The Effect of Hydrogen on the Charge States of Oxygen Vacancies in Thermochemically Reduced Alkaline-Earth Oxides

1989 ◽  
Vol 152 ◽  
Author(s):  
Y. Chen ◽  
V. M. Orera ◽  
R. Gonzalezv ◽  
R. T. Williams ◽  
G. P. Williams ◽  
...  
Keyword(s):  
Hydrogen Concentration ◽  
Alkaline Earth ◽  
Oxygen Vacancies ◽  
High Pressures ◽  
Metallic Cation ◽  
Thermochemical Reduction ◽  
The One ◽  
Oxide Crystals ◽  
Positively Charged ◽  
F Centers

To a greater or lesser extent, all alkaline-earth oxide crystals contain hydrogen. Thermochemical reduction (TCR) of MgO and CaO crystals at high temperatures (˜2000K) and high pressures (4 to 7 atmospheres) of the metallic cation vapor (Mg and Ca respectively) results in a stoichiometric deficiency of oxygen ions, creating F centers (oxygen vacancies each with two electrons) and H− ions (protons in the anion sublattice, each occupied by two electrons). The positively-charged H− ions serve as traps for electrons excited from the F centers. Steady-state photo-excitation of the F absorption band results in F luminescence which typically extends to several minutes. This photoluminescence is detrimental for certain applications, such as tunable lasers. We have been able to reduce the hydrogen concentration prior to TCR of MgO and during TCR of CaO. The result is that the oxygen vacancies are predominantly in the one-electron F+ charge state. In contrast to the F luminescence, the decay of the F+ luminescence does not exhibit long phosphorescence. The prevalence of the F+ over the F state is found to be a function not only of the hydrogen concentration but also the severity of the thermochemical reduction.

The effect of cation concentration on the nitrogen splitting constant of nitroxide free radicals

1990 ◽  
Vol 55 (10) ◽  
pp. 2377-2380
Author(s):  
Hamza A. Hussain
Keyword(s):  
Hydrogen Peroxide ◽  
Hydrogen Bonding ◽  
Free Radicals ◽  
Esr Spectroscopy ◽  
The Other ◽  
Tetraethylammonium Bromide ◽  
Splitting Constant ◽  
The One ◽  
Positively Charged ◽  
Two Equilibria

Nitroxide free radicals prepared from diethylamine, piperidine and pyrrolidine by oxidation with hydrogen peroxide were studied by ESR spectroscopy. The changes in the 14N splitting constant (aN) caused by the addition of KBr or tetraethylammonium bromide were measured in dependence on the concentration of the ions. For diethylamine nitroxide and piperidine nitroxide, the results are discussed in terms of two equilibria: the one, involving the anion, is associated with a gain or loss of hydrogen bonds to the nitroxide oxygen atom, the other is associated with the formation of solvent shared units involving the cation, which results in changes in the hydrogen bonding strenght. The large increase in the aN value in the case of pyrrolidine nitroxide is explained in terms of an interaction from one side of the positively charged N atom; the increase in aN in the case of diethylamine and piperidine nitroxides is explained in terms of interactions with both sides of the positively charged N atom.

First Principles Investigation of the Stability and the Chemical Behavior of Hydrogen in ThCoH4

2011 ◽  
Vol 66 (3) ◽  
pp. 269-274
Author(s):  
Samir F. Matar
Keyword(s):  
Negative Charge ◽  
Geometry Optimization ◽  
Full Geometry Optimization ◽  
Intermetallic Matrix ◽  
Charge Analysis ◽  
The Stability ◽  
The One ◽  
Site Selective ◽  
Bader Charge Analysis ◽  
Positively Charged

We address the changes in the electronic structure brought by the insertion of hydrogen into ThCo leading to the experimentally observed ThCoH4. Full geometry optimization positions the hydrogen in three sites stabilized in the expanded intermetallic matrix. From a Bader charge analysis, hydrogen is found to be in a narrow iono-covalent (~−0.6) to covalent (~−0.3) bonding which should enable site-selective desorption. The overall chemical picture shows a positively charged Thδ+ with the negative charge redistributed over a complex anion {CoH4}δ− with δ~1.8. Nevertheless this charge transfer remains far from the one in the more ionic hydridocobaltate anion CoH54− in Mg2CoH5, due to the largely electropositive character of Mg.

