| Abstract
| - Detergent sequestration using micelles as a hydrophobic sink for dissociated drug molecules isan established technique for determination of dissociation rates. The anionic surfactant molecules aregenerally assumed not to interact with the anionic DNA and thereby not to affect the rate of dissociation.By contrast, we here demonstrate that the surfactant molecules sodium dodecyl sulfate (SDS), sodiumdecyl sulfate, and sodium octyl sulfate all induce substantial rate enhancements of the dissociation ofintercalators from DNA. Four different cationic DNA intercalators are studied with respect to surfactant-induced dissociation. Except for the smallest intercalator, ethidium, the dissociation rate constants increasemonotonically with surfactant concentration both below cmc and (more strongly) above cmc, much morethan expected from electrostatic effects of increased counterion concentration. The rate enhancement,most pronounced for the bulky, multicationic, hydrophobic DNA ligands in this study, indicates a reductionof the activation energy for the ligand to pass out from a deeply penetrating intercalation site of DNA. Thediscovery that surfactants enhance the rate of dissociation of cationic DNA−intercalators implies that rateconstants previously determined by micelle-sequestered dissociation may have been overestimated. Asan alternative, more reliable method, we suggest instead the addition of excess of dummy DNA as anabsorbent for dissociated ligand.
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