Icosahedral Core Research Articles

Monoplatinum Doping of Gold Nanoclusters and Catalytic Application

We report single-atom doping of gold nanoclusters (NCs), and its drastic effects on the optical, electronic, and catalytic properties, using the 25-atom system as a model. In our synthetic approach, a mixture of Pt(1)Au(24)(SC(2)H(4)Ph)(18) and Au(25)(SC(2)H(4)Ph)(18) was produced via a size-focusing process, and then Pt(1)Au(24)(SC(2)H(4)Ph)(18) NCs were obtained by selective decomposition of Au(25)(SC(2)H(4)Ph)(18) in the mixture with concentrated H(2)O(2) followed by purification via size-exclusion chromatography. Experimental and theoretical analyses confirmed that Pt(1)Au(24)(SC(2)H(4)Ph)(18) possesses a Pt-centered icosahedral core capped by six Au(2)(SC(2)H(4)Ph)(3) staples. The Pt(1)Au(24)(SC(2)H(4)Ph)(18) cluster exhibits greatly enhanced stability and catalytic activity relative to Au(25)(SC(2)H(4)Ph)(18) but a smaller energy gap (E(g) ≈ 0.8 eV vs 1.3 eV for the homogold cluster).

Structure-Correlated Dual Fluorescent Bands in BSA-Protected Au25 Nanoclusters

In this work, we investigated the temperature-dependent luminescence of bovine serum albumin-protected Au25 nanoclusters and the correlation with their structure. Our experiments reveal that the red luminescence consists of two bands, namely, band I at 710 nm and band II at 640 nm. The temperature dependence of band I exhibits similarity to semiconductors, such as a red shift of emission and bandwidth broadening upon increasing temperatures due to electron–phonon and electron–defect/surface scattering. In contrast, band II exhibits different temperature dependence. It is concluded that band I exclusively originates from the icosahedral core of 13 Au(0) atoms and band II dominantly arises from the [−S–Au(I)–S–Au(I)–S−] staples. Moreover, with increasing temperatures, the intensity of band I and band II decreases. A similar activation energy was extracted, which is attributed to thermally activated defect/surface trapping. In addition, the relaxation from band II to band I was found to be inactive from 300 ...

Formation of fivefold axes in the FCC-metal nanoclusters

Formation of atomistic structures of metallic Cu, Au, Ag clusters and bimetallic Cu–Au clusters was studied with the help of molecular dynamics using the many-body tight-binding interatomic potential. The simulation of the crystallization process of clusters with the number of atoms ranging from 300 to 1092 was carried out. The most stable configurations of atoms in the system, corresponding to the minimum of potential energy, was found during super-fast cooling from 1000K. Atoms corresponding to fcc, hcp, and Ih phases were identified by the method of common neighbor analysis. Incomplete icosahedral core can be discovered at the intersection of one of the Ih axes with the surface of monometallic cluster. The decahedron-shaped structure of bimetallic Cu–Au cluster with seven completed icosahedral cores was obtained. The principles of the construction of small bimetallic clusters with icosahedral symmetry and increased fractal dimensionality were offered.

Icosahedral to double-icosahedral shape transition of copper clusters

The lowest-energy isomers of Cu(N) clusters for N = 20-30 are identified using an unbiased search algorithm and density functional theory calculations. The low-energy structures over this size range are dominated by those based on a 13-atom icosahedral (I(h)) core and a 19-atom double icosahedron (DI(h)) core. A transition in the ground-state isomers from I(h)-based to DI(h)-based structures is predicted overt N = 21-23. We discuss this transition in the broader context of the growth pattern for Cu(N) over N = 2-30 that features regions of gradual evolution in which atoms successively add to the cluster surface, separated by sudden changes to a different structural organization and more compact shape. These transitions result from a competition between interatomic bonding energy and surface energy. The implications of this growth pattern for the further evolution of copper from microstructure to bulk are discussed.

