The effect of ligand–ligand interactions on the formation of photoluminescent gold nanoclusters embedded in Au(i)–thiolate supramolecules

Abstract

In this study, we prepared photoluminescent l-cysteine (Cys)-capped gold nanoclusters (Cys-Au NCs) via NaBH-mediated reduction of aggregated coordination polymers (supramolecules) of -[Cys-Au(i)]-. The -[Cys-Au(i)]- supramolecules with interesting chiral properties were formed through simple reactions of chloroauric acid (HAuCl) with Cys at certain pH values (pH 3-7). The -[Cys-Au(i)]- polymers could self-assemble into -[Cys-Au(i)]- supramolecules with irregular morphologies and diameters larger than 500 nm through stacked hydrogen bonding and zwitterionic interactions between Cys ligands and through Au(i)Au(i) aurophilic interactions in solutions with pH values ≤7. The photoluminescent Au NCs (quantum yield = 11.6%) dominated by a Au core were embedded in -[Cys-Au(i)]- supramolecules after NaBH-mediated reduction. The optical and structural properties of Cys-Au NCs/-[Cys-Au(i)]- nanocomposites were investigated, revealing that the interaction between Cys ligands plays a critical role in the self-assembly of -[Cys-Au(i)]- supramolecules and in the formation of photoluminescent Cys-Au NCs embedded in the supramolecules. To further demonstrate that the photoluminescence properties and structures of the nanocomposites are mediated by the intermolecular forces of thiol ligands, other thiol ligands (l-penicillamine, l-homocysteine, 3-mercaptopropionic acid, and l-glutathione) and a ligand-crosslinking agent [bis(sulfosuccinimidyl) suberate; BS3] were used. We concluded that the electrostatic interactions, hydrogen bonding and steric effects dominate the polymer self-assembly into thiol-ligand-Au(i) supramolecules and thus the formation of Au NCs. Our study provides insights into the bottom-up synthesis of photoluminescent Au NCs from thiol-ligand-Au(i) complexes, polymers, and supramolecules. The hybrid Au NCs/-[Cys-Au(i)]- nanocomposites can potentially be employed as drug carriers and bioimaging agents.

Sub-100 nanometer silver doped gold–cysteine supramolecular assemblies with enhanced nonlinear optical properties

“…In particular, by using cysteine as the thiolate compound, the synergetic interplay of the electrostatic interaction between -cysteine side chains and the Au(I)…Au(I) aurophilic attraction in the Au(I)-Cys polymeric backbone may result in some helicity. [4][5][6] On the other hand, under controlled external parameters (temperature, pH …), Au(I)-cysteine polymers can further assemble into bulky precipitate with lamellar structures. 7 This capability to self-assemble into hierarchical structures leads also to unusual structure−optical property relationship.…”

“…7 This capability to self-assemble into hierarchical structures leads also to unusual structure−optical property relationship. 4,7 Usually, a strong absorption band in the near UV range for Au(I)-thiolates supramolecular assemblies is attributed to a ligand-to-metal charge transfer (LMCT) mixed with ligand-to-metal-metal charge transfer (LMMCT) excitation. 4 The high order in Au(I)-thiolates supramolecular structures is a key factor for the aurophilic effect, which in turn provides luminescent properties.…”

“…4,7 Usually, a strong absorption band in the near UV range for Au(I)-thiolates supramolecular assemblies is attributed to a ligand-to-metal charge transfer (LMCT) mixed with ligand-to-metal-metal charge transfer (LMMCT) excitation. 4 The high order in Au(I)-thiolates supramolecular structures is a key factor for the aurophilic effect, which in turn provides luminescent properties. 8,9 Furthermore, due to the inherent chirality of cysteine molecules, cysteine Au(I)-supramolecular assemblies display circular dichroism (CD) and constitute efficient targets for biosensing in particular for enantiomeric drug analysis.…”

pH-Responsive Au(i)-disulfide nanoparticles with tunable aggregation-induced emission for monitoring intragastric acidity

“…The pH-responsive characteristics of Au(I)-disulde NPs were also investigated. The Au(I)-disulde NPs exhibited similar pHresponsive surface charged states to the Au(I)-Cys complex, 36 owing to Cys concentrated in the out layer of NPs. The Au(I)-disulde NPs underwent a decrease in positive charge from 26 mV to 0 mV by increasing pH from 2.2 to 3.0, as well as an increase in negative surface charge from 0 mV to À42 mV over the pH range of 3.0 to 7.4 (Fig.…”

Supramolecules‐Guided Synthesis of Brightly Near‐Infrared Au22 Nanoclusters with Aggregation‐Induced Emission for Bioimaging

“…An enhanced absorption at 275 nm occurs because of the ligand‐to‐metal charge transfer (LMCT: S→Au) mixed with ligand‐to‐metal‐metal charge transfer (LMMCT: S→Au···Au) absorption (Figure S1c, Supporting Information). The formation of supramolecules leads to a smaller Au(I) – S – Au(I) angle then a stronger aurophilic Au(I)···Au(I) interactions are conducted, enhancing LMMCT absorption . In addition, energy‐dispersive X‐ray spectroscopy (EDS) was carried out to identify the component of ‐[BSA‐Au(I)] n ‐supramolecules.…”