Molecular-Mechanical Switching at the Nanoparticle-Solvent Interface: Practice and Theory
Molecular-Mechanical Switching at the Nanoparticle-Solvent Interface: Practice and Theory
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DOI：
10.1021/ja9102327
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发表时间：
2010-03-31
影响因子：
15
通讯作者：
Stoddart, J. Fraser
中科院分区：
文献类型：
--
作者：
Coskun, Ali;Wesson, Paul J.;Stoddart, J. Fraser
一系列已经制备了金属纳米颗粒（MNP）的（Au，Pt，Pd），并用（a）含有四硫富瓦烯（TTF）单元的氧化还原活性茎，（B）[2]在这些茎和环双之间形成的假轮烷官能化，（百草枯对苯）（CBPQT（4+））环，和（c）其中哑铃组分含有1，5-二氧基萘（DNP）单元以及TTF单元的双[2]轮烷分子，被CBPQT（4+）环包围。发现存在于（a）和（c）中的分子和（B）中描述的超分子当它们被固定到MNP上时保留了它们先前在溶液中观察到的开关特性。此外，它们的氧化电位取决于纳米颗粒表面上的分子或超分子的分数chi。chi的变化影响TTF单元的氧化电位，其程度使得开关可以因此进行微调。具体地，增加chi导致（i）（a）（c）中TTF单元的氧化电位和（ii）（c）中CBPQT（4+）环的还原电位的正移。这些变化可以归因于周围的MNP的静电势的增加。这些位移的大小和方向都是由一个模型再现的，该模型基于泊松-玻尔兹曼方程，再加上电荷调节边界条件。此外，从亚稳态共构象（MSCC）的松弛动力学的基态共构象（GSCC）的α [2]轮烷分子也取决于chi，以及对纳米粒子的直径。增加这些参数中的任何一个都会加速从MSCC到GSCC的弛豫速率。该速率是（i）与溶液中的双[2]轮烷分子相关的弛豫过程的活化能和（ii）围绕MNP的静电势的函数。静电势取决于（i）MNP的直径，（ii）MNP表面上的[2]轮烷分子的量，和（iii）GSCC中DNP和TTF识别位点之间的CBPQT（4+）环的平衡分布。这种静电势也被量化使用泊松-玻尔兹曼方程，导致忠实的估计速率常数。
A range (Au, Pt, Pd) of metal nanoparticles (MNPs) has been prepared and functionalized with (a) redox-active stalks containing tetrathiafulvalene (TTF) units, (b) [2]pseudorotaxanes formed between these stalks and cyclobis(paraquat-p-phenylene) (CBPQT(4+)) rings, and (c) bistable [2]rotaxane molecules where the dumbbell component contains a 1,5-dioxynaphthalene (DNP) unit, as well as a TTF unit, encircled by a CBPQT(4+) ring. It transpires that the molecules present in (a) and (c) and the supermolecules described in (b) retain their switching characteristics, previously observed in solution, when they are immobilized onto MNPs. Moreover, their oxidation potentials depend on the fraction, chi, of the molecules or supermolecules on the surface of the nanoparticles. A variation in chi affects the oxidation potentials of the TTF units to the extent that switching can be subjected to fine tuning as a result. Specifically, increasing chi results in positive shifts (i) in the oxidation potentials of the TTF unit in (a) (c) and (ii) the reduction potentials of the CBPQT(4+) rings in (c). These shifts can be attributed to an increase in the electrostatic potential surrounding the MNPs. Both the magnitude and the direction of these shifts are reproduced by a model, based on the Poisson-Boltzmann equation coupled with charge-regulating boundary conditions. Furthermore, the kinetics of relaxation from the metastable state coconformation (MSCC) to the ground-state coconformation (GSCC) of the bistable [2]rotaxane molecules also depends on chi, as well as on the nanoparticle diameter. Increasing either of these parameters accelerates the rate of relaxation from the MSCC to the GSCC. This rate is a function of (i) the activation energy for the relaxation process associated with the bistable [2]rotaxane molecules in solution and (ii) the electrostatic potential surrounding the MNPs. The electrostatic potential depends on (i) the diameter of the MNPs, (ii) the amount of the bistable [2]rotaxane molecules on the surface of the MNPs, and (iii) the equilibrium distribution of the CBPQT(4+) rings between the DNP and TTF recognition sites in the GSCC. This electrostatic potential has also been quantified using the Poisson-Boltzmann equation, leading to faithful estimates of the rate constants.