The supramolecular chemistry of gold and l -cysteine: Formation of photoluminescent, orange-emitting assemblies with multilayer structure

Abstract

The protein mediated approach is a common method for the synthesis of photoluminescent gold quantum clusters (GQCs), where proteins, acting as reducing and stabilizing agents, react with gold salts through cysteine residues. For the better understanding of the phenomenon, the aqueous phase reaction of HAuCl4 and L-cysteine has been investigated at the supramolecular level by various experimental techniques and molecular mechanics simulations. We have observed the formation of a novel photoluminescent product, (AuCys)n β , which shows emission in the orange region of the spectrum. Small-and wide-angle X-ray scattering (SWAXS) measurements have revealed the presence of nanosized lamellae, which have an internal multilayer superlattice structure with a characteristic periodic distance of 1.3 nm. Based on the results, the layers are built up by zigzag shaped (AuCys)n polymer chains connected through aurophilic bonds. The aurophilic network is stabilized via salt bridges and hydrogen bonds, which are also responsible for the interlayer interactions. Here, the evolution of the multilayer structure has been monitored by the combined application of photoluminescence spectroscopy and time-resolved SAXS. It has been concluded that there is a strong correlation between the emission and the scattering intensity, which suggests that the two-and three-dimensional aggregation of the building blocks to form sheets and multilayers are simultaneous processes. Furthermore, we have revealed that the formation and behavior of (AuCys)n β show significant differences to that of Au-L-glutathione compounds desrcibed earlier despite the similarity of L-cysteine and L-glutathione. These results evidence that L-cysteine and gold species form building blocks that can be applied expansively in supramolecular and cluster chemistry.

Emergence of complexity in hierarchically organized chiral particles

“…An MD model of an Au-Cys zigzag gold chain was constructed, based on the structure reported by Söptei (19). The ratio of gold/sulfur/Cys was 1:1:1, which is consistent with the XPS spectra and all other structural data (figs.…”

“…X-ray photoelectron spectroscopy (XPS) spectra of Au-Cys CLIPs and related Au compounds in Au 4f region. A, Au-L-Cys CLIPs indicates that the oxidation state of gold in the CLIPs is between 0 and +1(19), which is fully consistent with the structure of gold cysteinate inFigure S2A. B, Freshly sputtered gold film.…”

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

“…[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. 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.…”

“…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.…”

Arany nanorészecskék és nanoklaszterek szintézise, szerkezetvizsgálata és szenzorikai alkalmazásaik

“…Korábban Söptei és mtsai. már vizsgálták a Cys és HAuCl4 kölcsönhatását [119]. Kisszögű röntgenszórásos (SWAXS: small and wide angle X- pH-értékét a magasabb pH tartomány (pH = 9-12) felé tolva azonban fluoreszcencia már nem detektálható.…”