A theoretical prediction on the ground‐state complexes bound by metal ions to thymine base isomers

Stability orderings of 150 stable complexes formed by metal ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, and Zn²⁺) and 13 stable thymine tautomers in both solvent and gas phases are obtained, and the optimal binding site for a metal ion in a specific thymine tautomer is identified. Results indicate that the complex with the canonical thymine tautomer (T1) is more stable than those with the rare ones, and the monodentate complex M–T1o4(o2) are their ground‐state form in the solvent phase. The ground‐state thymine complexes bound by Ca²⁺, Mg²⁺, or Zn²⁺ become bidentate M–T3o4lo2,n3, which is derived from a rare thymine tautomer T3o4l, whereas those bound by Na⁺ and K⁺ are still monodentate complexes M–T1o4(o2), however, in the gas phase. The differences in stability are discussed in detail from the binding strength of metal ions, relative energy of the corresponding thymine tautomers, and solution effect. Copyright © 2011 John Wiley & Sons, Ltd.     

Interaction studies of cysteine with Li+, Na+, K+, Be2+, Mg2+, and Ca2+ metal cation complexes

The coordination geometries, electronic features, metal ion affinities, entropies, and the energetics of Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺ metal cations with different possible conformations of cysteine complexes were studied. The complexes were optimized using density functional theory (B3LYP) and second order Moller–Plesset Perturbation (MP2) theory methods using 6‐311 + +G** basis set. The interactions of the metal cations at different nucleophilic sites of cysteine conformations were considered after a careful selection among several binding sites. All the metal cations coordinate with cysteine in a tridentate manner and also the most preferred position for the interaction. It is found that, the overall structural parameters of cysteine are not altered by metal ion substitution, but, the metal ion‐binding site has undergone a noticeable change. All the complexes were characterized by an electrostatic interaction between ligand and metal ions that appears slightly more pronounced for lithium and beryllium metal complexes. The metal ion affinity (MIA) and basis set superposition error (BSSE) corrected interaction energy were also computed for all the complexes. The effect of metal cations on the infrared (IR) stretching vibrational modes of amino N? H bond, side chain thiol group S? H bond, hydroxyl O? H bond, and Carbonyl C?O bond in cysteine molecules have also been studied. The nature of the metal ion‐ligand bond and the coordination properties were examined using natural bond order (NBO) at bond critical point (electron density and their Laplacian of electron density) through Atoms in Molecules (AIM) analyses. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental and theoretical insight into the cooperativity effect in composite wax powder and ternary complex of coronene with CH4 and Mn+ (Mn+ = Li+, Na+, K+, Be2+, Mg2+ or Ca2+)

The experimental infrared (IR) spectrum of composite wax powder was investigated. The frequency shifts of the C=C anti-symmetrical stretching mode were observed and the experimental cooperativity effect involving Na⁺···π interaction was suggested. In order to further reveal the nature of cooperativity effect, the interaction energies in Mⁿ⁺···coronene···CH₄ (Mⁿ⁺ = Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺ or Ca²⁺) as the model systems of composite wax powder were calculated by using the B3LYP, M06-2X and MP2 methods with 6-311++G^** basis set. The results show that the Mⁿ⁺···π interactions were strengthened upon the formation of ternary complexes. Although the changes of absolute values of the interactions between CH₄ and coronene were not obvious, the relative values were considerably significant upon the formation of ternary complexes. The cooperativity effect was perhaps the reason for the formation of notable advantage of composite wax powder upon the introduction of surfactant with cation into wax powder. Reduced density gradient and atoms-in-molecules analysis confirm the cooperativity effect in Mⁿ⁺···coronene···CH₄, and reveal the nature of the formation of the predominant advantage of composite wax powder.     

