Oligonucleotide-stabilized Ag nanocluster fluorophores

Single-stranded oligonucleotides stabilize highly fluorescent Ag nanoclusters, with emission colors tunable via DNA sequence. We utilized DNA microarrays to optimize these scaffold sequences for creating nearly spectrally pure Ag nanocluster fluorophores that are highly photostable and exhibit great buffer stability. Five different nanocluster emitters have been created with tunable emission from the blue to the near-IR and excellent photophysical properties. Ensemble and single molecule fluorescence studies show that oligonucleotide encapsulated Ag nanoclusters exhibit significantly greater photostability and higher emission rates than commonly used cyanine dyes.     

Investigation of Thermodynamic,Dynamic, and Structural Properties of H2 Adsorption on a Ag–Au Nanoalloy with a Carbon Nanotube Support

We have performed MD simulations to investigate H₂ adsorption on Ag–Au nanoclusters with the different Au mole fractions supported on the carbon nanotubes with the different diameters. Our thermodynamic results shown that the saturation value of coverage and the enthalpy of adsorption increases as the mole fraction of Au is increased. Our structural results showed that the presence of the H₂ gas exerts a significant effect on the nanocluster surface atoms and tends to stabilize the surface atoms on the nanocluster. Also, the structural changes are irreversible in such a way that by gradually decreasing the pressure to zero, the nanocluster geometry is not reversed to its initial structure in vacuum conditions. We have also shown that the nanoclusters have smaller values of the self‐diffusion coefficients in presence of H₂ molecules than those values in the initial state (vacuum), which is due to the increasing of the interface structure between the nanocluster and the nanotube.     

Anisole hydrogenation with well-characterized polyoxoanion- and tetrabutylammonium-stabilized Rh(0) nanoclusters: effects of added water and acid, plus enhanced catalytic rate, lifetime, and partial hydrogenation selectivity

Following a comprehensive look at the arene hydrogenation literature by soluble nanocluster catalysts, six key, unfulfilled goals in nanocluster arene hydrogenation catalysis are identified. To begin to address those six goals, well-characterized polyoxoanion- and tetrabutylammonium-stabilized Rh(0) nanoclusters have been synthesized by the reduction of the precisely defined precatalyst [Bu(4)N](5)Na(3)[(1,5-COD)Rh small middle dotP(2)W(15)Nb(3)O(62)] with H(2) in propylene carbonate solvent. These Rh(0) nanoclusters are characterized by their stoichiometry of formation, transmission electron microscopy, and the two rate constants which characterize their mechanism of formation; previous studies in our laboratories have provided additional characterization of polyoxoanion-stabilized Rh(0) nanoclusters. Propylene carbonate solutions of the Rh(0) nanoclusters catalyze the hydrogenation of anisole (methoxybenzene) under mild conditions (22-78 degrees C, 30-40 psig H(2)). Proton donors such as water or HBF(4) small middle dotEt(2)O are discovered to affect both nanocluster formation and nanocluster arene hydrogenation catalysis. Under identical conditions, the Rh(0) nanoclusters are 10-fold more active than a commercially available, oxide-supported 5% Rh/Al(2)O(3) catalyst of the same average metal-particle size. A series of lifetime experiments shows that the Rh(0) nanoclusters are capable of at least 2600 total turnovers (TTO), a lifetime significantly longer than the approximately 100 TTO often seen for nanocluster arene hydrogenation catalysts, and a lifetime slightly better than the prior record of 2000 TTO for a literature nanocluster system. The present polyoxoanion-stabilized Rh(0) nanoclusters also display a record, albeit modest, 30% selectivity for the partial hydrogenation of anisole to 1-methoxycyclohexene with an overall yield of up to 8% at higher temperatures. In comparison to the 5% Rh/Al(2)O(3) catalyst, the polyoxoanion-stabilized nanoclusters yield a 4.7-fold higher maximum yield of 1-methoxycyclohexene. Finally, the seven main findings of the present work are summarized, including how they address five of the aforementioned six main goals in nanocluster arene hydrogenation.     

