Atomically Tailored Gold Nanoclusters for Catalytic Application

Gold Nanocluster: A Photoelectric Converter for X-Ray-Activated Chemotherapy

Despite the promise of activatable chemotherapy, the development of a spatiotemporally controllable strategy for prodrug activation in deep tissues remains challenging. Herein, a proof-of-concept is proposed for a gold nanocluster-based strategy that utilizes X-ray irradiation to trigger the liberation of platinum (Pt)-based prodrug conjugates, thus enabling radiotherapy-directed chemotherapy. Mechanistically, the irradiated activation of prodrugs is achieved through direct photoelectron transfer from the excited-state gold nanoclusters to the Pt(IV) center, resulting in the release of cytotoxic Pt(II) agents. Compared to the traditional combination of chemotherapy and radiotherapy, this radiotherapy-directed chemotherapy strategy offers superior antitumor efficacy and safety benefits through spatiotemporal synergy at the tumor site. Additionally, this strategy elicits robust immunogenic cell death and yields profound outcomes for combined immunotherapy of breast cancer. This versatile strategy is ushering in a new era of radiation-mediated chemistry for controlled drug delivery and the precise regulation of biological processes.

A Cages-on-Cluster Structure Constructed by Post-Clustering Covalent Modifications and Guest-Enabled Stimuli-Responsive Luminescence

A gold(I)-cluster-based twin-cage has been constructed by post-clustering covalent modification of a hexa-aldehyde cluster precursor with triaminotriethylamines. The cages-on-cluster structure has double cavities and four binding sites, which show site-discriminative binding for silver(I) and copper(I) guests. The guests in the tripodal hats affect the luminescence of the cluster: the tetra-silver(I) host-guest complex is weakly red-emissive, while the bis-copper(I)-bis-silver(I) one is non-emissive but is a stimuli-responsive supramolecule. The copper(I) ion inside the tri-imine cavity is oxidation sensitive, which enables the release of the bright emissive precursor cluster triggered by H2O2 solution. The hybridization of a cluster with cavities to construct a cluster-based cage presents an innovative concept for functional cluster design, and the post-clustering covalent modification opens up new avenues for finely tuning the properties of clusters.

Aptamer functionalized gold nanoclusters as an emerging nanoprobe in biosensing, diagnostic, catalysis and bioimaging

DNA nanostructures, with their fascinating luminescent and detecting capabilities, provide a basis that can accommodate a wide range of applications. The unique electronic configurations, and physical and chemical properties of aptamer-assembled gold nanoclusters (apt-AuNCs) as a novel type of fluorophore have gradually piqued the interest of the scientific community. Bending DNA sequences and other templates/legends as a stabilizing agent with Au metal has produced an abundance of biosensors, along with catalytic and imaging properties. This review article summarizes the synthesis, conjugation tactics, advantages, and sensing mechanisms of AuNCs aptasensor after providing a brief introduction to the topic. Moreover, the application of DNA/aptamer functionalization has been briefly discussed in the fields of food safety and quality, catalysis, clinical diagnosis, cancer cell bioimaging, detection of cancer cell indicators, and therapy. We also concluded the current obstacles and made recommendations about the future prospects of AuNCs for fundamental research and applications in line with the developments in DNA/aptamer-AuNCs.

Structure control and evolution of atomically precise gold clusters as heterogeneous precatalysts

Metal clusters have distinct features from single atom and nanoparticle (>1 nm) catalysts, making them effective catalysts for various heterogeneous reactions. Nevertheless, the ambiguity and complexity of the catalyst structure preclude in-depth mechanistic studies. The evolution of metal species during synthesis and reaction processes represents another challenge. One effective solution is to precisely control the structure of the metal cluster, thus offering a well-defined pre-catalyst. The well-defined chemical formula and configurations make atomically precise metal nanoclusters optimal choices. To fabricate an atomically precise metal nanocluster-based heterogeneous catalyst with enhanced performance, careful structural design of both the nanocluster and support material, an effective assembling technique, and a pre-treatment method for these hybrids need to be developed. In this review, we summarize recent advances in in the development of heterogeneous catalysts using atomically precise gold and alloy gold nanoclusters as precursors. We will begin with a brief introduction to the structural properties of atomically precise nanoclusters and structure determination of cluster/support hybrids. We will then introduce heterogeneous catalysts prepared from medium size (tens to hundreds of metal atoms) and low nuclearity nanoclusters. We will illustrate how ligand modification, support-cluster interaction, hybrid fabrication, and heteroatom (Pt, Pd Ag, Cu, Cd, Fe) introduction affect the structural properties and pretreatment/reaction-induced structural evolution of gold nanocluster pre-catalysts. Lastly, we will highlight the synthetic method of NCs@MOF hybrids and their effectiveness in circumventing the adverse cluster structural evolution. These findings are expected to shed light on the structure-activity relationship studies and future catalyst design strategies using atomically precise metal nanocluster pre-catalysts.

