Coordination polyhedra of hydration shells of Na+ and K+ cations in aqueous solutions

Simulation of the hydration of Na⁺ and K⁺ cations in dilute solution was performed by the Monte Carlo method. A novel approach to structural analysis of hydration shells of ions was developed. Specific sets of coordination polyhedra formed by water molecules of the first coordination sphere were found. Structural and energy characteristics of hydration were calculated. The effect of Na⁺ and K⁺ cations on the structure of the network of H-bonds and mobility of water molecules in hydration shells was studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 852–857, May, 1999.     

Structural investigations of metal clusters by HREM

Silver clusters grown by the inert gas aggregation technique have been investigated by HREM. Undistorted cuboctahedra and icosahedra together with twinned particles have been observed. Three types of nucleation and growth mechanisms are proposed which can explain the observed particle structures. The untwinned large particles are created by the coalescence of liquid- like small clusters. The twins are produced by the coalescence of solid subunits.     

Solvation of Na+ in argon clusters

The structures and stabilities of Ar(n)Na+ clusters (n < or = 54) are investigated using atomistic potentials fitted to reproduce ab initio calculations performed at the coupled-cluster level on the smaller clusters. Polarization effects are described using either the interaction between dipoles induced by the sodium ion, or a small charge transfer in the framework of a fluctuating charges model. In both models, extra three-body contributions of the Axilrod-Teller type are also included between the sodium ion and all pairs of argon atoms. The two models predict essentially similar growth patterns, and a transition in the metal ion coordination from 8 (square antiprism) to 12 (icosahedron) is seen to occur near n = 50, in response to the intrasolvent constraints.     

Atomic and electronic structure of Na10K10Cs n clusters

Density functional theory is used to study the atomic and electronic structures of Na₁₀K₁₀Cs _n clusters with up to sixty atoms. The simplifying approximation has been made of replacing the external potential of the ionic background by its spherical average about the cluster centre in the iterative process of solving the Kohn-Sham equations for each geometry tested. The search for the equilibrium geometry is performed by employing the technique of simulated annealing. We have always found segregation of Cs atoms to the surface as well as a rather neat separation of different species in different (radial) regions of the cluster. This layering effect appears to be consistent with a tendency to maximize electronegativity differences. When the cluster is big enough, Cs atoms begin to appear also inside the cluster. Those geometrical effects do not perturb the electronic magic numbers well known for pure alkali metal clusters.     

Active transport of Na + and K + through animal cell membranes

The transport of Na⁺ out of the cell and K⁺ into the cell against a concentration gradient is catalyzed by a (Na⁺ + K⁺)-activated ATPase. The way in which the cations pass through the cell membrane has not yet been elucidated. Studies on the ATP hydrolysis revealed a Na⁺-dependent phosphorylation of the enzyme protein; the conformation of the enzyme also appears to change. The energy required for transport of the cations against their concentration gradients is probably provided by K⁺-dependent hydrolysis of the enzyme-bound phosphate. The enzyme can synthesize ATP from inorganic phosphate and ADP on reversal of the cation concentration gradient. By keeping the enzyme in a particular conformation, the cardiac glycoside ouabain specifically inhibits the Na⁺ pump.     

Flavonoid inhibitors of Na+,K+-ATPase

Summary A comparative investigation of the inhibiting influence on transport Na⁺,K⁺-ATPase of four flavone aglycones and eight of their glycosides has been performed on the microsomal fraction of the cells of the cerebral cortex.It has been shown that in concentrations of 1·10^–4 to 5·10^–6 M M myricetin, quercetin, luteolin, and myricetin 3-glucoside possess an appreciable inhibiting effect. For kaempferol and its glycosides, as for the glycosides of quercetin and luteolin, the inhibiting effect is extremely feeble.Institute of Biochemistry, Academy of Sciences of the Uzbek SSR, Tashkent. V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 44–46, January–February, 1977.     

Electronic decay following ionization of aqueous Li+ microsolvation clusters

Ionization in the energetical range between 35 eV and 75 eV of aqueous Li(+) microsolvation clusters may initialize several different electronic decay processes. Electronic decay following H(2)O 2s ionization in a cationic cluster is reported. Li ionization probes the efficiency of electron transfer mediated decay (ETMD) processes. We report estimated ETMD lifetimes in the range of 20-100 fs for clusters with one to five water monomers. Furthermore, tertiary electron emission may occur via a combined cascade of electron transfer mediated decay and intermolecular Coulombic decay.     

A new Na+ and K+ carrier from chemically modified monensin studied in human erythrocytes by 23Na nuclear magnetic resonance,K+ atomic absorption and H+ potentiometry

The transporting ability of a new monensin derivative 26-(1,2-diphenyl-1-ethoxy) monensin, highly active against Gram-positive bacteria, was explored with the human erythrocyte model using three technical approaches: ²³Na nuclear magnetic resonance (internal Na⁺), K⁺ atomic absorption (external K⁺) and H⁺ potentiometry (external H⁺) and compared with monensin 1 and 26-(4-chlorophenylurethane) monensin 3 of known transport selectivities for sodium and potassium respectively. Compound 2 proved to be a good carrier for both Na⁺ and K⁺ under our experimental conditions, thus constituting a new type of monensin derivative. The introduction of Li⁺, Rb⁺ or Cs⁺ in the external buffer as a replacement for Na⁺ led us to propose the transport sequence K⁺, Na⁺ ⪢ Rb⁺ > Li⁺ > Cs⁺ for 2.     

