Layered hydrous manganese dioxide saturated with alkaline-earth cations: Synthesis and sorption properties

Layered compounds based on hydrous manganese dioxides (hereafter, Mn-phases) saturated with alkaline-earth cations were synthesized at 3–6°C. These phases are analogues of manganese minerals from oceanic iron-manganese sediments (vernadite, birnessite, buserite-I, an asbolan-like phase, and a hybrid phase). All the Mn-phases, as a rule, had poorly ordered structures. The sorption properties of these phases were studied with respect to alkali-metal cations (Na⁺, K⁺), an s-metal cation (Ba²⁺), a p-metal cation (Pb²⁺), and d-metal cations (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Cd²⁺). The exchange capacities of the Mn-phases were 0.45–1.06 mg-equiv/g for the alkali cations and 0.94–5.78 mg-equiv/g for the other cations. The phase composition of the Mn-phase did not affect the alkali cation sorption but affected the divalent cation sorption. The divalent cation exchange capacity increased from well-ordered birnessite to poorly ordered vernadite.     

Synergistic effects of macrocyclic polyethers and converging anionic binding sites : Synthesis of biphenyl crown ethers and lipophilization of divalent cations

The synthesis of nine novel macrocyclic polyethers with a 1,1'-biphenyl subunit is described. Crown ethers 2,4,5 and 7 have substituents with terminal acid groups at the 4- and 4'- positions of the 1,1'-biphenyl subunit and crown ethers 9, 11, 12 and 14 have similar substituents at the 3- and 3'-positions. In the ionic form these crown ethers extract divalent cations (Ca²⁺, Sr²⁺ and Ba²⁺) from basic aqueous solutions into chloroform. The degree of lipophilization varies with the size of the cation and of the crown ether cavity, with the position and the length of the substituents and with the nature of the terminal acid groups. ¹H NMR spectroscopic data of the complexes in chloroform are in agreement with a structure of the complexes in which the cation is encapsulated by oxygen atoms and anionic groups.     

Effect of ring annelation on cations [M = H+, Li+, Na+, K+, Be2+, Mg2+, and Ca2+]…benzene interaction: A density functional theory investigation

Density functional theory calculation was carried out on cation‐π complexes formed by cations [M = H⁺, Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺] and π systems of annelated benzene. The cation‐π bonding energy of Be²⁺ or Mg²⁺ with annelated benzene is very strong in comparison with the common cation‐π intermolecular interaction, and the bonding energies follow the order Be²⁺ > Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺ > K⁺. Similarly, the interaction energies follow the trend 1‐M < 2‐M < 3‐M for all the metal cations considered. These outcomes may be due to the weak interactions of the metal cations with C? H and the interactions of metal cations with π in addition to the nature of a metal cation. We have also investigated on all the possible substituted sites, and find that the metal ion tends to interact with all ring atoms while proton prefers to bind covalently to one of the ring carbons. The binding of metal cations with annelated benzenes has striking effect on nuclear magnetic resonance chemical shifts using the gauge independent atomic orbital method. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Origin of the quadrupole splitting in the Mössbauer 57Fe spectrum of cubic (disordered) LiFeO2

The room-temperature Mössbauer ⁵⁷Fe spectrum of polycrystalline disordered cubic α-LiFeO₂ contains a quadrupole splitting |Δ_obs| of 0.65(2) mm/sec. This value is relatively large for an Fe atom in an essentially Fe³⁺_HS state. To account for its magnitude, the distribution of the electric-field gradient (EFG) values associated with the Fe atoms was investigated by means of exact geometric analysis involving the 12 nearest cation neighbors (model A) as well as large-scale computer simulation involving more distant cations (models B to E). It is found that (1) the major contribution to |Δ_obs| comes from the distribution of +1 and +3 charges among the 12 nearest cation neighbors of a reference Fe atom; (2) this contribution by itself largely accounts for |Δ_obs|; (3) the contribution from cations beyond the seventh-nearest neighbors is marginal; (4) displacing the oxygen atoms from their lattice sites toward adjacent Fe atoms produces a significant effect on the distribution of EFG values at a reference Fe atom, while incipient cation ordering appears to have a relatively small effect; and (5) the contribution of the EFG = 0 component to model |EFG| distributions will be overemphasized unless cations beyond the first-nearest neighbors are included in the EFG summation. The 144 distinct (up to rotation and reflection) Li¹⁺_12?kFe³⁺_k configurations on the coordination cuboctahedron of nearest cation neighbors (required for the examination of model A) are listed, together with their symmetries and multiplicities, and it is shown that the 144 configurations engender only 17 distinct |EFG| values. Observations are also made on various geometric aspects of calculating EFG at ⁵⁷Fe³⁺_HS on cubic lattices.     