New algorithm in the basin hopping Monte Carlo to find the global minimum structure of unary and binary metallic nanoclusters

The basin-hopping Monte Carlo algorithm was modified to more effectively determine a global minimum structure in pure and binary metallic nanoclusters. For a pure metallic Ag55 nanocluster, the newly developed quadratic basin-hopping Monte Carlo algorithm is 3.8 times more efficient than the standard basin-hopping Monte Carlo algorithm. For a bimetallic Ag42Pd13 nanocluster, the new algorithm succeeds in finding the global minimum structure by 18.3% even though the standard basin-hopping Monte Carlo algorithm fails to achieve it.     

A test of the transition-metal nanocluster formation and stabilization ability of the most common polymeric stabilizer, poly(vinylpyrrolidone), as well as four other polymeric protectants

Following an introduction to the nanocluster stabilization literature and DLVO (Derjaugin-Landau-Verwey-Overbeek) theory of colloidal stability, the most common steric stabilizer of transition-metal nanoclusters, poly(vinylpyrrolidone) (PVP), has been examined for its efficacy in the formation, stabilization, and subsequent catalytic activity of prototype, test case Ir(0)n nanoclusters. First, the five criteria established previously for ranking nanocluster protectants for their nanocluster formation and stabilization ability were evaluated for 1 monomer equiv of 10000 average molecular weight (MWav) PVP in the absence, and then presence, of the traditionally weakly coordinating anion BF4- as well as the absence and presence of the strongly coordinating, superior anionic stabilizer P2W15Nb3O62(9-), all in propylene carbonate solvent. It is found that neither 1 equiv of BF4- in propylene carbonate nor 1 monomer equiv of (undried) PVP alone allows for isolable and redissolvable nanoclusters without bulk Ir(0)n metal formation. Careful predrying of the PVP, and by implication other polymers, is shown to be necessary for the formation and stabilization of the nanoclusters. Next, 40 monomer equiv of 10000 MWav PVP and 1 equiv of BF4- in propylene carbonate are shown to allow isolable, redissolvable nanoclusters. Control experiments reveal little difference on nanocluster stabilization by 3500 or 55000 (i.e., vs 10,000) MWav PVP, but yield interesting effects on nanocluster nucleation by the 3500 MWav PVP, as well as by the polymer poly(bis(ethoxy)phosphazene) (PBEP). Four other key polymers reported in the literature to be nanocluster stabilizers are tested by the five criteria method for their efficacy in the formation and stabilization of Ir0n nanoclusters (now in acetone due to the polymers' solubility) and in comparison to each other, specifically, poly(methyl methacrylate) (PMMA), poly(styrene) (PS), poly(methylhydrosilane) (PMHS), and PBEP. Only 40 monomer equiv dried PMMA allows isolable and redissolvable nanoclusters in acetone. Control/reference point experiments show that the electrostatic stabilizer P2W15Nb3O62(9-) is superior to each of the five polymeric stabilizers studied herein in both acetone and propylene carbonate, at least for the test case of Ir(0)n nanoclusters. Further controls show that 40 monomer equiv of PVP added to P2W15Nb3O(62)9--stabilized nanoclusters has no discernible effect on the five criteria other than to reduce by approximately 50% the nanocluster catalytic activity and total catalytic lifetime for cyclohexene hydrogenation. The main finding of this work is that DLVO theory as applied to nanocluster stabilization is fully supported; that is, surface-bound anions in high dielectric constant solvents provide superior stabilization. The importance of even traditionally weakly coordinating anions such as BF4- in nanocluster stabilization is a second, important finding of this work. The fact that HPO4(2-) has been shown to be a simple, cheap, commercially available, thermally robust, and 31P-NMR-handle-containing analogue of the more esoteric P2W15Nb3O62(9-) stabilizer is also discussed in the 14 total Conclusions from this first study ranking polymeric stabilizers of modern transition-metal nanoclusters.     

