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利用密度泛函理论方法研究了作为空穴迁移载体的蛋白质复合的DNA三聚体(Protonated arginine…guanine…cytosine,Arg H+-GC)的氢键性质.结果表明,空穴迁移通过该载体单元时此类氢键表现为亚稳态,且具有明显的负离解能.正常情况下Arg H+基团在大小沟均能与GC碱对形成氢键,且具有正的离解能.然而,当空穴转移至此将削弱氢键至亚稳态,使之具有一定的离解势垒和负的离解能.这种势垒抑制的负离解能现象意味着由于空穴俘获导致此三聚体结构单元在它的Arg H+…N7/O6键区储存了一定的能量(约108.78 k J/mol).该氢键离解通道受控于此键区两个相关组分之间的静电排斥和氢键吸引之间的平衡以及这两个相反作用随氢键距离不同的衰减速率.基于电子密度分布的拓扑性质以及键临界点的Laplacian数值分析澄清了此类特殊的能量现象主要源自通过高能氢键(Arg H+…N7/O6)连接的授受体间的静电排斥.进一步空穴俘获诱导的G→C质子转移可扩展负离解能区至Arg H+…N7/O6和Watson-Crick(WC)氢键区.另外,Arg H+结合到GC的大小沟增加其电离势,因此削弱其空穴传导能力,削弱程度取决于Arg H+与GC的距离.推而广之,在protonated lysine-GC和protonated histidine-GC体系也可观察到类似的现象.显然,此类性质可调的亚稳态氢键可调控DNA空穴迁移机理.此工作为理解蛋白质调控的DNA空穴迁移机理提供了重要的能量学信息.
The hydrogen bonding properties of the protein-complexed DNA trimer (guanine ... cytosine, Arg H + -GC) as a hole transport carrier were investigated by using density functional theory. The results show that when holes migrate through the carrier unit These hydrogen bonds appear to be metastable and have significant negative dissociation energies. Normally Arg H + groups can both form hydrogen bonds with GC base pairs and have positive dissociation energy in both size and size grooves. However, This will weaken the hydrogen bond to the metastable state, so that it has a certain dissociation barrier and negative dissociation energy. This barrier inhibition of the negative dissociation energy phenomenon means that due to hole trapping led to the trimer structural unit in its Arg H + ... N7 / O6 bonds store some energy (about 108.78 kJ / mol) .The hydrogen bond dissociation channels are controlled by the electrostatic repulsion and hydrogen bonding between the two related components Equilibrium and the decay rates of these two opposite effects with different hydrogen bond distances.The Laplacian numerical analysis based on the topological properties of the electron density distribution and the critical point of the bond clarifies that this special phenomenon of energy mainly comes from the binding of Arg H + N7 / O6) connected receptor . Further hole-trapping induced G → C proton transfer can extend the negative dissociation energy region to the Arg H + ... N7 / O6 and Watson-Crick (WC) hydrogen bonding regions. In addition, the size of the Arg H + binding to the GC increases Its ionization potential thus weakens its hole-conduction capacity, the degree of reduction depending on the distance between Arg H + and GC. By analogy, a similar phenomenon has also been observed in protonated lysine-GC and protonated histidine-GC systems Metastable metastable hydrogen bonds regulate the mechanism of DNA hole transport, providing important energetic information for understanding the protein-controlled mechanism of DNA hole transport.