476009-32-2Relevant academic research and scientific papers
Crossover from superexchange to hopping as the mechanism for photoinduced charge transfer in DNA hairpin conjugates
Lewis, Frederick D.,Zhu, Huihe,Daublain, Pierre,Fiebig, Torsten,Raytchev, Milen,Wang, Qiang,Shafirovich, Vladimir
, p. 791 - 800 (2006)
The mechanism and dynamics of photoinduced charge separation and charge recombination have been investigated in synthetic DNA hairpins possessing donor and acceptor stilbenes separated by one to seven A:T base pairs. The application of femtosecond broadband pump-probe spectroscopy, nanosecond transient absorption spectroscopy, and picosecond fluorescence decay measurements permits detailed analysis of the formation and decay of the stilbene acceptor singlet state and of the charge-separated intermediates. When the donor and acceptor are separated by a single A:T base pair, charge separation occurs via a single-step superexchange mechanism. However, when the donor and acceptor are separated by two or more A:T base pairs, charge separation occurs via a multistep process consisting of hole injection, hole transport, and hole trapping. In such cases, hole arrival at the electron donor is slower than hole injection into the bridging A-tract. Rate constants for charge separation (hole arrival) and charge recombination are dependent upon the donor-acceptor distance; however, the rate constant for hole injection is independent of the donor-acceptor distance. The observation of crossover from a superexchange to a hopping mechanism provides a "missing link" in the analysis of DNA electron transfer and requires reevaluation of the existing literature for photoinduced electron transfer in DNA.
Synthesis, structure, and photochemistry of exceptionally stable synthetic DNA hairpins with stilbene diether linkers
Lewis, Frederick D.,Wu, Yansheng,Liu, Xiaoyang
, p. 12165 - 12173 (2007/10/03)
The structure and properties of 18 hairpin-forming bis(oligonucleotide) conjugates possessing stilbene diether linkers are reported. Conjugates possessing bis(2-hydroxyethyl)stilbene 4,4′-diether linkers form the most stable DNA hairpins reported to date. Hairpins with as few as two T:A base pairs or four noncanonical G:G base pairs are stable at room temperature. Increasing the length of the hydroxyalkyl groups results in a decrease in hairpin thermal stability. On the basis of the investigation of their circular dichroism spectra, all of the hairpins investigated adopt B-DNA structures, except for a hairpin with a short poly(G:C) stem which forms a Z-DNA structure. Both the strong fluorescence of the stilbene diether linkers and their trans-cis photoisomerization are totally quenched in hairpins possessing neighboring T:A and G:C base pairs. Quenching is attributed to an electron-transfer mechanism in which the singlet stilbene serves as an electron donor and T or C serves as an electron acceptor. In contrast, in denatured hairpins and hairpins possessing neighboring G:G base pairs the stilbene diether linkers undergo efficient photoisomerization.
