Deuterium isotope effects observed during competitive binding chiral recognition electrospray ionization--mass spectrometry of cinchona alkaloid-based systems.

Deuterium isotope effects are reported for binding between tert-butylcarbamoyl-quinine/quinidine chiral selectors and isotopomeric quasienantiomers of N-(3,5-dinitrobenzoyl)leucine measured using electrospray ionization-mass spectrometry (ESI-MS) and competitive binding. Evaluation of mixtures of each selector with one labeled and one unlabeled enantiomeric selectand of identical configuration showed a significant difference in measured ion abundances of diastereomeric complexes between the selector and each selectand. It was found that in some cases, the complex containing the nondeuterated selectand was 15% more abundant than its deuterated counterpart. On the basis of an assessment of solution- and gas-phase isotope effects reported in the literature, a series of control experiments were performed to study the origin of the effects. On the basis of these measurements, our preliminary conclusion is that the differing gas-phase physicochemical nature of the deuterated versus nondeuterated selectand represents the strongest contribution to the observed effect in this chiral molecular recognition system. Copyright 2006 John Wiley & Sons, Ltd.