Ag7Au6: A 13‐Atom Alloy Quantum Cluster

An alloy cluster containing a 13-atom core, with a composition Ag 7 Au 6 (H 2 MSA) 10 (H 2 MSA=mercaptosuccinic acid) was synthesized from silver clusters by a galvanic exchange reaction. The clusters were characterized by several spectroscopic and microscopic methods. The alloy cluster shows luminescence with a quantum yield of 3.5×10 -2 at room temperature. Theoretical calculations for Ag 7 Au 6 (SCH 3 ) 10 suggest a distorted icosahedral core.

Surface decorated platinum carbonyl clusters

Four molecular Pt-carbonyl clusters decorated by Cd-Br fragments, i.e., [Pt(13)(CO)(12){Cd(5)(μ-Br)(5)Br(2)(dmf)(3)}(2)](2-) (1), [Pt(19)(CO)(17){Cd(5)(μ-Br)(5)Br(3)(Me(2)CO)(2)}{Cd(5)(μ-Br)(5)Br(Me(2)CO)(4)}](2-) (2), [H(2)Pt(26)(CO)(20)(CdBr)(12)](8-) (3) and [H(4)Pt(26)(CO)(20)(CdBr)(12)(PtBr)(x)](6-) (4) (x = 0-2), have been obtained from the reactions between [Pt(3n)(CO)(6n)](2-) (n = 2-6) and CdBr(2)·H(2)O in dmf at 120 °C. The structures of these molecular clusters with diameters of 1.5-2 nm have been determined by X-ray crystallography. Both 1 and 2 are composed of icosahedral or bis-icosahedral Pt-CO cores decorated on the surface by Cd-Br motifs, whereas 3 and 4 display a cubic close packed Pt(26)Cd(12) metal frame decorated by CO and Br ligands. An oversimplified and unifying approach to interpret the electron count of these surface decorated platinum carbonyl clusters is suggested, and extended to other low-valent organometallic clusters and Au-thiolate nanoclusters.

Epitaxial growth of Au@Pd core–shell nanocrystals prepared using a PVP-assisted polyol reduction method

Au@Pd core–shell nanocrystals were prepared using a two-step polyol reduction method. First, decahedral Au core seeds with small amounts of octahedral, triangular-platelike, and icosahedral Au particles were prepared by reducing HAuCl4·4H2O in diethylene glycol (DEG) under oil-bath heating in the presence of polyvinylpyrrolidone (PVP) as a polymer surfactant. Then Pd shells were overgrown epitaxially on Au core seeds by reducing Na2PdCl4 in EG with PVP, KBr, and H2O. The resultant crystal shapes were characterized using transmission electron microscopic (TEM), TEM-energy dispersed X-ray spectroscopic (EDS), and selected area electron diffraction (SAED) measurements. Effects of addition of KBr and H2O in the second step and reaction temperature for the yield of core–shell particles and their shape, size, and composition distributions were examined. Results show that both {111} and {100} facets of Pd shells were formed in the presence of KBr, depending on the shapes of Au core seeds, whereas only {111} facets were produced in the absence of KBr. New triangular-platelike, five-twin rod, decahedral, and icosahedral shapes of Au@Pd nanocrystals were prepared using triangular-platelike, decahedral, and icosahedral Au cores. When decahedral Au particles were used as seeds, monodispersed decahedral Au@Pd nanocrystals were prepared in high yield at low temperatures of 20–100 °C in PVP/EG solution. Au acts as a catalyst for Pd2+ reduction in the presence of PVP at low temperatures. This work demonstrates a simple two-step technique for the epitaxial growth of various shapes of Au@Pd nanocrystals.

