Hydration characteristics of Ca2+ and Mg2+: a density functional theory,polarized continuum model and molecular dynamics investigation

In this work, density functional theory, Møller–Plesset second-order perturbation theory, and ab initio molecular dynamics (AIMD) were used to investigate hydrated characteristics of Mg²⁺ and Ca²⁺ as a function of coordination number in the first hydration shell (CN) and cluster size. It is generally accepted that the CNs of Mg²⁺ and Ca²⁺ are both six. Calculations show that the hydration of Mg²⁺ generally prefers six-coordinated structures, whereas the CN value of Ca²⁺ varies from 6 to 8 as the hydration proceeds. Moreover, the first hydration of Ca²⁺ is found to be more flexible than that of Mg²⁺, as indicated by the results of transition state calculations and AIMD simulations. In addition, the constraint of Mg²⁺ on the first hydration shell is obviously stronger than that of Ca²⁺, while the constraint on the inner hydration shells fades slightly faster for Mg²⁺ than Ca²⁺. It is also found that the charge transfer from central cation to water molecules is affected only by the first hydration shell for Mg²⁺, whereas by the first and second hydration shells for Ca²⁺. Based on hydration characteristics, approximatively saturated ion hydration shells for the hydration of Mg²⁺ and Ca²⁺ were proposed.     

Studies on adsorptions of metallic ions in water by zirconium glyphosate (ZrGP): Behaviors and mechanisms

A new adsorbent named zirconium glyphosate [Zr(O₃PCH₂NHCH₂COOH)₂·0.5H₂O, denoted as ZrGP] and its selective adsorptions to Pb²⁺, Cd²⁺, Mg²⁺ and Ca²⁺ ions in water were reported in this paper. Compared to other zirconium adsorbents, such as zirconium phosphate [Zr(HPO₄)₂], ZrGP exhibited highly selective adsorption to Pb²⁺ in solution which contained Pb²⁺, Cd²⁺, Mg²⁺ and Ca²⁺ ions. The loaded ZrGP with metallic ions can be efficaciously regenerated by aqueous solution of HCl (1.0 M) without any noticeable capacity loss, and almost all of it can be reused and recycled. The memory effect on structural regeneration of ZrGP was also found when Mg²⁺ and Ca²⁺ were adsorbed. To be specific, the structure of ZrGP was destroyed due to adsorbing these two ions, but it could be regenerated after the loaded materials were dipped in HCl solution (1.0 M) for several minutes to remove metallic ions.     

Influence of divalent cationic impurities on plasticity of AgCl

The hardening effect of Mg²⁺, Ca²⁺, Sr²⁺, Cd²⁺ and Ba²⁺ impurities in polycrystalline AgCl was investigated. With exception of Mg²⁺ the hardening effect of the impurities decreases with increasing atomic number (atomic weight). The hardening effects of Mg²⁺ and Ca²⁺ are expressively stronger than those of the three remaining impurities. Approximately linear dependence of the stress at the beginning of plastic deformation on the impurity concentration was found. Possible causes of the different hardening effects of the divalent impurities are discussed.     

Electron microscopy and atomic force microscopy studies of chromatin and metaphase chromosome structure

