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The possible reaction mechanisms for CO oxidation on the perfect Cu2O(111) surface have been investigated by performing periodic density functional theoretical calculations. We find that Cu2O(111) is able to facilitate the CO oxidation with different mechanisms. Four possible mechanisms are explored (denoted as MER1, MER2, MLH1, and MLH2, respectively): MER1 is CO(gas)+O2(ads)→CO2(gas); MER2 is CO(gas)+O2(ads)→CO3(ads)→O(ads)+CO2(gas); MLH1 refers to CO(ads)+O2(ads)→O(ads)+CO2(ads); and MLH2 refers to CO(ads)+O2(ads)→OOCO(ads)→O(ads)+CO2(ads). Our transition state calculations clearly reveal that MER1 and MLH2 are both viable; but MER1 mechanism preferentially operates, in which only a moderate energy barrier (60.22 kJ/mol) needs to be overcome. When CO oxidation takes place along MER2 path, it is facile for CO3 formation, but is difficult for its decomposition, thereby CO3 species can stably exist on Cu2O(111). Of course, the reaction of CO with lattice O of Cu2O(111) is also considered. However, the calculated barrier is 600.00 kJ/mol, which is too large to make the path feasible. So, we believe that on Cu2O(111), CO reacts with adsorbed O, rather than lattice O, to form CO2. This is different from the usual Mars-van Krevene mechanism. The present results enrich our understanding of the catalytic oxidation of CO by copper-based and metal-oxide catalysts. [ABSTRACT FROM AUTHOR]

Coadsorption of carbon monoxide (CO) and nitric oxide (NO) on the Cu2O(111) surface was studied using periodic density functional theory calculations. It is interesting to find that CO+NO on Cu2O(111) could react to form adsorbed NCO surface species. Coadsorption of CO and NO could give rise to the formation of a O–C...N–O complex well bound to the Cu2O(111) surface, in which both the C–O and N–O bonds are greatly activated and the C–N bond is formed. Consequently, the reaction of CO with NO to form adsorbed NCO and CNO species may occur, for which it is disclosed that NCO formation is more possible than CNO formation both thermodynamically and kinetically. In addition, our calculations of searching transition states reveal that it is facile for NCO formation both kinetically and thermodynamically when CO+NO reaction takes place at CuCUS site, and is impossible when this reaction takes places at Ovac site. Moreover, CO2 species cannot form when CO+NO reaction occurs at Ovac site. Therefore, oxygen vacancy on Cu2O(111) does not play a positive role on CO+NO reaction to forming NCO, CNO, or CO2 species. [ABSTRACT FROM AUTHOR]

The NO oxidation on Cu 2 O(1 1 1) with molecular oxygen, dissociated oxygen, and lattice O, was studied by using periodic density functional theory. Cu 2 O could promote NO oxidation via the more favorable Elay–Rideal mechanism. For NO oxidation with molecular oxygen, path II (NO + O 2 * → O * ONO → NO 2 + O * ; NO + O* → NO 2 * → NO 2 ) was found as the most probable route, in which NO 2 desorption is the reaction rate determining step. The NO oxidation reaction with dissociated oxygen is also possible. In this case, O 2 dissociation occurs after surpassing a barrier of 105 kJ/mol. Thereafter, NO molecule can readily react with oxygen adatoms without barrier or with a moderate-low barrier of 49 kJ/mol. Both of the produced NO 2 molecules will release from the surface. The barrier to be surmounted is 53.3 and 103.2 kJ/mol, respectively. The reaction of NO with lattice O has a high barrier and it is very unlikely. The present results enrich our understanding of the catalytic oxidation of NO by metal-oxide catalysts. [ABSTRACT FROM AUTHOR]

Abstract: First-principles calculations based on density functional theory (DFT) and the generalized gradient approximation (GGA) have been used to study the adsorption of CO and NO molecules on the Cu2O(111) surface in the presence of oxygen vacancy. The calculations employ slab geometry and periodic boundary conditions with partial relaxation of atom positions. Two molecular orientations, X- and O-down (X=C, N), at two distinct sites, Cu1C and oxygen vacancy sites, have been considered. Total energy calculations indicate that the Cu1C position is relatively more favored than the oxygen vacancy site. The predicted binding energies are 144.5kJmol−1 (CO) and 124.1kJmol−1 (NO), respectively. The C–O and N–O stretching frequencies are unequally red-shifted upon adsorption. Upon adsorption at Cu1C site, CO molecule was found to bind to Cu1C atoms in vertical configuration whereas NO molecule adsorption in tilted mode. While upon adsorption at oxygen vacancy site, CO and NO molecules are both vertical to the Cu2O(111) surface. Interestingly, we found that their adsorption properties on oxygen vacancy site are dependent on the defect density. As the density of defective sites increased, the adsorption energies of the defect-XO configuration increase and the N–O bond is continuously weakened whereas the C–O bond remains constant. Therefore, such a process favors the dissociation of the NO molecule and has a small influence on the adsorbed CO molecule. [Copyright &y& Elsevier]

