First-principles investigation of copper diffusion barrier performance in defective 2D layered materials

This paper investigates the diffusion barrier performance of 2D layered materials with pre-existing vacancy defects using first-principles density functional theory. Vacancy defects in 2D materials may give rise to a large amount of Cu accumulation, and consequently, the defect becomes a diffusion path for Cu. Five 2D layered structures are investigated as diffusion barriers for Cu, i.e., graphene with C vacancy, hBN with B/N vacancy, and MoS2 with Mo/2S vacancy. The calculated energy barriers using climbing image - nudged elastic band show that MoS2-V2S has the highest diffusion energy barrier among other 2D layers, followed by hBN-VN and graphene. The obtained energy barrier of Cu on defected layer is found to be proportional to the length of the diffusion path. Moreover, the diffusion of Cu through vacancy defects is found to modulate the electronic structures and magnetic properties of the 2D layer. The charge density difference shows that there exists a considerable charge transfer between Cu and barrier layer as quantified by Bader charge. Given the current need for an ultra-thin diffusion barrier layer, the obtained results contribute to the field of application of 2D materials as Cu diffusion barrier in the presence of mono-vacancy defects.

Remarkable COx tolerance of Ni3+ active species in Ni2O3 catalyst for sustained electrochemical urea oxidation

The electrochemical urea oxidation reaction (UOR) provides a cost-effective way of generating hydrogen owing to its low thermodynamic energy barrier. Although UOR is an effective way to generate hydrogen, sustained...

Substrate Specificity for Human Histidine Methyltransferase SETD3

Histidine methyltransferase SETD3 plays an important role in human biology and diseases. Previously, we showed that SETD3 catalyzes N3-methylation of histidine 73 in β-actin (Kwiatkowski et al., 2018). Here we report integrated synthetic, biocatalytic, biostructural and computational analyses on human SETD3-catalyzed methylation of β-actin peptides possessing histidine and its structurally and chemically diverse mimics. Our enzyme assays supported by biostructural analyses demonstrate that SETD3 has a broader substrate scope beyond histidine, including N-nucleophiles on the aromatic and aliphatic side chains. Quantum mechanical/molecular mechanical (QM/MM) molecular dynamics and free-energy simulations provide insight into binding geometries and the free energy barrier for the enzymatic methyl transfer to histidine mimics, further supporting experimental data that histidine is the superior SETD3 substrate over its analogs. This work demonstrates that human SETD3 has a potential to catalyze efficient methylation of several histidine mimics, overall providing mechanistic, biocatalytic and functional insight into β-actin histidine methylation by SETD3.

Transformation of addimers >Ge=GeGe=SiSi=Si< on the relaxed side of Si (001) (4 × 2)

By the method of density functional theory (B3LYP, 6-31G **) three types of displacements are calculated, namely oscillations as a whole, rotation and diffusion of dimers > Ge = Ge <, > Ge = Si < and > Si = Si <, which are formed on the crystalline surface of Si (001) (4×2) during the deposition of germanium atoms under conditions of molecular beam epitaxy. Calculations of angles of buckling of addimers are carried out. It is shown that when the addimers as a whole oscillate around the equilibrium position, the energy barriers are quite low, the highest of them occurs for a mixed addimer > Si = Ge <. Pure adders > Ge = Ge < and > Si = Si < oscillate between two degenerate states with an energy barrier of 0.042 and 0.014 eV, respectively. The structures of the transition state and the intermediate when the addimer > Ge = Ge < is moved between adjacent cells in the approximation of the constant bond length > Ge = Ge < are obtained. As calculations have shown, all transformations of surface dimers occur with relatively small activation energies, the numerical values of which agree satisfactorily with the results of STM experiments available in the literature.

