Larger Alkali Metal Research Articles

Optical spectroscopy of europium 3,5-dinitrosalicylates—Intense red luminophores

It was found, that alkali metal-europium dinitrosalicylates of composition M 3Eu(3,5-NO 2-Sal) 3· nH 2O (M = Li, Na, K, Cs) are intense red luminophores with wide excitation band. Using methods of optical spectroscopy we studied the influence of nitrogroups and alkali metal counterions on Eu 3+ luminescence efficiency and on processes of excitation energy transfer to Eu 3+ ion in compounds synthesized. The Eu 3+ luminescence and Eu 3+ luminescence excitation spectra, as well as vibrational IR and Raman spectra were investigated. Details of the structure of compounds were discussed. The network of hydrogen bonds in lanthanide dinitrosalicylates is weakening at introduction of large alkali metal ions in compounds and at the increase of the temperature. As a consequence, the long-wavelength shift of the intraligand charge transfer (ILCT) band in Eu 3+ excitation spectra arises at inclusion of Cs + cations instead of Li + in the crystal lattice of europium dinitrosalicylates and at heating of these compounds. To obtain the energy of the lowest excited triplet state the phosphorescence spectra of alkali metal-gadolinium compounds M 3Gd(3,5-NO 2-Sal) 3· nH 2O, of alkali metal dinitrosalicylate and salicylate salts were measured with time delay. Change of the energies of ligand electronic states and ligand–metal charge transfer state (LM CTS) can give a two-three orders of magnitude enhancement of the Eu 3+ luminescence efficiency in dinitrosalicylates in comparison with salicylates and ten-fold enhancement at the substitution of Li + and Na + for Cs + in dinitrosalicylates.

Coordination Cages of Rhodium and Iridium as Exoreceptors for Alkali Metal Ions

Hexanuclear coordination cages of the formula [(C5Me4R)M(C7H3NO4)]6 (M = Rh, Ir; R = Me, H) were obtained by stepwise reaction of [(C5Me4R)MCl2]2 with, first, AgOAc and, then, pyridine-3,5-dicarboxylic acid. Crystallographic analyses show that the cages adopt a distorted octahedral geometry with the pyridine-3,5-dicarboxylates functioning as dianionic, bridging ligands, each of which connects three different (C5Me4R)M fragments. The cages act as exoreceptors for the large alkali metal ions K(+) and Cs(+) but show low affinity for Na(+). Crystallographic and NMR spectroscopic analyses indicate that two metal ions can be coordinated to the surface of the cages. The respective binding sites comprise three carbonyl O-atoms from the bridging pyridine-3,5-dicarboxylate ligand.

Polymer-like Structures of LiSCN, NaSCN, KSCN, RbSCN, and CsSCN Complexes with an Armed Monoaza-15-crown-5 Ether Bearing a 3‘,5‘-Difluoro-4‘-hydroxybenzyl Group

Structures of LiSCN, NaSCN, KSCN, RbSCN, and CsSCN complexes with 3',5'-difluoro-4'-hydroxybenzyl-armed monoaza-15-crown-5 ether (5) were investigated. The Li+ and Na+ complexes are (1:1)n polymer-like complexes bridged by hydrogen bonding. On the other hand, the K+, Rb+, and Cs+ complexes are polymer-like complexes bridged by the fluorine atoms of the side arms. The titration calorimetry and 19F NMR titration experiments suggest that one or both fluorine atoms along with the oxygen atom of the phenolic OH group coordinate to the alkali metal ions incorporated in the crown part of a second armed ligand to give polymer-like complexes in solution. The FAB-MS data indicated that larger alkali metal ions form more stable polymer-like complexes.

Evolution of Organo‐Cyanometallate Cages: Supramolecular Architectures and New Cs+‐Specific Receptors

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Ion Specificity and Ionic Strength Dependence of the Osmoregulatory ABC Transporter OpuA

