High genetic abundance of Rpi-blb2/Mi-1.2/Cami gene family in Solanaceae

Relative genomic positions of genes among potato (upper), pepper (middle) and tomato (lower) along chromosome 6. (DOCX 282 kb

Gold Nanocluster-Catalyzed Semihydrogenation: A Unique Activation Pathway for Terminal Alkynes

We report high catalytic activity of ultrasmall spherical Au₂₅(SC₂H₄Ph)₁₈ and rod-shaped Au₂₅(PPh₃)₁₀(CCPh)₅X₂ (X = Br, Cl) nanoclusters supported on oxides for the semihydrogenation of terminal alkynes into alkenes with >99% conversion of alkynes and ∼100% selectivity for alkenes. In contrast, internal alkynes cannot be catalyzed by such “ligand-on” Au₂₅ catalysts; however, with “ligand-off” Au₂₅ catalysts the internal alkynes can undergo semihydrogenation to yield <i>Z</i>-alkenes, similar to conventional gold nanoparticle catalysts. On the basis of the results, a unique activation pathway of terminal alkynes by “ligand-on” gold nanoclusters is identified, which should follow a deprotonation activation pathway via a R′CC[Au_<i>n</i>L_<i>m</i>] (where L represents the protecting ligands on the cluster), in contrast with the activation mechanism on conventional gold nanocatalysts. This new activation mode is supported by observing the incorporation of deprotonated CCPh as ligands on rod-shaped Au₂₅(PPh₃)₁₀(CCPh)₅X₂ nanoclusters under conditions similar to the catalytic reaction and by detecting the R′CC[Au_<i>n</i>(SC₂H₄Ph)_<i>m</i>] via FT-IR spectroscopy

Thermally Robust Au₉₉(SPh)₄₂ Nanoclusters for Chemoselective Hydrogenation of Nitrobenzaldehyde Derivatives in Water

We report the synthesis and catalytic application of thermally robust gold nanoclusters formulated as Au₉₉(SPh)₄₂. The formula was determined by electrospray ionization and matrix-assisted laser desorption ionization mass spectrometry in conjunction with thermogravimetric analysis. The optical spectrum of Au₉₉(SPh)₄₂ nanoclusters shows absorption peaks at ∼920 nm (1.35 eV), 730 nm (1.70 eV), 600 nm (2.07 eV), 490 nm (2.53 eV), and 400 nm (3.1 eV) in contrast to conventional gold nanoparticles, which exhibit a plasmon resonance band at 520 nm (for spherical particles). The ceria-supported Au₉₉(SPh)₄₂ nanoclusters were utilized as a catalyst for chemoselective hydrogenation of nitrobenzaldehyde to nitrobenzyl alcohol in water using H₂ gas as the hydrogen source. The selective hydrogenation of the aldehyde group catalyzed by nanoclusters is a surprise because conventional nanogold catalysts instead give rise to the product resulting from reduction of the nitro group. The Au₉₉(SPh)₄₂/CeO₂ catalyst gives high catalytic activity for a range of nitrobenzaldehyde derivatives and also shows excellent recyclability due to its thermal robustness. We further tested the size-dependent catalytic performance of Au₂₅(SPh)₁₈ and Au₃₆(SPh)₂₄ nanoclusters, and on the basis of their crystal structures we propose a molecular adsorption site for nitrobenzaldehyde. The nanocluster material is expected to find wide application in catalytic reactions

Self-Assembly of Silver Clusters into One- and Two-Dimensional Structures and Highly Selective Methanol Sensing

The development of new materials for the design of sensitive and responsive sensors has become a crucial research direction. Here, two silver cluster-based polymers (Ag-CBPs), including one-dimensional {[Ag22(L1)8(CF3CO2)14](CH3OH)2}n chain and two-dimensional {[Ag12(L2)2(CO2CF3)14(H2O)4(AgCO2CF3)4](HNEt3)2}n film, are designed and used to simulate the human nose, an elegant sensor to smells, to distinguish organic solvents. We study the relationship between the atomic structures of Ag-CBPs determined by x-ray diffraction and the electrical properties in the presence of organic solvents (e.g., methanol and ethanol). The ligands, cations, and the ligated solvent molecules not only play an important role in the self-assembly process of Ag-CBP materials but also determine their physiochemical properties such as the sensing functionality

