Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Barium Compounds”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,027 records · Page 57Linked to original sources
PubMed2004

The structure of Ba@C74.

The title compound has been produced by using the radio frequency (RF) method. Barium and carbon were evaporated simultaneously under dynamic flow of helium at different temperatures. About 0.5 mg of pure Ba@C(74) was isolated via a three-step high-pressure liquid chromatography separation. For the first time, the structure of a monometallofullerene has been analyzed by means of single-crystal synchrotron diffraction on microcrystals of Ba@C(74).Co(OEP).2C(6)H(6) (Co(II)(OEP): cobalt(II) octaethylporphyrin) at 100 K. The monometallofullerene exhibits a high degree of localization of the endohedral metal ion, with just two split positions for Ba and two orientations of the C(74)-cage. The barium atom is localized inside the C(74)-cage and displaced off-center, toward the Co(OEP) molecule (d approximately 127 pm). The shortest Ba-C distance is 265 pm. The Co(OEP) molecules form dimers in which the coordination of the cobalt is (4 + 1). Due to the all-syn conformation of the ethyl groups, each Co(OEP) molecule of the dimer coordinates one C(74)-fullerene. The units (Ba@C(74))[Co(OEP)](2)(Ba@C(74)) are arranged in a distorted primitive hexagonal packing. The free space between these complex units is filled by benzene molecules of crystallization. The Ba L(III) XANES spectrum of a thin film sample of Ba@C(74) exhibits a pronounced double maximum structure at about E = 5275 eV. The comparison of the shape resonances of the experimental data with simulated XANES spectra, based on different exo- and endohedral structure models, confirm that the Ba atom is located inside the C(74)-cage (D(3)(h)()) in an off-center position. The Ba atom is shifted by about 130-150 pm from the geometric center of the C(74)-cage. This is in good agreement with quantum chemical results. Thus, despite the disorder still present, a consistent and conclusive structure model for the title compound has been derived by employing a combination of X-ray diffraction, XANES spectroscopy, and quantum chemical calculations.

Journal Article↗
PubMed1995

Human alpha 7 nicotinic acetylcholine receptor responses to novel ligands.

Responses of the human alpha 7 nicotinic acetylcholine receptor (nAChR) in Xenopus laevis oocytes were quantified using two-electrode voltage clamp in the presence of barium (10 mM) to block secondary activation of Ca(2+)-dependent chloride currents. The effect of (S)-3-methyl-5-(1-methyl-2-pyrrolidinyl) isoxazole (ABT-418) and (2,4)-dimethoxybenzylidene anabaseine (GTS-21), two potential compounds for the treatment of Alzheimer's Disease, and of the natural product (+/-)epibatidine were compared to (-)nicotine. (+/-)Epibatidine acted as an agonist and was 64-fold more potent than (-) nicotine (EC50s = 1.30 +/- 0.11 microM and 83 +/- 10 microM, respectively). ABT-418 also was an agonist, 3-fold less potent and 75% as efficacious as (-)nicotine (EC50 = 264 +/- 34 microM). GTS-21, in contrast, inhibited the response to (-)nicotine at concentrations < or = 10 microM and itself elicited only a small response at higher concentrations (12% of the (-)nicotine response at 1 mM). Reversible blockade by methyllycaconitine (10 nM) corroborated the responses as due to activation of alpha 7 nAChR. This represents the first characterization of human alpha 7 nAChR responses to these novel nicotinic agonists.

Anti-Anxiety Agents↗
PubMed2005

Crystal structure and magnetic properties of a pseudo-cubic close-packed array of oxalate linked {FeII6(mu3-OH)6}6+ clusters.

