带有蒽醌端帽的 DNA 发夹偶联物中光生三重自由基离子对的结构和动力学,Journal of the American Chemical Society

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带有蒽醌端帽的 DNA 发夹偶联物中光生三重自由基离子对的结构和动力学
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2012-06-28 , DOI: 10.1021/ja303721j
Raanan Carmieli ₁ , Amanda L. Smeigh ₁ , Sarah M. Mickley Conron ₁ , Arun K. Thazhathveetil ₁ , Masaaki Fuki ₂ , Yasuhiro Kobori _{2,

3} , Frederick D. Lewis ₁ , Michael R. Wasielewski ₁

Affiliation

合成了一系列具有系链蒽醌 (Aq) 封端基团的 DNA 发夹 (AqGn)，其中 Aq 与鸟嘌呤-胞嘧啶 (GC) 碱基对之间的距离通过改变数量 (n - 1) 系统地改变它们之间的腺嘌呤 - 胸腺嘧啶（AT）碱基对。使用纳秒瞬态吸收和时间分辨电子顺磁共振 (TREPR) 光谱研究了这些发夹的光物理和光化学。在光激发时，(1*)Aq 经历快速系统间交叉以产生 (3*)Aq，其能够氧化嘌呤核碱基，导致 (3)(Aq(-•)Gn(+•)) 的形成。所有 (3)(Aq(-•)Gn(+•)) 自由基离子对都表现出不对称的 TREPR 光谱，由于它们不同的三重自旋亚能级群，具有吸收和增强发射 (A/E) 的电子自旋极化相模式，这来自 (3*)Aq 前体的相应非玻尔兹曼自旋亚级群。(3)(Aq(-•)Gn(+•)) 自由基离子对的 TREPR 谱强烈依赖于它们的自旋-自旋偶极相互作用，弱依赖于它们的自旋-自旋交换耦合。(3)(Aq(-•)Gn(+•)) 的各向异性使得可以确定自由基离子对内的 Aq(-•) 和 G(+•) 的 π 系统彼此平行。

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

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 π 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 to coherent superexchange for n > 4.

更新日期：2012-06-28

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