Magnesium Atoms Research Articles

Comparison of experiment and theory for superelastic electron-collision studies from laser-aligned magnesium

A combined experimental and theoretical study of superelastic electron collisions from laser-aligned magnesium atoms for a range of collision energies from 35 to 55 eV is presented. $^{24}\mathrm{Mg}$ atoms were excited from the $3\phantom{\rule{0.16em}{0ex}}^{1}S_{0}$ ground state to the $3\phantom{\rule{0.16em}{0ex}}^{1}P_{1}$ excited state using continuous-wave linearly polarized laser radiation at \ensuremath{\sim}285 nm. Electrons of well-defined energy ${E}_{\mathrm{inc}}$ then deexcited the targets, and the superelastically scattered electrons emerging from the collision were detected as a function of scattering angle and laser polarization. Results for alignment of the target by the electron beam are presented for a range of scattering angles, for outgoing energies from ${E}_{\mathrm{out}}=35$ to $55\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. The agreement between the measurements and the results of the convergent close-coupling theory are encouraging, but some discrepancies remain.

One-pot green synthesis of magnesium oxide nanoparticles using Penicillium chrysogenum melanin pigment and gamma rays with antimicrobial activity against multidrug-resistant microbes

Melanin pigment is well-known as a common photo-protective polymer, insoluble in water. It drews considerable attention for many applications in nanotechnology, and medical fields. Penicillium chrysogenum was employed for the green synthesis of melanin after optimizing the media compositions. A method has been designed that included one-step synthesis of magnesium oxide nanoparticles (MgO NPs) by fungal melanin under the influence of different doses of gamma rays. Antimicrobial activity of MgO NPs was examined against some selected highly pathogenic microbes. The fungal melanin acted simultaneously as a photo-protector of the magnesium atom, and at the same time as a stabilizer towards the uncontrolled free radical attack resulting from gamma rays. Afterwards, gamma rays forced a condensation reaction to occur at room temperature. A proposed reaction mechanism for MgO NPs synthesis was discussed. MgO NPs were characterized and structurally identified by UV–Vis., XRD, DLS, TEM and FTIR. Results obtained from DLS and XRD with TEM images determined the mean diameter as 10.28 nm. In addition, MgO NPs were found to be promising antimicrobial agents against' Enterococcus faecalis, Candida albicans, and Klebsiella pneumoniae having activity of 22.0, 20.0, and 20.0 mm ZOI, respectively. Based on the capability of MgO NPs as effective antimicrobial agents, they possess a potential role – in different applications such as biomedicine, food control, pharmaceutics, and cosmetics.

Photoionization microscopy: Hydrogenic theory in semiparabolic coordinates and comparison with experimental results

Photoionization microscopy (PM) is an experimental method allowing for high-resolution measurements of the electron current probability density in the case of photoionization of an atom in an external uniform static electric field. PM is based on high-resolution velocity-map imaging and offers the unique opportunity to observe the quantum oscillatory spatial structure of the outgoing electron flux. We present the basic elements of the quantum-mechanical theoretical framework of PM for hydrogenic systems near threshold. Our development is based on the computationally more convenient semiparabolic coordinate system. Theoretical results are first subjected to a quantitative comparison with hydrogenic images corresponding to quasibound states and a qualitative comparison with nonresonant images of multielectron atoms. Subsequently, particular attention is paid on the structure of the electron's momentum distribution transversely to the static field (i.e., of the angularly integrated differential cross-section as a function of electron energy and radius of impact on the detector). Such 2D maps provide at a glance a complete picture of the peculiarities of the differential cross-section over the entire near-threshold energy range. Hydrogenic transverse momentum distributions are computed for the cases of the ground and excited initial states and single- and two-photon ionization schemes. Their characteristics of general nature are identified by comparing the hydrogenic distributions among themselves, as well as with a presently recorded experimental distribution concerning the magnesium atom. Finally, specificities attributed to different target atoms, initial states, and excitation scenarios are also discussed, along with directions of further work.

