Staple Motifs Research Articles

Molecular Gold Nanocluster Au156 Showing Metallic Electron Dynamics.

The boundary between molecular and metallic gold nanoclusters is of special interest. The difficulty in obtaining atomically precise nanoclusters larger than 2 nm limits the determination of such a boundary. The synthesis and total structural determination of the largest all-alkynyl-protected gold nanocluster (Ph4P)6[Au156(C≡CR)60] (R = 4-CF3C6H4-) (Au156) are reported. It presents an ideal platform for studying the relationship between the structure and the metallic nature. Au156 has a rod shape with the length and width of the kernel being 2.38 and 2.04 nm, respectively. The cluster contains a concentric Au126 core structure (Au46@Au50@Au30) protected by 30 linear RC≡C-Au-C≡CR staple motifs. It is interesting that Au156 displays multiple excitonic peaks in the steady-state absorption spectrum (molecular) and pump-power-dependent excited-state dynamics as revealed in the transient absorption spectrum (metallic), which indicates that Au156 is a critical crossover cluster for the transition from molecular to metallic state. Au156 is the smallest-sized gold nanocluster showing metal-like electron dynamics, and it is recognized that the cluster shape is one of the important factors determining the molecular or metallic nature of a gold nanocluster.

Raman Spectroscopic Fingerprints of Atomically Precise Ligand Protected Noble Metal Clusters: Au38 (PET)24 and Au38-x Agx (PET)24.

Distinct Raman spectroscopic signatures of the metal core of atomically precise, ligand-protected noble metal nanoclusters are reported using Au38 (PET)24 and Au38-x Agx (PET)24 (PET = 2-phenylethanethiolate, -SC2 H4 C6 H5 ) as model systems. The fingerprint Raman features (occurring <200 cm-1 ) of these clusters arise due to the vibrations involving metal atoms of their Au23 or Au23-x Agx cores. A distinct core breathing vibrational mode of the Au23 core has been observed at 90 cm-1 . Whereas the breathing mode shifts to higher frequencies with increasing Ag content of the cluster, the vibrational signatures due to the outer metal-ligand staple motifs (between 200 and 500 cm-1 ) do not shift significantly. DFT calculations furthermore reveal weak Raman bands at higher frequencies compared to the breathing mode, which are associated mostly with the rattling of two central gold atoms of the bi-icosahedral Au23 core. These vibrations are also observed in the experimental spectrum. The study indicates that low-frequency Raman spectra are a characteristic fingerprint of atomically precise clusters, just as electronic absorption spectroscopy, in contrast to the spectrum associated with the ligand shell, which is observed at higher frequencies.

Elucidating the stabilities and properties of the thiolate-protected Au nanoclusters with detaching the staple motifs.

Thiolate-protected Au nanoclusters (AuNCs) have been widely studied in areas of catalysis, biosensors, and bioengineering. In real applications, e.g., catalytic reactions, the thiolate groups are normally partially detached. However, which of the thiolate groups are easily detached and how the detachment of the ligands affects the geometries and electronic structures of the Au nanoclusters have been rarely studied. In this work, we employed the density functional theory calculations as well as the molecular orbital analysis to explore the detachment effect of the ligands using nine thiolate-protected AuNCs as examples. Our results showed that there existed a nearly linear relationship between the averaged detachment energies and the numbers of Au atoms in the motifs. Detaching longer motifs normally required more energies owing to the stronger aurophilic effects. For detaching a full motif, based on the structure decomposition via the grand unified model, analysis on the inner Au core indicated that the change in Au-Au bond length was more sensitive for the inter-block compared to the intra-block. The detachment of the -SH fragment generally needs less energy and brings less structural deformations when compared to the removal of a full motif. Molecular orbital analysis showed that the relative energies of the HOMO orbitals were elevated, which led to the narrow down of the HOMO-LUMO gap. This work provides a primary description of the correlation of the ligands' detachment with the relative stabilities and structures of the AuNCs, which would be beneficial for establishing the structure-property relationship of AuNCs in real applications.

