Is the largest aqueous gold cluster a superatom complex? Electronic structure & optical response of the structurally determined Au146(pMBA)57

The new water-soluble gold cluster Au146(pMBA)57, the structure of which has been recently determined at sub-atomic resolution by Vergara et al. [1], is the largest aqueous gold cluster ever structurally determined and likewise the smallest cluster with a stacking fault. The core presents a twinned truncated octahedron, while additional peripheral gold atoms follow a C2 rotational symmetry. According to the usual counting rules of the superatom complex (SAC) model, the compound attains a number of 92 SAC electrons if the overall net charge is 3- (three additional electrons). As this is the number of electrons required for a major shell closing, the question arises if Au146(pMBA)57 should be regarded as a superatom complex. Starting from the experimental coordinates we have analyzed the structure using density-functional theory. The optimized (relaxed) structure retains all the connectivity of the experimental coordinates, while removing much of its irregularities in interatomic distances, thereby enhancing the C2-symmetry feature. Analyzing the angular-momentum projected states, we show that, despite a small gap, the electronic structure does not exhibit SAC model character. In addition, optical absorption spectra are found to be relatively smooth compared to the example of the Au144(SR)60 cluster. The Au146(SR)57 cluster does not derive its stability from SAC character; it cannot be considered a superatom complex

Gold−Copper Nano-Alloy, “Tumbaga”, in the era of nano: phase diagram and segregation

Gold–copper (Au–Cu) phases were employed already by pre-Columbian civilizations, essentially in decorative arts, whereas nowadays, they emerge in nanotechnology as an important catalyst. The knowledge of the phase diagram is critical to understanding the performance of a material. However, experimental determination of nanophase diagrams is rare because calorimetry remains quite challenging at the nanoscale; theoretical investigations, therefore, are welcomed. Using nanothermodynamics, this paper presents the phase diagrams of various polyhedral nanoparticles (tetrahedron, cube, octahedron, decahedron, dodecahedron, rhombic dodecahedron, truncated octahedron, cuboctahedron, and icosahedron) at sizes 4 and 10 nm. One finds, for all the shapes investigated, that the congruent melting point of these nanoparticles is shifted with respect to both size and composition (copper enrichment). Segregation reveals a gold enrichment at the surface, leading to a kind of core–shell structure, reminiscent of the historical artifacts. Finally, the most stable structures were determined to be the dodecahedron, truncated octahedron, and icosahedron with a Cu-rich core/Au-rich surface. The results of the thermodynamic approach are compared and supported by molecular-dynamics simulations and by electron-microscopy (EDX) observations

Quantitative tunneling spectroscopy of nanocrystals

The proposed goals of this collaborative work were to systematically characterize the electronic structure and dynamics of 3-dimensional metal and semiconducting nanocrystals using scanning tunneling microscopy/spectroscopy (STM/STS) and ballistic electron emission spectroscopy (BEES). This report describes progress in the spectroscopic work and in the development of methods for creating and characterizing gold nanocrystals. During the grant period, substantial effort also was devoted to the development of epitaxial graphene (EG), a very promising materials system with outstanding potential for nanometer-scale ballistic and coherent devices ("graphene"Â refers to one atomic layer of graphitic, sp2 -bonded carbon atoms [or more loosely, few layers]). Funding from this DOE grant was critical for the initial development of epitaxial graphene for nanoelectronic

Quantitative tunneling spectroscopy of nanocrystals

The proposed goals of this collaborative work were to systematically characterize the electronic structure and dynamics of 3-dimensional metal and semiconducting nanocrystals using scanning tunneling microscopy/spectroscopy (STM/STS) and ballistic electron emission spectroscopy (BEES). This report describes progress in the spectroscopic work and in the development of methods for creating and characterizing gold nanocrystals. During the grant period, substantial effort also was devoted to the development of epitaxial graphene (EG), a very promising materials system with outstanding potential for nanometer-scale ballistic and coherent devices ("graphene"Â refers to one atomic layer of graphitic, sp2 -bonded carbon atoms [or more loosely, few layers]). Funding from this DOE grant was critical for the initial development of epitaxial graphene for nanoelectronic

Atomically precise Au144(SR)60 nanoclusters (R = Et, Pr) are capped by 12 distinct ligand types of 5-fold equivalence and display gigantic diastereotopic effects

For two decades, Au144(SR)60 has been one of the most studied and used thiolate (SR) protected gold nanoclusters. In many ways, however, it proved to be a challenging and elusive case, also because of the difficulties in solving its structure by single-crystal X-ray crystallography. We used very short thiols and could prepare Au144(SC2H5)60 and Au144(SC3H7)60 in a very pure form, which was confirmed by UV-vis absorption spectroscopy and very regular electrochemistry patterns. Inductively coupled plasma and electrospray ionization mass spectrometries gave definite proof of the Au144(SR)60 stoichiometry. Highresolution 1D and 2D NMR spectroscopy in the solution phase provided the result of assessing the presence of 12 ligand types in exactly the same amount (5-fold equivalence). Equally important, we found that the two protons belonging to each methylene group along the thiolate chain are diastereotopic. For the a-CH2 protons, the diastereotopic effect can be indeed gigantic, as it reaches chemical-shift differences of 2.9 ppm. DFT calculations provided insights into the relationship between structure and NMR results. In particular, the 12 ligand types and corresponding diastereotopic effects may be explained by considering the presence of C\u2013H/S hydrogen bonds. These results thus provide fundamental insights into the structure of the thiolate layer capping this long-studied gold nanocluster

