Photocurrents due to the capture of dry and hydrated electrons by nucleic acid molecules: A preliminary report

Abstract

The photocurrent waveforms produced by the irradiation of a DME, in contact with an inert electrolyte solution containing DNA, or various types of RNA, native or denatured, with a long duration UV (360 nm) light pulse have been studied. The photocurrent waveforms observed for denatured nucleic acids at the potentials where large peaks, connected with segmental desorption, are observed on the SWP polarograms, are caused mainly by the capture of hydrated photoelectrons by nucleic acid loops produced by partial desorption of the adsorbed nucleic acid molecule and the moderately slow return of captured hydrated electrons to the electrode, by “hopping” from base to base. It is likely that the captured electrons may react homogeneously with nitrous oxide at high concentration, and also that their effective diffusion coefficient is much smaller than that of the hydrated electron. Competitive electron scavenging experiments have been carried out which throw some light on the photocurrent mechanisms for denatured DNA at potentials where the nucleic acid molecules either are not adsorbed or are strongly adsorbed. Studies of the photocurrent increase produced by native DNA at low concentration indicate a decline in the photocurrent for constant electron emission, in the range of potential in which the native material is adsorbed, as the potential becomes more negative. This decline may be due to gradual desorption of parts of the relatively inflexible double helices, making penetration of the helices by “dry” and hydrated electrons less probable. The relevance of these observations to problems connected with radiation-induced genetic damage is discussed briefly.