Theoretical study of interaction of 2,6-dithiopurine with Li+, Na+, K+, Be2+, Mg2+, and Ca2+ metal cations

The geometries of the complexes of Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺ metal cations with different possible 2,6-dithiopurine anions (DTP) were studied. The complexes were optimized at the B3LYP level and the 6-311++G(d, p) basis set. The interactions of the metal cations at different nucleophilic sites of various possible 2,6-dithiopurine anions were considered. It was revealed that metal cations would interact with 2,6-dithiopurine anions in a bicoordinate manner. In the gas phase, the most preferred position for the interaction of Li⁺, Na⁺, and K⁺ cations is between the N₃ and S₂ sites, while all divalent cations Be²⁺, Mg²⁺, and Ca²⁺ prefer binding between the N₇ and S₆ sites of the corresponding 2,6-dithiopurine. The influence of aqueous solvent on the relative stability of different complexes has been examined using the Tomasi’s polarized continuum model. The basis set superposition error (BSSE) corrected interaction energy was also computed for complexes. The AIM theory has been applied to analyze the properties of the bond critical points (electron densities and their Laplacians) involved in the coordination between 2,6-dithiopurine anions and the metal cations. It was revealed that aqueous solution would have significant effect on the relative stability of complexes obtained by the interaction of 2,6-dithiopurine anions with Mg²⁺ and Ca²⁺ cations. The effect of metal cations on different NH and CS stretching vibrational modes of 2,6-dithiopurine has also been discussed.     

Computational study of the interaction of metal ions (Na+, K+, Mg2+, Ca2+, and Al3+) with Quercetin and its antioxidant properties

In recent years, the chelation between quercetin and transition metals has attracted much attention because the complexes formed have higher antioxidant and medicinal activities. However, the theoretical investigation of the mechanisms of flavonoid functioning along with the structures of quercetin–metal complexes is still not sufficiently studied. In this research work, quercetin–complexes with Na⁺, K⁺, Mg²⁺, Ca²⁺, and Al³⁺ are studied theoretically by using density functional theory (DFT) method in order to investigate the stability, reactivity, nature of interaction, and the application of the quercetin-metal complexes as potential antioxidants. From the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) results, the K-quercetin salt was observed to be more stable as compared to the other metals while Ca seemed to be the most reactive with the least values in the neutral form of the metal - quercetin interaction. The results of the antioxidant activity in the neutral state present Ca and Mg to have the higher values of ionization potential (IP) indicating that the antioxidant activity of Ca/Mg complexes with quercetin are less pronounced, while K-complex with the least value indicating the higher the electron donating reactivity. In comparison, it is worth to note that Mg-Q and Ca-Q in the deprotonated state of quercetin showcase lower IP, higher ability of H-atom transfer and electron transfer reactivity, therefore, better antioxidant candidates of the quercetin complexes than their other counterparts.     

Effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water coordination on the structure of glycine and zwitterionic glycine