Au130−xAgx Nanoclusters with Non‐Metallicity: A Drum of Silver‐Rich Sites Enclosed in a Marks‐Decahedral Cage of Gold‐Rich Sites

The synthesis and structure of atomically precise Au_130?xAg_x (average x=98) alloy nanoclusters protected by 55 ligands of 4‐tert‐butylbenzenethiolate are reported. This large alloy structure has a decahedral M₅₄ (M=Au/Ag) core. The Au atoms are localized in the truncated Marks decahedron. In the core, a drum of Ag‐rich sites is found, which is enclosed by a Marks decahedral cage of Au‐rich sites. The surface is exclusively Ag?SR; X‐ray absorption fine structure analysis supports the absence of Au?S bonds. The optical absorption spectrum shows a strong peak at 523 nm, seemingly a plasmon peak, but fs spectroscopic analysis indicates its non‐plasmon nature. The non‐metallicity of the Au_130?xAg_x nanocluster has set up a benchmark to study the transition to metallic state in the size evolution of bimetallic nanoclusters. The localized Au/Ag binary architecture in such a large alloy nanocluster provides atomic‐level insights into the Au?Ag bonds in bimetallic nanoclusters.     

Novel application of Ag nanoclusters in fluorescent imaging of human serum proteins after native polyacrylamide gel electrophoresis (PAGE)

We have developed a novel application for DNA oligonucleotide-stabilized Ag nanoclusters in fluorescent imaging of human serum proteins after native polyacrylamide gel electrophoresis (PAGE). Oligonucleotide-stabilized Ag nanoclusters were used as fluorescent probes for direct detection of proteins after native PAGE. Some relatively low-abundance proteins, such as α-1-antichymotrypsin (ACT) and α-2-glycoprotein 1, zinc (ZAG) were easily detected by oligonucleotide-stabilized Ag nanocluster-based fluorescent imaging and identified by MS and MS/MS techniques, without the need of expensive antibodies or tedious immunoassay procedures. The pH condition for the oligonucleotide-stabilized Ag nanocluster solution was optimized and the possible mechanism of interaction between proteins and DNA oligonucleotide-stabilized Ag nanoclusters was analyzed. As a novel fluorescent detection method it is simple, fast, nontoxic and sensitive, and it shows great analytical potential in proteome research and in biochemistry.     

银镍合金团簇Ag4Ni2(SPhMe2)8 (SPhMe2 = 2, 4-二甲基苯硫酚)的合成及其结构表征

具有精确结构的纳米团簇因其有利于分析团簇结构与性质之间的关系而被广为研究。之前的研究结果表明金属银和金属镍在亚纳米尺寸可以形成团簇(Ag₄Ni₂(DMSA)₄ (DMSA =二巯基丁二酸),但其晶体结构并没有得到具体表征。在本工作中,我们合成了硫醇配体保护的银镍合金纳米团簇：Ag₄Ni₂(SPhMe₂)₈ (SPhMe₂ = 2, 4-二甲基苯硫酚),并通过X射线单晶衍射、X射线光电子能谱、质谱和热失重等分析手段对结构进行了表征和确认。该工作拓展了合金团簇的基础研究。     

CO oxidation on unsupported Au55, Ag55, and Au25Ag30 nanoclusters

Using density functional calculations, we demonstrate a catalytic reaction path with activation barriers of less than 0.5 eV for CO oxidation on the neutral and unsupported icosahedral nanoclusters of Au(55), Ag(55), and Au(25)Ag(30). Both CO and O(2) adsorb more strongly on these clusters than on the corresponding bulk surfaces. The reaction path consists of an intermediate involving OOCO complex through which the coadsorption energy of CO and O(2) on these clusters is expected to play an important role in the reaction. Based on the studies for the Au and Ag nanoclusters, a model alloy nanocluster of Au(25)Ag(30) was designed to provide a larger coadsorption energy for CO and O(2) and was anticipated to be a better catalyst for CO oxidation from energetic analysis.     

