Metal Nanoclusters Research Articles

Metal ion-induced alloying and size transformation of water-soluble metal nanoclusters

Metal ion-induced alloying and size transformation of water-soluble metal nanoclusters

Structural modification and performance regulation of atomically precise metal nanoclusters by phosphine

Structural modification and performance regulation of atomically precise metal nanoclusters by phosphine

Polyelectrolyte Complex Hydrogels from Controlled Kneading and Annealing-Induced Tightly Wound and Highly Entangled Natural Polysaccharides.

Hydrogels usually are fabricated by using monomers or preexisting polymers in precursor solutions. Here, a polyelectrolyte complex biohydrogel (Bio-PEC hydrogel) made from a precursor dough, by kneading, annealing, and crosslinking the dough of two oppositely charged polysaccharides, cationic chitosan quaternary ammonium salt (HACC) and anionic sodium hyaluronate (HA), photoinitiator (α-ketoglutaric acid), crosslinker glycidyl methacrylate (GMA), and water of very small quantity is reported. Controlled kneading and annealing homogenized the dough with respect to transforming randomly distributed, individual polymer chains into tightly wound double-stranded structures, which, upon UV irradiation, covalently sparsely crosslinked into a highly entangled network and subsequently, upon fully swollen in water, results in Bio-PEC hydrogel, HACC/HA, exhibiting near-perfect elasticity, high tensile strength, and high swelling resistance. Via the same kneading and annealing, tetracarboxyphenylporphyrin iron (Fe-TCPP) metal nanoclusters are incorporated into HACC/HA to obtain photocatalytic, antibacterial, and biocompatible Bio-PEC hydrogel composite, Fe-TCPP@HACC/HA. Using SD rat models, the efficacy of Fe-TCPP@HACC/HA in inhibiting Escherichia coli (E. coli) growth in vitro and the ability to promote wound healing and scar-free skin regeneration in vivo, or its high potential as a wound dressing material for biomedical applications are demonstrated.

Effect of cooling rate on solidification points and atomic structures of metal nanoclusters: a molecular dynamics simulation study

In this work, the micro-structural evolution during the solidification process of three metal nanoclusters (copper, nickel, and silver) containing 2048 atoms each, subjected to different cooling rates are investigated. Molecular dynamics (MD) simulations in conjunction with modified embedded atom method (MEAM) potentials have been employed to carry out the work. For different cooling rates, the solidification points of the nanoclusters are estimated from the variation in average potential energy of the systems during the crystallization process, and the structural evolutions are analysed by utilising radial distribution function and common neighbour analysis method. The results advocate that the cooling rate has a profound impact on the structures of the solidified nanoclusters. The critical cooling rate for each nanocluster has been captured, where a glassy/amorphous structure is observed. Polycrystalline nano-structures (consisting of amorphous, FCC and HCP) are observed below these critical cooling rates and the number of close-packed structures (FCC, HCP) are found to decrease with the increase in cooling rate. The findings of this work would be helpful in various practical applications of the metal nanoclusters, where the structure of nanoclusters directly affect.

Surface Functionalization and Escherichia coli Detection Using Surface-Enhanced Raman Spectroscopy Driven by Functional Organic Polymer/Gold Nanofilm-Based Microfluidic Chip.

In this work, a microfluidic prototype based on polymeric materials was developed to monitor surface processes using surface-enhanced Raman spectroscopy (SERS), keeping the reagents free of environmental contamination. The prototype was fabricated on poly(methyl methacrylic acid) (PMMA). A micrometric membrane of a functional organic polymer (FOP) based on p-terphenyl and bromopyruvic acid monomers was formed on the PMMA surface to promote the formation of metal nanoclusters. Au nanosized film was deposited on the FOP membrane to give rise to the SERS effect. A microchannel was formed on another piece of PMMA using micromachining. A representative 3D model of the prototype layer arrangement was built and simulated in COMSOL Multiphysics® to approximate the electric field distribution and calculate the power enhancement factor as the Au film changes over time. The fabrication process was characterized using UV-visible and Raman spectroscopies and XPS. The prototype was tested using a Raman microscope and liquid solutions of cysteamine and Escherichia coli (E. coli). The simulation results demonstrated that the morphological characteristics of the Au layer give rise to the SERS effect, and the power enhancement factor reaches values as high as 8.8 × 105 on the FOP surface. The characterization results showed the formation of the FOP and the Au film on PMMA and the surface functionalization with amine groups. The Raman spectra of the prototype showed temporal evolution as different compounds were deposited on the upper wall of the microchannel. Characteristic peaks associated with these compounds were detected with continuous monitoring over time. This prototype offers many benefits for applications like monitoring biological processes. Some advantages include timely surface evaluation while avoiding environmental harm, decreased use of reagents and samples, minimal interference with the process by measuring, and detecting microorganisms in just 1 h, as demonstrated with the E. coli sample.