Hidden components in aqueous "Gold-144' fractionated by PAGE: high resolution orbitrap ESI-MS identifies the Gold-102 and higher all-aromatic Au-pMBA cluster compounds

Accepted author manuscriptExperimental and theoretical evidence reveals the resilience and stability of the larger aqueous gold clusters protected with p-mercaptobenzoic acid ligands (pMBA) of composition Aun(pMBA)p or (n, p). The Au144(pMBA)60, (144, 60), or gold-144 aqueous gold cluster is considered special because of its high symmetry, abundance, and icosahedral structure as well as its many potential uses in material and biological sciences. Yet, to this date, direct confirmation of its precise composition and total structure remains elusive. Results presented here from characterization via high-resolution electrospray ionization mass spectrometry on an Orbitrap instrument confirm Au102(pMBA)44 at isotopic resolution. Further, what usually appears as a single band for (144, 60) in electrophoresis (PAGE) is shown to also contain the (130, 50), recently determined to have a truncated-decahedral structure, and a (137, 56) component in addition to the dominant (144, 60) compound of chiral-icosahedral structure. This finding is significant in that it reveals the existence of structures never before observed in all-aromatic water-soluble species while pointing out the path toward elucidation of the thermodynamic control of protected gold nanocrystal formation.Ye

Tetrahedral (T) closed-shell cluster of 29 silver atoms & 12 lipoate ligands, [Ag29(R-a-LA)12](3-): antibacterial and antifungal activity

Accepted author manuscriptHere we report on the identification and applications of an aqueous 29-atom silver cluster stabilized with 12 lipoate ligands, i.e. Ag29(R-α–LA)12 or (29,12), wherein R-α–LA = R-α-lipoic acid, a natural dithiolate. Its uniformity is checked by HPLC-ESI-MS and analytical ultracentrifugation, which confirms its small dimension (∼3 nm hydrodynamic diameter). For the first time, this cluster has been detected intact via electrospray ionization mass spectrometry, allowing one to confirm its composition, its [3-] charge-state, and the 8-electron shell configuration of its metallic silver core. Its electronic structure and bonding, including T-symmetry and profound chirality in the outer shell, have been analyzed by DFT quantum-chemical calculations, starting from the known structure of a nonaqueous homologue. The cluster is effective against Methicillin-Resistant Staphylococcus aureus bacteria (MRSA) at a minimum inhibitory concentration (MIC) of 0.6 mg-Ag/mL. A preformed Candida albicans fungal biofilm, impermeable to other antifungal agents, was also inhibited by aqueous solutions of this cluster, in a dose–response manner, with a half-maximal inhibitory concentration (IC50) of 0.94 mg-Ag/mL. Scanning electron micrographs showed the post-treatment ultrastructural changes on both MRSA and C. albicans that are characteristic of those displayed after treatment by larger silver nanoparticles.Ye

Differential Detection of Genetic Loci Underlying Stem and Root Lignin Content in Populus

In this study, we established a comprehensive genetic map with a large number of progeny from a three-generation hybrid Populus intercross, and phenotyped the lignin content, S/G ratio and 28 cell wall subcomponents both in stems and roots for the mapping individuals. Phenotypic analysis revealed that lignin content and syringyl-to-guaiacyl (S/G) ratio using pyrolysis molecular beam mass spectroscopy (pyMBMS) varied among mapping individuals. Phenotypic analysis revealed that stem lignin content is significantly higher than that in root and the quantified traits can be classified into four distinct groups, with strong correlations observed among components within organs. Altogether, 179 coordinating QTLs were detected, and they were co-localized into 49 genetic loci, 27 of which appear to be pleiotropic. Many of the detected genetic loci were detected differentially in stem and root. This is the first report of separate genetic loci controlling cell wall phenotypes above and below ground. These results suggest that it may be possible to modify lignin content and composition via breed and/or engineer as a means of simultaneously improving Populus for cellulosic ethanol production and carbon sequestration

Análise crítica da aplicação do custeio-meta no desenvolvimento de empreendimentos de habitação de interesse social

O custeio-meta é uma abordagem amplamente aplicada na manufatura e representa uma inovação no processo de desenvolvimento de produtos, em que o custo, a qualidade e a funcionalidade não são conseqüências do processo de projeto, mas parâmetros de entrada. Este artigo investiga a aplicabilidade da abordagem custeio-meta no desenvolvimento de empreendimentos habitacionais de interesse social (EHIS). Tais empreendimentos possuem muitas peculiaridades em relação a produtos da manufatura, não havendo evidências de que esta abordagem seja adequada ao desenvolvimento de EHIS, nem mesmo de produtos da construção civil em geral. Este artigo se propõe a investigar como e por que algumas características dos EHIS - a maioria delas comuns também a outros tipos de empreendimentos de construção - influenciam a aplicabilidade do custeio-meta. Estas questões foram analisadas com base na adaptação de conceitos da manufatura para a construção civil e num estudo de caso exploratório conduzido em uma companhia estadual de provisão habitacional. O estudo propõe adaptar o custeio-meta às condições do contexto de análise, concentrar esforços nas atividades mais vantajosas ou ajustar o contexto de análise de modo a maximizar os seus benefícios e minimizar incertezas