A semiempirical model for the electrophoretic mobilities of peptides in free-solution capillary electrophoresis

In this study an attempt is made to explore the effect of a peptide's size, charge, and hydrophobicity on its electrophoretic mobility (mu) as measured by free-solution capillary electrophoresis with the aim of developing a semiempirical model which incorporates these effects. The effects of peptide size (which is measured by the number of amino acids in the polypeptide chain (n] and charge on mu are independently determined by experiment in a single solvent system and combined to give the relationship (formula; see text) where the constant 5.23 X 10(-4) is postulated to depend on the solvent system used. The form of Eq. [A.1] was confirmed, and the values of the constants 5.23 X 10(-4) and 2.47 X 10(-5) were determined, by measuring the electrophoretic mobilities of 40 peptides varying in size from 3 to 39 amino acids and varying in charge from 0.33 to 14.0. Furthermore, the effect of noncharged neutral amino acids on mobility was investigated and shown to be present, but only as a minor perturbation on the effects of size and charge.