Gold Nanoparticles Stabilized by Thioether Dendrimers

Abstract

Ligand-stabilized gold nanoparticles (Au NPs) are promising materials for nanotechnology with applications in electronics, catalysis, and sensors. These applications depend on the ability to synthesize stable and monodisperse NPs. Herein, the design and synthesis of two series of dendritic thioether ligands and their ability to stabilize Au NPs is presented. The dendrimers have 1,3,5-trisubstituted benzene branching units bridged by either meta-xylene or ethylene moieties. A comparison between the two ligands shows how both size control and the stability of the NPs are influenced by the nature of the ligand-NP wrapping interaction. The meta-xylene-bridged ligands provided NPs with a narrow size distribution centered around a diameter of 1.2 nm, whereas the NPs formed with ethylene-bridged dendrimers lack long-term stability with NP aggregation detected by UV/Vis spectroscopy and transmission electron microscopy. The bulkier tert-butyl-functionalized meta-xylene bridges form larger ligand shells that inhibit further growth of the NPs and thus provide a simple route to stable and monodisperse Au NPs that may find use as functional components in nanoelectronic devices.

Synthesis and biological evaluation of largazole zinc-binding group analogs

“…The coupling of 36 with trityl-protected ethane dithiol 37 13 using K 2 CO 3 as a base resulted in the Trt-protected mercaptosulfide analog precursor 38 . The Trt-deprotection of 38 by treatment with TFA in the presence of triisopropylsilane completed the synthesis of the mercaptosulfide analog 8 .…”

Size Matters: Influence of Gold‐to‐Ligand Ratio and Sulfur‐Sulfur Distance of Linear Thioether Heptamers on the Size of Gold Nanoparticles

“…Interestingly, already the reaction with eight equiv. of the gold salt featured a slight reddish hue, pointing towards larger AuNPs compared to previously reported NPs, which themselves were – with eight equiv. of gold salt – dark brown in solution.…”

“…An adapted protocol of the two‐phase Brust–Schiffrin method was used to synthesize AuNPs stabilized by the here investigated heptamers ( Xyl , TPM , and Ter , see Scheme ). The main difference to our former studies on thioether stabilized AuNPs was that the molar ratio of ligand to gold salt was varied. So far we kept the growth conditions for the particles as uniform as possible enabling the comparison of stabilization features due to the ligands design and thus, a 1:1 molar ratio of thioether moieties to gold equiv.…”

“…Note that the reaction conditions were kept as similar as possible throughout all the AuNPs‐syntheses for better comparison along the different ligand structures. Even when comparing the dendritic ligands with a fairly prior determined cage‐like form, and the linear ligands with no further predetermined curvature, the resulted NPs featured almost the same size. Also the spacing between the thioether sulfur atoms in the oligomeric ligand seems to have only a minor influence on the dimension of the stabilized nanoparticle, as demonstrated by the very comparable dimensions of nanoparticles stabilized by linear heptamers based either on a m ‐xylene‐based motive and the more bulky tetraphenylmethane‐based ligand with an increased spacing between the sulfur atoms.…”

“…oligomers, and might even allow the macromolecule to self‐rearrange for optimal conformation for the NPs coating. Inspired by this concept, we explored various multidentate macromolecules like linear oligomers, and dendritic systems for the stabilization of small NPs. The low integer number of molecules per NPs decorated with a masked ethynyl moieties allowed mono‐ or bifunctionalized NPs to create supramolecular dumbbell, trikes and quads or linear pearl‐necklace hybrid materials via mild acetylene homo‐coupling or acetylene/azide‐click reactions.…”