Noninvasive 31P NMR probes of free Mg2+, MgATP, and MgADP in intact Ehrlich ascites tumor cells

³¹P NMR spectra of Ehrlich ascites tumor cells, suspended in a physiological medium, show well-defined αP, βP, and γP resonances of intracellular ATP. A comparison of the separation of 360 ± 1 Hz between the resonances of αP and βP in intact cells with the corresponding separations of 349 ± 0.5 and 438 ± 1 Hz in noncellular MgATP and ATP standards, measured at 10°C and 40.5 MHz NMR frequency, reveals that 88% of the total intracellular ATP (3.3 mM) is complexed to Mg²⁺. The corresponding value for intracellular free Mg²⁺ is 0.44 μmol/ml out of a total Mg²⁺ content of 8.5 μmol/ml cell water. A similar value of free Mg²⁺ is obtained from a comparison of the separation of 560 ± 1 Hz between the βP and γP resonances of intracellular ATP with the corresponding values of 552 ± 0.5 and 621 ± 1 Hz in noncellular MgATP and ATP standards. The fraction of total cellular ATP complexed to Mg²⁺ decreased to 80% in tumor cells incubated in a medium containing adenosine, glucose, and P_i without Mg²⁺, the corresponding level of intracellular free Mg²⁺ being significantly lower (0.24 mM) than that in the unincubated cells. With Mg²⁺ present in the incubation medium, MgATP and total Mg²⁺ levels increased by ≈2.5 mM, whereas with no added Mg²⁺, the MgATP increased 1.6 mM apparently at the expense of other Mg²⁺-complexed constituents since total Mg²⁺ remained essentially unchanged. At the measured levels of free Mg²⁺, intracellular ADP will be only 35-50% complexed to Mg²⁺. A knowledge of the state of Mg²⁺ complexation of ATP and ADP in intact Ehrlich tumor cells allows an accurate estimation of the phosphorylation potential and the extent of deviation of the mass action ratio ([MgATP][AMP]_f/[MgADP][ADP]_f) in cells with high phosphorylation potential from the Mg²⁺-dependent equilibrium value of the adenylate kinase reaction. The significance of the free Mg²⁺ value measured by the noninvasive NMR method in relation to the existence of Mg²⁺ complexation and compartmentation in tumor cells is discussed.     

Statistical Optimisation of Chemical Stability of Hybrid Microwave-Sintered Alumina Ceramics in Nitric Acid

The goal of this research is the statistical optimisation of the chemical stability of hybrid microwave-sintered alumina ceramics in nitric acid. The chemical stability of ceramic materials in corrosive media depends on many parameters, such as the chemical and phase composition of the ceramics, the properties of the aggressive medium (concentration, temperature, and pressure), and the exposure time. Therefore, the chemical stability of alumina ceramics in different aqueous nitric acid solution concentrations (0.50 mol dm⁻³, 1.25 mol dm⁻³, and 2.00 mol dm⁻³), different exposure times (up to 10 days), as well as different temperatures (25, 40, and 55 °C), was investigated, modelled, and optimised. The chemical stability of high purity alumina ceramics (99.8345 wt.% of Al₂O₃) was determined by measuring the amount of eluted ions (Al³⁺, Ca²⁺, Fe³⁺, Mg²⁺, Na⁺, and Si⁴⁺) obtained by inductively coupled plasma atomic emission spectrometry. The changes in the density of alumina ceramics during the chemical stability monitoring were also determined. The Box–Behnken approach was employed to reach the optimum conditions for obtaining the highest possible chemical stability of alumina at a given temperature range, exposure time, and molar concentration of nitric acid. It was found that an increase in exposure time, temperature, and nitric acid concentration led to an increase in the elution of ions from hybrid microwave-sintered alumina. Higher amounts of eluted ions, Al³⁺ (14.805 µg cm⁻²), Ca²⁺ (7.079 µg cm⁻²), Fe³⁺ (0.361 µg cm⁻²), Mg²⁺ (3.654 µg cm⁻²), and Na⁺ ions (13.261 µg cm⁻²), were obtained at 55 °C in the 2 mol dm^{− 3} nitric acid. The amount of eluted Si⁴⁺ ions is below the detection limit of inductively coupled plasma atomic emission spectrometry. The change in the alumina ceramic density during the corrosion test was negligible.     

