Contribution of Capillary Electrophoresis and Ion Mobility Spectrometry to probe conformational change during desolvation

The transfer of ions from the solution to the gas phase is a critical step to produce « native species ». Coming from a highly solvating medium, ionic species will tend to find a new equilibrium conformation in the gas phase. The pathway to reach the thermodynamically stable conformation involves crossing potential barriers of different heights. When these barriers are too high compared to the internal energy of the ions, it will result in “partial memories” (as structural preservation) of the conformation in solution.
In order to evaluate the effect of the solvent evaporation and of the various collision processes encountered by the ions in the mass spectrometer, we developed two strategies:
The first strategy consists in comparing in a single experiment the shape of the ions in solution and in the gas phase. Data are obtained by coupling Capillary Electrophoresis (CE) with Ion Mobility Mass Spectrometry (IMS). Drift times in solution and in the gas phase are directly compared. Deviations from their correlation points out changes in folding upon desolvatation. Preliminary results show that some of peptides issued from tryptic digest of BSA clearly change their conformation during desolvatation.
The second strategy consists to monitor the shape of the different conformers observed for the intact cytochrome C during native runs in capillary electrophoresis and “native” ion mobility mass spectrometry, both using a physiological TRIS acetic pH7 buffer compared to a “MS friendly” ammonium acetate pH7 buffer.
Finally as preliminary study, we proposed to use homopolymers for better understanding about the folding behavior in gas phase and the resulting shape of these ions using ion mobility spectrometry.