Nanocluster formation and stabilization fundamental studies: ranking commonly employed anionic stabilizers via the development,then application,of five comparative criteria

To start, a brief introduction is provided on the importance of transition-metal nanoclusters, on the need to develop and then apply methods to rank the nanocluster formation and then stabilizing abilities of commonly employed anions, solvents, cations, and polymers, and on the somewhat confused literature of nanocluster stabilization. The fundamental importance of surface-adsorbed anions in transition-metal nanocluster stabilization is noted, the reason the present studies begin with a study of nanocluster-stabilizing anions. Next, five criteria, as well as the associated experimental methods, are developed to evaluate the efficacy of nanocluster stabilizing agents. The criteria are of fundamental significance in that they allow the separation of stabilizing agent effects on nanocluster formation from those on nanocluster stabilization. The results from applying the five criteria to four commonly employed anions lead to the first "anion series" of relative nanocluster-formation and stabilizing abilities, at least for the Ir(0) nanoclusters examined and by the following five criteria: [(P(2)W(15)Nb(3)O(61))(2)O](16-) (a Brphinsted-basic polyoxoanion) > C(6)H(5)O(7)(3-) (citrate trianion) > [-CH(2)-CH(CO(2))-](n)(n-) (polyacrylate) approximately Cl(-). In addition to the needed methods and the first anion series, six other (8 total) conclusions are reached, important insights in an area previously lacking hard information about which anions are the better choices for nanocluster formation and stabilization. The results are also of significance in establishing polyoxoanions, notably highly charged and basic polyoxoanions such as [(P(2)W(15)Nb(3)O(61))(2)O](16)(-), as the present "Gold Standards" among currently known nanocluster stabilizing anions, and according to the above five criteria. Such standards provide a reference point for future work aspiring to develop even better nanocluster stabilizing anions, solvents, cations, and polymers or their combinations.     

Formation of bimetallic Ag-Pd nanoclusters via the reaction between Ag nanoclusters and Pd2+ ions

We have investigated systematically the mechanistic aspects of the Ag-Pd bimetallic cluster formation within sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles by using in-situ X-ray absorption spectroscopy (XAS). A two-step sequential reduction method is employed for the synthesis of Ag-Pd bimetallic clusters. The first step involves preparation of Ag nanoclusters, by mixing the Ag+ ions containing the AOT microemulsion system with a reducing agent hydrazine (N2H4) containing the AOT microemulsion system. In the second step, the addition of Pd2+ ions to Ag nanoclusters led to the formation of Ag-Pd bimetallic clusters via the reaction between Ag nanoclusters and Pd2+ ions in AOT reverse micelles. The reduction of silver ions and the formation of corresponding Ag nanoclusters are monitored as a function of the dosage of the reducing agent, hydrazine. In-situ XAS allowed probing of the reaction between Ag nanoclusters and Pd2+ ions during the formation of Ag-Pd bimetallic clusters. Analysis of Ag and Pd K-edge XAS spectra reveals that in the final stage Ag-Pd clusters, in which "Ag" atoms prefer to be surrounded by "Pd" and "Pd" atoms prefer to be surrounded by "Pd", were formed. On the basis of XAS results presented here, we are able to propose a structural model for each step so that this work provides a detailed insight into the mechanism of nucleation and growth of Ag-Pd bimetallic clusters. We also discussed the atomic distribution of Ag and Pd atoms in Ag-Pd bimetallic clusters based on the calculated XAS structural parameters.     

