title: 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.
authors: University of Tartu, Institute of Chemistry, Ravila 14a, 50411 Tartu (Estonia), Phone: +372-51-84-176.
authors: Sandip A
authors: SA
authors: Kadam
authors: Kerli
authors: K
authors: Martin
authors: Kristjan
authors: K
authors: Haav
authors: Lauri
authors: L
authors: Toom
authors: Charly
authors: C
authors: Mayeux
authors: Astrid
authors: A
authors: Pung
authors: Philip A
authors: PA
authors: Gale
authors: Jennifer R
authors: JR
authors: Hiscock
authors: Simon J
authors: SJ
authors: Brooks
authors: Isabelle L
authors: IL
authors: Kirby
authors: Nathalie
authors: N
authors: Busschaert
authors: Ivo
authors: I
authors: Leito
keywords: NMR spectroscopy; carboxylate anions; hydrophobic effects; molecular recognition; receptors