Synthesis and Optical Properties of Unique Pt1Ag24 Nanoclusters with Mixed Exterior Motif Structures.

The atomic arrangement of metal nanoclusters plays a significant role in the structure-property correlation. Herein, we present a novel Pt1Ag24(SR)16(PPh3)3 nanocluster with a unique structure, different from two reported Pt1Ag24 nanoclusters. The nanocluster was prepared via one-pot synthesis and solvent extraction. It has a centered icosahedral Pt1Ag12 kernel and an open shell composed of three Ag2(SR)3(PPh3) staple motifs and a unique trefoil-like Ag6(SR)7 motif. The three kinds of Pt1Ag24 nanoclusters have the same kernel but different shell configurations. The fine-tuning of structures is necessary and significant for the investigation of the relationship of structures and properties. The different UV-vis absorption spectra indicate that the optical properties of three Pt1Ag24 nanoclusters mainly depend on the exterior shell configuration and the metal-ligand interface. This work provides insights toward growth mechanism and the structure-property correlation of metal nanoclusters.

Au7(SR)7] Ring as a New Type of Protection Ligand in a New Atomic Structure of Au15(SR)13 Nanocluster.

We present a [Au7(SR)7] ring as a new type of protection ligand in a new atomic structure of Au15(SR)13 nanocluster for the first time based on the ring model developed to understand how interfacial interaction dictates the structures of protection motifs and gold cores in thiolate-protected gold nanoclusters. This new Au15(SR)13 model shows a tetrahedral Au4 core protected by one [Au7(SR)7] ring and two [Au2(SR)3] "staple" motifs. Density functional theory (DFT) calculations show that the newly predicted Au15(SR)13 (R = CH3/Ph) has a lower energy of 0.24/0.68 eV than previously proposed isomers. By comparing calculated optical absorption spectra (UV), circular dichroism (CD) spectra, and powder X-ray diffraction (XRD) patterns with related experimental spectra, the calculated CD spectra of the newly predicted Au15(SR)13 (R = CH3/Ph) cannot reproduce the experimental results, indicating that the newly predicted Au15(SR)13 is a new structure that needs to be confirmed by experiment. In addition, DFT calculations also show that the newly predicted Au15(SR)13 (R = CH3/Ph) exhibits a large HOMO-LUMO gap, suggesting its high chemical stability. The proposition of the [Au7(SR)7] ring as a protection ligand in the newly predicted Au15(SR)13 not only enriches the types of protection ligands in thiolate-protected gold nanoclusters but also further confirms the effectiveness and rationality of the ring model for understanding the interfacial interaction between the protection motifs and gold cores in thiolate-protected gold nanoclusters.

Atomically Precise Gold Nanoclusters as Model Catalysts for Identifying Active Sites for Electroreduction of CO2

AbstractAccurate identification of active sites is critical for elucidating catalytic reaction mechanisms and developing highly efficient and selective electrocatalysts. Herein, we report the atomic‐level identification of active sites using atomically well‐defined gold nanoclusters (Au NCs) Au25, Au38, and Au144 as model catalysts in the electrochemical CO2 reduction reaction (CO2RR). The studied Au NCs exhibited remarkably high CO2RR activity, which increased with increasing NC size. Electrochemical and X‐ray photoelectron spectroscopy analyses revealed that the Au NCs were activated by removing one thiolate group from each staple motif at the beginning of CO2RR. In addition, density functional theory calculations revealed higher charge densities and upshifts of d‐states for dethiolated Au sites. The structure–activity properties of the studied Au NCs confirmed that dethiolated Au sites were the active sites and that CO2RR activity was determined by the number of active sites on the cluster surface.

Atomically Precise Gold Nanoclusters as Model Catalysts for Identifying Active Sites for Electroreduction of CO2.

