G-四链体DNA中电子态行为的理论模拟研究

Recently, long-range charge transport in G-quadruplex DNA (G4-DNA) molecules has been become a novel hot topic in the field of nanoscience. The higher stability of G4-DNA molecules as well as the more inner channels for charge transport makes it to be one of most promising molecules used as the conductive molecular wires to construct electronic devices at nanoscale. However, for the electronic state behavior in this kind of macromolecules, previous theoretical models and methods had some defects. The finite lengths and helix structures of the G4-DNA macromolecules were seldom considered when the electronic structures were calculated because the large molecular size and the coupling between electronic states and molecular geometries in the dynamical evolution process of electrons were not dealt suitably in the most previous study. In the present project, at first a fragment combination scheme will be developed to calculate the electronic structures of several G4-DNA molecules with long length and large size. Then the effective lattice model will be constructed, on basis of which the simulation methods for dynamics of electronic states in G4-DNA molecules will be developed; at last, these developed theoretical methods will be used to study the influences of molecular length, twist angle in the molecular helix, types of metal cation encapsulated and solvent condition to the electronic state behavior in the G4-DNA molecules. The results will strengthen understanding to the mechanism of long-range charge transport in G4-DNA molecules, which could provide a theoretical guideline for further regulation and optimization of the conductivity of such DNA-based molecular wires by structural design and modification.

最近，G-四链体DNA（G4-DNA）分子中的长程电荷输运成为纳米科学界中新的研究热点，原因在于它具有较高的稳定性和较多的电荷输运通道，有希望作为导电分子线以用于构筑纳米器件。但对这类大分子体系中的电子态行为，现有的理论计算研究尚存在一些欠缺，例如对其链长的有限性、结构的螺旋性以及电子态在演化过程中与分子结构的耦合等考虑不足。本项目拟发展分子片段拼接方法，以计算G4-DNA长链分子体系中的电子态；进而构建有效格点模型，发展适用于G4-DNA的电子态动力学模拟方法；最后应用这些方法研究链长、螺旋角度、内嵌金属离子以及外部环境等因素对G4-DNA分子中电子态行为的影响。研究结果将加深人们对G4-DNA分子中的长程电荷输运机制的理解，为进一步通过结构设计来调控和优化DNA基分子线的导电能力提供理论指导。

G-四链体DNA是潜在的导电分子线，深入理解其中的电子态行为对其进一步应用至关重要。本项目整合出了一套适用于处理G-四链体DNA分子链中电子态行为的理论计算方案，然后通过计算模拟研究了不同结构的G-四链体DNA分子链的电子态行为。在方法上，我们提出了“定向原子轨道”的概念，充分利用螺旋周期对称性，解决了中央插件延长方法中一维有限螺旋链体系的哈密顿扩展问题。我们还发展了G-四链体DNA分子的紧束缚模型方法，通过第一性原理计算模型中参数，进而在紧束缚模型框架下研究该类体系中的电子态行为。我们重点研究了螺旋角度、内嵌金属离子种类以及碱基间距等因素对G-四链体DNA中电子态行为的影响。我们发现，相邻G-四分体之间的螺旋角度对分子线整体的电子结构有较大的影响。当不在螺旋扭转时，相邻G碱基之间的迁移积分最大，而当螺旋角为15°时，将使迁移积分下降两个数量级。当不存在螺旋旋转时，G-四链体DNA中将存在电荷极化子，有助于电荷输运；而当存在螺旋角为15°时，空穴电荷在整个链上均匀分布，不利于电荷输运。因此通过对G-四链体DNA的外围磷酸-糖环骨架进行修饰以调整相邻G-四分体之间的螺旋扭转角度，是调控G-四链体DNA分子线的电子结构和导电性能的有效方法。这些研究结果加深了人们对G-四链体DNA中的电子态行为的理解，为进一步发展DNA基分子电子器件提供了理论指导。