The ATPase subunit of the osmoregulatory ATP-binding cassette transporter OpuA from Lactococcus lactis has a C-terminal extension, the tandem cystathionine beta-synthase (CBS) domain, which constitutes the sensor that allows the transporter to sense and respond to osmotic stress (Biemans-Oldehinkel, E., Mahmood, N. A. B. N., and Poolman, B. (2006) Proc. Natl. Acad. Sci. U. S. A. 103, 10624-10629). C-terminal of the tandem CBS domain is an 18-residue anionic tail (DIPDEDEVEEIEKEEENK). To investigate the ion specificity of the full transporter, we probed the activity of inside-out reconstituted wild-type OpuA and the anionic tail deletion mutant OpuADelta12; these molecules have the tandem CBS domains facing the external medium. At a mole fraction of 40% of anionic lipids in the membrane, the threshold ionic strength for activation of OpuA was approximately 0.15, irrespective of the electrolyte composition of the medium. At equivalent concentrations, bivalent cations (Mg(2+) and Ba(2+)) were more effective in activating OpuA than NH(4)(+), K(+), Na(+), or Li(+), consistent with an ionic strength-based sensing mechanism. Surprisingly, Rb(+) and Cs(+) were potent inhibitors of wild-type OpuA, and 0.1 mM RbCl was sufficient to completely inhibit the transporter even in the presence of 0.2 M KCl. Rb(+) and Cs(+) were no longer inhibitory in OpuADelta12, indicating that the anionic C-terminal tail participates in the formation of a binding site for large alkali metal ions. Compared with OpuADelta12, wild-type OpuA required substantially less potassium ions (the dominant ion under physiological conditions) for activation. Our data lend new support for the contention that the CBS module in OpuA constitutes the ionic strength sensor whose activity is modulated by the C-terminal anionic tail.

Formation laws for scheelite-like triple molybdates LiMLn2(MoO4)4

The size factor is shown to be decisive in the structure formation of triple molybdates LiMLn2(MoO4)4. The LiMLn2(MoO4)4 compounds (where M is a large alkali metal) are formed when 0.48 A ≤ rM+ − rLn3+ ≤ 0.60 A.

Electrospray ionization mass spectrometric study of the metal cation complexation capabilities of a novel, doubly cage-annulated molecular box

An unusual molecular box, 4, obtained as a mixture of diastereoisomeric, doubly cage-annulated host molecules, i.e., 4a and 4b, has been prepared. The metal cation complexation properties of the mixture of 4a and 4b thereby obtained have been assessed, with comparison to another bis crown 2, via application of electrospray ionization mass spectrometric (ESI-MS) methods. Both host systems 2 and 4 bind selectively to Li + and Na + , thereby demonstrating preference over the other larger alkali metals. Addition of Ag + to the solutions containing alkali metals does not result in substantial Ag + complexation. Analysis of a solution containing only transition metal, not alkali metal, cations indicates that 4 forms complexes with Zn + and Ag + along with substantial complexation of Na + from residual sodium present in the solvents.

ChemInform Abstract: Ternary Chlorides of the Trivalent Early Lanthanides Phase Diagrams, Crystal Structures and Thermodynamic Properties.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Irreversible inhibition of pig kidney copper-containing amine oxidase by sodium and lithium ions.

Copper amine oxidase was found to be inhibited in a complex way by small alkali metal ions. Classic enzyme kinetic studies showed that Li+ and Na+ were weak noncompetitive inhibitors, whereas the larger alkali metals K+, Rb+ and Cs+ were not inhibitors. However, freezing in the presence of Na+ or Li+ surprisingly resulted in complete and irreversible inactivation. In the case of Li+, it was possible to show that one ion per subunit was retained permanently in the inactivated enzyme, suggesting a structural rearrangement. The mechanism of inhibition was studied using a wide range of spectroscopic and analytic techniques. Only minor changes in the protein structure could be detected, except for a significant change in the geometry of the copper site. The unique topaquinone cofactor was apparently functional and able to proceed through the reductive half of the catalytic cycle, but the enzyme no longer reacted with oxygen. The effect of Na+ and Li+ was source-specific for pig kidney and bovine kidney amine oxidases, while the enzymes from bovine serum or plants were not inactivated, consistent with a mechanism dependent on small structural differences. A model for irreversible inactivation is proposed in which the cofactor is co-ordinated directly to copper, in analogy with the inactivation reported for Escherichia coli amine oxidase under crystal growth conditions.

The Crystal Structures at 10 K of the Trigonal Salts KMIII(NH3)6(ClO4)2Cl2, MIII = Os and Cr, and the Possibility of Phase Transitions

The crystal structures of KOs(NH3)3(ClO4)2Cl2 and KCr(NH3)6(ClO4)2Cl2 were determined at 10 K by X-ray diffraction, and for the osmium salt also at 293 K. At 293 K the osmium salt is trigonal, space group R 3m, with the same simple structure as others of this class of double salt. At 10 K, in agreement with previous radius ratio predictions, both crystals are best described as remaining R 3m. All previously studied members, with larger alkali metal cations, are twinned R 3 at low temperatures, with small, symmetry-breaking rotations of the hexaamminemetal(III) and perchlorate ions about the threefold axis. Differential scanning calorimetry on CsRu(NH3)6(ClO4)2Cl2 suggests that the R 3m to R 3 change is very extended in temperature with only a small discontinuity at the transition temperature.