Insight into crystal structure and Eu/Tb doped luminescence property of a new phosphate

Luminescent materials were of vital importance in the display, lighting, and biomedical fields. Exploration of novel inorganic host materials and groping for novel color-tunable phosphor materials with good thermal stability is still a major challenge for the quality-improvement of FLs and LEDs. In the present work, a new magnesium indium phosphate, Mg3In4P6O24 (MIP), was successfully synthesized by conventional high-temperature solid-state reaction and was structurally characterized by powder X-ray diffraction analysis, in which magnesium and indium atoms co-occupy four metal cation sites, coordinating with adjacent oxygen atoms forming distorted MO5 and MO6 polyhedra. The VUV-UV excited luminescence properties of a series of Eu3+/Tb3+ doped MIP phosphors were investigated, with the temperature-dependence of photoluminescence and relative mechanism analyzed. Under the excitation of 254 nm, the MIP: EuxTby phosphors can generate bright color-tunable green-yellow-red light by changing the doping concentration. In addition, the color of emission can also be adjusted by altering the excitation wavelength for a very phosphor, MIP: Eu0.01Tb0.05. As an interesting discovery, the plot of integrated dominant emission intensities of Eu and Tb in phosphor MIP: Eu0.01Tb0.05 versus excitation wavelength exhibits analogical profile with the excitation spectra of Eu3+/Tb3+ single-doped MIP phosphor. Moreover, the representative phosphor MIP: Eu0.01Tb0.05 shows favorable thermal stability. Present work indicates that Mg3In4P6O24 is a promising host material for the fabrication of new phosphors.

Shape resonances of Be− and Mg− investigated with the method of analytic continuation

The regularized method of analytic continuation is used to study the low-energy negative ion states of beryllium (configuration 2$s^2\varepsilon p\; ^2P$) and magnesium (configuration 3$s^2\varepsilon p\; ^2P$) atoms. The method applies an additional perturbation potential and it requires only routine bound-state multi-electron quantum calculations. Such computations are accessible by most of the free or commercial quantum chemistry software available for atoms and molecules. The perturbation potential is implemented as a spherical Gaussian function with a fixed width. Stability of the analytic continuation technique with respect to the width and with respect to the input range of electron affinities is studied in detail. The computed resonance parameters $E_r$=0.282 eV, $\Gamma$=0.316 eV for the $2p$ state of Be$^-$ and $E_r$=0.188 eV, $\Gamma$=0.167 for the $3p$ state of Mg$^-$, agree well with the best results obtained by much more elaborated and computationally demanding present-day methods.

Operational compensation for higher order uncertainties in frequency standards of magnesium and calcium atoms in optical lattices

The possibilities and ways for operational tuning of optical lattice parameters, which make it possible to minimise the frequency-standard uncertainties caused by nonlinear, nondipole, and anharmonic effects of interaction of magnesium and calcium atoms with the optical lattice field of a magic wavelength, have been investigated.

Laser frequency stabilisation on narrow resonances of cold magnesium atoms at the 1S0 – 3P1 transition

Experimental studies aimed at developing an optical frequency standard based on ultracold magnesium atoms with a relative uncertainty of Δν/ν < 10–16 are performed. The frequency of the clock laser system at a wavelength of 457 nm is stabilised to narrow optical resonances (Ramsey fringes) in time-separated laser fields interacting with cold magnesium atoms localised in a magneto-optical trap (MOT). The frequency stability of the laser system is investigated using a femtosecond comb based on a Ti:sapphire laser. Long-term frequency stability (determined by the Allan function) of ∼5 × 10–15 at averaging time τ = 1000 s is obtained.

Semi-synthesis and HPLC analysis of (bacterio)chlorophyllides possessing a propionic acid residue at the C17-position

Various chlorophyll and bacteriochlorophyll derivatives possessing a magnesium or zinc atom at the central position and a free carboxylic acid group at the C17[Formula: see text]-position, also known as (bacterio)chlorophyllides, were synthesized through a combination of organic synthesis techniques and enzymatic steps. The semi-synthetic (bacterio)chlorophyllides were purified and analyzed using reversed-phase high-performance liquid chromatography with UV-vis spectroscopy and mass spectrometry. These free propionic acid-containing chlorophyllous pigments can be useful research materials for the study of (bacterio)chlorophyll metabolisms.

