Institució Catalana de Recerca i Estudis Avançats, Barcelona 08010, Spain.
Phys Chem Chem Phys. 2010 Jul 21;12(27):7403-8. doi: 10.1039/c003131c. Epub 2010 Jun 9.
Using the INDO/S method, we study the effects of structural fluctuations on the interaction of singlet excited states in homogeneous poly(dA)-poly(dT) and alternating poly(dAdT)(2) stacks. The coupling for excitation energy transfer (EET) between intra- and inter-strand nucleobases is derived with the fragment excitation difference scheme (Hsu, et al. J. Phys. Chem. C 2008, 112, 1204). In this approach, both Coulomb and short-range contributions to the EET coupling are properly accounted for. 15 000 conformations for each nucleobase dimer were considered. Conformational fluctuations of DNA are shown to result in a large variation of the transfer integral. The root mean square coupling values are used to characterize the interaction of pi-pi* states in DNA. The intra-strand and inter-strand couplings between adenines are found to be significantly smaller than those for thymines. Our findings suggest that (1) EET couplings in DNA are significantly more sensitive to conformational changes of the pi stack than is estimated within the dipole-dipole scheme; (2) singlet excitation energy transfer in poly(dA)-poly(dT) should dominantly occur through thymine bases; (3) pi-pi* excited states in homogeneous stacks are more delocalized than in alternating sequences; (4) structural fluctuations can strongly affect the exciton distribution.
使用 INDO/S 方法，我们研究了结构波动对同聚体 poly(dA)-poly(dT) 和交替聚体 poly(dAdT)(2) 堆积中 singlet 激发态相互作用的影响。通过片段激发差分方案（Hsu 等人，J. Phys. Chem. C 2008, 112, 1204）得出了碱基对内和碱基对间激发能量转移（EET）的耦合。在这种方法中，EET 耦合的库仑和短程贡献都得到了适当的考虑。每个碱基对二聚体考虑了 15000 种构象。DNA 的构象波动导致转移积分的很大变化。均方根耦合值用于表征 DNA 中 pi-pi态的相互作用。发现腺嘌呤的碱基对内和碱基对间耦合明显小于胸腺嘧啶的耦合。我们的发现表明：(1) DNA 中的 EET 耦合对 pi 堆积的构象变化比偶极子偶极子方案估计的更为敏感；(2) poly(dA)-poly(dT)中的单重激发能量转移应主要通过胸腺嘧啶碱基发生；(3) 同聚体堆积中的 pi-pi激发态比交替序列更弥散；(4) 结构波动会强烈影响激子分布。
