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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Kv2.1 channels play opposing roles in regulating membrane potential, Ca 2+ channel function, and myogenic tone in arterial smooth muscle

The accepted role of the protein Kv2.1 in arterial smooth muscle cells is to form K + channels in the sarcolemma. Opening of Kv2.1 channels causes membrane hyperpolarization, which decreases the activity of L-type Ca V 1.2 channels, lowering intracellular Ca 2+ ([Ca 2+ ] i ) and causing smooth muscle relaxation. A limitation of this model is that it is based exclusively on data from male arterial myocytes. Here, we used a combination of electrophysiology as well as imaging approaches to investigate the role of Kv2.1 channels in male and female arterial myocytes. We confirmed that Kv2.1 plays a canonical conductive role but found it also has a structural role in arterial myocytes to enhance clustering of Ca V 1.2 channels. Less than 1% of Kv2.1 channels are conductive and induce membrane hyperpolarization. Paradoxically, by enhancing the structural clustering and probability of Ca V 1.2–Ca V 1.2 interactions within these clusters, Kv2.1 increases Ca 2+ influx. These functional impacts of Kv2.1 depend on its level of expression, which varies with sex. In female myocytes, where expression of Kv2.1 protein is higher than in male myocytes, Kv2.1 has conductive and structural roles. Female myocytes have larger Ca V 1.2 clusters, larger [Ca 2+ ] i , and larger myogenic tone than male myocytes. In contrast, in male myocytes, Kv2.1 channels regulate membrane potential but not Ca V 1.2 channel clustering. We propose a model in which Kv2.1 function varies with sex: in males, Kv2.1 channels control membrane potential but, in female myocytes, Kv2.1 plays dual electrical and Ca V 1.2 clustering roles. This contributes to sex-specific regulation of excitability, [Ca 2+ ] i , and myogenic tone in arterial myocytes.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2001

Model study of ATP and ADP buffering, transport of Ca(2+) and Mg(2+), and regulation of ion pumps in ventricular myocyte

We extended the model of the ventricular myocyte by Winslow et al. (Circ. Res 1999, 84:571-586) by incorporating equations for Ca(2+) and Mg(2+) buffering and transport by ATP and ADP and equations for MgATP regulation of ion transporters (Na(+)-K(+) pump, sarcolemmal and sarcoplasmic Ca(2+) pumps). The results indicate that, under normal conditions, Ca(2+) binding by low-affinity ATP and diffusion of CaATP may affect the amplitude and time course of intracellular Ca(2+) signals. The model also suggests that a fall in ATP/ADP ratio significantly reduces sarcoplasmic Ca(2+) content, increases diastolic Ca(2+), lowers systolic Ca(2+), increases Ca(2+) influx through L-type channels, and decreases the efficiency of the Na(+)/Ca(2+) exchanger in extruding Ca(2+) during periodic voltage-clamp stimulation. The analysis suggests that the most important reason for these changes during metabolic inhibition is the down-regulation of the sarcoplasmic Ca(2+)-ATPase pump by reduced diastolic MgATP levels. High Ca(2+) concentrations developed near the membrane might have a greater influence on Mg(2+), ATP, and ADP concentrations than that of the lower Ca(2+) concentrations in the bulk myoplasm. The model predictions are in general agreement with experimental observations measured under normal and pathological conditions.

NASA Discipline Cardiopulmonary↗
NASA NTRS2001

The Ca(2+) status of the endoplasmic reticulum is altered by induction of calreticulin expression in transgenic plants

To investigate the endoplasmic reticulum (ER) Ca(2+) stores in plant cells, we generated tobacco (Nicotiana tabacum; NT1) suspension cells and Arabidopsis plants with altered levels of calreticulin (CRT), an ER-localized Ca(2+)-binding protein. NT1 cells and Arabidopsis plants were transformed with a maize (Zea mays) CRT gene in both sense and antisense orientations under the control of an Arabidopsis heat shock promoter. ER-enriched membrane fractions from NT1 cells were used to examine how altered expression of CRT affects Ca(2+) uptake and release. We found that a 2.5-fold increase in CRT led to a 2-fold increase in ATP-dependent (45)Ca(2+) accumulation in the ER-enriched fraction compared with heat-shocked wild-type controls. Furthermore, after treatment with the Ca(2+) ionophore ionomycin, ER microsomes from NT1 cells overproducing CRT showed a 2-fold increase in the amount of (45)Ca(2+) released, and a 2- to 3-fold increase in the amount of (45)Ca(2+) retained compared with wild type. These data indicate that altering the production of CRT affects the ER Ca(2+) pool. In addition, CRT transgenic Arabidopsis plants were used to determine if altered CRT levels had any physiological effects. We found that the level of CRT in heat shock-induced CRT transgenic plants correlated positively with the retention of chlorophyll when the plants were transferred from Ca(2+)-containing medium to Ca(2+)-depleted medium. Together these data are consistent with the hypothesis that increasing CRT in the ER increases the ER Ca(2+) stores and thereby enhances the survival of plants grown in low Ca(2+) medium.