Core-Packing-Related Vibrational Properties of Thiol-Protected Gold Nanoclusters and Their Excited-State Behavior

Thiolate-protected gold nanoclusters, with unique nuclearity- and structure-dependent properties, have been extensively used in energy conversion and catalysis; however, the mystery between kernel structures and properties remains to be revealed. Here, the influence of core packing on the electronic structure, vibrational properties, and excited-state dynamics of four gold nanoclusters with various kernel structures is explored using density functional theory combined with time-domain nonadiabatic molecular dynamics simulations. We elucidate the correlation between the geometrical structure and excited-state dynamics of gold nanoclusters. The distinct carrier lifetimes of the four nanoclusters are attributed to various electron-phonon couplings arising from the different vibrational properties caused by core packing. We have identified specific phonon modes that participate in the electron-hole recombination dynamics, which are related to the gold core of nanoclusters. This study paints a physical picture from the geometric configuration, electronic structure, vibrational properties, and carrier lifetime of these nanoclusters, thereby facilitating their potential application in optoelectronic materials.

Hemoglobin-stabilized gold nanoclusters displaying oxygen transport ability, self-antioxidation, auto-fluorescence properties and long-term storage potential

The development of hemoglobin (Hb)-based oxygen carriers (HBOCs) holds a lot of potential to overcome important drawbacks of donor blood such as a short shelf life or the potential risk of infection. However, a crucial limitation of current HBOCs is the autoxidation of Hb into methemoglobin (metHb), which lacks oxygen-carrying capacity. Herein, we address this challenge by fabricating a Hb and gold nanoclusters (AuNCs) composite (Hb@AuNCs) which preserves the exceptional features of both systems. Specifically, the Hb@AuNCs retain the oxygen-transporting properties of Hb, while the AuNCs provide antioxidant functionality as shown by their ability to catalytically deplete harmful reactive oxygen species (ROS). Importantly, these ROS-scavenging properties translate into antioxidant protection by minimizing the autoxidation of Hb into non-functional metHb. Furthermore, the AuNCs render Hb@AuNCs with auto-fluorescence properties which could potentially allow them to be monitored once administered into the body. Last but not least, these three features (i.e., oxygen transport, antioxidant and fluorescence properties) are well maintained following storage as a freeze-dried product. Thus, overall, the as-prepared Hb@AuNCs hold the potential to be used as a multifunctional blood surrogate in the near future.

Size Effects of Atomically Precise Gold Nanoclusters in Catalysis

The emergence of ligand-protected, atomically precise gold nanoclusters (NCs) in recent years has attracted broad interest in catalysis due to their well-defined atomic structures and intriguing properties. Especially, the precise formulas of NCs provide an opportunity to study the size effects at the atomic level without complications by the polydispersity in conventional nanoparticles that obscures the relationship between the size/structure and properties. Herein, we summarize the catalytic size effects of atomically precise, thioate-protected gold NCs in the range of tens to hundreds of metal atoms. The catalytic reactions include electrochemical catalysis, photocatalysis, and thermocatalysis. With the precise sizes and structures, the fundamentals underlying the size effects are analyzed, such as the surface area, electronic properties, and active sites. In the catalytic reactions, one or more factors may exert catalytic effects simultaneously, hence leading to different catalytic-activity trends with the size change of NCs. The summary of literature work disentangles the underlying fundamental mechanisms and provides insights into the size effects. Future studies will lead to further understanding of the size effects and shed light on the catalytic active sites and ultimately promote catalyst design at the atomic level.

