Study of bound water of poly-adenine using high frequency dielectric measurements.

The high frequency dielectric constant of poly-adenine (poly-A) was measured
between 1 MHz and 1 GHz. The purpose of these experiments was to investigate the
state of water molecules that are bound to the charged groups of the poly-A
molecule. Analysis of the data using the Maxwell's mixture equation revealed the
dielectric constant of bound water higher than we expected. Using Onsager's
internal field in Debye's equation, we calculated the dielectric constant of
water in the vicinity of a charged ion. The result of this computation
demonstrates that the dielectric constant of bound water is much smaller than the
normal value only in the immediate proximity of charged ions (within 2 A). The
dielectric constant increases rapidly to the normal value as the distance
increases from 2 to 4 A. This observation indicates that charged sites of
polyions have only short range interactions with the surrounding water molecules.
However, this conclusion pertains only to rotary diffusion of bound water since
dielectric measurement is unable to detect translational diffusion.