Nanoclusters In Solution Research Articles

Dynamic Metal Exchange in Nanoclusters: Isotope Labeling Sheds Light on Cellular‐like Fusion Processes

AbstractGrasping the behavior of metal nanoclusters in solution at the atomic level is a pinnacle challenge in nanoscience. In addressing this, our work utilizes the Ag13@Ag16(BDT)12(TPP)4 (Ag29) nanocluster (where BDT represents 1,3‐benzenedithiol, and TPP is triphenylphosphine) as a template. We employ isotopic layering labeling, such as a109 Ag13@107 Ag16 core ‐shell structure, to mark the clusters. Subsequently, we conduct reactions with clusters featuring two different layering structures. Finally, we employ isotopic labeling to replace Ag in the shell, followed by analysis using ESI‐MS, enabling us to discern the process of intercluster reactions. We observed that the reactions primarily involve metal exchanges between the cores of different clusters and separately between their shells, highlighting distinct patterns of atomic‐level exchanges within these structures. This study thus offers pivotal insights into the molecular‐level mechanisms of metal exchange between clusters, significantly contributing to the development of metal nanocluster design and synthesis.

Transforming Silver Nanoclusters from Racemic to Homochiral via Seeded Crystallization.

Chirality has risen as an attractive topic in materials research in recent years, but the attainment of enantiopure materials remains a major challenge. Herein, we obtained homochiral nanoclusters by a recrystallization strategy, without any chiral factors (i.e., chiral ligands, counterions, etc.). Through the rapid flipping of configuration of silver nanoclusters in solution, the initial racemic Ag40 (triclinic) nanoclusters are converted to homochiral (orthorhombic) as revealed by X-ray crystallography. In the seeded crystallization, one homochiral Ag40 crystal is used as a seed to direct the growth of crystals with specific chirality. Furthermore, enantiopure Ag40 nanoclusters can be used as amplifiers for the detection of chiral carboxylic drugs. This work not only provides chiral conversion and amplification strategies to obtain homochiral nanoclusters but also explains the chirality origin of nanoclusters at the molecular level.

White light-emitting, biocompatible, water-soluble metallic magnesium nanoclusters for bioimaging applications

Ultra-small (1.6 nm), water-soluble, white light-emitting (WLE), highly stable (∼8 months) BSA templated metallic (Mg0) nanoclusters (fluorescent magnesium nanoclusters = FMNCs) is developed using the green and facile route. Synthesis was facilitated by the reduction of magnesium salt, where template bovine serum albumin is utilized as a reducing agent and ascorbic acid act as a capping agent to impart stability in water, thereby obtaining stabilized Mg0 nanoclusters In solution, stabilized Mg0 nanoclusters produce white light (450–620 nm with FWHM ∼120 nm) upon 366 nm light excitation. This white light emission was found to have a CIE coordinate of 0.30, 0.33 [pure white light CIE (0.33, 0.33)]. Taking advantage of WLE and ultrasmall size, FMNCs were used for in vitro fluorescence imaging of HaCaT cell lines, yielding blue (τ = 2.94 ns, with a relative of QY = 1.2 % w.r.t QS), green (τ = 3.07 ns; relative quantum yield of 4.6% w.r.t R6G) and red (τ = 0.3 ns) images. Further, incubation of FMNCs with HEK293 (Human embryonic kidney cell) and cancerous MDA-MB-231 (Breast cancer cell line) human cell lines yielded 100 % cell viability. Current work is envisioned to contribute significantly in the area of science, engineering, and nanomedicine.

Quantifying the Solution Structure of Metal Nanoclusters Using Small‐Angle Neutron Scattering

AbstractMetal nanoclusters are a unique class of synthetic material, as their crystal structures can be resolved using X‐ray diffraction, and their chemical formula can be precisely determinated from mass spectroscopy. However, a complete structure characterization by these two techniques is often a challenging task. Here, we utilize small‐angle neutron scattering (SANS) to directly quantify the key structure parameters of a series of silver and gold nanoclusters in solution. The results not only correlate well to their crystallographic structures, but also allow the quantification of the counterions layer surrounding charged nanoclusters in solution. Furthermore, when combining with X‐ray scattering, it is possible to estimate the molecular weight of both the metal core and the ligand shell of nanoclusters. This work offers an alternative characterization tool for nanoclusters without the requirement of crystallization or gas phase ionization.

