Blue metal complex pigments involved in blue flower color

The blue pigment of cornflower, protocyanin, has been investigated for a long time, but its precise structure was not entirely explained until recently. The molecular structure of the pigment was recently shown to be a metal complex of six molecules each of anthocyanin and flavone glycoside, with one ferric iron, one magnesium and two calcium ions by X-ray crystallographic analysis. The studies provided the answer to the question posed in the early part of the last century, “why is the cornflower blue and rose red when both flowers contain the same anthocyanin?” This work was achieved on the basis of the results of long years of the studies made by many researchers. In this review, the author focuses on the investigations of the blue metal complex pigments involved in the bluing of flowers, commelinin from Commelina commusis, protocyanin from Centaurea cyanus, protodelphin from Salvia patens and hydrangea blue pigment.     

Calculation of the speed of sound in seawater from the known ion concentrations

It is shown that the method proposed earlier for calculating the speed of sound in seawater from the known ion concentrations, in a strict sense, can be applied for computing the sound speed in seas if, as a model of seawater, one uses a solution containing six ions or a solution containing four ions, namely, Na⁺, Mg²⁺, SO ₄ ^2? , and Cl^?, with the mole concentration of Na⁺ being replaced by the sum of mole concentrations of Na⁺ and K⁺ and the mole concentration of Mg²⁺ being replaced by the sum of mole concentrations of Mg²⁺ and Ca²⁺. An algorithm of calculation is proposed. It is demonstrated that, when the seawater is considered as a solution containing six ions, the computed value of the speed of sound does not depend on the choice of the specific ion whose concentration is determined from the condition of electric neutrality.     

Theoretical studies on the single proton transfer process in adenine base

The effect of metal ions (Mⁿ⁺ = Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺ and hydrated Mg²⁺ ions) and water molecules on the tautomerism of adenine induced by single intramolecular proton transfer (SPT) have been investigated theoretically. Calculated results show that the single proton transfer process in adenine base is favored and even becomes thermodynamically spontaneous because of the presence of Mⁿ⁺ interacting at the N₃ position of adenine. On the contrary, if Mⁿ⁺ coordinated to N₇ site, the single proton transfer process will become unfavorable than that in the neutral system. The effects of metal ions on the SPT of adenine base are more pronounced if Lewis acidity of metal ion is increased. Water plays a more important role than metal ions during the SPT process. It is found that water can act not only as a solvent but also as a mediator which gives and accepts protons to promote SPT, playing a bridge role. As a result, inclusion of a water molecule drastically reduces the energy barrier for the SPT. Moreover, two water molecules can yield larger assisting effect on the SPTs compared with one water molecule. We can conclude that the tautomerism of DNA adenine base can be modulated by the metal ions and water molecules. Copyright © 2015 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.     

Gas phase interaction of L‐proline with Be2+, Mg2+ and Ca2+ ions: a computational study

Geometry optimisation and metal ion affinities (MIAs) of the binding configurations of Be²⁺, Mg²⁺ and Ca²⁺ to L ‐proline were calculated using the hybrid Density Functional Theory (DFT‐B3LYP) and second order Møllet?Plesset perturbation theory (MP2) methods. Be²⁺ was found to bind preferentially in a charge transfer type arrangement through the carbonyl oxygen (? C?O) and the lone pair of the imino‐group nitrogen atom (? NH? ). On the contrary Mg²⁺ and Ca²⁺ were found to prefer binding in a bi‐dentate manner through the carboxylate group of L ‐proline (OCO) in a zwitterion form. The main types of interactions found to influence the binding preference of M²⁺ ions to L ‐proline were (i) charge transfer in the case of Be²⁺ ions and (ii) electrostatic interactions in the case of Mg²⁺ and Ca²⁺ ions. Inspection of the IR stretching of the N? H and the O? H groups of L ‐proline with M²⁺ ions in a chelating configuration (to both O and N atoms) indicated a considerable shift to higher frequency with decreasing MIA. On the other hand, the MIA for the zwitterion L ‐proline with M²⁺ tracks the reciprocal distance of the M²⁺? OCO bond further confirming that the nature of the bond is mainly electrostatic. Comparison with other molecules containing the carboxylic function is also included in order to gain more insight on the types of interaction of this amino acid with metal ions in general. Copyright © 2007 John Wiley & Sons, Ltd.     

