Magnesium Atoms Research Articles

All-Atom Molecular Dynamics Reveals Mechanism of Zinc Complexation with Therapeutic F10.

Advancing the use of therapeutic nucleic acids requires understanding the chemical and structural properties that allow these polymers to promote the death of malignant cells. Here we explore Zn2+ complexation by the fluoropyrimidine polymer F10, which has strong activities in multiple preclinical models of cancer. Delivery of fluoropyrimidine FdUMP in the 10-residue polymer F10 rather than the nucleobase (5-fluorouracil) allows consideration of metal ion binding effects on drug delivery. The differences in metal ion interactions with fluoropyrimidine compared to normal DNA results in conformation changes that affect protein binding, cell uptake, and codelivery of metals such as zinc, and the cytoxicity thereof. Microsecond-time-scale, all-atom simulations of F10 predict that zinc selectively stabilizes the polymer via interactions with backbone phosphate groups and suggest a mechanism of complexation for the zinc-base interactions shown in previous experimental work. The positive zinc ions are attracted to the negatively charged phosphate groups. Once the Zn2+ ions are near F10, they cause the base's N3 nitrogen to deprotonate. Subsequently, magnesium atoms displace zinc from their interactions with phosphate, freeing the zinc ions to interact with the FdU bases by forming weak interactions with the O4 oxygen and the fluorine attached to C5. These interactions of magnesium with phosphate groups and zinc with nucleobases agree with previous experimental results and are seen in MD simulations only when magnesium is introduced after N3 deprotonation, indicating a specific order of metal binding events. Additionally, we predict interactions between zinc and F10's O2 atoms, which were not previously observed. By comparison to 10mers of polyU and polydT, we also predict that the presence of fluorine increases the binding affinity of zinc to F10 relative to analogous strands of RNA and DNA consisting of only native nucleotides.

Dealloying Mechanism of Bulk-AlCu Intermetallic Phases (Al2Cu, Al7Cu2Fe, Al2CuMg) : Effect of Crystallographic Structure and Electrolyte

The aluminum alloys with high mechanical properties, the 2xxx and 7xxx series, are very sensible to corrosion because of the presence of numerous coarse intermetallic phases in the aluminum matrix. These phases are often responsible of the formation of pits in corrosion conditions, or the formation of defects in the anticorrosion coatings such as anodized layers. The objective of this work is to study the behavior of different AlCu intermetallic phases (Al2Cu, Al7Cu2Fe, Al2CuMg) in the 7XXX and 2XXX alloys in NaCl electrolyte and H2SO4 electrolyte.Firstly, bulk-samples of phases (centimeter size) were synthesized by quick melting in an induction furnace followed by several annealing steps under argon. The electrochemical behavior of the three phases was characterized by stationary electrochemical measurements and electrochemical impedance spectroscopy in function of immersion time at open-circuit potential. The surface layers on each phase were observed on surface and metallographic cross-section by FEG-SEM, EDX spectroscopy and X-ray Photoelectron Spectroscopy.In NaCl electrolyte, all the studied intermetallic phases undergo a dealloying phenomenon which leads to the formation of a pure copper nanometer sponge. On the surface, the copper sponge can be partially embedded and covered in an aluminum hydroxide gel according to the hydrodynamic conditions. In sulfuric acid, the dealloying phenomenon depends on the copper content in the intermetallic phase and on its crystallographic structure. According to the density of the Cu plan, some phases can form a compact layer of copper that passivate the phase, some others form a nanometer sponge of copper. In conclusion, after the dissolution of aluminum, magnesium or iron atoms, copper atoms diffuse on the surface of phases to form either crystalline copper nanometer particles, or compact copper layer according to the electrolyte properties and their crystallographic structure.

In situ observation of sublimation-enhanced magnesium oxidation at elevated temperature

Oxidation plays a tremendous role in the long-term performance of metals. As an important lightweight metal for industrial applications, magnesium suffers from its high reactivity with oxygen and increased evaporation at high temperatures. To understand the oxidation mechanism of magnesium at elevated temperatures, in situ environmental transmission electron microscopy (E-TEM) was performed on magnesium nanoparticles. At a relatively low temperature, the growth of a MgO lamellae via the outward diffusion of bulk magnesium atoms dominated the oxidation process. In contrast, a sublimation-enhanced oxidation via gas phase reaction occurred at 200 °C, leading to the growth of MgO dendrites over the particle that finally leads to the degradation of the magnesium structure. This study provides a direct observation and model of the oxidation mechanism of a direct gas–gas reaction that improves our understanding of the oxidation mechanism at elevated temperatures.