NASA Discipline Plant Biology↗
DOE OSTI2020

Materials Data on Ca(Pr2Se3)4 by Materials Project

Ca(Pr2Se3)4 crystallizes in the monoclinic Cc space group. The structure is three-dimensional. Ca is bonded to eight Se atoms to form distorted CaSe8 hexagonal bipyramids that share corners with eight PrSe8 hexagonal bipyramids, edges with four PrSe8 hexagonal bipyramids, and faces with eight PrSe8 hexagonal bipyramids. There are a spread of Ca–Se bond distances ranging from 3.01–3.24 Å. There are eight inequivalent Pr sites. In the first Pr site, Pr is bonded to eight Se atoms to form distorted PrSe8 hexagonal bipyramids that share a cornercorner with one CaSe8 hexagonal bipyramid, corners with seven PrSe8 hexagonal bipyramids, an edgeedge with one CaSe8 hexagonal bipyramid, edges with three PrSe8 hexagonal bipyramids, a faceface with one CaSe8 hexagonal bipyramid, and faces with seven PrSe8 hexagonal bipyramids. There are a spread of Pr–Se bond distances ranging from 3.02–3.23 Å. In the second Pr site, Pr is bonded to eight Se atoms to form distorted PrSe8 hexagonal bipyramids that share a cornercorner with one CaSe8 hexagonal bipyramid, corners with seven PrSe8 hexagonal bipyramids, edges with four PrSe8 hexagonal bipyramids, a faceface with one CaSe8 hexagonal bipyramid, and faces with seven PrSe8 hexagonal bipyramids. There are a spread of Pr–Se bond distances ranging from 3.02–3.22 Å. In the third Pr site, Pr is bonded to eight Se atoms to form distorted PrSe8 hexagonal bipyramids that share corners with two equivalent CaSe8 hexagonal bipyramids, corners with six PrSe8 hexagonal bipyramids, edges with four PrSe8 hexagonal bipyramids, a faceface with one CaSe8 hexagonal bipyramid, and faces with seven PrSe8 hexagonal bipyramids. There are a spread of Pr–Se bond distances ranging from 3.02–3.22 Å. In the fourth Pr site, Pr is bonded to eight Se atoms to form distorted PrSe8 hexagonal bipyramids that share corners with two equivalent CaSe8 hexagonal bipyramids, corners with six PrSe8 hexagonal bipyramids, edges with four PrSe8 hexagonal bipyramids, a faceface with one CaSe8 hexagonal bipyramid, and faces with seven PrSe8 hexagonal bipyramids. There are a spread of Pr–Se bond distances ranging from 3.03–3.22 Å. In the fifth Pr site, Pr is bonded to eight Se atoms to form distorted PrSe8 hexagonal bipyramids that share a cornercorner with one CaSe8 hexagonal bipyramid, corners with seven PrSe8 hexagonal bipyramids, an edgeedge with one CaSe8 hexagonal bipyramid, edges with three PrSe8 hexagonal bipyramids, a faceface with one CaSe8 hexagonal bipyramid, and faces with seven PrSe8 hexagonal bipyramids. There are a spread of Pr–Se bond distances ranging from 3.03–3.23 Å. In the sixth Pr site, Pr is bonded to eight Se atoms to form distorted PrSe8 hexagonal bipyramids that share a cornercorner with one CaSe8 hexagonal bipyramid, corners with seven PrSe8 hexagonal bipyramids, edges with four PrSe8 hexagonal bipyramids, a faceface with one CaSe8 hexagonal bipyramid, and faces with seven PrSe8 hexagonal bipyramids. There are a spread of Pr–Se bond distances ranging from 3.01–3.22 Å. In the seventh Pr site, Pr is bonded to eight Se atoms to form distorted PrSe8 hexagonal bipyramids that share corners with eight PrSe8 hexagonal bipyramids, edges with two equivalent CaSe8 hexagonal bipyramids, edges with two PrSe8 hexagonal bipyramids, and faces with eight PrSe8 hexagonal bipyramids. There are a spread of Pr–Se bond distances ranging from 3.03–3.22 Å. In the eighth Pr site, Pr is bonded to eight Se atoms to form distorted PrSe8 hexagonal bipyramids that share corners with eight PrSe8 hexagonal bipyramids, edges with four PrSe8 hexagonal bipyramids, faces with two equivalent CaSe8 hexagonal bipyramids, and faces with six PrSe8 hexagonal bipyramids. There are a spread of Pr–Se bond distances ranging from 3.03–3.21 Å. There are twelve inequivalent Se sites. In the first Se site, Se is bonded to one Ca and five Pr atoms to form distorted SeCaPr5 octahedra that share corners with fifteen SeCaPr5 octahedra, edges with six SeCaPr5 octahedra, and faces with five SePr6 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the second Se site, Se is bonded to one Ca and five Pr atoms to form a mixture of distorted edge, face, and corner-sharing SeCaPr5 octahedra. The corner-sharing octahedra tilt angles range from 17–51°. In the third Se site, Se is bonded to one Ca and five Pr atoms to form a mixture of distorted edge, face, and corner-sharing SeCaPr5 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the fourth Se site, Se is bonded to six Pr atoms to form a mixture of distorted edge, face, and corner-sharing SePr6 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the fifth Se site, Se is bonded to six Pr atoms to form a mixture of distorted edge, face, and corner-sharing SePr6 octahedra. The corner-sharing octahedra tilt angles range from 16–51°. In the sixth Se site, Se is bonded to one Ca and five Pr atoms to form a mixture of distorted edge, face, and corner-sharing SeCaPr5 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the seventh Se site, Se is bonded to one Ca and five Pr atoms to form a mixture of distorted edge, face, and corner-sharing SeCaPr5 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the eighth Se site, Se is bonded to one Ca and five Pr atoms to form a mixture of distorted edge, face, and corner-sharing SeCaPr5 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the ninth Se site, Se is bonded to one Ca and five Pr atoms to form a mixture of distorted edge, face, and corner-sharing SeCaPr5 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the tenth Se site, Se is bonded to six Pr atoms to form distorted SePr6 octahedra that share corners with fifteen SeCaPr5 octahedra, edges with six SeCaPr5 octahedra, and faces with five SePr6 octahedra. The corner-sharing octahedra tilt angles range from 16–50°. In the eleventh Se site, Se is bonded to one Ca and five Pr atoms to form a mixture of distorted edge, face, and corner-sharing SeCaPr5 octahedra. The corner-sharing octahedra tilt angles range from 17–51°. In the twelfth Se site, Se is bonded to six Pr atoms to form a mixture of distorted edge, face, and corner-sharing SePr6 octahedra. The corner-sharing octahedra tilt angles range from 16–51°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(Ce2Se3)4 by Materials Project

