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At least 199 records · Page 11

Spectroscopic identification of Ca-bearing uranyl silicates formed in C–S–H systems

Portland cement-based grouts used for radioactive waste immobilisation contain a Ca- and Si-rich binder phase, known as calcium–silicate–hydrate (C–S–H). Depending on the blend of cement used, the Ca/Si ratio can vary considerably. A range of C–S–H minerals with Ca/Si ratios from 0.6 to 1.6 were synthesised and contacted with aqueous U(VI) at 0.5 mM and 10 mM concentrations. Solid-state 29 Si MAS-NMR spectroscopy was applied to probe the Si coordination environment in U(VI)-contacted C–S–H minerals and, in conjunction with U L III -edge X-ray absorption spectroscopy analysis, inferences of the fate of U(VI) in these systems were made. At moderate or high Ca/Si ratios, uranophane-type uranyl silicates or Ca-uranates dominated, while at the lowest Ca/Si ratios, the formation of a Ca-bearing uranyl silicate mineral, similar to haiweeite (Ca[(UO 2 ) 2 Si 5 O 12 (OH) 2 ]·3H 2 O) or Ca-bearing weeksite (Ca 2 (UO 2 ) 2 Si 6 O 15 ·10H 2 O) was identified. This study highlights the influence of Ca/Si ratio on uranyl sequestration, of interest in the development of post-closure safety models for U-bearing radioactive waste disposal.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

Design and structural basis of selective 1,4-dihydropyridine inhibitors of the calcium-activated potassium channel K Ca 3.1

The 1,4-dihydropyridines, drugs with well-established bioavailability and toxicity profiles, have proven efficacy in treating human hypertension, peripheral vascular disorders, and coronary artery disease. Every 1,4-dihydropyridine in clinical use blocks L-type voltage-gated calcium channels. We now report our development, using selective optimization of a side activity (SOSA), of a class of 1,4-dihydropyridines that selectively and potently inhibit the intermediate-conductance calcium-activated K + channel K Ca 3.1, a validated therapeutic target for diseases affecting many organ systems. One of these 1,4-dihydropyridines, DHP-103, blocked K Ca 3.1 with an IC 50 of 6 nM and exhibited exquisite selectivity over calcium channels and a panel of >100 additional molecular targets. Using high-resolution structure determination by cryogenic electron microscopy together with mutagenesis and electrophysiology, we delineated the drug binding pocket for DHP-103 within the water-filled central cavity of the K Ca 3.1 channel pore, where bound drug directly impedes ion permeation. DHP-103 inhibited gain-of-function mutant K Ca 3.1 channels that cause hereditary xerocytosis, suggesting its potential use as a therapeutic for this hemolytic anemia. In a rat model of acute ischemic stroke, the second leading cause of death worldwide, DHP-103 administered 12 h postischemic insult in proof-of-concept studies reduced infarct volume, improved balance beam performance (measure of proprioception) and decreased numbers of activated microglia in infarcted areas. K Ca 3.1-selective 1,4-dihydropyridines hold promise for the many diseases for which K Ca 3.1 has been experimentally confirmed as a therapeutic target.

Ong, Seow Theng [Lee Kong Chian School of Medicine↗

Microscopic study of the fusion reactions 40,48 Ca+ 78 Ni and the effect of the tensor force

In this work, we provide a microscopic description of the fusion reactions between 40,48 Ca and 78 Ni. The internuclear potentials are obtained using the density-constrained (DC) time-dependent Hartree-Fock (TDHF) approach and fusion cross sections are calculated via the incoming wave boundary condition method. By performing DC-TDHF calculations at several selected incident energies, the internuclear potentials for both systems are obtained and the energy-dependence of fusion barrier are revealed. The influence of tensor force on internuclear potentials of 48 Ca+ 78 Ni is more obvious than those of 40 Ca+ 78 Ni. By comparing the calculated fusion cross sections between 40 Ca+ 78 Ni and 48 Ca+ 78 Ni, an interesting enhancement of subbarrier fusion cross sections for the former system is found, which can be explained by the narrow width of internuclear potential for 40 Ca+ 78 Ni while the barrier heights and positions are very close to each other. The tensor force suppresses the subbarrier fusion cross sections of both two systems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Flg22‐induced Ca 2+ increases undergo desensitization and resensitization

