Theoretical prediction of superatom WSi12-based catalysts for CO oxidation by N2O.

Catalytic conversion of N2O and CO into nonharmful gases is of great significance to reduce their adverse impact on the environment. The potential of the WSi12 superatom to serve as a new cluster catalyst for CO oxidation by N2O is examined for the first time. It is found that WSi12 prefers to adsorb the N2O molecule rather than the CO molecule, and the charge transfer from WSi12 to N2O results in the full activation of N2O into a physically absorbed N2 molecule and an activated oxygen atom that is attached to an edge of the hexagonal prism structure of WSi12. After the release of N2, the remaining oxygen atom can oxidize one CO molecule via overcoming a rate-limiting barrier of 28.19 kcal mol-1. By replacing the central W atom with Cr and Mo, the resulting MSi12 (M = Cr and Mo) superatoms exhibit catalytic performance for CO oxidation comparable to the parent WSi12. In particular, the catalytic ability of WSi12 for CO oxidation is well maintained when it is extended into tube-like WnSi6(n+1) (n = 2, 4, and 6) clusters with energy barriers of 25.63-29.50 kcal mol-1. Moreover, all these studied MSi12 (M = Cr, Mo, and W) and WnSi6(n+1) (n = 2, 4, and 6) species have high structural stability and can absorb sunlight to drive the catalytic process. This study not only opens a new door for the atomically precise design of new silicon-based nanoscale catalysts for various chemical reactions but also provides useful atomic-scale insights into the size effect of such catalysts in heterogeneous catalysis.

On the Catalytic Performance of (ZrO)n (n=1-4) Clusters for CO Oxidation: A DFT Study.

The unique characteristic of superatoms to show chemical properties like those of individual atoms opens a new avenue towards replacing noble metals as catalysts. Given the similar electronic structures of the ZrO superatom and the Pd atom, the CO oxidation mechanisms catalysed by (ZrO)n (n=1-4) clusters were investigated in detail to evaluate their catalytic performance. Our results reveal that a single ZrO superatom exhibits superior catalytic ability in CO oxidation than both larger (ZrO)n (n=2-4) clusters and a Pd atom, indicating the promising potential of ZrO as a "single-superatom catalyst". Moreover, the mechanism of CO oxidation catalysed by ZrO+/- suggests that depositing a ZrO superatom onto the electron-rich substrates is a better choice for practical catalysis application. Accordingly, a graphene nanosheet (coronene) was chosen as a representative substrate for ZrO and Pd to assess their catalytic performances in CO oxidation. Acting as an "electron sponge", this carbon substrate can both donate and accept charges in different reaction steps, enabling the supported ZrO to achieve enhanced catalytic performance in this process with a low energy barrier of 19.63 kcal/mol. This paper presents a new realization on the catalytic performance of Pd-like superatom in CO oxidation, which could increase the interests in exploring noble metal-like superatoms as efficient catalysts for various reactions.

Polymeric tungsten carbide nanoclusters as potential non-noble metal catalysts for CO oxidation.

The discovery of tungsten carbide (WC) as an analog of the noble metal Pt atom is of great significance toward designing novel highly-active catalysts from the viewpoint of the superatom concept. The potential of such a superatom to serve as building blocks of replacement catalysts for Pt has been evaluated in this work. The electronic properties, adsorption behaviors, and catalytic mechanisms towards the CO oxidation of (WC)n and Ptn (n = 1, 2, 4, and 6) were compared. Counterintuitively, these studied (WC)n clusters exhibit quite different electronic properties and adsorption behaviours from the corresponding Ptn species. For instance, (WC)n preferentially adsorbs O2, whereas Ptn tends to first combine with CO. Even so, it is interesting to find that the catalytic performances of (WC)n are always superior to the corresponding Ptn, and especially, the largest (WC)6 cluster exhibits the best catalytic ability towards CO oxidation. Therefore, assembling superatomic WC clusters into larger polymeric clusters can be regarded as a novel strategy to develop efficient superatom-assembled catalysts for CO oxidation. It is highly expected to see the realization of non-noble metal catalysts for various reactions in the near future experiments by using superatoms as building blocks.

Designing Special Nonmetallic Superalkalis Based on a Cage-like Adamanzane Complexant.

In this study, to examine the possibility of using cage-like complexants to design nonmetallic superalkalis, a series of X@36adz (X = H, B, C, N, O, F, and Si) complexes have been constructed and investigated by embedding nonmetallic atoms into the 36adamanzane (36adz) complexant. Although X atoms possess very high ionization energies, these resulting X@36adz complexes possess low adiabatic ionization energies (AIEs) of 0.78-5.28 eV. In particular, the adiabatic ionization energies (AIEs) of X@36adz (X = H, B, C, N, and Si) are even lower than the ionization energy (3.89 eV) of Cs atoms, and thus, can be classified as novel nonmetallic superalkalis. Moreover, due to the existence of diffuse excess electrons in B@36adz, this complex not only possesses pretty low AIE of 2.16 eV but also exhibits a remarkably large first hyperpolarizability (ß 0) of 1.35 × 106 au, indicating that it can also be considered as a new kind of nonlinear optical molecule. As a result, this study provides an effective approach to achieve new metal-free species with an excellent reducing capability by utilizing the cage-like organic complexants as building blocks.

