Effect of Mg²⁺ Cations on the Dynamics and Efficiency of Hole Transport in DNA

The effect of Mg²⁺ cations on the electronic spectra and dynamics and efficiency of hole transport has been determined by means of femtosecond time-resolved transient absorption spectroscopy for DNA hairpins possessing stilbene electron acceptor and donor chromophores. The results are compared with those obtained previously for the same hairpins in the presence of Na⁺ cations and for one hairpin with no added salt. Quantum yields and rate constants for charge separation are smaller in the presence of Mg²⁺ than Na⁺, the largest differences being observed for the hairpins with the largest number of base pairs. Slower charge separation is attributed to minor groove binding by Mg²⁺, which results in a stiffer duplex structure rather than a change in ground state geometry. Reduction in the Na⁺ concentration has little effect on either the dynamics or efficiency of hole transport

Dynamics and Efficiency of Hole Transport in LNA:DNA Hybrid Diblock Oligomers

We report here the effect of replacing one or both of the purine or pyrimidine blocks of a diblock stilbene donor–acceptor capped hairpin with locked nucleic acid (LNA) bases on the dynamics and efficiency of hole transport. The structures of the DNA and LNA:DNA hybrids are tentatively assigned to B- or A-type structures on the basis of their circular dichroism spectra. Replacing the bases in either the A-block or the G-block of the diblock DNA hairpin with LNA bases results in a modest decrease in the base-to-base hopping rate constant and quantum yield for charge separation. Somewhat larger decreases are observed when all of the purine or pyrimidine bases are replaced by LNA bases