Binding Energy Of Ca Research Articles

Phytochemicals and in silico investigations of Sudanese roselle

We analysed four different Sudanese roselle samples for their potential as novel xanthine oxidase (XO) inhibitors. Phytochemical screening showed the presence of polyphenols, flavonoids, organic acids, saponins and sterols in all samples. Liquid chromatography with tandem mass spectrometry (LC-MS/ MS) was used to identify and characterise five anthocyanins in all samples: cyanidin-3-glucoside (cy-3-glu), delphinidin-3-sambubioside (dp-3-sam), cyanidin-3-rhamnoside (cy-3-rhm), delphinidin-3‑rhamnoside (dp-3-rhm) and pelargonidin-3-glucoside (pg-3-glu). Identification of cy-3-rhm, dp-3-rhm and pg-3-glu confirmed the selectivity and sensitivity of LC-MS as a powerful technique for identifying anthocyanins. In silico studies of the identified anthocyanins were performed to explore their promising inhibitory activity toward XO. Interactions between the ligand and the enzyme were via the H-bond, and hydrophobic (π-alkyl, π-sigma and alkyl) and/or electrostatic (π-cation) bonds. Inhibition of the anthocyanins was compared with that of topiroxostat, a commercial drug for hyperuricaemia. Dp-3-rhm was the most active inhibitor with a binding energy of ca. -10.90 kcal/mol compared to topiroxostat’s binding energy of ca. -8.60 kcal/mol. The good inhibition results obtained from anthocyanins toward XO suggest their application as a drug candidate to treat gout and other diseases related to the activity of XO.Significance: Sudanese roselle is rich in phytochemicals, particularly polyphenols and anthocyanins. The isolated anthocyanins in this study were explored as novel potential XO inhibitors. Further pharmacological and clinical studies are necessary for the development of new potential anthocyanin drugs to treat gout and other diseases related to XO increased activity such as hypertension.

Intense green‐, red‐emitting Tb3+, Tb3+/Bi3+‐doped and Sm3+, Sm3+/La3+‐doped Ca2Al2SiO7 phosphors

This paper focuses on an optical study of a Tb3+ /Bi3+ -doped and Sm3+ /La3+ - doped Ca2 Al2 SiO7 phosphor synthesized using combustion methods. Here, Ca2 Al2 SiO7 :Sm3+ showed a red emission band under visible light excitation but, when it co-doped with La3+ ions, the emission intensity was further enhanced. Ca2 Al2 SiO7 :Tb3+ shows the characteristic green emission band under near-ultraviolet light excitation wavelengths, co-doping with Bi3+ ions produced enhanced photoluminescence intensity with better colour tunable properties. The phosphor exhibited better phase purity and crystallinity, confirmed by X-ray diffraction. Binding energies of Ca(2p), Al(2p), Si(2p), O(1s) were studied using X-ray photoelectron spectroscopy. The reported phosphor may be a promising visible light excited red phosphor for light-emitting diodes and energy conversion devices.

Calcium doped graphane as a hydrogen storage material

On the basis of first principle density functional theory, we have studied the stability, electronic structure, and hydrogen storage capacity of a monolayer calcium doped graphane (CHCa). The stability of CHCa was further investigated using the ab initio molecular dynamics study. The binding energy of Ca on graphane sheet was found to be higher than its bulk cohesive energy, which indicates the stability of CHCa. It was observed that with a doping concentration of 11.11% of Ca on graphane sheet, a reasonably good H2 storage capacity of 6 wt. % could be attained. The adsorption energies of H2 were found to be 0.1 eV, within the range of practical H2 storage applications.

Metal-decorated defective BN nanosheets as hydrogen storage materials

Density functional theory computations were performed to investigate hydrogen adsorption in metaldecorated defective BN nanosheets. The binding energies of Ca and Sc on pristine BN nanosheets are much lower than the corresponding cohesive energies of the bulk metals; however, B vacancies in BN nanosheets enhance the binding of Ca and Sc atoms dramatically and avoid the clustering of the metal atoms on the surface of BN nanosheets. Ca and Sc strongly bind to defective BN nanosheets due to charge transfer between metal atoms and BN nanosheets. Sc-decorated BN nanosheets with B vacancies demonstrate promising hydrogen adsorption performances with a hydrogen adsorption energy of −0.19∼ −0.35 eV/H2.