Ca(Ce2Se3)4 crystallizes in the monoclinic Cc space group. The structure is three-dimensional. Ca is bonded to eight Se atoms to form distorted CaSe8 hexagonal bipyramids that share corners with eight CeSe8 hexagonal bipyramids, edges with four CeSe8 hexagonal bipyramids, and faces with eight CeSe8 hexagonal bipyramids. There are a spread of Ca–Se bond distances ranging from 2.99–3.19 Å. There are eight inequivalent Ce sites. In the first Ce site, Ce is bonded to eight Se atoms to form distorted CeSe8 hexagonal bipyramids that share a cornercorner with one CaSe8 hexagonal bipyramid, corners with seven CeSe8 hexagonal bipyramids, edges with four CeSe8 hexagonal bipyramids, a faceface with one CaSe8 hexagonal bipyramid, and faces with seven CeSe8 hexagonal bipyramids. There are a spread of Ce–Se bond distances ranging from 3.00–3.17 Å. In the second Ce site, Ce is bonded to eight Se atoms to form distorted CeSe8 hexagonal bipyramids that share corners with two equivalent CaSe8 hexagonal bipyramids, corners with six CeSe8 hexagonal bipyramids, edges with four CeSe8 hexagonal bipyramids, a faceface with one CaSe8 hexagonal bipyramid, and faces with seven CeSe8 hexagonal bipyramids. There are a spread of Ce–Se bond distances ranging from 2.99–3.17 Å. In the third Ce site, Ce is bonded to eight Se atoms to form distorted CeSe8 hexagonal bipyramids that share a cornercorner with one CaSe8 hexagonal bipyramid, corners with seven CeSe8 hexagonal bipyramids, an edgeedge with one CaSe8 hexagonal bipyramid, edges with three CeSe8 hexagonal bipyramids, a faceface with one CaSe8 hexagonal bipyramid, and faces with seven CeSe8 hexagonal bipyramids. There are a spread of Ce–Se bond distances ranging from 2.99–3.17 Å. In the fourth Ce site, Ce is bonded to eight Se atoms to form distorted CeSe8 hexagonal bipyramids that share corners with two equivalent CaSe8 hexagonal bipyramids, corners with six CeSe8 hexagonal bipyramids, edges with four CeSe8 hexagonal bipyramids, a faceface with one CaSe8 hexagonal bipyramid, and faces with seven CeSe8 hexagonal bipyramids. There are a spread of Ce–Se bond distances ranging from 2.99–3.16 Å. In the fifth Ce site, Ce is bonded to eight Se atoms to form distorted CeSe8 hexagonal bipyramids that share corners with eight CeSe8 hexagonal bipyramids, edges with two equivalent CaSe8 hexagonal bipyramids, edges with two CeSe8 hexagonal bipyramids, and faces with eight CeSe8 hexagonal bipyramids. There are four shorter (3.00 Å) and four longer (3.16 Å) Ce–Se bond lengths. In the sixth Ce site, Ce is bonded to eight Se atoms to form distorted CeSe8 hexagonal bipyramids that share a cornercorner with one CaSe8 hexagonal bipyramid, corners with seven CeSe8 hexagonal bipyramids, edges with four CeSe8 hexagonal bipyramids, a faceface with one CaSe8 hexagonal bipyramid, and faces with seven CeSe8 hexagonal bipyramids. There are a spread of Ce–Se bond distances ranging from 2.99–3.17 Å. In the seventh Ce site, Ce is bonded to eight Se atoms to form distorted CeSe8 hexagonal bipyramids that share corners with eight CeSe8 hexagonal bipyramids, edges with four CeSe8 hexagonal bipyramids, faces with two equivalent CaSe8 hexagonal bipyramids, and faces with six CeSe8 hexagonal bipyramids. There are four shorter (3.01 Å) and four longer (3.16 Å) Ce–Se bond lengths. In the eighth Ce site, Ce is bonded to eight Se atoms to form distorted CeSe8 hexagonal bipyramids that share a cornercorner with one CaSe8 hexagonal bipyramid, corners with seven CeSe8 hexagonal bipyramids, an edgeedge with one CaSe8 hexagonal bipyramid, edges with three CeSe8 hexagonal bipyramids, a faceface with one CaSe8 hexagonal bipyramid, and faces with seven CeSe8 hexagonal bipyramids. There are a spread of Ce–Se bond distances ranging from 2.99–3.17 Å. There are twelve inequivalent Se sites. In the first Se site, Se is bonded to one Ca and five Ce atoms to form distorted SeCaCe5 octahedra that share corners with fifteen SeCaCe5 octahedra, edges with six SeCaCe5 octahedra, and faces with five SeCe6 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the second Se site, Se is bonded to one Ca and five Ce atoms to form a mixture of distorted face, edge, and corner-sharing SeCaCe5 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the third Se site, Se is bonded to one Ca and five Ce atoms to form a mixture of distorted face, edge, and corner-sharing SeCaCe5 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the fourth Se site, Se is bonded to six Ce atoms to form a mixture of distorted face, edge, and corner-sharing SeCe6 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the fifth Se site, Se is bonded to six Ce atoms to form a mixture of distorted face, edge, and corner-sharing SeCe6 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the sixth Se site, Se is bonded to one Ca and five Ce atoms to form a mixture of distorted face, edge, and corner-sharing SeCaCe5 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the seventh Se site, Se is bonded to one Ca and five Ce atoms to form a mixture of distorted face, edge, and corner-sharing SeCaCe5 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the eighth Se site, Se is bonded to one Ca and five Ce atoms to form a mixture of distorted face, edge, and corner-sharing SeCaCe5 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the ninth Se site, Se is bonded to one Ca and five Ce atoms to form a mixture of distorted face, edge, and corner-sharing SeCaCe5 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the tenth Se site, Se is bonded to six Ce atoms to form distorted SeCe6 octahedra that share corners with fifteen SeCaCe5 octahedra, edges with six SeCaCe5 octahedra, and faces with five SeCe6 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the eleventh Se site, Se is bonded to one Ca and five Ce atoms to form a mixture of distorted face, edge, and corner-sharing SeCaCe5 octahedra. The corner-sharing octahedra tilt angles range from 17–50°. In the twelfth Se site, Se is bonded to six Ce atoms to form a mixture of distorted face, edge, and corner-sharing SeCe6 octahedra. The corner-sharing octahedra tilt angles range from 17–50°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(BO4)2 by Materials Project

