Structure and Dynamics of Photogenerated Triplet Radical Ion Pairs in DNA Hairpin Conjugates with Anthraquinone End Caps

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作者：

R Carmieli，AL Smeigh，SM Mickley Conron，AK Thazhathveetil，M Fuki，Y Kobori，FD Lewis，MR Wasielewski

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摘要：

A series of DNA hairpins (AqGn) possessing a tethered anthraquinone (Aq) end-capping group were synthesized in which the distance between the Aq and a guanine-cytosine (G-C) base pair was systematically varied by changing the number (n - 1) of adenine-thymine (A-T) base pairs between them. The photophysics and photochemistry of these hairpins were investigated using nanosecond transient absorption and time-resolved electron paramagnetic resonance (TREPR) spectroscopy. Upon photoexcitation, (1*)Aq undergoes rapid intersystem crossing to yield (3*)Aq, which is capable of oxidizing purine nucleobases resulting in the formation of (3)(Aq(-)Gn(+)). All (3)(Aq(-)Gn(+)) radical ion pairs exhibit asymmetric TREPR spectra with an electron spin polarization phase pattern of absorption and enhanced emission (A/E) due to their different triplet spin sublevel populations, which are derived from the corresponding non-Boltzmann spin sublevel populations of the (3*)Aq precursor. The TREPR spectra of the (3)(Aq(-)Gn(+)) radical ion pairs depend strongly on their spin-spin dipolar interaction and weakly on their spin-spin exchange coupling. The anisotropy of (3)(Aq(-)Gn(+)) makes it possible to determine that the systems of Aq(-) and G(+) within the radical ion pair are parallel to one another. Charge recombination of the long-lived (3)(Aq(-)Gn(+)) radical ion pair displays an unusual bimodal distance dependence that results from a change in the rate-determining step for charge recombination from radical pair intersystem crossing for n 4.

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关键词：

phthalate esters dietary intake DEHP foodstuffs total diet survey

DOI：

10.1021/ja303721j

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年份：

2012