The folding of the chromatin filament and, in particular, the organization of genomic DNA within metaphase chromosomes has attracted the interest of many laboratories during the last five decades. This review discusses our current understanding of chromatin higher-order structure based on results obtained with transmission electron microscopy (TEM), cryo-electron microscopy (cryo-EM), and different atomic force microscopy (AFM) techniques.Chromatin isolated from different cell types in buffers without cations form extended filaments with nucleosomes visible as separated units. In presence of low concentrations of Mg²⁺, chromatin filaments are folded into fibers having a diameter of ∼30 nm. Highly compact fibers were obtained with isolated chromatin fragments in solutions containing 1–2 mM Mg²⁺. The high density of these fibers suggested that the successive turns of the chromatin filament are interdigitated. Similar results were obtained with reconstituted nucleosome arrays under the same ionic conditions. This led to the proposal of compact interdigitated solenoid models having a helical pitch of 4–5 nm. These findings, together with the observation of columns of stacked nucleosomes in different liquid crystal phases formed by aggregation of nucleosome core particles at high concentration, and different experimental evidences obtained using other approaches, indicate that face-to-face interactions between nucleosomes are very important for the formation of dense chromatin structures.Chromatin fibers were observed in metaphase chromosome preparations in deionized water and in buffers containing EDTA, but chromosomes in presence of the Mg²⁺ concentrations found in metaphase (5–22 mM) are very compact, without visible fibers. Moreover, a recent cryo-electron microscopy analysis of vitreous sections of mitotic cells indicated that chromatin has a disordered organization, which does not support the existence of 30-nm fibers in condensed chromosomes. TEM images of partially denatured chromosomes obtained using different procedures that maintain the ionic conditions of metaphase showed that bulk chromatin in chromosomes is organized forming multilayered plate-like structures. The structure and mechanical properties of these plates were studied using cryo-EM, electron tomography, AFM imaging in aqueous media, and AFM-based nanotribology and force spectroscopy. The results obtained indicated that the chromatin filament forms a flexible two-dimensional network, in which DNA is the main component responsible for the mechanical strength observed in friction force measurements. The discovery of this unexpected structure based on a planar geometry has opened completely new possibilities for the understanding of chromatin folding in metaphase chromosomes. It was proposed that chromatids are formed by many stacked thin chromatin plates oriented perpendicular to the chromatid axis. Different experimental evidences indicated that nucleosomes in the plates are irregularly oriented, and that the successive layers are interdigitated (the apparent layer thickness is 5–6 nm), allowing face-to-face interactions between nucleosomes of adjacent layers. The high density of this structure is in agreement with the high concentration of DNA observed in metaphase chromosomes of different species, and the irregular orientation of nucleosomes within the plates make these results compatible with those obtained with mitotic cell cryo-sections. The multilaminar chromatin structure proposed for chromosomes allows an easy explanation of chromosome banding and of the band splitting observed in stretched chromosomes.     

Determination of the Association Constants of Macrocyclic Ethers by the Aid of 13C Dipole-dipole Relaxation Time Measurements. I.,: Li+, Mg2+ and Ca2+ complexes of 1,4,7,10-tetraoxacyclododecane

Abstract

The association constants of Li⁺, Ca⁺² and Mg⁺² ions complexing with 1, 4, 7, 10-tetraoxcyclododecane in DHO were determined by the aid of ¹³C dipole-dipole relaxation time measurements. To obtain the K_a, association constant, the T^O ₁ values of the stoichiometric complex solutions and the T₁₀ of the free molecules were applied to the equation derived, 1/K_a· A_o + 2 = 1/P + P, for the 1:1 ratio of the complexing and to the equation 1/2K_a·A_o + 3/2 = P + 1/2P for the 1:2 ratio of the complexing where P, is molar ratio of the crown complexed ions.

Accordingly we found that the binding ability of the macrocyclic ether towards to the cations is in the following order of Li⁺ < Mg⁺² ? Ca⁺² in DHO solutions.     

Residues at the tip of the pore loop of NR3B-containing NMDA receptors determine Ca<Superscript>2+</Superscript> permeability and Mg<Superscript>2+</Superscript>block

Background  

Members of the complex N-methyl-D-aspartate receptor (NMDAR) subfamily of ionotropic glutamate receptors (iGluRs) conventionally assemble from NR1 and NR2 subunits, the composition of which determines receptor properties. Hallmark features of conventional NMDARs include the requirement for a coagonist, voltage-dependent block by Mg²⁺, and high permeability for Ca²⁺. Both Mg²⁺ sensitivity and Ca²⁺ permeability are critically dependent on the amino acids at the N and N+1 positions of NR1 and NR2. The recently discovered NR3 subunits feature an unprecedented glycine-arginine combination at those critical sites within the pore. Diheteromers assembled from NR1 and NR3 are not blocked by Mg²⁺ and are not permeable for Ca²⁺.     

Luminescent properties of Mg3Ca3(PO4)4: Eu2+ blue-emitting phosphor for white light emitting diodes

A blue-emitting phosphor, Eu²⁺-activated Mg₃Ca₃(PO₄)₄ phosphor was synthesized by conventional solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the phase formation. Photoluminescence (PL) results showed that Mg₃Ca₃(PO₄)₄: Eu²⁺ could be efficiently excited by UV–visible light from 250 to 430 nm, which matched well with the emission wavelengths of near-UV and UV LED chips. The effects of the doped-Eu²⁺ concentration in Mg₃Ca₃(PO₄)₄: Eu²⁺ on the PL were also investigated. The result reveals that Mg₃Ca₃(PO₄)₄: Eu²⁺ is a potential blue-emitting phosphor for white LEDs.     

