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ACE on a microchip (MC-ACE) is introduced as a fast and reliable method to determine binding affinities. It is based on monitoring the change in the ionic mobility of a receptor upon binding to a ligand, or vice versa. The method is complementary to other standard methods for binding affinity determinations, like isothermal titration calorimetry (ITC), NMR, UV-Vis spectroscopy, etc. and allows for affinity studies of weak to strong binding interactions. The method is attractive since it principally allows for the analysis of the binding affinity of multiple receptors to a given ligand and requires comparatively small quantities of the binding partners (particularly in comparison to affinity measurements on capillary). We demonstrate the applicability of MC-ACE for the determination of the binding affinities between acid-rich diketopiperazine receptors and basic tripeptides in aqueous solution.

The interactions between tetranucleotides or heptanucleotides and inorganic cations have been measured by affinity CZE. The variation in migration behavior with increasing concentrations of divalent cations (Ca(2+), Mg(2+) and Ni(2+)) in the running buffer was investigated and quantified by the calculation of binding constants for mononuclear and multinuclear interactions. In addition to these fundamental studies of binding equilibria, the effect of sequence and the position of the guanine transition metal-binding site in the oligonucleotide have been investigated.