Europhys. Lett.
Volume 71, Number 2, July 2005
Page(s) 304 - 310
Section Interdisciplinary physics and related areas of science and technology
Published online 17 June 2005
Europhys. Lett., 71 (2), pp. 304-310 (2005)
DOI: 10.1209/epl/i2004-10541-6

Why is the compact state of DNA preferred at higher temperature? Folding transition of a single DNA chain in the presence of a multivalent cation

T. Saito, T. Iwaki and K. Yoshikawa

Department of Physics, Graduate School of Science, Kyoto University Kyoto 606-8502, Japan

received 15 December 2004; accepted in final form 27 May 2005
published online 17 June 2005

Upon the addition of multivalent cations, a giant DNA chain exhibits a large discrete transition from an elongated coil into a folded compact state. We performed single-chain observation of long DNAs in the presence of a tetravalent cation (spermine), at various temperatures and monovalent salt concentrations. We confirmed that the compact state is preferred at higher temperatures and at lower monovalent salt concentrations. This result is interpreted in terms of an increase in the net translational entropy of small ions due to ionic exchange between higher and lower valence ions.

82.35.Rs - Polyelectrolytes.
87.14.Gg - DNA, RNA.
64.70.-p - Specific phase transitions.

© EDP Sciences 2005