Sharp Transition from Nonmetallic Au246 to Metallic Au279 with Nascent Surface Plasmon Resonance.

The optical properties of metal nanoparticles have attracted wide interest. Recent progress in controlling nanoparticles with atomic precision (often called nanoclusters) provide new opportunities for investigating many fundamental questions, such as the transition from excitonic to plasmonic state, which is a central question in metal nanoparticle research because it provides insights into the origin of surface plasmon resonance (SPR) as well as the formation of metallic bond. However, this question still remains elusive because of the extreme difficulty in preparing atomically precise nanoparticles larger than 2 nm. Here we report the synthesis and optical properties of an atomically precise Au279(SR)84 nanocluster. Femtosecond transient absorption spectroscopic analysis reveals that the Au279 nanocluster shows a laser power dependence in its excited state lifetime, indicating metallic state of the particle, in contrast with the nonmetallic electronic structure of the Au246(SR)80 nanocluster. Steady-state absorption spectra reveal that the nascent plasmon band of Au279 at 506 nm shows no peak shift even down to 60 K, consistent with plasmon behavior. The sharp transition from nonmetallic Au246 to metallic Au279 is surprising and will stimulate future theoretical work on the transition and many other relevant issues.

Reconstructing the Surface of Gold Nanoclusters by Cadmium Doping.

Atomically precise metal nanoclusters with tailored surface structures are important for both fundamental studies and practical applications. The development of new methods for tailoring the surface structure in a controllable manner has long been sought. In this work, we report surface reconstruction induced by cadmium doping into the [Au23(SR)16]- (R = cyclohexyl) nanocluster, in which two neighboring surface Au atomic sites "coalesce" into one Cd atomic site and, accordingly, a new bimetal nanocluster, [Au19Cd2(SR)16]-, is produced. Interestingly, a Cd(S-Au-S)3 "paw-like" surface motif is observed for the first time in nanocluster structures. In such a motif, the Cd atom acts as a junction which connects three monomeric -S-Au-S- motifs. Density functional theory calculations are performed to understand the two unique Cd locations. Furthermore, we demonstrate different doping modes when the [Au23(SR)16]- nanocluster is doped with different metals (Cu, Ag), including (i) simple substitution and (ii) total structure transformation, as opposed to surface reconstruction for Cd doping. This work greatly expands doping chemistry for tailoring the structures of nanoclusters and is expected to open new avenues for designing nanoclusters with novel surface structures using different dopants.

Gold Quantum Boxes: On the Periodicities and the Quantum Confinement in the Au28, Au36, Au44 , and Au52 Magic Series.

Revealing the size-dependent periodicities (including formula, growth pattern, and property evolution) is an important task in metal nanocluster research. However, investigation on this major issue has been complicated, as the size change is often accompanied by a structural change. Herein, with the successful determination of the Au44(TBBT)28 structure, where TBBT = 4-tert-butylbenzenethiolate, the missing size in the family of Au28(TBBT)20, Au36(TBBT)24, and Au52(TBBT)32 nanoclusters is filled, and a neat "magic series" with a unified formula of Au8n+4(TBBT)4n+8 (n = 3-6) is identified. Such a periodicity in magic numbers is a reflection of the uniform anisotropic growth patterns in this magic series, and the n value is correlated with the number of (001) layers in the face-centered cubic lattice. The size-dependent quantum confinement nature of this magic series is further understood by empirical scaling law, classical "particle in a box" model, and the density functional theory calculations.

Assessment of cardiovascular disease risk factors in the coastal region of South Carolina.

OBJECTIVE: To assess risk factors for cardiovascular disease, barriers to health care, and desired health care education topics for Hispanics in the coastal region of South Carolina known as the Lowcountry. METHODS: 174 Hispanic adults were surveyed at visits at the Mexican consulate using a novel interview instrument. The prevalence of cardiovascular risk factors was compared to the Behavioral Risk Factor Surveillance System (BRFSS), an annual telephone survey, to evaluate the validity of the survey instrument. RESULTS: Results are comparable to the BRFSS telephone study of the Hispanics in the same area. However, participants in our study were older (Age > 35 = 41.4% vs. 34.9%) and reported fewer years of formal education (higher level education = 12.9% vs. 44.2%). Cost of care (72.8%) and language barriers (46.8%) were the main difficulties reported in obtaining health care access. The main educational topics of interest were diabetes (61.5%), hypertension (43.7%), stress (42.5%), and cardiac disease (40.2%). CONCLUSION: Our study supports the evidence that there is a demand and need for cardiovascular disease and diabetes education among Hispanics. Our study also shows that a large proportion of Hispanics experience barriers to health care. and that large telephone studies may underrepresent higher risk Hispanic populations.

Improving the catalytic activity of semiconductor nanocrystals through selective domain etching.

Colloidal chemistry offers an assortment of synthetic tools for tuning the shape of semiconductor nanocrystals. While many nanocrystal architectures can be obtained directly via colloidal growth, other nanoparticle morphologies require alternative processing strategies. Here, we show that chemical etching of colloidal nanoparticles can facilitate the realization of nanocrystal shapes that are topologically inaccessible by hot-injection techniques alone. The present methodology is demonstrated by synthesizing a two-component CdSe/CdS nanoparticle dimer, constructed in a way that both CdSe and CdS semiconductor domains are exposed to the external environment. This structural morphology is highly desirable for catalytic applications as it enables both reductive and oxidative reactions to occur simultaneously on dissimilar nanoparticle surfaces. Hydrogen production tests confirmed the improved catalytic activity of CdSe/CdS dimers, which was enhanced 3-4 times upon etching treatment. We expect that the demonstrated application of etching to shaping of colloidal heteronanocrystals can become a common methodology in the synthesis of charge-separating nanocrystals, leading to advanced nanoparticles architectures for applications in areas of photocatalysis, photovoltaics, and light detection.

