Alkali Cation Binding Research Articles

Towards Responsive Spiroborate‐Based Assemblies of Podand‐Type Ligands Functionalized with Two Terminal/Peripheral Catecholate Moieties in the Presence of Alkali Cations

AbstractThe synthesis of two ligands bearing two terminal catecholate binding sites connected by an oligo(ethyleneglycol) bridge of two distinct lengths and their self‐assembly upon boron coordination and alkali cation binding (M=Li, Na, K, Cs) are reported. Attempts to synthesize positional isomers of the ligands are also described. Binding of the four alkali cations M+ through M−O interactions was studied depending on the length of the oligo(ethyleneglycol) chain in solution by 1H and DOSY NMR, mass spectrometry (MS) and in the solid‐state by X‐ray diffraction (XRD) on single crystals. MS spectrometry as well as 1H NMR revealed the presence of monomeric and oligomeric spiroborate compounds. Two monomeric macrocycles could be characterized by XRD, entrapping either lithium or cesium cations within the spiroborate macrocycle.

Does alkali cation binding to aromatic ring retard the fluxional haptotropic migration? Evidences from density functional study

DFT calculations were performed on the sandwich complexes of naphthalene (MNC) with alkali metal cation $$(\hbox {Li}^{+}/\hbox {Na}^{+}/\hbox {K}^{+})$$ on one $${\uppi }$$ face and the tripodal $$\hbox {Cr(CO)}_{3}$$ moiety on the other with a view to explore the role of cation on haptotropic migration. Cation binding not only enhances the complex interaction energy but also delicately affects the fluxionality in the molecule by increasing the barrier to haptotropic shift of $$\hbox {Cr(CO)}_{3}$$ . The competing nature of the bifacial acids with sandwiched aromatic ring is established. In line with Pearson’s HSAB principle, LiNC system with highest interaction energy is found to be the most stable one among all the systems under study. Synopsis:DFT calculations were performed on the sandwich complexes of naphthalene with alkali metal cation $$(\hbox {Li}^{+}/ \hbox {Na}^{+}/ \hbox {K}^{+})$$ on one $${\uppi }$$ face and the tripodal $$\hbox {Cr(CO)}_{3}$$ moiety on the other with a view to explore the role of cation on haptotropic migration.

Interactions of Alkali Metal Chlorides with Phosphatidylcholine Vesicles

We study the interaction of alkali metal chlorides with lipid vesicles made of palmitoyloleoylphosphatidylcholine (POPC). An elaborate set of techniques is used to investigate the binding process at physiological conditions. The alkali cation binding to POPC is characterized thermodynamically using isothermal titration calorimetry. The isotherms show that for all ions in the alkali group the binding process is endothermic, counterintuitively to what is expected for Coulomb interactions between the slightly negatively charged POPC liposomes and the cations. The process is entropy driven and presumably related to the liberation of water molecules from the hydration shells of the ions and the lipid headgroups. The measured molar enthalpies of the binding of the ions follows the Hofmeister series. The binding constants were also estimated, whereby lithium shows the strongest affinity to POPC membranes, followed by the rest of the ions according to the Hofmeister series. Cation adsorption increases the net surface potential of the vesicles as observed from electrophoretic mobility and zeta potential measurements. While lithium adsorption leads to slightly positive zeta potentials above a concentration of 100 mM, the adsorption of the rest of the ions mainly causes neutralization of the membrane. This is the first study characterizing the binding equilibrium of alkali metal chlorides to phosphatidylcholine membranes at physiological salt concentrations.

On the Concept of Critical Surface Excess of Micellization

The critical surface excess of micellization (CSEM) should be regarded as the critical condition for micellization of ionic surfactants instead of the critical micelle concentration (CMC). There is a correspondence between the surface excesses Γ of anionic, cationic, and zwitterionic surfactants at their CMCs, which would be the CSEM values, and the critical association distance for ionic pair association calculated using Bjerrum's correlation. Further support to this concept is given by an accurate method for the prediction of the relative binding of alkali cations onto dodecylsulfate (NaDS) micelles. This method uses a relative binding strength parameter calculated from the values of surface excess Γ at the CMC of the alkali dodecylsulfates. This links both the binding of a given cation onto micelles and the onset for micellization of its surfactant salt. The CSEM concept implies that micelles form at the air-water interface unless another surface with greater affinity for micelles exists. The process would start when surfactant monomers are close enough to each other for ionic pairing with counterions and the subsequent assembly of these pairs becomes unavoidable. This would explain why the surface excess Γ values of different surfactants are more similar than their CMCs: the latter are just the bulk phase concentrations in equilibrium with chemicals with different hydrophobicity. An intriguing implication is that CSEM values may be used to calculate the actual critical distances of ionic pair formation for different cations, replacing Bjerrum's estimates, which only discriminate by the magnitude of the charge.