Calculations of Li adsorption and diffusion on MgO(100) in comparison to Ca

Density-functional theory calculations are used to study the adsorption and growth of small Li clusters on MgO(100). The binding of Li is found to be similar to that of Ca in many respects. Monomers bind to oxygen sites on the terrace and diffuse at room temperature to defect sites. A range of defect sites will bind monomers with increasing energies from oxygen vacancies, steps, kinks, divacancies, and magnesium vacancies, as well as to peroxo species on step edges. The binding strength correlates with the amount of Bader charge transferred from the adsorbing metal to the substrate. Small clusters are found to be highly mobile on the surface at room temperature. In two cases, we have found qualitative differences in the binding energies of Ca and Li which lead to different growth modes. First, Ca binds less strongly to charged oxygen vacancy defects (${\text{F}}^{+}$ centers) than it does on the terrace whereas Li forms a bond with the electron in the vacancy, and is trapped at room temperature. Second, the gas phase Ca dimer distance is longer than the O-O distance on the MgO surface so that epitaxial Ca islands are strained whereas Li is not. These two differences have a profound effect on the growth of clusters. At room temperature, a Ca monomer will not trap at defect sites occupied by another Ca monomer. Thus, Ca atoms diffuse on the terrace until the defects are saturated before nucleating three-dimensional islands. On the other hand, two-dimensional epitaxial Li island nucleate at Li-bound defects. These calculations explain the lower initial heat of adsorption of Li and higher surface coverage as compared to Ca in adsorption microcalorimetry measurements by Farmer et al. [J. Am. Chem. Soc. 131, 3098 (2009)].

XPS analysis of the dentin irradiated by Er:YAG laser

The aim of this study was to investigate the effect of Er:YAG laser irradiation on human dentin surface using X-ray photoelectron spectroscopy (XPS). 10 human dentin disks were prepared from extracted human molars for XPS analysis. These specimens were divided into two groups of five: a control group and group that were irradiated by an Er:YAG laser beam (100 mJ, 1Hz). All specimens were analyzed by XPS over a wide scanning range and narrow scanning ranges. The Ca/P ratio was calculated from the XPS results. In the results, the binding energies of Ca, P, and N in the laser-irradiated group were higher than those in the control group. The Ca/P ratio of the Er:YAG laser irradiated group (1.24+/-0.05) was significantly lower than that of the control group (1.52+/-0.16). This study showed that Er:YAG laser irradiation decreased Ca/P ratio and denatured the collagen of human dentin.

The Effect of Coadsorbed Oxygen on the Adsorption and Diffusion of Potassium on Rh(110): A First-Principles Study

The adsorption and diffusion of potassium and oxygen on Rh(110), as well as the co-adsorption of K and O and its effect on K diffusion, has been studied using periodic density functional theory (DFT) calculations (PW91-GGA). On both the non-reconstructed (1x1) and the missing-row (MR) reconstructed surfaces, O prefers the short bridge site at low coverage, with a binding energy of ca. -5.2 eV at 1/4 ML. At theta_O>1/2 ML O atoms occupy alternating threefold sites along the ridge and forms a zigzag pattern. Interaction with the ridge sites is enhanced by the MR reconstruction. K prefers to be in the trough, with a binding energy of -2.3 eV on the (1x1) surface and -2.9 eV on the MR surface at 1/8 ML. Thus the adsorption of both O and K at low to medium coverage promotes the MR reconstruction. The co-adsorption of K and O enhances the binding energy of K to a maximum of -3.6 eV at the highest oxygen coverage studied, 1-3/8 ML. Oxygen adsorption is also stabilized by K, though to a smaller extent on a per-O atom basis. On both surfaces, K prefers to diffuse in the [110] direction with a barrier of ca. 0.05more » eV. O diffusion also prefers the [110] direction on the MR surface but is not clearly anisotropic on the (1x1) surface. The barrier to O diffusion ranges from 0.6~0.8 eV depending on the coverage and reconstruction. In the presence of co-adsorbed O, the diffusion barrier of K tops out at ca. 0.12 eV, much lower than earlier estimates based on mean-field models. Possible reasons for this apparent contradiction are discussed.« less