Metal ion interaction with ribosomal RNA

Summary We have used UV differential spectroscopy in order to detect small modifications in the ribosomal RNA absorption spectrum due to the binding of rRNA molecules with the metal ions Na⁺, K⁺, Mg²⁺, Ca²⁺, Mn²⁺, Co²⁺ and Ni²⁺. Our data show that all the ions, investigated are involved in ion-type bond with the phosphate groups of rRNA and cause a refolding of the molecules with an overall increase in basebase ?stacking? interactions. Besides this ion-type binding with phosphate groups, transition metal ions Mn²⁺, Co²⁺, and Ni²⁺ are also able to bond directly to the bases To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Effect of additional metal ions on the ratio between the rates of the transformation of the intermediate products of the hydrolysis of adenosine-5′-triphosphoric acid catalyzed the Cu2+ ion (Communication 2: Mathematical modeling of the kinetics of the hydrolysis in the presence of additional Mg2+ ions)

It was previously shown that the hydrolysis of the (CuATP^2? · OH₂)₂ dimeric complex to CuADP^? and an inorganic phosphate occurs in a sequence of two rapid and irreversible steps. Along with the hydrolysis through a common intermediate product, (CuATP^2?)₂OH^?-(DOH^?), the OH^? nucleophile at the Cu²⁺ ion is replaced by OH^? at the positively charged phosphorus atom to form an IntK pentacovalent intermediate (step 1). A mathematical modeling of the kinetics of the hydrolysis catalyzed by the Cu²⁺ base metal ion in the presence of additional Mg²⁺ ions at two pH values, 6.48 and 6.71 (at the ascending branch of the dependence of the initial rate of the hydrolysis on the pH value) is performed. Additional ions affect only the pathway of coupling of the conformational conversion of DOH^?. The rate constant for the forward reaction (IntK→ DOH^?), k ₁, increases from 2 · 10⁷ L mol^?1 min^?1 in the absence of Mg²⁺ to 2.9 · 10⁷ L mol^?1 min^?1 upon introduction of Mg²⁺ ions; rate constant of the reverse reaction IntK → DOH→, k ^?1, decreases from 1 · 10⁵ L mol^?1 min^?1 in the absence of Mg²⁺ to 3 · 10⁴ L mol^?1 min^?1 in the presence of Mg²⁺. The relative concentrations of the intermediate products are demonstrated to change during the irreversible hydrolysis. In the presence of Mg²⁺, IntK emerges at much earlier stages of the hydrolysis, the fraction of formed IntK in the balance of NuP₀ is substantially higher, and the growth of its relative concentration with time in the earlier stages of hydrolysis is much more dramatic.     

The effect of Mg ions on the photoluminescence of Ce-doped silica

In this paper, we report enhanced luminescence of Mg-co-doped silica gels, which were prepared by a sol-gel method. The total amount of Ce³⁺ ions was kept constant in this experiment at 0.5 mol% total doping. Structural, morphological, thermal, optical absorption and photoluminescence studies were employed. The XRD spectra show that all the samples are non-crystalline. Scanning electron microscopy (SEM) images show that the particles were in nano-range and spherical in shape. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) of samples depict that the presence of dopant and co-dopant decreases the endothermic peak temperature; while Ce³⁺ increase the yield, Mg²⁺ reduces it. UV analyses revealed that the presence of Ce³⁺ ions increases transmittance but lowers absorbance of annealed silica xerogels, while that of Mg²⁺ ions reduces transmittance but increases absorbance. Luminescence intensities were compared for different gels with and without Mg particles by varying the different concentrations of Mg. Silica containing Mg²⁺ ions had broad blue emission due to energy transfer from Mg²⁺ to Ce³⁺, which is due to radiative recombination. An increase in luminescence intensity was observed as the Mg²⁺ to Ce³⁺ ratio increased for the range investigated.     

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.     

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.     

Insights into copper coordination in the EcoRI–DNA complex by ESR spectroscopy

The EcoRI restriction endonuclease requires one divalent metal ion in each of two symmetrical and identical catalytic sites to catalyse double-strand DNA cleavage. Recently, we showed that Cu²⁺ binds outside the catalytic sites to a pair of new sites at H114 in each sub-unit, and inhibits Mg²⁺-catalysed DNA cleavage. In order to provide more detailed structural information on this new metal ion binding site, we performed W-band (～94 GHz) and X-band (～9.5 GHz) electron spin resonance spectroscopic measurements on the EcoRI–DNA–(Cu²⁺)₂ complex. Cu²⁺ binding results in two distinct components with different g_zz and A_zz values. X-band electron spin echo envelope modulation results indicate that both components arise from a Cu²⁺ coordinated to histidine. This observation is further confirmed by the hyperfine sub-level correlation results. W-band electron nuclear double resonance spectra provide evidence for equatorial coordination of water molecules to the Cu²⁺ ions.     