Interactions between metal ions and amino acids are common both in solution and in the gas phase. Here, the effect of metal ions and water on the structure of glycine is examined. The effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water on structures of Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (m = 0, 2, 5) complexes have been determined theoretically by employing the hybrid B3LYP exchange-correlation functional and using extended basis sets. Selected calculations were carried out also by means of CBS-QB3 model chemistry. The interaction enthalpies, entropies, and Gibbs energies of eight complexes Gly.Mn+ (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) were determined at the B3LYP density functional level of theory. The computed Gibbs energies DeltaG degrees are negative and span a rather broad energy interval (from -90 to -1100 kJ mol(-1)), meaning that the ions studied form strong complexes. The largest interaction Gibbs energy (-1076 kJ mol(-1)) was computed for the NiGly2+ complex. Calculations of the molecular structure and relative stability of the Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+; m = 0, 2, and 5) systems indicate that in the complexes with monovalent metal cations the most stable species are the NO coordinated metal cations in non-zwitterionic glycine. Divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ prefer coordination via the OO bifurcated bonds of the zwitterionic glycine. Stepwise addition of two and five water molecules leads to considerable changes in the relative stability of the hydrated species. Addition of two water molecules at the metal ion in both Gly.Mn+ and GlyZwitt.Mn+ complexes reduces the relative stability of metallic complexes of glycine. For Mn+ = Li+ or Na+, the addition of five water molecules does not change the relative order of stability. In the Gly.K+ complex, the solvation shell of water molecules around K+ ion has, because of the larger size of the potassium cation, a different structure with a reduced number of hydrogen-bonded contacts. This results in a net preference (by 10.3 kJ mol(-1)) of the GlyZwitt.K+H2O5 system. Addition of five water molecules to the glycine complexes containing divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ results in a net preference for non-zwitterionic glycine species. The computed relative Gibbs energies are quite high (-10 to -38 kJ mol(-1)), and the NO coordination is preferred in the Gly.Mn+(H2O)5 (Mn+ = Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) complexes over the OO coordination.     

Comprehensive study on the solvation of mono- and divalent metal cations: Li+, Na+, K+, Be2+, Mg2+ and Ca2+

Hydration of mono- and divalent metal ions (Li(+), Na(+), K(+), Be(2+), Mg(2+) and Ca(2+)) has been studied using the DFT (B3LYP), second-order M?ller-Plesset (MP2) and CCSD(T) perturbation theory as well as the G3 quantum chemical methods. Double-zeta and triple-zeta basis sets containing both (multiple) polarization and diffuse functions were applied. Total and sequential binding energies are evaluated for all metal-water clusters containing 1-6 water molecules. Total binding energies predicted at lower levels of theory are compared with those from the high level G3 calculations, whereas the sequential binding energies are compared with available experimental values. An increase in the quality of the basis set from double-zeta to triple-zeta has a significant effect on the sequential binding energies, irrespective of the geometries used. Within the same group (I or II), the sequential binding energy predictions at the MP2 and B3LYP vary appreciably. We noticed that, for each addition of a water molecule, the change of the M-O distance in metal-water clusters is higher at the B3LYP than at the MP2 level. The charge of the metal ion decreases monotonically as the number of water molecules increase in the complex.     

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.     

Effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water coordination on the structure and properties of L-arginine and zwitterionic L-arginine

Interactions between metal ions and amino acids are common both in solution and in the gas phase. The effect of metal ions and water on the structure of L-arginine is examined. The effects of metal ions (Li(+), Na(+), K(+), Mg(2+), Ca(2+), Ni(2+), Cu(2+), and Zn(2+)) and water on structures of Arg x M(H2O)m , m = 0, 1 complexes have been determined theoretically by employing the density functional theories (DFT) and using extended basis sets. Of the three stable complexes investigated, the relative stability of the gas-phase complexes computed with DFT methods (with the exception of K(+) systems) suggests metallic complexes of the neutral L-arginine to be the most stable species. The calculations of monohydrated systems show that even one water molecule has a profound effect on the relative stability of individual complexes. Proton dissociation enthalpies and Gibbs energies of arginine in the presence of the metal cations Li(+), Na(+), K(+), Mg(2+), Ca(2+), Ni(2+), Cu(2+), and Zn(2+) were also computed. Its gas-phase acidity considerably increases upon chelation. Of the Lewis acids investigated, the strongest affinity to arginine is exhibited by the Cu(2+) cation. The computed Gibbs energies DeltaG(o) are negative, span a rather broad energy interval (from -150 to -1500 kJ/mol), and are appreciably lowered upon hydration.     