Quantifying the Solution Structure of Metal Nanoclusters Using Small-Angle Neutron Scattering.

Metal nanoclusters are a unique class of synthetic material, as their crystal structures can be resolved using X-ray diffraction, and their chemical formula can be precisely determinated from mass spectroscopy. However, a complete structure characterization by these two techniques is often a challenging task. Here, we utilize small-angle neutron scattering (SANS) to directly quantify the key structure parameters of a series of silver and gold nanoclusters in solution. The results not only correlate well to their crystallographic structures, but also allow the quantification of the counterions layer surrounding charged nanoclusters in solution. Furthermore, when combining with X-ray scattering, it is possible to estimate the molecular weight of both the metal core and the ligand shell of nanoclusters. This work offers an alternative characterization tool for nanoclusters without the requirement of crystallization or gas phase ionization.

Computational Prediction of Speciation Diagrams and Nucleation Mechanisms: Molecular Vanadium, Niobium, and Tantalum Oxide Nanoclusters in Solution.

Understanding the aqueous speciation of molecular metal-oxo-clusters plays a key role in different fields such as catalysis, electrochemistry, nuclear waste recycling, and biochemistry. To describe the speciation accurately, it is essential to elucidate the underlying self-assembly processes. Herein, we apply a computational method to predict the speciation and formation mechanisms of polyoxovanadates, -niobates, and -tantalates. While polyoxovanadates have been widely studied, polyoxoniobates and -tantalates lack the same level of understanding. First, we propose a pentavanadate cluster ([V5O14]3-) as a key intermediate for the formation of the decavanadate. Our computed phase speciation diagram is in particularly good agreement with the experiments. Second, we report the formation constants of the heptaniobate, [Nb7O22]9-, decaniobate, [Nb10O28]6-, and tetracosaniobate [H9Nb24O72]15-. Additionally, we compute the speciation and phase diagram of niobium, which so far was restricted to Lindqvist derivates. Finally, we predict the formation constant of the decatantalate ([Ta10O26]6-) in water, even though it had only been synthesized in toluene. Furthermore, we also calculate the corresponding speciation and phase diagrams for polyoxotantalates. Overall, we show that our method can be successfully applied to different families of molecular metal oxides without any need for readjustments; therefore, it can be regarded as a trustworthy tool for exploring polyoxometalates' chemistry.

Study of stabilization of self-assembly processes in fullerene C60 solution

The dynamics of changes in the values of the refractive index of solutions of C60 in xylene at various concentrations has been studied by the refractometric method. It was found that the deviation from the linear form of the dependence of the refractive index on the C60 concentration occurs at a C60 concentration of 1.8 mg/ml. The deviation is associated with the largest number of molecular interactions between C60−C60 and the formation of large nanoclusters on their basis in solution. It was found by the dynamic light scattering (DLS) that the final size of C60 nanoclusters in solution depends on the initial concentration of the solute. A higher initial concentration of C60 leads to the synthesis of nanoclusters with a larger diameter. Using the method of optical spectroscopy, the processes of self-organization of fullerene C60 molecules in a xylene solution in time are studied. The character of stability of synthesized fullerene nanoclusters in solution is discussed. The results obtained are of particular importance for numerous applications of nanotechnology for understanding self-assembly processes and the development of new nanomaterials.

