Highly resolutive separations of hardly soluble synthetic polypeptides by capillary electrophoresis

This study deals with the separation by capillary zone electrophoresis (CE) of hardly soluble synthetic polypeptides such as poly(L-alanine). The characterization of the molar mass distribution of these polypeptides with neutral lateral chain is a prerequisite for a good understanding of the relationship between their structure and their biological activity. Nevertheless, these polypeptides are hardly soluble in a limited number of solvents such as strong acids (trifluoroacetic acid, methanesulfonic acid) and hexafluoroisopropanol (HFIP). Highly resolutive separations of end-charged hydrophobic alanine oligomers (up to 110 residues) were obtained by CE in a mixed hydro-organic HFIP/water solvent system under optimal conditions. The analyzed polyalanines possess a single positive charge on the N-terminus of their chain, and the potential negative charge at the C-terminus of their chain is suppressed by replacement of C-terminal alanine for alaninol. A careful optimization of the different constituents of the electrolyte (HFIP content, nature and concentration of the acid, nature and concentration of the cellulose derivative) was required to limit solute adsorption onto the capillary wall and to achieve the characterization of the entire molar mass distribution.