Characterization of selective binding of alkali cations with carboxylate by x-ray absorption spectroscopy of liquid microjets

We describe an approach for characterizing selective binding between oppositely charged ionic functional groups under biologically relevant conditions. Relative shifts in K-shell x-ray absorption spectra of aqueous cations and carboxylate anions indicate the corresponding binding strengths via perturbations of carbonyl antibonding orbitals. XAS spectra measured for aqueous formate and acetate solutions containing lithium, sodium, and potassium cations reveal monotonically stronger binding of the lighter metals, supporting recent results from simulations and other experiments. The carbon K-edge spectra of the acetate carbonyl feature centered near 290 eV clearly indicate a preferential interaction of sodium versus potassium, which was less apparent with formate. These results are in accord with the Law of Matching Water Affinities, relating relative hydration strengths of ions to their respective tendencies to form contact ion pairs. Density functional theory calculations of K-shell spectra support the experimental findings.

Alkali Cation Binding and Permeation in the Rat Organic Cation Transporter rOCT2

Organic cation transporters of the OCT family mediate downhill transport of organic cations, compatible with carrier, pore, or gate-lumen-gate mechanisms. We studied rat OCT2 expressed in Xenopus oocytes by the two-electrode voltage-clamp technique, including membrane capacitance (C(m)) monitoring. Choline, a transported cationic substrate, elicited the expected inward currents but also elicited decreases of C(m). Similar C(m) decreases were caused by the non-transported inhibitors tetrabutylammonium (a cation) and corticosterone (uncharged). Effects on C(m) were voltage-dependent, with a maximum at -140 mV. These findings suggest that the empty rOCT2 protein can undergo an electrogenic conformation change, with one conformation highly favored at physiological voltage. Moreover, alkali cations elicited considerable inward currents and inhibited uptake of [(14)C]tetraethylammonium with a sequence Cs(+) > Rb(+) > K(+) > Na(+) approximately Li(+). Cs(+) affected current and capacitance with similar affinity (K(0.5) approximately 50 mm). Tetraethylammonium inhibited Cs(+) currents in a concentration-dependent manner. Conversely, Cs(+) inhibited tetraethylammonium uptake by a competitive mechanism. Activation energy of the currents estimated from measurements between 12 degrees C and 32 degrees C was approximately 81 kJ/mol for Cs(+) and 39 kJ/mol for tetramethylammonium, compatible with permeation of Cs(+) through rOCT2 along the same path as organic substrates and by a mechanism different from simple electrodiffusion. Rationalization of Cs(+) selectivity in terms of a pore pointed to a pore diameter of approximately 4 A. Intriguingly, that value matches the known selectivity of rOCT2 for organic compounds. Our data show that selective permeability of rOCT2 is not determined by ligand affinity but might rather be understood in terms of the ion channel concept of a distinct "selectivity filter."

The synthesis of tetracarbonyl derivatives of thiacalix[4]arene in different conformations and their complexation properties towards alkali metal ions

The three conformations of 5,11,17,23-tetra- tert-butyl-25,26,27,28-tetrakis[(benzoyl)methoxy]-2,8,14,20-tetrathiacalix[4]arene 1 : cone, partial cone and 1,3- alternate, were prepared by the treatment of 5,11,17,23-tetra- tert-butyl-2,8,14,20-tetrathiacalix[4]arene-25,26,27,28-tetraol (TCA) with α-bromo acetophenone in the presence of appropriate alkali carbonate M 2CO 3 (M=Na, K, Cs) as base catalyst in acetonitrile. Structure of the conformers were established by 1H NMR, 1H– 1H COSY, 1D NOE, 2D ROESY and X-ray experiments. The alkali cation binding selectivity of the obtained macrocycles was investigated by the ion-pair extraction method.