Ca(BO4)2 crystallizes in the triclinic P-1 space group. The structure is two-dimensional and consists of one Ca(BO4)2 sheet oriented in the (0, 1, 1) direction. Ca is bonded in a 7-coordinate geometry to seven O atoms. There are a spread of Ca–O bond distances ranging from 2.38–2.71 Å. There are two inequivalent B sites. In the first B site, B is bonded in a tetrahedral geometry to four O atoms. There are a spread of B–O bond distances ranging from 1.41–1.47 Å. In the second B site, B is bonded in a tetrahedral geometry to four O atoms. There are a spread of B–O bond distances ranging from 1.43–1.46 Å. There are eight inequivalent O sites. In the first O site, O is bonded in a distorted bent 150 degrees geometry to one Ca and one B atom. In the second O site, O is bonded in a distorted single-bond geometry to one Ca and one B atom. In the third O site, O is bonded in a distorted bent 120 degrees geometry to one Ca and one B atom. In the fourth O site, O is bonded in a single-bond geometry to one Ca and one B atom. In the fifth O site, O is bonded in a single-bond geometry to one B atom. In the sixth O site, O is bonded in a distorted bent 150 degrees geometry to one Ca and one B atom. In the seventh O site, O is bonded in a distorted bent 150 degrees geometry to one Ca and one B atom. In the eighth O site, O is bonded in a distorted bent 150 degrees geometry to one Ca and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(NO5)2 by Materials Project