New approaches in deep laser cooling of magnesium atoms for quantum metrology

Two approaches for solving the long-standing problem of deep laser cooling of neutral magnesium atoms are proposed. The first one uses optical molasses with orthogonal linear polarizations of light waves. The second approach involves a ‘nonstandard’ magneto-optical trap (NMOT) composed of light waves with elliptical polarizations (in general). Both the widely used semiclassical approach based on the Fokker–Planck equation and quantum treatment fully taking into account the recoil effect are employed for theoretical analysis. The results show the possibility of obtaining temperatures lower than 100 µK simultaneously with a large number of cold atoms ~106 ÷ 107. A new velocity-selective cooling technique allowing one to reach the microkelvin temperature range is also proposed. This technique may have some advantages over, for instance, the shallow-dipole-trap technique utilized by other authors. In the case of magnesium atoms this new technique may be used for obtaining a large number of ultracold atoms (T ~ 1 µK, N > 105). Such a large number of ultracold atoms is crucial issue for metrological and many other applications of cold atoms.

Combined Hot Isostatic Pressing and Heat Treatment of Aluminum A356 Cast Alloys*

Abstract The mechanical and microstructural properties of aluminum A356 cast alloy are investigated as a function of hot isostatic pressing and heat treatment parameters. The combined hot isostatic pressing and heat treatment process leads to an improvement of mechanical properties when compared to regular hot isostatic pressing with no separate heat treatment. An oversaturated state with magnesium and silicon atoms dissolved in the aluminum matrix can be achieved by increasing the quenching rate to 6.9 K/s within the temperature range between 813 K and 473 K. Aging can be performed directly after hot isostatic pressing, without the necessity of a separate solution annealing step. Thereby, the overall processing costs could be reduced.

Effect of thermal tempering on microstructure and mechanical properties of Mg-AZ31/Al-6061 diffusion bonding

The objective of this study is to investigate the effect of the types thermal tempering of aluminum alloy on microstructure and mechanical properties of AZ31-O Mg and Al 6061-T6 diffusion bonding. Using Optical Microscope (OM) and Scanning Electron Microscopes (SEM) equipped with EDS analysis and line scan the interfaces of joints were evaluated. The XRD analysis was carried out to characterize phase constitution near the interface zone. The mechanical properties of joints were measured using Vickers micro-hardness and shear strength. According to the results in bonding of AZ31-Mg/Al-6061-O, in less plastic deformation in magnesium alloy, diffusion rate of most magnesium atoms occurred to aluminum alloy and formation of diffusion zone with minimum micro-hardness (140 HV) and maximum shear strength (32MPa) compared to Al 6061-T6/Mg-AZ31 bonding. Evaluation of fracture surfaces indicates an occurrence of failure from the brittle intermetallic phases.

Visualization of oil migration in chocolate using scanning electron microscopy–energy dispersive X-ray spectroscopy

Abstract We have developed a novel method to observe oil migration in chocolate using scanning electron microscopy and energy dispersive X-ray spectroscopy (EDX). If silicone oil is used as the mobile phase in migration, the amount of migrated silicone oil can be evaluated using the EDX signal. Compound chocolate placed on the silicone-oiled cotton resulted in the appearance of liquid oil droplets on the surface of the chocolate within 10 days at 24 °C. Fat blooming was also induced by these oil droplets at 2.5 months. The amount of silicone oil that migrated into the chocolate was evaluated based on the weight change of the chocolate and the EDX signal from the silicone oil. Quantitative analysis indicated that two independent migration mechanisms, diffusion and capillary force, induced migration. In addition, the EDX signal indicated superfast migration from a spot that was distinct from the area of diffusion or capillary force migration. The EDX signals from phosphorus or magnesium atoms were helpful in identifying cacao particles in chocolate since these elements were specific to the particles in chocolate. Homogeneous distribution of silicone oil was observed around the particles in chocolate, thus, these particles might not help to produce a specific migration pathway in chocolate.