Spectroscopic Study of Some Alkali and Alkaline Earth Complexes with Benzo Crown Ethers in Ethanol Solution

The interaction between Na⁺, K⁺, Mg²⁺ and Ca²⁺ ions and benzo crown ethers B15C5, DB18C6, DB21C7, DB24C8 and DB30C10 in ethanol solution has been studied spectrophotometrically at 25°C. The formation constants for 1:1 complexes were determined by computer fitting of the resulting UV-absorbance-mole ratio data. In the case of all crown ethers used, K⁺ ion was found to form the most stable complexes. The observed selectivities of different benzo crowns for the cations used are discussed in terms of the cavity-cation size ratio, number of the donating oxygens participating in the cation binding, conformations of the free and complexed ligands and ionic solvation.     

Ion exchange equilibrium between cation exchange membranes and aqueous solutions of K+/Na+, K+/Ca2+, and Na+/Ca2+

Equilibrium between synthetic ion exchangers and solutions of cations has been the subject of this investigation. Competitive ion exchange reactions were studied for two cation exchange membranes (CMX and CRP) involving K⁺, Na⁺, and Ca²⁺ ions. The ionic strength of the equilibrating solutions was maintained constant, but the molar fraction varied; all experiments were conduced with nitrate as nonexchanging anions at 25 °C. Adsorption isotherm for the three binaries systems: K⁺/Na⁺, K⁺/Ca²⁺, and Na⁺/Ca²⁺ were studied. The obtained results show that potassium was the most strongly sorbed and the selectivity order for CMX and CRP membranes is K⁺>Ca²⁺>Na⁺ at 0.1 M, under the experimental conditions. Selectivity coefficients , , and for the three binaries and for the two membranes were determined at an ionic strength of 0.1 M and at a constant temperature of 25 °C. We remark that all the selectivity coefficient values are quite different from the unit. Ternary equilibrium was taken for the Ca²⁺/K⁺/Na⁺ system. It was found that binary selectivity data could be successfully used to predict the ternary ion exchange equilibrium.     

Swelling of K+, Na+ and Ca2+-montmorillonites and hydration of interlayer cations: a molecular dynamics simulation

This paper performs molecular dynamics simulations to investigate the role of the monovalent cations K, Na and the divalent cation Ca on the stability and swelling of montmorillonite. The recently developed CLAYFF force field is used to predict the basal spacing as a function of the water content in the interlayer. The simulations reproduced the swelling pattern of these montmorillonites, suggesting a mechanism of their hydration different (K+ 相似文献   

INDIRECT METAL ION (K+, NA+, MG2+, AND CA2+) QUANTIFICATION FROM INFRARED SPECTROSCOPY

ABSTRACT

In this paper, we report the use of Mid-FTIR spectroscopy coupled with Partial Least Squares method for the quantitative determination of various alkaline and alkaline earth metals in aqueous solution owing to their interactions with sucrose. First of all, prediction equations that linked cation concentration to the spectral data were established independently for each ion (K⁺, Na⁺, Mg²⁺ or Ca²⁺): very high correlation coefficient values between the two first axes and the chemical values were obtained. Moreover, a good prediction could be made whatever the nature of ion involved in interaction with sucrose. Then, all spectral data have been gathered for generating a common prediction equation. In this case, the predictions of metal ion concentration are almost as much accurate. For both regression models, Mg²⁺ appears to provide the best precision in quantification. Nevertheless, the different types of aqueous solution, regarding to ions, can be discriminated on the basis of their spectral data set up with the three mostly correlated axes of the PCA.     

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.     

Interplay between the intramolecular hydrogen bonds and cation–π interactions in various complexes of salicylaldehyde,thiosalicylaldehyde and selenosalicylaldehyde with Li+, Na+, K+, Mg2+ and Ca2+ cations