Complexation of citric and tartaric acids with Na and K ions in aqueous solution

The formation of MTar^–, MCit^2– and M₂Cit^– complexes (M is Na⁺ or K⁺) was established in reactions of aqueous solutions of citric and tartaric acids with sodium or potassium chloride solutions; their stability constants were determined by potentiometric titration in aqueous solution at 298.15 K and ionic strength 0.1 and 0.3 mol/l with tetraethylammonium chloride (TEACl) as a supporting electrolyte. Heat effects of reactions between citric acid solutions and sodium or potassium chlorides were measured by calorimetric method at 288.15, 298.15, and 308.15 K and at the ionic strength 0.1, 0.2, and 0.3 M TEACl. The increasing ionic strength was found to decrease exothermic effect of complex formation processes, while the temperature produced the opposite effect. Extrapolation to zero ionic strength was used to find thermodynamic stability constants and standard heat effects of complex formation reactions in solutions of oxyacids. The changes in entropy and heat capacity were calculated as well as standard enthalpies of formation of Na and K complexes of the indicated oxyacids in aqueous solution at 298.15 K.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 4, 2005, pp. 253–261.Original Russian Text Copyright © 2005 by Zelenina, Zelenin.     

Structural and spectroscopic investigations on Eu3+-doped alkali fluoroborate glasses

Eu³⁺-doped alkali fluoroborate glasses B₂O₃–XCO₃–NaF–Eu₂O₃ (where X = Li₂, Na₂, K₂, and Ca, Mg) have been prepared using the conventional melting technique and their structural and optical properties have been evaluated. The XRD pattern of the glasses confirmed the amorphous nature and the FTIR spectra reveal the presence of BO₃ and BO₄ units as their local structures along with the strong OH^? groups. From the absorption spectra the bonding parameters have been calculated and confirmed that the Eu–O bonds in the studied glasses are of covalent nature. Judd–Ofelt (JO) analysis has been carried out from the emission spectra. The JO parameters have been used to calculate transition probabilities (A), lifetime (τ_R) and branching ratios (β_R) and peak stimulated emission cross-section (σ_P^E) for the ⁵D₀ → ⁷F_J (J = 1, 2, 3 and 4) transitions of the Eu³⁺ ions. The decay from the ⁵D₀ level of Eu³⁺ ions in the title glasses has been measured and analysed. The lifetime of the ⁵D₀ level is found to be shorter than the reported glasses which may be due to the presence of OH^? groups.     

Encasing of Na+ ion in dimer‐formed acetic acid clusters

Peaks with anomalous abundance found in the mass spectra are associated with ions with enhanced stability. Among the scientific community focused on mass spectrometry, these peaks are called ‘magic peaks’ and their stability is often because of suggestive symmetric structures. Here, we report findings on ionised Na‐acetic acid clusters [Na⁺‐(AcA)_n] produced by Na‐doping of (AcA)_n and UV laser ionisation. Peaks labelled n = 2, 4, 8 are clearly distinguishable in the mass spectra from their anomalous intensity. Ab initio calculations helped elucidate cluster structures and energetic. A plausible interpretation of the magic peaks is given in terms of (AcA)_n formed by dimer aggregation. The encasing of Na⁺ by twisted dimers is proposed to be the origin of the enhanced cluster stability. A conceivable dimer‐formed tube‐like closed structure is found for the Na⁺‐(AcA)₈. Copyright © 2015 John Wiley & Sons, Ltd.     

计算机模拟冠醚和穴醚对钠钾离子的选择

通过计算机模拟,先用分子力学MM2方法对不同类型的冠醚和穴醚进行能量优化,获得其优势构象,在此基础上运用分子力学MM 方法,考察它们与金属离子Na 和K 所形成配合物的稳定性。结果显示,使用两种分子力学方法,可以比较准确快速地推测冠醚与穴醚对Na 和K 的选择及其选择性规律。对运用分子力学方法进行计算机模拟的局限性也进行了讨论。     

Calculation of photoionization cross sections of Na2–8 and K2–8 clusters

Analysis of free metal clusters studied with photoionization mass spectrometry or photoelectron spectroscopy requires theoretical predictions of the photoionization cross sections to gain a deeper physical understanding. Calculated energy-dependent photoionization cross sections of Na_2–8 and K_2–8 clusters are presented in this study. The ground state electronic structure of the clusters are calculated using the Local Spin Density method (LSD) which is also the starting point for the cross section calculation with the continuum multiple scattering method. A basic analysis of the photoionization process is given within the independent electron picture. Strong resonances are predicted in the UV cross sections (5–10 eV) of K_3–8 but not for Na_3–8, interpreted as shape resonances, i.e. quasibound states in which electrons are trapped by a potential barrier. Unfortunately experimental data are only known close to the ionization threshold and a comparison between our values and experimental data in a broad energy range is not possible.     