The flagellin epitope flg22, a pathogen-associated molecular pattern (PAMP), binds to the receptor-like kinase FLAGELLIN SENSING2 (FLS2), and triggers Ca 2+ influx across the plasma membrane (PM). The flg22-induced increases in cytosolic Ca 2+ concentration ([Ca 2+ ]i) (FICA) play a crucial role in plant innate immunity. It's well established that the receptor FLS2 and reactive oxygen species (ROS) burst undergo sensitivity adaptation after flg22 stimulation, referred to as desensitization and resensitization, to prevent over responses to pathogens. However, whether FICA also mount adaptation mechanisms to ensure appropriate and efficient responses against pathogens remains poorly understood. Here, we analysed systematically [Ca 2+ ]i increases upon two successive flg22 treatments, recorded and characterized rapid desensitization but slow resensitization of FICA in Arabidopsis thaliana. Pharmacological analyses showed that the rapid desensitization might be synergistically regulated by ligand-induced FLS2 endocytosis as well as the PM depolarization. The resensitization of FICA might require de novo FLS2 protein synthesis. FICA resensitization appeared significantly slower than FLS2 protein recovery, suggesting additional regulatory mechanisms of other components, such as flg22-related Ca 2+ permeable channels. Taken together, we have carefully defined the FICA sensitivity adaptation, which will facilitate further molecular and genetic dissection of the Ca 2+ -mediated adaptive mechanisms in PAMP-triggered immunity.

59 BASIC BIOLOGICAL SCIENCES↗

Rationalizing Calcium Electrodeposition Behavior by Quantifying Ethereal Solvation Effects on Ca 2+ Coordination in Well-Dissociated Electrolytes

Ca-ion electrochemical systems have been pushed to the forefront of recent multivalent energy storage advances due to their use of earth-abundant redox materials and their high theoretical specific densities in relation to monovalent or even other more widely explored multivalent-charge carriers. However, significant pitfalls in metal plating and stripping arise from electrolyte decomposition and can be related to the coordination environment around Ca 2+ with both the negatively charged anion and the organic–aprotic solvent. Here, we apply multiple spectroscopic techniques in conjunction with density functional theory to evaluate the coordination environment of Ca 2+ across a class of ethereal solvents. Through the combination of X-ray absorption fine structure and time-dependent density functional theory, descriptive measures of the local geometry, coordination, and electronic structure of Ca–ethereal complexes provide distinct structural trends depending on the extent of the Ca 2+ –solvent interaction. Finally, we correlate these findings with electrochemical measurements of calcium tetrakis(hexafluoroisopropoxy)borate (CaBHFIP 2 ) salts dissolved within this class of solvents to provide insight into the preferred structural configuration of Ca 2+ electrolytic solutions for optimized electrochemical plating and stripping.

25 ENERGY STORAGE↗

Nebular Models of Sub-Chandrasekhar Mass Type Ia Supernovae: Clues to the Origin of Ca-rich Transients

In this work we use non-local thermal equilibrium radiative transport modeling to examine observational signatures of sub-Chandrasekhar mass double detonation explosions in the nebular phase. Results range from spectra that look like typical and subluminous Type Ia supernovae (SNe) for higher mass progenitors to spectra that look like Ca-rich transients for lower mass progenitors. This ignition mechanism produces an inherent relationship between emission features and the progenitor mass as the ratio of the nebular [Ca II ]/[Fe III ] emission lines increases with decreasing white dwarf mass. Examining the [Ca II ]/[Fe III ] nebular line ratio in a sample of observed SNe we find further evidence for the two distinct classes of SNe Ia identified in Polin et al. by their relationship between Si ii velocity and B-band magnitude, both at time of peak brightness. This suggests that SNe Ia arise from more than one progenitor channel, and provides an empirical method for classifying events based on their physical origin. Furthermore, we provide insight to the mysterious origin of Ca-rich transients. Low-mass double detonation models with only a small mass fraction of Ca (1%) produce nebular spectra that cool primarily through forbidden [Ca II ] emission.

79 ASTRONOMY AND ASTROPHYSICS↗

Observations of interstellar Ca I lines.

Evaluation of interferometric, photoelectric scans of the interstellar Ca I line at 4226 A for four stars having strong interstellar Ca II K-lines. The Ca I line is detected in three, and possibly all four, cases, of which one was kn*wn previously. Negative Ca I results are also obtained for six stars with weaker K-lines. The significance of the resulting electron densities deduced from the Ca I and Ca II lines is discussed.