Ca(NO5)2 crystallizes in the monoclinic P2_1/c space group. The structure is one-dimensional and consists of two Ca(NO5)2 ribbons oriented in the (1, 0, 0) direction. Ca is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Ca–O bond distances ranging from 2.39–2.88 Å. There are two inequivalent N sites. In the first N site, N is bonded in a trigonal planar geometry to three O atoms. There are a spread of N–O bond distances ranging from 1.22–1.31 Å. In the second N site, N is bonded in a trigonal planar geometry to three O atoms. There are a spread of N–O bond distances ranging from 1.23–1.29 Å. There are ten inequivalent O sites. In the first O site, O is bonded in a water-like geometry to one Ca and one N atom. In the second O site, O is bonded in a water-like geometry to one Ca and one O atom. The O–O bond length is 1.33 Å. In the third O site, O is bonded in a distorted bent 150 degrees geometry to one Ca and one O atom. The O–O bond length is 1.23 Å. In the fourth O site, O is bonded in a water-like geometry to one Ca and one N atom. In the fifth O site, O is bonded in a bent 120 degrees geometry to one Ca and one O atom. The O–O bond length is 1.28 Å. In the sixth O site, O is bonded in a 3-coordinate geometry to two equivalent Ca and one N atom. In the seventh O site, O is bonded in a bent 120 degrees geometry to two O atoms. In the eighth O site, O is bonded in a single-bond geometry to one N atom. In the ninth O site, O is bonded in a distorted L-shaped geometry to one Ca and one N atom. In the tenth O site, O is bonded in a single-bond geometry to one N atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Role of Eu-Doping in the Electron Transport Behavior in the Zintl Thermoelectric Ca 5-x-y Yb x Eu y Al 2 Sb 6 System

A series of Eu-doped Zintl compounds belonging to theCa 5-x-y Yb x Eu y Al 2 Sb 6 (x = 0, 1.12; 0 ≤ y ≤ 0.63(2)) system have been successfully synthesized by both the arc-melting and the molten Pb-flux methods. All of the five title compounds initially crystallized in the Ca 5 Ga 2 As 6 -type phase (space group Pbam, Z = 2, Pearson code oP26) and maintained their original structure even after the post-heat treatment, unlike the recently reported n-type Zintl analogues in the Ca 5-x-y Yb x RE y Al 2 Sb 6 (RE = Pr, Nd, Sm) systems, which underwent a phase transition from the Ca 5 Ga 2 As 6 -type to the Ca 5 Al 2 Bi 6 -type phase after annealing. This research aimed to understand the origin of the structural preference of the title Ca 5-x-y Yb x Eu y Al 2 Sb 6 system, whether it was affected by the valence electron count or the cationic size. Electrical transport property measurements showed an increase in electrical conductivities and a decrease of Seebeck coefficients for Ca 4.89(1) Eu 0.11 Al 2 Sb 6 , Ca 4.82(1) Eu 0.18 Al 2 Sb 6 , and Ca 4.62(1) Eu 0.38 Al 2 Sb 6 , compared to the parental compound Ca 5 Al 2 Sb 6 . Hole effect measurements proved that these changes should be attributed to the reduced carrier concentration and enhanced carrier mobility. The comprehensive density functional theory calculations including electron density map analysis for the hypothetical model Ca 4.5 Eu 0.5 Al 2 Sb 6 revealed that the polarity between Al and Sb forming the anionic frameworks decreased as the Eu-dopants were introduced, which eventually affected the carrier mobility in the anionic frameworks. Thermal conductivity measurements proved that the Eu-doping successfully lowered the lattice thermal conductivity because of the enhanced atomic disordering. In conclusion, the magnetization measurements for Ca 4.37(2) Eu 0.63 Al 2 Sb 6 showed a typical Curie–Weiss behavior with weak antiferromagnetic nearest-neighbor interactions with θ p = -5.07 K.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(BO4)3 by Materials Project

