Bridge influences electron transfer

According to the Marcus theory [9], the electron transfer rate depends upon the reaction enthalpy (AG), the electronic coupling (V) and the reorganization energy (A). By changing the electron donor and the bridge we measured the influence of these parameters on the charge transfer rate. The re-... 

The influence of the electronic coupling on the electron transfer rate was determined by changing the length of the (A T)n bridge. As expected, the rate decreased as the number n of the A T base pairs between electron donor and electron acceptor increased [4, 7]. But, surprisingly, the exponential correlation of Eq. (1) between the rate kEr and the distance is not valid for short distances. The plots in Fig. 3 and Fig. 4 show that at 6 A the electron transfer rate /cEt is much faster than expected [4, 7]. 

Fig. 5 Influence of the bridging substituent Y on the electron transfer rate from a 7 -deazaguanine Gz (see Fig. 2)...

Single stranded oligomers exhibit a completely different behavior than double strands. As shown in Fig. 6, the increase of the number n of thymine bases in the bridge between the electron donor guanine and the enol ether radical cation as electron acceptor influence the rate of the electron transfer only slightly. This can be explained by the flexibility of the single strand, which levels out the distance between donor and acceptor [13]. 

The photoinduced electron transfer reaction rates depend strongly on the molecular structures of the donor and acceptor entities [16]. The nature of the linker between them influences the charge or energy transfer, which is facilitated considerably when both partners are connected by bridging ligands [13,17,31],... 

Many of the models for electron-transfer (ET) reactions discussed in this work assume the following 1) just one electron is transferred, 2) the transfer occurs from donor to acceptor in a single step, and 3) the bridge is rigid during the process. Recent experimental and theoretical advances indicate that these assumptions are insufficient in many circumstances. Indeed, multi-electron, multistate, and dynamic bridge effects enrich the subject substantially. In this chapter we shall examine the influence of these effects on chemical and biological ET reactions. 

---