scholarly journals Simple Nanoparticles from the Assembly of Cationic Polymer and Antigen as Immunoadjuvants

Vaccines ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 105 ◽  
Author(s):  
Yunys Pérez-Betancourt ◽  
Bianca de Carvalho Lins Fernandes Távora ◽  
Mônica Colombini ◽  
Eliana L. Faquim-Mauro ◽  
Ana Maria Carmona-Ribeiro
Keyword(s):  
Delayed Type Hypersensitivity ◽  
Hydrodynamic Diameter ◽  
Spherical Nanoparticles ◽  
Diallyldimethylammonium Chloride ◽  
The One ◽  
Antigen Presenting ◽  
Th 1 ◽  
Positively Charged ◽  
Stimulation Of

Since antigens are negatively charged, they combine well with positively charged adjuvants. Here, ovalbumin (OVA) (0.1 mg·mL−1) and poly (diallyldimethylammonium chloride) (PDDA) (0.01 mg·mL−1) yielded PDDA/OVA assemblies characterized by dynamic light scattering (DLS) and scanning electron microscopy (SEM) as spherical nanoparticles (NPs) of 170 ± 4 nm hydrodynamic diameter, 30 ± 2 mV of zeta-potential and 0.11 ± 0.01 of polydispersity. Mice immunization with the NPs elicited high OVA-specific IgG1 and low OVA-specific IgG2a production, indicating a Th-2 response. Delayed-type hypersensitivity reaction (DTH) was low and comparable to the one elicited by Al(OH)3/OVA, suggesting again a Th-2 response. PDDA advantages as an adjuvant were simplicity (a single-component adjuvant), low concentration needed (0.01 mg·mL−1 PDDA) combined with antigen yielding neglectable cytotoxicity, and high stability of PDDA/OVA dispersions. The NPs elicited much higher OVA-specific antibodies production than Al(OH)3/OVA. In vivo, the nano-metric size possibly assured antigen presentation by antigen-presenting cells (APC) at the lymph nodes, in contrast to the location of Al(OH)3/OVA microparticles at the site of injection for longer periods with stimulation of local dendritic cells. In the future, it will be interesting to evaluate combinations of the antigen with NPs carrying both PDDA and elicitors of the Th-1 response.

scholarly journals Gaseous combustion at high pressures. Part IV.—The influence of varying initial pressures upon the rate of pressure development and the activation of nitrogen in carbon monoxide-air explosions

1924 ◽  
Vol 105 (732) ◽  
pp. 406-433
Keyword(s):  
Carbon Monoxide ◽  
High Pressures ◽  
Vibrational Energy ◽  
Initial Pressure ◽  
Maximum Pressure ◽  
Time Interval ◽  
Pressure Development ◽  
The One ◽  
Air Explosion ◽  
Energy Absorbing

In the previous paper of this series it was shown :— (1) that when nitrogen is added as a diluent to a mixture of 2CO+O 2 undergoing combustion in a bomb at an initial pressure of 50 atmospheres, it exerts a peculiar energy-absorbing influence upon the system, far beyond that of other diatomic gases, or of argon; (2) that by virtue of such influence, it retards the attainment of maximum pressure in a much greater degree than can be accounted for on the supposition of its acting merely as a diatomic diluent; (3) that the energy so absorbed by the nitrogen during the combustion period, which extends right up to the attainment of maximum pressure, is slowly liberated thereafter as the system cools down ; and that consequently the rate of cooling is greatly retarded for a considerable time interval after the attainment of maximum pressure; (4) that there is no such energy-absorbing effect ( i. e ., other than a purely "diluent" one) when nitrogen is present in a 2H 2 +O 2 mixture similarly undergoing combustion ; but that, on the contrary, the presence of hydrogen in a CO-air mixture undergoing combustion at such high pressures so strongly counteracts the said " energy-absorbing " influence of the nitrogen, that it must be excluded as far as possible from the system before any large nitrogen-effect can be observed. These facts were explained on the supposition that there is some constitutional correspondence between CO and N 2 molecules (whose densities are identical) whereby the vibrational energy (radiation) emitted when the one burns is of such a quality as can be readily absorbed by the other, the two thus acting in resonance. It was further supposed that, in consequence of such resonance, nitrogen becomes chemically " activated " when present during the combustion of carbon monoxide at such high pressures ; and in conformity with this supposition, it was shown that such "activated" nitrogen is able to combine with oxygen more readily than does nitrogen which has merely been raised to a correspondingly high temperature in a hydrogen-air explosion.