The ionic hexanuclear cluster aggregate [FeII6(mu3-OH)6]6+ has been synthesised using hydrothermal conditions starting from ferrous oxalate in the presence of barium and bromide or iodide ions. A single crystal X-ray structure on the compound Ba4[FeII6(mu3-OH)6(C2O4)6]Br2.6H2O shows that the [FeII6(mu3-OH)6]6+ units are held together by bridging oxalates in a pseudo-cubic close-packed array. The barium ions in conjunction with oxalate groups provide a barrel-shaped cage between the FeII6 aggregates containing the bromide counterions and lattice waters and corresponding to an 'octahedral hole' in the pseudo-cubic close-packed structure. A magnetic susceptibility study shows that the FeII centres are antiferromagnetically coupled. Below 10 K the system displays a long range antiferromagnetic ordering mediated by the oxalate bridges and a molecular-based description of the magnetism is no longer valid.

Journal Article↗
PubMed1979

The effect of alkaline earth cations on the release of histamine from rat peritoneal mast cells treated with compound 48/80 and peptide 401.

1 Extracellular calcium ions have a dual effect on the release of histamine from rat peritoneal mast cells treated with compound 48/80 and peptide 401. The release is either potentiated or inhibited according to the relative concentrations of ion and inducer.2 Strontium similarly potentiates the release produced by optimal concentrations of inducer but higher concentrations are required than in the case of calcium. Strontium is markedly less inhibitory than calcium.3 Mast cells may be depleted of intracellular calcium by incubation for short periods with the chelating agent, ethylenediamine tetraacetic acid (EDTA). They thereby become unresponsive to compound 48/80 and peptide 401 unless calcium is reintroduced into the incubation medium. Strontium and barium, but not magnesium, will substitute for calcium in this system. Barium additionally produces a marked release of histamine even in the absence of inducer. Pretreatment with the ionophore A23187 similarly inhibits the subsequent response to peptide 401 in divalent cation-free medium. This inhibition is reversed on the reintroduction of calcium.4 Compound 48/80 and peptide 401 release histamine from mast cells incubated in isotonic sucrose in the complete absence of added metal ions. However, the corrected release under these conditions is potentiated by both mono and divalent cations.5 On the basis of these results, the possible mechanism of action of the basic releasing agents and their usefulness as models for studying histamine secretion is discussed.

Animals↗
PubMed2000

The first noncoordinated phosphonium diylide, [Me2P(C13H8)2]-, and its ylidic and cationic counterparts: synthesis, structural characterization, and interaction with the heavy group 2 metals.

Treatment of potassium or lithium fluorenide with MePCl2 generates the organophosphine MeP(C13H9)2, which on reaction with methyl iodide produces the phosphonium species [Me2P(C13H9)2]I in 74% yield. In the solid state, H...I contacts of < 3.3 A help generate a layered structure in which the fluorenyl rings are nearly parallel. On subsequent reaction of [Me2P(C13H9)2]I with either KH or K[N(SiMe3)2], the corresponding neutral phosphoylide, Me2P(C13H9)(C13H8), forms in 67% yield and was structurally characterized. The phosphonium iodide [Me2P(C13H9)2]I was allowed to react with Ae[N(SiMe3)2]2 (Ae = Ca, Ba), and the product from the reaction with the calcium complex was structurally identified as the salt [CaI(thf)5][Me2P(C13H8)2]. The anion, which is outside the coordination sphere of the calcium, represents the first structurally authenticated example of a free phosphonium diylide. The P-C(ylidic) bond length of 1.748(4) A reflects some partial multiple bond character. 1H and 31P NMR spectra suggest that the barium analogue is similar. Density functional theory calculations were performed on representative phosphonium diylides as an aid to interpreting the bonding in this class of compounds. Despite the strong electrostatic attraction that usually drives metal-ligand binding in highly ionic systems, calcium and barium prefer to coordinate to a single iodide ion and several neutral oxygen donors rather than to the charged diylide.

Journal Article↗
PubMed1979

Simple metallic compounds as pulp-capping agents.