Intracellular magnesium content in hypertension

A method to determine total Mg²⁺ content in lymphocytes was developed, offering advantages for routine measurements as compared to fluorescence methods. Intracellular Mg²⁺ measurements were performed in lymphocytes of 16 normotensive, 20 essential hypertensive, 15 renal hypertensive patients (patients with a chronic glomerulonephritis), and 10 normotensive, renal insufficient patients. Mg²⁺ content was referred to lymphocytic protein, which was determined according to Bradford's method. Mg²⁺ measurements were performed by atomic absorption spectroscopy using an electrothermal atomic absorption spectroscope. The results show that in patients with essential hypertension, intralymphocytic Mg²⁺ content is significantly lower (0.07±0.04 mmol/g lymphocytic protein, mean ± SD) compared with controls (0.11±0.03 mmol/g lymphocytic protein, mean ± SD,p<0.05). In renal hypertensive patients, intracellular Mg²⁺ concentrations are significantly increased compared with normotensive or essential hypertensive patients (0.35±0.10 mmol/g lymphocytic protein, mean ± SD,p<0.05). In the normotensive renal insufficient group, intracellular Mg²⁺ concentrations were measured (0.37±0.05 mmol/g lymphocytic protein, mean ± SD being significantly increased compared to the normotensive or hypertensive group (p<0.05). There was no significant difference between the renal insufficient group with and without arterial hypertension. In plasma Mg²⁺ concentrations there was no significant difference in the four groups of patients. Furthermore, this method also seems suitable for routine measurements of cellular Mg²⁺ concentrations in even larger groups of patients.     

The Gd2−xMgxZr2O7−x/2 Solid Solution: Ionic Conductivity and Chemical Stability in the Melt of LiCl-Li2O

Materials with pyrochlore structure A₂B₂O₇ have attracted considerable attention owing to their various applications as catalysts, sensors, electrolytes, electrodes, and magnets due to the unique crystal structure and thermal stability. At the same time, the possibility of using such materials for electrochemical applications in salt melts has not been studied. This paper presents the new results of obtaining high-density Mg²⁺-doped ceramics based on Gd₂Zr₂O₇ with pyrochlore structure and comprehensive investigation of the electrical properties and chemical stability in a lithium chloride melt with additives of various concentrations of lithium oxide, performed for the first time. The solid solution of Gd_2−xMg_xZr₂O_7−x/2 (0 ≤ x ≤ 0.10) with the pyrochlore structure was obtained by mechanically milling stoichiometric mixtures of the corresponding oxides, followed by annealing at 1500 °C. The lattice parameter changed non-linearly as a result of different mechanisms of Mg²⁺ incorporation into the Gd₂Zr₂O₇ structure. At low dopant concentrations (x ≤ 0.03) some interstitial positions can be substituted by Mg²⁺, with further increasing Mg²⁺-content, the decrease in the lattice parameter occurred due to the substitution of host-ion sites with smaller dopant-ion. High-density ceramics 99% was prepared at T = 1500 °C. According to the results of the measurements of electrical conductivity as a function of oxygen partial pressure, all investigated samples were characterized by the dominant ionic type of conductivity over a wide range of pO₂ (1 × 10^–18 ≤ pO₂ ≤ 0.21 atm) and T < 800 °C. The sample with the composition of x = 0.03 had the highest oxygen-ion conductivity (10⁻³ S·cm⁻¹ at 600 °C). The investigation of chemical stability of ceramics in the melt of LiCl with 2.5 mas.% Li₂O showed that the sample did not react with the melt during the exposed time of one week at the temperature of 650 °C. This result makes it possible to use these materials as oxygen activity sensors in halide melts.     

Effect of Sulfate Ions on Galvanized Post-Tensioned Steel Corrosion in Alkaline Solutions and the Interaction with Other Ions

Zinc protection of galvanized steel is initially dissolved in alkaline solutions. However, a passive layer is formed over time which protects the steel from corrosion. The behavior of galvanized steel exposed to strong alkaline solutions (pH values of 12.7) with a fixed concentration of sulfate ions of 0.04 M is studied here. Electrochemical measurement techniques such as corrosion potential, linear polarization resistance and electrochemical impedance spectroscopy are used. Synergistic effects of sulfate ions are also studied together with other anions such as chloride Cl⁻ or bicarbonate ion HCO₃⁻ and with other cations such as calcium Ca²⁺, ammonium NH₄⁺ and magnesium Mg²⁺. The presence of sulfate ions can also depassivate the steel, leading to a corrosion current density of 0.3 µA/cm² at the end of the test. The presence of other ions in the solution increases this effect. The increase in corrosion current density caused by cations and anions corresponds to the following orders (greater to lesser influence): NH₄⁺ > Ca²⁺ > Mg²⁺ and HCO₃⁻ > Cl⁻ > SO₄²⁻.     