For the first time, the mutual influences of the intramolecular hydrogen bond (IMHB) and cation–π interactions in various complexes of salicylaldehyde, thiosalicylaldehyde and selenosalicylaldehyde with Li⁺, Na⁺, K⁺, Mg²⁺ and Ca²⁺ cations were studied. First, the strength of IMHB and cation–π interactions of the mentioned complexes by energetic, geometrical, spectroscopic, topological and molecular orbital parameters was evaluated and compared with the corresponding results of benzene–cation complexes and salicylaldehyde analogues. The results show that the coexistence of IMHB and cation–π interactions increases the IMHB strength and decreases the cation–π interactions. Second, the significance of π–electron delocalisation (π–ED) within the resonance-assisted hydrogen bond (RAHB) unit and aromaticity of benzene ring in the studied complexes were estimated by using the harmonic oscillator model of aromaticity and compared with the respective amounts of references. The results indicated that the mentioned coupling decreases the π–ED of RAHB unit and aromaticity of the benzene ring. In addition, it was found that variations in the strength of the interactions, π–ED and aromaticity, depend on the charge-to-radius ratio of cations. Finally, the effects of replacement of O by S and Se atoms in both of the mentioned cases were explored.     

Luminescent Cu2+ Probes Based on Rare-Earth (Eu3+ and Tb3+) Emissive Transparent Cellulose Hydrogels

Cellulose hydrogels are biodegradable materials that can be applied as accommodating hosts for various species. Here we report the preparation of novel thin films based on luminescent cellulose hydrogels. The spectroscopic behavior of these soft materials and their sensing effects are investigated. Interestingly, we found that these films only give selective signal changes in the presence of Cu²⁺ in water in comparison with Na⁺, K⁺, Ag⁺, Mn²⁺, Co²⁺, Ca²⁺, Cd²⁺, Hg²⁺, Pd²⁺, Mg²⁺, Ni²⁺, Fe²⁺, and Fe³⁺. High visible-light transmittance and good flexibility for these films can be observed. More importantly, the thermal stability of rare-earth complexes could be significantly enhanced in aqueous solution as result of the protection by hydrogel matrix.     

Density functional theory study of the bis‐3‐benzo‐crown ethers and their complexes with alkali metal cations Na+, K+, Rb+ and Cs+

The binding interactions of bis‐3‐benzo‐15‐crown‐5 ethers and bis‐3‐benzo‐18‐crown‐6 ethers (neutral hosts) with a series of alkali metal cations Na⁺, K⁺, Rb⁺ and Cs⁺ (charged guests) were investigated using quantum chemical density functional theory. Different optimized structures, binding energies and various thermodynamic parameters of free crown ethers and their metal cation complexes were obtained based on the Becke, three‐parameter, Lee–Yang–Parr functional using mixed basis set (C, H, O, Na⁺ and K⁺ using 6‐31 g, and the heavier cation Rb⁺ and Cs⁺ using effective core potentials). Natural bond orbital analysis is conducted on the optimized geometric structures. The main types of driving force host–guest interactions are investigated. The electron donating O offers a lone pair of electrons to the contacting LP* (1‐center valence antibond lone pair) orbitals of metal cations. The bis‐3‐benzocrown ethers are assumed to have sandwich‐like conformations, considering the binding energies to gauge the exact interactions with alkali cations. It is found that there are two different types of complexes: one is a tight ion pair and the other is a separated ion pair. Copyright © 2011 John Wiley & Sons, Ltd.     

Interaction of cations with 2′‐deoxythymidine nucleoside and analysis of the nature and strength of cation bonds

Binding of Mg²⁺, Ca²⁺, Zn²⁺, and Cu⁺ metal ions with 2′‐deoxythymidine (dT) nucleoside was studied using a density functional theory method and a 6‐311++G(d,p) basis set. This work demonstrated that the interaction of dT with these cations is tri‐coordinated η (O2, O4′, O5′). Among the four types of cations, Zn²⁺ cation exhibited the most tendency to interact with the dT. Cations via their interaction with dT can affect the N‐glycosidic bond length, the values of pseudorotation of the sugar ring, the orientation of the base unit with respect to the sugar ring, and the acidity of the O5′H, O3′H, and N3H groups in the dT nucleoside. Natural bond orbital analysis was performed to calculate the charge transfer and natural population analysis of the complexes. Quantum theory of atoms in molecules was also applied to determine the nature of interactions. It was shown that in dT–Mg²⁺ and dT–Ca²⁺ complexes, the bonds are electrostatic (closed‐shell) interactions, although they are partially covalent and partially electrostatic interactions in dT–Zn²⁺ and dT–Cu⁺ complexes. Copyright © 2011 John Wiley & Sons, Ltd.     