Hobbs, L. M.↗

Ca isotope fractionation on the moon

Ca has been measured in a lunar soil in order to establish the presence of isotopically mass-fractionated components. Ca was extracted by a series of water leaches after the soils were 'activated' by brief exposures to fluorine gas. The O2 obtained by this fluorination is found to have delta (O-18) of +21 per mil and to be, therefore, significantly mass-fractionated. Ca obtained in the leaches was analyzed using the double-spike technique. Very small Ca isotope fractionation is found in the leaches of this soil of up to 1 per mil per mass unit difference. The small Ca effects are in marked contrast to the measured delta (O-18) for the same sample and to large effects observed in many soils for oxygen, silicon, sulfur, and potassium. The data on Ca provide stringent constraints on models which attempt to explain the isotope mass-fractionation effects in lunar soils.

Russell, W. A.↗

Ca isotopes in refractory inclusions

The present absolute isotope abundance measurements of Ca in Ca-Al-rich inclusions from the Allende and Leoville meteorites show the extreme rarity of nonlinear isotope effects in Ca, in sharp contrast to the endemic effects in Ti. The Ca in the Ca-Al-rich inclusions shows mass-dependent isotope fractionation effects whose range is a factor of 20 wider than the range previously established for bulk meteorites and for terrestrial and lunar samples. A correlation is found between Ca and Mg isotope fractionation effects and inclusion type, and a possible correlation between isotope fractionation and rare earth element abundance patterns is discussed.

Niederer, F. R.↗

Ca-Rich Carbonate Melts: A Regular-Solution Model, with Applications to Carbonatite Magma + Vapor Equilibria and Carbonate Lavas on Venus

A thermochemical model of the activities of species in carbonate-rich melts would be useful in quantifying chemical equilibria between carbonatite magmas and vapors and in extrapolating liquidus equilibria to unexplored PTX. A regular-solution model of Ca-rich carbonate melts is developed here, using the fact that they are ionic liquids, and can be treated (to a first approximation) as interpenetrating regular solutions of cations and of anions. Thermochemical data on systems of alkali metal cations with carbonate and other anions are drawn from the literature; data on systems with alkaline earth (and other) cations and carbonate (and other) anions are derived here from liquidus phase equilibria. The model is validated in that all available data (at 1 kbar) are consistent with single values for the melting temperature and heat of fusion for calcite, and all liquidi are consistent with the liquids acting as regular solutions. At 1 kbar, the metastable congruent melting temperature of calcite (CaCO3) is inferred to be 1596 K, with (Delta)bar-H(sub fus)(calcite) = 31.5 +/- 1 kJ/mol. Regular solution interaction parameters (W) for Ca(2+) and alkali metal cations are in the range -3 to -12 kJ/sq mol; W for Ca(2+)-Ba(2+) is approximately -11 kJ/sq mol; W for Ca(2+)-Mg(2+) is approximately -40 kJ/sq mol, and W for Ca(2+)-La(3+) is approximately +85 kJ/sq mol. Solutions of carbonate and most anions (including OH(-), F(-), and SO4(2-)) are nearly ideal, with W between 0(ideal) and -2.5 kJ/sq mol. The interaction of carbonate and phosphate ions is strongly nonideal, which is consistent with the suggestion of carbonate-phosphate liquid immiscibility. Interaction of carbonate and sulfide ions is also nonideal and suggestive of carbonate-sulfide liquid immiscibility. Solution of H2O, for all but the most H2O-rich compositions, can be modeled as a disproportionation to hydronium (H3O(+)) and hydroxyl (OH(-)) ions with W for Ca(2+)-H3O(+) (approximately) equals 33 kJ/sq mol. The regular-solution model of carbonate melts can be applied to problems of carbonatite magma + vapor equilibria and of extrapolating liquidus equilibria to unstudied systems. Calculations on one carbonatite (the Husereau dike, Oka complex, Quebec, Canada) show that the anion solution of its magma contained an OH mole fraction of (approximately) 0.07, although the vapor in equilibrium with the magma had P(H2O) = 8.5 x P(CO2). F in carbonatite systems is calculated to be strongly partitioned into the magma (as F(-)) relative to coexisting vapor. In the Husereau carbonatite magma, the anion solution contained an F(-) mole fraction of (approximately) 6 x 10(exp -5).

