Thermodynamic interactions of the alkaline earth metal ions with citric acid

By using the isothermal titration calorimetry (ITC) technique, thermodynamic parameters have been determined for reactions of the Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ ions with the citrate anion. The measurements were run in the Cacodylate, Pipes and Mes buffer solutions of a pH of 6, at 298.15 K, as well as in the Tricine, Tapso, and Tris–HCl buffer solutions of a pH of 8. Further, based on the results of potentiometric titration, the conditional stability constants were determined for the citrate complexes at both pH values. The effect of the reaction environment and the metal ion identity on the interaction energy with the citrate ligand and the stability of the resulting compounds have been discussed.     

3D coordination polymers with vanadyl fragments and alkaline earth metal ions

The reactions of vanadyl sulfate VOSO₄·3H₂O with barium or strontium cyclopropane-1,1-dicarboxylate (MCpdc, M = Ba, Sr, H₂Cpdc = C₃H₄(COOH)₂) afforded the polymeric heterometallic complexes {[(H₂O)₈Ba₂(VO)₂(Cpdc)₄]·2H₂O}n (1) and {[(H₂O)₆Sr(VO)(Cpdc)₂]}n (2), respectively. These complexes differ in the binding mode of mononuclear vanadyl fragments with alkaline earth metal ions. Coordination polymers 1 and 2 were characterized by ESR spectroscopy.     

Charge remote fragmentation of fatty acids cationized with alkaline earth metal ions

Fatty acids can be collisionally activated as [M ? H + Cat]⁺, where Cat is an alkaline earth metal, by using tandem mass spectrometry. High-energy collisional activation induces charge remote fragmentation to give structural information. In the full scan mass spectra molecular ions are easily identified, particularly when barium is used as a cationizing agent; ions are shifted to a higher mass, lower chemical noise region of the mass spectrum. Moreover, the isotopic pattern of barium is characteristic, and the high mass defect of barium allows an easy separation of the cationized analyte from any remaining interfering ions (chemical noise), provided medium mass-resolving power is available. An additional advantage is that most of the ion current is localized in [M ? H + Cat]⁺ species. Structural analysis of fatty acids can be performed when the sample size is as low as 1 ng.     

Ground and excited state complexation of ketocyanine dyes with alkaline earth metal ions

Electronic absorption and emission spectral characteristics of two ketocyanine dyes have been studied in solution in the presence of alkaline earth metal ions. Absorption spectral studies indicate complex formation between the ions and the dyes in the ground state. Values of the equilibrium constant and the enthalpy change characterizing dye (S0)-metal ion interaction have been determined from the absorption spectral data. In the presence of the metal ions the fluorescence spectrum of the dyes shows two bands pointing to the existence of two emitting species, viz., the solvated and the complexed dye in solution. Time-resolved studies of the dyes in solution containing the metal ions can be explained by a two-state model and indicate the presence of two emitting species in equilibrium. Values of the equilibrium constant for the interaction of metal ion and the dyes in the S1 state have also been estimated.     

Investigation of exchange reactions between alkaline earth metal oxides and some transition metal halides

DTA and the simultaneous recording of electrical conductivity were applied for the investigation of exchange reactions between alkaline earth metal oxides and some lead, copper and nickel halides. Although the possibility of the gaseous phase is not excluded for the majority of the reactions investigated, it is either the appearance of a liquid phase or the polymorphous transformation of CaO that has the decisive effect on the interaction mechanism.     

Apparent molar volumes and compressibilities of alkaline earth metal ions in methanol and dimethylsulfoxide

Temperature dependencies of density of magnesium (II), calcium (II), strontium (II), barium (II) perchlorates as well as beryllium (II), and sodium trifluoromethanesulfonates in methanol and dimethylsulfoxide have been determined over the composition range studied. From density data the apparent molar volumes and partial molar volumes of the salts at infinite dilution as well as the expansibilities have been evaluated. The apparent molar isentropic compressibilities of alkaline earth metal perchlorates and beryllium (II) and sodium triflates in methanol and DMSO have been calculated from sound speed data obtained at T = 298.15 K.     

The thermal decomposition of alkaline earth metal salicylates

The thermal decompositions of the salicylates of magnesium, calcium, strontium and barium were investigated using thermogravimetry and differential thermal analysis, together with the analysis of intermediate products formed during the decomposition processes. One intermediate product was isolated and identified during the decomposition of the magnesium salt, and two for each of the remaining metal salts.

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Zusammenfassung Die thermische Zersetzung der Salicylate von Magnesium, Calcium, Strontium und Barium sowie die Analyse der während des Vorganges gebildeten Zwischenprodukte wurden durch die thermogravimetrische und Differential-Thermal-Analyse untersucht. Im Verlaufe der Zersetzung des Magnesiumsalzes wurde ein Zwischenprodukt isoliert und identifiziert, bei den übrigen Metallsalzen je zwei.

