Migration, holes

GG and GGG sequences have been widely used in strand cleavage studies of hole migration in DNA [4-6]. According to conventional wisdom, GG and GGG sequences serve as hole traps . The calculated gas phase ionization potentials reported by Sugiyama and Saito [14] provide relative energies for G vs GG (0.47 eV) and G vs GGG (0.68 eV) that continue to be cited as evi-... 

The pulse radiolysis of ODN conjugated with Py and Ptz showed a transient absorption spectrum with a peak at 470 or 520 nm, assigned to Py+ or Ptz + respectively (Fig. 9). The formation rates of Py+ and Ptz+ obtained for Py-1 and Ptz-1 were almost identical to that of the decay of TIOH+ and no secondary formation was observed. These results indicate that a hole migrates from... 

On the other hand, when the distance between Py and Ptz was longer (PtzPy-3) with five A-T base pairs, the formation and decay of Py + were observed in the time range of 0-100 /zs after an electron pulse. At 100 /US only Ptz + was observed (Fig. 10b). This result indicates that a hole migrates from Py + to Ptz within 100 fis. >From the time profiles of absorption peaks at 470 nm for Py + and 520 nm for Ptz +, secondary formation of Ptz + was also observed concomitant with the decay of Py + for PtzPy-3, while no secondary formation of Ptz + was observed for PtzPy-1 due to the rapid hole transfer (Fig. 10c,d). The rate constant of the hole transfer from Py + to Ptz was determined to be 2.0X104 s 1 for PtzPy-3 from the decay of Py +. 

In a another experiment, we confirmed that the hole migration from the G+ to the remote GG step through four intervening AT base pairs is extremely difficult (Table 2 and Fig. 4). These observations are consistent with... 

Electron and hole migration through the electron and hole transport layers... 

Photoexcited electrons or holes migrate in a space charge layer towards the electrode interface, where they participate in transfer reactions of cathodic electrons or anodic holes to provide a reaction current as shown in Pig. 10-9. Such a reaction current of photoexcited electrons or holes is called the photoexcited reaction current or simply the photocurrent. 

As noted, the twisted conformer, which has a lower IP, rapidly scavenges the chair form of the cation-radical. Being endothermic, the backward transfer is relatively slow, and equilibrium is reached in 20-30 min. Thus, the electron transfer can be described as a series of periods of very fast hole migration between the chair forms and intermittent migration with the participation of the twist forms. 

The basic principle of semiconductor photocatalysis involves photogenerated electrons and holes migrating to the surface. (From Wang et ah, 2006)... 

The rate and extent of electron and hole migration within DNA had been a topic of intense experimental [1] and theoretical [2] interest and dispute. However, as other chapters in this volume point out, the overall picture is now becoming increasingly understood. Several earlier reviews have dealt with the radiation damage to DNA and subsequent chemical processes including electron and hole transfer [3]. This chapter will focus on recent contributions to hole and electron transfer in DNA from high-energy radiation studies. We first present a brief overview on electron transfer processes in DNA from radiation studies and describe in more detail our most recent results on electron and hole transfer in DNA at low temperatures. 

DNA - a Molecular Wire or an Insulator - The rate, as well as the extent, of electron and hole migration within DNA had been a topic of intense experimental and theoretical interest and dispute.60 ESR studies have made significant contributions to the understanding of these important phenomenon. 

In the discussions of semiconductors and electrochemistry in this section, it has been assumed that the sole source of electrons and holes that are transported to the interface to take part in electrode reactions is the electrons injected into the conduction band from doping (n-type) and holes made in the valence band by doping for p-type. In the latter, holes migrate to the electrode surface to receive electrons from ions in the solution. 

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