Study of metal ions (Na+, K+) interaction with different conformations of glycine molecule

Interaction of metal ions (Na⁺, K⁺) with different binding sites, such as amino nitrogen, hydroxyl oxygen, and carbonyl oxygen for all gaseous conformers of glycine molecule were investigated using Density Functional Theory (B3LYP/6‐311++G**, B3PW91/6‐311++G**) methods. It was found that the order of stability of the conformers was changed due to the binding of the metal ion. The relative energy values show that the 7p conformer is more stable than the 1p conformer when a metal ion binds with the carbonyl oxygen. The intensity of interaction on hydroxyl oxygen is very low due to the low basicity of hydroxyl oxygen. The binding affinities of the complexes were calculated using the thermochemical properties. The relative energy and chemical hardness values predicted the most stable complex. The calculated condensed Fukui functions predict the favorable reactive site among the three binding sites. It is concluded that the reactivity of each binding site varies for each conformation due to the presence of intramolecular hydrogen bonding. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Molecular structure and bonding character of mono and divalent metal cations (Li+, Na+, K+, Be2+, Mg2+, and Ca2+) with substituted benzene derivatives: AIM,NBO, and NMR analyses

Cation–π complexes between several cations (Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺) and different π-systems such as para-substituted (F, Cl, OH, SH, CH₃, and NH₂) benzene derivatives have been investigated by UB3LYP method using 6-311++G** basis set in the gas phase and the water solution. The ions have shown cation–π interaction with the aromatic motifs. Vibrational frequencies and physical properties such as dipole moment, chemical potential, and chemical hardness of these compounds have been systematically explored. The natural bond orbital analysis and the Bader’s quantum theory of atoms in molecules are also used to elucidate the interaction characteristics of the investigated complexes. The aromaticity is measured using several well-established indices of aromaticity such as NICS, HOMA, PDI, FLU, and FLUπ. The MEP is given the visual representation of the chemically active sites and comparative reactivity of atoms. Furthermore, the effects of interactions on NMR data have been used to more investigation of the studied compounds.     

金属离子(Na~+、K~+、Ca~(2+)、Mg~(2+)、Zn~(2+))与鸟嘌呤异构体配合物的稳定性

在B3LYP/6-311++G**水平上用极化连续介质模型(PCM)系统研究了金属离子(M+/2+=Na+,K+,Ca2+,Mg2+,Zn2+)和十三种鸟嘌呤异构体形成的配合物GnxM+/2+(n为鸟嘌呤异构体的编号,x表示M+/2+与鸟嘌呤异构体的结合位点)在气(g)液(a)两相中的稳定性顺序.着重探讨了液相中配合物的稳定性差异,并且从溶质-溶剂效应、结合能、形变能及异构体的相对能量等几个方面分析了造成稳定顺序发生变化的原因.报道了溶液中这五种金属离子与鸟嘌呤异构体结合形成的六种基态配合物:aG1N2,N3Na+,aG1N2,N3K+,aG1O6,N7Ca2+,aG1N2,N3Mg2+(aG1O6,N7Mg2+),aG2N3,N9Zn2+.可以看出,除了在Zn2+配合物中鸟嘌呤异构体为G2外,构成其余四种金属离子配合物的鸟嘌呤异构体都是G1,但结合位点不同.同时对气相中各类配合物稳定性也进行了系统的排序,并报道了几种较稳定的配合物,如:gG3N1,O6K+,gG5N1,O6K+,gG3N1,O6Ca2+/Mg2+,gG4O6,N7Ca2+/Mg2+.     

Ionophoric properties of atropine: complexation and transport of Na+, K+, Mg2+ and Ca2+ ions across a liquid membrane

The activity of atropine on the complexation and transport of Na(+), K(+), Mg(2+) and Ca(2+) ions across a liquid membrane was investigated using a spectrophotometric method. Atropine is a natural drug that blocks muscarinic receptors. It is a competitive antagonist of the action of acetylcholine and other muscarinic agonists. Atropine is shown to extract Na(+), K(+), Mg(2+) and Ca(2+) ions from an aqueous phase into an organic one with a preference for Ca(2+) ions. According to a kinetic study, divalent cations (Mg(2+) and Ca(2+)) are more rapidly transported than monovalent ones (Na(+) and K(+)). In both complexation and transport, the flux of the ions increases with the increase of atropine concentration. Atropine might act on the membrane permeability; its complexation and ionophoric properties shed new lights on its therapeutic properties.     

