Ligand Effects of Thiolate-Protected Au₁₀₂ Nanoclusters

The Au₁₀₂(<i>p</i>-MBA)₄₄ (<i>p</i>-MBA = <i>para</i>-mercaptobenzoic acid) nanocluster is an ideal model to study the structures of gold nanoclusters, the motifs of the monolayer ligand groups, and the crystal formation of Au nanoparticles. Based on the partially exchanged Au₁₀₂(<i>p</i>-MBA)₄₀(<i>p</i>-BBT)₄ (<i>p</i>-BBT = <i>para</i>-bromobenzene thiol) crystal structure (<i>J. Am. Chem. Soc.</i> <b>2012</b>, <i>134</i>, 13316–13322), we employed density functional theory to investigate the ligand effects for different thiolate substitutions. It was found that the intermolecular π–π stacking plays an important role for the crystal’s stability in addition to the increased intrinsic stability from the substituent monomer. Furthermore, we suggested <i>para</i>-(dimethylamino) benzenethiol (N­(CH₃)₂–C₆H₄–SH) and <i>para</i>-amino benzenethiol (NH₂–C₆H₄–SH) would be more favorable than <i>p</i>-BBT for the stabilities of partially exchanged Au₁₀₂(<i>p</i>-MBA)₄₄ crystal structures due to their stronger intermolecular π–π stacking. This study provides a theoretical template for surface chemical engineering

Carboxylic Acid Group-Induced Oxygen Vacancy Migration on an Anatase (101) Surface

Dye-sensitized solar cells (DSSCs) have aroused intensive interest for the replacement of conventional crystalline silicon solar cells. Through carboxylic acid groups, the dyes attach to the TiO₂ anatase (101) surface, on which the subsurface oxygen vacancies (Vo^subs) are predominant. The performance of DSSCs can be affected by the presence and positions of oxygen vacancies (Vos). By applying density functional theory calculations, we found that the adsorption of a carboxylic acid group-decorated dye molecule reverses the relative stability between the surface oxygen vacancy (Vo^surf) and Vo^sub on the anatase (101) surface, which facilitates the migration of the Vo from the subsurface to the surface by overcoming an energy barrier of less than 0.16 eV, which is significantly lower than the 1.01 eV energy barrier on the clean surface. Further, ab initio molecular dynamics simulations indicate that the Vo^sub can easily migrate to the surface at room temperature. This dynamic interplay between the Vo of the anatase (101) surface and the carboxylic acid group would be important for future studies concerning the stability and photovoltaic efficiency of the solar cells

Water-Promoted O₂ Dissociation on Small-Sized Anionic Gold Clusters

Although thermodynamically O₂ favors dissociative adsorption over molecular adsorption on small-sized anionic gold clusters (except Au₂^–), O₂ dissociation is unlikely to proceed under ambient conditions because of the high activation energy barrier (>2.0 eV). Here, we present a systematic theoretical study of reaction pathways for the O₂ dissociation on small-sized anionic gold nanoclusters Au_<i>n</i>^– (<i>n</i> = 1–6) with and without involvement of a water molecule. The density functional theory calculations indicate that the activation barriers from the molecular adsorption state of O₂ to dissociative adsorption can be significantly lowered with the involvement of a H₂O molecule. Once the O₂ dissociates on small-size gold clusters, atomic oxygen is readily available for other reactions, such as the CO oxidation, on the surface of gold clusters. This theoretical study supports previous experimental evidence that H₂O can be used to activate O₂, which suggests an alternative way to exploit catalytic capability of gold clusters for oxidation applications