Accurate identification of active sites is critical for elucidating catalytic reaction mechanisms and developing highly efficient and selective electrocatalysts. Herein, we report the atomic-level identification of active sites using atomically well-defined gold nanoclusters (Au NCs) Au25 , Au38 , and Au144 as model catalysts in the electrochemical CO2 reduction reaction (CO2 RR). The studied Au NCs exhibited remarkably high CO2 RR activity, which increased with increasing NC size. Electrochemical and X-ray photoelectron spectroscopy analyses revealed that the Au NCs were activated by removing one thiolate group from each staple motif at the beginning of CO2 RR. In addition, density functional theory calculations revealed higher charge densities and upshifts of d-states for dethiolated Au sites. The structure-activity properties of the studied Au NCs confirmed that dethiolated Au sites were the active sites and that CO2 RR activity was determined by the number of active sites on the cluster surface.

Site-Specific Electronic Properties of [Ag25 (SR)18 ]- Nanoclusters by X-Ray Spectroscopy.

Silver nanoclusters (NCs) are of significant interest owing to their interesting structural, electronic, and catalytic properties. Among these NCs, Ag25 (SR)18 is particularly attractive due to its identical geometry as its Au counterpart, Au25 (SR)18 . Herein, the site-specific electronic properties of Ag25 (SR)18 and Au25 (SR)18 using X-ray spectroscopy experiments and quantum simulations are presented. To overcome the final state effect observed in X-ray photoelectron spectroscopy (XPS), a unique method is developed to reliably analyze the charge transfer behavior of the NCs. Density functional theory calculations are combined with XPS to provide more insight into the electronic properties of the NCs. The differences in the XPS valence bands of these two NCs are further compared and interpreted using the relativistic effect. The first derivative of the X-ray absorption near-edge structure (XANES) spectrum is further used as a tool to sensitively probe the bonding properties of Ag25 (SR)18 . By combining the experimental XANES data and their site-specific quantum simulations, the large impact of the staple motif on the bonding properties of the NC is demonstrated. These findings highlight the unique electronic properties of each atomic site in Ag25 (SR)18 ; the effective X-ray analysis techniques developed here can offer new opportunities for the site-specific study of other NCs.

First-principles exploration of the versatile configurations at an alkynyl-protected coinage metal(111) interface

Alkynyl groups (R-C[triple bond, length as m-dash]C-) have attracted intense interest recently as alternative ligands to thiolates to protect atomically precise coinage metal nanoclusters, and more than two dozen compositions have been structurally resolved. However, structure determinations indicated that the interface shows strong metal sensitivity, where a staple motif is the common structural feature at the interface of Au-alkynyl nanoclusters, while the bridging motif dominates at the RC[triple bond, length as m-dash]C-/Ag and RC[triple bond, length as m-dash]C-/Cu interface. To understand their interfacial differences, we employed density functional theory (DFT) calculations to examine the versatile interfacial structures between CH3C[triple bond, length as m-dash]C- and the coinage metal surface; both the (111) surface as well as a surface with a metal adatom are investigated. We find that the alkynyl/gold(111) interface does prefer to form the staple motifs, and a linear flat-lying staple motif is preferred. The adatom occupies the bridge position and two CH3C[triple bond, length as m-dash]C- ligands lie diagonally at the fcc hollow sites with the C[triple bond, length as m-dash]C bond interacting with the surface Au by both σ- and π-coordination modes. In contrast, the bridging motif is energetically more favored on Ag(111) and Cu(111). The alkynyl carbons form strong σ, π- or σ-only bonds with the surface Ag/Cu, forming μ3-bridge coordination over the fcc hollow site. The binding strengths have the order of Cu(111) > Ag(111) > Au(111). The difference in structural preference is attributed to the intrinsic metal attributes with the different gaps of energetic penalty for surface energy, adatom creation and vacancy formation. The other two reasons are the differences of alkynyl-metal bond character and vdW interaction. We further show that this structure preference is also the preferred bonding mode of CH3C[triple bond, length as m-dash]C- on M55 clusters and the CH3S-/M(111) interface. Our insights greatly facilitate the structural elucidation and provide useful guidelines for future structure predictions in alkynyl-protected metal nanosystems.