A study is described in which six metallic compounds identified in a previous pilot experiment were tested as pulp-capping agents using the exposed rat molar. Barium sulfate, calcium carbonate, cupric oxide, ferric oxide, and heavy magnesium oxide gave poor results. Stannic oxide gave more favorable results and is being studied further.

Animals↗
PubMed1985

Roles of cyclic AMP and Ca in epithelial ion transport across corneal epithelium: a review.

The messenger roles of cyclic AMP and the calcium ion in stimulus-secretion coupling are considered in the frog and bovine corneal epithelium, respectively. In the frog cornea, epinephrine stimulates net C1 transport by increasing cyclic AMP content. This stimulation is associated with a larger apical membrane C1 conductance and basolateral membrane ionic conductance. The response of the apical membrane conductance is thought to result from an increase in cyclic AMP content whereas the basolateral membrane ionic conductance increase is unrelated based on measurements of the effects of the calcium channel antagonist, diltiazem, and the beta agonist, isoproterenol, on the electrical parameters and cyclic AMP content. The basolateral membrane is essentially K permselective since the K channel blocker, Ba, depolarized the intracellular potential difference and increased the basolateral membrane resistance. Diltiazem had even larger effects on these parameters suggesting that this compound is a more effective inhibitor of K channel activity than barium. In broken cell preparations of bovine corneal epithelium, a high affinity form of Ca + Mg activated ATPase is present (Km = .06 microM for Ca) and is essentially of plasma membrane origin. This ATPase activation is at a Ca activity similar to the expected intracellular value and suggests that this activity is the enzymatic basis for net Ca transport.

Animals↗
PubMed2001

Calcium-sensitive potassium channel inhibitors antagonize genistein- and daidzein-induced arterial relaxation in vitro.

Estradiol-17beta relaxes rabbit coronary artery rings via large conductance Ca2+-activated K+-channels (K(Ca)). Genistein and daidzein are plant-derived estrogen-like compounds. The aim of the present study was to investigate whether potassium channels participate in the genistein- and daidzein-induced arterial relaxation like they do in the case of estradiol-17beta. Endothelium-denuded superior mesenteric arterial rings from non-pregnant Wistar female rats were used. At a concentration of 10 microM, estradiol-17beta, genistein and daidzein relaxed noradrenaline precontracted arterial rings, (58 +/- 4%, 45 +/- 5% and 31 +/- 3%, respectively; (n=6-8)). Genistein- and daidzein-induced relaxations were inhibited both by iberiotoxin (1-10 nM) and charybdotoxin (30 nM), the antagonists of large conductance Ca2+-activated K+-channels (K(Ca)). Estradiol-17beta-induced relaxation was reduced by iberiotoxin (30 nM). Estradiol-17beta- and daidzein-induced relaxations were also decreased by apamin (0.1-0.3 microM), an antagonist of small conductance Ca2+-activated K+-channels. The antagonists of voltage-dependent K+-channels (K(V)) (4-aminopyridine), ATP-sensitive K+-channels (K(ATP)) (glibenclamide), or inward rectifier K+-channels (KIR) (barium) had no effect on the relaxation responses of any of the compounds studied. Estrogen receptor antagonist tamoxifen did not inhibit the relaxations. In conclusion, in the noradrenaline precontracted rat mesenteric arteries, the relaxations caused by estradiol-17beta, genistein and daidzein were antagonized by large and small conductance K(Ca)-channel inhibitors, suggesting the role of these channels as one of the relaxation mechanisms.

Animals↗
PubMed2001

Superconductivity in the filled cage compounds Ba6Ge25 and Ba4Na2Ge25.