Methylene blue as a DNA probe for a comparative study of Cd, Pb and Cr ions binding to calf thymus DNA

Methylene blue (MB) was developed as a sensitive DNA probe for a comparative study of Cd²⁺, Pb²⁺ and Cr³⁺ ions binding with calf thymus DNA (ctDNA). The fluorescence intensity of the MB-ctDNA system increased dramatically when heavy metal ions (Cd²⁺, Pb²⁺ and Cr³⁺ ions) were added, which indicated that some of the bound MB molecules were released from the ctDNA base pairs. To compare the binding affinity of these three different heavy metal ions with ctDNA, the relationships between the fluorescence intensity of the MB-ctDNA-M (Metal ions) system and the concentration ratio of [M]/[DNA(p)] were investigated. The results showed that the order of the binding affinity of heavy metal ions with ctDNA had the following sequence: Cr³⁺> Cd²⁺>Pb²⁺. This order was further proved by the effects of heavy metal ions on the number of MB bound to ctDNA, the measurements of binding constants of these heavy metal ions to ctDNA, and the effects of heavy metal ions on the absorption of the MB-ctDNA system. In addition, the interaction mechanisms of Cd²⁺, Pb²⁺ and Cr³⁺ ions with ctDNA were also discussed in detail. These results indicated that their interaction mechanisms are related to the concentration ratios of heavy metal ions to DNA.     

Photoluminescence and persistent luminescence properties of non-doped and Ti4+-doped Mg2SnO4 phosphors

Mg₂SnO₄ exhibits green photoluminescence and persistent luminescence, which originate from oxygen vacancies. When Ti⁴⁺ ions were doped, an interesting Mg₂SnO₄:Ti⁴⁺ phosphor with bluish white photoluminescence under ultraviolet irradiation and with green persistent luminescence was first obtained. Our investigation reveals that two emission centres exist in Mg₂SnO₄:Ti⁴⁺. The centres responsible for the green emission are considered to be the F centres (oxygen vacancies) and the blue centres are the TiO₆ complex. Trap clusters in the band gap with different depths, such as [Sn_Mg^‥—O_i^″], [Sn_Mg^‥—V_O^·], [Sn_Mg^‥—V_O^×] and Mg_Sn^″, correspond to the components at 85 ℃, 146 ℃ and 213 ℃ of the thermoluminescence curve.     

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.     

Screening effect of Ti ions on the electrical conductivity and thermoelectric power of Mg ferrite

The samples Mg_1+xTi_xFe_2−2xO₄ were prepared in a single phase spinel structure as indicated from X-ray analysis. The preference of Mg²⁺ ions to the octahedral site decreases the ratio of the normal spinel in the investigated ferrite where the Mg²⁺ increases on the expense of the Fe³⁺ ions on the same site. The increase in the conductivity was found to be due to thermally activated mobility of charge carriers. The mobility data enhances the use of Verway model of conductivity which depends on the electron exchange between iron ions of different valences located on the same crystallographic sites. The existence of Ti⁴⁺ ions on the octahedral site screens the polarization and decreases the conductivity of the samples. Peculiar behavior was obtained for Ti content of 0.7 and 0.8 due to the presence of secondary phases.     

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.     

Molecular dynamics simulations of carbon dioxide hydrate growth in electrolyte solutions of NaCl and MgCl2

Molecular dynamics simulations are performed to study the growth of carbon dioxide (CO₂) hydrate in electrolyte solutions of NaCl and MgCl₂. The kinetic behaviour of the hydrate growth is examined in terms of cage content, density profile, and mobility of ions and water molecules, and how these properties are influenced by added NaCl and MgCl₂. Our simulation results show that both NaCl and MgCl₂ inhibit the CO₂ hydrate growth. With a same mole concentration or ion density, MgCl₂ exhibits stronger inhibition on the growth of CO₂ hydrate than NaCl does. The growth rate of the CO₂ hydrate in NaCl and MgCl₂ solutions decreases slightly with increasing pressure. During the simulations, the Na⁺, Mg²⁺, and Cl^? ions are mostly excluded by the growing interface front. We find that these ions decrease the mobility of their surrounding water molecules, and thus reduce the opportunity for these water molecules to form cage-like clusters toward hydrate formation. We also note that during the growth processes, several 5¹²6³ cages appear at the hydrate/solution interface, although they are finally transformed to tetrakaidecahedral (5¹²6²) cages. Structural defects consisting of one water molecule trapped in a cage with its hydrogen atoms being attracted by two Cl^? ions have also been observed.     