Conformation of cyclo(-L-Pro-Gly-)(3) and its Ca and Mg complexes

The synthetic hexapeptide cyclo(-L-Pro-Gly-)₃ is an ionophore that shows interesting conformational changes upon binding metal ions. X-ray crystallographic studies of this peptide show that when it is crystallized from an ethanol/ethyl acetate mixture the ring takes up an asymmetric conformation containing one cis peptide bond. In crystals of a Ca²⁺ complex, the cation is sandwiched between two peptide molecules that differ markedly in conformation. However, both exhibit threefold symmetric forms, with all six peptide bonds in the molecule occurring in the usual trans conformation. The Ca²⁺ is octahedrally surrounded by six glycyl carbonyl oxygens from the two peptides at an average distance of 2.26 Å and can easily be released by the disruption of the peptide sandwich. In the magnesium complex, the peptide forms a 1:1 complex with the ion. The Mg²⁺ is octahedrally coordinated to three glycyl carbonyls and three water oxygens. The average coordination distance between magnesium and the peptide oxygens is 2.03 Å and that between magnesium and water oxygen is 2.11 Å. The two peptide molecules in the asymmetric unit have similar conformations and have approximate threefold symmetry.     

Extra-large pore zeolite (ITQ-40) with the lowest framework density containing double four- and double three-rings

The first zeolite structure (ITQ-40) that contains double four (D4) and double three (D3) member ring secondary building units has been synthesized by introducing Ge and NH₄F and working in concentrated synthesis gels. It is the first time that D3-Rs have been observed in a zeolite structure. As was previously analyzed [Brunner GO, Meier, WM (1989) Nature 337:146–147], such a structure has a very low framework density (10.1 T/1,000 Å³). Indeed, ITQ-40 has the lowest framework density ever achieved in oxygen-containing zeolites. Furthermore, it contains large pore openings, i.e., 15-member rings parallel to the [001] hexagonal axis and 16-member ring channels perpendicular to this axis. The results presented here push ahead the possibilities of zeolites for uses in electronics, control delivery of drugs and chemicals, as well as for catalysis.     

Formation of calcium pyrophosphate crystals in vitro: implications for calcium pyrophosphate crystal deposition disease (pseudogout)

Little is known about how calcium pyrophosphate dihydrate (CaPPD) crystals form in vivo and give rise to chondrocalcinosis or pseudogout (pyrophosphate arthropathy or calcium pyrophosphate crystal deposition disease). In this study a simple method has been devised to define the conditions necessary for the deposition of crystals in vitro. Crystal formation is monitored by ⁴⁵Ca in the presence of 1·5 mmol/l Ca and increasing concentrations of inorganic pyrophosphate (PPi) under simulated physiological conditions of pH and ionic strength. Concentrations of PPi required to initiate crystal formation were about 40 mmol/l in the absence and 175 mmol/l in the presence of 0·5 mmol/l Mg²⁺ at pH 7·4. Less PPi was required at higher pH values. The naturally occurring monoclinic and triclinic forms of CaPPD were produced after prolonged incubation in vitro, but the initial deposits were amorphous or orthorhombic. The physiological significance of these observations is discussed. Since much higher concentrations of PPi are required to form crystals in vitro than are found to occur naturally in synovial fluids from patients with pyrophosphate arthropathy, it is suggested that crystals are more likely to deposit initially within cartilage and that nucleating mechanisms may be important in vivo. Since other workers have observed a slow interconversion of other calcium pyrophosphate crystal forms into monoclinic and triclinic allomorphs under laboratory conditions, the reason why only these 2 forms occur under clinical conditions may reflect the long time available in vivo for the formation of crystals.     

Dynamics of calcium-induced insulin release

Summary Extracellular Ca²⁺, at concentrations exceeding 10 mmol/l, causes a dose-related stimulation of insulin release. The dynamics of Ca²⁺-induced insulin release are characterized by a quick onset, a progressive build-up and a later return towards basal secretory rate. The release of insulin evoked by Ca²⁺ is inhibited in the presence of either Mg²⁺ (10 mmol/l) or the organic Ca²⁺-antagonist verapamil (81 mol/l), both of which are known to inhibit Ca²⁺ entry in the B-cell. Glucose and theophylline, which are thought to affect the net uptake or intracellular distribution of Ca²⁺ in the B-cell, both enhance Ca²⁺-induced insulin release. As little as 2.7 mmol/l glucose is sufficient to augment Ca²⁺-induced insulin secretion. Exposure of the pancreas to somatostatin significantly retards the secretory response to Ca²⁺. Cytochalasin B potentiates the insulin release evoked by Ca²⁺ (12 mmol/l) and lowers the threshold concentration of Ca²⁺ required to stimulate secretion. These data suggest that high extracellular Ca²⁺ concentrations may sufficiently increase the amount of Ca²⁺ accumulated in the B-cell to eventually trigger insulin release. Agents known to cause a remodelling of Ca²⁺ fluxes across membrane systems in the B-cell interfere with Ca²⁺-induced insulin release, a process also dependent on the integrity of the cytochalasin B-sensitive microfilamentous effector system.     