Abstract: Density functional theory has been employed to investigate the adsorption and the dissociation of an N2O at different sites on perfect and defective Cu2O(111) surfaces. The calculations are performed on periodic systems using slab model. The Lewis acid site, CuCUS, and Lewis base site, OSUF are considered for adsorption. Adsorption energies and the energies of the dissociation reaction N2O→N2 +O(s) at different sites are calculated. The calculations show that adsorption of N2O is more favorable on CuCUS adsorption site energetically. CuCUS site exhibits a very high activity. The CuCUS–N2O reaction is exothermic with a reaction energy of 77.45kJmol−1 and an activation energy of 88.82kJmol−1, whereas the OSUF–N2O reaction is endothermic with a reaction energy of 205.21kJmol−1 and an activation energy of 256.19kJmol−1. The calculations for defective surface indicate that O vacancy cannot obviously improve the catalytic activity of Cu2O. [Copyright &y& Elsevier]

Till date numerous microRNAs (miRNAs) have been discovered from various organisms, including mammals, plants, insects, nematodes and viruses. They are known to have antiviral functions in crustaceans such as shrimp Marsupenaeus japonicas. However, little is known about the role of miRNAs against bacterial infection in this shrimp caused by Vibrio alginolyticus . We performed small RNA sequencing to characterize the differentially expressed microRNAs in V. alginolyticus challenged shrimp, in comparison to that in control uninfected shrimp, at 24 h and 48 h. In total, 55 host miRNAs were differentially expressed in response to the infection and most of these were downregulated at both the time-points. TargetScan and miRanda algorithms showed that the target genes of these down-regulated miRNAs were related to innate immune functions such as production of phenoloxidase enzyme, apoptosis and phagocytosis. Further, gene ontology analysis revealed that many immune signaling pathways were mediated by these miRNAs. This study is one of the earliest attempts at characterizing shrimp miRNAs that respond to V. alginolyticus infection, and will help unravel the miRNA pathways involved in antibacterial action in shrimp. [ABSTRACT FROM AUTHOR]

A comprehensive investigation has been made on the ground state, magnetic, ferroelectric and optical properties of the recently synthesized ferroelectric-like LiOsO 3 by first-principle calculations. It is found that the ground state of perfect LiOsO 3 is G type antiferromagnetic (G-AFM) order by both LSDA + U with U eff > 0 eV and HSE. For the G-AFM order, when U eff > 1.75 eV the charge gap opens for LiOsO 3 while the gap is about 0.60 eV by HSE. So the perfect LiOsO 3 should be a G-AFM semiconductor. As for the Li-defected Li 0.94 OsO 3 , the Fermi level shifts to the valence bands. On the other hand the translational periodicity is destroyed by various defects, leading to the disappearance of magnetic order which is responsible for the ferroelectric metal state observed in experiment. This is proved by the decrease of the Os average magnetic moments of Li-defected LiOsO 3 . The calculated spontaneous polarization of perfect LiOsO 3 is about 22.23 μC/cm 2 and the largest component of second order nonlinear optical coefficient is 80.795 pm/V, which indicate that it should be a potential ferroelectric and nonlinear optical material. [ABSTRACT FROM AUTHOR]

Rhombohedral BiFeO 3 which has a large spontaneous polarization is a candidate material for ferroelectric random access memory (FeRAM). And the polarization reversal is the key factor for the application of FeRAM. Here, the electronic, linear and nonlinear optical properties, structure and its stability of BiFeO 3 during the continuous polarization reversal from reference cubic phase to ferroelectric R3c phase were systematically investigated by LSDA + U (local spin density approximation plus Hubbard U) and DFPT (density functional perturbation theory) method. We proposed that the nonlinear optical second order coefficients could be indicators to check the polarization reversal of BiFeO 3 and our result showed that the coefficient reach its maximum between 20% distortion and 40% distortion during the half path of the reversal. The relationship between the nonlinear optical second order coefficient and the Bader charge was also compared and we found the coefficient is also dependent on the Bader charge. In addition, the linear optical absorption coefficient was calculated; the obvious change in absorption peaks was observed during the transition. By comparing the crystal orbital of the reference cubic phase and distorted R3c phase we found that the hybridized Bi 6s and O 2p is the main reason that causes the structure distortion. The local phonon density of states proves that the Bi and O interaction is the origin of the instability of cubic phase BiFeO 3 . The factor group analysis showed the change of Raman and IR modes during the transition. [ABSTRACT FROM AUTHOR]