[Heat capacity of native DNA fibers at 2-25 K]

The data on low-temperature heat capacity (2-25 K) of native DNA strands at different humidities are presented, which take into account the specificity of hydration of DNA due to its chemical composition (GC-content). The temperature dependence of DNA heat capacity (Cp = f(T)) at 2-4 K was analyzed. Analysis of Cp = f(T) involves both the ordinary Debay density and excessive low-energy density of oscillatory states (DOS) peculiar to noncrystalline solids. It is concluded that heat capacity of DNA at very energies (less than 1 K) is well described in terms of the generally accepted model of two-level systems. The nature of excessive DOS at energies 3-10 K is related to oscillatory excitations on structural inhomogeneities, which can represent clusters of hydrate water molecules (approximately 1-2 nm) "grown" in DNA matrix.