“…[10][11][12][13][14] To the best of our knowledge, entropy-driven complexation has been reported for only one thiourea-based anion recognition system: thiourea-substituted quinoline with biarylamide groups exhibited exothermic and entropy-driven complexation reaction with halide anions in DMSO, although its complexation reaction is enthalpy-driven in chloroform. 13 On the other hand, the present study confirms the endothermic and entropy-driven complexation of thiourea-based receptor with acetate in water/MeCN mixtures.…”

“…8 Bisthiourea-based receptors and modified thiourea-based receptors have been developed to enhance binding affinity and regulate binding selectivity. [9][10][11][12] Thiourea-based receptors rely on the structure and strength of hydrogen bonds between the thiourea group and an anion (see Fig. 1).…”

“…[1][2][3][4][5][6] Since the complex formation is strongly inhibited by hydration of both receptor and anion, thiourea-based receptors have usually been examined in organic solvents 7 or water/ organic solvent mixtures. 8 In thermodynamic studies of ureaand thiourea-based receptors in organic solvents such as acetonitrile (MeCN), 10 dimethyl sulfoxide (DMSO), [11][12][13][14] and chloroform, 13 complex formation is usually reported to be an exothermic and enthalpy-driven reaction. This means that, in organic solvents, the complexes are stabilized by hydrogen bonds between the receptor and the anion.…”

Chromogenic and fluorogenic chemosensors and reagents for anions. A comprehensive review of the years 2010–2011

“…11, were tested in CH 3 CN in the presence of selected anions. 29 The charge transfer bands of 25 and Calix [4]pyrrole-based derivatives 34-37 ( Fig. 13) were described to display colour modulations in the presence of certain basic anions.…”