COLL 531 |
| Nancy C. Stellwagen and Earle Stellwagen. Department of Biochemistry, University of Iowa, Iowa City, IA 52242 |
| Free solution mobility of 20-bp double-stranded DNA oligomer was measured in diethylmalonate (DM) and Tris-acetate buffers, with and without added NaCl or TrisCl. The mobility decreases linearly with the logarithm of ionic strength when increasing the buffer concentration, and also when NaCl is added to NaDM buffer or TrisCl is added to Tris DM buffer. Non-linear effects are observed when the counterion in the added salt differs from the counterion in the buffer. The dependence of the mobility on ionic strength cannot be predicted using the Henry, Debye-Huckel or Pitts equations for electrophoresis. However, the mobilities observed in all buffer and buffer/salt solutions can be predicted within ~ 20 % from the Manning equation for electrophoresis, using no adjustable parameters. The results suggest that the electrostatic shielding of DNA is determined not only by the relative concentrations of the various ions in the solution, but also by their equivalent conductivities. |
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Colloidal and Molecular Electro-Optics
Division of Colloid and Surface Chemistry |