Influence of cation binding on the electro-optically determined electric moments of purple membranes

Analysis of the elect ro-optically determined permanent dipole moment and electric polarizability of purple membrane fragments reveals the complex nature of the membrane electric moments.The problem to distinguish between the contribution of the membrane structural charges (charged groups of the polypeptide chain and polar lipid headarouos), bound cations and the electric double layer structure deserves particular attention not only because of its importance for electro-optics but also in respect to the relation of the membrane surface electric properties to the membarans transport function.The removal of divalent cations (Ca²⁺ and Mg²⁺) bound to purple membrane in the native state induces a cat ion-free species or purple membrane (deionized - blue membrane) with drastically changed spectroscopic properties and function. The preseent paper summarizes our study on the electric moments of blue membrane and their changes during the blue to purple transition. We intended to provide an insight into the possible regulation of this reversible transition (purple-to-blue and blue-to-purple) through changes of the asymmetric charge distribution and the importance of the asymmetric interfacial charge distribution for the proton transfer in purple membranes.The changes in the electric moments (permanent and induced dipole moments) of purple membrane fragments upon di- and trivalent cations binding to cation-depleted purple membranes were studied by electric light scattering (rotational electrokinetics) in d.c. and a.c. electric fields, and by electric pulses with reversing polarity, the results show a recovery of the membrane charge asymmetry (permanent dipole moment) though not of the induced dipole moment.     

Dual Control of Peptide Conformation with Light and Metal Coordination

The design of a stimuli-responsive peptide whose conformation is controlled by wavelength-specific light and metal coordination is described. The peptide adopts a defined tertiary structure and its conformation can be modulated between an α-helical coiled coil and β-sheet. The peptide is designed with a hydrophobic interface to induce coiled coil formation and is based on a recently described strategy to obtain switchable helix dimers. Herein, we endowed the helix dimer with 8-hydroxyquinoline (HQ) groups to achieve metal coordination and shift to a β-sheet structure. It was found that the conformational shift only occurs upon introduction of Zn²⁺; other metal ions (Cu²⁺, Fe³⁺, Co²⁺, Mg², and Ni²⁺) do not offer switching likely due to non-specific metal-peptide coordination. A control peptide lacking the metal-coordinating residues does not show conformational switching with Zn²⁺ supporting the role of this metal in stabilizing the β-sheet conformation in a defined manner.     

Study of Bulk Membrane Transport of Some Heavy Metal Cations Using Three Macrocyclic Ligands Containing Oxygen and Nitrogen Heteroatoms

The transport experiments of Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Ag⁺ and Pb²⁺ metal cations were carried out by dibenzo-18-crown-6 (DB18C6), dibenzyl-diaza-18-crown-6 (Dibenzyl-diaza-18C6) and di-tert-butyl-dibenzo-18-crown-6 (Di-tert-butyl-DB18C6) using chloroform (CHCl₃), 1,2-dichloroethane (1,2-DCE) and nitrobenzene (NB) organic solvents as liquid membranes. The source phase contained equimolar concentration of these metal cations and the source and receiving phases being buffered at pH=5 and pH=3, respectively. The obtained results show that the selectivity and the efficiency of transport for these heavy metal cations change with the nature of the ligand and also the organic solvents, which were used as liquid membranes in these experiments. A good selectivity was observed for silver (I) ion by dibenzyl-diaza-18C6 in all membrane systems. Dibenzo-18C6 and di-tert-butyl-DB18C6 showed the highest transport efficiency for cobalt (II) ion. The effect of stearic acid on transport efficiency was also investigated and the results show that the efficiency of transport of the heavy metal cations increases in the presence of this organic acid.     

Mass transfer determining parameter in facilitated transport through di-(2-ethylhexyl) dithiophosphoric acid activated composite membranes

Activated composite membranes (ACMs) containing di-(2-ethylhexyl) dithiophosphoric acid (D2EHDTPA) as a carrier have been found to facilitate the transport and separation of several cations. This paper describes an approach to the chemical characterisation of the transport phenomena of Zn²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Sn²⁺ and In³⁺ by an ACM. The selectivity of D2EHDTPA based ACM towards different metal ions is presented and discussed focusing in Zn²⁺ and Cd²⁺ transport and recovery. Selectivity demonstrates that zinc ions are removable from mixtures due to the different extraction strength of D2EHDTPA. Such selectivity is based on the differences of the dynamic behaviour of the metal ions transport. In addition, a correlation of the chemical behaviour of those ACM systems with the corresponding solvent extraction systems has been found.     

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.     