Reversible isomerization of metal nanoclusters induced by intermolecular interaction

Reversible isomerization of metal nanoclusters induced by intermolecular interaction

Thiolate‐Protected Metal Nanoclusters: Recent Development in Synthesis, Understanding of Reaction, and Application in Energy and Environmental Field

Metal nanoclusters (NCs), which are composed of about 250 or fewer metal atoms, possess great potential as novel functional materials. Fundamental research on metal NCs gradually started in the 1960s, and since 2000, thiolate (SR)-protected metal NCs have been the main metal NCs actively studied. The precise and systematic isolation of SR-protected metal NCs has been achieved in 2005. Since then, research on SR-protected metal NCs for both basic science and practical application has rapidly expanded. This review describes this recent progress in the field of SR-protected metal NCs in three areas: synthesis, understanding, and application. Specifically, the recent study of alloy NCs and connected structures composed of NCs is highlighted in the "synthesis" section, recent knowledge on the reactivity of NCs in solution is highlighted in the "understanding" section, and the applications of NCs in the energy and environmental field are highlighted in the "application" section. This review provides insight on the current state of research on SR-protected metal NCs and discusses the challenges to be overcome for further development in this field as well as the possibilities that these materials can contribute to solving the problems facing modern society.

Atomistic insight into the aggregation of [Au25(SR)18] q nanoclusters.

Atomically precise nanoclusters have been proven to give solid state aggregates with intriguing optical properties. However, the mechanism that regulates this aggregation remains unclear. Here, the aggregation of two Au25 nanoclusters in solution is investigated through enhanced sampling molecular dynamics simulations. To understand how the free energy of the systems depends on the nanocluster features, calculations were performed on three nanocluster pairs which differ in charge states and substituent nature and dimension. Our results show that the choice of the ligands heavily affects the free energy profile of the systems when the structures are nearby and, in some cases, the formation of a dimeric phase is observed. This phase is particularly stable in long-chain substituted nanoclusters, where the long alkane chains can generate bundles and the gold cores are closer compared to the short-chain ligands. We found a remarkable agreement between our calculations and the literature-available solid-state structures, especially for the orientation of the interacting nanoclusters. Moreover, some of the dimeric structures are prodromal to the formation of the aurophilic intercluster bond observed in the crystal structures, meaning that the dimer can act as a precursor and can drive the whole crystallization mechanism toward the formation of stable crystal species.

Synthesis of folic acid functionalized gold nanoclusters for targeting folate receptor-positive cells

We report on the synthesis of water-soluble gold nanoclusters capped with polyethylene glycol (PEG)-based ligands and further functionalized with folic acid for specific cellular uptake. The dihydrolipoic acid-PEG-based ligands terminated with –OMe, –NH2 and –COOH functional groups are produced and used for surface passivation of Au nanoclusters (NCs) with diameters <2 nm. The produced sub 2 nm Au NCs possess long-shelf life and are stable in physiologically relevant environments (temperature and pH), are paramagnetic and biocompatible. The paramagnetism of Au NCs in solution is also reported. The functional groups on the capping ligands are used for direct conjugation of targeting molecules onto Au NCs without the need for post synthesis modification. Folic acid (FA) is attached via an amide group and effectively target cells expressing the folate receptor. The combination of targeting ability, biocompatibility and paramagnetism in FA-functionalized Au NCs is of relevance for their exploitation in nanomedicine for targeted imaging.

Micropatterning of fluorescent silver nanoclusters in polymer films by Laser Interference

Hybrid films of poly (methacrylic acid) (PMAA) and silver fluorescent nanoclusters were structured by the Direct Laser Interference Patterning technique (DLIP) using few nanosecond laser pulses (355 nm) to obtain an arranged and well-defined periodic surface pattern. It is shown that the films of neat PMAA are not structured by irradiation at 355 nm due to its low absorbance at this wavelength. However, the silver nanoclusters act as chromophores increasing the absorbance of the film and allowing the surface patterning. Also, the interaction of the laser beam with a film of PMAA doped with Ag+ induces the formation of fluorescent silver nanoclusters and the subsequent surface patterning. The patterned films maintain the luminescent properties of the PMAA/Ag nanoclusters in solution. The structured and unstructured films were characterized by optical, atomic force and spectral laser confocal scanning microscopy showing highly oriented lines patterning already after just one laser pulse.

Toward Solution Syntheses of the Tetrahedral Au20 Pyramid and Atomically Precise Gold Nanoclusters with Uncoordinated Sites.