An attempt to distinguish between the actions of neuromuscular blocking drugs on the acetylcholine receptor and on its associated ionic channel

The effects of lobeline and tubocurarine on the voltage-clamped endplates of frog sartorius and cutaneous pectoris muscles were examined at room temperature (20-23°C). Like tubocurarine, lobeline causes nondepolarizing neuromuscular blockade. The half-time of decay (t_½) of endplate currents (e.p.c.s) recorded at a holding potential (V_m) of -90 mV was significantly shorter in endplates treated with lobeline (50 μM; mean t_½ ± SEM = 0.41 ± 0.02 ms) or tubocurarine (11.4 μM; t_½ = 0.64 ± 0.04 ms) than in those treated with Mg²⁺ (13 mM; t_½ = 1.39 ± 0.11 ms) or a low concentration of tubocurarine (3 μM; t_½ = 0.87 ± 0.05 ms). Similarly, lobeline (10 μM) shortened the t_½ of untreated miniature e.p.c.s by 35%; tubocurarine, however, abolished miniature e.p.c.s at the concentration required to observe its actions on e.p.c. decay kinetics. The t_½ of e.p.c.s recorded from preparations treated with Mg²⁺ (13 mM), tubocurarine at low concentrations (3 μM), or untreated miniature e.p.c.s was logarithmically related to V_m, being slower at more hyperpolarized values. By contrast, the t_½s of e.p.c.s recorded in either lobeline (50 μM) or tubocurarine (11.4 μM) were independent of voltage in the range -150 to -80 mV. The ability of lobeline to shorten t_½ and to remove the voltage dependence of t_½ was partially antagonized by Mg²⁺ (13 mM). As expected, when lobeline or tubocurarine was removed from the bath or when acetylcholine release from the motor nerve terminals was increased by 4-aminopyridine (20 μM) and Ca²⁺ (10 mM) (in the presence of lobeline or tubocurarine), the amplitude of e.p.c.s increased as a function of time. However, the t_½ of the decay phase of the e.p.c.s remained shortened (i.e., unaltered from the earlier treatment). These results suggest that both tubocurarine and lobeline have at least two distinct postjunctional actions including: (i) a block of the acetylcholine receptor and (ii) a block of the ionic channel associated with the acetylcholine receptor.     

