Indications of Glass Transition in DNA

Abstract

The thermally stimulated depolarization current (TSDC) and d.c. conductivity methods have been used in the search for a glass transition in solid NaDNA and in the studies of its origin. The existence and properties of a dipolar TSDC relaxation peak with a maximum at temperature, T,,, , in the range of (160 + 250) K (depending on the water content in the samples) and an exponentially increasing d.c. conductivity above T, indicate the existence of a glass transition effect in solid DNA. The use of the same methods in the samples of pure ice and frozen aqueous solutions of NaCl (models of the ion-water shell in DNA) confirms that the glass transition origin is in melting of hydrogen bonds of adsorbed (bound) water molecules on the surface of the biopolymer.

Ionic conductivity on a wetting surface

“…Experiments on flat DNA films show a similar exponential dependence [10,11,12,13]. While the mechanism for electrical conduction in DNA remains controversial, it is widely believed to occur through the movement of ions along the outer surface of the double-helix [10,14,15].…”

Materials science of DNA

“…However, based on their experimental results performed at 10 KHz, Neubert et al 190 pointed out that the second type of relaxation might be due to Na + counterions, rather than to the intrinsic semiconductivity of DNA. Moreover, based on their DC conductivity and low-frequency dielectric measurements using thermally stimulated depolarization current (TSDC), Laudat et al 191 revealed an apparent mobility of H 3 + O and OH À ions and counterions in the close vicinity of the DNA backbone, i.e., in the first hydration shell.…”

Dynamics of tin nuclei in alkyltin(IV)–deoxyribonucleic acid condensates by variable-temperature tin-119 Mössbauer spectroscopy

“…It clearly appears that fare'qabs, as well as the corresponding ( x 2 ) , coincide for the DNA condensates spontaneously formed with SntVMe2, SnIVEt2 and SnIVEt, by addition of ethanol solutions of the alkyltin chlorides to aqueous DNA, method (I) (see Experimental section), as shown in Fig. 3 for representative series, while sensibly differing for the Sn'"Me,-DNA condensate precipitated by a standard procedure for DNA [method (11), addition of NaCl and EtOH], as well as for all SnIVMe3-DNA systems (as exemplified in Fig. 3).…”