How Does Guanine–Cytosine Base Pair Affect Excess-Electron Transfer in DNA?

Abstract

Charge transfer and proton transfer in DNA have attracted wide attention due to their relevance in biological processes and so on. Especially, excess-electron transfer (EET) in DNA has strong relation to DNA repair. However, our understanding on EET in DNA still remains limited. Herein, by using a strongly electron-donating photosensitizer, trimer of 3,4-ethylenedioxythiophene (3E), and an electron acceptor, diphenylacetylene (DPA), two series of functionalized DNA oligomers were synthesized for investigation of EET dynamics in DNA. The transient absorption measurements during femtosecond laser flash photolysis showed that guanine:cytosine (G:C) base pair affects EET dynamics in DNA by two possible mechanisms: the excess-electron quenching by proton transfer with the complementary G after formation of C(•-) and the EET hindrance by inserting a G:C base pair as a potential barrier in consecutive thymines (T's). In the present paper, we provided useful information based on the direct kinetic measurements, which allowed us to discuss EET through oligonucleotides for the investigation of DNA damage/repair.

Dynamics of Excess‐Electron Transfer through Alternating Adenine:Thymine Sequences in DNA

“…As mentioned previously, it is reported that the quantum efficiency of HT through three base pairs of alternating A:T is four times smaller than that of consecutive As 9. In AT3 , on the other hand, the quantum efficiency of EET is 0.20, which is smaller than T3 (0.33)6f by a factor of 1.6. Thus, EET in DNA is less affected by the alternating sequence of nucleotides than HT in DNA, probably due to efficient interactions of LUMOs in the case of EET.…”

Sequence‐Dependent Photocurrent Generation through Long‐Distance Excess‐Electron Transfer in DNA

“…This tendency agrees with those of our previous study based on laser flash photolysis . By contrast, significant suppression of I p was observed with both CT6 and GT6, thus indicating that excess‐electron hopping between T residues was affected by the insertion of a C or G residue …”

“…The estimated factor is similar to our present results for interstrand and intrastrand EET from AT5 through a hopping mechanism (0.68) and almost consistent to our previous results obtained by laser flash photolysis for interstrand and intrastrand EET via an A:T sequence through a hopping mechanism (0.50) . C can thus be an electron carrier for EET through a hopping mechanism when a single G:C base pair is inserted between consecutive T residues, although multiple G:C pairs in Ts completely terminate EET in DNA through proton transfer from G to C .− in the G:C .− base pair …”

Charge transfer dynamics in DNA revealed by time-resolved spectroscopy

“…12). 65 In the transient absorption spectra of C4, the transient absorption band at 580 nm, which can be attributed to G(–H) –  : C(H)˙, the product of the proton-transfer reaction of G : C˙ – base pairs, was observed as well as 3E ˙ + . From the global analysis, the proton transfer rate was estimated to be 2.6 × 10 10 s –1 , which agreed with the theoretical estimation.…”