Theoretical study on the interaction of glutathione with group IA (Li+, Na+, K+), IIA (Be2+, Mg2+, Ca2+), and IIIA (Al3+) metal cations

The structures and energies of complexes obtained upon interaction between glutathione (GSH) and alkali (Li⁺, Na⁺, K⁺), or alkaline earth metal (Be²⁺, Mg²⁺, Ca²⁺), or group IIIA (Al³⁺) cations were studied using quantum chemical density functional theory. The characteristics of the interactions between GSH and the metal cations at different nucleophilic sites of GSH were examined selecting systematically, both mono- and multi-coordinating were taken into account. The results indicated that the heteroatom of GSH, the radius and charge of metal ion, and the coordination number of the metal cation with the ligand played important roles in determining the stability of these complexes. Moreover, the intramolecular hydrogen migration in GSH could be promoted by the metal cations during coordination reaction. Furthermore, the Al³⁺ cation might catalyze the decarboxylation reaction and stimulate the formation of covalent bond between S atom and adjacent O atom of GSH.     

Crown-containing butadienyl dyes 8. Structures and complexation of chromogenic dithia-15(18)-crown-5(6) ethers

The structures of new butadienyl dyes of the benzothiazole series containing the dithia-15-crown-5 (2a) or dithia-18-crown-6 (2b) fragments were established by X-ray diffraction. Complexation of dyes 2a,b with Hg²⁺, Pb²⁺, Cd²⁺, Ag⁺, Zn²⁺, and alkaline-earth cations in aqueous-acetonitrile solutions was studied by spectrophotometry. At a high percentage of water in solutions (P _w ≈ 50%), these dyes have a very low ability to bind Pb²⁺ cations (logK < 2) and virtually do not bind Cd²⁺, Zn²⁺, and alkaline-earth cations. At the same time, these dyes form stable 1: 1 complexes with Hg²⁺ and Ag⁺ cations at all P _w. The stability constants of complexes with the Ag⁺ cation increase with increasing P _w because the free energy of hydration of this cation is much lower than the free energy of solvation in acetonitrile. In the P _w range from 0 to 75%, the stability constants of the complexes of dyes 2a,b with the Hg²⁺ cation are larger than those of the corresponding complexes with the Ag⁺ cation by more than four orders of magnitude. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 90–96, January, 2006.     

Pentavalent Neptunyl ([O≡Np≡O]<Superscript>+</Superscript>) Cation–Cation Interactions in Aqueous/Polar Organic Mixed-Solvent Media

Bonding interactions between polyvalent cations and oxo-anions are well known and characterized by predictably favorable Gibbs energies in solution-phase coordination chemistry. In contrast, interactions between ions of like charge are generally expected to be repulsive and strongly influenced by cation solvation. An exception to this instinctive rule is found in the existence of complexes resulting from interactions of pentavalent actinyl cations ([O≡An≡O]⁺) with selected polyvalent cations. Such cation–cation complexes have been known to exist since the 1960s, when they were first reported by Sullivan and co-workers. The weak actinyl cation–cation complex, resulting from a bonding interaction between a pentavalent linear dioxo actinyl cation donor and hexavalent actinyl or trivalent/tetravalent metal cation acceptor, has been most commonly seen in media in which water activities are reduced, principally highly-salted aqueous media. Such interactions of pentavalent actinides are of relevance in ongoing research that focuses on advanced nuclear fuel processing systems based on the upper oxidation states of americium. This investigation focuses on exploring the thermodynamic stability of complexes between selected highly-charged metal cations (Al³⁺, Sc³⁺, Cr³⁺, Fe³⁺, In³⁺ and \( {\text{UO}}_{2}^{2 + } \)) and the pentavalent neptunyl cation (\( {\text{NpO}}_{2}^{ + } \), whose coordination chemistry is similar to that of \( {\text{AmO}}_{2}^{ + } \) while exhibiting significantly greater oxidation state stability) in aqueous–polar organic mixed-solvents. The Gibbs energies for the cation–cation complexation reactions are correlated with general features of electrostatic bonding models; the \( {\text{NpO}}_{2}^{ + } \cdot {\text{Cr}}^{3 + } \) complex exhibits unexpectedly strong interactions that may indicate significant covalency in the cation–cation bonding interaction.     