Testing the cation-hydration effect on the crystallization of Ca–Mg–CO3 systems

Dolomite and magnesite are simple anhydrous calcium and/or magnesium carbonate minerals occurring mostly at Earth surfaces. However, laboratory synthesis of neither species at ambient temperature and pressure conditions has been proven practically possible, and the lack of success was assumed to be related to the strong solvation shells of magnesium ions in aqueous media. Here, we report the synthesis of MgCO₃ and Mg_xCa_(1−x)CO₃ (0 < x < 1) solid phases at ambient conditions in the absence of water. Experiments were carried out in dry organic solvent, and the results showed that, although anhydrous phases were readily precipitated in the water-free environment, the precipitates’ crystallinity was highly dependent on the Mg molar percentage content in the solution. In specific, magnesian calcite dominated in low [Mg²⁺]/[Ca²⁺] solutions but gave way to exclusive formation of amorphous Mg_xCa_(1−x)CO₃ and MgCO₃ in high-[Mg²⁺]/[Ca²⁺] and pure-Mg solutions. At conditions of [Mg²⁺]/[Ca²⁺] = 1, both nanocrystals of Ca-rich protodolomite and amorphous phase of Mg-rich Mg_xCa_(1−x)CO₃ were formed. These findings exposed a previously unrecognized intrinsic barrier for Mg²⁺ and CO₃²⁻ to develop long-range orders at ambient conditions and suggested that the long-held belief of cation-hydration inhibition on dolomite and magnesite mineralization needed to be reevaluated. Our study provides significant insight into the long-standing “dolomite problem” in geochemistry and mineralogy and may promote a better understanding of the fundamental chemistry in biomineralization and mineral-carbonation processes.Rarely is there a geological challenge that has endured as long a search for answers as the “dolomite problem” has. Identified more than 220 y ago by the French mineralogist Déodat de Dolomieu, the calcium magnesium carbonate mineral known as dolomite [CaMg(CO₃)₂] has since been synthesized repeatedly but exclusively at high-temperature and, in some instances, high-pressure conditions (1–4). However, in many cases other than igneous-originated carbonatite and deep-burial dolomitization, the formation of dolomitic phases (e.g., microbial and cave deposits) are certainly not associated with such high-temperature and/or -pressure environments (5–8). This obvious discrepancy, compounded by the sharp contrast of massive ancient dolomite formations to the scarcity of modern observations, prompted an arduous search for answers for the past two centuries and, because of a lack of success, has been referred to as the dolomite problem (6, 9–16). Our inability to form dolomite at ambient conditions is hardly the only challenge in mineralogy; a similar situation exists in the case of pure magnesium carbonate [magnesite (MgCO₃)], which has posed the same level of difficulty to nucleate and grow at room temperature and atmospheric pressure in laboratories but frequently occurs in natural sedimentary settings at earth (sub)surfaces. Interestingly, both dolomite and magnesite belong to the mineral class of anhydrous carbonates. Thus, it becomes logical to surmise that the dolomite problem and the magnesite problem probably share the same root, that is, the difficulty to incorporate unhydrated magnesium ions into carbonate from aqueous solutions without appealing to temperature and/or pressure changes. Given the 50% abundance of dolomites in the world’s carbonate reservoirs (6, 17) and the potential of magnesium carbonate for carbon sequestration (18, 19), as well as the critical role of Mg in carbonate biomineralization (20–22), it is safe to assume that scientific interests in the Ca–Mg–CO₃ system will remain for years to come.Aqueous-phase reactions between Mg²⁺ cations and CO₃²⁻ anions at ambient temperature and pressure conditions yield exclusively hydrated [e.g., barringtonite MgCO₃⋅2H₂O; nesquehonite MgCO₃⋅3H₂O; and lansfordite, MgCO₃⋅5H₂O] or basic forms [e.g., hydromagnesite, Mg₅(CO₃)₄(OH)₂⋅4H₂O; dypingite, Mg₅(CO₃)₄(OH)₂⋅5H₂O; and artinite, Mg₂(CO₃)(OH)₂⋅3H₂O] of Mg-carbonate (23, 24). Nesquehonite is the most commonly formed phase under low temperature and pressure [e.g., 25 °C and a pCO₂ of ∼10⁻² atm (25–27)], whereas hydromagnesite and other basic forms become dominant in an intermediate temperature range [e.g., 40–60 °C (28–30)]. Despite being the most stable phase at all conditions, the anhydrous salt, magnesite, was reported to form only at a much elevated temperature and pressure [e.g., ∼90–180 °C and pCO₂ > 50 atm (31–34)].The difficulty in precipitating magnesite (and dolomite) from ambient aqueous solutions was first suggested to be related to the strong hydration status of Mg²⁺ ions in a hypothesis (35) that has since been corroborated by numerous pieces of circumstantial evidence (15, 22, 36). Indeed, both experimental and computational studies revealed the presence of a stable inner-sphere hydration shell around Mg²⁺ ions that contains six water molecules in an octahedral arrangement and has a water exchange rate five orders of magnitude slower than that for Ca²⁺ (37–39). An additional outer shell composed of up to 12 water molecules also exists through hydrogen bonding to the inner shell. The presence of tight hydration shells around Mg²⁺ is consistent with the results of molecular-orbital calculations that show the solvation free energy (per water molecule) for Mg²⁺ ions is as much as 60% higher than that of Ca²⁺ in both the inner and outer shells (40, 41). The strong Mg²⁺–water association is rationalized by the high charge density of Mg²⁺ ions resulting from their small ionic radius. In addition, the net charge on the central magnesium ion of a stabilized [Mg(H₂O)₆]²⁺ complex was found to be only ∼1.18 (42), indicating the occurrence of significant charge transfer between Mg²⁺ and the surrounding water molecules and a more covalent nature of the Mg–O bonding within the hydration shells. Such finding is further validated by recent experimental observations that collision between [Mg(H₂O)_n]²⁺ clusters can generate solvated magnesium hydroxide complexes MgOH⁺(H₂O)_n or monocations Mg⁺(H₂O)_n by inducing electron transfer from the associated H₂O molecules to the Mg²⁺ cations (39, 43–45).Despite the large body of literature documenting the assumed inhibitory role of cation hydration, little work has been found to directly test the solvation effect. Thus, the current understanding of the part that water plays in obstructing magnesite (and dolomite) formation leads to an intriguing and yet fundamental question: will anhydrous Mg carbonate salts precipitate readily if the cation solvation is nonaqueous and weaker than hydration shells? To the best of our knowledge, no data are available in the literature concerning the crystallization of magnesite (or dolomite) in nonaqueous solutions. In the present study, we explored the possibility of magnesite (MgCO₃) and dolomite [CaMg(CO₃)₂] formation under ambient conditions in dry formamide [an organic solvent (O=CH–NH₂)]. We chose formamide because it has a high dielectric constant (ε = 109.8) and resembles water in many physical properties, such as density, dipole moment, and surface tension. The strong polarity of formamide allows us to prepare high-concentration solutions containing Mg²⁺ (and Ca²⁺) cations or CO₃²⁻ anions. In addition, the hydrogen bonding between formamide molecules is more poorly developed than that between water molecules because of the stronger steric effect (46), indicative of a much weaker solvation around the solute ions.     

