Structure and properties of citrate overlayers adsorbed at the aqueous Au(111) interface.
Structure and properties of citrate overlayers adsorbed at the aqueous Au(111) interface.
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DOI：
10.1021/la503690t
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发表时间：
2014-12
期刊：
影响因子：
--
通讯作者：
L. Wright;Rodger Pm;T. Walsh
中科院分区：
文献类型：
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作者：
L. Wright;Rodger Pm;T. Walsh
金纳米粒子（AuNP）生物功能化的最常见手段之一涉及通过配体置换操纵前体柠檬酸盐封端的AuNP。然而，在中性pH下吸附在水Au界面的柠檬酸盐覆盖层的分子水平的结构特征在很大程度上仍然未知。访问这些接口的原子级细节将有助于了解如何在水溶液中操纵和利用金纳米粒子。在这里，这种柠檬酸盐覆盖层的结构吸附在水Au（111）界面在pH 7的预测和特征在于使用原子分子动力学模拟，柠檬酸盐表面密度的范围。我们发现，在考虑的表面密度范围内的覆盖层是无序的，并且它们的许多关键特性与表面密度是不变的。特别是，我们预测的覆盖层有3-D，而不是2-D，形态，与最接近的金表面的阴离子被定向与他们的羧酸基团指向远离表面。我们预测条纹和岛屿形态的覆盖层，根据柠檬酸盐的表面密度，在所有情况下，我们发现裸露的补丁的黄金表面存在。我们的模拟表明，柠檬酸盐-金吸附和柠檬酸盐-反式配对有助于这些柠檬酸盐覆盖层形态的稳定性。我们还计算了单个柠檬酸盐分子在水Au（111）界面的吸附自由能，并将其与单个精氨酸分子的相应值进行了比较。这些研究结果使我们能够预测的条件下，精氨酸的表面吸附的柠檬酸盐的配体置换可能发生。我们的研究结果代表了阐明与柠檬酸盐封端的金纳米颗粒的生物功能化相关的更精细，更详细的原子尺度模型的第一步。
One of the most common means of gold nanoparticle (AuNP) biofunctionalization involves the manipulation of precursor citrate-capped AuNPs via ligand displacement. However, the molecular-level structural characteristics of the citrate overlayer adsorbed at the aqueous Au interface at neutral pH remain largely unknown. Access to atomistic-scale details of these interfaces will contribute much needed insight into how AuNPs can be manipulated and exploited in aqueous solution. Here, the structures of such citrate overlayers adsorbed at the aqueous Au(111) interface at pH 7 are predicted and characterized using atomistic molecular dynamics simulations, for a range of citrate surface densities. We find that the overlayers are disordered in the surface density range considered, and that many of their key characteristics are invariant with surface density. In particular, we predict the overlayers to have 3-D, rather than 2-D, morphologies, with the anions closest to the gold surface being oriented with their carboxylate groups pointing away from the surface. We predict both striped and island morphologies for our overlayers, depending on the citrate surface density, and in all cases we find bare patches of the gold surface are present. Our simulations suggest that both citrate-gold adsorption and citrate-counterion pairing contribute to the stability of these citrate overlayer morphologies. We also calculate the free energy of adsorption at the aqueous Au(111) interface of a single citrate molecule, and compare this with the corresponding value for a single arginine molecule. These findings enable us to predict the conditions under which ligand displacement of surface-adsorbed citrate by arginine may take place. Our findings represent the first steps toward elucidating a more elaborate, detailed atomistic-scale model relating to the biofunctionalization of citrate-capped AuNPs.