Department of Chemistry and Centre for Scientific Computing, University of Warwick , Gibbett Hill Road, Coventry, CV4 7AL, United Kingdom.
ACS Appl Mater Interfaces. 2014 Jul 9;6(13):10524-33. doi: 10.1021/am502119g. Epub 2014 Jun 25.
Adsorption of small biomolecules onto the surface of nanoparticles offers a novel route to generation of nanoparticle assemblies with predictable architectures. Previously, ligand-exchange experiments on citrate-capped gold nanoparticles with the amino acid arginine were reported to support linear nanoparticle assemblies. Here, we use a combination of atomistic modeling with experimental characterization to explore aspects of the assembly hypothesis for these systems. Using molecular simulation, we probe the structural and energetic characteristics of arginine overlayers on the Au(111) surface under aqueous conditions at both low- and high-coverage regimes. In the low-density regime, the arginines lie flat on the surface. At constant composition, these overlayers are found to be lower in energy than the densely packed films, although the latter case appears kinetically stable when arginine is adsorbed via the zwitterion group, exposing the charged guanidinium group to the solvent. Our findings suggest that zwitterion-zwitterion hydrogen bonding at the gold surface and minimization of the electrostatic repulsion between adjacent guanidinium groups play key roles in determining arginine overlayer stability at the aqueous gold interface. Ligand-exchange experiments of citrate-capped gold nanoparticles with arginine derivatives agmatine and N-methyl-l-arginine reveal that modification at the guanidinium group significantly diminishes the propensity for linear assembly of the nanoparticles.
小分子生物分子在纳米粒子表面的吸附为生成具有可预测结构的纳米粒子组装体提供了一条新途径。此前，有报道称，在柠檬酸封端的金纳米粒子与氨基酸精氨酸的配体交换实验中，支持线性纳米粒子组装体的形成。在这里，我们使用原子建模与实验表征相结合的方法来探索这些系统的组装假设的各个方面。通过分子模拟，我们在低覆盖度和高覆盖度条件下，在水相条件下探测了精氨酸在 Au(111)表面上的覆盖层的结构和能量特性。在低密度区域，精氨酸分子平躺于表面。在组成不变的情况下，与密集堆积的膜相比，这些覆盖层的能量更低，尽管在后一种情况下，当通过两性离子基团吸附精氨酸时，即暴露带电荷的胍基基团于溶剂中时，动力学上是稳定的。我们的研究结果表明，在金表面上两性离子-两性离子氢键和相邻胍基之间的静电排斥的最小化在决定水溶液中金界面上精氨酸覆盖层的稳定性方面起着关键作用。带有胍基的精氨酸衍生物胍丁胺和 N-甲基-L-精氨酸与柠檬酸封端的金纳米粒子的配体交换实验表明，胍基的修饰显著降低了纳米粒子线性组装的趋势。