The clathrate compound Ba 6Ge25 and its relatives consist of a rigid germanium skeleton, into which barium or other metal atoms are coordinated. These guest atoms can "rattle" freely at high temperatures, but in Ba 6Ge25 some of them lock randomly into split positions below T(S) approximately 200 K. The resulting bad metal undergoes a BCS-like superconducting transition at T(c) approximately 0.24 K. T(c) increases more than 16-fold, as T(S) is suppressed by hydrostatic pressure p, but changes only slightly with p from T(c) approximately 0.84 K in the undistorted sister compound Ba 4Na2Ge25. The large enhancement of T(c) in Ba 6Ge25 may be attributed mainly to the pressure tuning of strong disorder caused by the random displacement of Ba atoms at T(S).

Journal Article↗
PubMed1985

Mechanism of rhythmic contractions induced by uranyl ion in the ileal longitudinal muscle of guinea-pig.

The uranyl ion (UO2(2+)) produces rhythmic contractions of the longitudinal muscle of the ileum, similar to those induced by repetitive transmural stimulation. Hexamethonium inhibited the action of UO2(2+), indicating a preganglionic site of action of UO2(2+) and interneurons possibly being involved in the ACh-releasing effect of UO2(2+). In addition, the action of UO2(2+) was enhanced by physostigmine but antagonized by atropine, ATP, adrenaline and morphine suggesting multiple sites of action of UO2(2+). The effects of Ba2+ were studied simultaneously in order to compare them with those of UO2(2+). Atropine and hexamethonium had no effect on the rhythmic contractions with Ba2+ but physostigmine enhanced contractions induced by low concentration of Ba2+ indicating that Ba2+ induces contractions mainly by acting on the smooth muscle and releases ACh from the nerve to a lesser extent.

Acetylcholine↗
PubMed1989

Inhibition of the liver cell receptor-activated Ca2+ inflow system by metal ion inhibitors of voltage-operated Ca2+ channels but not by other inhibitors of Ca2+ inflow.

The properties of the receptor-activated Ca2+ inflow system in the liver cell plasma membrane were compared with those of voltage-operated Ca2+ channels and receptor-operated Ca2+ channels present in other cell types by testing the susceptibility of the Ca2+ inflow system to inhibition by other metal ions and known inhibitors of Ca2+ movement across membranes. Co2+ inhibited Ca2+ inflow through the receptor-activated Ca2+ inflow system, as assessed by measurement of (a) the activation by extracellular Ca2+ (Cao2+) of glycogen phosphorylase in the presence of vasopressin and (b) 45Ca2+ exchange in the presence of the hormone. The concentration of Co2+ which gave half-maximal inhibition was 280 microM. The inhibition by Co2+ was reversed by high Cao2+. Co2+ did not inhibit basal Ca2+ inflow as measured by 45Ca2+ exchange in the absence of vasopressin. Zn2+, Cd2+, Ni2+ and Mn2+ each inhibited Ca2+ inflow through the receptor-activated Ca2+ inflow system. The concentrations of these ions which gave half-maximal inhibition were 10, 50, 220 and 400 microM, respectively. Little inhibition of receptor-activated Ca2+ inflow was observed in the presence of Sr2+ or Ba2+. However, substantial amounts of 90Sr2+ were taken up by hepatocytes. Rates of 90Sr2+ uptake increased from 0.5-8 nmol per min per mg wet wt. when the extracellular concentration of Sr2+ was varied from 0.25 to 2.5 mM. Sr2+ uptake was inhibited 50% by Cao2+ with half-maximal inhibition at 100 microM Cao2+, but was not inhibited by verapamil and was not stimulated by vasopressin. The movement of Ca2+ through the receptor-activated Ca2+ inflow system was not inhibited by high concentrations of each of a number of inhibitors of voltage-operated and receptor-operated Ca2+ channels and intracellular Ca2+ movement. It is concluded that while the susceptibility to inhibition by metal ions of the receptor-activated Ca2+ inflow system in the liver cell plasma membrane is similar to that of voltage-operated Ca2+ channels, there are significant differences between the liver cell receptor-activated Ca2+ inflow system and both voltage-operated Ca2+ channels and some other receptor-operated Ca2+ channels with respect to inhibition by organic compounds.

Animals↗