How Divalent Cations Interact with the Internal Channel Site of Guanine Quadruplexes

The formation of guanine quadruplexes (GQ) in DNA is crucial in telomere homeostasis and regulation of gene expression. Pollution metals can interfere with these DNA superstructures upon coordination. In this work, we study the affinity of the internal GQ channel site towards alkaline earth metal (Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺), and (post-)transition metal (Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺) cations using density functional theory computations. We find that divalent cations generally bind to the GQ cavity with a higher affinity than conventional monovalent cations (e. g. K⁺). Importantly, we establish the nature of the cation-GQ interaction and highlight the relationship between ionic and nuclear charge, and the electrostatic and covalent interactions. The covalent interaction strength plays an important role in the cation affinity and can be traced back to the relative stabilization of cations’ unoccupied atomic orbitals. Overall, our findings contribute to a deeper understanding of how pollution metals could induce genomic instability.     

Effect of metal cations on corrosion behavior and surface film structure of the A3003 aluminum alloy in model tap waters

The effect of the metal cations, Na⁺, K⁺, Ca²⁺, Mg²⁺, Zn²⁺, and Ni²⁺, on the oxide film structure and morphology changes during long-term immersion corrosion tests of aluminum alloy (A3003) in model tap waters was investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy. The effect of the metal cations on the corrosion behavior was also investigated with mass change and electrochemical tests. The hardness of the metal cations, X, based on the hard and soft acids and bases (HSAB) concept was applied to explain the effect of metal cations on the passive oxide film structure and corrosion resistance. The mass change rate and corrosion current density decreased with increasing metal cation hardness. The XPS results showed that hard metal cations like Zn²⁺ and Ni²⁺ were incorporated in the oxide films, while the four soft metal cations were not incorporated in the oxide films. The results are in good agreement with those which could be expected from the HSAB hardness of the metal cations.     

Synthesis and evaluation of 3-acyltetronic acid-containing metal complexing agents

Potential metal chelators containing one or several acyltetronic acid moieties were prepared from cyclic or acyclic amines and polyamines, and from bis(phenols) by reaction with 1–4 equiv of 3-bromoacetyltetronic acid in the presence of potassium carbonate. The affinity constants of the chelating agents for toxic metallic cations Cd²⁺, Cs⁺, and Pb²⁺ and for dimethylarsinic acid were measured, at pH 7.5 and 9.3. Compound 4, an acyclic triamine containing four acyltetronic moieties, was found to complex efficiently all the tested species.     

Structure and Stability of Complexes of <Emphasis Type="Italic">N,N</Emphasis>′-Di(9-anthrylmethyl)-1,2-diaminoethane with Cations of Metals from IIB group: Quantum-chemical Study

Structural and energy characteristics of N,N′-di(9-anthrylmethyl)-1,2-diaminoethane complexes with Z²⁺, Cd²⁺, and Hg²⁺ cations were investigated applying the method DFT (B3LYP/LanL2DZ). The interaction of the diamine with the metal cations results in formation of complexes with various types of structures containing a di-, tri-, or tetracoordinated metal, the latter complexes being the most stable. In all types of complexes the energy of complexing decreases in the series Zn²⁺, Hg²⁺, Cd²⁺ and is determined by combined effect of steric and orbital factors.     

Effect of Na+ and Ca2+ Ions on a Lipid Langmuir Monolayer: An Atomistic Description by Molecular Dynamics Simulations

Studying the effect of alkali and alkaline‐earth metal cations on Langmuir monolayers is relevant from biophysical and nanotechnological points of view. In this work, the effect of Na⁺ and Ca²⁺ on a model of an anionic Langmuir lipid monolayer of dimyristoylphosphatidate (DMPA^?) is studied by molecular dynamics simulations. The influence of the type of cation on lipid structure, lipid–lipid interactions, and lipid ordering is analyzed in terms of electrostatic interactions. It is found that for a lipid monolayer in its solid phase, the effect of the cations on the properties of the lipid monolayer can be neglected. The influence of the cations is enhanced for the lipid monolayer in its gas phase, where sodium ions show a high degree of dehydration compared with calcium ions. This loss of hydration shell is partly compensated by the formation of lipid–ion–lipid bridges. This difference is ascribed to the higher charge‐to‐radius ratio q/r for Ca²⁺, which makes ion dehydration less favorable compared to Na⁺. Owing to the different dehydration behavior of sodium and calcium ions, diminished lipid–lipid coordination, lipid–ion coordination, and lipid ordering are observed for Ca²⁺ compared to Na⁺. Furthermore, for both gas and solid phases of the lipid Langmuir monolayers, lipid conformation and ion dehydration across the lipid/water interface are studied.     