scholarly journals MRI Relaxivity Changes of the Magnetic Nanoparticles Induced by Different Amino Acid Coatings

Nanomaterials ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 394 ◽  
Author(s):  
Iryna Antal ◽  
Oliver Strbak ◽  
Iryna Khmara ◽  
Martina Koneracka ◽  
Martina Kubovcikova ◽  
...  
Keyword(s):  
Magnetic Nanoparticles ◽  
Chemical Properties ◽  
Hydrodynamic Diameter ◽  
Contrast Imaging ◽  
Dispersed Particles ◽  
Physico Chemical ◽  
The One ◽  
Molecular Contrast ◽  
The Impact ◽  
Positively Charged

In this study, we analysed the physico-chemical properties of positively charged magnetic fluids consisting of magnetic nanoparticles (MNPs) functionalised by different amino acids (AAs): glycine (Gly), lysine (Lys) and tryptophan (Trp), and the influence of AA–MNP complexes on the MRI relaxivity. We found that the AA coating affects the size of dispersed particles and isoelectric point, as well as the zeta potential of AA–MNPs differently, depending on the AA selected. Moreover, we showed that a change in hydrodynamic diameter results in a change to the relaxivity of AA–MNP complexes. On the one hand, we observed a decrease in the relaxivity values, r1 and r2, with an increase in hydrodynamic diameter (the relaxivity of r1 and r2 were comparable with commercially available contrast agents); on the other hand, we observed an increase in r2* value with an increase in hydrodynamic size. These findings provide an interesting preliminary look at the impact of AA coating on the relaxivity properties of AA–MNP complexes, with a specific application in molecular contrast imaging originating from magnetic nanoparticles and magnetic resonance techniques.

scholarly journals Перенос заряда и центры F типа в щелочноземельных фторидах, активированных ионами Cd-=SUP=-2+-=/SUP=- или Zn-=SUP=-2+-=/SUP=-

2020 ◽  
Vol 128 (10) ◽  
pp. 1462
Author(s):  
А.В. Егранов ◽  
Р.Ю. Шендрик ◽  
Т.Ю. Сизова
Keyword(s):  
Charge Transfer ◽  
Alkaline Earth ◽  
Anionic Vacancy ◽  
Luminescence Spectra ◽  
Photoluminescence Spectra ◽  
Impurity Centers ◽  
Impurity Ion ◽  
F Centers

The photoluminescence spectra of impurity centers containing the anionic vacancy Cd+va or Zn+va in alkaline-earth fluorides are studied. A comparison with the luminescence spectra of photochromic centers (РC), which can be considered as perturbed F centers, shows that the luminescence of the Cd+va or Zn+va centers is similar to the luminescence of F centers and, therefore, is associated with charge transfer from an impurity ion to an anionic vacancy.

Hydrothermal shape controllable synthesis of La0.5Sr0.5MnO3 crystals and facet effect on electron transfer of oxygen reduction

2018 ◽  
Vol 5 (3) ◽  
pp. 732-738 ◽  
Author(s):  
Keke Huang ◽  
Long Yuan ◽  
Yilan Jiang ◽  
Jiaxin Zhang ◽  
Zhibin Geng ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Rare Earth ◽  
Valence State ◽  
Alkaline Earth ◽  
Mixed Valence ◽  
Controllable Synthesis ◽  
Controllable Growth ◽  
A Site ◽  
Oxide Crystals ◽  
Alkaline Earth Cations

Controllable growth of perovskite structure oxide crystals with well-defined facets is challenging, especially in the mixed-valence state manganites with both rare-earth and alkaline-earth cations in their A-site.

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