Dual effects of water vapor on ceria-supported gold clusters

Atomically precise nanocatalysts are currently being intensely pursued in catalysis research. Such nanocatalysts can serve as model catalysts for gaining fundamental insights into catalytic processes. In this work we report a discovery that water vapor provokes the mild removal of surface long-chain ligands on 25-atom Au-25(SC12H25)(18) nanoclusters in a controlled manner. Using the resultant Au-25(SC12H25)(18-x)/CeO2 catalyst and CO oxidation as a probe reaction, we found that the catalytic activity of cluster/CeO2 is enhanced from nearly zero conversion of CO (in the absence of water) to 96.2% (in the presence of 2.3 vol% H2O) at the same temperature (100 degrees C). The cluster catalysts exhibit high stability during the CO oxidation process under moisture conditions (up to 20 vol% water vapor). Water vapor plays a dual role in gold cluster-catalyzed CO oxidation. FT-IR and XPS analyses in combination with density functional theory (DFT) simulations suggest that the "-SC12H25" ligands are easier to be removed under a water vapor atmosphere, thus generating highly active sites. Moreover, the O-2(2-) peroxide species constitutes the active oxygen species in CO oxidation, evidenced by Raman spectroscopy analysis and isotope experiments on the CeO2 and cluster/CeO2. The results also indicate the perimeter sites of the interface of Au-25(SC12H25)(18-x)/CeO2 to be active sites for catalytic CO oxidation. The controlled exposure of active sites under mild conditions is of critical importance for the utilization of clusters in catalysis

Magic Size Au₆₄(S‑<i>c</i>‑C₆H₁₁)₃₂ Nanocluster Protected by Cyclohexanethiolate

We report a new magic-sized gold nanocluster of atomic precision formulated as Au₆₄(S-<i>c</i>-C₆H₁₁)₃₂. The Au₆₄ nanocluster was obtained in relatively high yield (∼15%, Au atom basis) by a two-step size-focusing methodology. Obtaining this new magic size through the previously established “size focusing” method relies on the introduction of a new synthetic “parameter”the type of protecting thiolate ligand. It was found that Au₆₄(S-<i>c</i>-C₆H₁₁)₃₂ was the most thermodynamically stable specie of the cyclohexanethiolate-protected gold nanoclusters in the size range from ~5k to 20k (where, k = 1000 dalton); hence, it can be selectively synthesized through a careful control of the size-focusing kinetics. The Au₆₄ nanocluster is the first gold nanocluster achieved through direct synthesis (i.e., without postsynthetic size separation) in the medium size range (i.e., ∼40 to ∼100 gold atoms). This medium-sized Au₆₄(S-<i>c</i>-C₆H₁₁)₃₂ exhibits a highly structured optical absorption spectrum, reflecting its discrete electronic states. The discovery of this new Au₆₄(S-<i>c</i>-C₆H₁₁)₃₂ nanocluster bridges the gap of the gold nanoclusters in the medium size range and will facilitate the understanding of the structure and property evolution of magic-size gold nanoclusters

Stable Au₂₅(SR)₁₈/TiO₂ Composite Nanostructure with Enhanced Visible Light Photocatalytic Activity

We report the visible light photocatalytic properties of a composite material consisting of Au₂₅(SR)₁₈ nanoclusters (R:CH₂CH₂Ph) and TiO₂ nanocrystals. The effects of Au₂₅(SR)₁₈ nanoclusters on the photocatalytic activity of TiO₂ nanocrystals were evaluated in the reaction of photocatalytic degradation of methyl orange. The loading of Au₂₅(SR)₁₈ nanoclusters onto TiO₂ results in strong visible light absorption by the composite and, more importantly, a 1.6 times increase in visible light photocatalytic activity. Furthermore, the Au₂₅(SR)₁₈/TiO₂ composite nanostructure exhibits high stability in recycling tests. The Au₂₅(SR)₁₈ nanolusters dispersed on the TiO₂ surface can act as a small-band-gap semiconductor to absorb visible light, giving rise to electron–hole separation and producing singlet oxygen (¹O₂). Both the generated hydroxyl radicals (HO^•) and ¹O₂ are rationalized to be responsible for the decomposition of the dye