Spectroscopic properties, energy transfer and structural analysis of Sr2CeO4:M+ and Sr2CeO4:Eu3+, M+ (M+ = Li+, Na+, K+)

The room-temperature luminescent emission characteristics of Sr₂CeO₄:M⁺ and Sr₂CeO₄:Eu³⁺,M⁺ (M⁺ = Li⁺, Na⁺, K⁺) have been investigated under UV excitation. By introducing appropriate alkali metal cations dopants (Li⁺, Na⁺, K⁺) into the crystalline lattice, not only emission color of the blue-white-emitting Sr₂CeO₄ doped with low Eu³⁺ content can be tuned to green, but also the red emission intensity of Sr₂CeO₄ doped with high Eu³⁺ concentration is strengthened significantly. The relevant mechanisms have been elucidated in detail.     

Theoretical kinetics study of thymine tautomerism and interaction of Na+ with its tautomers

The current work is a theoretical study of the tautomerism of thymine in the gas phase. Eighteen structures were found in the isomerisation reaction of thymine, some of which are reported for the first time. Thirty hydrogen transfer reactions were carried out. In 24 of the reactions, the hydrogen abstractions N―H→O, N―H→C and C―H→O were considered. The potential energy surface for all trajectories was determined for 18 tautomers and 40 transition states. The RRKM-TST model was used to calculate the rate constants of the reactions to examine their kinetics. Nonlinear least-squares fitting was used to calculate the rate constants expressions. The interaction of sodium ion and tautomers in the gas phase was also investigated. Three types of interaction of metal cations with thymine were found. In the first, metal cations interact with a lone pair of nitrogen or oxygen tautomers. The second type is the interaction of metal cations with two nitrogen and oxygen of tautomers. The last type is the interaction of metal cations and the electron density of the π-system of thymine in which the metal ion is perpendicular to the ring of tautomers. The stability ranking of the thymine tautomers and their complexes was also determined.     

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.     

Density functional investigation of metal encapsulated X@C12Si8 heterofullerene (X=Li, Na, K, Be, Mg, Ca, Al, Ga)

The stability and the possible application of our recently reported SiC heterofullerenes inspire the investigation of their further stabilization through ion encapsulation. The endohedral complexes X@C₁₂Si₈, where X=Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, Ca²⁺, Al³⁺, and Ga³⁺, are probed at the MPWB1K/6-311G? and B3LYP/6-311G* levels of theory. The optimized geometries show the expanding or contracting capability of C₁₂Si₈ in order to accommodate metal ion guests. The inclusion energies indicate the stability of the complexes compared to the components. Meanwhile, the calculated binding energies show the stabilization of C₁₂Si₈ through the inclusion of Be²⁺, Mg²⁺, Al³⁺, and Ga³⁺. The host-guest interaction that is probed through NBO atomic charges supports the obtained results. This study refers to “metal ion encapsulation” as a strategy for stabilization of SiC heterofullerenes.     

Stability of aqueous silica nanoparticle dispersions

In this study, we present quantification methods for nanoparticle stability analysis using non-intrusive analytical techniques: attenuated total reflectance, Fourier transform infrared (ATR-FTIR) spectroscopy, ultraviolet–visible (UV–vis) spectrophotometer, zeta potential analyses, and dynamic light scattering (DLS). We use these techniques to study the stability of silica nanoparticle dispersions and the effects of pH, temperature, and electrolytes that would be encountered in oil field brines in a reservoir. Spectral analysis of the Si–O bond at wavenumber of 1110 cm⁻¹ with the ATR-FTIR indicates a structural change on the surface of silica particles as the dispersion pH changes, which agrees with zeta potential measurements. We define a critical salt concentration (CSC) for different salts, NaCl, CaCl₂, BaCl₂, and MgCl₂, above which the silica dispersion becomes unstable. Three distinct stages of aggregation occur in the presence of salt: clear dispersed, turbid, and separated phases. Divalent cations Mg²⁺, Ca²⁺, and Ba²⁺ are more effective in destabilizing silica nanoparticle dispersion than the monovalent cation Na⁺. The CSC for Na⁺ is about 100 times more than for Ca²⁺, Ba²⁺, and Mg²⁺. Among the divalent cations studied, Mg²⁺ is the most effective in destabilizing the silica particles. The CSC is independent of silica concentration, and lowers at high temperature.     

