Deoxypentose nucleic acids: XII. The denaturation of deoxyribonucleic acid in aqueous solution: Changes produced by environment

Abstract

An investigation of salt free DNA solutions has yielded further information on the critical concentration phenomenon reported earlier. This phenomenon appears to arise from denaturation by dilution below a certain critical concentration. The critical concentration can be arbitrarily set at 21 ± 2 · 10 −5 M DNA for several salt free DNA preparations. Conductivity measurements show, however, that the structural transition actually occurs over a concentration zone extending from 50 to 4 · 10 −5 M DNA. The process is at least in part irreversible. The effects, on the phenomenon, of ionic strength, gegenion radius, dielectric constant, EDTA and thermal denaturation were investigated. The results reported on the effect of thermal denaturation in particular support the premise that the critical concentration originates from a denaturation process. These findings are in agreement with the changes observed by Cavalieri et al. 4, who find a large decrease in mean end-to-end distance on dilution of salt free DNA solutions to low concentrations. This change was not accompanied by a light scattering molecular weight change.