Epitaxial Growth of Au@Ni Core−Shell Nanocrystals Prepared Using a Two-Step Reduction Method

Au@Ni core−shell nanocrystals were prepared using a two-step reduction method. First, mixtures of octahedral, triangular and hexagonal platelike, decahedral, and icosahedral Au core seeds were prepared by reducing HAuCl4·4H2O in ethylene glycol (EG) using microwave (MW) heating in the presence of polyvinylpyrrolidone (PVP) as a polymer surfactant. Then, Ni shells were overgrown on Au core seeds by reducing Ni(NO3)2·6H2O in EG with NaOH and PVP using oil bath heating. Resultant crystal structures were characterized using transmission electron microscopic (TEM), high-resolution TEM, TEM−energy dispersed X-ray spectroscopic (EDS), selected area electron diffraction (SAED), and X-ray diffraction (XRD) measurements. Because a very large mismatch (13.6%) exists in lattice constants between Au (0.4079 nm) and Ni (0.3524 nm), the epitaxial growth of Ni shells over Au cores was expected to be difficult. Nevertheless, about 40 monolayers of Ni{111} shells were grown epitaxially on flat planes and sharp corners of Au{111} cores after heating reagent solution at 175 °C for 2 h. The SAED patterns showed Ni layers parallel to Au layers. This result is contrasted with our recent result for Au@Cu with a smaller lattice mismatch between Au and Cu (11.4%). In the case of Au@Cu, although the epitaxial growth of Cu{111} shells over Au core was observed, the growth rate on sharp corners was slower than that on flat {111} facets. Our results and reported data show that the lattice mismatch is not a significant factor for the crystal growth of Au@Ni on sharp corners.

In vivo phosphorylation patterns of key stressosome proteins define a second feedback loop that limits activation of Bacillus subtilis σB

The Bacillus subtilis stressosome is a 1.8 MDa complex that orchestrates activation of the σ(B) transcription factor by environmental stress. The complex comprises members of the RsbR co-antagonist family and the RsbS antagonist, which together form an icosahedral core that sequesters the RsbT serine-threonine kinase. Phosphorylation of this core by RsbT is associated with RsbT release, which activates downstream signalling. RsbRA, the prototype co-antagonist, is phosphorylated on T171 and T205 in vitro. In unstressed cells T171 is already phosphorylated; this is a prerequisite but not the trigger for activation, which correlates with stress-induced phosphorylation of RsbS on S59. In contrast, phosphorylation of RsbRA T205 has not been detected in vivo. Here we find (i) RsbRA is additionally phosphorylated on T205 following strong stresses, (ii) this modification requires RsbT, and (iii) the phosphorylation-deficient T205A substitution greatly increases post-stress activation of σ(B) . We infer that T205 phosphorylation constitutes a second feedback mechanism to limit σ(B) activation, operating in addition to the RsbX feedback phosphatase. Loss of RsbX function increases the fraction of phosphorylated RsbS and doubly phosphorylated RsbRA in unstressed cells. We propose that RsbX both maintains the ready state of the stressosome prior to stress and restores it post-stress.

Templated self-assembly of patchy particles

We explore the use of templated self-assembly to facilitate the formation of complex target structures made from patchy particles. First, we consider the templating of high-symmetry shell structures around a spherical core particle. We find that nucleation around the core particle can inhibit aggregate formation, a process which often hinders self-assembly. In particular, this new assembly pathway allows dodecahedral shells to form readily, whereas these structures never form in the absence of the template. Secondly, we consider the self-assembly of multi-shell structures, where the central icosahedral core is known to form readily on its own, and which could then template the growth of further layers. We are able to find conditions under which two- and three-shell structures successfully assemble, illustrating the power of the templating approach.

