Ulf Olsson

In the present work, the interactions between double-stranded (ds) or single-stranded (ss) DNA and nonionic ethylene oxide (EO) surfactants, with special attention to the possible contributions from hydrophobic interactions, have been investigated using a multitechnique approach. It was found that the presence of ss as well as dsDNA induces a slight decrease of the cloud point of pentaethylene glycol monododecyl ether (C12E5). Assessment of the partitioning of DNA between the surfactant-rich and surfactant-poor phases formed above the cloud point showed that the polymer was preferably located in the surfactant-poor phase. Surface tcnsiometry experiments revealed that neither of the DNA forms induced surfactant micellization. Finally, it was shown by DNA melting measurements that another EO surfactant (C12E8) did not affect the relative stabilities of ss and dsDNA. To summarize, all experiments suggest that the net interaction between DNA and nonionic surfactants of the EO type is weakly repulsive, which can be attributed mainly to steric effects. In general, the results were practically identical for the ds and ss forms of DNA, except those from the cloud point experiments, where the decrease of the cloud point was less pronounced with ssDNA. This finding indicates the presence of an attractive component in the interaction, which can reasonably be ascribed to hydrophobic effects.