In determining structure-activity relationships, it is advantageous if binding constants for a variety of ligands to a given target molecule can be directly obtained from a single aqueous solution containing a mixture of ligands and the target molecule. In this paper further evidence is provided showing that electrospray ionization mass spectrometry (ESI-MS) can be used in the rapid quantitative analysis of mixtures of vancomycin-group antibiotics and their bacterial cell-wall receptors allowing the identification of even subtle differences in binding constants. Differences in affinities are quantified for a mixture of vancomycin antibiotics (vancomycin, dechlorovancomycin and N-demethylvancomycin) and for a mixture of ristocetin A and its pseudoaglycone. Binding constants determined by ESI-MS were found to be in close agreement with those determined by more direct methods in aqueous solution.
Journal of the Chemical Society. Perkin Transactions 2 (2001), 1999, Issue 9, p. 1859-1863