Supramolecular Chemistry: Computer-Assisted Instruction in Undergraduate and Graduate Chemistry Courses

An interactive electronic textbook (SC-WEB) based on Supramolecular Chemistry, by J.-M. Lehn, is described. It includes the text, which has been specially adapted for teaching, and data on the structures of molecules and supermolecules. The list includes about 100 structures retrieved from the Cambridge Structural Database (version 1997) as well as those obtained from molecular dynamics simulations in solution. The structures can be retrieved either from the text or, independently, from the list.SC-WEB uses two types of programs: the first one reads files in HTML format (Word97, Netscape, or Internet Explorer), and WebLab Viewer Lite is used for visualizing and manipulating the structures. It can run on any PC (W95/NT4.0) computer.The application of SC-WEB for a course in supramolecular chemistry, as well as in other chemical courses, is discussed. A few examples related to the binding of alkali cations by organic and inorganic receptors, and of R-NH3+ cations by organic receptors, are considered in more ...

Cation binding properties of photodimerizable polymers bearing benzodiglyme units

AbstractThe polymers which have glyme units as alkali cation binding sites and photodimerizable cinnamoyl units were prepared by the radical polymerization of corresponding monomers. The alkali cation binding ability and selectivity of the polymers, which were studied by a method of picrate salts extraction, were strongly dependent on the length of glyme chains. When irradiated with ultraviolet light, the cinnamoyl groups caused dimerization in dilute solutions. Although the photodimerization of the polymers with relatively short glyme chains enhanced their cation binding ability, the photodimerization of the polymers bearing long glyme chains reduced their cation binding ability. The use of alkali metal cations as templates emphasized the effect of photodimerization on the cation binding properties. The effect of alkali metal cations on the quantum yields of the photodimerization of the polymers showed that two or more benzodiglyme units took part in the binding of one cation. The polymers bearing benzodiglymes, crown ethers, and cinnamoyl moieties were also prepared by the radical copolymerization of the corresponding monomers. It was found that the crown ether units of the copolymers predominantly participated in the cation binding. The photodimerization of the copolymers with suitable alkali metal cations as templates strongly enhanced their cation binding ability.

Synthesis and alkali cation binding properties of photodimerizable polymers with differently sized crown ethers

Polymers, with differently sized crown ethers as alkali cation binding sites and photodimerizable cinnamoyl moieties in their side-chains, were prepared by the cationic copolymerization of the corresponding monomers. The form of the crown-cation complexes (1:1 or 2:1) was studied by measuring quantum yields for the photodimerization of the crown-connected cinnamoyl units in the presence of alkali metal chlorides and by measuring the shift of λ max of alkali metal picrates in THF on addition of the crown polymers. The alkali metal cation binding ability and selectivity of the photodimerizable polymers with different crown ethers (studied by a method of picrate salts extraction) were compared with those of blended samples of the photodimerizable polymers with one kind of crown ether unit. On irradiation with u.v. light, the crown-connected cinnamoyl moieties of the polymers dimerized even in dilute solutions. Studies were made of the effects on the alkali cation binding ability and selectivity of: the photo- The effects on the alkali cation binding ability and selectivity of: the photodimerization of the cinnamoyl moieties of the polymers; the degree of photodimerization of the polymers; and the kind of alkali cations used as templates during the photodimerization of the polymers; were studied.

Synthesis and ionophore properties of a series of new tetrapyrazolic macrocycles

The synthesis of several macrocycles containing two bipyrazolic subunits, with different cavity sizes and with donor-group-bearing side arms attached, is reported. Their alkali cation binding ability has been studied from two aspects : extraction and transport through an artificial liquid membrane. Macrocycles described here show a high selectivity towards Li + and Na + cations; furthermore one of them is remarkably well adapted to extract selectively and to transport efficiently the lithium cation in competitive conditions.

Alkali cation binding of polymers with different sized crown ethers and photodimerizable units

AbstractThe polymers which have different sized crown ethers as alkali cation binding sites and photodimerizable cinnamoyl units were prepared by the cationic copolymerization of corresponding monomers. The crown–cation complexation ratio (1:1 or 2:1) was investigated by measuring quantum yields ϕ of the photodimerization of the crown‐connected cinnamoyl units in the presence of alkali metal chlorides and also by measuring the shift of λmax of alkali metal picrates in THF on addition of the crown polymers. A significant 1:2 complex formation of alkali cations with two different sized crown ether units in the side chain of the polymers was confirmed. The alkali metal cation binding ability and selectivity of the polymers, which were studied by a method of picrate salts extraction, were markedly different from those expected from the combination of polymers of same ring‐size crown ether units. When irradiated with ultraviolet (UV) light, the cinnamic acid ester groups of the polymers caused dimerization even in dilute solutions. The cation binding ability of the polymers was largely enhanced by the photodimerization of the cinnamoyl moieties with suitable template cations.

