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.     

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.     

Calculation of anharmonic effects in the unimolecular dissociation of M2+(H2O)2 (M = Be,Mg, and Ca)

The anharmonic and harmonic rate constants of the unimolecular dissociation of M²⁺(H₂O)₂ (M = Be, Mg, and Ca) were calculated using the Rice–Ramsperger–Kassel–Marcus theory. The anharmonic effects of the reactions were investigated. The results show that the energy barrier of the dissociation of Be²⁺(H₂O)₂ is 68.47 kcal/mol, and the anharmonic (T_4000K = 4.28×10⁸ s^?1) and harmonic (T_4000K = 4.22×10⁸ s^?1) rate constants were close in value in both the canonical and microcanonical systems. The energy barriers of the two steps for the dissociation, Mg²⁺(H₂O)₂ → MgOH⁺+H₃O⁺, were 37.41 and 11.39 kcal/mol, and those for the dissociation, Ca²⁺(H₂O)₂ → CaOH⁺+H₃O⁺, were 21.15 and 26.42 kcal/mol. The anharmonic effect of the two reactions is significant and cannot be neglected in both the canonical and microcanonical systems. The comparison also shows that the rate constants of the dissociation of Ca²⁺(H₂O)₂ have the maximum values, while those of Be²⁺(H₂O)₂ have the minimum values in the three reactions; however, the anharmonic effect also shows the similar trend in the comparison.     

Theoretical explanation for the DNA cleavage by GO with cation: anti-cooperativity effect among the π⋯π, cation⋯π/σ and H-bonding interactions in cytosine⋯GO⋯Mn+ (Mn+ = Na+, Mg2+, Al3+)

In order to reveal the nature of DNA cleavage by inorganic intercalator GO (graphene oxide) with cation, the cooperativity effects among the π?π, cation?π/σ and H-bonding interactions were evaluated in the cytosine?GO?Mⁿ⁺ (Mⁿ⁺?=?Na⁺, Mg²⁺, Al³⁺) model systems using the M06-2X, MP2 and ω B97X-D methods with the 6-311++G(2d,p) and 6-311++G(3df,3pd) basis sets. The Mⁿ⁺?O (ether) and N–H?O interactions induce the formation of the π?π stacking between cytosine and GO, and the anti-cooperativity effect are dominant in controling of the aggregation process of cytosine, GO and Mⁿ⁺, which was confirmed by the AIM (atoms-in-molecules) and RDG (reduced density gradient) analyses. Furthermore, the solvent effects of H₂O weaken greatly the anti-cooperativity effects. Thus, a deduction on the DNA cleavage by GO?cation with the intercalation mode is put forward: due to the anti-cooperativity effect and solvent effect, the π?π stacking is weakened in the complexes with Na⁺ or broken in those with Mg²⁺ or Al³⁺. Then the GO?Mg²⁺ moiety is squeezed out from the intercalating sites, leading to an invalid cleavage of DNA, while Na⁺ or Al³⁺ is bound tightly to cytosine, with a notable DNA cleavage. This deduction was used to explain reasonably the previous experimental phenomena.     

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.     

Proton NMR of isomorphous paramagnetic and diamagnetic monohydrates MeSO4.1 H2O Me = Mn2+, Fe2+, Ni2+ AND Mg2+

Nuclear magnetic resonance of protons of crystallization water in isomorphous paramagnetic and diamagnetic monohydrates MeSO₄. 1 H₂O with Me = Mn²⁺, Fe²⁺, Ni²⁺ and Mg²⁺ is studied in the present paper. Proton NMR spectra in paramagnetic hydrates are asymmetric and their second moments, M₂, depend linearly on the square of the induction of the external magnetic field B₀. NMR spectrum of diamagnetic hydrate MgSO₄. 1 H₂O is symmetric and its shape and the second moment do not change with B₀. The parameters M₂₀ andK which characterize nuclear dipole-dipole interaction of protons and interaction of protons and paramagnetic ions, respectively, are derived from experimentally obtained dependences M₂ vs B ₀ ² and on the other hand, they are calculated by means of crystallographic data for substances studied. Calculations were realized in approximation where two nearest neighbour ions Me²⁺ to each water molecule are considered. The influence of the demagnetizing magnetic field of the sample was neglected.     

Hydration characteristics of Ca2+ and Mg2+: a density functional theory,polarized continuum model and molecular dynamics investigation

In this work, density functional theory, Møller–Plesset second-order perturbation theory, and ab initio molecular dynamics (AIMD) were used to investigate hydrated characteristics of Mg²⁺ and Ca²⁺ as a function of coordination number in the first hydration shell (CN) and cluster size. It is generally accepted that the CNs of Mg²⁺ and Ca²⁺ are both six. Calculations show that the hydration of Mg²⁺ generally prefers six-coordinated structures, whereas the CN value of Ca²⁺ varies from 6 to 8 as the hydration proceeds. Moreover, the first hydration of Ca²⁺ is found to be more flexible than that of Mg²⁺, as indicated by the results of transition state calculations and AIMD simulations. In addition, the constraint of Mg²⁺ on the first hydration shell is obviously stronger than that of Ca²⁺, while the constraint on the inner hydration shells fades slightly faster for Mg²⁺ than Ca²⁺. It is also found that the charge transfer from central cation to water molecules is affected only by the first hydration shell for Mg²⁺, whereas by the first and second hydration shells for Ca²⁺. Based on hydration characteristics, approximatively saturated ion hydration shells for the hydration of Mg²⁺ and Ca²⁺ were proposed.     