Treiman, Allan H.↗

LabHEART: an interactive computer model of rabbit ventricular myocyte ion channels and Ca transport

An interactive computer program, LabHEART, was developed to simulate the action potential (AP), ionic currents, and Ca handling mechanisms in a rabbit ventricular myocyte. User-oriented, its design allows switching between voltage and current clamp and easy on-line manipulation of key parameters to change the original formulation. The model reproduces normal rabbit ventricular myocyte currents, Ca transients, and APs. We also changed parameters to simulate data from heart failure (HF) myocytes, including reduced transient outward (I(to)) and inward rectifying K currents (I(K1)), enhanced Na/Ca exchange expression, and reduced sarcoplasmic reticulum Ca-ATPase function, but unaltered Ca current density. These changes caused reduced Ca transient amplitude and increased AP duration (especially at lower frequency) as observed experimentally. The model shows that the increased Na/Ca exchange current (I(NaCa)) in HF lowers the intracellular [Ca] threshold for a triggered AP from 800 to 540 nM. Similarly, the decrease in I(K1) reduces the threshold to 600 nM. Changes in I(to) have no effect. Combining enhanced Na/Ca exchange with reduced I(K1) (as in HF) lowers the threshold to trigger an AP to 380 nM. These changes reproduce experimental results in HF, where the contributions of different factors are not readily distinguishable. We conclude that the triggered APs that contribute to nonreentrant ventricular tachycardia in HF are due approximately equally (and nearly additively) to alterations in I(NaCa) and I(K1). A free copy of this software can be obtained at http://www.meddean.luc.edu/lumen/DeptWebs/physio/bers.html.

NASA Discipline Cardiopulmonary↗

Materials Data on Ca(ZnSi)2 by Materials Project

CaZn2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ca is bonded in a 8-coordinate geometry to eight equivalent Zn and eight equivalent Si atoms. All Ca–Zn bond lengths are 3.31 Å. All Ca–Si bond lengths are 3.23 Å. Zn is bonded to four equivalent Ca and four equivalent Si atoms to form a mixture of distorted face, edge, and corner-sharing ZnCa4Si4 tetrahedra. All Zn–Si bond lengths are 2.53 Å. Si is bonded in a 9-coordinate geometry to four equivalent Ca, four equivalent Zn, and one Si atom. The Si–Si bond length is 2.35 Å.

36 MATERIALS SCIENCE↗

Materials Data on Ca(AlZn)2 by Materials Project

CaAl2Zn2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ca is bonded in a 8-coordinate geometry to eight equivalent Zn and eight equivalent Al atoms. All Ca–Zn bond lengths are 3.18 Å. All Ca–Al bond lengths are 3.51 Å. Zn is bonded in a 9-coordinate geometry to four equivalent Ca, one Zn, and four equivalent Al atoms. The Zn–Zn bond length is 2.48 Å. All Zn–Al bond lengths are 2.62 Å. Al is bonded to four equivalent Ca, four equivalent Zn, and four equivalent Al atoms to form a mixture of distorted edge, corner, and face-sharing AlCa4Al4Zn4 cuboctahedra. All Al–Al bond lengths are 2.93 Å.

36 MATERIALS SCIENCE↗

Materials Data on Ca(Ni2Sn)2 by Materials Project

CaNi4Sn2 crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. Ca is bonded in a 8-coordinate geometry to eight equivalent Ni and eight equivalent Sn atoms. All Ca–Ni bond lengths are 3.05 Å. All Ca–Sn bond lengths are 3.51 Å. Ni is bonded in a 10-coordinate geometry to two equivalent Ca, four equivalent Ni, and four equivalent Sn atoms. There are a spread of Ni–Ni bond distances ranging from 2.53–2.75 Å. There are a spread of Ni–Sn bond distances ranging from 2.55–2.66 Å. Sn is bonded in a 12-coordinate geometry to four equivalent Ca and eight equivalent Ni atoms.

