Dielectric behavior of water in biological solutions: studies on myoglobin, human low-density lipoprotein, and polyvinylpyrrolidone.

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.

Microwave dielectric measurements (0.8-70 GHz) on Artemia cysts at variable water content.

Dielectric permittivity measurements are reported for cysts of Artemia, a crustacean known as the brine shrimp. Using coaxial and waveguide techniques we examined the frequency range from 0.8 to 70 GHz. Taking advantage of the ability of this system to reversibly lose essentially all intracellular water, we determined the permittivity over the entire range of cyst water contents. Although experimental errors prevent a rigorous treatment of the data, we advance the general conclusion that little of the water in this system behaves dielectrically like pure water, regardless of water content. This conclusion is supported by, and is consistent with, the results of previously published studies that probe the motional properties of water in this system using nuclear magnetic resonance spectroscopy and quasi-elastic neutron scattering.

A generalized model for the interaction of microwave radiation with bound water in biological material.

Calculations have been performed concerning the deposition of microwave energy in bound water surrounding a biological macromolecule immersed in a continuum consisting of free water and dissolved ions. In particular a previous model of a hydrated macromolecule has been generalised to one where the relaxation frequency of the bound water varies across the layer, and the calculations have been carried out for three combinations of values of ionic conductivity of the bound water and the continuum. When these conductivities are equal, but low, the average energy deposition per unit volume in the bound water is greater, sometimes by at least an order of magnitude, than that in the continuum at frequencies in the region of hundreds of MHz to a few GHz. As the ionic conductivity increases this effect decreases and at conductivities equal to that of physiological saline the specific energy deposition in the bound water is not more than around twice that in the surrounding electrolyte continuum over this frequency range. Therefore, for tissues of high bound water content exposed to microwaves of a given power density the biological effect produced is enhanced. For a biological tissue of high ionic conductivity with 20% of its water in the bound state the overall energy absorption would be 25% greater at certain frequencies than if all the water were in the free state. For materials of low ionic conductivity the increase would be more than one order of magnitude.