Effect of Pb2+ on L‐glutathione monolayers on a silver surface investigated by surface‐enhanced Raman scattering spectroscopy

Surface‐enhanced Raman scattering (SERS) spectroscopy was applied to observe reduced L ‐glutathione [L‐Glut(R)] molecules self‐assembled on a silver surface and the effect of Pb²⁺ on them. The adsorption structure suggests that the mercapto group of the L‐Glut(R) molecule is covalently bonded to the silver surface along with the imine group, amino group and entire carboxyl group in a perpendicular orientation after self‐reorganization. Results of SERS experiment show that Pb²⁺ influences the structure of L‐glutathione monolayers as a result of the binding reaction possibly occurring between Pb²⁺ and the carboxyl and the amino groups. Copyright © 2009 John Wiley & Sons, Ltd.     

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.     

Role of monovalent alkali ions in the Yb3+ centers of CaF2 laser crystals

Yb³⁺ and M⁺ monovalent alkali ions (M⁺ = Li⁺, Na⁺, K⁺)-co-doped CaF₂ cubic laser crystals were grown by the micro-pulling-down method (μ-PD) under CF₄ atmosphere. Structural and spectroscopic characterizations of Yb³⁺ in substitution of Ca²⁺ (absorption, emission and decay curves) were carried out to study the effect of M⁺ ions as charge compensators.     

Studies on adsorptions of metallic ions in water by zirconium glyphosate (ZrGP): Behaviors and mechanisms

A new adsorbent named zirconium glyphosate [Zr(O₃PCH₂NHCH₂COOH)₂·0.5H₂O, denoted as ZrGP] and its selective adsorptions to Pb²⁺, Cd²⁺, Mg²⁺ and Ca²⁺ ions in water were reported in this paper. Compared to other zirconium adsorbents, such as zirconium phosphate [Zr(HPO₄)₂], ZrGP exhibited highly selective adsorption to Pb²⁺ in solution which contained Pb²⁺, Cd²⁺, Mg²⁺ and Ca²⁺ ions. The loaded ZrGP with metallic ions can be efficaciously regenerated by aqueous solution of HCl (1.0 M) without any noticeable capacity loss, and almost all of it can be reused and recycled. The memory effect on structural regeneration of ZrGP was also found when Mg²⁺ and Ca²⁺ were adsorbed. To be specific, the structure of ZrGP was destroyed due to adsorbing these two ions, but it could be regenerated after the loaded materials were dipped in HCl solution (1.0 M) for several minutes to remove metallic ions.     

Substitutional site of Co2+ ion in RbMgF3 crystal

The spin-Hamiltonian (SH) parameters (g factors g _//, g _⊥ and hyperfine structure constants A _//, A _⊥) for Co²⁺ ions at the trigonal Mg²⁺ (I) and Mg²⁺ (II) sites of RbMgF₃ crystal are calculated from the second-order perturbation formulas based on the cluster approach for 3d⁷ ions in trigonal symmetry. From the calculations, it is found that the calculated SH parameters for Co²⁺ ion at the Mg²⁺ (I) site are in poor agreement with, but those for Co²⁺ at the Mg²⁺ (II) site are close to, the experimental values. Therefore, we suggest that Co²⁺ in RbMgF₃ crystal substitutes for Mg²⁺ (II) ion. The results are discussed.     

Simultaneous registration of Ca2+ transients and volume changes in rat mesangial cells: Evaluation of the effects of protein kinase C down-regulation

The intracellular free Ca²⁺ concentration ([Ca²⁺]_i) could be correlated with the contractile response in rat mesangial cells using an apparatus which measured both biochemical processes simultaneously. Long-term pretreatment of mesangial cells with 12-O-tetradecanoly-phorbol 13-acetate (24 h, 500 nM) increased the (20 nM) angiotensin II-induced mobilization of Ca²⁺ and led to an enhanced and sustained contraction of the cells. The contractile response was delayed by approximately 3.5 s with respect to the intracellular increase in Ca²⁺ concentration. The simultaneous registration of Ca²⁺ transients and cell contractions confirms that [Ca²⁺]_i is the major determinant of the angiotensin II-mediated mesangial cell contraction.Dedicated to Professor Horst H. A. Linde on the occasion of his 60th birthday.     

