Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, USA.
J Phys Chem A. 2010 Jan 14;114(1):256-67. doi: 10.1021/jp908055h.
8-Vinyladenosine (8VA) is an adenosine analog, like 2-aminopurine (2AP), that has a red-shifted absorption and high fluorescence quantum yield. When introduced into double-stranded DNA (dsDNA), its base-pairing and base-stacking properties are similar to those of adenine. Of particular interest, the fluorescence quantum yield of 8VA is sensitive to base stacking, making it a very useful real-time probe of DNA structure. The fundamental photophysics underlying this fluorescence quenching by base stacking is not well understood, and thus exploring the excited state electronic structure of the analog is warranted. In this study, we report on changes in the electronic structure of 8VA upon optical excitation. Stark spectroscopy was performed on 8VA monomer in frozen ethanol glass at 77 K to obtain the direction and degree of charge redistribution in the form of the difference dipole moment, Deltamu(01) = 4.7 +/- 0.3 D, and difference static polarizability, tr(Delta(alpha)01) = 21 +/- 11 A(3), for the S(0)-->S(1) transition. In addition, solvatochromism experiments were performed on 8VA in various solvents and analyzed using Bakhshiev's model. High level ab initio methods were employed to calculate transition energies, oscillator strengths, and dipole moments of the ground and excited states of 8VA. The direction of Deltamu(01) was assigned in the molecular frame for the lowest optically accessible state. Our study shows that the angle between ground and excited state dipole moment plays a critical role in understanding the change in electronic structure upon optical excitation. Compared to 2AP, 8VA has a larger difference dipole moment which, with twice the extinction coefficient, suggests that 8VA is superior as a two-photon probe for microscopy studies. To this end, we have measured the ratio of the two-photon fluorescence yields of the two analogs by excitation at the respective monomer absorption maxima. We show that 8VA is indeed a significantly brighter two-photon fluorophore, based on our experimental and computational results.
8- 乙烯基腺苷（8VA）是一种类似于 2-氨基嘌呤（2AP）的腺苷类似物，它具有红移的吸收和高荧光量子产率。当引入双链 DNA（dsDNA）时，其碱基配对和碱基堆积性质与腺嘌呤相似。特别有趣的是，8VA 的荧光量子产率对碱基堆积敏感，使其成为研究 DNA 结构的非常有用的实时探针。这种荧光猝灭与碱基堆积有关的基本光物理性质尚未得到很好的理解，因此有必要探索类似物的激发态电子结构。在这项研究中，我们报告了 8VA 在光激发下电子结构的变化。在 77 K 的冷冻乙醇玻璃中对 8VA 单体进行 Stark 光谱研究，以获得 S(0)-->S(1)跃迁形式的电荷重分布方向和程度，其差分偶极矩为 Deltamu(01) = 4.7 +/- 0.3 D，差分静态极化率为 tr(Delta(alpha)01) = 21 +/- 11 A(3)。此外，在各种溶剂中对 8VA 进行了溶剂化变色实验，并使用 Bakhshiev 模型进行了分析。采用高级从头算方法计算了 8VA 的基态和激发态的跃迁能、振子强度和偶极矩。在分子框架中分配了最低可光激发态的 Deltamu(01)的方向。我们的研究表明，基态和激发态偶极矩之间的角度在理解光激发后电子结构的变化中起着关键作用。与 2AP 相比，8VA 的差分偶极矩更大，其消光系数是 2AP 的两倍，这表明 8VA 作为显微镜研究的双光子探针具有优越性。为此，我们通过各自单体吸收最大值的激发测量了两个类似物的双光子荧光产率的比值。基于我们的实验和计算结果，我们表明 8VA 确实是一种明显更亮的双光子荧光团。
