Two-Dimensional Semiconducting Boron Monolayers

The two-dimensional boron monolayers were reported to be metallic both in previous theoretical predictions and experimental observations, however, we have firstly found a family of boron monolayers with the novel semiconducting property as confirmed by the first-principles calculations with the quasi-particle G0W0 approach. We demonstrate that the vanished metallicity characterized by the pz-derived bands cross the Fermi level is attributed to the motif of a triple-hexagonal-vacancy, with which various semiconducting boron monolayers are designed to realize the band-gap engineering for the potential applications in electronic devices. The semiconducting boron monolayers in our predictions are expected to be synthesized on the proper substrates, due to the similar stabilities to the ones observed experimentally.Comment: 12 pages, 4 figure

Inverse NiO_1–<i>x</i>/Cu Catalyst with High Activity toward Water–Gas Shift

Ni additives into Cu catalyst can enhance the activity to the water–gas shift (WGS) reaction. However, an undesirable side reaction (methanation) would arise synchronously, consequently sharply degrading the selectivity to WGS. Herein, we propose an improved CuNi model system with potential excellent performance (both activity and selectivity) toward WGS, i.e., the inverse NiO_1–<i>x</i>/Cu­(111) (<i>x</i> < 1). The unsaturated Ni^δ+ species are expected to facilitate the rate-limiting step of WGS remarkably, H₂O dissociation, and subsequently, a rather smooth potential energy surface is found in the rest of the steps of WGS over the interface of NiO_1–<i>x</i>/Cu­(111), indicating a high reactivity. Meanwhile, a weak interaction between CO and NiO_1–<i>x</i> and a low activity of NiO_1–<i>x</i>/Cu­(111) toward CO dissociation imply that the oxidized Ni^δ+ species can effectively suppress the undesirable methanation found in CuNi catalysts, expecting to improve its selectivity toward WGS. The model system may be also applied to catalyze CO oxidation at proper conditions

Competition between Pauli Exclusion and H‑Bonding: H₂O and NH₃ on Silicene

We demonstrate that the competition between Pauli exclusion and H-bonding dominates the adsorption of H₂O on silicene through first-principles calculations. It explains the bewildering problem that isolated H₂O is inert on silicene while isolated NH₃ tends to chemisorption. Moreover, Pauli exclusion can be overcome by the synergetic effect of Si···O dative bonding and intermolecular H-bonding. As a result, H₂O molecules are readily to chemisorb in clusters. It is expected that the competition is in general polar molecule adsorption on silicene and, thus, crucial for the adsorption mechanism

A Practical Criterion for Screening Stable Boron Nanostructures

Due to the electron deficiency, boron clusters evolve strikingly with the increasing size as confirmed by experimentalists and theorists. However, it is still a challenge to propose a model potential to describe the stabilities of boron. On the basis of the 2c-2e and 3c-2e bond models, we have found the constraints for stable boron clusters, which can be used for determining the vacancy concentration and screening the candidates. Among numerous tubular structures and quasi-planar structures, we have verified that the stable clusters with lower formation energies bounded by the constraints, indicating the competition of tubular and planar structures. Notably, we have found a tubular cluster of B₇₆ which is more stable than the B₈₀ cage. We show that the vacancies, as well as the edge, are necessary for the 2c-2e bonds, which will stabilize the boron nanostructures. Therefore, the quasi-planar and tubular boron nanostructures could be as stable as the cages, which have no edge atoms. Our finding has shed light on understanding the complicated electron distributions of boron clusters and enhancing the efficiency of searching stable B nanostructures

Expression profile of <i>TwFPS1</i> and <i>TwFPS2</i> when treated with 1mM methyl jasmonate (MeJA) over 48h.

<p>RT-PCR analysis was performed using total RNA isolated from suspension cells of <i>T</i>. <i>wilfordii</i>. <b>A</b><i>TwFPS1</i> expression at 0h was set as 1; <b>B</b><i>TwFPS2</i> expression at 0h was set as 1. Data are presented as mean±SE from three experimental replicates.</p

Comparison of the deduced amino acid sequences of<i>TwFPS1</i>, <i>TwFPS2</i> and related proteins.

<p>The five conserved domains of prenyltransferases are boxed and numbered. The highly conserved aspartate-rich motif (DDXX(XX)D) was present in domains II and V.</p

Expression patterns of <i>TwFPS1</i>and <i>TwFPS2</i> in different <i>T</i>. <i>wilfordii</i> tissues.

<p>Total RNA isolated from roots, stems and leaves. <b>A</b><i>TwFPS1</i> expression in leaves was set as1; <b>B</b><i>TwFPS2</i> expression in leaves was set as 1. Data are presented as mean±SE from three experimental replicates.</p

The main medicinal active substances of <i>Tripterygium wilfordii</i>.

<p>The main medicinal active substances of <i>Tripterygium wilfordii</i>.</p

SDS-PAGE analysis of recombinant <i>TwFPS1</i>and <i>TwFPS2</i> protein expressed in <i>E</i>. <i>coli</i>.

<p><b>A</b> Lane M, protein molecular weight marker(low); Lane 1, the supernatant of the empty vector without the induction; Lane2, the sediment of the empty vector without the induction; Lane 3, the supernatant of the empty vector with the induction; Lane 4, the sediment of the empty vector with the induction; Lane 5, the supernatant of the<i>TwFPS1</i> protein without the induction; Lane 6, the sediment of the <i>TwFPS1</i> protein without the induction; Lane7, the supernatant of the<i>TwFPS1</i> protein with the induction; Lane 8, the sediment of <i>TwFPS1</i> protein with the induction; <b>B</b> Lane M, protein molecular weight marker (low); Lane 1, the supernatant of the<i>TwFPS2</i>protein with the induction; Lane 2,the supernatant of the empty vector bacteria with the induction; Lane 3,the supernatant of the<i>TwFPS2</i> bacteria with the induction; Lane 4, the sediment of the empty vector with the induction; Lane 5, the supernatant of the empty vector with the induction; Lane 6, the sediment of <i>TwFPS2</i> protein with the induction.</p

GC—MS analysis of reaction products catalyzed by purified recombinant <i>TwFPS</i> incubated with IPP and DMAPP.

<p><b>A</b> Control (the empty vector). <b>B</b> The reaction products catalyzed by purified recombinant <i>TwFPS1</i> (IPP and DMAPP were added to the reaction mixture). <b>C</b> The reaction products catalyzed by purified recombinant <i>TwFPS2</i> (IPP and DMAPP were added to the reaction mixture). <b>D</b> GC—MS analysis of dephosphorylated FPP (farnesol) as standards. <b>E</b> The mass spectrogram of the reaction products catalyzed by purified recombinant <i>TwFPS1</i>.<b>F</b> The mass spectrogram of the reaction products catalyzed by purified recombinant <i>TwFPS2</i>. <b>G</b> The mass spectrogram of the dephosphorylated FPP(farnesol).</p