Mesitylene Tribenzoic Acid as a Linker for Novel Zn/Cd Metal-Organic Frameworks

Three new Metal-Organic Frameworks, containing mesitylene tribenzoic acid as a linker and zinc (1) or cadmium as metals (2,3), were synthesized through solvothermal reactions, using DMF/ethanol/water as solvents, at temperatures of 80 °C (structures 1 and 3) and 120 °C (structure 2). Following single-crystal X-ray diffraction, it was found that 1 and 3 crystallize in the P2₁/c and C2/c space groups and form 2D networks, while 2 crystallizes in the Fdd2 space group, forming a 3D network. All three frameworks, upon heating, were found to be stable up to 350 °C. N₂ sorption isotherms revealed that 1 displays a BET area of 906 m²/g. Moreover, the porosity of this framework is still present after five cycles of sorption/desorption, with a reduction of 14% of the BET area, down to 784 m²/g, after the fifth cycle. The CO₂ loading capacity of 1 was found to be 2.9 mmol/g at 0 °C.     

Preliminary In Vitro Study of Fluoride Release from Selected Ormocer Materials

The purpose of the in vitro study presented in this paper was to determine the long-term release of fluoride ions from selected ormocer materials (Admira (A), Admira Flow (AF), Admira Seal (AS)). The release of fluoride ions from these materials into a saline solution (0.9% NaCl) and deionized water was tested for 14 weeks. In a long-term study the measurements were taken after 1 and 3 h, then 1, 2, and 3 days and then at weekly intervals for 14 weeks. In a short-term study the measurements were made after 3, 24, 48, 72, 69, 168 h, i.e., within 7 days. All materials used in the test showed a constant level of fluoride release. The highest level of cumulative release of fluoride ions into deionized water was found in the AS material (23.95 ± 4.30 μg/mm²), slightly lower in the A material (23.26 ± 4.16 μg/mm²) and the lowest in the AF material (16.79 ± 2.26 μg/mm²). The highest level of cumulative release into saline solution was found in AF (8.08 ± 1.30 μg/mm²), slightly lower in AS (7.36 ± 0.30 μg/mm²) and the lowest in A (6.73 ± 1.10 μg /mm²). After 1 h of immersion of the samples in the saline solution, the highest level of fluoride was released by AF (0.57 ± 0.06 μg/mm²) followed by A (0.20 ± 0.03 μg/mm²) and AS (0.19 ± 0.02 µg/mm²). Moreover, in the 14-week study, the total amount of fluoride release into the saline, which imitates the environment of the oral cavity, was observed as the highest in the AF sample.     

Differences in Glycemic Variability Between Normoglycemic and Prediabetic Subjects

So far the criteria for NGT and abnormal glucose tolerance (AGT) are based on HbA1c and 75 g oGTT. We present data on GV and diurnal profiles in stratified cohorts with AGT versus controls. 28 NGT, 42 AGT (15 IGT, 11 IFG, 16 CGI) matched for age and BMI classified by 75 g oGTT underwent a CGM with test meal (TM). Diurnal profiles, glucose excursion after TM, and GV (SD, MAGE) were calculated for day 2 and 3. HbA1c, with its values of 5.5 ± 0.37% versus 5.65 ± 0.36%, was within normal range. Average interstitial glucose (AiG) was 5.84 ± 0.52 mmol/l) in NGT and 6.35 ± 0.65 mmol/l in AGT (P = .002). The 2 h incremental area under curve (iAUC) from TM until 2 h after TM was 1.94 ± 1.31 mmol/l*h versus 2.89 ( ± 1.75) mmol/l*h (P = .012), AiG 2 hours after TM was 5.99 ± 1.14 mmol/l*d versus 6.64 ± 1.30 mmol/l (P = .035). Peaks of AiG after TM were 7.69 ± 1.48 mmol/l*d versus 9.18 ± 1.67 mmol/l*d (P = .001). SD was significantly higher for AGT (1.12 ± 0.37 vs. 0.85 ± 0.32 mmol/l, P = .01) and MAGE 2.26 ± 0.84 vs. 1.60 ± 0.69 mmol/l, P = .005). In this comparative analysis NGT and AGT well matched for age, BMI, and comorbidities, CGM revealed significant differences in daytime AiG, pp glucose excursion and postprandial peaks. SD and MAGE was significantly higher for subjects with AGT. I Impaired glucose homeostasis a better characterizes degree of AGTe than HbA1c and 75 g OGTT.     

