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

H₂ + H₂O → H₄O: Synthesizing Hyperhydrogenated Water in Small-Sized Fullerenes?

Nanoscale confinement provides an ideal platform to rouse some exceptional reactions which cannot happen in the open space. Intuitively, H2 and H2O cannot react. Herein, through utilizing small-sized fullerenes (C24, C26, C28, and C30) as nanoreactors, we demonstrate that a hyperhydrogenated water species, H4O, can be easily formed using H2 and H2O under ambient conditions by ab initio molecular dynamics simulations. The H4O molecule rotates freely in the cavity of the cages and maintains its structure during the simulations. Further theoretical analysis indicates that H4O in the fullerene possesses high stability thermodynamically and chemically, which can be rationalized by the electron transfer between H4O and the fullerene. This work highlights the possibility of utilizing fullerene as a nanoreactor to provide confinement constraints for unexpected chemistry

Au₄₂: An Alternative Icosahedral Golden Fullerene Cage

We present a new icosahedral gold fullerene, Au42, based on density functional theory calculations. The Au42 fullerene has a nanoscale hollow space that can hold up to 13 Au atoms. The Au42 fullerene also has a larger HOMO−LUMO gap compared to the compact-filling geometries. However, unlike the known gold fullerene Au32, the Au42 fullerene does not satisfy the 2(N + 1)2 aromatic rule and has a positive NICS value at the center of the cage. These two nanometer-sized gold fullerenes can be used as golden cages to accommodate other atoms or molecules for the purpose of studying fundamental chemistry because of their apparently dissimilar chemical characteristics, or they can be used as structural motifs to build highly stable core−shell nanoclusters or novel cluster-assembled materials

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

Fig 9 -

Compression test of mud film of naturally weathered red-bed soil (A) Mud film; (B) Application of 100 N pressure to mud film; (C) Application of 200 N pressure to mud film; (D) Application of 400 N pressure to mud film; (E) Application of 800 N pressure to mud film.</p

Effects of mud viscosity, water content and particle content smaller than 1 mm on the infiltration distance of a mud film.

Effects of mud viscosity, water content and particle content smaller than 1 mm on the infiltration distance of a mud film.</p

Fig 14 -

Infiltration of 8 mm thick naturally weathered red-bed soil films after dropping water (A) Water dropped on an 8 mm thick naturally weathered red-bed soil film for 3 m; (B) Water dropped on an 8 mm thick naturally weathered red-bed soil film for 6 min; (C) Water dropped on an 8 mm thick naturally weathered red-bed soil film for 9 min; (D) Water dropped on an 8 mm thick naturally weathered red-bed soil film for 12 min.</p

S5 File -

(XLSX)</p

Mud film permeability test.

Mud film permeability test.</p