Titanium‐implanted CaTiO3 films and their changes in Hanks' solution

AbstractTitanium‐implanted CaTiO3 film was prepared and then characterized by x‐ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS) before and after immersion in Hanks' solution for 7 days. An as‐prepared specimen contained a small amount of Ar implanted during sputtering, although the pressure was as low as 10−4 Torr. Even though Ar convolution increased with an increase in the relative Ti ion dose, most of the convoluted Ar was not from the Ar gas used for Ti ion production but rather was from the Ar gas used for sputtering the CaTiO3. During Ti implantation, the CaTiO3 films were ion‐etched by Ti ions. The composition of the CaTiO3 film was not changed to any great degree by the Ti implantation, however its properties changed considerably. After immersion in Hanks' solution, the thickness of the specimen not implanted with Ti decreased the most whereas the [Ca]/[P] ratio, which was nearly unity before exposure, decreased significantly, becoming 0.23 on the Ti‐implanted specimen prepared at 200 W and 0.13 on the Ti‐implanted specimen prepared at 50 W. It was also observed by XPS that the ratio [Ca]/[P] was ∼1.9 for all Ti‐implanted specimens after immersion in Hanks' solution for 7 days. Judging from the binding energies of Ca 2p3/2 and P 2p electrons and the [Ca]/[P] ratio, it was suggested that a hydroxyapatite‐like substance had formed on the surfaces of the Ti‐implanted specimens after immersion in Hanks' solution. Copyright © 2003 John Wiley & Sons, Ltd.

Adsorption and dissociation of O 2 on Cu( [formula omitted]): thermochemistry, reaction barrier and the effect of strain

The adsorption and dissociation of dioxygen on the Cu(1 1 1) surface have been studied using periodic self-consistent density functional calculations. Two types of di-σ-type chemisorbed molecular precursors are identified: a non-magnetic type located over threefold hollows and a paramagnetic type over bridge sites, both with a binding energy of ca. −0.50 eV with respect to a gas-phase O 2 molecule. Atomic oxygen is found to prefer threefold hollows, with a binding energy of ca. −4.3 eV with respect to a gas-phase O atom. Possible pathways for the dissociation of O 2 are explored, and the lowest activation energy is calculated to be ca. 0.20 eV. Expansive strain parallel to the surface plane is shown to enhance the binding of atomic and molecular oxygen on the surface as well as to decrease the transition state energy of O 2 dissociation.

The ab initio neon–water potential-energy surface and its relationship with the hydrophobic hydration shell

The neon–water system has been investigated by abinitio quantum-chemical calculations. The potential-energy surface (PES) for the 1:1 Ne–H2O interaction has been scanned at the MP2(full) level, with the 6-311++G(3df,2pd) basis set augmented with bond functions located midway between Ne and O. The most stable neon–water arrangement has r = 320 pm, θ = 120°, with a counterpoise-corrected binding energy of −0.54 kJ mol−1. The PES is otherwise quite flat (with binding energies of ca. −0.4 kJ mol−1) for all θ values if r > ca. 310 pm. The off-plane, perpendicular approach is unfavourable. NMR shielding and the electric field gradient at all nuclei show only very small changes with respect to the isolated components.

XPS STUDIES OF Bi2Sr2CaCu2-xLixOy CERAMICS SERFACES

The XPS(X-ray photoelectron spectroscope) measurements of the 80K phase Bi-Sr-Ca-Cu-Li-O ceramics were carried out on surfaces obtained by polishing in ultrahigh vacuum. The results show that the chemical bond natures of Bi and Sr almost did not change, but the binding energies of Ca, Cu and O shifted apparently toward higher energy when Li doped in the Bi-Sr-Ca-Cu-O system. The XPS spectrum of O Is has only singe peak (528.8eV) from clean surfaces polished in vacuum and consists of the OH (531eV) and OL (528.8eV) components from conventionally polished surfaces.