Determination of peptide dissociation constants and Stokes radius at different protonation stages by capillary electrophoresis

Peptide electrophoretic mobility measured by capillary zone electrophoresis can be regarded as deriving from the mean of mobilities of different protonated forms, each one participating according to its charge, Stokes radius and relative percentage. The percentage is a function of the peptide dissociation constant and solution pH. Therefore, mobility modifications due to pH variations can be related to peptide dissociation constant, charge, and Stokes radius throughout general binding equations. Thus, not only can peptide dissociation constants be measured, but information about Stokes radius modifications linked to proton loss can also be obtained with picomoles of peptide.