Voltage-dependent calcium release in guinea-pig cardiac ventricular muscle as antagonized by magnesium and calcium

Summary An increase in extracellular potassium concentration from 4 to 16 mmol/l caused a decrease in membrane potential from –92 to –59 mV and selectively diminished the earlier of two contraction components of guinea-pig papillary muscles at 0.2 Hz stimulation frequency in the presence of noradrenaline. The influence on the early contraction component had a threshold of 8 mmol/l K⁺, corresponding to a membrane potential of –77 mV. However, test contractions elicited 800 ms after the 5 s stimulation interval exhibited an unimpaired early component. Since the activator calcium responsible for the early contraction component is derived, in mammalian ventricular muscle, from the junctional sarcoplasmic reticulum (20), it is assumed that the release site of the reticulum was filled with calcium shortly (800 ms) after a regular contraction, and lost its calcium at 16 mmol/l extracellular K⁺ during the 5 s stimulation interval. The potassium-induced depolarization determined the rate of calcium leakage during rest from the intracellular store. The depolarization-induced decline of the early contraction component was equally well antagonized by Mg²⁺ or Ca²⁺ without influencing the measured transmembrane potential. Both divalent cations shifted the relation between potassium concentration or membrane potential and the strength of the early contraction component to less negative membrane potentials. In order to reduce the early contraction component by 25% in the presence of 9.6 instead of 1.2 mmol/l Mg²⁺, the potassium concentration had to be increased from 9.6 to 22.0 mmol/l, with a respective decrease in resting membrane potential from –72.6 to –51.1 mV. The antagonistic effect of both divalent cations is thought to result from the neutralization of negative charges outside the sarcolemma with a respective decrease in the outside surface potential.     

SBA-15 with Crystalline Walls Produced via Thermal Treatment with the Alkali and Alkali Earth Metal Ions

Crystalline walled SBA-15 with large pore size were prepared using alkali and alkali earth metal ions (Na⁺, Li⁺, K⁺ and Ca²⁺). For this work, the ratios of alkali metal ions (Si/metal ion) ranged from 2.1 to 80, while the temperatures tested ranged from 500 to 700 °C. The SBA-15 prepared with Si/Na⁺ ratios ranging from 2.1 to 40 at 700 °C exhibited both cristobalite and quartz SiO₂ structures in pore walls. When the Na⁺ amount increased (i.e., Si/Na increased from 80 to 40), the pore size was increased remarkably but the surface area and pore volume of the metal ion-based SBA-15 were decreased. When the SBA-15 prepared with Li⁺, K⁺ and Ca²⁺ ions (Si/metal ion = 40) was thermally treated at 700 °C, the crystalline SiO₂ of quartz structure with large pore diameter (i.e., 802.5 Å) was observed for Ca⁺² ion-based SBA-15, while no crystalline SiO₂ structures were observed in pore walls for both the K⁺ and Li⁺ ions treated SBA-15. The crystalline SiO₂ structures may be formed by the rearrangement of silica matrix when alkali or alkali earth metal ions are inserted into silica matrix at elevated temperature.     

Synthesis and Characterization of Zeolites Produced from Low-Quality Coal Fly Ash and Wet Flue Gas Desulphurization Wastewater

This study investigated a low-energy-consuming procedure for the synthesis of zeolite materials from coal fly ash (CFA). Materials containing zeolite phases, namely Na–X, Na–P1, and zeolite A, were produced from F–class fly ash, using NaOH dissolved in distilled water or in wastewater obtained from the wet flue gas desulphurization process, under atmospheric pressure at a temperature below 70 °C. The influence of temperature, exposure time, and alkaline solution concentration on the synthesized materials was tested. In addition, chemical, mineralogical, and textural properties of the obtained materials were determined by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and cation exchange capacity (CEC). Cd(II), Ni(II), NH₄⁺ cation, and Se(VI) anion sorption experiments were conducted to compare the sorption properties of the produced synthetic zeolites with those of the commercially available ones. Zeolitization resulted in an increase of CEC (up to 30 meq/100 g) compared to raw CFA and enhanced the ability of the material to adsorb the chosen ions. The obtained synthetic zeolites showed comparable or greater sorption properties than natural clinoptilolite and synthetic Na–P1. They were also capable of simultaneously removing cationic and anionic compounds. The structural, morphological, and textural properties of the final product indicated that it could potentially be used as an adsorbent for various types of environmental pollutants.     