Nucleation and Growth of Stellated Gold Clusters: Experimental Synthesis and Theoretical Study

An experimental and theoretical study on the structure and energetics of stellated gold clusters at several sizes is presented. Systematic molecular dynamics simulations on Kepler−Poisont classified clusters are performed based on cuboctahedral and icosahedral cores, following present and previous studies that suggest that stellated clusters grew from these seeds. For cluster sizes up to 10802 atoms, full atomistic molecular dynamics simulations at room temperature have been carried out. Results show that stellated clusters in the bigger size regime maintain their star-like shape at room temperature, and by means of linear fitting of energy data to proper function models, it is predicted that the two types of stellated structures might coexist at room temperature for relatively large sizes, these findings being in good agreement with experimental results.

Epitaxial Growth of Au@Cu Core−Shell Nanocrystals Prepared Using the PVP-Assisted Polyol Reduction Method

Au@Cu core-shell nanocrystals were prepared using a two-step polyol reduction method. First, mixtures of ochedral, triangular and hexagonal platelike, decahedral, and icosahedral Au core seeds were prepared by reducing HAuCl 4 ·4H 2 O in ethylene glycol (EG) using microwave (MW) heating in the presence of polyvinylpyrrolidone (PVP) as a polymer surfactant. Then Cu shells were overgrown on Au core seeds by reducing Cu 2 (OAc) 4 in EG with PVP using oil-bath heating. Resultant crystal structures were characterized using TEM, high-resolution (HR)-TEM, TEM-EDS, and selected area electron diffraction (SAED) measurements. A large mismatch exists in lattice constants between Au (0.4079 nm) and Cu (0.3615 nm). No monometallic Cu nanocrystals having well-defined facets were prepared by reducing Cu 2 (OAc) 4 in EG. Therefore, the epitaxial growth ofCu shells over Au cores was expected to be difficult. Nevertheless, flat {111} facets of Cu shells were grown epitaxially on {111} facets of Au cores. The SAED patterns and Moire patterns showed Cu layers parallel to Au layers. The Cu shell growth on sharp Au-core corners was slower than that on flat {111} facets and single twin facets. This report is the first describing epitaxial growth of core—shell nanocrystals despite a large lattice mismatch (11.4%). The Au@Cu nanoparticles were more antioxidative than pure Cu particles prepared under identical conditions.

Crystal Structures and Growth Mechanisms of Icosahedral Au@Ag Core−Shell and Au/Ag Twin Nanocrystals Prepared by PVP-Assisted N,N-Dimethylformamide Reduction

Icosahedral Au@Ag core−shell nanocrystals have been prepared using a two-step reduction method. In the first step, icosahedral Au core seeds were prepared by reducing HAuCl4·4H2O in tetraethylene glycol (TEG) under microwave (MW) heating in the presence of polyvinylpyrrolidone (PVP) as a polymer surfactant. In the second step, Ag shells were overgrown on icosahedral Au seeds in N,N-dimethylformamide (DMF) in the presence of PVP under oil-bath heating for 3 h or MW heating for 10 min. Crystal structures of products were characterized using TEM, TEM-EDS, and SEM. Under oil-bath heating, Au@Ag icosahedral nanocrystals nearly fully covered by Ag shells were prepared, whereas those partially covered by tetrahedral units of Ag shells were formed under MW heating. On the basis of these findings, it was concluded that icosahedral Au@Ag core−shell particles are formed through stepwise growth of tetrahedral units, as observed in the crystal growth of monometallic icosahedral Ag crystals in DMF. There were minor Au/...