Sandwich-Kernelled AgCu Nanoclusters with Golden Ratio Geometry and Promising Photothermal Efficiency

Metal nanoclusters have recently attracted extensive interest from the scientific community. However, unlike carbon-based materials and metal nanocrystals, they rarely exhibit a sheet kernel structure, probably owing to the instability caused by the high exposure of metal atoms (particularly in the relatively less noble Ag or Cu nanoclusters) in such a structure. Herein, we synthesized a novel AgCu nanocluster with a sandwich-like kernel (diameter≈0.9 nm and length≈0.25 nm) by introducing the furfuryl mercaptan ligand (FUR) and the alloying strategy. Interestingly, the kernel consists of a centered silver atom and two planar Ag₁₀ pentacle units with completely mirrored symmetry after a rotation of 36 degrees. The two Ag₁₀ pentacles and some extended structures show an unreported golden ratio geometry, and the two inner five-membered rings and the centered Ag atom form an unanticipated full-metal ferrocene-like structure. The featured kernel structure causes the dominant radial direction transition of excitation electrons, as determined via time-dependent density functional theory calculations, which affords the protruding absorption at 612 nm and contributes to the promising photothermal conversion efficiency of 67.6 % of the as-obtained nanocluster, having important implications for structure-property correlation and the development of nanocluser-based photothermal materials.     

Adsorption of sarin and chlorosarin onto the Al12N12 and Al12P12 nanoclusters: DFT and TDDFT calculations

This study provides details of the electronic and optical structures and binding energies of sarin (SF) and chlorosarin (SC) with Al–N and Al–P surfaces of Al₁₂N₁₂ and Al₁₂P₁₂ nanoclusters in the gas phase. The adsorption mechanism of SF and SC on these nanoclusters containing the Al³⁺ central cation was studied. Optimized geometries and thermodynamic parameters of SF and SC adsorption complexes were calculated. SF and SC are chemisorbed on these nanoclusters because of the formation of PO···Al bonds. The chemical bond is formed between an oxygen atom of SF and SC and an aluminum atom of fullerene-likes (chemisorption). However, the binding energies of the complexes with the Al₁₂N₁₂ nanocluster are larger than these values for the Al₁₂P₁₂ nanocluster. The interaction enthalpy and Gibbs free energy of all studied systems were found to be negative. We can conclude that SF and SC will be adsorbed preferably on Al₁₂N₁₂ nanocluster.     

Effect of the organic solvent on the formation and stabilization of CdS and PbS nanoclusters

Nanoclusters of CdS and PbS were prepared using two different organic solvents as stabilizers in order to understand the factors affecting their formation and stabilization. Growth of the nanoclusters was monitored by optical absorption spectroscopy at regular intervals of time. Mean cluster size was characterized by X-ray diffraction (XRD). The surface structure of nanoclusters was analyzed using infrared (IR) spectroscopy. Spectroscopic studies under identical experimental conditions reveal interesting correlations between the stability of the nanoclusters formed, the nature of the solvent and the size of metal ion involved, leading to a better understanding of nanocluster formation.     

An Ultrastable,Small {Ag7}5+ Nanocluster within a Triangular Hollow Polyoxometalate Framework

Small Ag_n nanoclusters (n<10) have been emerging as promising materials as sensing, biolabeling, and catalysis because of their unique electronic states and optical properties. However, studying synthesis, structure determination, and exploration of their properties remain major challenges as a result of the low stability of small Ag nanoclusters. Herein, we synthesized an atomically precise face-centered-cubic-type small {Ag₇}⁵⁺ nanocluster supported by a novel triangular hollow polyoxometalate (POM) framework [Si₃W₂₇O₉₆]¹⁸⁻. The cluster showed unique {Ag₇}⁵⁺-to-POM charge transfer bands in both visible and UV light regions. Furthermore, this small {Ag₇}⁵⁺ nanocluster exhibited an unprecedented ultrastability in solution, despite having exposed Ag sites that can be accessed by small molecules, such as O₂, water, and solvents.     

Combined synthesis of interconvertible Au11Cd and Au26Cd5 for photocatalytic oxidations involving singlet oxygen

A novel Au₁₁Cd nanocluster was synthesized by developing a combined method and controlling the kinetics, and another Au₂₆Cd₅ nanocluster was also obtained after the conditions were changed in the same reaction, which could transfer to Au₁₁Cd in a two-way style. Both alloy nanoclusters can photocatalyze the production of singlet oxygen (¹O₂) and exhibit enhanced efficiencies in photocatalyzing two kinds of organic oxidations involving singlet oxygen compared with their non-alloyed mother nanoclusters, indicating that the Cd-doping might be an efficient way to enhance the photocatalysis performance of gold nanoclusters and metal nanoclusters are promising photocatalysts for organic oxidation involving singlet oxygen.     

