Faculty of Physical Chemistry, University of Belgrade, Studentski trg 12-16, Belgrade 11000, Serbia.
Institute of Chemistry, Technology and Metallurgy, University of Belgrade, Njegoševa 12, Belgrade 11000, Serbia.
J Phys Chem A. 2020 Oct 8;124(40):8101-8111. doi: 10.1021/acs.jpca.0c05022. Epub 2020 Sep 25.
Guanine self-assemblies are promising supramolecular platforms for optoelectronic applications. The study (Hua , , , 14,682-14,689) reported that alkaline cations cannot modulate the electronic absorption spectrum of G-quadruplexes, although a cation effect is observable during electronic relaxation due to different mobility of Na and K cations. In this work, we theoretically examined whether divalent Mg and Ca cations and hydration might shift excited charge-transfer states of a cation-templated stacked G-quartet to the absorption red tail. Our results showed that earth alkaline cations blue-shifted nπ* states and stabilized charge-transfer ππ* states relative to those of complexes with alkaline cations, although the number of charge-separation states was not significantly modified. Earth alkaline cations were not able to considerably increase the amount of charge-transfer states below the L excitonic states. Hydration shifted charge-transfer states of the Na-coordinated G-octet to the absorption red tail, although this part of the spectrum was still dominated by monomer-like excitations. We found G-octet electron detachment states at low excitation energies in aqueous solution. These states were distributed over a broad range of excitation energies and could be responsible for oxidative damage observed upon UV irradiation of biological G-quadruplexes.
鸟嘌呤自组装体是用于光电应用的有前途的超分子平台。研究表明，尽管在电子弛豫过程中由于 Na 和 K 阳离子的不同迁移率可以观察到阳离子效应，但碱性阳离子不能调节 G-四链体的电子吸收光谱。在这项工作中，我们从理论上研究了二价 Mg 和 Ca 阳离子以及水合作用是否可以将受阳离子模板堆叠的 G-四联体的激发电荷转移态转移到吸收红尾。我们的结果表明，与具有碱性阳离子的配合物相比，地球碱性阳离子使 nπ态蓝移并稳定了电荷转移ππ态，尽管电荷分离态的数量没有明显改变。地球碱性阳离子不能显著增加低于 L 激子态的电荷转移态的数量。水合作用将 Na 配位的 G-八聚体的电荷转移态转移到吸收红尾，尽管该光谱部分仍主要由单体样激发组成。我们在水溶液中发现了 G-八聚体电子脱离态在低激发能量下。这些状态分布在很宽的激发能量范围内，可能是在 UV 辐照生物 G-四链体时观察到的氧化损伤的原因。