Insight into Mg-S Battery Mechanism

Magnesium batteries are a promising technology as future energy storage system. Due to non-dendritic deposition of magnesium, Mg metal anode can be used, which significantly lowers weight and size of the batteries. Mg metal has a higher volumetric specific capacity (3833 mAh cm-3)1 in comparison to lithium (2062 mAh cm-3). Additional advantages of magnesium are its abundance and low price, since it is one of the ten most abundant elements in Earth’s crust. Nowadays, the biggest challenges are development of high-capacity cathode materials and electrolytes, compatible with both anode and cathode. Sulfur as a cathode material is of great interest, due to its high capacity, low price and natural abundance. Even though the concept of metal-sulfur batteries is relatively old, the first reports on magnesium-sulfur (Mg-S) batteries were only published in 2011.2 Non-nucleophilic magnesium electrolytes were needed to enable use of electrophilic sulfur cathode and magnesium anode. Problems, present in first batteries, such as self-discharge, capacity fade in initial cycles and high polarization, are still challenges that remain to be addressed. Even though some improvements were proposed, lack of fundamental understanding of the system hinders development of this battery system. Here we present an application of different analytical techniques, which were employed to obtain better insight into the mechanism of Mg-S battery and processes occurring on the cathode. The electrochemical reaction of sulfur with magnesium proceeds through two well-defined plateaus, which correspond to the equilibrium between sulfur and magnesium polysulfides (MgSx) in the high-voltage plateau and magnesium polysulfides (MgSx) and magnesium sulfide (MgS) in the low-voltage plateau as presented in figure 1. The use of operando X-ray absorption near edge structure (XANES), resonant inelastic X-ray scattering (RIXS), and ex situ 25Mg MAS NMR studies, have shown that the end discharge product involves MgS with magnesium atoms in a tetrahedral environment resembling the wurtzite structure, while synthesized MgS crystallizes in the rock-salt structure with magnesium atoms in a octahedral coordination.3 Our results represent a step further towards better understanding of the fundamentals of Mg-S system. These advances will enable us to tackle challenges such as polysulfide diffusion from cathode, high polarization and self-discharge more systematically and successfully. References (1) Yoo, H. D.; Shterenberg, I.; Gofer, Y.; Gershinsky, G.; Pour, N.; Aurbach, D. Mg Rechargeable Batteries: An on-Going Challenge. Energy Environ. Sci. 2013, 6, 2265–2279. (2) Kim, H. S.; Arthur, T. S.; Allred, G. D.; Zajicek, J.; Newman, J. G.; Rodnyansky, A. E.; Oliver, A. G.; Boggess, W. C.; Muldoon, J. Structure and Compatibility of a Magnesium Electrolyte with a Sulphur Cathode. Nat. Commun. 2011, 2, 427. (3) Robba, A.; Vizintin, A.; Bitenc, J.; Mali, G.; Arčon, I.; Kavčič, M.; Žitnik, M.; Bučar, K.; Aquilanti, G.; Martineau-Corcos, C.; Vitanova, A. R.; Dominko, R.; Mechanistic Study of Magnesium–Sulfur Batteries. Chem. Mater. 2017, 29, 9555–9564. Figure 1

Mg thermal diffusion behavior on the band modulation of MgxZn1-xO/ZnO metal-semiconductor-metal photodetectors

By magnesium (Mg) atom diffusion in ZnO layer, the detection band of MgxZn1-xO/ZnO metal-semiconductor-metal photodetectors (MSM-PDs) could be modulated from two distinct bands to one band. ZnO and MgxZn1-xO layers were deposited consecutively on a sapphire substrate using an radio-frequency magnetron sputtering system. With increasing annealed temperature, Mg atoms diffuse from MgxZn1-xO into the underlying ZnO layer, which tunes the composition of ZnO into MgyZn1-yO and thus modulate the detection band of MSM-PDs. For the annealed temperature below 900 °C, two distinct bands were detected in the MSM-PDs with wavelength region of 280–330 nm and 360–400 nm due to the absorption of MgxZn1-xO and underlying ZnO layers. Further increasing the annealed temperature to 900 °C, the deeply diffusing Mg atom causes the MgxZn1-xO and ZnO layers were homogenized into a uniform MgzZn1-zO layer, hence the detection band was transformed into one band with a wavelength region of 280–340 nm. Secondary ion mass spectrometry depth profile showed the Mg atom diffusing downwards with increasing annealed temperature, causing the Mg content to decrease from ~ 30% in the as deposited MgxZn1-xO to ~ 8% in the homogenized MgzZn1-zO layer. Photoluminescence demonstrated the as-deposited MgxZn1-xO/ZnO bi-layer having two distinct emission peaks around 340 and 400 nm, and the MgxZn1-xO and ZnO layers were homogenized into a MgzZn1-zO layer in 900 °C and hence only one emission peak (355 nm).