Unraveling the Atomic Structures of the Au₆₈(SR)₃₄ Nanoparticles

The atomic structure prediction of thiolate-protected gold nanoparticle (RS-AuNP) Au₆₈(SH)₃₄ is performed based on the “divide and protect” concept and experimental studies on 14 kDa RS-AuNPs. Four low-lying energy isomers, <b>Iso1</b>–<b>Iso4</b>, were identified by the density-functional theory. Our results indicate the most stable structure <b>Iso2</b> adopts the <i>C</i>_2<i>v</i> Au₅₀ core with Marks-decahedral (m-Dh) Au₁₈ inner core. The calculated HOMO–LUMO gap is 0.74 eV, which is very close to that of Au₆₇(SR)₃₅^2–. Further analysis suggests the 14 kDa RS-AuNPs might be not only the turn point between the fused core structure and the compact core structure but also the turn point between the one-shell inner core structure and the multishell inner core structure. The threshold number of Au atoms in bulk-like RS-AuNPs is evaluated as ∼263 based on the linear fitting of the HOMO–LUMO gaps of various RS-AuNPs including Au₆₈(SR)₃₄. The research on the medium-sized Au₆₈(SR)₃₄ establishes a bridge between smaller and larger RS-AuNPs, which is beneficial for us to better understand the structures of the RS-AuNPs

Histogram presentation of gene ontology (GO) classification.

<p>The results are summarized in three main categories: biological process, molecular function and cellular component. The y-axis indicates the number of genes in a category. In three main categories of GO classification, there are 16, 17, and 20 functional groups, respectively. Metabolic process (GO: 0008152), with 851 genes, are dominant in the main category of biological process. Binding (GO: 0005488) and cell part (GO: 0044464) consisted of 6892 and 2688 genes, are dominant in the main categories of molecular function and cellular component, respectively.</p

Effect of Water Adsorption on the Photoluminescence of Silicon Quantum Dots

The optical properties of silicon quantum dots (Si QDs) are strongly influenced by circumjacent surface-adsorbed molecules, which would highly affect their applications; however, water, as the ubiquitous environment, has not received enough attention yet. We employed the time-dependent density functional calculations to investigate the water effect of photoluminescence (PL) spectra for Si QDs. In contrast with the absorption spectra, PL spectra exhibit distinct characteristics. For Si₃₂H₃₈, PL presents the single maximum in the dry and humid environment, while the emission spectrum displays a dual-band fluorescence spectroscopy in the low-humidity environment. This phenomenon is also observed in the larger Si QDs. The distinct character in spectroscopy is dominated by the stretching of the Si–Si bond, which could be explained by the self-trapped exciton model. Our results shed light on the Si–water interaction that is important for the development of optical devices based on Si-coated surfaces

Subgroup analysis stratified by geographic distribution for the association of <i>H. pylori</i> infection with pancreatic cancer.

<p>OR, odds ratio; CI, confidence interval.</p

Anisotropy Enhancement of Thermal Energy Transport in Supported Black Phosphorene

Thermal anisotropy along the basal plane of materials possesses both theoretical importance and application value in thermal transport and thermoelectricity. Though common two-dimensional materials may exhibit in-plane thermal anisotropy when suspended, thermal anisotropy would often disappear when supported on a substrate. In this Letter, we find a strong anisotropy enhancement of thermal energy transport in supported black phosphorene. The chiral preference of energy transport in the zigzag rather than the armchair direction is greatly enhanced by coupling to the substrate, up to a factor of approximately 2-fold compared to the suspended one. The enhancement originates from its puckered lattice structure, where the nonplanar armchair energy transport relies on the out-of-plane corrugation and thus would be hindered by the flexural suppression due to the substrate, while the planar zigzag energy transport is not. As a result, thermal conductivity of supported black phosphorene shows a consistent anisotropy enhancement under different temperatures and substrate coupling strengths

Changes in gene expression profile among the different developmental stages.

<p>The number of up-regulated and down-regulated genes between R1 and R2, R2 and R3 are summarized. Between the R1 (3 DAP) and R2 (7 DAP) rice embryo libraries, there are 275 genes up-regulated and 397 genes down-regulated, while there are 128 up-regulated genes and 376 down-regulated genes between the R2 (7 DAP) and R3 (14 DAP) rice embryo libraries.</p

Flow diagram of literature search and study selection.

<p>Flow diagram of literature search and study selection.</p