Free Energy Surfaces and Barriers for Vacancy Diffusion on Al(100), Al(110), Al(111) Reconstructed Surfaces

Metadynamics is a popular enhanced sampling method based on the recurrent application of a history-dependent adaptive bias potential that is a function of a selected number of appropriately chosen collective variables. In this work, using metadynamics simulations, we performed a computational study for the diffusion of vacancies on three different Al surfaces [reconstructed Al(100), Al(110), and Al(111) surfaces]. We explored the free energy landscape of diffusion and estimated the barriers associated with this process on each surface. It is found that the surfaces are unique regarding vacancy diffusion. More specically, the reconstructed Al(110) surface presents four metastable states on the free energy surface having sizable and connected passage-ways with an energy barrier of height 0.55 eV. On the other hand, the reconstructed Al(100)/Al(111) surfaces exhibit two/three metastable states, respectively, with an energy barrier of height 0.33 eV. The findings in this study can help to understand surface vacancy diffusion in technologically relevant Al surfaces.

Water Gas Shift Reaction Activity on Fe (110): A DFT Study

Metal Fe is one of the phases existing on iron-based catalysts for a high-temperature water gas shift reaction (WGSR), but research on the activity of metal Fe in WGSR is almost not reported. In this work, the density functional theory (DFT) method was used to systematically study the reaction activity and mechanisms of WGSR on metal Fe (110), including the dissociation of H2O, the transformation of CO and the formation of H2, as well as the analysis of surface electronic properties. The results show that (1) the direct dissociation of H2O occurs easily on Fe (110) and the energy barrier is less than 0.9 eV; (2) the generation of CO2 is difficult and its energy barrier is above 1.8 eV; (3) H migrates easily on the Fe surface and the formation of H2 also occurs with an energy barrier of 1.47 eV. Combined with the results of Fe3O4, it can be concluded that the active phase should be Fe3O4 with O vacancy defects, and the iron-rich region plays an important role in promoting the formation of H2 in WGSR.

ENERGY OF THE INITIATION REACTION OF CATIONIC POLYMERIZATION OF 2-METHYLPENTENE-1 IN THE PRESENCE OF AQUACOMPLEX OF ETHYLALUMINUM CHLORIDE AND HEPTANE

The ab initio 3.21G method was used to study the initiation mechanism of 2-methylpentene-1 under the action of a complex catalyst AlClCH - HO in heptane of stoichiometric composition 1:1:1:1. The energetics of this reaction is estimated, the values of its energy barrier and enthalpy are obtained.

Reaction Mechanism About Isomerization of Resin Acids and Synthesis of Acrylopimaric Acid Based on DFT Calculation

Acrylopimaric acid is considered one of the possible substitutes for petroleum-based polymeric monomers, which is an important industrial product. Resin acids were isomerized to form levopimaric acid(4), which reacted with acrylic acid to synthesize isomers of acrylopimaric acid. Density functional theory calculation was used to investigate the reaction mechanisms with seven reaction paths in five different solutions. The values of ΔG were sorted from highest to lowest by levopimaric acid(4), neoabietic acid(3), palustric acid(2), and bietic acid(1). From the perspective of dynamics, the energy barrier in the isomerization of palustric acid(2) to levopimaric acid(4) was the lowest, whereas the highest energy barrier was the isomerization of neoabietic acid(3) to levopimaric acid(4) in the same solution. The addition reaction of levopimaric acid(4) and acrylic acid(5) to acrylopimaric acid c(8) was the optimal reaction path dynamically. However, ΔG of acrylopimaric acid c(8) was higher than that of acrylopimaric acid d(9). In general, the rates of isomerization reactions for rosin resin acids and addition reaction for acrylopimaric acid in water were higher than those in other solvents. HOMO-LUMO and ESP were analyzed for 8 kinds of molecules. For acylpyimaric acid, the non-planar six-memed ring and the C-C double bonds were easily attacked by nucleophile, while the non-planar six-memed ring and the carboxyl group are easily reacted with electrophiles. The highest electrostatic potential of the eight molecules is located at H of the carboxyl group, while the highest electrostatic potential is located at C-O double bond of the carboxyl group.