Towards the Discrimination of Carboxylates by Hydrogen‐Bond Donor Anion Receptors

Abstract

The binding constants (log Kass ) of small synthetic receptor molecules based on indolocarbazole, carbazole, indole, urea and some others, as well as their combinations were measured for small carboxylate anions of different basicity, hydrophilicity and steric demands, that is, trimethylacetate, acetate, benzoate and lactate, in 0.5 % H2 O/[D6 ]DMSO by using the relative NMR-based measurement method. As a result, four separate binding affinity scales (ladders) including thirty-eight receptors were obtained with the scales anchored to indolocarbazole. The results indicate that the binding strength is largely, but not fully, determined by the strength of the primary hydrogen-bonding interaction. The latter in turn is largely determined by the basicity of the anion. The higher is the basicity of the anion the stronger in general is the binding, leading to the approximate order of increasing binding strength, lactate<benzoate<acetate≤trimethylacetate, which holds with all investigated receptors. Nevertheless, there are a number of occasions when the binding order changes with changing of the carboxylate anion, sometimes quite substantially. Principal component analysis (PCA) reveals that this is primarily connected to preferential binding of trimethylacetate, supposedly caused by an additional hydrophobic/solvophobic interaction. These findings enable making better predictions, which receptor framework or cavity is best suited for carboxylate anions in receptor design.

Deltamides and Croconamides: Expanding the Range of Dual H‐bond Donors for Selective Anion Recognition

“…K a in [D 6 ]DMSO (0.5 % water) at 298 K (estimated error in K a <15 %). [e] Value from reference . K a in [D 6 ]DMSO (0.5 % water) at 298 K (error in K a ±18 %).…”

Protonation and Anion Binding Properties of Aromatic Bis‐Urea Derivatives—Comprehending the Proton Transfer

“…It should be noted that the compounds 1 H 2 and 4 H 2 have been included in a previous study reported by Gale et al., and their anion binding (1:1 complex stoichiometry) was characterized by 1 H NMR titrations in DMSO containing 0.5 % water. Most recently, Gunnlaugsson et al.…”

“…In this field, urea derivatives have been among the most studied receptors, and numerous studies of their complexation with diverse anionic species have been reported . In pursuit of higher affinity and selectivity, original concepts have been examined with the goal of achieving the desired receptor properties . A prerequisite facilitating the anion receptor development is comprehensive understanding of the thermodynamics underlying anion binding, leading to appreciation of structure–reactivity correlation, assessment of the individual contributions to the complex stability, better insight into the solvent effect on the corresponding equilibria, etc .…”

Exploring Selectivity of 22 Acyclic Urea‐, Carbazole‐ and Indolocarbazole‐Based Receptors towards 11 Monocarboxylates

“…The summary of experimental results is presented in Scheme . The anion–receptor complex structures with receptors 8 , 10 , 11 and 15 have been computed for all 11 anions (complexes between 8 , 11 , 15 and lactate, benzoate, acetate, and pivalate are available from ref …”

“…Receptor Molecules: Receptors 1 – 6 , 8 , 11 , 14 – 16 are the same as used in ref., 17 – 19 , 22 are from ref., and 20 , 21 from ref . Synthesis procedures of compounds 9 and 10 are described in ref .…”