Photomechanical Laser Fragmentation of IrO2 Microparticles for the Synthesis of Active and Redox-Sensitive Colloidal Nanoclusters

Pulsed laser fragmentation of microparticles (MPs) in liquid is a synthesis method for producing high-purity nanoparticles (NPs) from virtually any material. Compared with laser ablation in liquids (LAL), the use of MPs enables a fully continuous, single-step synthesis of colloidal NPs. Although having been employed in several studies, neither the fragmentation mechanism nor the efficiency or scalability have been described. Starting from time-resolved investigations of the single-pulse fragmentation of single IrO₂ MPs in water, the contribution of stress-mediated processes to the fragmentation mechanism is highlighted. Single-pulse, multiparticle fragmentation is then performed in a continuously operated liquid jet. Here, 2 nm-sized nanoclusters (NCs) accompanied by larger fragments with sizes ranging between several ten nm and several µm are generated. For the nanosized product, an unprecedented efficiency of up to 18 µg J^-1 is reached, which exceeds comparable values reported for high-power LAL by one order of magnitude. The generated NCs exhibit high catalytic activity and stability in oxygen evolution reactions while simultaneously expressing a redox-sensitive fluorescence, thus rendering them promising candidates in electrocatalytic sensing. The provided insights will pave the way for laser fragmentation of MPs to become a versatile, scalable yet simple technique for nanomaterial design and development.

DFT Insights into the Variety in the Coordination Modes of the Equatorial Halides in [Au13 Ag12 (PR3 )10 X8 ]+ (X=Cl/Br) Clusters

The bonding character within metal nanoclusters represents an intriguing topic, shedding light on the inherent driving force for the packing preference in nanomaterials. Herein, density functional theory (DFT) calculations were conducted to investigate the correlation of the series of isomeric [Au₁₃ Ag₁₂ (PR₃ )₁₀ X₈ ]⁺ (X=Cl/Br) clusters, which are mainly differentiated by the coordination mode of the equatorial halides (μ₂ -, μ₃ - and μ₄ -) in the rod-like, bi-icosahedral framework. The theoretical simulation corroborates the variety in the configuration of the Au₁₃ Ag₁₂ clusters and elucidates the fast isomerization kinetics among the different configurations. The easy tautomerization and the variety in chloride binding modes correspond to a fluxionality character of the equatorial halides and are verified by the potential energy curve analysis. The structural flexibility of the central Au₃ Ag₁₀ block is the main driving force, while the relatively stronger Ag-X bonding interaction (compared to that of Au-X), and a sufficient number of halides are also requisite for the associating Ag-X tautomerizations.

Confining Gold Nanoparticles in Preformed Zeolites by Post-Synthetic Modification Enhances Stability and Catalytic Reactivity and Selectivity

Confining Au nanoparticles (NPs) in a restricted space (e.g., zeolite micropores) is a promising way of overcoming their inherent thermal instability and susceptibility to aggregation, which limit catalytic applications. However, such approaches involve complex, multistep encapsulation processes. Here, we describe a successful strategy and its guiding principles for confining small (<2 nm) and monodisperse Au NPs within commercially available beta and MFI zeolites, which can oxidize CO at 40 °C and show size-selective catalysis. This protocol involves post-synthetic modification of the zeolite internal surface with thiol groups, which confines AuCl _x species inside microporous frameworks during the activation process whereby Au precursors are converted into Au nanoparticles. The resulting beta and MFI zeolites contain uniformly dispersed Au NPs throughout the void space, indicating that the intrinsic stability of the framework promotes resistance to sintering. By contrast, in situ scanning transmission electron microscopy (STEM) studies evidenced that Au precursors in bare zeolites migrate from the matrix to the external surface during activation, thereby forming large and poorly dispersed agglomerates. Furthermore, the resistance of confined Au NPs against sintering is likely relevant to the intrinsic stability of the framework, supported by extended X-ray absorption fine structure (EXAFS), H₂ chemisorption, and CO Fourier transform infrared (FT-IR) studies. The Au NPs supported on commercial MFI maintain their uniform dispersity to a large extent after treatment at 700 °C that sinters Au clusters on mesoporous silicas or beta zeolites. Low-temperature CO oxidation and size-selective reactions highlight that most gold NPs are present inside the zeolite matrix with a diameter smaller than 2 nm. These findings illustrate how confinement favors small, uniquely stable, and monodisperse NPs, even for metals such as Au susceptible to cluster growth under conditions often required for catalytic use. Moreover, this strategy may be readily adapted to other zeolite frameworks that can be functionalized by thiol groups.