lin-Benzo-ATP and-ADP: Versatile fluorescent probes for spectroscopic and biochemical studies

lin-Benzo-adenine nucleotides can act not only as probes for fluorescence studies but also as structural active site probes for enzymes. To understand the basic properties oflin-benzo-ATP and-ADP, protolysis and Mg²⁺ and Ca²⁺, binding are investigated between pH 6.2 and pH 8.5 by spectrophotometric and spectrofluorometric titrations. Based on a reaction model, a set of equilibrium constants is determined which is consistent with all available experimental results. The pK values of the Mg²⁺ and Ca²⁺ complex oflin-benzo-ATP in the chosen medium are 4.6 and 4.1, respectively, and those for the corresponding diphosphate are 3.1 and 2.8, respectively. Fluorescence and absorption spectra are reported.This is a peer-reviewed conference proceeding article from the Third Conference on Methods and Applications of Fluorescence Spectroscopy, Prague, Czech Republic, October 18–21, 1993.     

Electrochemical luminescence of Mg1−xCaxIn2O4:Er electrodes

Improvement for electrochemical luminescence (ECL) property of MgIn₂O₄ is attempted by partial exchange of Mg²⁺ ion in MgIn₂O₄ to Ca²⁺ ion. Mg_1−xCa_xIn₂O₄ solid solution was obtained in the region 0<x<0.4. Efficiency for ECL per unit current for Mg_1−xCa_xIn₂O₄:Er³⁺ increased with the increase in the ratio of Ca²⁺ ion, and showed a peak at x=0.25 and then decreased steeply. ECL efficiency for other rare-earth ion-(RE:Sm, Eu, Ho) doped Mg_1−xCa_xIn₂O₄ also increased comparing with those for MgIn₂O₄:RE. This Ca²⁺ addition effect on the ECL efficiency seems to be caused by the improvement of the efficiency for the impact activation.     

Comparison of the stability of thymine tautomers and the interaction of its tautomers with Na+, K+, Mg2+ and Ca2+ in gas and solvent phases

The present study compared the interactions among Na ⁺, K ⁺, Mg²⁺ and Ca²⁺, thymine and its tautomers in the gas and solvent phase, an interaction dependent upon the electronic construction of the tautomers. Three types of cation interaction with thymine and its tautomers were observed. In the first one, the metal cations interacted with a lone pair of nitrogen or oxygen of the tautomers. In the second type, there was an interaction among the cations, nitrogen and oxygen at the same time; the last one was that of cations with the electron density of thymine π-system, where the cations were perpendicular to the ring of thymine. The interaction of metals cation with tautomers was studied in the gas and solvent phases; a comparison was then made between interactions in two phases. The interaction energy for all complexes indicated the stability of complexes, an energy which was higher in Ca²⁺ and Mg²⁺ compared with Na⁺ and K⁺. Concerning K⁺ and Na⁺, the stability of all complexes of tautomers was greater than that of thymine complexes; however, the stability of certain Ca²⁺ and Mg²⁺ complexes was lower than the complexes of thymine.     

Magnetic isotopic effect in the plasticity of diamagnetic crystals

A magnetic isotopic effect in the plasticity of diamagnetic crystals is predicted. This effect consists in that the replacement of nonmagnetic isotopic nuclei by magnetic nuclei in ionic crystals (e.g., the introduction of ²⁵Mg²⁺ or ⁴³Ca²⁺ in place of ²⁴Mg²⁺ or ⁴⁰Ca²⁺ in NaCl) increases the plasticity of the crystals even in the absence of an external magnetic field. On the contrary, such a replacement in covalent crystals (e.g., the introduction of ²⁹Si into silicon or ¹³C into diamond) is expected to reduce the plasticity and to produce dislocation strengthening.     

Crystal structure and luminescence properties of Lu3+ and Mg2+ incorporated silicate garnet [Ca3−(x+0.06)LuxCe0.06](Sc2−yMgy)Si3O12

The yellow-emitting phosphor [Ca_3?(x+0.06)Lu_xCe_0.06](Sc_2?yMg_y)Si₃O₁₂ obtained from Lu³⁺ and Mg²⁺ co-modified green-emitting silicate garnet Ca₃Sc₂Si₃O₁₂:Ce³⁺ (CSS:Ce³⁺) exhibits promising applications for white LEDs. In this paper, we discuss the effect of charge balance on the garnet structure formation. The changes of bond length and covalence caused by the replacement of Lu³⁺ and Mg²⁺ for Ca²⁺ and Sc³⁺ are analyzed. The shift of the Ce³⁺ emission and excitation can be attributed to the combined results from crystal field splitting effect and centroid shift of Ce³⁺ 5d levels. Thermal stability is analyzed according to configurational coordinate diagram.     

