Excess electrons in ice

Abstract

CONSIDERABLE evidence has accumulated for a highly structrued, ice-like nature of the aqueous medium in certain cellular systems, particularly in the vicinity of macromolecules such as DNA (refs 1–7). A consequence of this ordering of water molecules is that the dielectric relaxation time of the medium becomes considerably longer than the 10 ps or so found for normal water8. A correlation has been found in recent experiments between the time required for solvation of electrons in polar liquids9–13 and the dielectric relaxation time. On the basis of this a longer lifetime for unsolvated (‘dry’14) electrons in biological systems, than the few picoseconds15,16 found in normal aqueous media, would be expected. An extended lifetime for dry electrons, particularly if coupled with a high electron mobility, would increase the probability of this species playing a role in cellular radiation damage, as has recently been suggested17, and also in intra- and inter-molecular charge transport processes in biological systems. To obtain an insight into the properties of electrons in a structured aqueous medium, we have studied the conductivity change resulting from nanosecond pulse ionisation (irradiation) of ice. We outline here some conclusions we have reached concerning the yield and mobility of excess electrons as well as the processes of electron trapping and ion recombination in this medium.