Poly(ethylene glycol)-induced DNA condensation in aqueous/methanol containing low-molecular-weight electrolyte solutions Part II. Comparison between experiment and theory

Viscometry, UV/Vis-centrifugation and dynamic light scattering (DLS) were u sed to monitor the coil-globule transition of calf-thymus DNA by poly(ethyl ene glycol) (PEG) in aqueous/methanolic NaCl solutions. All three methods c onfirm that methanol and PEG promote the transition synergistically. The PE G concentration at which the DNA collapses decreases as the methanol fracti on of the solvent is increased. The values found for the critical PEG and m ethanol concentrations agree quite well with those predicted by the modifie d Flory-Huggins theory. This is rather surprising, because effects such as selective solvent adsorption or intramolecular charge repulsion are neglect ed. The most informative experimental technique for the present investigati ons is DLS. The DNA molecules are not affected by outside forces and DLS al lows the measurement of molecular size as well as the distribution of the c onformational states. It was observed that there are no intermediate confor mational states. A DNA molecule is either in the expanded coil state or in the collapsed state. (C) 1999 Elsevier Science Ltd. All rights reserved.