Search results for "CALCIUM"
showing 10 items of 1740 documents
CaSO4 and its pressure-induced phase transitions. A density functional theory study
2012
Theoretical investigations concerning possible calcium sulfate, CaSO(4), high-pressure polymorphs have been carried out. Total-energy calculations and geometry optimizations have been performed by using density functional theory at the B3LYP level for all crystal structures considered. The following sequence of pressure-driven structural transitions has been found: anhydrite, Cmcm (in parentheses the transition pressure) → monazite-type, P2(1)/n (5 GPa) → barite-type, Pnma (8 GPa), and scheelite-type, I4(1)/a (8 GPa). The equation of state of the different polymorphs is determined, while their corresponding vibrational properties have been calculated and compared with previous theoretical r…
Quasi-hydrostatic X-ray powder diffraction study of the low- and high-pressure phases of CaWO4 up to 28 GPa
2014
We have studied CaWO4 under compression using Ne as pressure-transmitting medium at room temperature by means of synchrotron X-ray powder diffraction. We have found that CaWO4 beyond 8.8 GPa transforms from its low-pressure tetragonal structure (scheelite) into a monoclinic structure (fergusonite). The high-pressure phase remains stable up to 28 GPa and the low-pressure phase is totally recovered after full decompression. The pressure dependence of the unit-cell parameters, as well as the pressure volume equation of state, has been determined for both phases. Compared with previous studies, we found in our quasi-hydrostatic experiments a different behavior for the unit-cell parameters of th…
Negative pressures in CaWO4 nanocrystals
2009
Tetragonal scheelite-type CaWO4 nanocrystals recently prepared by a hydrothermal method show an enhancement of its structural symmetry with the decrease in nanocrystal size. The analysis of the volume dependence of the structural parameters in CaWO4 nanocrystals with the help of ab initio total-energy calculations shows that the enhancement of the symmetry in the scheelite-type nanocrystals is a consequence of the negative pressure exerted on the nanocrystals; i.e., the nanocrystals are under tension. Besides, the behavior of the structural parameters in CaWO4 nanocrystals for sizes below 10 nm suggests an onset of a scheelite-to-zircon phase transformation in good agreement with the predic…
Calcium, iron and zinc uptakes by Caco-2 cells from white beans and effect of cooking
2006
White beans (Phaseolus vulgaris L.) have an interesting content of essential elements, calcium, iron and zinc, but they content also phytates, oxalates, proteins, polyyphenols and complex polysaccharides that are known to interact with minerals and to affect their bioavailability. The bioavailability of calcium, iron and zinc from raw and cooked white beans was estimated using their uptake by Caco-2 cells as the criteria. Previously, the mineral fraction (soluble or dialysable) to be added to the Caco-2 cell monolayer was selected. The results obtained show that cooking increases the Caco-2 cells' uptake percentages (calcium, 18.8 versus 3.6; iron, 33.7 versus 1.7; and zinc, 17.2 versus 2.1…
Rho-mediated activation of PI(4)P5K and lipid second messengers is necessary for promotion of angiogenesis by Semaphorin 4D
2011
Phosphatidylinositol 4-phosphate 5-kinase (PI(4)P5K) is a type I lipid kinase that generates the lipid second messenger phospholipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and functions downstream of RhoA in actin organization. It is known to play an essential role in neurite remodeling, yielding a phenotype identical to that seen in cells treated with Semaphorin 4D (Sema4D), a protein that regulates proliferation, adhesion and migration in many different cell types. Plexin-B1, the receptor for Sema4D, activates RhoA in order to generate a pro-angiogenic signal in endothelial cells. Therefore, we looked in human umbilical vein endothelial cells (HUVEC) to determine if Plexin-B1 e…
Modulation of neuronal phospholipase D activity under depolarizing conditions
1999
Neuronal phospholipase D (PLD) activity was hypothesized to be involved in vesicle trafficking and endocytosis and, possibly, transmitter release. We here report that prolonged depolarization of rat hippocampal slices by potassium chloride (KCl) or 4-aminopyridine inhibited PLD activity. Similarly, PLD activity in rat cortical synaptosomes was significantly inhibited by depolarizing agents including veratridine and ouabain. Inhibition of calcium/calmodulin kinase II (CaMKII) which positively modulates synaptosomal PLD activity [Sarri et al. (1998) FEBS Lett. 440, 287-290] by KN-62 caused a further reduction of PLD activity in depolarized synaptosomes. Depolarization-induced inhibition of PL…
Control of cellular phosphatidylinositol 4,5-bisphosphate levels by adhesion signals and Rho GTPases in NIH 3T3 fibroblasts
2000
The involvement of small GTPases of the Rho family in the control of phosphoinositide metabolism by adhesion signals was examined in NIH 3T3 fibroblasts. Abrogation of adhesion signals by detachment of cells from their substratum resulted in a time-dependent decrease in the cellular level of PtdIns(4,5)P2 by approximately 50%. This effect could be mimicked by treatment of adherent cells with Clostridium difficile toxin B and toxin B-1470, which inhibit specific subsets of Rho and Ras GTPases. Detachment of cells that had been pretreated with the clostridial toxins did not cause a further reduction in PtdIns(4,5)P2 levels, suggesting that the target GTPases are integrated into the control of…
Distribution of rare earth elements in marine sediments from the Strait of Sicily (western Mediterranean Sea): Evidence of phosphogypsum waste contam…
2010
Concentrations of rare earth elements (REE), Y, Th and Sc were recently determined in marine sediments collected using a box corer along two onshore–offshore transects located in the Strait of Sicily (Mediterranean Sea). The REE + Y were enriched in offshore fine-grained sediments where clay minerals are abundant, whereas the REE + Y contents were lower in onshore coarse-grained sediments with high carbonate fractions. Considering this distribution trend, the onshore sediments in front of the southwestern Sicilian coast represent an anomaly with high REE + Y concentrations (mean value 163.4 lg g 1) associated to high Th concentrations (mean value 7.9 lg g 1). Plot of shale-normalized REE + …
Effects and future trends of casein phosphopeptides on zinc bioavailability
2007
This review focuses on studies of the effects of CPPs on zinc bioavailability. It evaluates the main differences in studies performed in the last two decades, such as methodology used to measure zinc, food matrix, CPP preparation, CPP dose, CPP:Zn molar ratio and presence and concentration of zinc absorption inhibitors, such as phytate, iron and calcium. The future trends of CPPs as functional ingredients in zinc-enriched or zinc-containing foods are also discussed.
Effects of different infant formula components on calcium dialysability
1999
The in vitro methods proposed for estimating calcium bioavailability can be useful in studying the effect of dietetic factors. The aim of our work was to study the possible influence of different infant formula components – calcium, phosphorus, lactose, citric acid, ascorbic acid and proteins – on calcium bioavailability, considering dialysability to be an estimate of bioavailability. The 1981 method of Miller et al. with slight modifications (concerted action no 10 – FLAIR project) was applied to 18 commercial infant formulas of six different types: adapted, follow-up, preterm, hydrolysates, lactose-free and soy-based. Significant positive linear correlations between the amount of calcium …