Influence of the cation distribution on the magnetization of Y-type hexagonal ferrites

Mössbauer absorption and magnetization measurements have been made in Mg₂?Y and Co₂?Y ferrites. The magnetizations of the various iron sublattices did not show any marked difference in Mg₂?Y, whilst in the case of Co₂?Y three different behaviours of the sublattice magnetizations have been detected. Low-temperature magnetization measurements in Mg₂Y gave evidence of a noncollinear magnetic order. The different magnetic properties of these compounds have been explained on the ground of a preferential occupation by Mg²⁺ and Co²⁺ ions of the inner octahedral sites of the T crystallographic block. The presence in these sites of a non-magnetic ion such as Mg²⁺ is responsible for the peculiar magnetic order observed in Mg₂?Y.     

White light-emitting Mg0.1Sr1.9SiO4:Eu phosphors

Divalent europium-activated strontium orthosilicate Sr₂SiO₄:Eu²⁺ and Mg_0.1Sr_1.9SiO₄:Eu²⁺ phosphors were synthesized through the solid-state reaction technique. Their luminescent properties under ultraviolet excitation were investigated. The X-ray diffraction (XRD) results show that these phosphors are of α′-Sr₂SiO₄ phase with a trace of β-Sr₂SiO₄. Doping of Eu²⁺ ion into the crystal lattice results in the lattice constant being expended, while Mg²⁺ makes the lattice constant shrinking. A solid solution with the same crystal structure is formed when Eu²⁺ or Mg²⁺ substitutes part of Sr²⁺ ions and occupies the same lattice sites. The Sr₂SiO₄:Eu²⁺ phosphors show two emission spectra peaked at 535 and 473 nm originated from the 5d-4f transition of Eu²⁺ ion doped in two different Sr²⁺ sites in the host lattice. By substitution of 0.1 mol of Sr²⁺ with Mg²⁺, these two emission bands are tuned to be in the blue and yellow region (459 and 564 nm for Mg_0.1Sr_1.88SiO₄:Eu_0.02), respectively. The tuning effect is discussed. With a combination of the blue and yellow emission bands the phosphors show white color, indicating that these phosphors may become promising phosphor candidates for white light-emitting diodes (LEDs).     

Solvation structure of magnesium,zinc, and alkaline earth metal ions in N,N‐dimethylformamide,N,N‐dimethylacetamide,and their mixtures studied by means of Raman spectroscopy and DFT calculations—Ionic size and electronic effects on steric congestion

The solvation structure of magnesium, zinc(II), and alkaline earth metal ions in N,N‐dimethylformamide (DMF) and N,N‐dimethylacetamide (DMA), and their mixtures has been studied by means of Raman spectroscopy and DFT calculations. The solvation number is revealed to be 6, 7, 8, and 8 for Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, respectively, in both DMF and DMA. The δ (O C N) vibration of DMF shifts to a higher wavenumber upon binding to the metal ions and the shift Δν(= ν_bound − ν_free) becomes larger, when the ionic radius of the metal ion becomes smaller. The ν (N CH₃) vibration of DMA also shifts to a higher wavenumber upon binding to the metal ions. However, the shift Δν saturates for small ions, as well as the transition‐metal (II) ions, implying that steric congestion among solvent molecules takes place in the coordination sphere. It is also indicated that, despite the magnesium ion having practically the same ionic radius as the zinc(II) ion of six‐coordination, their solvation numbers in DMA are significantly different. DFT calculations for these metalsolvate clusters of varying solvation numbers revealed that not only solvent–solvent interaction through space but also the bonding nature of the metal ion plays an essential role in the steric congestion. The individual solvation number and the Raman shift Δν in DMF–DMA mixtures indicate that steric congestion is significant for the magnesium ion, but not appreciable for calcium, strontium, and barium ions, despite the solvation number of these metal ions being large. Copyright © 2006 John Wiley & Sons, Ltd.