Fluorescent excimers and exciplexes of the purine base derivative 8-phenylethynyl-guanine in DNA hairpins. (24th January 2018) - Brown, Kristen E.
Abstract : We characterize the ground- and excited-state electronic interactions between nucleobase analog 8-(4′-phenylethynyl)deoxyguanosine, EG, with natural nucleobases and 7-deazaguanine, as well as between adjacentEG base analogs. Abstract : The ground- and excited-state electronic interactions between the nucleobase analog 8-(4′-phenylethynyl)deoxyguanosine, EG, with natural nucleobases and 7-deazaguanine, as well as between adjacentEG base analogs, have been characterized using a combination of steady-state spectroscopy and time-resolved fluorescence, absorption, and stimulated Raman spectroscopies. The properties of the nucleosideEG-H2 are only weakly perturbed upon incorporation into synthetic DNA hairpins in which thymine, cytosine or adenine are the bases flankingEG . Incorporation of the nucleoside to be adjacent to guanine or deazaguanine results in the formation of short-lived (40–80 ps) exciplexes, the charge transfer character of which increases as the oxidation potential of the donor decreases. Hairpins possessing two or three adjacentEG base analogs display exciton-coupled circular dichroism in the ground state and form long-lived fluorescent excited states upon electronic excitation. Incorporation ofEG into the helical scaffold of the DNA hairpins places it adjacent to its neighboring nucleobases or a secondEG, thus providing the close proximity required for the formation of exciplex or excimer intermediates upon geometric relaxation of the short-livedEG excited state. The three time-resolved spectroscopic methods employed permit both the characterization of the several intermediates and the kinetics of their formation and decay.