Elastic scattering of electrons and positrons by atomic magnesium

The elastic, differential and integrated, and total cross sections for the scattering of electrons and positrons by magnesium atom have been calculated. These calculations are done within the framework of complex electron/positron-atom optical potential and relativistic Dirac partial wave analysis at the impact energies 0.1–1000 eV for both the projectiles. The present results are compared with available experimental data and some other theoretical calculations.

Retrieval of sodium number density profiles in the mesosphere and lower thermosphere from SCIAMACHY limb emission measurements

Abstract. An algorithm has been developed for the retrieval of sodium atom (Na) number density on a latitude and altitude grid from SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) limb measurements of the Na resonance fluorescence. The results are obtained between 50 and 150 km altitude and the resulting global seasonal variations of Na are analyzed. The retrieval approach is adapted from that used for the retrieval of magnesium atom (Mg) and magnesium ion (Mg+) number density profiles recently reported by Langowski et al. (2014). Monthly mean values of Na are presented as a function of altitude and latitude. This data set was retrieved from the 4 years of spectroscopic limb data of the SCIAMACHY mesosphere and lower thermosphere (MLT) measurement mode (mid-2008 to early 2012). The Na layer has a nearly constant peak altitude of 90–93 km for all latitudes and seasons, and has a full width at half maximum of 5–15 km. Small but significant seasonal variations in Na are identified for latitudes less than 40°, where the maximum Na number densities are 3000–4000 atoms cm−3. At middle to high latitudes a clear seasonal variation with a winter maximum of up to 6000 atoms cm−3 is observed. The high latitudes, which are only measured in the summer hemisphere, have lower number densities, with peak densities being approximately 1000 Na atoms cm−3. The full width at half maximum of the peak varies strongly at high latitudes and is 5 km near the polar summer mesopause, while it exceeds 10 km at lower latitudes. In summer the Na atom concentration at high latitudes and at altitudes below 88 km is significantly smaller than that at middle latitudes. The results are compared with other observations and models and there is overall a good agreement with these.

Structural, electronic, thermodynamic and spectral properties of Mgn (n = 2–31) clusters. A DFT study

Small clusters of magnesium Mgn (n=2–31) are of particular interest for coordination chemistry and organometallic chemistry, as they are convenient models of Grignard reagent formation reaction on the surface of activated metallic magnesium, and also are directly involved in this reaction under vacuum atomized state conditions. In this study, the structure, thermodynamic functions (total energy, enthalpy and Gibbs free energy of formation of Mgn systems), and the electronic parameters (dipole moments, band-gap energy, distribution of partial atomic charges) for optimized clusters were investigated using the density functional theory (B3PW91/6-31G (d), B3PW91/6-311+G (2d)). The energies and thermodynamic functions of cluster atomization and isomerization, energies of S0→T1 singlet-triplet transitions, and energies of separation of single or multiple magnesium atoms from clusters, which are described within the framework of simple statistical models, were determined. The calculated parameters allow to estimate the properties of the clusters whose structure corresponds to different centers of magnesium surface involved in Grignard reagent formation reaction, and therefore, to estimate their contribution to reactivity. The calculated Mg2–Mg31 IR spectra enable identification of individual clusters under experimental conditions.

A Porous Electrode Model for the Magnesiation and Demagnesiation of a Bismuth Electrode in Rechargeable Magnesium-Ion Cells

The transport and electrochemical properties of magnesium ions (Mg2+) in a magnesium organohaloaluminate electrolyte were estimated experimentally. The key properties of a Bismuth (Bi) electrode; such as solid-state Mg2+ diffusion, electronic conductivity, particle size, and electrode porosity were also estimated, both experimentally and theoretically. The magnesium organohaloaluminate electrolyte was utilized in an electrochemical cell to study the Mg2+ insertion/extraction reactions in a Bi electrode. The existing porous electrode pseudo two-dimensional model was extended in the proposed study to describe the behavior of the α-Mg3Bi2/Mg cell system during charge-discharge reactions. The model was also modified to include experimentally evaluated parameters such as internal resistance, electrode kinetics, thermodynamics, and the diffusion of Mg2+ in the active particles. This electrochemical model, modified with estimated parameters for the electrolyte, Mg, and α-Mg3Bi2 electrodes, was formulated with both, direct 2-electron transfer and multi-electron transfer from each magnesium atom of the magnesium dimer present in the electrolyte. Details of the electrochemical performance from both mechanisms are compared with the experimental data, and factors governing the performance of the α-Mg3Bi2/Mg cell are discussed in the present study.

