Predictive model for capillary electrophoretic peptide mobility in 2,2,2-trifluoroethanol-water solution

Using capillary electrophoresis (CE) on a set of 21 peptides with a molecular mass ranging from about 350 to 1850 Da, the Stokes radii at different protonation stages and the acidic dissociation constants in water and in a 2,2,2-trifluoroethanol (TFE) water mixture (30% v/v) were determined. These results permitted us to establish separately the reliability of semiempirical models utilized for the prediction of peptide size and charge at different acidic pH(app) (pH(app) range: 2.00-4.25). The data obtained on size and charge were utilized in order to provide suitable mobility predictions on the basis of the charge-to-size ratio. The best predictive conditions for size and charge were found at the most acidic range of pH(app) studied (2.00-2.25), either in water or a TFE-water mixture, and reliable predictive equations for peptide mobility were established at this pH(app).