Ca(BO4)3 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of two Ca(BO4)3 clusters. Ca is bonded in a 6-coordinate geometry to six O atoms. There are a spread of Ca–O bond distances ranging from 2.21–2.99 Å. There are three inequivalent B sites. In the first B site, B is bonded in a trigonal planar geometry to three O atoms. There are a spread of B–O bond distances ranging from 1.35–1.40 Å. In the second B site, B is bonded in a trigonal planar geometry to three O atoms. There are a spread of B–O bond distances ranging from 1.29–1.55 Å. In the third B site, B is bonded in a trigonal planar geometry to three O atoms. There is one shorter (1.36 Å) and two longer (1.38 Å) B–O bond length. There are twelve inequivalent O sites. In the first O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the second O site, O is bonded in a single-bond geometry to one B atom. In the third O site, O is bonded in a linear geometry to one Ca and one O atom. The O–O bond length is 1.33 Å. In the fourth O site, O is bonded in a single-bond geometry to one O atom. The O–O bond length is 1.23 Å. In the fifth O site, O is bonded in a single-bond geometry to one O atom. The O–O bond length is 1.23 Å. In the sixth O site, O is bonded in a bent 120 degrees geometry to one Ca and one B atom. In the seventh O site, O is bonded in a bent 150 degrees geometry to one Ca and one O atom. In the eighth O site, O is bonded in a distorted single-bond geometry to one B and one O atom. In the ninth O site, O is bonded in a bent 120 degrees geometry to one Ca and one B atom. In the tenth O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the eleventh O site, O is bonded in a distorted bent 150 degrees geometry to one Ca and one B atom. In the twelfth O site, O is bonded in a distorted bent 150 degrees geometry to one Ca and one O atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(BO4)3 by Materials Project

Ca(BO4)3 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of two Ca(BO4)3 clusters. Ca is bonded in a 7-coordinate geometry to seven O atoms. There are a spread of Ca–O bond distances ranging from 2.30–2.81 Å. There are three inequivalent B sites. In the first B site, B is bonded in a trigonal planar geometry to three O atoms. All B–O bond lengths are 1.37 Å. In the second B site, B is bonded to four O atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.42–1.61 Å. In the third B site, B is bonded to four O atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.42–1.56 Å. There are twelve inequivalent O sites. In the first O site, O is bonded in a distorted water-like geometry to one Ca and one B atom. In the second O site, O is bonded in a distorted bent 120 degrees geometry to one Ca and one B atom. In the third O site, O is bonded in a single-bond geometry to one B atom. In the fourth O site, O is bonded in a distorted bent 120 degrees geometry to one Ca and one B atom. In the fifth O site, O is bonded in a single-bond geometry to one O atom. The O–O bond length is 1.23 Å. In the sixth O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the seventh O site, O is bonded in a bent 150 degrees geometry to one Ca and one O atom. In the eighth O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the ninth O site, O is bonded in a single-bond geometry to one O atom. The O–O bond length is 1.23 Å. In the tenth O site, O is bonded in a distorted bent 120 degrees geometry to two equivalent Ca and two B atoms. In the eleventh O site, O is bonded in a bent 150 degrees geometry to one Ca and one O atom. In the twelfth O site, O is bonded in a single-bond geometry to one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(BO3)3 by Materials Project

Ca(BO3)3 crystallizes in the triclinic P-1 space group. The structure is one-dimensional and consists of one Ca(BO3)3 ribbon oriented in the (1, 0, 0) direction. Ca is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Ca–O bond distances ranging from 2.43–2.79 Å. There are three inequivalent B sites. In the first B site, B is bonded in a trigonal planar geometry to three O atoms. There are a spread of B–O bond distances ranging from 1.36–1.40 Å. In the second B site, B is bonded to four O atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.42–1.58 Å. In the third B site, B is bonded to four O atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.41–1.54 Å. There are nine inequivalent O sites. In the first O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the second O site, O is bonded in a distorted bent 120 degrees geometry to one Ca and two B atoms. In the third O site, O is bonded in a distorted bent 120 degrees geometry to two equivalent Ca and two B atoms. In the fourth O site, O is bonded in a single-bond geometry to one B atom. In the fifth O site, O is bonded in a distorted bent 120 degrees geometry to one Ca and one B atom. In the sixth O site, O is bonded in a distorted water-like geometry to one Ca and one B atom. In the seventh O site, O is bonded in a distorted single-bond geometry to two equivalent Ca and one B atom. In the eighth O site, O is bonded in a single-bond geometry to one B atom. In the ninth O site, O is bonded in a single-bond geometry to one Ca atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(ReO5)2 by Materials Project

