Zhang Baohua, Yuan Tianhu, Jiang Hua, Lei Ming
Institute of Material Medical/Department of Chemistry, School of Science, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China.
J Phys Chem B. 2009 Aug 6;113(31):10934-41. doi: 10.1021/jp9033358.
The polymer of 7-amino-8-fluoro-2-quinoline carboxylic acid (abbreviated as QF(n), n denotes polymerization degree, where n = 4 or 8) can form artificial helices that do not exist in nature. The crystal structures of the quadruplex of QF(4) and the duplex of QF(8) (abbreviated as QP_4 and DP_8, respectively) have been unveiled by some researchers recently. In this paper, QP_4 and DP_8 were built based on their crystal structures. Though the quadruplex of QF(8) and the duplex of QF(4) (abbreviated as QP_8 and DP_4, respectively) were not observed in experiments, they were built using molecular modeling tools. The molecular dynamics (MD) method was used to study the stabilities and assembly mechanisms of these helices at different temperatures. In MD simulations, the disassembled QP_4 was observed above 480 K. The results indicate that these oligoamide helices showed slippage of strands to some extent and that double-helical oligoamides act as a basic block in the slippage during the formation of the quadruple-helical structure. DP_4 and QP_4 showed dynamical features with helix-handedness inversion and following slippage of strands at higher temperatures. In addition, the pi-pi conjugations between the different chains are supposed to be responsible for the stability of the helices.
7-氨基-8-氟-2-喹啉羧酸聚合物（简称为QF(n)，n表示聚合度，其中n = 4或8）能够形成自然界中不存在的人工螺旋结构。近期，一些研究人员已揭示了QF(4)的四链体和QF(8)的双链体（分别简称为QP_4和DP_8）的晶体结构。在本文中，QP_4和DP_8是基于它们的晶体结构构建的。尽管在实验中未观察到QF(8)的四链体和QF(4)的双链体（分别简称为QP_8和DP_4），但利用分子建模工具构建了它们。采用分子动力学（MD）方法研究了这些螺旋结构在不同温度下的稳定性和组装机制。在MD模拟中，观察到在480 K以上QP_4发生解聚。结果表明，这些寡酰胺螺旋在一定程度上表现出链的滑动，并且在四重螺旋结构形成过程中，双螺旋寡酰胺在滑动过程中起到基本单元的作用。DP_4和QP_4在较高温度下表现出螺旋手性反转及随后的链滑动等动力学特征。此外，不同链之间的π-π共轭作用被认为是螺旋结构稳定性的原因。