Gas phase interaction of L‐proline with Be2+, Mg2+ and Ca2+ ions: a computational study

Geometry optimisation and metal ion affinities (MIAs) of the binding configurations of Be²⁺, Mg²⁺ and Ca²⁺ to L ‐proline were calculated using the hybrid Density Functional Theory (DFT‐B3LYP) and second order Møllet?Plesset perturbation theory (MP2) methods. Be²⁺ was found to bind preferentially in a charge transfer type arrangement through the carbonyl oxygen (? C?O) and the lone pair of the imino‐group nitrogen atom (? NH? ). On the contrary Mg²⁺ and Ca²⁺ were found to prefer binding in a bi‐dentate manner through the carboxylate group of L ‐proline (OCO) in a zwitterion form. The main types of interactions found to influence the binding preference of M²⁺ ions to L ‐proline were (i) charge transfer in the case of Be²⁺ ions and (ii) electrostatic interactions in the case of Mg²⁺ and Ca²⁺ ions. Inspection of the IR stretching of the N? H and the O? H groups of L ‐proline with M²⁺ ions in a chelating configuration (to both O and N atoms) indicated a considerable shift to higher frequency with decreasing MIA. On the other hand, the MIA for the zwitterion L ‐proline with M²⁺ tracks the reciprocal distance of the M²⁺? OCO bond further confirming that the nature of the bond is mainly electrostatic. Comparison with other molecules containing the carboxylic function is also included in order to gain more insight on the types of interaction of this amino acid with metal ions in general. Copyright © 2007 John Wiley & Sons, Ltd.     

Fluorescence lifetime characterization of magnesium probes: Improvement of Mg2+ dynamic range and sensitivity using phase-modulation fluorometry

We measured the Mg²⁺-dependent absorption spectra, emission spectra, quantum yields, and intensity decays of most presently available fluorescent magnesium probes. The lifetimes were found to be strongly Mg²⁺ dependent for Mag-quin-1, Mag-quin-2, magnesium green, and magnesium orange and increased 2- to 10-fold upon binding of Mg²⁺. The lifetimes of Mag-fura-2, Mag-fura-5, Mag-fura red, and Mag-indo-1 were similar in the presence and absence of Mg²⁺. Detailed timeresolved measurements were carried out for Mag-quin-2 and magnesium green using phase-modulation fluorometry. Apparent dissociation constants (K _d) were determined from the steady-state and time-resolved data. Their values were compared and discussed. Mg²⁺ sensing is described using phase and modulation data measured at a single modulation frequency. Phase angle and modulation data showed the possibility of obtaining a wider Mg²⁺-sensitive range than available from intensity measurements. A significant expansion in the Mg²⁺-sensitive range was found for Mag-quin-2 using excitation wavelengths from 343 to 375 nm, where the apparentK _d from the phase angle was found to vary from 0.3 to about 100 mM. Discrimination against Ca²⁺ was also measured for Mag-quin-2 and magnesium green. Significant phototransformation and/or photode-composition, which affect the sensitivity to Mg²⁺, were observed for Mag-quin-2 and magnesium green under intense and long illumination.     

Rhod-5N as a Fluorescent Molecular Sensor of Cadmium(II) Ion

The photophysical and complexing properties of Rhod-5N (commercially available) in MOPS buffer are reported. This fluorescent molecular sensor consists of a BAPTA chelating moiety bound to a rhodamine fluorophore. Its fluorescence quantum yield is low and a drastic enhancement of fluorescence intensity upon cation binding was observed. Special attention was paid to the complexation with Cd²⁺, a well known toxic metal ion. Possible interference with other metal ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, Pb²⁺) was examined. Rhod-5N was found to be highly selective of Cd²⁺ over those interfering cations except Pb²⁺. The limit of detection is 3.1 μg l⁻¹.     