Ca(ReO5)2 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Ca is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Ca–O bond distances ranging from 2.36–2.66 Å. There are two inequivalent Re sites. In the first Re site, Re is bonded in a tetrahedral geometry to four O atoms. There are a spread of Re–O bond distances ranging from 1.73–1.81 Å. In the second Re site, Re is bonded in a tetrahedral geometry to four O atoms. There is one shorter (1.73 Å) and three longer (1.76 Å) Re–O bond length. There are ten inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Re atom. In the second O site, O is bonded in a bent 120 degrees geometry to two equivalent Ca atoms. In the third O site, O is bonded in a distorted bent 150 degrees geometry to one Ca and one Re atom. In the fourth O site, O is bonded in a distorted bent 150 degrees geometry to one Ca and one Re atom. In the fifth O site, O is bonded in a linear geometry to one Ca and one Re atom. In the sixth O site, O is bonded in a linear geometry to one Ca and one Re atom. In the seventh O site, O is bonded in a single-bond geometry to one Re atom. In the eighth O site, O is bonded in a single-bond geometry to one Re atom. In the ninth O site, O is bonded in a single-bond geometry to one Ca atom. In the tenth O site, O is bonded in a bent 150 degrees geometry to one Ca and one Re atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(ClO2)2 by Materials Project

Ca(O2Cl)2 crystallizes in the triclinic P-1 space group. The structure is one-dimensional and consists of one Ca(O2Cl)2 ribbon oriented in the (1, 0, 0) direction. Ca is bonded in a 5-coordinate geometry to five O and one Cl atom. There are a spread of Ca–O bond distances ranging from 2.28–2.62 Å. The Ca–Cl bond length is 3.02 Å. There are four inequivalent O sites. In the first O site, O is bonded in a trigonal planar geometry to two equivalent Ca and one Cl atom. The O–Cl bond length is 1.67 Å. In the second O site, O is bonded in a bent 120 degrees geometry to one Ca and one O atom. The O–O bond length is 1.27 Å. In the third O site, O is bonded in a bent 120 degrees geometry to one Ca and one Cl atom. The O–Cl bond length is 1.63 Å. In the fourth O site, O is bonded in a bent 120 degrees geometry to one Ca and one O atom. There are two inequivalent Cl sites. In the first Cl site, Cl is bonded in a distorted bent 120 degrees geometry to one Ca and one O atom. In the second Cl site, Cl is bonded in a distorted single-bond geometry to one O atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Thermodynamic properties of Ca–Pb electrodes determined by electromotive force measurements

Thermodynamic properties of Ca–Pb alloys are investigated by electromotive force (emf) measurements to determine equilibrium cell potentials and phase properties for their application in energy storage systems such as liquid metal batteries. Using the electrochemical cell Ca(s) | CaF 2 (s) | Ca(in Pb) at 700–1060 K, cell emf is measured for thirteen Ca–Pb alloys at mole fractions, x Ca = 0.06–0.80. At 873 K, the equilibrium potentials of liquid Ca–Pb alloys are 0.57–0.62 V versus Ca and the activity values are as low as a Ca = 6.2 × 10 -8 at x Ca = 0.06. In addition, the emf values as a function of temperature provide partial molar quantities (entropy and enthalpy) as well as phase transitions which are corroborated by determining transition temperatures and phase constituents using differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD). This study establishes the fundamental data necessary for the design of Pb-containing liquid metal electrodes through the integration of electrochemical, thermal, and structural properties of Ca–Pb electrodes.

25 ENERGY STORAGE↗
DOE OSTI2025

The role of Ca-bridged organic matter in an alkaline soil, as revealed by multimodal chemical imaging

Mineral–organic matter (OM) studies have predominantly focused on acidic soils that are abundant in iron (Fe) oxides and aluminum (Al) oxides. We have probed mineral–OM interactions in an alkaline or calcareous soil of the Aridisols class. Unlike the role of Fe and Al, the role of Ca-minerals (particularly calcite), which are ubiquitous in alkaline soils, in OM sequestration is not well understood. Multiple recent model studies with aqueous Ca2+ or synthetic calcite and a suite of OM compounds have shown Ca-OM assemblages to be spatially correlated with calcite at the microscale. To study the chemical state of both Ca and Fe and their competing role in soil organic matter (SOM) stabilization, we performed laboratory characterization using x-ray diffraction, Mössbauer spectroscopy, x-ray photoelectron spectroscopy, scanning electron microscopy, and scanning transmission electron microscopy, alongside synchrotron-based microscale chemical imaging using scanning transmission x-ray microscopy combined with near-edge x-ray absorption fine structure. Ca mineral–organic associations were found to be ubiquitous in this system and are likely critical for understanding SOM stabilization/degradation in alkaline soils. From our findings on mineralogy, speciation, and the nature of Ca-OM bridging, we identified differences in C and Ca chemistry based on the relative location of OM to Ca minerals. The OM near the calcite crystal was enriched in lipid and protein moieties, Ca-OM next to Fe minerals displayed a strong contribution from aromatic compounds, while on the surface of microbes, the carbonate was believed to be of microbial in origin, as also suggested by preliminary works reporting on the formation of amorphous calcite or nano-calcite. In Ca-OM admixed with carbonate, it was difficult to distinguish Ca-associated OM from amorphous calcite or nano-calcite.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Coupling of Ca 2+ and voltage activation in BK channels through the αB helix/voltage sensor interface