Density Functional Theory Studies of the Electronic Structure and Muon Hyperfine Interaction in [Au25(SR)18]0 and [Au25(SeR)18]0 Nanoclusters.

Density functional theory computational investigation was performed to study the electronic structures, muon sites, and the associated hyperfine interactions in [Au25(SR)18]0 and [Au25(SeR)18]0 where R is phenylethane. The calculated electronic structures show inhomogeneous spin density distribution and are also affected by different ligands. The two most stable muon sites near Au atoms in the thiolated system are MAu11 and MAu6. When the thiolate ligands were replaced by selenolate ligands, the lowest energy positions of muons moved to MAu6 and MAu5. Muons prefer to stop inside the Au12 icosahedral shell, away from the central Au and the staple motifs region. Muonium states at phenyl ring and S/Se atoms in the ligand were found to be stable and the Fermi contact fields are much larger as compared to the field experienced by muons near Au atoms.

Optical Activity of Chiral Metal Nanoclusters

ConspectusThe emerging chirality in nanomaterials represents one of the most dynamic areas in modern science. Although many novel chiral nanomaterials have been reported, the origin of their chirality and related optical activity have been not unveiled unambiguously. Thanks to the fast development of noble metal cluster chemistry, the structures of many chiral nanoclusters (CNCs) have been precisely determined and their chirality origin has been decoded as four different levels including chiral ligand, helix staple motif, asymmetry metal kernel, and chiral arrangement of organic ligands. Generally, the strong optical activity associated with the electron transitions of the noble metal core is popularly reported among CNCs protected by chiral ligands, following the so-called “outside-in” chirality transfer theory, namely, from organic ligand to metal core. Exceptionally, inherent chiral structures are discerned inside CNCs consisting of achiral ligands, such as the helix staples found in Au38(SR)24 and Au102(SR)44 (SR = thiolate) and the chiral metal kernel existing in Au20(PP3)4Cl4 (PP3 = tris(2-(diphenylphosphino)ethyl) phosphine). These chiral nanostructures induce distinct optical activity and even present reversed chirality transformation in the case of Au38(SR)24 (i.e., from chiral core structure to organic ligand). In the past decade, our group has carried out extensive research work on preparation, enantioseparation, optical activity, and application of chiral inorganic nanostructures. As representatives, enantiopure right-handed and left-handed Au20(PP3)4Cl4 clusters of intrinsic kernel chirality were acquired through an innovative supramolecular self-assembly method and their circular dichroism (CD) feature involving only the metal core was systematically studied; Au3[R/S-Tol-BINAP]3Cl (R/S-Tol-BINAP: R/S-2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl) clusters with the smallest metal-atom number among the reported CNCs were designed and synthesized by using the privileged chiral Tol-BINAP ligand, which exhibited not only strongly enhanced CD signal also remarkable circular polarized luminescence (CPL) response as self-assembled into monodispersed nanocubes.In this Account, we aim at reviewing the fast development of CNCs featuring strong chiral attributes and optical activity. We will briefly introduce the preparation methods of CNCs, such as direct synthesis, ligand exchange, and enantioseparation. In the following parts, the commonly used tools for characterizing the chirality of CNCs are summarized, including CD, vibrational circular dichroism (VCD), CPL, single X-ray diffraction, nuclear magnetic resonance (NMR), and theoretical prediction. Then, the optical activity of CNCs will be systematically discussed, especially their CD, VCD, and CPL activity along with their chirality origin. Finally, future strategies for fabricating CNCs possessing strong optical activity as well as potential chirality-related applications will be proposed. We believe that this Account will trigger more research interest to not only study the amazing optical activity of CNCs but also employ them in many fields.

