A method for the determination of binding constants by electrospray ionization mass spectrometry

A new method for the determination of binding constants using electrospray ionization mass spectrometry is presented. The intensity of a reference complex with a known log K value is monitored before and after addition of a second host or guest. On the basis of the change in intensity of the reference complex and extrapolation from a calibration curve, the log K value is then derived for the complex of interest using a set of simultaneous equilibrium equations. Binding constants of several crown ether-alkali metal cation complexes that were previously studied were determined to validate this strategy. Log K values for complexes involving dibenzo-16-crown-5 and its sym-oxyacetate derivative with Na+ or K+ were also determined.