Untersuchungen an Oxidischen Katalysatoren. XXX [1] Charakterisierung der Me2+ -Kationenlokalisierung in CaNaY-, MgNaY- und CaMgNaY-Zeolithen

Studies on Oxide Catalysts. XXX. Characterization of the Me²⁺ Localization in Zeolites CaNaY, MgNaY, and CaMgNaY Data for exchange of the cations Ca²⁺, Mg²⁺, as well as Ca²⁺ and Mg²⁺ into the zeolite NaY have been determined. From this it was concluded on the localization of Me²⁺ cations in hydrated samples. The adsorption of ammonia in the temperature region of 420 to 670 K, the determination of the heats of immersion in water and nitromethane and the Me²⁺ ? CO-interaction indicated by IR spectroscopy yielded informations on the localization of cations in dehydrated samples. The results show that cations Ca²⁺ more selectively than cations Mg²⁺ occupy positions in the small cages. In the case of the competitive cation exchange this fact causes a site directed distribution of cations in zeolite cages.     

Molecular Machines: Stimulation of Cation Motion in Molecular Switches

The theoretical aspects of the mechanism of the motion of cations and ligands in molecular machines referred to as redox switches are presented. The interrelated properties of cations—the energetic, electrochemical, spectral, and magnetic properties; their propensity to form either covalent or ionic bonds; and the relative softness and hardness of cations and ligands—stimulate molecular motion. These properties determine the thermal stability and stability to destruction caused by electrochemical processes and, eventually, the maximal number of transformation cycles. The maximal efficiency of redox switches is attained when the redox reaction involves a cation with a half-filled (d ⁵, f ⁷) or complete (d ¹⁰, f ¹⁴) electronic shell. The role of the Jahn-Teller effect is considered: it is responsible for geometry distortion, which stimulates cation motion. The properties of nd and 4f cations are compared from the standpoint of their use for designing redox switches. In switches constructed on the basis of supramolecular compounds containing hard and soft moieties, softer cations (Fe²⁺, Co²⁺, Cu⁺, etc.) prefer to coordinate to soft ligands and harder cations (Fe³⁺, Co³⁺, Cu²⁺, etc.) prefer to coordinate to hard ligands. A cation moves due to the soft-hard change of its coordination sphere in the course of the redox reaction. Design of redox switches based on solid compounds with a cation in mixed oxidation state is shown to be promising. Cations can change their oxidation state with a change in temperature or pressure. The possibility of designing “magnetic switches” is considered.     

Spectroscopic Study of Azo- and Azoxycrowns Binding with Cations of Similar Ionic Radius

The complexation of 13- and 16-memberedazo- and azoxycrowns with metal cations of similarionic diameter (Na⁺ and Ca²⁺; and K⁺,Ba²⁺, Ag⁺ and Pb²⁺) was studied byuv/visible spectroscopic titration in acetonitrile andMeOH. In MeOH the 13-membered azo- and azoxycrowns 1 and 2 are weakly and non-selectively bound tohard cations of similar ionic diameter, but differentcharge (Na⁺ and Ca²⁺). At the same time thebinding to the soft cation Ag⁺ of larger sizethan the macrocycle cavity is considerably stronger.In contrast to solutions in acetonitrile no bindingwith the small Li⁺ cation was found.The 16-membered azocrowns 3 and 4 alsodiscriminate silver cation in MeOH withlog K = 3.65 ± 0.1 for both compounds.Unexpectedly low bindingwith the hard barium divalent cation of similar size(log K = 1.55 ± 0.4 and 1.95 ± 0.2, respectively)was found for these compounds. Similarly to13-membered compounds no binding with the smallLi⁺ cation was detected. A reverse order ofselectivity was observed for these crowns inacetonitrile with binding constant for association of3 with Ba²⁺ (log K 5.3) considerablyhigher than for other cations. The previously observedstrong binding with the smaller Li⁺ and Na⁺cations is confirmed.     

Macrocyclic pyridone pentamer‐modified polystyrene nanofiber for selective metal ion removal from aqueous solution

Macrocyclic pyridone pentamer‐functionalized nanofiber was fabricated through electrospinning for selective heavy metal cation removal from aqueous solution. Parameters influencing the adsorption process, including contact time, initial metal cation concentration, and solution pH, were evaluated, and the optimized adsorption condition was figured out accordingly. The adsorption study demonstrated that the process followed the pseudosecond‐order kinetic models and Langmuir isothermal model. The selectivity of the nanofiber toward metal cations was studied, and it was found that it showed a high adsorption affinity toward Pb²⁺ over other metal cations such as Cu²⁺, Ca²⁺, Co²⁺, Zn²⁺, and Ni²⁺. The nanofiber could be easily regenerated by deadsorption with ethylenediaminetetraacetic acid solution. The above results indicate the potential application of the nanofiber in the metal cation separation field.     