Electric field-driven up-and-down motion of the flexible tail of Al13+ cluster system-a nano-scale flipper.

Dynamic metal nanoclusters have become a hot area of research in the field of nanoscience and nanotechnology due to their potential applications in micro devices. One such dynamic cluster is a quasi-planar ground state (GS) Al13+ cluster which exhibits anelectric field driven up and down flipping motion of the flexible tail which oscillates with respect to the mean plane. A Car-Parrinello molecular dynamics (CPMD) simulation has been carried out to understand the nature of dynamics of the cluster. CPMD simulation study reveals that the flexible tail region of the Al13+ isomeric system (two ground states M1, M2 and a transition state TS connecting them) can be engaged in a systematic up down flipping motion by the application of a transverse electric field. A saw tooth electric field of amplitude 5.19V/nm is sufficient to induce the up-and-down flipping oscillation of the cluster, which has an average oscillation frequency of around 20 THz. AIM, NICS and AdNDP analyses also have been carried out to understand the fluxional nature of the cluster from the electronic structural perspective. Electronic structural analysis of selected optimized intermediate states in the presence of transverse electric field has also been analyzed to correlate the electronic structure with the dynamic nature of the cluster. Single-point energies of all intermediate states between two minima of Al13+ clusters connected through a transition state cluster. Optimized geometries of Al13+ clusters in the presence of electric field of different strengths have been carried out by using the Gaussian 03 package. 6-311 + G(d) basis set and B3LYP hybrid density functional have been utilized for these studies. To establish the flipping motion, Car-Parrinello molecular dynamics (CPMD) has been performed using the cp.x module of the Quantum ESPRESSO 6.3.0 program package using the Perdew-Burke-Ernzerhof (PBE) functional, plane-wave basis set and ultrasoft pseudopotentials. ORTEP-3 and POV ray-3.7 software packages have been used for visualization and graphics generation. Atoms in molecule (AIM), Adaptive Natural Density Partitioning (AdNDP) analysis have been carried out using Multiwfn 3.7 program package.

Self-Assembly of Atomically Precise Silver Nanoclusters in Crowded Colloids into Ultra-Long Ribbons with Tunable Supramolecular Chirality.

Atomically precise metal nanoclusters (NCs) emerge as fascinating synthons in self-assembled materials. The self-assembly of metal NCs are highly sensitive to the environment because they have an inorganic-organic hybridized structure and a relatively complicated conformation. Here, it is shown that when confined in crowded colloids, a water-soluble Ag9 -cored nanocluster (Ag9 -NC) can self- assemble into ultra-long (up to millimeters) and photoluminescent ribbons with high flexibility. The ribbon contains rectangularly organized columns of Ag9 -NCs and can undergo secondary self-assembly to form bundled and branched structures. Formation of ribbons is observed in all the tested colloids, including lyotropic liquid crystals and disordered, three-dimensional network. The high viscosity/elasticity of the crowded colloids weakens gravity-induced sedimentation of the ribbons, leading to the formation of an interesting class of inorganic-organic composite materials where the hard Ag-containing skeleton strengthens the soft matter. The simultaneously occurring symmetry breaking during the self-assembly of Ag9 -NCs gives uncontrolled supramolecular chirality, which can be tuned through the majority rule and soldier-and-sergeant rule by the introduction of chiral seeds. The regulated chirality and the intrinsic photoluminescence of the Ag9 -NCs ribbons impart the composite material circularly polarized luminescence, opening the door for a variety of potential applications.