Manipulation of inherent characteristics of graphene through N and Mg atom co-doping; a DFT study

First-principles calculations were performed to investigate the structural, electronic, magnetic and optical properties of nitrogen (N) and magnesium (Mg) atom co-doped graphene systems. We observed that, N and Mg atom co-doping in graphene, introduces half-metallic properties in the electronic structure of graphene, introduces ferromagnetism behavior along with new trends in optical properties of graphene. Doping site and concentration of N and Mg atoms in graphene was changed and resulting effects of these changes on aforementioned properties were investigated. Through density of states plots we observed that, Mg atom sp orbitals mainly induced magnetic moments in graphene. It was revealed that, N/Mg atoms substitution in graphene introduces a red shift in absorption spectrum towards visible range and a finite absorption coefficient quantity value in 0 to 3 eV and 7 to 11 eV energy intervals is also produced, that is unavailable for absorption spectrum of intrinsic graphene. Moreover, N/Mg atoms co-doping produces increment in the reflectivity parameter of graphene in low lying energy region, while producing diminishing behavior in the higher energy range. These results offer a possibility to tune electronic, magnetic and optical characteristics of graphene sufficiently for utilization in graphene based spintronic and optoelectronic devices.

Synthesis of MgO thin films grown by SILAR technique

Different thickness MgO thin films were grown on the glass substrate by successive ionic layer adsorption and reaction (SILAR) method as the first study in literature. X-ray diffraction (XRD) measurements demonstrate the cubic MgO structures and samples have (002), and (220) peaks. All film has nanoball structures observed from the scanning electron microscope (SEM) images. The band gap and transmittance values of MgO thin films decrease with increasing thickness. The photoluminescence (PL) spectrum demonstrates that samples have three visible emissions changing with thickness at 381 nm violet emission, 457 nm blue emission and 535 nm green emission. X-ray photoelectron spectroscopy (XPS) spectrum present confirms the elemental signals from carbon (C), oxygen (O) and magnesium (Mg) atoms in the sample. Both Moss and Herve and Vandamme relations refractive index values n, ε0, and ε∞ values and amount of oxygen increase with raising thickness of MgO thin films.

Crystal Chemistry Study of Two Magnesium Complexes with Trifluoroacetylacetone

Single crystal X-ray diffraction at a temperature of 150(2) K is used to determine the structures of two magnesium complexes with trifluoroacetylacetone: [Mg(tfac)2]3I and [Mg(H2O)2(tfac)2]·H2O II. Crystallographic data for I: space group P21/n, a = 12.5226(10) A, b = 13.0591(7) A, c = 12.6034(13) A, β = 95.243(2)°, V = 2052.5(3) A3, Z = 2; for II: space group P21/c, a = 10.826(2) A, b = 7.0742(13) A, c = 21.858(4) A, β = 102.712(5)°, V = 1632.9(5) A3, Z = 4. The isle structure of I is formed by linear trimeric molecules; in the structure of II the molecules of the complex and crystallization water form a layered framework using hydrogen bondings; the coordinated water molecules are in a trans position. The magnesium atoms have a distorted octahedral coordination environment, the Mg–O distances are 1.991(4)- 2.146(4) A and 2.040(5)-2.073(5) A in molecules of I and II respectively.

On the structure of superbasic (MgO)n sites solvated in a faujasite zeolite.

