Water in some DNA model systems
In order to facilitate the interpretation of the DNA dielectric spectrum, dielectric properties of poly ∼ (N-methyl-capryl-amide) PMCA and modified poly-(caprolactam) PKMG were measured in a range of −50° −90°C, and 10−1 Hz −104 Hz. All measurements were performed under defined humidity conditions. Several absorption regions were observed. Only the low temperature region γ at −140°C was found to be humidity independent. The non-Arrhenius region α is connected with the glass transition of the amorphous phase. We assume that the hydrogen bonds linking the polyamide groups act as temporary physical crosslinks. The sorption of water probably diminishes the effective network density and thus the glass transition temperature. The polyamide groups pairing is seriously destroyed at 5 wt% of water. If the hydration goes on, the water molecules act merely as a plasticizing agent via lowering the internal viscosity. The relaxation region β is interpreted as local motion of water-polyamide groups complex and the region β′ (PKMG) as the motion of side groups with water molecules attached. Both types of kinetic units move in surroundings of similar internal viscosity.
Key wordsDielectric relaxation polyamides DNA humidity plasticizing effects
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