Rapid Screening of Binding Constants by Calibrated Competitive 1H NMR Spectroscopy

A calibrated competitive NMR method has been developed that is appropriate for the rapid screening of binding constants. This method involves the initial characterisation of a receptor–substrate binding event for which the 1H NMR spectrum of a given receptor (calibrant) is modified by the substrate of interest at a range of concentrations. For all subsequent “unknown” receptors, Ka values are then determined by using a competition assay (in the presence of the calibrant receptor) by measuring a single standard 1H NMR spectrum. This enables a rapid assessment of the recognition properties of a library of potential receptors. Only the calibrant receptor needs to be NMR active, while the library of putative receptors, as well as the substrate, can be NMR silent. This method assumes the formation of complexes of 1:1 stoichiometry. To demonstrate this methodology, the binding of a number of crown ether type compounds with K+ ions has been studied. Comparison of the binding strengths obtained by using this approach with those in the literature shows excellent agreement. A range of new compounds that have recently been synthesised within our group has also been screened in order to illustrate how this approach can rapidly assess binding ability. This method has significance for chemists working in the fields of combinatorial receptor/substrate design and supramolecular chemistry as a means of rapid optimisation of binding strength. A method of NMR analysis is reported that enables the rapid assessment of a binding constant by measuring a single standard 1H NMR spectrum (see sketch). This methodology has significance for chemists working in the fields of combinatorial receptor/substrate design and supramolecular chemistry.