Ligand-Shell Engineering of a Au28 Nanocluster Boosts Electrocatalytic CO2 Reduction

Subtle tailoring of gold nanoclusters (NCs) could significantly change their physicochemical properties. However, direct comparison of the catalytic performance of gold NCs with identical metal cores but distinct ligand shells is rarely elucidated. In this work, a novel gold NC, Au₂₈ (C₂ B₁₀ H₁₁ S)₁₂ (tht)₄ Cl₄ (Au₂₈ -S), was isolated by a facile self-reducing synthesis. Au₂₈ -S adopts an identical Au₂₈ metal framework to that of the reported alkynyl-protected Au₂₈ -C. The different protective layers lead to distinctions in their electronic structure and optical properties. Furthermore, Au₂₈ -S shows better catalytic activity for the electrochemical reduction of CO₂ to CO. Theoretical calculations identified the active sites and shed light on the catalytic mechanism to elucidate the different catalytic performances. This work provides an ideal platform to study the protective layer-activity relationship of gold NCs, and may also provide guidance in the design of metal NC-based catalysts.

CeO2 Supported Gold Nanocluster Catalysts for CO oxidation: Surface Evolution Influenced by the Ligand Shell

Monolayer protected Au nanocluster catalysts are known to undergo structural changes during catalytic reactions, including dissociation and migration of ligands onto the support, which strongly affects their activity and stability. To better understand how the nature of ligands influences the catalytic activity of such catalysts, three types of ceria supported Au nanoclusters with different kinds of ligands (thiolates, phosphines and a mixture thereof) have been studied, employing CO oxidation as model reaction. The thiolate‐protected Au₂₅/CeO₂ showed significantly higher CO conversion after activation at 250 °C than the cluster catalysts possessing phosphine ligands. Temperature programmed oxidation and in situ infrared spectroscopy revealed that while the phosphine ligands seemed to decompose and free Au surface was exposed, temperatures higher than 250 °C are required to efficiently remove them from the whole catalyst system. Moreover, the presence of residues on the support seemed to have much greater influence on the reactivity than the gold particle size.

Symmetric Growth of Dual-Packed Kernel: Exploration of the Evolution of Au40(SR)24 to Au49(SR)27 and Au58(SR)30 Clusters via the 2e --Reduction Cluster Growth Mechanism

The symmetric and periodic growth of metal core and ligand shell has been found in a number of ligand-protected metal clusters. So far, the principle of symmetric growth has been widely used to understand and predict the cluster structure evolution. In this work, based on the experimentally resolved crystal structure of Au40(o-MBT)24 and Au49(2,4-DMBT)27 clusters and a newly proposed two-electron (2e -) reduction cluster growth mechanism, the evolution pathway from the quasi-face-centered-cubic (fcc)-structured Au40(SR)24 cluster to the dual fcc- and nonfcc-packed Au49(SR)27 and Au58(SR)30 clusters was studied. The current research has clarified two important issues of cluster structure evolution. First, the formation of the dual-packed fcc and nonfcc kernel structure has been rationalized based on a 2e -reduction-based seed-mediated cluster growth pathway. Second, it is found that the symmetrical growth does not necessarily lead to the formation of stable cluster structures. It was found that the formation of dual-packed kernels in the Au49(SR)27 cluster is favorable because of the stability of the intermediate cluster structures and the relatively high thermodynamic stability of the cluster itself. However, although the structure of Au58(SR)30 cluster conforms to the principle of symmetric growth, the tension between the ligand shell and the gold atom of the metal nucleus increases significantly during the cluster size evolution, and the stability of the intermediate clusters is poor, so the formation of the Au58(SR)30 cluster is unfavorable. This study also shows that the 2e --reduction cluster growth mechanism can be used to explore the structural evolution and stability of thiolate-protected gold clusters.

Robust Gold Nanocluster Protected with Amidinates for Electrocatalytic CO2 Reduction

The first all-amidinate-protected gold nanocluster [Au₂₈ (Ph-form)₁₂ ](OTf)₂ (Ph-form=N,N'-diphenylformamidinate) (Au₂₈ ) has been synthesized and structurally resolved. Single crystal X-ray diffraction reveals that Au₂₈ has a compact Au₄ @Au₂₄ tetrahedral core-shell structure of T symmetry, which is fully protected by 12 bridging formamidinate ligands. This cluster is quite robust as indicated by the fact that it can stay intact in solution at 80 °C for 6 d. It exhibits excellent catalytic performance for the electroreduction of CO₂ with 96.5 % Faradaic efficiency (FE) at -0.57 V and a maximum TOF of 1731 h^-1 at -0.87 V. Its superior stability is also manifested in the fact that the supported catalyst Au₂₈ /CNTs maintains stable potentials at ca. -0.69 V for 40 h with FE(CO)s>91 %. A superatomic electron configuration of 1S² 1P⁶ 2S² 1D⁴ has been clarified by DFT computations, and the strong gold-ligand binding and geometric shell closure account for the superior stability of Au₂₈ .