We report the synthesis and characterisation of a HY/MgO zeolite/oxide nanocomposite material with high crystallinity and highly dispersed, highly basic MgO sites. Preparation was optimized in order to preserve sample crystallinity, to avoid the formation of mesoporosity and to minimize the formation of separate Mg-containing phases. These features were checked by means of electron microscopy, X-ray powder diffraction, porosimetry and IR spectroscopy. A highly dispersed material was obtained, comprising nanoclusters of magnesium oxide and hydroxide hosted by the microporous zeolite framework. The location and structure of the Mg-containing clusters have been studied by means of a combination of Rietveld refinement of XRPD data and high quality quantum mechanical simulations. The refinement has shown the presence of magnesium and oxygen atoms in the double six-membered ring cages, consistent with the presence of mononuclear Mg moieties. However, the composition and IR spectroscopy demonstrate that other Mg species must exist, likely located in the zeolite pores. In order to propose candidate structures for these species, several hypothetic periodic models of the material were built by placing (MgO)n clusters in different locations of the zeolite structure, taking into account the material composition and other constraints imposed by the experimental observations. Periodic structures with P1 symmetry were optimized at the B3LYP-D*/DZVP level with the CRYSTAL code and classified according to their stability. Two families of possible sites were identified: highly solvated (MgO)n units in narrow cavities and less coordinated clusters in the supercages. The stability of these clusters appears to be regulated by the ability of Mg2+ and O2- ions to interact with the pore walls and by the formation of Mg-OH species as result of the reaction of Mg-O couples with remaining acidic protons. The reactivity of four representative models with CO2 has been simulated at the B3LYP-D*/TZVP level. CO2 forms very stable linear end-on adducts with low coordinated Mg ions in most cases. Isolated sites give rise to bridge bidentate complexes in agreement with previous spectroscopic observations. The formation of hydrogen-carbonates is observed only on specific sites, through a process having a low adsorption energy because of the high deformation of the adsorption site.

Exploring the Liquid Structure and Ion Formation in Magnesium Borohydride Electrolyte Using Density Functional Theory

Rechargeable magnesium batteries have attracted much interest due their high volumetric capacity, potential for safe operation, and the natural abundance of magnesium. However, the development of magnesium batteries for practical applications has been obstructed by the lack of understanding of the liquid structure of electrolytes. Herein, we use quantum density functional theory coupled with a continuum solvation model to investigate the structure of Mg(BH4)2 in two ethereal solvents: tetrahydrofuran (THF), and monoglyme (G1). The most energetically favorable clusters of Mg(BH4)2, MgBH4+, and Mg2+, with associated solvent molecule ligands, are determined. The free energy required to generate monovalent ions in the electrolyte is positive and the formation of divalent complexes is prohibitive. Singly and doubly charged complexes are more stable in G1 than THF, which is consistent with experimental findings. From the standpoint of free energy, clusters containing multiple magnesium atoms are not favored. Theoretical 25Mg-NMR, 11B-NMR spectra, and infrared vibrational modes of borohydride were calculated for each cluster. The relationships between cluster charge and the signals of each spectrum are determined. These analytical descriptors could be useful to characterize the degree of ion dissociation in the electrolyte.

Molecular Magnesium Hydrides.

Solid magnesium hydride [MgH2 ]∞ has been pursued as a potential hydrogen-storage material. Organic chemists were rather interested in soluble magnesium hydride reagents from mid-20th century. It was only in the last two decades that molecular magnesium hydride chemistry received a major boost from organometallic chemists with a series of structurally well-characterized examples that continues to build a whole new class of compounds. More than 40 such species have been isolated, ranging from mononuclear terminal hydrides to large hydride clusters with more than 10 magnesium atoms. They provide not only insights into the structure and bonding of Mg-H motifs, but also serve as models for hydrogen-storage materials. Some of them are also recognized to participate in catalytic transformations, such as hydroelementation. Herein, an overview of these molecular magnesium hydrides is given, focusing on their synthesis and structural characterization.

Y6Mg9Co2 and Y9Mg30Co2: Novel magnesium-rich compounds representing new structure types

The crystal structures of the magnesium-rich Y6Mg9Co2 and Y9Mg30Co2 compounds have been determined from single crystal X-ray diffraction data. Both compounds represent new structure types: Y6Mg9Co2 is orthorhombic, Pnnm, oP34, a = 8.7883 (2), b = 15.9669 (3), c = 5.9984 (2) Å; Y9Mg30Co2 is hexagonal, P63/mmc, hP82, a = 10.1564 (3), c = 22.498 (1) Å. The crystal structures of these compounds are discussed in comparison with each other and with other magnesium containing compounds. Electronic structure calculations revealed that magnesium atoms form Mg4-tetrahedra with significant covalent Mg–Mg interaction (-iCOHP = 0.732 eV for Y6Mg9Co2 and 0.815 eV for Y9Mg30Co2). The ELF and Bader charge analyses confirm that valence electrons localized around Mg atoms present a covalent bonding character.