Effect of metal cations on corrosion behavior and surface film structure of the A3003 aluminum alloy in model tap waters

The effect of the metal cations, Na⁺, K⁺, Ca²⁺, Mg²⁺, Zn²⁺, and Ni²⁺, on the oxide film structure and morphology changes during long-term immersion corrosion tests of aluminum alloy (A3003) in model tap waters was investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy. The effect of the metal cations on the corrosion behavior was also investigated with mass change and electrochemical tests. The hardness of the metal cations, X, based on the hard and soft acids and bases (HSAB) concept was applied to explain the effect of metal cations on the passive oxide film structure and corrosion resistance. The mass change rate and corrosion current density decreased with increasing metal cation hardness. The XPS results showed that hard metal cations like Zn²⁺ and Ni²⁺ were incorporated in the oxide films, while the four soft metal cations were not incorporated in the oxide films. The results are in good agreement with those which could be expected from the HSAB hardness of the metal cations.     

A model for cation adsorption to clays and membranes

A cation adsorption model is presented and its recent applications are discussed. The model combines electrostatic equations with specific binding, and considers neutral and positively charged complexes between the negative surface sites and organic cations in a closed system. Extensions in the model account for dye aggregation in solution, and for the formation of solution complexes of inorganic cations, such as [M⁺⁺ Cl^–]⁺. The amounts of 45Ca²⁺ adsorbed to vesicles extracted from the plasma membranes of melon root cells could be adequately simulated and predicted. The binding coefficients determined for Ca²⁺, Na⁺, and Mg²⁺ are in the range of values previously deduced for binding to phospholipid components. Model calculations were applied to the test of hypotheses on the effect of salt stress on the growth of roots. The adsorption of monovalent organic cations to montmorillonite is characterized by binding coefficients that are at least six orders of magnitude larger than those of Na⁺, Mg²⁺, Ca²⁺, and Cd²⁺, or those of CdCl⁺ or CaCl⁺. Monovalent organic cations were found to adsorb 140–200% of the cation exchange capacity of the clay and to cause charge reversal. Deductions from adsorption results of acriflavin are consistent with those drawn from the application of other experimental methods. Preliminary results on the adsorption of divalent organic cations are presented. Agro-environmental applications of organo-clays are discussed.     

Interaction of divalent metal cations and nucleotides: A computational study

In this study, the anionic phosphate group of nucleotides was found to be the best site to bind the divalent metal cations Be²⁺, Mg²⁺, Zn²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ to form the most stable complexes. Molecular orbital calculations at the semiempirical level were performed on nucleotidemetal cation complexes to report energies of complexation reactions, geometrical parameters of complexes and charge distributions on the complexes. In the discussion, complexational preferences of divalent metal cations, the charge transfer involved in the binding of the metal cations to the phosphate anion of the nucleotides and their conformational effects are included.     

Sorption of transition metal cations on natural heulandite

The cation exchange equilibrium in the systems of natural heulandite-binary aqueous solutions of NaCl, NiCl₂, CuCl₂, ZnCl₂, and MnCl₂ was studied. The corrected coefficients of the selectivity (k ^a _M/Na) and thermodynamic constants (K _M/Na) of the cation exchange of Na⁺ cations for transition metal cations were determined. The selectivity of the cation exchange on natural heulandite increases in the following order: Ni²⁺ < Cu²⁺ < Zn²⁺ < Na²⁺ < Mn²⁺.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1101–1103, May, 1996.     

How Divalent Cations Interact with the Internal Channel Site of Guanine Quadruplexes

The formation of guanine quadruplexes (GQ) in DNA is crucial in telomere homeostasis and regulation of gene expression. Pollution metals can interfere with these DNA superstructures upon coordination. In this work, we study the affinity of the internal GQ channel site towards alkaline earth metal (Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺), and (post-)transition metal (Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺) cations using density functional theory computations. We find that divalent cations generally bind to the GQ cavity with a higher affinity than conventional monovalent cations (e. g. K⁺). Importantly, we establish the nature of the cation-GQ interaction and highlight the relationship between ionic and nuclear charge, and the electrostatic and covalent interactions. The covalent interaction strength plays an important role in the cation affinity and can be traced back to the relative stabilization of cations’ unoccupied atomic orbitals. Overall, our findings contribute to a deeper understanding of how pollution metals could induce genomic instability.     