Fe3+ assisted water-soluble nickel nanocluster for the “on-off-on” fluorescence determination of ascorbic acid

An “on-off-on” fluorescent sensor has been constructed to determine ascorbic acid (AA) based on water-soluble glutathione-decorated nickel nanoclusters (NiNCs) with assistance of trivalent iron ions (Fe3+). The fluorescence could be effectively quenched (off) upon adding Fe3+ due to aggregation-caused quenching (ACQ) and the internal filtering effect (IFE). Meanwhile, the fluorescence of NiNCs–Fe3+ systems could be again recovered (on) after introducing AA, which is attributed for the redox reaction between Fe3+ and AA. The sensor can detect AA in the linear range of 20–200 μmol/L with a LOD of 7.45 μmol/L. More importantly, the proposed approach has been successfully applied for the detection of AA content in commercially available tablets and beverages as well as in common fruits with satisfactory recovery ranges, suggesting the potential sensing platform for AA detection. Therefore, the prepared sensor offers distinct advantages including low cost, simple operation, good sensitivity, and high selectivity, which has a broad application prospect of metal nanoclusters.

Core atoms escape from the shell: reverse segregation of Pb–Al core–shell nanoclusters via nanoscale melting

Melting is a phase transition that profoundly affects the fabrication and diverse applications of metal nanoclusters. Core–shell clusters offer distinctive properties and thus opportunities compared with other classes of nano-alloys. Molecular dynamics simulations have been employed to investigate the melting behaviour of Pb–Al core–shell clusters containing a fixed Pb147 core and varying shell thickness. Our results show that the core and shell melt separately. Surprisingly, core melting always drives the core Pb atoms to break out the shell and coat the nanoclusters in a reversed segregation process at the nanoscale. The melting point of the core increases with the shell thickness to exceed that of the bare core cluster, but the thinnest shell always supresses the core melting point. These results can be a reference for the future fabrication, manipulation, and exploitation of the core–shell nanoalloys chosen. The system chosen is ideally suited for experimental observations.

Dual Catalysis of Gold Nanoclusters: Photocatalytic Cross-Dehydrogenative Coupling by Cooperation of Superatomic Core and Molecularly Modified Staples.

Thiolate-protected gold nanoclusters (AuNCs) have attracted significant attention as nano-catalysts, revealing a superatomic core and gold-thiolate staples as distinct structural units. Here, we demonstrate the unprecedented dual catalytic activity of thiolate-protected [Au25 (SR)18 ]- nanoclusters, involving both photosensitized 1 O2 generation by the Au13 superatomic core and catalytic carbon-carbon bond formation facilitated by Au2 (SR)3 staples. This synergistic combination of two different catalytic units enables efficient cross-dehydrogenative coupling of terminal alkynes and tertiary aliphatic amines to afford propargylamines in high yields of up to 93 %. Mixed-ligand AuNCs bearing both thiolate and alkynyl ligands revealed the intermediacy of the alkynyl-exchanged AuNCs toward both photosensitization and C-C bond-forming catalytic cycles. Density functional theory calculations also supported the intermediacy of the alkynyl-exchanged AuNCs. Thus, the use of ligand-protected metal nanoclusters has enabled the development of an exceptional multifunctional catalyst, wherein distinct nanocluster components facilitate cooperative photo- and chemo-catalysis.

Dual Catalysis of Gold Nanoclusters: Photocatalytic Cross‐Dehydrogenative Coupling by Cooperation of Superatomic Core and Molecularly Modified Staples**

AbstractThiolate‐protected gold nanoclusters (AuNCs) have attracted significant attention as nano‐catalysts, revealing a superatomic core and gold‐thiolate staples as distinct structural units. Here, we demonstrate the unprecedented dual catalytic activity of thiolate‐protected [Au25(SR)18]− nanoclusters, involving both photosensitized 1O2 generation by the Au13 superatomic core and catalytic carbon‐carbon bond formation facilitated by Au2(SR)3 staples. This synergistic combination of two different catalytic units enables efficient cross‐dehydrogenative coupling of terminal alkynes and tertiary aliphatic amines to afford propargylamines in high yields of up to 93 %. Mixed‐ligand AuNCs bearing both thiolate and alkynyl ligands revealed the intermediacy of the alkynyl‐exchanged AuNCs toward both photosensitization and C−C bond‐forming catalytic cycles. Density functional theory calculations also supported the intermediacy of the alkynyl‐exchanged AuNCs. Thus, the use of ligand‐protected metal nanoclusters has enabled the development of an exceptional multifunctional catalyst, wherein distinct nanocluster components facilitate cooperative photo‐ and chemo‐catalysis.