Effect of magnesium on FOX-7 and its tautomers-A DFT treatment

Abstract FOX-7 and its cisoid and transoid 1,5-tautomers as well as magnesium composites of all have been investigated quantum chemically within the restrictions of density functional theory (B3LYP/6–311++G(d,p)). Certain physico-chemical and quantum chemical properties, energies, stabilities, calculated IR and UV-VIS spectra are discussed. The influence of magnesium atom is investigated. It has been found that in FOX-7 composites the magnesium is not a silent ingredient, but interacts with the organic constituents.

Modification of band gaps and optoelectronic properties of binary calcium chalcogenides by means of doping of magnesium atom(s) in rock-salt phase- a first principle based theoretical initiative

The band gaps and optoelectronic properties of binary calcium chalcogenide semiconductors have been modified theoretically by doping magnesium atom(s) into their respective rock-salt unit cells at some specific concentrations x = 0.0, 0.25, 0.50, 0.75 and 1.0 and confirmed such modifications by studying their structural, electronic and optical properties using DFT based FP-LAPW approach. The WC-GGA functional is used to calculate structural properties, while mBJ, B3LYP and WC-GGA are used for calculating electronic and optical properties. The concentration dependences of lattice parameter, bulk modulus and fundamental band gap for each alloy system exhibit nonlinearity. The atomic and orbital origin of different electronic states in the band structure of each compound are explored from its density of states (DOS). The microscopic origin of band gap bowing for each of the alloy systems is explored in terms of volume deformation, charge exchange and structural relaxation. The chemical bonds between the constituent atoms in each compound are found as ionic in nature. Optical properties of each specimen are calculated from its computed spectra of dielectric function, refractive index, extinction coefficient, normal incidence reflectivity, optical conductivity, optical absorption and energy loss function. Several calculated results have been compared with available experimental and other theoretical data.

PARAMETER OPTIMIZATION AND VIRTUAL SCREENING INDONESIAN HERBAL DATABASE AS HUMAN IMMUNODEFICIENCY VIRUS -1 INTEGRASE INHIBITOR USING AUTODOCK AND VINA

Objective: Human immunodeficiency virus (HIV-1) is a virus that causes acquired immunodeficiency syndrome, a disease considered to be one of themost dangerous because of its high mortality, morbidity, and infectivity. The emergence of mutant HIV strains has led treatment to target proteaseas reverse transcriptase and integrase enzyme become less effective. This study aims to provide knowledge about the potential of HIV-1 integraseinhibitors for use as guiding compounds in the development of new anti-HIV drugs.Methods: This study used AutoDock and AutoDock Vina for virtual screening of the Indonesian herbal database for inhibitors of HIV-1 integrase andis validated using a database of the directory of useful decoys. Optimization was accomplished by selecting the grid size, the number of calculations,and the addition of two water molecules and a magnesium atom as cofactor.Results: This study determined that the best grid box size is 21.1725×21.1725×21.1725 in unit space size (1 unit space equals to macromolecules 1Ǻ),using AutoDock Vina with EF and AUC values, 3.93 and 0.693, respectively. Three important water molecules have meaning in molecular dockingaround the binding pocket.Conclusions: This study obtained the top ten ranked compounds using AutoDock Vina. The compounds include: Casuarinin; Myricetin-3-O-(2’’,6’’-di-O-α-rhamnosyl)-β-glucoside; 5,7,2’,4’-tetrahydroxy-6,3’-diprenylisoflavone 5-O-(4’’-rhamnosylrhamnoside); myricetin 3-robinobioside; cyanidin3-[6-(6-ferulylglucosyl)-2-xylosylgalactoside]; mesuein, cyanidin 7-(3-glucosyl-6-malonylglucoside)-4’-glucoside; kaempferol 3-[glucosyl-(1→3)-rhamnosyl-(1→6)-galactoside]; 3-O-galloylepicatechin-(4-β→8)-epicatechin-3-O-gallate; and quercetin 4’-glucuronide.