Highly efficient and selective membrane transport of silver(I) using 15-crown-5 as a selective ion carrier

Selective transport of Ag⁺ cation through a nitrobenzene bulk liquid membrane with 15-crown-5 as an efficient carrier was studied. The maximum transport value of 88.02 ± 0.78% was observed for Ag⁺ ion after 8 h at Ag⁺ concentration of 4 × 10^?4 M. The selectivity and efficiency of Ag⁺ cation transport from aqueous solutions containing equimolar amounts of Cr³⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, and Pb²⁺ cations were also investigated.     

Cation transport at 25°c from binary Na+Mn+, Cs+Mn+ and Sr2+Mn+ nitrate mixtures in a H2OCHCl3H2O liquid membrane system containing a series of macrocyclic carriers

Cation fluxes from binary mixtures of either Na⁺, Cs⁺ or Sr²⁺ with other alkali metal cations, alkaline earth metal cations, and Pb²⁺ through a H₂OCHCl³H₂O bulk liquid membrane system containing one of several macrocyclic carriers have been determined Nitrate salts were used in all cases. The most selective transport of Na⁺ over all other cations studied was found with the carrier cryptand [2.2.1]. Selective transport of Na⁺ relative to Li⁺, Cs⁺ and the alkaline earth cations was found with cryptand [2.2.2B] and cryptand [2.2.2D]. The ligands 21-crown-7 and dibenzo-24-crown-8 showed selective transport of Cs⁺ over the second cation in all cases. Several macrocycles showed selectivity for Sr²⁺ over the second cation with the macrocycle 1,10-diaza-18-crown-6 showing the highest selectivity for this cation of all ligands studied. Relative fluxes from binary cation mixtures are rationalized in terms of macrocycle cavity size, donor atom type and ring substituents.     

An insight into aggregation kinetics of polystyrene nanoplastics interaction with metal cations

Once inevitably released into the aquatic environment, polystyrene nanoplastics (PS-NPs) will present complicated environmental behaviors, of which the aggregation is a key process determining their environmental fate and impact. In this study, the aggregation kinetics of different sizes (30 nm and 100 nm) of PS-NPs with metal cations (Na⁺, K⁺, Ca²⁺, Mg²⁺ and Pb²⁺) at different solution pH (3, 6 and 8) were investigated. The results showed that the aggregation of PS-NPs increased with cation concentration. Taking Pb²⁺ as an example, the adsorption behavior of cations onto PS-NPs was determined by transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) spectroscopy, which demonstrated Pb²⁺ could be adhered onto the surface of PS-NPs with the effect of charge neutralization. The critical coagulation concentrations (CCC) of smaller PS-NPs were higher than that of larger PS-NPs for monovalent cations, whereas a different pattern is observed for divalent cations. It was suggested that there were other factors that DLVO theory does not consider affect the stability of NPs with different particle sizes. In addition, it should be noted that PS-NPs had the capacity of adsorbing large amounts of heavy metal cations and carried them transport to a long distance, and the corresponding ecological risks need to further elucidate.     

Polarographic and voltammetric investigations in N-methylpyrrolidinone(2) and N-methylthiopyrrolidinone(2)

Polarographic and voltammetric methods were employed to study the influence of N-methylpyrrolidinone(2) (NMP) and N-methylthiopyrrolidinone(2) (NMTP) towards a series of cations. In NMP reversible electrode reactions were observed for Na⁺, K⁺, Tl⁺, Zn²⁺, Cd²⁺, Cu²⁺, Ag⁺ and irreversible reductions for Ba²⁺, Mn²⁺, Co²⁺ and Ni²⁺. 0.1 mol l^?1 tetraethylammoniumperchlorate solutions served as supporting electrolytes. Li⁺ was not electroactive in the supporting electrolyte mentioned, but yielded an irreversible cathodic wave in tetra-n-butylammonium perchlorate. In NMTP, Li⁺, Na⁺, Tl⁺, Zn²⁺, Cd²⁺, Cu⁺ and Ag⁺ gave reversible cathodic waves on the DME, while Mn²⁺, Co²⁺ and Ni²⁺ were reduced in an irreversible electrode process. Bisbiphenylchromium iodide serving as a reference system throughout this study showed reversible behaviour in both solvents. A comparison of E_1/2 for given ions in both solvents showed a shift of about 0.5 V to more positive values in the case of a typically hard cation such as Na⁺ whereas soft cations such as Ag⁺ and Cu⁺ shifted by more than 0.8 V to more negative values. The effects of these two solvents on the cations studied is discussed in terms of donor acceptor interactions between the cation and the solvent molecules with special respect to the changes caused by replacing the oxygen atom in NMP by a sulphur atom.