Dynamics of Photochemical Electron Injection and Efficiency of Electron Transport in DNA

Abstract

Table S1. m/z values for oligomer sequences determined by MALDI-TOF mass spectrometry. Sequence Calculated Found Sequence Calculated Found APy-T 4886.3 4881.6 APy-1 Br U 4951.2 4948.2 APy-2 Br U 4951.2 4948.0 APy-2U 4872.3 4875.2 APy-3 Br U 4951.2 4948.3 APy-3U 4872.3 4869.5 APy-4 Br U 4951.2 4955.6 APy-4U 4872.3 4874.8 APy-5 Br U 5568.6 5576.7 APy-5U 5489.5 5489.1 APy-6 Br U 6186.0 6190.7 APy-6U 6107.1 6106.3 APy-7 Br U 6803.4 6805.4 APy-7U 6724.3 6726.9 APy-8 Br U 7420.9 7416.0 APy-8U 7341.8 7345.2 APy-2 I U 4998.3 4998.5 APy-2U 4872.3 4875.6 APy-3 I U 4998.3 4996.2 APy-3U 4872.3 4868.1 APy-4 I U 4998.3 4997.9 APy-4U 4872.3 4871.1 APy-5 I U 5615.7 5618.2 APy-5U 5489.6 5492.1

Mechanism and Dynamics of Electron Injection and Charge Recombination in DNA. Dependence on Neighboring Pyrimidines

“…[5][6] There is ample evidence for the occurrence of electron transport over multiple base pairs in low or undetermined quantum yield using methods based on chemical detection, including loss of bromide ion from bromouracil and reductive splitting of thymine dimer. [7][8][9][10][11][12] However, a recent claim of faster electron vs. hole transport in DNA 13 is not consistent with earlier reports and with the failure to observe arrival of an electron at a trap site when the electron donor and acceptor are separated by more than a few intervening A-T base pairs. [13][14][15][16][17] Our studies of photoinduced charge separation in DNA have led to the conclusion that the initial steps in many hole transport processes are the formation of a radical ion pair or exciplex between a covalently attached electron acceptor and an adjacent purine base followed by the transport of the hole to the closest hole trap, which can either be a base of low oxidation potential such as guanine or deazaguanine or a second chromophore which serves as a hole trap.…”

“…k inj for T6, the APy capped hairpin, and the 2T linked hairpin with (T-A) n stems, as determined from single wavelength decays, are 2 ps -1 , 1.8 ps -1 and 0.84 ps -1 , respectively, and their values of k r1 are 0.031 ps -1 , 0.14 ps -1 and 0.029 ps -1 9,. 24, 26 The values of k inj for the three acceptors are not well-correlated with estimated values G inj (-0.18, +0.02, and -0.16 eV for Sd, APy and 2T, respectively).…”

“…3 ps, an order of magnitude shorter than those for hairpins having T n sequences. This difference in the lifetimes of the radical ion pairs for the T-A and C-G series may explain the usual choice of poly(T) sequences for the study of electron transport in DNA,9, 28,51 rather than poly(C) as recently suggested.26 The behavior of the hairpins possessing halo-pyrimidines in the first and/or second base pair adjacent to the Sd linker is the most complex and most promising from the viewpoint of electron 20 transport in DNA over more than a few base pairs. All of these hairpins display nonmonoexponential decay (Scheme 1c) and have slow decay components corresponding to radical ion pair lifetimes ranging from 30-90 ps and quantum yields for formation of the long-lived charge separated state of 0.04-0.26.…”

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

“…The injected excess electrons are expected to migrate through the DNA by a hopping mechanism, and then are trapped by an electron acceptor attached to the DNA. To date, various photosensitizing electron donors have been used for the excess electron injection to DNA, such as stilbenediether, 36,37 pyrene and its derivatives, 22,23,38,39 phenothiazine, 21 and oligothiophenes. 40−42 In our previous report, we used a bithiophene derivative as a photosensitizing electron donor, and we expected the excess electron hopping rate among consecutive C's to be 10 9 −10 10 s −1 , which is slower than the excess electron hopping rate among T's.…”

Sequence Dependence of Excess Electron Transfer in DNA

“…27 Lewis, Fiebig, and their coworkers recently reported the laser flash photolysis study on electron injection from aminopyrene to DNA, while electron transfer among the DNA was analyzed by means of product analysis. 28,29 In the previous paper, 30 we have investigated the EET in naphthalimide (NI) conjugated DNA by using pulse radiolysis experiments, in which injected excess electron on DNA was expected to move to NI to form NI radical anion. Unfortunately, the rate constant of EET was not obtained, because the kinetic trace of the transient absorption of NI radical anion showed generation behavior with the same rate as the collision of solvated electron with DNA, indicating a rapid EET.…”