Conformation of cyclo(Gly-L-Pro-L-Pro-Gly-L-Pro-L-Pro)(2)Mg complex crystallized from CH(3)CN solution

The cyclic hexapeptides (Gly-L-Pro-L-Pro-Gly-L-Pro-L-Pro) in the (peptide—Mg—peptide)²⁺ complex have nearly identical asymmetric conformations. Each has two cis Pro-Pro linkages and lacks any intraring hydrogen bonds. The Mg²⁺ ion forms six ligands in a regular octahedral array with the carbonyl oxygen atoms of the two Gly residues and one Pro residue of each peptide. The “sandwich” complex has an approximate 2-fold rotation axis through the Mg²⁺ relating the two peptide moieties. Cyclo(Gly-Pro-Pro-Gly-Pro-Pro)₂Mg(ClO₄)₂· 4C²H₃CN crystallizes in space group P3₁ with a = b = 15.744(4) Å, c = 24.002(6) Å, γ = 120°, and Z = 3. A highlight of the structure determination is the ready location of the Mg self-vector in a Harker section and the development of the entire structure by use of the tangent formula starting with the known position of the Mg atom.     

Two-dimensional confocal images of organization, density, and gating of focal Ca2+ release sites in rat cardiac myocytes

In cardiac myocytes Ca²⁺ cross-signaling between Ca²⁺ channels and ryanodine receptors takes place by exchange of Ca²⁺ signals in microdomains surrounding dyadic junctions, allowing first the activation and then the inactivation of the two Ca²⁺-transporting proteins. To explore the details of Ca²⁺ signaling between the two sets of receptors we measured the two-dimensional cellular distribution of Ca²⁺ at 240 Hz by using a novel confocal imaging technique. Ca²⁺ channel-triggered Ca²⁺ transients could be resolved into dynamic “Ca²⁺ stripes” composed of hundreds of discrete focal Ca²⁺ releases, appearing as bright fluorescence spots (radius 0.5 μm) at reproducible sites, which often coincided with t-tubules as visualized with fluorescent staining of the cell membrane. Focal Ca²⁺ releases triggered stochastically by Ca²⁺ current (I_Ca) changed little in duration (7 ms) and size (100,000 Ca ions) between −40 and +60 mV, but their frequency of activation and first latency mirrored the kinetics and voltage dependence of I_Ca. The resolution of 0.95 ± 0.13 reproducible focal Ca²⁺ release sites per μm³ in highly Ca²⁺-buffered cells, where diffusion of Ca²⁺ is limited to 50 nm, suggests the presence of about one independent, functional Ca²⁺ release site per half sarcomere. The density and distribution of Ca²⁺ release sites suggest they correspond to dyadic junctions. The abrupt onset and termination of focal Ca²⁺ releases indicate that the cluster of ryanodine receptors in individual dyadic junctions may operate in a coordinated fashion.     

Association of beta-catenin with the alpha-subunit of neuronal large-conductance Ca2+-activated K+ channels

The association of Ca²⁺-activated K⁺ channels with voltage-gated Ca²⁺ channels at the presynaptic active zones of hair cells, photoreceptors, and neurons contributes to rapid repolarization of the membrane after excitation. Ca²⁺ channels have been shown to bind to a large set of synaptic proteins, but the proteins interacting with Ca²⁺-activated K⁺ channels remain unknown. Here, we report that the large-conductance Ca²⁺-activated K⁺ channel of the chicken's cochlear hair cell interacts with β-catenin. Yeast two-hybrid assays identified the S10 region of the K⁺ channel's α-subunit and the ninth armadillo repeat and carboxyl terminus of β-catenin as necessary for the interaction. An antiserum directed against the α-subunit specifically coprecipitated β-catenin from brain synaptic proteins. β-Catenin is known to associate with the synaptic protein Lin7/Velis/MALS, whose interaction partner Lin2/CASK also binds voltage-gated Ca²⁺ channels. β-Catenin may therefore provide a physical link between the two types of channels at the presynaptic active zone.