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Résumé On a étudié par thermogravimétrie et analyse thermique différentielle la décomposition thermique des salicylates de magnésium, calcium, strontium et baryum et l'on a analysé les produits intermédiaires qui se forment pendant la décomposition. C'est ainsi que l'on a isolé et identifié un produit intermédiaire au cours de la décomposition du sel de magnésium et deux pour chacun des autres sels.

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Metal complex formation with dicarbonyl-ligands. Calculations on glyoxal complexes with alkali and alkaline earth metal ions

Ab initio MO SCF calculations on the complexes of Li, Na, K, Be, Mg and Ca ions with glyoxal have been performed. These calculations represent the first part of a series of theoretical investigations on the dependence of complex formation properties of ligands containing two carbonyl groups on the structure of the cordinative center. Special attention has been paid to the chelate effect, which is found to increase with increasing atomic number within the series of ions. The calculated values are compared with our recent data obtained from UV spectroscopy of ion complexes with dicarbonyl ligands.     

Quantitative parameters for the sequestering capacity of polyacrylates towards alkaline earth metal ions

The complex formation constants of polyacrylic (PAA) ligands (1.4≤log N≤2.4, N=number of monomer units) with calcium and magnesium ions were determined in different ionic media at different ionic strengths, 0≤I≤1 mol l⁻¹, at t=25 °C. Experimental pH-metric data in the presence of Ca²⁺ or Mg²⁺ were firstly analysed in terms of apparent protonation constants, log K^H*, using the “three parameter model” proposed by Högfeldt; differences in log K^H*, determined in different ionic media, were interpreted in terms of complex species formation. The only species present in the system M-PAA (M=Ca²⁺ or Mg²⁺) is ML₂: attempts to find species of different stoichiometry were unsuccessful. The stability dependence of this species on ionic strength, on the degree of neutralisation (α) and on PAA molecular weight is discussed using empirical equations. The formation constant, log β₂, is significantly higher for Ca²⁺ than for Mg²⁺: at I=0.1 mol l⁻¹ (NaCl), log N=1.8 and α=0.5, log β₂^Ca=4.43 and log β₂^Mg=4.24. The formation of polyacrylate-alkaline earth metal complexes is discussed in the light of sequestering effects in natural waters.     

Cation exchange, interlayer spacing, and thermal analysis of Na/Ca-montmorillonite modified with alkaline and alkaline earth metal ions

Na-montmorillonites were exchanged with Li⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, while Ca-montmorillonites were treated with alkaline and alkaline earth ions except for Ra²⁺ and Ca²⁺. Montmorillonites with interlayer cations Li⁺ or Na⁺ have remarkable swelling capacity and keep excellent stability. It is shown that metal ions represent different exchange ability as follows: Cs⁺?>?Rb⁺?>?K⁺?>?Na⁺?>?Li⁺ and Ba²⁺?>?Sr²⁺?>?Ca²⁺?>?Mg²⁺. The cation exchange capacity with single ion exchange capacity illustrates that Mg²⁺ and Ca²⁺ do not only take part in cation exchange but also produce physical adsorption on the montmorillonite. Although interlayer spacing d ₀₀₁ depends on both radius and hydration radius of interlayer cations, the latter one plays a decisive role in changing d ₀₀₁ value. Three stages of temperature intervals of dehydration are observed from the TG/DSC curves: the release of surface water adsorbed (36?C84?°C), the dehydration of interlayer water and the chemical-adsorption water (47?C189?°C) and dehydration of bound water of interlayer metal cation (108?C268?°C). Data show that the quantity and hydration energy of ions adsorbed on montmorillonite influence the water content in montmorillonite. Mg²⁺-modified Na-montmorillonite which absorbs the most quantity of ions with the highest hydration energy has the maximum water content up to 8.84%.     

Spectroscopic, thermal and antitumor investigations of sulfasalazine drug in situ complexation with alkaline earth metal ions

The complexes of sulfasalazine (H₃Suz) with some of alkaline metals Mg(II), Ca(II), Sr(II) and Ba(II) have been investigated. Sulfasalazine complexes were synthesized and characterized by spectroscopic tools; infrared spectra, electronic and mass spectra. The IR spectra of the prepared complexes were suggested that the H₃Suz behaves as a bi-dentate ligand through the carboxylic and phenolic groups. The molar conductance measurements gave an idea about the non-electrolytic behavior of the H₃Suz complexes. The thermal decomposition processes for metal(II) complexes of H₃Suz viz: [M(HSuz)(H₂O)₄] (where M = Mg(II), Ca(II), Sr(II) or Ba(II)) have been accomplished on the basis of TG/DTG and DTA studies, and the formula conforms to the stoichiometry of the complexes based on elemental analysis. The kinetic analyses of the thermal decomposition were studied using the Coats–Redfern and Horowitz–Metzger equations. The antitumor and antimicrobial activities of the H₃Suz and their alkaline metal(II) complexes were evaluated.     