A long-standing objective of cluster science is to discover highly stable clusters and to use them as models for catalysts and building blocks for cluster-assembled materials. The discovery of catalytic properties of gold nanoparticles (AuNPs) has stimulated wide interests in gaseous size-selected gold clusters. Ligand-protected AuNPs have also been extensively investigated to probe their size-dependent catalytic and optical properties. However, the need to remove ligands can introduce uncertainties in both the structures and sizes of ligand-protected AuNPs for catalytic applications. Ideal model catalysts should be atomically precise AuNPs with well-defined structures and uncoordinated surface sites as in situ active centers. The tetrahedral ( Td) Au20 pyramidal cluster, discovered to be highly stable in the gas phase, provided a unique opportunity for such an ideal model system. The Td-Au20 consists of four Au(111) faces with all its atoms on the surface. Bulk synthesis of Td-Au20 with appropriate ligands would allow its catalytic and optical properties to be investigated and harnessed. The different types of its surface atoms would allow site-specific chemistry to be exploited. It was hypothesized that if the four corner atoms of Td-Au20 were coordinated by ligands the cluster would still contain 16 uncoordinated surface sites as potential in situ catalytically active centers. Phosphine ligands were deemed to be suitable for the synthesis of Td-Au20 to maintain the integrity of its pyramidal structure. Triphenyl-phosphine-protected Td-Au20 was first observed in solution, and its stability was confirmed both experimentally and theoretically. To enhance the synthetic yield, bidentate diphosphine ligands [(Ph)2P(CH2) nP(Ph)2 or L n] with different chain lengths were explored. It was hypothesized that diphosphine ligands with the right chain length might preferentially coordinate to the Td-Au20. Promising evidence was initially obtained by the formation of the undecagold by the L3 ligand. When the L8 diphosphine ligand was used, a remarkable Au22 nanocluster with eight uncoordinated Au sites, Au22(L8)6, was synthesized. With a tetraphosphine-ligand (PP3), a new Au20 nanocluster, [Au20(PP3)4]Cl4, was isolated with high yield. The crystal structure of the new Au20 core did not reveal the expected pyramid but rather an intrinsically chiral gold core. The surface of the new chiral-Au20 was fully coordinated, and it was found to be highly stable chemically. The Au22(L8)6 nanocluster represents the first and only gold core with uncoordinated gold atoms, providing potentially eight in situ catalytically active sites. The Au22 nanoclusters dispersed on oxide supports were found to catalyze CO oxidation and activate H2 without ligand removal. With further understanding about the formation mechanisms of gold nanoclusters in solution, it is conceivable that Td-Au20 can be eventually synthesized, allowing its novel catalytic and optical properties to be explored. More excitingly, it is possible that a whole family of new atomically precise gold nanoclusters can be created with different phosphine ligands.

Ligands Modulate Reaction Pathway in the Hydrogenation of 4‐Nitrophenol Catalyzed by Gold Nanoclusters

AbstractProtective ligands are key components of ligand‐protected metal nanoclusters (NCs), as they offer good stability and multiple functionalities to the metal NCs in solution. Herein, we demonstrated that the ligand landscape on the NC surface could also be used to modulate the catalytic active sites of metal NCs in solution thus to direct the catalytic reaction towards desirable products through a different pathway. We found that thiolate ligands, namely, p‐mercaptobenzoic acid (p‐MBA), in Au25(p‐MBA)18 NCs could influence the reaction pathway in the catalytic hydrogenation of 4‐nitrophenol in solution. In particular, the well‐defined ligand structure of Au25(p‐MBA)18 NCs in solution provided a unique environment for the coadsorption of two substrate molecules (4‐nitrophenol) on the Au NC surface, and this ligand modulation could activate a reaction pathway involving the formation of azobenzene intermediates from the two adsorbed substrate molecules, which are missing in nanogold catalysts without protective ligands. The discovery of this alternative reaction pathway highlights the importance of ligands on nanogold catalysts in modulating their active sites and directing their catalytic reaction pathways in solution and provides good opportunities to tailor the selectivity of ligand‐protected metal NC catalysts.

Light‐Emitting Devices: All‐Copper Nanocluster Based Down‐Conversion White Light‐Emitting Devices (Adv. Sci. 11/2016)

Andrey L. Rogach and co-workers describe the enhanced emission of photoluminescent copper nanoclusters in solution and in powder state, in article 1600182. These blue- and orange-emitting Cu nanoclusters are combined to create white light-emitting devices.