Effect of Pendant Group Length Upon Metal Ion Complexation in Acetonitrile by Di-Ionized Calix[4]Arenes Bearing Two Dansyl Fluorophores

A series of three di-ionizable calix[4]arenes with two pendant dansyl (1-dimethylaminonaphthalene-5-sulfonyl) groups linked to the lower rims was synthesized. Structures of the three ligands were identical except for the length of the spacers which connected the two dansyl groups to the calix[4]arene scaffold. Following conversion of the ligands into their di-ionized di(tetramethylammonium) salts, absorption and emission spectrophotometry were utilized to probe the influence of metal cation (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Ag⁺, Cd²⁺, Co²⁺, Fe²⁺, Hg²⁺, Mn²⁺, Pb²⁺, Zn²⁺ and Fe³⁺) complexation in acetonitrile. Upon complexation with these metal cations, emission spectra underwent marked red shifts and quenching of the dansyl group fluorescence for the di-ionized ligand with the shortest spacer. A similar effect was noted for the di-ionized ligand with an intermediate spacer for all of the metal ions, except Ba²⁺. For the di-ionized ligand with the longest spacer, the metal cations showed different effects on the emission spectrum. Li⁺, Mg²⁺, Ca²⁺ and Ba²⁺ caused enhancement of emission intensity with a red shift. Other metal cations produce quenching with red shifts in the emission spectra. Transition metal cations interacted strongly with all three di-ionized ligands. In particular, Fe³⁺ and Hg²⁺ caused greater than 99% quenching of the dansyl fluorescence in the di-ionized ligands.     

Boron-, nitrogen-, aluminum-, and phosphorus-doped graphite electrodes for non-lithium ion batteries

Intercalation of Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, and Al³⁺ ions into B-, N-, Al-, and P-doped graphite has been studied using density functional theory calculations. While the intercalation of Li⁺, K⁺, and Ca²⁺ ions into graphite is thermodynamically favorable, that of Na⁺, Mg²⁺, Zn²⁺, and Al³⁺ ions into graphite is unfavorable. When doped in the form of graphitic structure, B, Al, and P dopants significantly stabilize the ion-intercalated graphite compounds. As a result, Na⁺ ions that are unable to intercalate into graphite can intercalate into B-, Al-, and P-doped graphite. The electron transfer from B, Al, and P dopants to host C atoms reinforces the ion–graphene electrostatic interaction, enhancing the thermodynamic driving force for ion intercalation. The catalytic activity of the dopant to promote the ion intercalation increases in the order of N < B < P < Al, which is associated with the electronegativity of the dopant.     

Comparison of Inductively Coupled Plasma with Classical Analytical Techniques in the Analysis of Southern Oregon Lithia Water: Inclusion of a Local Resource in the Undergraduate Chemistry Curriculum

Abstract

Lithia water, a community resource of local historical significance, is described as a central theme in the undergraduate analytical chemistry sequence. A statistical comparison of the classical determination of major cations (Na⁺, K⁺, Ca²⁺, Mg²⁺) and anions (HCO₃ ^?, Cl^?) reinforces statistical and charge‐balance concepts covered in analytical chemistry. Subsequent determination of these major cations by inductively coupled plasma (ICP) enables students to statistically evaluate the presence of bias between instrumental and classical methods. The effect of easily ionized elements on ICP calibration sensitivity and linearity via the use of cesium as an ionization suppressor is reported.