Cation binding properties of polyesters with photodimerizable groups and oxyethylene units. Effect of photocrosslinking with template cations

Polyesters with p-phenylene diacrylate units as photodimerizable groups and oxyethylene units as cation binding sites were prepared, COCHCHC 6H 4CHCHCOO+CH 2CH 2O+ m . The numbers m of repeating oxyethylene units in the oligoethylene glycols were 4, 5, 6 and 7. The alkali cation binding ability of the polymers increased with increases of m for all alkali metal cations examined. The cation selectivity order was found to be K + ≈ Rb + > Cs + > NH 4 + > Na + for all the polymers used. On irradiation with u.v. light, the polymers became insoluble. The polymer ( m = 7) which was crosslinked photochemically in the presence of potassium acetate as a template showed enhanced cation binding ability for alkali cations, especially for K + and Rb + cations, compared with the photocrosslinked polymers without templates.

Cation binding to “crown” ethers: An ab initio model study

An STO/3G study of the binding of alkali cations to dimethylether is performed. The study of the conformation of free 12-crown-4 and of its Li + complex indicates that a modification of the conformation of the polyether accompanies the complexation.

A molecular mechanism for biological calcification

A general mechanism for calcification in biological systems is outlined which consists of organization of macromolecules and simultaneous or subsequent binding of alkali cations (principally Ca 2+) by the molecules to create compartments with higher pH values than the bulk phase of the solution. The higher pH value in this microcompartment would raise the concentration of PO 4 3− and OH − to an extent sufficient to induce their precipitation with Ca 2+.

The detection of ionophorous antibiotic-cation complexes in water with fluorescent probes.

The binding of alkali cations by the ionophorous antibiotics valinomycin, nigericin, alamethicin, and the macrotetralide actins has been shown to occur, in aqueous media, by the use of the fluorescent probes 1-anilino-8-naphthalene sulfonate and 2-p-toluidinyl-6-naphthalene sulfonate. The interaction of the ionophore-cation complexes with the fluorescent dyes produced enhanced fluorescence emission, increased lifetime and polarization, and a significant blue-shift of the emission maxima of the fluorescence spectrum. At constant antibiotic and fluorophore concentrations in water, the intensity of the fluorescence emission was found to be a function of the cation concentration. This permitted relative cation affinities to be determined for alamethicin (Na(+) congruent with K(+)), valinomycin (Rb(+) > K(+) > Cs(+)), nigericin (K(+) > Rb(+) > Na(+) > Cs(+)) and trinactin (NH(4) (+) > K(+) > Rb(+) > Cs(+)).

A KINETIC STUDY OF THE ABSORPTION OF ALKALI CATIONS BY BARLEY ROOTS

The absorption of inorganic salts by plant roots and other biological systems depends upon metabolic processes. When absorption proceeds against a concentration gradient, an expenditure of metabolically derived energy is obviously required. In some systems, such as barley roots, even absorption along a concentration gradient is negligible under conditions of arrested metabolism; and the concentration of the salt in the sap fails to reach the level of the outside solution (12, 13, 17). The absorption process is characterized by a considerable degree of selectivity. The discrimination on the part of living cells between potassium and sodium is particularly striking. Most living cells accumulate potassium in preference to sodium, even when the external environment is rich in sodium and poor in potassium. The view has come to the fore in recent years that both the role of metabolism and the specificity in the absorption process can best be accounted for by assuming that ion binding compounds are generated by metabolic processes. General reviews which make this point include those by Ussing (29), Robertson (25), and Steinbach (27). Osterhout (22) has succinctly stated some of the problems for whose solution such a concept would be useful. Osterhout (22) and Jacobson and Overstreet (14) have outlined several properties which the ion binding compounds must possess to account for characteristic features of the absorption process. These workers also stress the need for assuming that the complex is labile and breaks down again, releasing the ions. Cowie et al. (5), Roberts et al. (23), Conway et al. (4), Eddy et al. (7), and Eddy and Hinshelwood (8, 9) have investigated the problem of ion binding in microorganisms, arriving at similar views. Roberts and his co-workers (23, 24) and Eddy and co-workers (7, 8) have related the binding of alkali cations to carbohydrate metabolism, and Bolton and Roberts (1) have produced evidence that the hexose phosphates are responsible for the binding of potassium in Escherichia coli. The hypothesis that the absorption of inorganic ions involves their combination with binding compounds forms the basis of the present study. Evidence will be presented for the existence of several distinct reactive sites involved in the binding of alkali cations by barley roots. It will be demonstrated that there are large differences in the affinity of these sites for various cations.