Silver migration between Au38(SC2H4Ph)24 and doped AgxAu38-x(SC2H4Ph)24 nanoclusters.

A fast redistribution of metal atoms occurs upon mixing the AgxAu38-x and Au38 nanoclusters in solution, as observed by mass spectrometry. Physical separation of AgxAu38-x and Au38 species by a dialysis membrane prohibits the metal migration, which suggests that collisions between the reacting clusters are at the origin of the observation.

Enhancing stability through ligand-shell engineering: A case study with Au25(SR)18 nanoclusters

While thiolate-protected Au nanoclusters (NCs) have drawn considerable interest in various fields, their poor stability in aqueous solution remains a major hurdle for practical applications. Here, we report a unique strategy based on ligand-shell engineering to improve the stability of thiolated Au NCs in solution. By employing two thiol-terminated ligands having oppositely charged functional groups on the surface of the NCs, we demonstrate that the electrostatic attraction between the oppositely charged functional groups of neighboring ligands could amplify the coordination among surface ligands, leading to the formation of pseudo-cage-like structures on the NC surface that could offer higher protection to the Au core in aqueous solution. The strategy developed in this study could be extended to other metal NCs, further paving the way toward practical applications.

Palladium nanoparticles stabilised by PTA derivatives in glycerol: Synthesis and catalysis in a green wet phase

Palladium nanoparticles stabilised by N-substituted 1,3,5-triaza-7-phosphaadamantane ionic ligands were synthesised from Pd(II) precursors and characterised in neat glycerol, observing an important effect of the phosphine nature in the dispersion of the nanoclusters in solution. The most homogeneously dispersed nanoparticles (Pd1a) led to the best catalytic behaviour in the benchmark Suzuki–Miyaura reaction. From this screening, Pd1a was applied in different CC cross-couplings and hydrogenation reactions, isolating the expected products in high yields (>90%). An efficient catalyst immobilisation in glycerol was attained (up to ten runs without any sign of activity loss).

A Review of Luminescent Anionic Nano System: d10 Metallocyanide Excimers and Exciplexes in Alkali Halide Hosts.

Dicyanoaurate, dicyanoargentate, and dicyanocuprate ions in solution and doped in different alkali halide hosts exhibit interesting photophysical and photochemical behavior, such as multiple emission bands, exciplex tuning, optical memory, and thermochromism. This is attributed to the formation of different sizes of nanoclusters in solution and in doped hosts. A series of spectroscopic methods (luminescence, UV-reflectance, IR, and Raman) as well as theoretical calculations have confirmed the existence of excimers and exciplexes. This leads to the tunability of these nano systems over a wide wavelength interval. The population of these nanoclusters varies with temperature and external laser irradiation, which explains the thermochromism and optical memory. DFT calculations indicate an MLCT transition for each nanocluster and the emission energy decreases with increasing cluster size. This is in agreement with the relatively long life-time for the emission peaks and the multiple emission peaks dependence upon cluster concentration.

Nondestructive Size Determination of Thiol-Stabilized Gold Nanoclusters in Solution by Diffusion Ordered NMR Spectroscopy

Diffusion ordered NMR spectroscopy (DOSY) was used as an analytical tool to estimate the size of thiol-stabilized gold nanoclusters in solution, namely, phenylethanethiol (PET) stabilized Au25(PET)18, Au38(PET)24, and Au144(PET)60. This was achieved by determining the diffusion coefficient and hydrodynamic radius from solution samples that were confirmed to be monodispersed by electrospray ionization mass spectrometry. The average cluster diameters obtained by this technique were estimated to be 1.7, 2.2, and 3.1 nm for the Au25(PET)18, Au38(PET)24, and Au144(PET)60 nanoclusters, respectively, which were shown to agree well with the average diameters of the corresponding single crystal or theoretical structures reported in the literature. Consequently, the DOSY technique is demonstrated to be a potentially valuable nondestructive tool for characterization of nanoparticle mixtures and verifying the purity of product solutions.