Shedding Light on the Interfacial Structure of Low-Coverage Alkanethiol Lattices

A comprehensive description of the self-assembly process of alkanethiols on Au(111) is presented, focused on the initial formation of the lying down phases. Low-coverage monolayers are prepared by the disintegration of Au144(RS)60 nanoclusters on the reconstructed (22 × ?3)-Au(111) surface. The method provides a limited number of thiols together with a large excess of gold adatoms. Scanning tunneling microscopy and density functional theory calculations were employed to study the transition between low to high thiolate coverage phases. The process involves different lattices and surface transformations, including thiyl radicals on the herringbone reconstruction, radical-induced herringbone lifting, and the formation of energetically similar metastable phases formed by RS-Au-RS moieties. Results also show that the transition is slow, and different surface structures can coexist on the same sample. Along the process, the first source of Au adatoms to form the RS-Au-SR moieties is the lifting of the herringbone reconstruction because of the lower energetic cost to extract the extra Au atom. However, for hexanethiol (and shorter alkanethiols) at low coverage, additional Au adatoms must be taken from terraces leading to vacancy islands. This process can be entirely suppressed by growing the lying down phases in the presence of an excess of Au adatoms. Taken together, our results shed light on the elusive initial steps of thiol adsorption on clean reconstructed Au, showing that the RS-Au-SR staple motif is also present at the interface of low-coverage self-assembled monolayers.

Synergistic Effect of Bridging Thiolate and Hub Atoms for the Aromaticity Driven Symmetry Breaking in Atomically Precise Gold Nanocluster.

The symmetry of atomically precise nanoclusters is influenced by the specific geometry of the kernel and the arrangement of staple motifs. To understanding the role of ligand and its effect on the breaking of symmetry during ligand exchange transformation, it is necessary to have a mechanism of transformation in an atomically precise manner. Herein, we report the structural transformation from bipyramidal kernel to icosahedral kernel via ligand exchange. The transformation of [Au23(CHT)16]- to [Au25(2-NPT)18]- through ligand (aromatic) exchange revealed two important principles. First, the combined effort of experimental and theoretical study on structural analysis elucidated the mechanism of this structural transformation where "bridging thiolate" and "hub" gold atoms play a crucial role. Second, we have found that the higher crystal symmetry of the Au23 cluster is broken to lower crystal symmetry during the ligand exchange process. This showed that during ligand exchange, the hub atoms and μ3-S atoms get distorted and contributed to the ligand-staple motif formation. These phenomena specified that the ligand effects might be the pivotal factor to impose lower symmetry of the crystal system in the product clusters.

Gold(I)‐Thiolate Oligomers for Catalytic Hydrogenation of Nitroaromatics in Aqueous and Organic Medium

AbstractThiolated gold nanoclusters (AuNCs) have been introduced to efficiently and selectively catalyze the hydrogenation of nitroaromatics due to the strong interaction of their S−Au‐S staple motifs with the nitro groups of nitroaromatics. However, without a gold core, gold(I)‐thiolate oligomers (AuSOs) with S−Au‐S staple motifs are rarely explored as catalysts for nitroaromatics. Here, we report a straightforward strategy for the synthesis of AuSOs through hydroxyl radical‐induced leaching of glutathione‐capped gold nanoparticles (GSH‐AuNPs). Raman spectroscopy and matrix‐assisted laser desorption/ionization‐time of flight mass spectrometry demonstrated that hydroxyl radical‐triggered etching of the GSH‐AuNPs resulted in the production of AuSOs, including Au4(GSH)7 and Au7(GSH)9. The AuSOs were found to catalyze NaBH4‐mediated hydrogenation of 4‐nitrophenol to 4‐aminophenol with a chemoselectivity of ∼100 % and a normalized rate constant (Knor) of 4.8×105 s− g−1. In addition to the high affinity of the S−Au−S staple motifs for 4‐nitrophenol, the unusual catalytic activity of the AuSOs was attributable to the fact that they efficiently catalyzed the production of H2 from NaBH4 and the reaction of dissolved oxygen and NaBH4. The chemoselectivity and applicability of the AuSOs were further verified by performing the catalytic reaction of methyl 2‐(2‐nitrophenyl) acetate or methyl 4‐nitrobenzoate with NaBH4.

