NMR Method for Simultaneous Host–Guest Binding Constant Measurement

An NMR-based relative binding affinity measurement method has been developed in which differences in the binding affinities of different hosts toward a particular guest (Δlog<i>K</i>_ass values) are measured in the same solution. As an advancement, the method allows the simultaneous determination of several Δlog<i>K</i>_ass values in a single run. As a proof of principle, the method was used to measure binding affinity differences of a number of indolocarbazole- and urea-based synthetic receptors toward acetate ion in DMSO-<i>d</i>₆/H₂O (99.5%:0.5% m/m). As a result, a binding affinity scale containing 33 receptors and spanning 2.32 log units with excellent self-consistency (consistency standard deviation = 0.01 log unit) was created. Together with the very good agreement of the results with those obtained by UV–vis spectrophotometry, this demonstrates the high accuracy of the method and the fact that the NMR and UV–vis techniques can be used interchangeably (in spite of the very different concentrations used in these techniques). Additionally, it was found for symmetrical receptor molecules from the same compound family that there is a correlation between the acetate binding affinity of a receptor and the ¹⁵N chemical shift of the nitrogen atoms of its binding centers