Large-Scale Synthesis, Crystal Structure, and Optical Properties of the Ag146Br2(SR)80 Nanocluster.

Solving the atomic structure of large-sized metal nanoclusters is a highly challenging task yet critically important for understanding the properties and developing applications. Herein, we report a stable silver nanocluster-Ag146Br2(SR)80 (where SR = 4-isopropylbenzenethiolate)-with its structure solved by X-ray crystallography. Gram-scale synthesis with high yield has been achieved by a one-pot reaction, which offers opportunities for functionalization and applications. This silver nanocluster possesses a core-shell structure with a Ag51 core surrounded by a shell of Ag95Br2S80. The Ag51 core can be viewed as a distorted decahedron, endowing this nanocluster with quantized electronic transitions. In the surface-protecting layer, five different types of S-Ag coordination modes are observed, ranging from the linear Ag-S-Ag to S-Ag3 (triangle) and S-Ag4 (square). Furthermore, temperature-dependent optical absorption and ultrafast electron dynamics are conducted to explore the relationship between the properties and structure, demonstrating that the distorted metal core and "flying saucer"-like shape of this nanocluster have significant effects on the electronic behavior. A comparison with multiple sizes of Ag nanoclusters also provides some insights into the evolution from molecular to metallic behavior.

Models for potential dendritic nitric oxide donors: crystal structures of two 2-nitroanilino precursors and nitric oxide-release behavior of the nitrosated derivatives.

Two molecular precursors to dendrimeric materials that could serve as slow and sustained NO-releasing therapeutic agents have been synthesized and characterized. N1,N4-Bis(2-nitrophenyl)butane-1,4-diamine, C16H18N4O4, (I), crystallizes in a lattice with equal populations of two molecules of different conformations, both of which possess inversion symmetry through the central C-C bond. One molecule has exclusively anti conformations along the butyl chain, while the other has a gauche conformation of the substituents on the first C-C bond. N2,N2-Bis[2-(2-nitroanilino)ethyl]-N1-(2-nitrophenyl)ethane-1,2-diamine, C24H27N7O6, (II), crystallizes with one unique molecule in the asymmetric unit. Neighboring pairs of molecules are linked into dimers via N-H...O amine-nitro hydrogen bonds. The dimers are assembled into layers that stack in an A-B-A-B sequence such that the repeat distance in the stacking direction is over 46 Å. Molecular NO-release agents N1,N4-bis(2-nitrophenyl)-N1,N4-dinitrosobutane-1,4-diamine, C16H16N6O6, (III), and N1-(2-nitrophenyl)-N2,N2-bis{2-[(2-nitrophenyl)(nitroso)amino]ethyl}-N1-nitrosoethane-1,2-diamine, C24H24N10O9, (IV), were prepared via treatment of (I) and (II), respectively, with NaNO2 and acetic acid. The release of NO from solid-phase samples of (III) and (IV) suspended in phosphate buffer was monitored spectroscopically over a period of 21 days. Although (IV) released a greater amount of NO, as expected due to it having three NO moieties for every two in (III), the (IV):(III) ratio of the rate and extent of NO release was significantly less than 1.5:1, suggesting that some combination of electronic, chemical, and/or steric factors may be affecting the release process.

Site-selective substitution of gold atoms in the Au24(SR)20 nanocluster by silver.

The synthesis and structure determination of atomically precise alloy nanoclusters have attracted much attention in recent research. Herein, we report a new alloy nanocluster Au24-xAgx(TBBM)20 (x∼1) synthesized via a ligand-exchange-induced size/structure transformation method. Its X-ray structure is obtained successfully and the dopant Ag is found to occupy three special positions in the kernel, rather than equivalently over all the kernel sites. This selective occupancy is interesting and DFT calculation results suggest that the relative oxidation state (rationalized as difference in the charge) of the Ag when doped into the cluster is likely determining the most favorable doping positions. This work provides a new strategy for controlled synthesis of new Au-Ag nanoclusters and also reveals a new scenario for the doping position of Ag atoms in Au-Ag bimetal nanoclusters.

Emergence of hierarchical structural complexities in nanoparticles and their assembly.

We demonstrate that nanoparticle self-assembly can reach the same level of hierarchy, complexity, and accuracy as biomolecules. The precise assembly structures of gold nanoparticles (246 gold core atoms with 80 p-methylbenzenethiolate surface ligands) at the atomic, molecular, and nanoscale levels were determined from x-ray diffraction studies. We identified the driving forces and rules that guide the multiscale assembly behavior. The protecting ligands self-organize into rotational and parallel patterns on the nanoparticle surface via C-H⋅⋅⋅π interaction, and the symmetry and density of surface patterns dictate directional packing of nanoparticles into crystals with orientational, rotational, and translational orders. Through hierarchical interactions and symmetry matching, the simple building blocks evolve into complex structures, representing an emergent phenomenon in the nanoparticle system.

Heavily doped Au25-xAgx(SC6H11)18(-) nanoclusters: silver goes from the core to the surface.

We report a method for heavy doping of the Au25(SR)18 nanocluster (where R = C6H11) with silver through the Ag(I)-thiolate complex induced size/structure transformation of Au23(SR)16(-) into Au25-xAgx(SR)18(-). X-ray crystallographic analysis revealed that Ag dopants are distributed not only in the icosahedral core but also in the surface staple motifs; the latter was not achieved in earlier studies of alloy Au25-xAgx nanoclusters.