Iida Ryo, Kawamura Hitoshi, Niikura Kenichi, Kimura Takashi, Sekiguchi Shota, Joti Yasumasa, Bessho Yoshitaka, Mitomo Hideyuki, Nishino Yoshinori, Ijiro Kuniharu
‡Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo 060-8628, Japan.
§Graduate School of Information Science and Technology, Hokkaido University, Sapporo 060-0814, Japan.
Langmuir. 2015 Apr 14;31(14):4054-62. doi: 10.1021/la504647z. Epub 2015 Apr 1.
This study aims at the synthesis of Janus gold nanoparticles (Janus GNPs) with hydrophilic/hydrophobic faces by a simple ligand exchange reaction in an homogeneous system and at the elucidation of the self-assembled structures of the Janus GNPs in water. As hydrophilic surface ligands, we synthesized hexaethylene glycol (E6)-terminated thiolate ligands with C3, C7, or C11 alkyl chains, referred to as E6C3, E6C7, and E6C11, respectively. As a hydrophobic ligand, a butyl-headed thiolate ligand C4-E6C11, in which a C4 alkyl was introduced on the E6C11 terminus, was synthesized. The degree of segregation between the two ligands on the GNPs (5 nm in diameter) was examined by matrix-assisted laser desorption/ionization time-of fright mass spectrometry (MALDI-TOF MS) analysis. We found that the choice of immobilization methods, one-step or two-step addition of the two ligands to the GNP solution, crucially affects the degree of segregation. The two-step addition of a hydrophilic ligand (E6C3) followed by a hydrophobic ligand (C4-E6C11) produced a large degree of segregation on the GNPs, providing Janus-like GNPs. When dispersed in water, these Janus-like GNPs formed assemblies of ∼160 nm in diameter, whereas Domain GNPs, in which the two ligands formed partial domains on the surface, were precipitated even when the molar ratio of the hydrophilic ligand and the hydrophobic ligand on the surface of the NPs was almost 1:1. The assembled structure of the Janus-like GNPs in water was directly observed by pulsed coherent X-ray solution scattering using an X-ray free-electron laser, revealing irregular spherical structures with uneven surfaces.
本研究旨在通过均相体系中的简单配体交换反应合成具有亲水性/疏水性表面的Janus金纳米颗粒（Janus GNPs），并阐明Janus GNPs在水中的自组装结构。作为亲水性表面配体，我们合成了分别带有C3、C7或C11烷基链的六甘醇（E6）封端的硫醇盐配体，分别称为E6C3、E6C7和E6C11。作为疏水性配体，合成了一种丁基头硫醇盐配体C4-E6C11，其中在E6C11末端引入了一个C4烷基。通过基质辅助激光解吸/电离飞行时间质谱（MALDI-TOF MS）分析研究了两种配体在直径为5 nm的GNPs上的分离程度。我们发现，固定方法的选择，即将两种配体一步或两步添加到GNP溶液中，对分离程度有至关重要的影响。先添加亲水性配体（E6C3），然后添加疏水性配体（C4-E6C11）的两步添加法在GNPs上产生了很大程度的分离，得到了类Janus GNPs。当分散在水中时，这些类Janus GNPs形成了直径约为160 nm的聚集体，而在纳米颗粒表面两种配体形成部分区域的结构域GNPs即使在纳米颗粒表面亲水性配体和疏水性配体的摩尔比几乎为1:1时也会沉淀。使用X射线自由电子激光通过脉冲相干X射线溶液散射直接观察了水中类Janus GNPs的组装结构，揭示了表面不均匀的不规则球形结构。