Vibrational analysis of complexes of urate with IA group metal cations (Li+, Na+ and K+)

Vibrational frequency analysis was performed for the complexes of alkali metal cations (Li+, Na+ and K+) with urate in the gas phase. The geometries of all possible metal cation-urate complexes were optimized at the B3LYP/6-311++G(d,p) level. The most stable complex corresponding to the each cation was used for the vibrational frequency analysis including the computation of % potential energy distribution (%PED). For comparison, the vibrational frequency analysis was also performed for the uric acid. The computed results are discussed in terms of the available experimental data. It was revealed that the characteristic stretching vibrational modes corresponding to the metal cation and the interacting nucleophilic sites of urate can be used to identify metals involved in the stone formation in the living system. Changes in different vibrational frequencies of uric acid consequent to the metal cation interactions are discussed.     

A joint experimental and theoretical study of cation-pi interactions: multiple-decker sandwich complexes of ferrocene with alkali metal ions (Li+, Na+, K+, Rb+, Cs+)

A systematic study of cation-pi interactions between alkali metal ions and the cyclopentadienyl ring of ferrocene is presented. The alkali metal (Li+, Na+, K+, Rb+, Cs+) salts of the ditopic mono(pyrazol-1-yl)borate ligand [1,1'-fc(BMe2pz)2]2- crystallize from dimethoxyethane as multiple-decker sandwich complexes with the M+ ions bound to the pi faces of the ferrocene cyclopentadienyl rings in an eta5 manner (fc = (C5H4)2Fe; pz = pyrazolyl). X-ray crystallography of the lithium complex reveals discrete trimetallic entities with each lithium ion being coordinated by only one cyclopentadienyl ring. The sodium salt forms polyanionic zigzag chains where each Na+ ion bridges the cyclopentadienyl rings of two ferrocene moieties. Linear columns [-CpR-Fe-CpR-M+-CpR-Fe-CpR-M+-](infinity) (R = [-BMe2pz]-) are established by the K+, Rb+, and Cs+ derivatives in the solid state. According to DFT calculations, the binding enthalpies of M+-eta5(ferrocene) model complexes are about 20% higher as compared to the corresponding M+-eta6(benzene) aggregates when M+ = Li+ or Na+. For K+ and Rb+, the degree of cation-pi interaction with both aromatics is about the same. The binding sequence along the M+-eta5(ferrocene) series follows a classical electrostatic trend with the smaller ions being more tightly bound.     

啤酒酵母生理代谢过程中钠、钾、镁、钙离子含量变化的跟踪检测

采用空气-乙炔火焰原子吸收光谱法分别测定了啤酒酵母发酵液中的Na^ 、K^ 、Mg^2 、Ca^2 离子动态变化中的含量,用La^3 盐消除P对Ca^3 的干扰,以Sr^2 盐作为Na^ 、K^ 的消电离剂。本实验室采用配制培养基,通过对不同种类及不同发酵阶段培养的发酵液样品进行测定,以研究在啤酒酵母生长代谢过程中Na^ 、K^ 、Mg^2 、Ca^2 离子代谢动态变化。方法的Na^ 、K^ 、Mg^2 、Ca^2 相对标准偏差(RSD)分别为0．31％,0．73％。1．78％,0．28％;样品加标回收率为98％-107％;检出限：Na^ 为0．159mg／L,K^ 为0．789nag／L,Mg^2 为0．039mg／L,Ca^2 为0．029mg／L。该方法简便快速,具有很好的精密度。     

Correlated ab initio quantum chemical study of the interaction of the Na+, Mg2+, Ca2+, and Zn2+ ions with the tautomers of cytosine

The interaction of the metal ions Na(+), Mg(2+), Ca(2+), and Zn(2+) with cytosine have been reinvestigated at the density functional, M?ller-Plesset, and coupled cluster levels of theory, including hitherto unstudied tautomeric forms. It has been found that the interaction of the metal ion has a varying and often significant effect on the stabilities of the various tautomers, in some cases making most stable rare tautomeric forms. The results have been analyzed with respect to method and role of ion in binding, and confirm that, as has been found for the base cytosine tautomers, B3LYP does not give energetics consistent with highly accurate post-SCF methods for their interaction with these metal ions.     