Influence of Pyramidal M20 (M= Cu, Ag and Au) Clusters on SERS and Noncovalent Interactions toward Tuberculosis Drug Pretomanid (PTD): DFT Study

The study of interaction and adsorption of drug molecules on the active surface of noble metal nanocluster is of particular interest due to effective change in the properties of the drug molecules. Surface-enhanced Raman scattering (SERS) theoretical calculations were performed to investigate the adsorption properties of pretomanid (PTD) on pyramidal [Formula: see text]/[Formula: see text]/[Formula: see text] metal clusters. The charge transfer process from the [Formula: see text] pyramids is revealed by MEP and electronic analysis. The frequencies of PTD are enhanced in the PTD–metal complexes due to the noticeable SERS effect, and the binding energies were calculated to be −36.2 kcal/mol, −46.3 kcal/mol and −43.6 kcal/mol with Ag, Au and Cu structures, respectively. For the PTD–metal clusters, there is an entire potential rearrangement due to adsorption process which is due to charge transfer and adsorptions as chemisorption. The polarizability variations are predicted in the order PTD–Au > PTD–Cu > PTD–Ag which contribute the SERS enhancement due to adsorption. Changes in thermodynamic parameters reveal that adsorption is exothermic and at the same time spontaneous with ordered interactions due to the negative values. There is a redshift for the ultraviolet–visible (UV–vis) absorption of PTD–metal complexes with a lowering intensity in comparison with that of PTD, more likely indicating a chemisorption process. SERS enhancement factors are remarkable due to adsorption of conformationally flexible PTD on metal clusters. The noncovalent interactions between PTD and the metal pyramids were also determined. The study provided key information on designing a molecular structure with a good pharmacological profile by calculating bioactivity and drug similarity parameters for bioactive drug molecules.

Single thiolate replacement of metal nanoclusters

Single thiolate replacement of metal nanoclusters

Recent Advances in the Preparation and Application of DNA-Encoded Metal Nanoclusters

DNA as an intriguing organic ligand has been widely employed for synthesizing metal nanoclusters and engineering their properties. This review aims to present recent progress on DNA-encoded metal (Ag, Cu, Au, Ag/Pt, Cu/Ag, etc.) nanoclusters (DNA-MNCs), focusing on their applications in the fields of analysis, logic operation, and therapy based on properties including fluorescence, electrochemiluminescence (ECL), and antibacterial and catalytic activity, and summarizes the attractive features of the latest research. The key points are briefly described as follows. (1) Analytical systems have been constructed based on fluorescence regulation, and nuclease-assisted and enzyme-free amplification strategies have been extensively adopted with fluorescent DNA-MNCs for amplified analysis. (2) DNA-MNCs may play more than one role (emitter, quencher, or catalyst) in ECL-based analytical systems. (3) Apart from antibacterial activity, DNA-MNCs also possess apparent catalytic capability, such as enzyme-like activity (i.e., nanozymes), which has been applied in colorimetric systems. (4) Reversibly regulating the catalytic activity of DNA-MNCs has been attained with DNA systems. It is believed that through in-depth investigation of the relationship between atomic structure and property, more novel DNA-MNCs will be explored and applied in the future.

Isomorphous Substitution of Organic Cage Crystal by Pd Nanoclusters for Selective Hydrogenation.

For supporting active metal, the cavity confinement and mass transfer facilitation lie not in one sack, a trade-off between high activity and good stability of the catalyst is present. Porous organic cages (POCs) are expected to break the trade-off when metal particles are properly loaded. Herein, three organic cages (CC3, RCC3, and FT-RCC3) are employed to support Pd nanoclusters for catalytic hydrogenation. Subnanometer Pd clusters locate differently in different cage frameworks by using the same reverse double-solvents approach. Compared with those encapsulated in the intrinsic cavity of RCC3 and anchored on the outer surface of CC3, the Pd nanoclusters orderly assembled in FT-RCC3 crystal via isomorphous substitution exhibit superior activity, high selectivity, and good stability for semi-hydrogenation of phenylacetylene. Isomorphous substitution of FT-RCC3 crystal by Pd nanoclusters is originated from high crystallization capacity of FT-RCC3 and specific interaction of each Pd nanocluster with four cage windows. Both confinement function and H2 accumulation capacity of FT-RCC3 are fully utilized to support active Pd nanoclusters for efficient selective hydrogenation. The present results provide a new perspective to the heterogeneous catalysis field in terms of crystalizing metal nanoclusters in POC framework and outside the cage for making the best use of both parts.