Structural Characterizations of Spherical Octadecavanadates Encapsulating Na+, K+ or I- and Ellipsoidal Octadecamolybdate Encapsulating two Anions of SO42-

Polyoxoanions of tungsten, molybdenum, and vanadium have been the subject of interest since their wide variety of compositions, structures, and properties give rise to numerous important applications^[1]. From the NH₄VO₃/Na₂S_x (or (NH₄)₂S_x) reaction system we synthesized several spherical octadecavanadates with Na⁺,K⁺, NH₄⁺ or I encapsulated using hydrothermal method. These complexes include (NH₄)₁₁[V₁₈O₄₂(Na)]·(H₂O)₂₀ 1; (NH₄)₁₁[V₁₈O₄₂(K)]·(H₂O)₆, 2; (NH₄)₁₀(Na)[V₁₈O₄₂(Na)]·(H₂O)₂₆, 3; (NH₄)₁₁[V₁₈O₄₂(NH4]·(H₂O)₂₀, 4; and (NH₄)₂₀(I)₇[V₁₈O₄₂(I)]·(H₂O)₁₂, 5, in which the structures of 1, 2, 3, and 5 have been determined by X-ray analyses. In the analogous reaction system of (NH₄)₂MoS₄/(NH₄)₂S_x, we also obtained one ellipsoidal octadecamolybdate, (NH₄)₄[Mo₁₈O₅₄(2SO₄)]·(H₂O)₄, 6 with a standard Wells-Dawson structure^[2]. The Ortep drawings of the two kinds of structures are viewed as follows.     

Reversible organogels triggered by dynamic K+ binding and release

In this study, a new lipophilic guanosine derivative was synthesized as an organogelator. The self-aggregation behavior of this organogelator was investigated by NMR, XRD and AFM. In solution, the lipophilic guanosine derivative can form a stable ribbon-like structure through NH(1)–N(7) and NH(2)–O(6) hydrogen bonds. However, gelation would occur in some aprotic solvents after the concentration reached a definite value. More interesting, the ribbon-like structure was able to change to G-quartets in the presence of K⁺, which led to the transformation from a gel to a sol. Upon the addition of the cryptand [2.2.2], which can efficiently complex with K⁺, G-quartets reverted to the original ribbon-like structure and the gel recovered. Subsequently, upon the addition of acids, K⁺ was released from the cryptate with the transformation of gel-to-sol simultaneously. Finally, upon the addition of bases which deprotonated [H⁺ ? 2.2.2], the liberated cryptand [2.2.2] recaptured K⁺ and the gel was regenerated again. This process of interconversion between G-ribbon 1_n and octamer 1₈·K⁺ was well monitored by circular dichroism spectra.     

Structural Insights into the Interactions of Digoxin and Na+/K+-ATPase and Other Targets for the Inhibition of Cancer Cell Proliferation

Digoxin is a cardiac glycoside long used to treat congestive heart failure and found recently to show antitumor potential. The hydroxy groups connected at the C-12, C-14, and C-3′a positions; the C-17 unsaturated lactone unit; the conformation of the steroid core; and the C-3 saccharide moiety have been demonstrated as being important for digoxin’s cytotoxicity and interactions with Na⁺/K⁺-ATPase. The docking profiles for digoxin and several derivatives and Na⁺/K⁺-ATPase were investigated; an additional small Asn130 side pocket was revealed, which could be useful in the design of novel digoxin-like antitumor agents. In addition, the docking scores for digoxin and its derivatives were found to correlate with their cytotoxicity, indicating a potential use of these values in the prediction of the cancer cell cytotoxicity of other cardiac glycosides. Moreover, in these docking studies, digoxin was found to bind to FIH-1 and NF-κB but not HDAC, IAP, and PI3K, suggesting that this cardiac glycoside directly targets FIH-1, Na⁺/K⁺-ATPase, and NF-κB to mediate its antitumor potential. Differentially, digoxigenin, the aglycon of digoxin, binds to HDAC and PI3K, but not FIH-1, IAP, Na⁺/K⁺-ATPase, and NF-κB, indicating that this compound may target tumor autophagy and metabolism to mediate its antitumor propensity.     

Specific Ion and Concentration Effects in Acetate Solutions with Na+, K+ and Cs+

How salt ions affect solutes and the water beyond the solvation shell is not well understood. Molecular dynamics simulations of alkali-acetate solutions were analysed here in order to examine if, and how, different cations and solute concentrations affect the water structure and the interactions between water and acetates. The results revealed that water structure is perturbed to more than 1 nm away from the acetates and that this effect is more pronounced in physiological than in molar electrolyte concentrations. Analysis of simulations of a soluble protein revealed that the water orientation is perturbed to at least 1.5 nm from the protein structure. Furthermore, modifications to the orientation of water around carboxylate side chains were shown to depend on the local environment on the protein surface, and could extend to well over 1 nm, which may have an effect on protein dynamics during MD simulations in small water boxes.