The Story of a Monodisperse Gold Nanoparticle: Au25L18

Au nanoparticles (NPs) with protecting organothiolate ligands and core diameters smaller than 2 nm are interesting materials because their size-dependent properties range from metal-like to molecule-like. This Account focuses on the most thoroughly investigated of these NPs, Au(25)L(18). Future advances in nanocluster catalysis and electronic miniaturization and biological applications such as drug delivery will depend on a thorough understanding of nanoscale materials in which molecule-like characteristics appear. This Account tells the story of Au(25)L(18) and its associated synthetic, structural, mass spectrometric, electron transfer, optical spectroscopy, and magnetic resonance results. We also reference other Au NP studies to introduce helpful synthetic and measurement tools. Historically, nanoparticle sizes have been described by their diameters. Recently, researchers have reported actual molecular formulas for very small NPs, which is chemically preferable to solely reporting their size. Au(25)L(18) is a success story in this regard; however, researchers initially mislabeled this NP as Au(28)L(16) and as Au(38)L(24) before correctly identifying it by electrospray-ionization mass spectrometry. Because of its small size, this NP is amenable to theoretical investigations. In addition, Au(25)L(18)'s accessibility in pure form and molecule-like properties make it an attractive research target. The properties of this NP include a large energy gap readily seen in cyclic voltammetry (related to its HOMO-LUMO gap), a UV-vis absorbance spectrum with step-like fine structure, and NIR fluorescence emission. A single crystal structure and theoretical analysis have served as important steps in understanding the chemistry of Au(25)L(18). Researchers have determined the single crystal structure of both its "native" as-prepared form, a [N((CH(2))(7)CH(3))(4)(1+)][Au(25)(SCH(2)CH(2)Ph)(18)(1-)] salt, and of the neutral, oxidized form Au(25)(SCH(2)CH(2)Ph)(18)(0). A density functional theory (DFT) analysis correctly predicted essential elements of the structure. The NP is composed of a centered icosahedral Au(13) core stabilized by six Au(2)(SR)(3) semirings. These semirings present interesting implications regarding other small Au nanoparticle clusters. Many properties of the Au(25) NP result from these semiring structures. This overview of the identification, structure determination, and analytical properties of perhaps the best understood Au nanoparticle provides results that should be useful for further analyses and applications. We also hope that the story of this nanoparticle will be useful to those who teach about nanoparticle science.

Icosahedral B12-containing core–shell structures of B80

Low-lying icosahedral (I(h)) B(12)-containing structures of B(80) are explored, and a number of core-shell isomers are found to have lower energy than the previous predicted B(80) fullerene. The structural transformation of boron clusters from tubular structure to core-shell structure may occur at a critical size less than B(80).

Study of the structure evolution and ground state energy of ConCu55－n(n=0—55) bimetallic clusters by using the Gupta potential combined with a genetic algorithm

The ground-state structures and energies of the bimetallic clusters ConCu55－n(n=0—55) were obtained by using the semi-empirical Gupta potential combined with a genetic algorithm. The ground-state geometries of those bimetallic clusters can be characterized by the basic Mackay icosahedron of the pure Co55 (Cu55) cluster. Beginning with n=0 (Cu55), the Cu atom(s) is(are) replaced in order and continuously by the Co atom(s) from the center to the surface and from the edge to the vertex. The ground-state structure depends on the number of the Co—Co bonds which have the largest energy, the number of the Co-Cu bonds with large energy and the average bond length of those bonds. Co13Cu42 is a magic cluster with an icosahedral core formed by 13 Co atoms, which plays a key role in the high stability of those bimetallic clusters.

Electronic and Geometric Structure of the Cluster Compound Au55[P(C6H5)3]12Cl6. A Computational Study

Relativistic density functional calculations have been carried out on the model cluster Au55(PH3)12Cl6 assuming a cuboctahedral or an icosahedral Au55 metal core to model the experimentally suggested cluster compound assigned as Au55[P(C6H5)3]12Cl6. Besides the overall shape of the metal core, the study focused on the unresolved issue at which sites the chlorine ligands are attached. The calculations reproduce characteristic interatomic distances within ∼ 2 pm, with the exception of the Au-Cl bonds. Chlorine ligands were calculated to prefer higher coordinated sites whereas the previously postulated on-top coordination at the center of the Au (100) facets of a cuboctahedron was found to be unstable. In fact, the present model results suggest an ensemble of several higher coordinated sites. The often assumed cuboctahedral shape of the metal cluster core was determined to be slightly less stable than an approximately icosahedral shape. The calculations allow a rationalization of the difficulties faced in experiments that attempted to discriminate cluster isomers