Stapled Helical Peptides Bearing Different Anchoring Residues.

A large proportion of protein-protein interactions (PPIs) occur between a short peptide and a globular protein domain; the peptides involved in surface interactions play important roles, and there is great promise for using peptide motifs to interfere with protein interactions. Peptide inhibitors show more promise in blocking large surface protein interactions compared to small molecule inhibitors. However, peptides have drawbacks including poor stability against circulating proteolytic enzymes and an intrinsic inability to penetrate cell membranes. Stapled helical peptides, by adopting a preformed, stable α-helical conformation, exhibit improved proteolytic stability and membrane permeability compared to linear bioactive peptides. In this review, we summarize the broad aspects of peptide stapling for chemistry, biophysics, and biological applications and specifically highlight the methodology by providing an inventory of different anchoring residues categorized into two natural amino acids, two nonnatural amino acids, or a combination of natural and nonnatural amino acids. Additional advantages of specific peptide stapling techniques, including but not limited to reversibility, bio-orthogonal reactivity, and photoisomerization, are also discussed individually. This review is expected to provide a broad reference for the rational design of druggable stapled peptides targeting therapeutic proteins, particularly those involved in PPIs, by considering the impact of anchoring residues, functional cross-linkers, physical staple length, staple components, and the staple motif on the biophysical properties of the peptides.

Understanding the Chemical Insights of Staple Motifs of Thiolate-Protected Gold Nanoclusters.

Improving the fundamental understanding of the basic structures of ligand-protected gold nanoclusters is essential to their bottom-up synthesis as well as their further application explorations. The thiolate ligands that cover the central metal core in staple motifs are vital for the stability of the gold clusters. However, the knowledge about the geometrical and bonding characters of the thiolate ligands has not been fully uncovered yet. In this work, density functional theory calculations and molecular orbital analysis are applied to show that the Au atoms in the thiolate ligands are hypervalent. The chemical insights of the linear SAuS configuration as well as the lengthened AuS bond by combining the 3-center 4-electron (3c-4e) model and the well-recognized valence shell electron pair repulsion theory are revealed. Valence bond formulations of the motifs are given to provide more chemical insights, for example, the resonant structures, to show how the thiolate motif forms one covalent bond and one dative covalent bond with the Au core. This work provides a thorough understanding of the structure and bonding pattern of thiolate ligands of Au nanoclusters, which is important for the rational design of ligands-protected Au nanoclusters.

Force Field Parameter Development for the Thiolate/Defective Au(111) Interface.

A molecular-level understanding of the interplay between self-assembled monolayers (SAMs) of thiolates and gold surface is of great importance to a wide range of applications in surface science and nanotechnology. Despite theoretical research progress of the past decade, an atomistic model, capable of describing key features of SAMs at reconstructed gold surfaces, is still missing. In this work, periodic ab initio density functional theory (DFT) calculations were utilized to develop a new atomistic force field model for alkanethiolate (AT) SAMs on a reconstructed Au(111) surface. The new force field parameters were carefully trained to reproduce the key features, including vibrational spectra and torsion energy profiles of ethylthiolate (C2S) in the bridge or staple motif model on the Au(111) surface, wherein, the force constants of the bond and angle terms were trained by matching the vibrational spectra, while the torsion parameters of the dihedral angles were trained via fitting the torsion energy profiles from DFT calculations. To validate the developed force field parameters, we performed classical molecular dynamics (MD) simulations for both pristine and reconstructed Au-S interface models with a (2√3 × 3) unit cell, which includes four dodecanethiolate (C10S) molecules on the Au(111) surface. The simulation results showed that the geometrical features of the investigated Au-S interface models and structural properties of the C10S SAMs are in good agreement with the ab initio MD studies. The newly developed atomistic force field model provides new fundamental insights into AT SAMs on the reconstructed Au(111) surface and adds advancement to the existing interface research knowledge.

