Hydration Effects on the Microwave Dielectricity in Dry Poly(dA)-Poly(dT) DNA(Cross-disciplinary physics and related areas of science and technology)

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Using a microwave cavity-perturbation method, the temperature dependence of the complex dielectric constant (ε=ε_1+iε_2) at 16.3 GHz is measured on a dry poly(dA)-poly(dT) DNA sample prepared under three-different relative humidity (RH) of 0,11 and 93%. For RH=0%, the temperature dependence of both ε_1 and ε_2 are explained by the rotational motion of water molecules electrostatically bonding to the negatively charged phosphate group in the primary hydration shell. The activation-type behavior in ε_2 is discussed with a double-well potential for a process that the electric dipole of the hydrated water is thermally rotated to the adjacent phosphate groups. For RH=11%, ε_2 takes a broad maximum at 280K due to the collective motion of water molecules in the primary hydration shell. While these features qualitatively resemble to those of free water, the absolute values are much small due to an extremely small number of hydrated water molecules. Moreover the conformation is expected to be of A form, in which the hydration bridge could be constructed in the major groove via hydrogen bonds as suggested by previous X-ray and neutron diffraction experiments. For RH=93%, in addition to the collective motion of the primary hydration shell, a freezing process of the secondary hydration shell appears. Independently on RH, the hydrated water molecules at low temperatures around 200K or below are hard to respond to microwave electric fields, and hence both the rotational and collective motions cannot be permitted. Approaching to 420K, ε_2 becomes suppressed converging to the same value. The suppression comes from a thermally induced dehydration resulting in eventual reduction of the hydration density down to 0.1 water molecules per nucleotide as revealed by our previous infrared spectroscopy.
社団法人日本物理学会の論文
2008-04-15

Hydration Effects on the Microwave Dielectricity in Dry Poly(dA)-Poly(dT) DNA(Cross-disciplinary physics and related areas of science and technology)

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