Cucurbit[8]uril-improved recognition using a fluorescent sensor for different metal cations

ABSTRACT

Metal cations in aqueous solutions at different pHs (1.5, 4.5 and7.2) can be detected using the known inclusion complex H33258@Q8 as a fluorescent probe. Indeed, the fluorescence intensity of H33258 increases rapidly upon increasing the amount of Q[8] up to a Q[8]:H33258 ratio of 2:1, even at pH 1.5. The experimental results reveal that the probe not only exhibited selective recognition of metal cations at different pH but also showed different recognition for metal cations at different pHs. At pH 7.2, the probe responded to quite a variety metal cations, including one of the third main group elements, Al³⁺, four transition metal cations, Hg²⁺, Fe³⁺, Fe²⁺, and Cr³⁺ and three lanthanide cations Eu³⁺, Tm³⁺ and Yb³⁺; At pH 4.5, the probe responded to only two transition metal cations, Hg²⁺ and Fe³⁺. Unexpectedly, the probe lost its recognition properties at pH 1.5.     

Cation Complexation by a Lower Rim Calix(4)arene Derivative: Structural,Electrochemical and Thermodynamic Studies

The synthesis and characterization (¹H and ¹³C NMR) of a partially substituted lower rim p-tert-butylcalix(4)arene, namely, 5,11,17,23-tetra-4-tert-butyl-25,27-bis(diethylphosphate amino)ethoxy-26,28-dihydroxycalix[4]arene (1), are reported. The solution thermodynamics of the ligand in a variety of solvents at 298.15?K was investigated through solubility (hence standard Gibbs energy of solution) measurements while the calorimetric technique was used to derive the standard solution enthalpy. These data were used to calculate the standard entropy of solution. An enthalpy–entropy compensation effect is shown and, as a result, slight variations are observed in the transfer Gibbs energies of this ligand from the reference to other solvents. ¹H NMR, conductance and calorimetric measurements were carried out to establish the degree of interaction of the ligand with univalent (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ and Ag⁺) and bivalent (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺, Cd²⁺, Hg²⁺, Cu²⁺, Zn²⁺) cations in acetonitrile, methanol, N,N-dimethylformamide and propylene carbonate. No complexation was found between this ligand and univalent cations in these solvents. As far as the bivalent cations are concerned, interaction between 1 and these cations was found only in acetonitrile. The versatile behaviour of this ligand with bivalent cations in this solvent is reflected by the formation of complexes of different stoichiometry. Thus the interaction of 1 with alkaline-earth (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) and Pb²⁺ metal cations leads to the formation of 1:2 (cation:ligand) complexes. However, for other bivalent metal cations (Cu²⁺, Zn²⁺, Cd²⁺ and Hg²⁺) the complex stoichiometry was found to be 1:1. The results are discussed in terms of the key role played by acetonitrile in processes involving calix[4]arene derivatives.     

A new rhodamine-based fluorescent chemosensor for transition metal cations synthesized by one-step facile condensation

A new rhodamine-based fluorescent chemosensor (1) for transition metal cations was synthesized by one-step facile condensation of rhodamine B and 2-aminopyridine. Without metal cations, 1 is colorless and nonfluorescent, whereas addition of metal cations (Fe³⁺, Hg²⁺, Pb²⁺, and Fe²⁺) leads to an obvious color change to pink and an appearance of orange fluorescence.     

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.     

Influence of Cations on the Formation of Cobalt(II) Complexes with Thiocyanate Ions in Solutions of Nonionic Micelles

The influence of additives of alkali, alkaline-earth, and several transition metal cations, protonated amines, and quaternary ammonium on the state of the tetrahedral cobalt(II) thiocyanate complex is studied in an aqueous solution of the nonionogenic surfactant Triton X-100. It is shown that alkali and alkaline-earth metal cations and compounds containing protonated primary amino groups favor the formation of additional amounts of the micellar-bonded [Co(NCS)₄]^2– complex anion. This fact is explained by the interaction of these cations with the oxyethylene chains of the nonionogenic surfactant as was observed in the crown ether coordination. This provides the formation and transfer into micelles of additional amounts of their associates with [Co(NCS)₄]^2–. The Mn²⁺, Ni²⁺, and Cd²⁺ cations decompose cobalt tetrathiocyanate due to the formation of their own complexes with the ligand. This effect is not observed in the case of the quaternary ammonium compounds, which is explained by their incapability of coordinating the oxyethylene chains of the nonionogenic surfactant.     