Synthesis of chromogenic crown ethers and liquid—liquid extraction of alkaline earth metal ions

New crown ether dyes carrying two pendent anionic side-arms were synthesized for the extraction-spectrophotometry of alkaline earth metal ions. In the extraction of alkaline earth metal ions by these dianionic reagents, size recognition by the crown ether ring was more remarkable than in the case of alkali metal ion extraction by a similar type of monoanionic reagents. Dramatic changes in metal selectivity were observed when the nature of the anionic side-arm was changed while the crown ether skeleton was kept the same. The structure/selectivity relationship is discussed in terms of “chelate” and “intramolecular ion-pair” formation. Typically, when the basicity of the pendent anions was relatively high and a six-membered chelate was structurally possible for the pendent anions and the crown-bound metal, the extraction of calcium was favored by up to a factor of 3000 in the ratio of the Ca/Ba extraction constants for reagents of the diaza-18-crown-6 type. In contrast, the reagents which had pendent anions with only poor coordination ability for metal ions seemed to form complexes of the ion-pair type, and calcium ion was 10⁵ times less extractable than barium ion for the same diaza-18-crown-6-skeleton. Strontium ion seemed to be extracted most effectively when the extracted complex assumed properties intermediate between the chelate and intramolecular ion-pair.     

Luminescence of vanadium and rare earth ions in alkaline earth sulfates

The luminescence of samples MeSO₄V, RE (Me = Mg, Ca, Ba) depends strongly on the nature of the Me ions. The amount of association of the V⁵⁺ and RE³⁺ ions can be estimated from the measured quantum efficiencies.     

Selectivity of potassium cobalt hexacyanoferrate (II) for alkali and alkaline earth metal ions

The distribution coefficients for alkali and alkaline earth metal ions on potassium cobalt hexacyanoferrate (II), K₂CoFe(CN)₆×1.4H₂O, show high selectivity for cesium. The uptake values of the ions vary widely. The uptake is most probably an ion exchange process.     

Basicities of alumina-supported alkaline earth metal oxides

A series of alumina-supported alkaline earth metal oxide catalysts were prepared by incipient-wetness impregnation. These catalysts were characterized by nitrogen-sorption to determine their surface areas and pore size distributions. The basicities of these catalysts were characterized by temperature-programmed desorption of carbon dioxide. The TPD results demonstrate that all of the catalysts have one-peak profiles. The basicity increases with increasing atomic number of the alkaline earth metal. The alumina-supported alkaline earth oxides exhibit the same basic properties as bulk metal oxides. However, the presence of alumina can increase the mechanical strength of the catalyst, since the alkaline earth oxides have a weak mechanical strength. The basic properties of the catalysts are strongly influenced by the calcination temperature.     

Thermal stability of alkali metal borates and alkaline earth metal borates

The correlation between the enthalpies of formation of alkali metal and alkaline earth metal borates and the composition of the vapor in equilibrium with their melts is considered. The thermal stabilities of the studied borates have been estimated. A method is suggested for determination of the relative composition of the vapor over borate melts on the basis of their enthalpies of formation.

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Zusammenfassung Es wurde die Beziehung zwischen den Bildungsenthalpien von Alkali- (Erdalkali-)metallboraten und der Zusammensetzung der sich mit der Schmelze im Gleichgewicht befindlichen Gasphase betrachtet. Die thermische Stabilität der untersuchten Borate wurde geschätzt. Es wurde ein Verfahren entwickelt, die relative Zusammensetzung der Gasphase über Boratschmelzen auf Grund ihrer Bildungsenthalpien zu bestimmen.

     

Effective interaction potentials for alkali and alkaline earth metal ions in SPC/E water and polarization model of hydrated ions

In the first paper (J. Phys. Chem. B, 2006, 110, 10878), effective ion-ion potentials in SPC/E water were obtained for Me-Me, Me-Cl-, and Cl(-)-Cl- pairs, where Me is Li+, Na+, K+, Mg2+, Ca2+, Sr2+, and Ba2+ cations. In this second part of the study of effective interionic potentials, ion-ion distribution functions obtained from implicit-water Monte Carlo simulations of electrolyte solution with these potentials have been explored. This analysis verifies the range of applicability of the primitive model of electrolyte. It is shown that this approximation can be applied to monovalent electrolyte solutions in a wide range of concentrations, whereas the nature of ion-ion interactions is notably different for 2:1 electrolytes. An improved model of ions is discussed. The model includes approximations of the ion hydration shell polarization and specific short-range ion-ion interaction. It allows approximation of the potential of mean force acting on ions in strong electric fields of highly charged macromolecules and bilayers.