Electron-molecular-vibration coupling for small polarons in DNAs

Within a tight-binding electron-phonon interacting model, we calculated the spectrally resolved polaron binding energy between electrons and phonons and between holes and phonons on poly(dA)∙poly(dT) and poly(dG)∙poly(dC). Poly(dA)∙Poly(dT) is a DNA where one single strand consists only of adenine(A) and the other single strand consists only of thymine(T), while Poly(dG)∙Poly(dC) is a DNA where one single strand consist only of guanine(G) and the other of cytosine(C). We found that the polaron binding energies of poly(dA)∙poly(dT) were larger than those of poly(dG)∙poly(dC), and that the polaron binding energy and the electrical conductance were strongly temperature dependent. These findings agree well with the current experimental data. We concluded that small polaron hopping occurs by a conduction mechanism on the DNA molecules examined.

Figure 1

(Color) Polaron binding energy spectra of (a) electron-molecular-vibration coupling and (b) hole-molecular-vibration coupling on poly(dA)∙poly(dT) and poly(dG)∙poly(dC) as a function of wave numbers.

Figure 2

(Color) Temperature dependence of (a) polaron activation energy and (b) electrical conductance of poly(dA)∙poly(dT) and poly(dG)∙poly(dC). $E_{\mathrm{ep}}$ and $E_{\mathrm{hp}}$ represent the activation energy of the electron-phonon and hole-phonon, respectively. The $e\text{−}p$ and $h\text{−}p$ indicate the conductance for electron-phonon and hole-phonon coupling, respectively.