NMR Determination of the Binding Constant of Ionic Species: A Caveat.

Determination of the dissociation constant of ionic complexes with the standard NMR titration and NMR dilution techniques may yield a severely compromised result, due to the typically unconsidered chemical shift alteration induced by the gradual change of the ionic strength during the experiment. We show that the reliability of an NMR titration experiment is markedly improved upon keeping the overall ionic strength constant.