Thermally Stimulated Relaxations in DNA

Abstract

The thermally stimulated depolarization current (TSDC) measurements in frozen aqueous solutions, gels and solid layers of NaDNA show typically up to three dipolar overlapping peaks in the low-temperature range of 80-150 K. Up to four discrete relaxation peaks have been observed at higher temperatures above 150 K. The low-temperature TSDC peaks are due to the dipolar relaxations of free and loosely bound water which crystallizes. Part of bound water especially in the first hydration shell of DNA molecule is at low temperatures in the form of glass. The transition of this glass from solidlike behavior to liquidlike behavior observed mainly in gels and solid samples is associated with a previously founded TSDC relaxation peak. The peak is at its maximum at 165-250 K depending on the sample humidity. Existence of this relaxation in the samples with water contents in a broad range confirms, that the slowly relaxing shell (minimally 5-7 water molecules/nucleotide) closely associated with DNA double helix retains its characteristics. Also another peak of the high-temperature band at 180-205 K which was observed in the samples at hydration 2-1800 g H2O/g dry NaDNA is due to a relaxation in the sample volume. At the highest temperatures relax the space charges trapped at the electrodes.

Glass transition in DNA from molecular dynamics simulations.

“…The origin of the glass transition was interpreted as the melting of hydrogen bonds of bound water molecules on the surface of the DNA (13). At low temperatures part of the bound water, especially in the first hydration shell, of DNA was in the glass form (14). From dielectric relaxation spectroscopy on solid calf thymus DNA at water content up to 32% the glass transition was estimated to 238 K (15).…”

“…A previous experiment (12) indicated that the glass transition of a protein was induced by the surrounding solvent. Indications of a glass transition in solid calf thymus DNA, with around 40% water content, have been given by thermally stimulated depolarization current measurements (13,14). The origin of the glass transition was interpreted as the melting of hydrogen bonds of bound water molecules on the surface of the DNA (13).…”