Density functional study of ion hydration for the alkali metal ions (Li+, Na+, K+) and the halide ions (F-, Br-, Cl-)

We performed first principles density functional calculations to study the effect of monovalent ions M+ (M = Li,Na,K) and A- (A = F,Cl,Br) in water with the aim of characterizing the local molecular properties of hydration. For this reason, several ion-water clusters, up to five or six water molecules were considered; such structures were optimized, and the Wannier analysis was then applied to determine the average molecular dipole moment of water. We found that with an increasing number of water molecules, the molecular polarization is determined by the water-water interaction rather than the water-ion interaction, as one would intuitively expect. These results are consistent with those obtained in previous density functional calculations and with other results obtained by employing classical polarizable water models. The main message of this work is that as one increases the number of molecules the average dipole moment of all water molecules and the ones in the first shell tends to the same value as the average of a similar sized cluster of pure water. This supports the use of nonpolarizable classical models of water in classical atomistic simulations.     

Interaction of Na+, K+, Li+ and Ca2+ ions in Tris-HCl buffer substrate with monolayers of phosphatidic acid and homologous phosphatidic acid alkyl esters

The interaction of ions (Na⁺, K⁺, Li⁺, Ca²⁺) with monolayers of phosphatidic acid alkyl esters (alkyl = methyl, ethyl,n-propyl,n-pentyl) were investigated at the air/water interface on Tris-HCl buffer, as well as on the electrolytes containing subphases.Qualitatively it can be stated that there are no considerable interactions between Na⁺ ions in the substrate and the head groups of phosphatidic acid esters in the monolayers. On the whole, the modification of the shape in the /a and v/a isotherms ( ^s = film pressure, v ^s = film potential) of the homologous phosphatidic acid esters as a function of the length of the ester group on the subphase containing NaCl, KCl, and LiCl corresponds to that on Tris-HCl buffer without admixture of electrolytes.On the other hand the strength of interaction between Ca²⁺ ions and the homologous phosphatidic acid esters depends on the length of the ester group. The film-condensing effect of Ca²⁺ ions becomes smaller with increasing length of the ester group.     

Redox Hyperactive MOF for Li+, Na+ and Mg2+ Storage

To create both greener and high-power metal-ion batteries, it is of prime importance to invent an unprecedented electrode material that will be able to store a colossal amount of charge carriers by a redox mechanism. Employing periodic DFT calculations, we modeled a new metal-organic framework, which displays energy density exceeding that of conventional inorganic and organic electrodes, such as Li- and Na-rich oxides and anthraquinones. The designed MOF has a rhombohedral unit cell in which an Ni(II) node is coordinated by 2,5-dicyano-p-benzoquinone linkers in such a way that all components participate in the redox reaction upon lithiation, sodiation and magnesiation. The spatial and electronic changes occurring in the MOF after the interaction with Li, Na and Mg are discussed on the basis of calculated electrode potentials versus Li⁰/Li⁺, Na⁰/Na⁺ and Mg⁰/Mg²⁺, respectively. In addition, the specific capacities and energy densities are calculated and used as a measure for the electrode applicability of the designed material. Although the highest capacity and energy density are predicted for Li storage, the greater structural robustness toward Na and Mg uptake suggests a higher cycling stability in addition to lower cost. The theoretical results indicate that the MOF is a promising choice for a green electrode material (with <10% heavy metal content) and is well worth experimental testing.