The effect of alkaline earth metallic ions on the photoluminescence properties of sol-gel silica glass

Mg²⁺-, Ca²⁺-, Sr²⁺- and Ba²⁺-doped silica glasses have been prepared using sol-gel processing by employing Si(OC₂H₅)₄, MgCl₂6H₂O, CaCl₂2H₂O, SrCl₂6H₂O and BaCl₂2H₂O as precursors, with HCl as a catalyst. The UV–visibleabsorption spectra of the doped samples are almost the same as those of the undoped sample. The absorption bands of alkaline earth metallic ions have not been observed in the doped samples. Strong visible light has been observed from sol- gel silica glasses doped with alkaline earth metallic ions. The relative fluorescence intensity of the Sr²⁺-doped (the impurity mole ratio of Sr²⁺ was 0.268%) and the Ba²⁺-doped (the impurity mole ratio of Ba²⁺ was 0.448%) samples was about 4 times that of the undoped sample. The relative fluorescence intensity of the Mg²⁺-doped (the impurity mole ratio of Mg²⁺ was 0.069%) sample was about 2.5 times that of the pure glass sample. The relative fluorescence intensity of the Ca²⁺- doped (the impurity mole ratio of Ca²⁺ was 0.179%) sample was about 3 times that of the pure glass sample. Alkaline earth metallic ions affect the formation and conversion of luminescent defects in sol-gel silica glass. Thus, the relative fluorescence intensity of the doped samples increases more than that of the undoped sample. Received: 17 April 2001 / Accepted: 6 June 2001 / Published online: 30 August 2001     

EPR spectra of Mn2+ ions in precipitated divalent impurity phases in monocrystalline NaCl

The EPR spectra of Mn²⁺ ions embedded into precipitated phases of Mg²⁺, Cd²⁺, Fe²⁺ and Ca²⁺ in NaCl single crystals have been investigated. The spectrum from samples whose major impurity is Mg, Cd or Fe corresponds to Mn²⁺ substituting some divalent cation inside the Suzuki phase (6NaCl.MCl₂). The existence of such a phase has been ascertained by means of Raman spectroscopy. On the other hand, the EPR spectrum of Ca²⁺ doped samples has been attributed to Mn²⁺ inside various CaCl₂ precipitates.     

Calcium substituting B-site in relaxor ferroelectrics with perovskite structure probed by chemical ordering

Chemical ordering of Ca²⁺ doped 0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃ ceramics were investigated by dielectric spectra, TEM diffraction and A_1g mode in Raman spectra. It is found degree of relaxor behavior increases first, and then decreases. It conflicts the prediction Ca²⁺ substitutes for A-site ion Pb²⁺ according to crystal chemistry theory. In this letter, a new mechanism that Ca²⁺ substitutes for B-site ions has been proposed, which satisfactorily explained change of chemical ordering. It exhibits strong evidence doped ions with larger ionic radius (Ca²⁺) are quite possibly substitute much smaller ones (Nb⁵⁺ or Ti⁴⁺) in B-site rather than all substitute larger A-site ion in relaxor ferroelectrics.     

Preparation,characterization, and ion exchange behavior of nanocomposite polyaniline zirconium(IV) selenotungstophosphate for the separation of toxic metal ions

A conducting polymer-based advanced nanocomposite ion exchanger was synthesized by incorporating polyaniline (PANI) into the inorganic counterpart zirconium(IV) selenotungstophosphate (ZSWP). The nanocomposite exhibited an excellent ion exchange capacity of 1.20 meq g^?1 in addition to high thermal stability. The polymeric–inorganic nanocomposite ion exchanger was characterized by Fourier transform infrared (FTIR), XRD, SEM, and TEM studies. The DC conductivity of PANI/ZSWP was also investigated. The nanocomposite ion exchanger was found to be highly selective for Cu²⁺ ions with a distribution coefficient value of 650 mL/g. The analytical applications of the material were explored by achieving selective separations of Cu²⁺ and Ca²⁺ ions from a synthetic mixture of Cu²⁺, Pb²⁺, Zn²⁺, Ni²⁺, Fe³⁺, Mg²⁺, and Al³⁺ and Ca²⁺, Pb²⁺, Zn²⁺, Ni²⁺, Al³⁺, Mg²⁺, and Ba²⁺.     

Quinoline group grafted carbon nanotube fluorescent sensor for detection of Cu ion

A carbon nanotube-based fluorescent chemosensor MWNTs-glycine-N-8-quinolylamide (MWNTs-GNQ) has been designed and synthesized. Steady-state fluorescence emission studies showed that this material displays high selectivity and sensitivity for the Cu²⁺ ion over other cations such as Zn²⁺, Cd²⁺, Mg²⁺, Ca²⁺, and Ni²⁺.