36 MATERIALS SCIENCE↗

Materials Data on Ca(PO3)2 by Materials Project

Ca(PO3)2 crystallizes in the monoclinic Cc space group. The structure is three-dimensional. there are four inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ca–O bond distances ranging from 2.33–2.57 Å. In the second Ca2+ site, Ca2+ is bonded to seven O2- atoms to form distorted CaO7 pentagonal bipyramids that share corners with five PO4 tetrahedra, edges with two equivalent CaO7 pentagonal bipyramids, and an edgeedge with one PO4 tetrahedra. There are a spread of Ca–O bond distances ranging from 2.34–2.73 Å. In the third Ca2+ site, Ca2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ca–O bond distances ranging from 2.32–2.58 Å. In the fourth Ca2+ site, Ca2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ca–O bond distances ranging from 2.34–2.82 Å. There are eight inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one CaO7 pentagonal bipyramid, corners with two equivalent PO4 tetrahedra, and an edgeedge with one CaO7 pentagonal bipyramid. There are a spread of P–O bond distances ranging from 1.50–1.61 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.50–1.61 Å. In the third P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.50–1.61 Å. In the fourth P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent CaO7 pentagonal bipyramids and corners with two PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.62 Å. In the fifth P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one CaO7 pentagonal bipyramid and corners with two PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.50–1.61 Å. In the sixth P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one CaO7 pentagonal bipyramid and corners with two PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.62 Å. In the seventh P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.62 Å. In the eighth P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.62 Å. There are twenty-four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one Ca2+ and one P5+ atom. In the second O2- site, O2- is bonded in a linear geometry to one Ca2+ and one P5+ atom. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ca2+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a linear geometry to two P5+ atoms. In the fifth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two equivalent Ca2+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a 1-coordinate geometry to two Ca2+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the eighth O2- site, O2- is bonded in a 1-coordinate geometry to two Ca2+ and one P5+ atom. In the ninth O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the tenth O2- site, O2- is bonded in a distorted linear geometry to one Ca2+ and one P5+ atom. In the eleventh O2- site, O2- is bonded in a 1-coordinate geometry to two Ca2+ and one P5+ atom. In the twelfth O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the thirteenth O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Ca2+ and one P5+ atom. In the fourteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the fifteenth O2- site, O2- is bonded in a 1-coordinate geometry to two Ca2+ and one P5+ atom. In the sixteenth O2- site, O2- is bonded in a 1-coordinate geometry to two Ca2+ and one P5+ atom. In the seventeenth O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the eighteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the nineteenth O2- site, O2- is bonded in a distorted linear geometry to one Ca2+ and one P5+ atom. In the twentieth O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the twenty-first O2- site, O2- is bonded in a distorted linear geometry to one Ca2+ and one P5+ atom. In the twenty-second O2- site, O2- is bonded in a 1-coordinate geometry to two Ca2+ and one P5+ atom. In the twenty-third O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Ca2+ and one P5+ atom. In the twenty-fourth O2- site, O2- is bonded in a 1-coordinate geometry to two Ca2+ and one P5+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Ca(ClO2)2 by Materials Project

Ca(O2Cl)2 crystallizes in the orthorhombic Ccce space group. The structure is two-dimensional and consists of two Ca(O2Cl)2 sheets oriented in the (0, 1, 0) direction. Ca is bonded in a 8-coordinate geometry to eight equivalent O atoms. All Ca–O bond lengths are 2.51 Å. O is bonded in a trigonal planar geometry to two equivalent Ca and one Cl atom. The O–Cl bond length is 1.58 Å. Cl is bonded in a water-like geometry to two equivalent O atoms.

36 MATERIALS SCIENCE↗

Materials Data on Ca(CuSn)2 by Materials Project

CaCu2Sn2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Ca is bonded in a 10-coordinate geometry to six equivalent Cu and eight equivalent Sn atoms. There are two shorter (3.16 Å) and four longer (3.27 Å) Ca–Cu bond lengths. There are four shorter (3.46 Å) and four longer (3.67 Å) Ca–Sn bond lengths. Cu is bonded in a 9-coordinate geometry to three equivalent Ca, two equivalent Cu, and four equivalent Sn atoms. Both Cu–Cu bond lengths are 2.55 Å. There are two shorter (2.63 Å) and two longer (2.68 Å) Cu–Sn bond lengths. Sn is bonded in a 9-coordinate geometry to four equivalent Ca, four equivalent Cu, and one Sn atom. The Sn–Sn bond length is 3.01 Å.

36 MATERIALS SCIENCE↗

Materials Data on Ca(BRh)2 by Materials Project

CaRh2B2 is alpha Pu-derived structured and crystallizes in the orthorhombic Fddd space group. The structure is three-dimensional. Ca is bonded in a 10-coordinate geometry to eight equivalent Rh and six equivalent B atoms. There are four shorter (3.04 Å) and four longer (3.28 Å) Ca–Rh bond lengths. There are two shorter (3.02 Å) and four longer (3.12 Å) Ca–B bond lengths. Rh is bonded in a 4-coordinate geometry to four equivalent Ca and four equivalent B atoms. There are two shorter (2.08 Å) and two longer (2.14 Å) Rh–B bond lengths. B is bonded in a 4-coordinate geometry to three equivalent Ca and four equivalent Rh atoms.

36 MATERIALS SCIENCE↗