Understanding the Nascent Plasmons and Metallic Bonding in Atomically Precise Gold Nanoclusters

Thermostable protein-stabilized gold nanoclusters as a peroxidase mimic

Protein-stabilized gold nanoclusters (AuNCs) are fascinating nanostructures with exciting properties owing to their ultra-small sizes and functional shell. However, their applications under extreme conditions are still complicated, waiting for programmable solutions. Therefore, the design of a multi-functional protein stabilizer for specific purposes gains attention to improve the stability and functionality of AuNCs. Herein, we exploited the thermostability of genetically engineered KlenTaq DNA polymerase containing five cysteine residues (KTQ5C) to synthesize heat-stable AuNCs (AuNC@KTQ5C) and characterize optical, structural, and hydrodynamic properties. Besides their excellent photophysical properties, AuNC@KTQ5C also exhibit superior peroxidase-like (POD-like) catalytic activity following typical Michaelis-Menten kinetics together with a high affinity towards the POD substrate 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)-diammonium salt (ABTS). Moreover, FTIR and relative catalytic activity analysis of AuNC@KTQ5C reveal that KTQ5C is resistant to changes in protein secondary structure while the AuNCs conserve 70-80% of their catalytic performance after heat treatments up to more than 80 °C. Our findings show that stabilizing AuNCs with thermostable KTQ5C not only preserves the advantages of protein-stabilized AuNCs but can also promote the resistance of AuNCs against aggregation due to protein denaturation under extreme reaction temperatures, protecting their fluorescent emission or catalytic activity.

Developing a Ruthenium(III) Complex to Trigger Gasdermin E-Mediated Pyroptosis and an Immune Response Based on Decitabine and Liposomes: Targeting Inhibition of Gastric Tumor Growth and Metastasis

To develop next-generation metal drugs with high efficiency and low toxicity for targeting inhibition of gastric tumor growth and metastasis, we not only optimized a series of ruthenium (Ru, III) 2-hydroxy-1-naphthaldehyde thiosemicarbazone complexes to obtain a Ru(III) complex (4b) with remarkable cytotoxicity in vitro but also constructed a 4b-decitabine (DCT)/liposome (Lip) delivery system (4b-DCT-Lip). The in vivo results showed that 4b-DCT-Lip not only had a stronger capacity to inhibit gastric tumor growth and metastasis than 4b-DCT but also addressed the co-delivery problems of 4b-DCT and improved their targeting ability. Furthermore, we confirmed the mechanism of 4b-DCT/4b-DCT-Lip inhibiting the growth and metastasis of a gastric tumor. DCT-upregulated gasdermin E (GSDME) was cleaved by 4b-activated caspase-3 to afford GSDME-N terminal and then was aggregated to form nonselective pores on the cell membrane of a gastric tumor, thereby inducing pyroptosis and a pyroptosis-induced immune response.

Metal nanoclusters: from fundamental aspects to electronic properties and optical applications

Monolayer-protected noble metal clusters, also called nanoclusters, can be produced with the atomic precision and in large-scale quantity and are playing an increasingly important role in the field of nanoscience. To outline the origin and the perspectives of this new field, we overview the main results obtained on free metal clusters produced in gas phase including mainly electronic properties, the giant atom concept, the optical properties, briefly the role of the metal atom (alkali, divalent, noble metal) and finally the atomic structure of clusters. We also discuss the limitations of the free clusters. Then, we describe the field of monolayer-protected metal clusters, the main results, the new offered perspectives, the added complexity, and the role of the ligand beyond the superatom concept.

Intrinsic Optical Properties and Emerging Applications of Gold Nanostructures

The collective oscillation of free electrons at the nanoscale surface of gold nanostructures is closely modulated by tuning the size, shape/morphology, phase, composition, hybridization, assembly, and nanopatterning, along with the surroundings of the plasmonic surface located at a dielectric interface with air, liquid, and solid. This review first introduces the physical origin of the intrinsic optical properties of gold nanostructures and further summarizes stimuli-responsive changes in optical properties, metal-field-enhanced optical signals, luminescence spectral shaping, chiroptical response, and photogenerated hot carriers. The current success in the landscape of nanoscience and nanotechnology mainly originates from the abundant optical properties of gold nanostructures in the thermodynamically stable face-centered cubic (fcc) phase. It has been further extended by crystal phase engineering to prepare thermodynamically unfavorable phases (e.g., kinetically stable) and heterophases to modulate their intriguing phase-dependent optical properties. A broad range of promising applications, including but not limited to full-color displays, solar energy harvesting, photochemical reactions, optical sensing, and microscopic/biomedical imaging, have fostered parallel research on the multitude of physical effects occurring in gold nanostructures.

Tailoring the Electron-Phonon Interaction in Au25(SR)18 Nanoclusters via Ligand Engineering and Insight into Luminescence

Understanding the electron-phonon interaction in Au nanoclusters (NCs) is essential for enhancing and tuning their photoluminescence (PL) properties. Among all the methods, ligand engineering is the most straightforward and facile one to design Au NCs with the desired PL properties. However, a systematic understanding of the ligand effects toward electron-phonon interactions in Au NCs is still missing. Herein, we synthesized four Au₂₅(SR)₁₈^- NCs protected by different -SR ligands and carefully examined their temperature-dependent band-gap renormalization behavior. Data analysis by a Bose-Einstein two-oscillator model revealed a suppression of high-frequency optical phonons in aromatic-ligand-protected Au₂₅ NCs. Meanwhile, a low-frequency breathing mode and a quadrupolar mode are attributed as the main contributors to the phonon-assisted nonradiative relaxation pathway in aromatic-ligand-protected Au₂₅ NCs, which is in contrast with non-aromatic-ligand-protected Au₂₅ NCs, in which tangential and radial modes play the key roles. The PL measurements of the four Au₂₅ NCs showed that the suppression of optical phonons led to higher quantum yields in aromatic-ligand-protected Au₂₅ NCs. Cryogenic PL measurements provide insights into the nonradiative energy relaxation, which should be further investigated for a full understanding of the PL mechanism in Au₂₅ NCs.

Coherent vibrational dynamics of Au144(SR)60 nanoclusters

The coherent vibrational dynamics of gold nanoclusters (NCs) provides important information on the coupling between vibrations and electrons as well as their mechanical properties, which is critical for understanding the evolution from a metallic state to a molecular state with diminishing size. Coherent vibrations have been widely explored in small-sized atomically precise gold NCs, while it remains a challenge to observe them in large-sized gold NCs. In this work, we report the coherent vibrational dynamics of atomically precise Au144(SR)60 NCs via temperature-dependent femtosecond transient absorption (TA) spectroscopy. The population dynamics of Au144(SR)60 consists of three relaxation processes: internal conversion, core-shell charge transfer and relaxation to the ground state. After removing the population dynamics from the TA kinetics, fast Fourier transform analysis on the residual oscillation reveals distinct vibrational modes at 1.5 THz (50 cm-1) and 2 THz (67 cm-1), which arise from the wavepacket motions along the ground-state and excited-state potential energy surfaces (PES), respectively. These results are helpful for understanding the physical properties of gold nanostructures with a threshold size that lies in between those of molecular-like NCs and metallic-state nanoparticles.