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ION–SOLVENT INTERACTIONS 195


























             One  can then use  the  time course of the  fluorescence  decay. The  change in
          frequency of  the  emitted  light  compared with  that of  the  incident light contains
          information from which the rotational and internal dynamics can be studied.
             The rotational frequency in lysozomes decreases with increase of water. This type
          of study throws some light on protein–micellar interactions and how they are affected
          by hydration.
             X-ray and neutron  diffraction measurements on polyion  hydration  give the
          number of water molecules involved per repeat group in the structures. About one
          water molecule per repeat group is the result for polymethyl methacrylate. The results
          of hydration for a variety of proteins are given in Table 2.31.

          2.24.4. Dielectric Behavior of DNA

             The rotation of large molecules in solution together with their hydration is the
          basis of many of the  properties of solutions  containing  polyions.  One has to  ask
          questions, however, about the decrement of the dielectric constant in the case of linear
          polyelectrolytes,  which include DNA.  Substances  such as this  exhibit dielectric
          decrements as expected but it is difficult to account for their magnitude in terms of
          hydration. Thus, there might be a rotation but this cannot be about the long axis because
          in such  a  case   (Section 2.24)  should  increase when the  molecules are oriented
          perpendicularly to the electric field and this is not found to be the case.
                                                                     50
             Could this  be behavior in  terms of the Maxwell–Wagner dispersion,  which
          would arise through conductivity in the double layer near the polyanion. In support of
          this, the dielectric constant falls as the frequency increases (Fig. 2.79).

          50
           This is the variation of the resistance or capacitance with frequency.
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