Structural effects of DNA on thermodynamic stability of DNA-dendronized polymer nanoclusters and nanoclusteration process

We studied the means by which DNA-dendronized polymer nanoclusters and the nanoclusteration process are affected by structural properties of the nanocluster components, including the length of dendronized polymer, wrapping radius of DNA, and surface charge densities on the DNA and dendronized polymer, by calculating the total free energy of the system and free energy of the nanoclusteration process. The most thermodynamically stable nanocluster conformation was then predicted based on the values of the free energies. It was found that the nanoclusters with longer dendronized polymers, shorter DNA wrapping radius, and larger surface charge density on both the DNA and dendronized polymers are more stable.     

An Ultrastable,Small {Ag7}5+ Nanocluster within a Triangular Hollow Polyoxometalate Framework

Small Ag_n nanoclusters (n<10) have been emerging as promising materials as sensing, biolabeling, and catalysis because of their unique electronic states and optical properties. However, studying synthesis, structure determination, and exploration of their properties remain major challenges as a result of the low stability of small Ag nanoclusters. Herein, we synthesized an atomically precise face‐centered‐cubic‐type small {Ag₇}⁵⁺ nanocluster supported by a novel triangular hollow polyoxometalate (POM) framework [Si₃W₂₇O₉₆]^18?. The cluster showed unique {Ag₇}⁵⁺‐to‐POM charge transfer bands in both visible and UV light regions. Furthermore, this small {Ag₇}⁵⁺ nanocluster exhibited an unprecedented ultrastability in solution, despite having exposed Ag sites that can be accessed by small molecules, such as O₂, water, and solvents.     

Rapid Conversion of a Au9Ag12 into a AuxAg16-x Nanocluster via Bisphosphine Ligand Engineering

The [Au_xAg_16-x(SAdm)₈(Dppe)₂] nanocluster with aggregation-induced emission (AIE) was synthesized from a non-fluorescent [Au₉Ag₁₂(SAdm)₄(Dppm)₆Cl₆](SbF₆)₃ nanocluster via a ligand-exchange engineering (Dppe=1,2-Bis(diphenylphosphino)ethane, Dppm=Bis(diphenylphosphino)methane, HSAdm=1-Adamantanethiol). The nanocluster has a Au-doped icosahedral Au_xAg_13-x core, capped by two Ag(SR)₃, one Ag(SR)₂ and two Dppe ligands. By changing the achiral Dppe ligand into a chiral dbpb ligand ((2S,3S)-(-)-Bis(diphenylphosphino)butane or (2R,3R)-(+)-2,3-Bis(diphenylphosphino)butane), chiral nanoclusters are obtained. ESI-MS and UV-vis spectroscopy were performed to track the reaction. This work provides guidance for the construction of new clusters by etching clusters with multidentate phosphine ligands.     

透光导电金属及氧化铂半导体薄膜的制备与表征

通过PPh~3对“非保护型”铂金属纳米簇进行表面修饰,并将其萃取至甲苯中,制备的PPh~3修饰的Pt金属钠米簇于空气中可自发地在玻璃表面生长出均匀透光的金属钠米簇薄膜。该金属钠米簇薄膜经空气中加热处理后可转化为透光导电的氧化铂半导体薄膜。考察了金属钠米簇薄膜生长过程中UV-vis吸收光谱的变化。采用SEM和TEM等方法,表征了纳米簇的粒径及膜的多孔结构,由此解释了其透光原因。研究了薄膜的导电性与处理条件的关系,并采用XPS表征了处理过程中的物质变化。初步探索了PPh~3-Pt纳米簇自发成膜过程的机理,确定了氧气在此过程中的重要作用。