Quantum treatment of two-stage sub-Doppler laser cooling of magnesium atoms

The problem of deep laser cooling of $^{24}$Mg atoms is theoretically studied. We propose two-stage sub-Doppler cooling strategy using electro-dipole transition $3^3P_2$$\to$$3^3D_3$ ($\lambda$=383.9 nm). The first stage implies exploiting magneto-optical trap with $\sigma^+$ and $\sigma^-$ light beams, while the second one uses a lin$\perp$lin molasses. We focus on achieving large number of ultracold atoms (T$_{eff}$ < 10 $\mu$K) in a cold atomic cloud. The calculations have been done out of many widely used approximations and based on quantum treatment with taking full account of recoil effect. Steady-state average kinetic energies and linear momentum distributions of cold atoms are analysed for various light-field intensities and frequency detunings. The results of conducted quantum analysis have revealed noticeable differences from results of semiclassical approach based on the Fokker-Planck equation. At certain conditions the second cooling stage can provide sufficiently lower kinetic energies of atomic cloud as well as increased fraction of ultracold atoms than the first one. We hope that the obtained results can assist overcoming current experimental problems in deep cooling of $^{24}$Mg atoms by means of laser fields. Cold magnesium atoms, being cooled in large number down to several microkelvins, have certain interest, for example, in quantum metrology.

Influence of transition metal atoms doping on structural, electronic and nonlinear optical properties of Mg12O12 nanoclusters: A DFT study

Using density functional theory, we investigated the effect of transition metal doping on structural, electronic, energetic, linear and nonlinear optical properties of Mg12O12 nanocluster. The result revealed that transition metal atoms doping lead to reduce the Eg and increase the dipole moment. The doping of transition metal atom on Mg12O12 nanocluster enhances its polarizability value. Also polarizability values for doped nanoclusters decrease as the atomic number of transition metal increase. The first hyperpolarizability value dramatically increases as substitute a magnesium atom with a transition metal atom. Among the transition metal atom doped nanocage, scandium has the largest first hyperpolarizability value (β◦≈47,872au). The stability and remarkable values of β◦ (for Sc, Ti and V doped of nanocage) suggest that these compounds may be applicable as NLO material in industrial.

Crystal structure, equation of state, and elasticity of phase H (MgSiO4H2) at Earth's lower mantle pressures.

Dense hydrous magnesium silicate (DHMS) phases play a crucial role in transporting water in to the Earth’s interior. A newly discovered DHMS, phase H (MgSiO4H2), is stable at Earth’s lower mantle, i.e., at pressures greater than 30 GPa. Here we report the crystal structure and elasticity of phase H and its evolution upon compression. Using first principles simulations, we have explored the relative energetics of the candidate crystal structures with ordered and disordered configurations of magnesium and silicon atoms in the octahedral sites. At conditions relevant to Earth’s lower mantle, it is likely that phase H is able to incorporate a significant amount of aluminum, which may enhance the thermodynamic stability of phase H. The sound wave velocities of phase H are ~2–4% smaller than those of isostructural δ-AlOOH. The shear wave impedance contrast due to the transformation of phase D to a mixture of phase H and stishovite at pressures relevant to the upper part of the lower mantle could partly explain the geophysical observations. The calculated elastic wave velocities and anisotropies indicate that phase H can be a source of significant seismic anisotropy in the lower mantle.

Empirically constructed dynamic electric dipole polarizability function of magnesium and its applications

The dynamic electric dipole polarizability function for the magnesium atom is formed by assembling the atomic electric dipole oscillator strength distribution from combinations of theoretical and experimental data for resonance oscillator strengths and for photoionization cross sections of valence and inner shell electrons. Consistency with the oscillator strength (Thomas-Reiche-Kuhn) sum rule requires the adopted principal resonance line oscillator strength to be several percent lower than the values given in two critical tabulations, though the value adopted is consistent with a number of theoretical determinations. The static polarizability is evaluated. Comparing the resulting dynamic polarizability as a function of the photon energy with more elaborate calculations reveals the contributions of inner shell electron excitations. The present results are applied to calculate the long-range interactions between two and three magnesium atoms and the interaction between a magnesium atom and a perfectly conducting metallic plate. Extensive comparisons of prior results for the principal resonance line oscillator strength, for the static polarizability, and for the van der Waals coefficient are given in the Appendix.