Designing an alkali-metal-like superatom Ca3B for ambient nitrogen reduction to ammonia.

Converting earth-abundant nitrogen (N2) gas into ammonia (NH3) under mild conditions is one of the most important issues and a long-standing challenge in chemistry. Herein, a new superatom Ca3B was theoretically designed and characterized to reveal its catalytic performance in converting N2 into NH3 by means of density functional theory (DFT) computations. The alkali-metal-like identity of this cluster is verified by its lower vertical ionization energy (VIE, 4.29 eV) than that of potassium (4.34 eV), while its high stability was guaranteed by the large HOMO-LUMO gap and binding energy per atom (Eb). More importantly, this well-designed superatom possesses unique geometric and electronic features, which can fully activate N2via a "double-electron transfer" mechanism, and then convert the activated N2 into NH3 through a distal reaction pathway with a small energy barrier of 0.71 eV. It is optimistically hoped that this work could intrigue more endeavors to design specific superatoms as excellent catalysts for the chemical adsorption and reduction of N2 to NH3.

DFT study on the adsorption of 5-fluorouracil on B40, B39M, and M@B40 (M = Mg, Al, Si, Mn, Cu, Zn).

Based on density functional theory, the adsorption behavior of 5-fluorouracil (5-Fu) on B40 and its derivatives has been explored. It was observed that 5-Fu prefers to combine with the corner boron atom of the B40 cage via one of its oxygen atoms, forming a strong polar covalent B-O bond. The adsorption energy of 5-Fu on B40 was calculated to be -11.15 kcal mol-1, and thus, it can be duly released from B40 by protonation in the slightly acidic environment of tumor tissue, which makes for reducing the toxic and side effects of this drug. Additionally, the substituent and embedding effect of Mg, Al, Si, Mn, Cu, and Zn atoms on the drug delivery performance of B40 have been also considered. We hope this work could offer some implications for the potential application of boron-based nanomaterials, such as B40 in drug delivery.

On the Role of Alkali-Metal-Like Superatom Al12 P in Reduction and Conversion of Carbon Dioxide.

Developing efficient catalysts for the conversion of CO2 into fuels and value-added chemicals is of great significance to relieve the growing energy crisis and global warming. With the assistance of DFT calculations, it was found that, different from Al12 X (X=Be, Al, and C), the alkali-metal-like superatom Al12 P prefers to combine with CO2 via a bidentate double oxygen coordination, yielding a stable Al12 P(η2 -O2 C) complex containing an activated radical anion of CO2 (i.e., CO2 .- ). Thereby, this compound could not only participate in the subsequent cycloaddition reaction with propylene oxide but also initiate the radical reaction with hydrogen gas to form high-value chemicals, revealing that Al12 P can play an important role in catalyzing these conversion reactions. Considering that Al12 P has been produced in laboratory and is capable of absorbing visible light to drive the activation and transformation of CO2 , it is anticipated that this work could guide the discovery of additional superatom catalysts for CO2 transformation and open up a new research field of superatom catalysis.

Diverse Hap43-independent functions of the Candida albicans CCAAT-binding complex.

The CCAAT motif is ubiquitous in promoters of eukaryotic genomes. The CCAAT-binding complex (CBC) is conserved across a wide range of organisms, specifically recognizes the CCAAT motif, and modulates transcription directly or in cooperation with other transcription factors. In Candida albicans, CBC is known to interact with the repressor Hap43 to negatively regulate iron utilization genes in response to iron deprivation. However, the extent of additional functions of CBC is unclear. In this study, we explored new roles of CBC in C. albicans and found that CBC pleiotropically regulates many virulence traits in vitro, including negative control of genes responsible for ribosome biogenesis and translation and positive regulation of low-nitrogen-induced filamentation. In addition, C. albicans CBC is involved in utilization of host proteins as nitrogen sources and in repression of cellular flocculation and adhesin gene expression. Moreover, our epistasis analyses suggest that CBC acts as a downstream effector of Rhb1-TOR signaling and controls low-nitrogen-induced filamentation via the Mep2-Ras1-protein kinase A (PKA)/mitogen-activated protein kinase (MAPK) pathway. Importantly, the phenotypes identified here are all independent of Hap43. Finally, deletion of genes encoding CBC components slightly attenuated C. albicans virulence in both zebrafish and murine models of infection. Our results thus highlight new roles of C. albicans CBC in regulating multiple virulence traits in response to environmental perturbations and, finally, suggest potential targets for antifungal therapies as well as extending our understanding of the pathogenesis of other fungal pathogens.