Electrophoretic separations of polyelectrolytes in free-solutions and sieving media.

摘要

Separations of charged species in solutions are at the heart of electrophoresis. Since many important biopolymers and certain polymers of industrial significance dissociate in aqueous solutions into macroions and small counterions, the electrophoretic methods are suitable for their separation. However, the electrophoretic velocity of uniformly charged polyelectrolytes is size-independent in free-solutions as a consequence of the symmetry between their charge and friction. To separate such polymers, this symmetry must be broken.; In this thesis research, electrophoretic separations of uniformly charged polyelectrolytes were investigated in the capillary format. The velocity size-dependence was induced through a solutes' end-labeling, or through the use of sieving media.; In the end-labeling strategy, the friction or charge of the solute was changed by an attachment of a suitable hydrophilic moiety. Consequently, the electrophoretic mobility of a small solute, in contrast to larger molecules, was significantly enhanced. This strategy was subsequently applied to the analysis of oligosaccharides. First, the migration model was tested with the uniformly charged oligomers of a partially hydrolyzed kappa carrageenan. Secondly, a novel end-label reagent, featuring fluorescent and enhanced frictional properties, was synthesized. This end-label was applied to the separations of low-molecular-weight heparins.; Different sieving media were explored for enhancing the size-dependent migrations of flexible polyelectrolytes such as DNA. It is shown that for either the large flexible polymers, or high electric-field strengths, the size-dependent migrations in polymer networks deteriorate. This phenomenon is explained by the solutes' orientation in the direction of a field which is a consequence of their reptative motion through a sieving medium. The velocity size-dependence of oriented chains was restored by employing alternating (pulsed) fields. Such fields force a polyelectrolyte molecule to reorient in a new direction while the reorientation time becomes size-dependent. Subsequently, the alternating electric fields were applied here to separate various polyelectrolytes such as large nucleic acids, polysaccharides and polystyrene sulfonates. Additionally, the dynamics of nucleic acids in alternating fields has been investigated and the appropriate mobility curves were explained at the molecular level. Finally, the aggregations of large polyelectrolytes in strong electric fields were briefly examined.