The a.c. conductivity of aperiodic DNA revisited

Recent measurements of the frequency-dependent a.c. conductivity of aperiodic DNA double helices have provided results which are in good agreement with our theoretical findings based on the variable range hopping mechanism in the 1–1011 s−1 frequency range at room temperature. At the frequencies 100 GHz–1 THz it is probable that not the hopping mechanism, but dipole energy loss of the water helices surrounding DNA is the dominant cause of the conductivity, because the experiments have given nearly the same conductivites for single and double DNA strands. eoretical temperature-dependence of the conductivity contrary to experiments, does not show a crossing point and the slopes of the theoretical curves do not become zero even below 60 K. This and the fact that at T≈125 K the experimental σ(ω) is by one order of magnitude larger than the theoretical value, indicates that at low temperatures not the hopping mechanism, but other ones (like multichannel tunneling, structural thermal fluctuations of the stack) become dominant.