The ordered structure of UV chromophores in DNA resembles photosynthetic light-harvesting complexes in which quantum coherence effects play a major role in highly efficient directional energy transfer. The possible role of coherent excitons in energy transport in DNA remains debated. Meanwhile, energy transport properties are greatly important for understanding the mechanisms of photochemical reactions in cellular DNA and for DNA-based artificial nanostructures. Here, we studied energy transfer in DNA complexes formed with silver nanoclusters and with intercalating dye (acridine orange). Steady-state fluorescence measurements with two DNA templates (15-mer DNA duplex and calf thymus DNA) showed that excitation energy can be transferred to the clusters from 21 and 28 nucleobases, respectively. This differed from the DNA–acridine orange complex for which energy transfer took place from four neighboring bases only. Fluorescence up-conversion measurements showed that the energy transfer took place within 100 fs. The efficient energy transport in the Ag–DNA complexes suggests an excitonic mechanism for the transfer, such that the excitation is delocalized over at least four and seven stacked bases, respectively, in one strand of the duplexes stabilizing the clusters. This result demonstrates that the exciton delocalization length in some DNA structures may not be limited to just two bases.

中文翻译：

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DNA作为紫外线收集天线

DNA中UV发色团的有序结构类似于光合作用的光捕获复合物，其中量子相干效应在高效的定向能量转移中起主要作用。相干激子在DNA能量传输中的可能作用仍存在争议。同时，能量传输特性对于理解细胞DNA中的光化学反应机理以及基于DNA的人工纳米结构非常重要。在这里，我们研究了由银纳米团簇和嵌入染料（ac啶橙）形成的DNA复合物中的能量转移。用两个DNA模板（15-mer DNA双链体和小牛胸腺DNA）进行稳态荧光测量表明，激发能可以分别从21和28个核碱基转移到簇中。这不同于DNA-ac啶橙复合物，后者仅从四个相邻的碱基进行能量转移。荧光上转换测量表明，能量转移发生在100英尺 Ag-DNA复合物中的有效能量传输表明了转移的激子机制，因此激发在稳定簇的双链体的一条链中分别在至少四个和七个堆叠的碱基上离域。该结果表明，某些DNA结构中的激子离域长度可能不仅限于两个碱基。