The dielectric behavior of the aqueous solutions of three widely differing macromolecules has been investigated: myoglobin, polyvinylpyrrolidone (PVP), and human serum low-density lipoprotein (LDL). It was not possible to interpret unambiguously the dielectric properties of the PVP solution in terms of water structure. The best interpretation of the dielectric data on the myoglobin and LDL solutions was that, in both cases, the macromolecule attracts a layer of water of hydration one or two water molecules in width. For LDL, this corresponds to a hydration factor of only 0.05 g/g, whereas for myoglobin the figure is nearer 0.6 g/g. With myoglobin, part of the water of hydration exhibits its dispersion at frequencies of a few GHz, and the rest disperses at lower frequencies, perhaps as low as 10-12 MHz. The approximate constancy of the width of the hydration shell for two molecules as dissimilar in size as LDL and myoglobin confirms that the proportion of water existing as water of hydration in a biological solution depends critically on the size of the macromolecules as well as on their concentration.

The problem of the absorption of the energy of plane electromagnetic radiation by an aqueous solution of macromolecules is considered. A simplified model for the hydrated molecule is employed, consisting of a spherical shell of bound water surrounding a spherical core. The power deposition per unit volume of the shell is calculated in the frequency range 100 MHz-100 GHz for several bound water relaxation frequencies. In each case the corresponding values are also calculated for free water for comparison. The values obtained for the bound water are shown to be significantly higher than those for the free water up to frequencies of at least 1 GHz. The maximum difference between these two sets of values is of the order of a factor of five and occurs roughly at the bound water relaxation frequency. Because of the strong coupling between the bound water molecules and the macromolecules present in biological material this result could be a significant factor in the explanation of the biological effects of microwaves at a molecular level.

The relative permittivity and conductivity of the cerebellum, cerebrum and brain stem of mouse brain were measured at a temperature of 37 degrees C over a frequency range of 72 MHz to over 5 GHz using time-domain spectroscopy. An analysis of the data suggests that the water exists in various forms of binding with an average relaxation frequency less than free water.

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