Insight into Lithium–sulfur batteries performance enhancement: from metal nanoparticles to metal nanoclusters to single metal atoms

Insight into Lithium–sulfur batteries performance enhancement: from metal nanoparticles to metal nanoclusters to single metal atoms

Probing the Fluorescence Intermittency of Bimetallic Nanoclusters using Single-Molecule Fluorescence Spectroscopy.

Single-molecule spectroscopy (SMS) is a unique and competent technique to study molecule dynamics and sense biomolecules precisely. The design of an ultrahigh-stability single fluorophore probe with excellent photostability and long-lived dark transient states for single-molecule fluorescence microscopy is challenging. Here, we found that the photostability of bimetallic AuAg28 nanoclusters is better than monometallic Ag29 nanoclusters. The photon antibunching experiments unveiled exceptional brightness and remarkable photostability with high survival times of up to 218 s with minimal blinking. AuAg28 NCs exhibited longer "on" times and shorter "off" times as compared to Ag29 NCs. The statistical analysis was performed on at least 100 molecules that showed single-step photobleaching and almost a 5-fold enhancement in intensity on Au doping in Ag29 NCs. The distinctive and tunable photophysics of metal NCs can offer huge potential in pushing single-molecule dynamic measurements to be carried out biologically.

Surface motifs regulated aggregation induced emission in AuAg nanoclusters combined with Ce(III)/Ce(IV) catalytic cyclic amplification strategy for sensitive bioanalysis

Achieving high luminescence intensity in electrochemiluminescence biosensors is a challenge for metal nanoclusters (MNCs) due to their non-radiative relaxation-mediated self-quenching tendency. Here, the surface motifs [M(I)-SR] of MNCs were regulated based on aggregation-induced emission (AIE) strategy was proposed to mitigate non-radiative relaxation vibrations, and an efficient luminescent AuAg NCs was designed via host-guest assembly as a signal probe. The Au(I)-SR of AuAg NCs used glutathione (GSH) as a template and reducing agent, and the introduction of Ag(I) made the Au(I)-SR of AuAg NCs cross-linked and interlocked, resulting in AuAg NCs with denser surface patterns. The aggregation of surface motifs limited the ligand movement to reduce the non-radiative energy dissipation. Furthermore, the spontaneous catalytic cycle amplification strategy of Ce(III)/Ce(IV) redox pairs in the matrix material of Ce-MOF promoted the reaction of more co-reactants triethylamine (TEA), obtaining potent reducing radicals TEA* for further improving the ECL efficiency of AuAg NCs. Using cardiac troponin I (cTnI) as the analytical model, the biosensor exhibited a wide linear relationship range (50 fg·mL−1 - 500 ng·mL−1) and a low detection limit (4.77 fg·mL−1). The breakthrough in surface motifs regulation of MNCs guides a new way to design high luminiferous MNCs, and further expands the application potential of MNCs.

MOLECULAR DYNAMIC STUDY OF THE CRATERING PROCESS DURING HIGH-VELOCITY IMPACT OF METALLIC CLUSTERS WITH A SUBSTRATE

In the presented work, numerical experiments were carried out in the framework of the molecular dynamics method to study the impact interaction of metallic nanoclusters of different sizes with a metallic substrate in a wide range of velocities. Analysis of the obtained data showed that the crater volume remains proportional to the impact energy and inversely proportional to the dynamic strength of the material, with the direct angle coefficient being independent of the cluster size and the cluster-substrate material.

Modeling the Formation of Noble Metal Nanocluster Systems during Deposition from a Colloid Solution

Modeling the Formation of Noble Metal Nanocluster Systems during Deposition from a Colloid Solution