On the Mechanisms of Hydrogen-Atom Transfer from Water to the Heteronuclear Oxide Cluster [Ga2 Mg2 O5 ](.+) : Remarkable Electronic Structure Effects.

Mechanistic insight into the homolytic cleavage of the O-H bond of water by the heteronuclear oxide cluster [Ga2 Mg2 O5 ](.+) has been derived from state-of-the-art gas-phase experiments in conjunction with quantum chemical calculations. Three pathways have been identified computationally. In addition to the conventional hydrogen-atom transfer (HAT) to the radical center of a bridging oxygen atom, two mechanistically distinct proton-coupled electron-transfer (PCET) processes have been identified. The energetically most favored path involves initial coordination of the incoming water ligand to a magnesium atom followed by an intramolecular proton transfer to the lone-pair of the bridging oxygen atom. This step, which is accomplished by an electronic reorganization, generates two structurally equivalent OH groups either of which can be liberated, in agreement with labeling experiments.

Coherent control of bond making: the performance of rationally phase-shaped femtosecond laser pulses**Dedicated to the memory of Moshe Shapiro.

The first step in the coherent control of a photoinduced binary reaction is bond making or photoassociation. We have recently demonstrated coherent control of bond making in multi-photon femtosecond photoassociation of hot magnesium atoms, using linearly chirped pulses (Levin et al 2015 Phys. Rev. Lett. 114 233003). The detected yield of photoassociated magnesium dimers was enhanced by positively chirped pulses which is explained theoretically by a combination of purification and chirp-dependent Raman transitions. The yield could be further enhanced by pulse optimization resulting in pulses with an effective linear chirp and a sub-pulse structure, where the latter allows for exploiting vibrational coherences. Here, we systematically explore the efficiency of phase-shaped pulses for the coherent control of bond making, employing a parametrization of the spectral phases in the form of cosine functions. We find up to an order of magnitude enhancement of the yield compared to the unshaped transform-limited pulse. The highly performing pulses all display an overall temporally increasing instantaneous frequency and are composed of several overlapping sub-pulses. The time delay between the first two sub-pulses fits very well the vibrational frequency of the generated intermediate wavepacket. These findings are in agreement with chirp-dependent Raman transitions and exploitation of vibrational dynamics as underlying control mechanisms.

A femtosecond-scale laser pulse makes molecular bonds

The shape of the pulse determines how diatomic molecules form in a gas of hot magnesium atoms.

Interaction of polyphenylsiloxane with magnesium acetylacetonate

Interaction of polyphenylsiloxane with magnesium acetylacetonate in boiling toluene has been studied. The products isolated via extraction and fractional precipitation have been characterized with elemental analysis, IR spectroscopy, X-ray diffraction analysis, and thermal analysis. The reaction products are polymers containing acetylacetonate group at magnesium atom. Structure of the major product has been suggested.

Study of formation mechanism of incipient melting in thixo-cast Al–Si–Cu–Mg alloys

Mechanical properties of thixo-cast Al–Si–Cu–Mg alloys can be enhanced by T61 heat treatment. Copper and magnesium atoms in aluminum matrix can form homogeneously distributed precipitations after solution and aging treatment which harden the alloys. However, microsegregation of these alloying elements could form numerous tiny multi-compound phases during solidification. These phases could cause incipient melting defects in subsequent heat treatment process and degrade the macro-mechanical properties of productions. This study is to present heterogeneous distribution of Cu, Si, and Mg elements and formation of incipient melting defects (pores). In this study, incipient melting pores that occurred during solution treatment at various temperatures, even lower than common melting points of various intermetallic phases, were identified, in terms of a method of investigating the same surface area in the samples before and after solution treatment in a vacuum environment. The results also show that the incipient melting mostly originates at the clusters with fine intermetallic particles while also some at the edge of block-like Al2Cu. The fine particles were determined being Al2Cu, Al5Cu2Mg8Si6 and Al8Mg3FeSi2. Tendency of the incipient melting decreases with decreases of the width of the clusters. The formation mechanism of incipient melting pores in solution treatment process was discussed using both the Fick law and the LSW theory. Finally, a criterion of solution treatment to avoid incipient melting pores for the thixo-cast alloys is proposed.