Structural Characterization of Pt−Pd and Pd−Pt Core−Shell Nanoclusters at Atomic Resolution

We describe the results of a study at atomic resolution of the structures exhibited by polymer-capped monometallic and bimetallic Pt and Pd nanoclusters--models for nanoscale material electrocatalysts--as carried out using an aberration-corrected scanning transmission electron microscope (STEM). The coupling of sub-nanometer resolution with Z-contrast measurements provides unprecedented insights into the atomic structures and relative elemental speciation of Pt and Pd within these clusters. The work further defines the nature of deeply quenched states that prevent facile conversions of core-shell motifs to equilibrium alloys and the nature of nonidealities such as twinning (icosahedral cores) and atomic segregation that these structures can embed. The nature of the facet structure present in these model systems is revealed by theory directed modeling in which experimental intensity profiles obtained in Z-contrast measurements at atomic resolution are compared to simulated intensity profiles using theoretically predicted cluster geometries. These comparisons show close correspondences between experiment and model and highlight striking structural complexities in these systems that are compositionally sensitive and subject to amplification by subsequent cluster growth processes. The work demonstrates an empowering competency in nanomaterials research for STEM measurements carried out using aberration corrected microscopes, approaches that hold considerable promise for characterizing the structure of these and other important catalytic materials systems at the atomic scale.

Drosophila A virus is an unusual RNA virus with a T=3 icosahedral core and permuted RNA-dependent RNA polymerase

The vinegar fly, Drosophila melanogaster, is a popular model for the study of invertebrate antiviral immune responses. Several picorna-like viruses are commonly found in both wild and laboratory populations of D. melanogaster. The best-studied and most pathogenic of these is the dicistrovirus Drosophila C virus. Among the uncharacterized small RNA viruses of D. melanogaster, Drosophila A virus (DAV) is the least pathogenic. Historically, DAV has been labelled as a picorna-like virus based on its particle size and the content of its RNA genome. Here, we describe the characterization of both the genome and the virion structure of DAV. Unexpectedly, the DAV genome was shown to encode a circular permutation in the palm-domain motifs of the RNA-dependent RNA polymerase. This arrangement has only been described previously for a subset of viruses from the double-stranded RNA virus family Birnaviridae and the T=4 single-stranded RNA virus family Tetraviridae. The 8 A (0.8 nm) DAV virion structure computed from cryo-electron microscopy and image reconstruction indicates that the virus structural protein forms two discrete domains within the capsid. The inner domain is formed from a clear T=3 lattice with similarity to the beta-sandwich domain of tomato bushy stunt virus, whilst the outer domain is not ordered icosahedrally, but forms a cage-like structure that surrounds the core domain. Taken together, this indicates that DAV is highly divergent from previously described viruses.

Femtosecond Relaxation Dynamics of Au25L18− Monolayer-Protected Clusters

Excited-state relaxation dynamics of a gold cluster, the anion Au25(SCH2CH2Ph)18−, with a known crystal structure are measured with femtosecond laser spectroscopies. The cluster consists of an icosahedral Au13 core bonded to six Au2(SCH2CH2Ph)3 semirings. Pump−probe experiments excite Au13 core electronic transitions and then monitor relaxation of the system as it reaches quasi-equilibrium in lower-energy fluorescing state(s) localized on the semiring moieties. The measurements show that an extremely rapid (<200 fs) internal conversion process takes place within the multilevel electronic structure of the Au13 core, whereas core to semiring relaxation requires 1.2 ps. Photoinduced optical anisotropy persists for up to 1 ps after excitation of the lowest-energy Au13 core-localized transition, which, as suggested by the “superatom” model, distinguishes the optical response from that of a system with spherical symmetry (i.e., jellium sphere). Detection of an 80 cm−1 vibration localized to the Au13 core reflec...