Size Dependence of Atomically Precise Gold Nanoclusters in Chemoselective Hydrogenation and Active Site Structure

We investigate the catalytic properties of water-soluble Au_<i>n</i>(SG)_<i>m</i> nanocluster catalysts (H-SG = glutathione) of different sizes, including Au₁₅(SG)₁₃, Au₁₈(SG)₁₄, Au₂₅(SG)₁₈, Au₃₈(SG)₂₄, and captopril-capped Au₂₅(Capt)₁₈ nanoclusters. These Au_<i>n</i>(SR)_<i>m</i> nanoclusters (SR represents thiolate generally) are used as homogeneous catalysts (i.e., without supports) in the chemoselective hydrogenation of 4-nitrobenzaldehyde (4-NO₂PhCHO) to 4-nitrobenzyl alcohol (4-NO₂PhCH₂OH) with ∼100% selectivity in water using H₂ gas (20 bar) as the hydrogen source. These nanocluster catalysts, except Au₁₈(SG)₁₄, remain intact after the catalytic reaction, evidenced by UV–vis spectra, which are characteristic of nanoclusters of each size and thus serve as spectroscopic “fingerprints”. We observe a drastic size dependence and steric effect of protecting ligands on the gold nanocluster catalysts in the hydrogenation reaction. Density functional theory (DFT) modeling of the 4-nitrobenzaldehyde adsorption shows that both the -CHO and -NO₂ groups closely interact with the S-Au-S staples on the gold nanocluster surface. The adsorptions of the 4-nitrobenzaldehyde molecule on the four different sized Au_<i>n</i>(SR)_<i>m</i> nanoclusters are moderately strong and similar in strength. The DFT results suggest that the catalytic activity of the Au_<i>n</i>(SR)_<i>m</i> nanoclusters is primarily determined by the surface area of the Au nanocluster, consistent with the observed trend of the conversion of 4-nitrobenzaldehyde versus the cluster size. Overall, this work offers molecular insight into the hydrogenation of 4-nitrobenzaldehyde and the catalytically active site structure on gold nanocluster catalysts

Chiral Ag-23 nanocluster with open shell electronic structure and helical face-centered cubic framework

We report the synthesis and crystal structure of a nanocluster composed of 23 silver atoms capped by 8 phosphine and 18 phenylethanethiolate ligands. X-ray crystallographic analysis reveals that the kernel of the Ag nanocluster adopts a helical face-centered cubic structure with C-2 symmetry. The thiolate ligands show two binding patterns with the surface Ag atoms: tri- and tetra-podal types. The tetra-coordination mode of thiolate has not been found in previous Ag nanoclusters. No counter ion (e.g., Na+ and NO3-) is found in the single-crystal and the absence of such ions is also confirmed by X-ray photoelectron spectroscopy analysis, indicating electrical neutrality of the nanocluster. Interestingly, the nanocluster has an open shell electronic structure (i.e., 23(Ag 5s(1))-18(SR) = 5e), as confirmed by electron paramagnetic resonance spectroscopy. Time-dependent density functional theory calculations are performed to correlate the structure and optical absorption/emission spectra of the Ag nanocluster

Photomediated Oxidation of Atomically Precise Au₂₅(SC₂H₄Ph)₁₈^– Nanoclusters

The anionic charge of atomically precise Au₂₅(SC₂H₄Ph)₁₈^– nanoclusters (abbreviated as Au₂₅^–) is thought to facilitate the adsorption and activation of molecular species. We used optical spectroscopy, nonaqueous electrochemistry, and density functional theory to study the interaction between Au₂₅^– and O₂. Surprisingly, the oxidation of Au₂₅^– by O₂ was not a spontaneous process. Rather, Au₂₅^––O₂ charge transfer was found to be a photomediated process dependent on the relative energies of the Au₂₅^– LUMO and the O₂ electron-accepting level. Photomediated charge transfer was not restricted to one particular electron accepting molecule or solvent system, and this phenomenon likely extends to other Au₂₅^––adsorbate systems with appropriate electron donor–acceptor energy levels. These findings underscore the significant and sometimes overlooked way that photophysical processes can influence the chemistry of ligand-protected clusters. In a broader sense, the identification of photochemical pathways may help develop new cluster-adsorbate models and expand the range of catalytic reactions available to these materials