用于白光LED的单一基质白光荧光粉Ca2SiO3Cl2:Eu2+，Mn2+的发光性质

用高温固相法合成了Eu²⁺，Mn²⁺共激活的Ca₂SiO₃Cl₂高亮度白色发光材料，并对其发光性质进行了研究. 该荧光粉在近紫外光激发下发出强的白色荧光，Eu^{2+中心形成峰值为419 nm和498 nm的特征宽带，通过Eu2+中心向Mn2+中心的能量传递导致了峰值为578 nm的发射，三个谱带叠加从而在单一基质中得到了白光. 激发光谱均分布在250—415 nm的波长范围，红绿蓝三个发射带的激发谱峰值分别位于385 nm，412 nm，370 nm和396 nm处，可以被InGaN管芯产生的紫外辐射有效激发. Ca₂SiO₃Cl₂:Eu2+，Mn2+是一种很有前途的单一基质白光LED荧光粉.}     

Ions and atoms in superfluid helium (4He)

New experimental results for mobilities in superfluid helium of the alkali earth ions Be⁺, Mg⁺, Ca⁺, Sr⁺ and Ba⁺ in the temperature region from 1.27 up to 1.66 K are reported. Surprisingly, the temperature dependence of the Be⁺ ion mobility, measured here for the first time, is more similar to that of the He⁺ ion than to the heavier alkali earth ions. This behavior may suggest a snowball like structure for the defect around Be⁺ in contrast to the bubble like defects around the heavier alkali earth ions.     

Residues at the tip of the pore loop of NR3B-containing NMDA receptors determine Ca<Superscript>2+</Superscript> permeability and Mg<Superscript>2+</Superscript>block

Background  

Members of the complex N-methyl-D-aspartate receptor (NMDAR) subfamily of ionotropic glutamate receptors (iGluRs) conventionally assemble from NR1 and NR2 subunits, the composition of which determines receptor properties. Hallmark features of conventional NMDARs include the requirement for a coagonist, voltage-dependent block by Mg²⁺, and high permeability for Ca²⁺. Both Mg²⁺ sensitivity and Ca²⁺ permeability are critically dependent on the amino acids at the N and N+1 positions of NR1 and NR2. The recently discovered NR3 subunits feature an unprecedented glycine-arginine combination at those critical sites within the pore. Diheteromers assembled from NR1 and NR3 are not blocked by Mg²⁺ and are not permeable for Ca²⁺.     

Relationship between cation–π and anion–π interactions: individual binding energies in the π–Mz+–π–X−–π system

The mutual influence of cation–π and anion–π interactions in the π–M^z+–π–X^?–π system (M^z+ = Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, Ca²⁺ and X^? = F^?, Cl^?) has been studied by quantum mechanical calculations. Both geometric parameters and energy data reveal that cation–π and anion–π interactions enhance each other in the π–M^z+–π–X^?–π system. Individual binding energies (E_ion···π) have been estimated in the quintuplet system using a simple new method from electron charge densities calculated at the bond critical points (BCPs) of the ion···π interaction by the atoms in molecules (AIM) method at the M062X/6-31+G(d) level of theory. With respect to the obtained individual binding energies, the strength of an ion···π interaction depends on the cooperative effects of other components.     

The effect of the next nearest neighbor ion on the X-ray photoelectron spectra of 2p levels for Co2+, Ni2+ and Cu2+ in MgO

The X-ray photoelectron spectra of Co, Ni and Cu 2p levels for samples of M_xMg_1-xO (M = Co, Ni, Cu), CoO, NiO and CuO were compared. The binding energies of metal 2p_{$\text{3}\text{2}$} levels did not change with their concentration. The shake-up satellite main peak intensity ratios and FWHM of metal 2p levels for Co²⁺ and Cu²⁺ in MgO were smaller than those for CoO and CuO. The Ni 2p_{$\text{3}\text{2}$} spectrum for Ni²⁺ in MgO had no shoulder, unlike NiO. Results indicate that next nearest neighbor ions (metal ions) may influence the final states after photoelectron ejection.     

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.     

Ca₂BO₃Cl:Ce³⁺,Tb³⁺:A novel tunable emitting phosphor for white light-emitting diode

<正>Ca₂BO₃Cl:Ce³⁺,Ca₂BO₃Cl:Tb³⁺,and Ca₂BO₃Cl:Ce³⁺,Tb³⁺ phosphors are synthesized by a high temperature solid-state reaction.The emission intensity of Ce³⁺ or Tb³⁺ in Ca₂BO₃Cl is influenced by the Ce³⁺ or Tb³⁺ doping content,and the optimum concentrations of Ce³⁺ and Tb³⁺ are 0.03 mol and 0.05 mol,respectively.The concentration quenching effect of Ce³⁺ or Tb³⁺ in Ca₂BO₃Cl occurs,and the concentration quenching mechanism is d-d interaction for either Ce³⁺ or Tb³⁺.The Ca₂BO₃Cl:Ce³⁺,Tb³⁺ can produce colour emission from blue to green by properly tuning the relative ratio between Ce³⁺ and Tb³⁺,and the emission intensity of Tb³⁺ in Ca₂BO₃Cl can be enhanced by the energy transfer from Ce³⁺ to Tb³⁺.The results indicate that Ca₂BO₃Cl:Ce³⁺,Tb³⁺ may be a promising double emission phosphor for UV-based white light emitting diodes.