分子动力学模拟3(5)-(9-蒽基)吡唑分子在自组装膜上的选择性沉积

doi:10.7503/cjcu20150781

摘要/Abstract

摘要：

采用平衡分子动力学和拉伸分子动力学模拟方法研究了模板诱导有机发光小分子3(5)-(9-蒽基)吡唑(ANP) 在自组装膜上的选择性沉积, 并利用伞形取样方法和加权柱状图分析法计算了沉积过程的均力势. 模拟中以二氧化硅为底板分别构筑2种不同密度的烷烃链自组装膜模板, 即低密度的液体扩展相和高密度的液体压缩相. 平衡分子动力学结果显示, ANP分子容易沉积至低密度的液体扩展相中, 难以沉积至高密度的液体压缩相中. 拉伸分子动力学结果表明, 当ANP分子沉积至液体压缩相表面时, 在进入烷烃膜时遇到较大阻力, 因而不易进入到烷烃链单层膜中; 而ANP分子在进入液体扩展相的过程中受到的阻力较小. 通过比较这2种不同密度自组装膜与ANP分子之间的结合自由能, 发现ANP分子进入液体压缩相的能垒较高, 而ANP分子与液体扩展相结合更加稳定, 导致有机发光小分子在不同密度的模板上具有选择吸附性. 所得模拟结果与实验现象一致, 在分子水平上为实验提供了更加丰富的微观信息.

关键词: 自组装膜(SAM), 定位沉积, 拉伸分子动力学, 伞形取样, 3(5)-(9-蒽基)吡唑, 低密度的液体扩展相, 高密度的液体压缩相, 均力势

Abstract:

The site-selective deposition behavior of 3(5)-(9-anthryl) pyrazole(ANP) onto self-assembled monolayers(SAMs) patterned substrate was studied via the equilibrium and steered molecular dynamics methods. Two kinds of different densely packed SAMs were constructed on silicon oxide substrates as the patterned templates, which represent liquid expanded(LE) and liquid condensed(LC) phases. Equilibrium molecular dynamics(MD) simulations showed that the packing density of alkyl chains on the substrate could influence the deposition behavior of the ANP molecules. On the LE covered SAM, the small molecule would submerge deeply into the alkyl chains film, while ANP molecule would deposit on the surface of LC film. Steered molecular dynamics showed that ANP molecule was hindered from the densely packed LC film. However, there was less hindrance for ANP to submerge into the LE film. Using umbrella sampling and the weighted histogram analysis method, the potential of mean force(PMF) of the deposition process of ANP onto the two patterned templates was calculated. From the PMF curves, the favorite deposition location of ANP onto the two SAMs was determined, which agreed well with that obtained from equilibrium MD simulations. The binding energies between ANP and the two SAMs can be estimated based on PMF, which could be used to explain the site-selective deposition of ANP on different densely packed SAMs.

Key words: Self-assembled monolayers(SAM), Site-selective deposition, Steered molecular dynamics, Umbrella sampling, 3(5)-(9-Anthryl)pyrazole, Low intensity liquid expanded phase, High intensity liquid condensed phase, Potential of mean force

中图分类号:

O641

TrendMD:

张鲁格, 薛泽旭, 张翀, 延辉. 分子动力学模拟3(5)-(9-蒽基)吡唑分子在自组装膜上的选择性沉积. 高等学校化学学报, 2016, 37(3): 505.

ZHANG Luge, XUE Zexu, ZHANG Chong, YAN Hui. Molecular Dynamics Studies on the Selective Deposition of 3(5)-(9-Anthryl) Pyrazole onto Self-assembled Monolayers^†. Chem. J. Chinese Universities, 2016, 37(3): 505.

图/表 9

Fig.1 Chemical structure of 3(5)-(9-anthryl) pyrazole(ANP)

Fig.2 Configurations of ANP deposited on LC(A, A') and LE(B, B') phases at the initial(A, B) and the end(5 ns, A', B') of the MD simulation

Fig.3 Time profiles of the vertical distance between the COM(center of mass) of the ANP molecule and the surface of the SiO2 substratea. LC phase; b. LE phase.

Fig.4 Number density profiles of components for LC and LE systemsa. SiO2; b. LC; c. LE; d. LC-ANP; e. LE-ANP. Values for ANP atoms were multiplied by 10 for clarity.

Fig.5 Results from simulations started with different initial configurations for the LE system(A) Time profiles of distance; (B) number density profiles (values for ANP atoms were multiplied by 10 for clarity).

Fig.6 Distance profiles of force using different pulling ratesVertical shifts of 200, 400 and 700 units were imposed for profiles at rates of 0.005, 0.0025 and 0.001 nm/ps, respectively. V/(nm·ps-1): a. 0.001; b. 0.0025; c. 0.005; d. 0.01.

Fig.7 Configurations at different time during the SMD simulation for the LC systemTime/ps: (A) 0; (B) 300; (C) 460; (D) 600.

Fig.8 Time profiles of the external force applied on ANP(A) and time profiles of the vertical

Fig.9 Potential of mean force along the reaction coordinate for ANP molecules deposited onto each SAMa. LC phase; b. LE phase.

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