Qualitative and quantitative 1H NMR spectroscopy for determination of divalent metal cation concentration in model salt solutions,food supplements,and pharmaceutical products by using EDTA as chelating agent

This paper introduces an ¹H NMR method to identify individual divalent metal cations Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Sn²⁺, and Pb²⁺ in aqueous salt solutions through their unique signal shift and coupling after complexation with the salt of ethylenediaminetetraacetic acid (EDTA). Furthermore, quantitative determination applied for the divalent metal cations Ca²⁺, Mg²⁺, Hg²⁺, Sn²⁺, Pb²⁺, and Zn²⁺ (limit of quantification: 5–22 μg/ml) can be achieved using an excess of EDTA with aqueous model salt solutions. An internal standard is not required because a known excess of EDTA is added and the remaining free EDTA can be used to recalculate the quantity of chelated metal cations. The utility of the method is demonstrated for the analysis of divalent cations in some food supplements and in pharmaceutical products.     

Metal ion complexation in acetonitrile by di-ionized calix[4]arenes bearing two dansyl fluorophores

The influence of metal cations (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Ag⁺, Cd²⁺, Co²⁺, Fe²⁺, Hg²⁺, Mn²⁺, Pb²⁺, Zn²⁺ and Fe³⁺) on the spectroscopic properties of two dansyl (1-dimethylaminonaphthalene-5-sulfonyl) groups linked to the lower rims of a series of three, structurally related, di-ionized calix[4]arenes was investigated by means of absorption and emission spectrophotometry. Di(tetramethylammonium) salts of the di-ionized ligands, (TMA)₂L1, (TMA)₂L2 and (TMA)₂L3, which differ in having zero, two and four tert-butyl groups, respectively, on the upper rim of the calix[4]arene scaffold were utilized for the spectrofluorimetric titration experiments in acetonitrile. On complexation by alkaline earth metal cations, both the absorption and emission spectra undergo marked red shifts and quenching of the dansyl fluorescence. These effects are weaker with alkali metal cations. Transition metal cations interact strongly with the ligands. In particular, Fe³⁺, Hg²⁺ and Pb²⁺ cause greater than 97% quenching of the dansyl fluorescence in the di-ionized ligands.     

Chromogenic derivatives of new bis(phenylhydrazono-1H-tetrazol-5-yl-acetonitriles) – synthesis and properties

Derivatives of bis(phenylhydrazono-1H-tetrazol-5-yl-acetonitriles) with oxygen and sulphur atoms in the structure of aliphatic chains were successfully synthesised. The correlation between the ligand structure and its complexation properties was investigated by absorption spectroscopy. The formation of complexes of presented compounds with metal cations (Cu²⁺, Ni²⁺, Zn²⁺, Co²⁺, Fe²⁺ and Pb²⁺) was studied. Ligands 5–8 were additionally applied as ion carriers in ion-selective membrane electrodes. Membranes of ion-selective electrodes doped with these ligands are selective to Cu²⁺ and Pb²⁺ cations.     

Synthesis of Novel 4‐((Substituted bis‐indolyl)methyl)‐benzo‐15‐crown‐5 for the Colorimetric Detection of Hg2+ Ions in an Aqueous Medium

A practical, two‐step synthesis of novel 4‐(substituted bis‐indolyl)methyl)benzo‐15‐crown‐5 has been reported. The strategy employed for the synthesis of the desired molecules involved Duff formylation of benzo‐15‐crown‐5 to get 4‐formyl benzo‐15‐crown‐5 followed by subsequent reactions with substituted indoles in trifluoroacetic acid to yield novel 4‐(substituted bis‐indolyl)methyl)benzo‐15‐crown‐5 in moderate to good yield. One of the reported novel molecule tested for the complexation behavior with various metal cations, such as Li⁺, Na⁺, K⁺, Mg²⁺ Ca²⁺, Al³⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Sn²⁺, Ba²⁺, Hg²⁺, and Pb²⁺, showed a visual colorimetric probe for the detection of mercury cations (Hg²⁺) in an aqueous medium.     

Complexes of Schiff base of gossypol with n-butylamine and some monovalent or bivalent cations studied by ESI MS, NMR, FT-IR as well as PM5 semiempirical methods

A Schiff base of gossypol with n-butylamine [GSBN] was shown to be capable of complexation of 2H⁺, Li⁺, Ca²⁺ and Ba²⁺ cations. This process of complex formation was studied by ESI mass spectrometry, ¹H and ¹³C NMR and FT-IR spectroscopy as well as by PM5 semiempirical method. It was found that gossypol Schiff base can form a 1:2 complex with H⁺ and 1:1 complexes with Li⁺, Ca²⁺ and Ba²⁺ cations. In all complexes the Schiff base of gossypol with metal cations exists in enamine-enamine tautomer, whereas in the 1:2 complex with H⁺ the imine-imine tautomer was found. The metal cations are coordinated through oxygen atoms of the O₁H(O₁,H) hydroxyl groups and a lone pair of an N-atom. The structures of these complexes were calculated by PM5 semiempirical method and discussed.