title: Synthesis of Janus-like gold nanoparticles with hydrophilic/hydrophobic faces by surface ligand exchange and their self-assemblies in water.
abstract: 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.
authors: ‡Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo 060-8628, Japan.
authors: Ryo
authors: R
authors: Iida
authors: §Graduate School of Information Science and Technology, Hokkaido University, Sapporo 060-0814, Japan.
authors: Hitoshi
authors: H
authors: Kawamura
authors: †Research Institute for Electronic Science, Hokkaido University, Kita 21 Nishi 10, Kita-ku, Sapporo 001-0021, Japan.
authors: Kenichi
authors: K
authors: Niikura
authors: †Research Institute for Electronic Science, Hokkaido University, Kita 21 Nishi 10, Kita-ku, Sapporo 001-0021, Japan.
authors: Takashi
authors: T
authors: Kimura
authors: ‡Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo 060-8628, Japan.
authors: Shota
authors: S
authors: Sekiguchi
authors: ⊥Japan Synchrotron Radiation Research Institute/SPring-8, 1-1-1 Kouto, , Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan.
authors: Yasumasa
authors: Y
authors: Joti
authors: ∥RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.|¶Institute of Physics, Academia Sinica, 128 Sec. 2, Academia Rd., Nankang, Taipei 11529, Taiwan.
authors: Yoshitaka
authors: Y
authors: Bessho
authors: †Research Institute for Electronic Science, Hokkaido University, Kita 21 Nishi 10, Kita-ku, Sapporo 001-0021, Japan.
authors: Hideyuki
authors: H
authors: Mitomo
authors: †Research Institute for Electronic Science, Hokkaido University, Kita 21 Nishi 10, Kita-ku, Sapporo 001-0021, Japan.
authors: Yoshinori
authors: Y
authors: Nishino
authors: †Research Institute for Electronic Science, Hokkaido University, Kita 21 Nishi 10, Kita-ku, Sapporo 001-0021, Japan.
authors: Kuniharu
authors: K
authors: Ijiro
mesh_terms: D006046:Gold / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008024:Ligands; D053768:Metal Nanoparticles / Q000737:chemistry*; D036103:Nanotechnology; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D008024:Ligands; D014867:Water; D006046:Gold