多金属介导DNA基分子导线电荷输运机理与功能研究

DNA is becoming a potential candidate material for constructing nanoelectronic devices. However, the natural DNA lacks sufficient electrical conductance for direct applications in molecular electronics. Therefore, it has aroused extensive interests in chemically functionalizing DNA to improve its conductivity currently. In this proposal, we will design a novel class of multi-metal-mediated base pairs in order to minimize the configuration distortion as compared to the case of single-metal modification. The combined effects of size expansion and metal doping will be especially investigated toward optimizing the modification scheme for the design of DNA-based molecular wires. The changes of the structural, electronic and spectral properties will be explored with a combination of density functional theory calculations and molecular dynamics simulation to reveal the intrinsic reasons at atomic and molecular levels for the enhancement of conductivity of the modified DNA compared with the natural one. The molecular junctions consisting of DNA and electrodes would be constructed and investigated. The improvement of the conductivity owe to the multi-metal-modification of DNA will be evaluated by some measurable parameters with electronic transport theory. The charge transport mechanisms of the native and the modified DNA are to be elucidated. The charge transport channels and carrier of the modified DNA will be clarified also. Based on our detailed studies, a comprehensive understanding on the enhancement of the DNA conductivity tuned by the metal ion kinds and the metal ligand base pairs will be obtained. The effective relationship between modified structures and the functions of molecular wires will be finally established. We believe that this work may not only provide important information for the design of promising biomolecular wires, but also shed light on the further understanding of charge transfer in DNA.

DNA近年来成为构建纳米器件的理想候选材料，但天然DNA的导电性还不足以直接应用于分子器件，进行功能化修饰以提高其导电性现已引起广泛的研究兴趣。鉴于常规的单金属离子修饰易引起构型的扭曲，本项目设计一种新颖的多金属离子碱基对修饰方案，并将考察扩环修饰和金属化修饰的联合效果，旨在寻找更佳的DNA基分子导线的修饰结构。利用密度泛函并结合分子动力学模拟，表征所做修饰对DNA结构、电子及光谱性质的影响，从原子分子水平上揭示DNA导电性增强的内在原因；将DNA与电极相组装，通过电子输运理论，用可测的导电性指标反映所做修饰对DNA电荷输运性质的改进效果；明确修饰前后的电荷传输机理，阐明传输通道和载体；找出金属离子的种类及金属配体碱基对调控DNA导电性的规律，建立有效的修饰结构与分子导线功能之间的构效关系。该工作的开展将为设计新型的生物分子导线提供必要信息，同时也有助于更好地理解DNA中的电荷转移。

鉴于天然DNA在导电性方面的限制，为实现其在分子电子学方面的应用，对其进行功能化修饰成为一种必然的选择。课题组围绕DNA的功能化修饰这一主题，以提高DNA的导电性为导向，从理论上详细研究了所做修饰对DNA电荷输运性质的促进作用。各项研究任务基本按照计划得以执行。已经完成的主要研究内容如下：（1）设计了几种DNA碱基对的修饰方案，有外扩环的修饰设计、银离子等位取代DNA中的氢键质子修饰、铜离子修饰错配碱基对、腺嘌呤A的N位修饰等。（2）用密度泛函方法进行了电子性质和光谱性质的探索：电子性质研究发现，修饰后体系的能隙都变窄，电离能都有所下降。紫外光谱的研究说明所做修饰促进了配对碱基之间的横向电子通讯。（3）采用非平衡态格林函数并结合密度泛函理论的方法，研究了体系修饰前后的电荷输运性质。通过计算修饰前后搭建的DNA分子片段的伏安特性曲线，直观地从横向和纵向电荷输运两个方面，说明所做修饰能较明显地提高DNA中电荷输运。并从各种偏压下的透射谱和分子投影自洽哈密顿量的本征值（MPSH）等微观角度阐述了所做修饰提高导电性的原因。（4）总结不同的修饰方案对于DNA导电性调控的差异，为设计DNA基分子导线提供理论支持。对于设计的多银离子等位取代天然碱基对中的氢键质子的修饰和错配碱基对的铜离子修饰来说，都大幅度地提高了所构成的DNA分子片段的导电性。但由于金属离子的半径要大于配对碱基中的氢键质子的半径，这种金属化修饰在一定程度上会增大碱基对的横向尺寸，因此对DNA骨架可能会有一定的扰动。相对而言，外扩环修饰和腺嘌呤A的N位取代，虽然对DNA导电性的提升不是特别大，但对DNA结构扰动较小，实验上也更容易制备，可以算是“物美价廉”的修饰。. 在项目执行期间，课题组共发表论文10篇，均被SCI收录。