Accuracy of the PM6 and PM7 Methods on Bare and Thiolate-Protected Gold Nanoclusters

Semiempirical quantum mechanical (SEQM) methods offer an attractive middle ground between fully ab initio quantum chemistry and force-field simulations, allowing for a quantum mechanical treatment of the system at a relatively low computational cost. However, SEQM methods have not been frequently utilized in the study of transition metal systems, mostly due to the difficulty in obtaining reliable parameters. This paper examines the accuracy of the PM6 and PM7 semiempirical methods to predict geometries, ionization potentials, and HOMO-LUMO energy gaps of several bare gold clusters (Aun) and thiolate-protected gold nanoclusters (AuSNCs). Contrary to PM6, the PM7 method can predict qualitatively correct geometries and ionization potentials when compared to DFT. PM6 fails to predict the characteristic gold core and gold-sulfur ligand shell (staple motifs) of the AuSNC structures. Both the PM6 and PM7 methods overestimate the HOMO-LUMO gaps. Overall, PM7 provides a more accurate description of bare gold and gold-thiolate nanoclusters than PM6. Nevertheless, refining the gold parameters could help achieve better quantitative accuracy.

Atomically resolved Au52Cu72(SR)55 nanoalloy reveals Marks decahedron truncation and Penrose tiling surface

Gold-copper alloys have rich forms. Here we report an atomically resolved [Au52Cu72(p-MBT)55]+Cl− nanoalloy (p-MBT = SPh-p-CH3). This nanoalloy exhibits unusual structural patterns. First, two Cu atoms are located in the inner 7-atom decahedral kernel (M7, M = Au/Cu). The M7 kernel is then enclosed by a second shell of homogold (Au47), giving rise to a two-shelled M54 (i.e. Au52Cu2) full decahedron. A comparison of the non-truncated M54 decahedron with the truncated homogold Au49 kernel in similar-sized gold nanoparticles provides for the first time an explanation for Marks decahedron truncation. Second, a Cu70(SR)55 exterior cage resembling a 3D Penrose tiling protects the M54 decahedral kernel. Compared to the discrete staple motifs in gold:thiolate nanoparticles, the Cu-thiolate surface of Au52Cu72 forms an extended cage. The Cu-SR Penrose tiling retains the M54 kernel’s high symmetry (D5h). Third, interparticle interactions in the assembly are closely related to the symmetry of the particle, and a “quadruple-gear-like” interlocking pattern is observed.

Density Functional Theory Studies of Muon Stopping Sites and Hyperfine Interaction in [Au25(SR)18]0 Nanocluster

The Density Functional Theory method was applied to determine muon stopping sites in [Au25(SR)18]0 nanocluster and the associated hyperfine interaction. The molecular electrostatic potential map indicates that the inner region of the Au13 icosahedron is more favorable for muon stopping sites. On the other hand, the potential in the region surrounding the ligands is positive and it is unlikely for muon to stop near any of the carbon atoms. Based on the DFT calculated energy, four muon sites near different Au atoms were found to be inside the icosahedron, while eight other Au sites are positioned slightly outside. The sites near Au atoms in the staple motifs were found to be energetically unstable. Local minima corresponding to muon sites near the S atoms in the staple motif have higher energies as compared to the Au sites. Three of the four sites inside the icosahedron, MAu10, MAu6, and MAu5, are the most stable with similar energies. The calculated Fermi contact coupling constant for these three Au sites are −2.85, 62.63, and 3.56 MHz, respectively.