Capillary Electrophoresis Using Concentrated Solution of Oligomeric Saccharides as the Medium : Elucidation of the Mechanism of the Size-dependent Separation and Its Development

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The present project originated serendipically from the accidental observation of size-dependent separation of proteins in the presence of SDS of about 0.1% and oligomeric dextran (molecular weight of about 1,000) in a high concentration around 10% by a PhD stident, M.R.Karim and Takagi. The mode of separation was apparently like that in SDS-polyacrylamide. Mobility and viscosity determinations as a function of concentration of the oligomeric dextran clearly showed that the observed size-dependent separation is not due to molecular-sieving, because no sign of the presence of network structure was observed. Under the condition of SDS-polyacrylamide gel electrophoresis, proteins are unfolded to become coiled chains and their polypeptide chains are heavily charged to show free-drainage behavior in free-solution electrophoresis. Such a chains can be naturally size-dependently separated in the presence of molecular-sieve. The new mode of separation we have observed can be interpreted, if the chains loose the free-drainage behavior as the result of the presence of concentrated oligomeric saccharide to become coils not penetrable to solvent and ions contained therein. Confirmation of this working hypothesis is left to be examined, and I will continue making efforts to do so.