Large-conductance Ca 2+ and voltage-activated K + (BK) channels control membrane excitability in many cell types. BK channels are tetrameric. Each subunit is composed of a voltage sensor domain (VSD), a central pore-gate domain, and a large cytoplasmic domain (CTD) that contains the Ca 2+ sensors. While it is known that BK channels are activated by voltage and Ca 2+ , and that voltage and Ca 2+ activations interact, less is known about the mechanisms involved. In this work we explore these mechanisms by examining the gating contribution of an interface formed between the VSDs and the αB helices located at the top of the CTDs. Proline mutations in the αB helix greatly decreased voltage activation while having negligible effects on gating currents. Analysis with the Horrigan, Cui, and Aldrich model indicated a decreased coupling between voltage sensors and pore gate. Proline mutations decreased Ca 2+ activation for both Ca 2+ bowl and RCK1 Ca 2+ sites, suggesting that both high-affinity Ca 2+ sites transduce their effect, at least in part, through the αB helix. Mg 2+ activation also decreased. The crystal structure of the CTD with proline mutation L390P showed a flattening of the first helical turn in the αB helix compared to wild type, without other notable differences in the CTD, indicating that structural changes from the mutation were confined to the αB helix. These findings indicate that an intact αB helix/VSD interface is required for effective coupling of Ca 2+ binding and voltage depolarization to pore opening and that shared Ca 2+ and voltage transduction pathways involving the αB helix may be involved.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

The Timing of Potential Last Nucleosynthetic Injections into the Protosolar Molecular Cloud Inferred from 41 Ca– 26 Al Systematics of Bulk CAIs

Short-lived radionuclides (SLRs) provide important information about the chronology of the early solar system. Among them, 41 Ca, due to its decay to 41 K with a half-life of only 0.1 Ma, is particularly valuable in constraining the timescales and origins of both SLRs and the formation of the oldest solar system materials, the Ca–Al-rich inclusions (CAIs). The initial abundance of 41Ca in the solar system, expressed as the ( 41 Ca/ 40 Ca)I ratio, is the key to unveiling the origin of this nuclide. Here, we report a new solar system ( 41 Ca/ 40 Ca)I ratio of 2.0 × 10 −8 derived from the K isotope compositions of two CAIs. This new ratio is about four times higher than the previous value inferred from a mineral isochron. Such a high ( 41 Ca/ 40 Ca)I ratio in the CAIs exceeds that expected for the protosolar molecular cloud by ∼1000×, implying very late injection of the 41 Ca (and possibly other SLRs) into the protosolar molecular cloud. The correlated enrichments of 41 Ca and 26 Al in the bulk CAI samples hint at a common stellar origin of both SLRs. The injection time estimated from our new data depends on the stellar source—it ranges from 0.6 Ma for a Wolf–Rayet wind to 1.0 Ma for a TP-AGB star ejecta.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2000

Ca(2+) regulates fluid shear-induced cytoskeletal reorganization and gene expression in osteoblasts

Osteoblasts subjected to fluid shear increase the expression of the early response gene, c-fos, and the inducible isoform of cyclooxygenase, COX-2, two proteins linked to the anabolic response of bone to mechanical stimulation, in vivo. These increases in gene expression are dependent on shear-induced actin stress fiber formation. Here, we demonstrate that MC3T3-E1 osteoblast-like cells respond to shear with a rapid increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) that we postulate is important to subsequent cellular responses to shear. To test this hypothesis, MC3T3-E1 cells were grown on glass slides coated with fibronectin and subjected to laminar fluid flow (12 dyn/cm(2)). Before application of shear, cells were treated with two Ca(2+) channel inhibitors or various blockers of intracellular Ca(2+) release for 0. 5-1 h. Although gadolinium, a mechanosensitive channel blocker, significantly reduced the [Ca(2+)](i) response, neither gadolinium nor nifedipine, an L-type channel Ca(2+) channel blocker, were able to block shear-induced stress fiber formation and increase in c-fos and COX-2 in MC3T3-E1 cells. However, 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM, an intracellular Ca(2+) chelator, or thapsigargin, which empties intracellular Ca(2+) stores, completely inhibited stress fiber formation and c-fos/COX-2 production in sheared osteoblasts. Neomycin or U-73122 inhibition of phospholipase C, which mediates D-myo-inositol 1,4,5-trisphosphate (IP(3))-induced intracellular Ca(2+) release, also completely suppressed actin reorganization and c-fos/COX-2 production. Pretreatment of MC3T3-E1 cells with U-73343, the inactive isoform of U-73122, did not inhibit these shear-induced responses. These results suggest that IP(3)-mediated intracellular Ca(2+) release is required for modulating flow-induced responses in MC3T3-E1 cells.

Non-NASA Center↗