Photoresponsive Tweezers for Alkali Metal Ions. Photochromic Diarylethenes Having Two Crown Ether Moieties

Alkali metal ion extraction was carried out using photochromic dithienylethene having two benzo-12-crown-4 ethers (1), benzo-15-crown-5 ethers (2), or benzo-18-crown-6 ethers moieties (3) and bis(benzothienyl)ethene having two benzo-18-crown-6 ether moieties (4). Two crown ether moieties of the open-ring form captured large metal ions cooperatively like tweezers, while the photogenerated closed-ring form released the ions. The reduced affinities for metal picrates were fully recovered by irradiation with visible light (>480 nm). The 1H NMR spectrum measurement of the solutions (CDCl3/CD3CN: 5/1) containing both alkali metal picrates and 2 or 3 confirmed that the large alkali metal ions were captured by the two intramolecular crown ethers.

Evaluation of binding selectivities of bis-crowned clefts by electrospray ionization/quadrupole ion trap mass spectrometry

Electrospray ionization (ESI) was used in conjunction with quadrupole ion trap mass spectrometry to measure metal binding selectivities of bis-crowned clefts in methanol solution. Each of the three cleft compounds contained two 15-crown-5 rings separated by different quinoline spacers. Binding selectivities were compared qualitatively with previous extraction results obtained for three bis-crown clefts complexing with the alkali metals sodium, potassium and rubidium in aqueous solution. The bis-crowned cleft molecules were found to form 1:1 and 2:1 metal—cleft complexes, and, in a few cases where larger alkali metals were involved, two cleft molecules were able to form 2:2 metal–cleft complexes cooperatively. The binding selectivity is greatly affected by the size of the alkali metal and by the flexibility of the quinoline bridge, factors that influence the degree of electrostatic repulsion between the two crown ether rings. © 1998 John Wiley & Sons, Ltd.

A Bis-Crown Ether Derivative of Triaminotriazine: Synthesis and Behavior of the Ion-Selective and Hydrogen-Bonding Responsive Rotamers

Abstract A bis-crown ether derivative of triaminotriazine was synthesized via a phthalic acid derivative of a polyether macrocycle obtained from benzo-18-crown-6. It exists in different conformers distinguishable by 1H NMR at room temperature, in which the macrocyclic side-arms take a closed, half-open, or fully open form, due to the rotational barrier of the C(triazine)–N bond. Large alkali metal ions, such as Rb+ and Cs+, the latter being particularly effective, promote the formation of the closed conformer. A barbiturate derivative also causes a similar equilibrium shift to the closed form by establishing complementary hydrogen bonds. The half-open and fully open conformers are induced by smaller alkali metal ions than Rb+, among which K+ is the most effective.

Strikingly Selective Ionophoric Properties of Rigid Cyclophanes Having a Small Number of Ligating Sites

Abstract Ionophores 4 and 5 having two acetate groups and two pyridyl groups, respectively, on the aromatic rings as well as oligo(oxyethylene) linked compounds 7a-c were prepared by Williamson ether synthesis between the corresponding halides or ditosylates and dihydroxycyclophane, which was prepared by Birch reduction of the three-bridged dimethoxycyclophane, followed by cleavage of the methoxyl groups. On the liquid-liquid extraction, 4 and 5 showed high affinities toward K+ ion and Ag+ ion, respectively. Compounds 7b and c effectively extracted large alkali metal cations.

New 2-methylenepropylene-bridged cryptands with high sodium ion selectivity: A thermodynamic study of complexation

Thermodynamic quantities for the interactions of mono- and tri(2-methylenepropylene)-bridged cryptands, cryptand [3.3.1], cryptand [2.2.2], and 18-crown-6-with Na+, K+, Rb+, and Cs+ have been determined by calorimetric titration in an 80:20 (v/v) methanol: water solution at 25°C. Incorporation of the 2-methylenepropylene (−CH2C(=CH2)CH2−) bridge(s) into cryptand [2.2.2] results in a large change in the ligand-cation binding properties. Tri(2-methylenepropylene)-bridged cryptand [2.2.2] (2) shows high selectivity factors for Na+ over K+ and other alkali cations, while 2-methylenepropylene-bridged cryptand [2.2.2.] (1) selects K+ over Na+, as does cryptand [2.2.2]. The K+/Na+ selectivity is reversed with increasing number of 2-methylenepropylene bridges. This observation indicates that increasing the number of 2-methylenepropylene bridges on cryptand [2.2.2] favors complexation of a small cation over a large one. The logK values for the formation of 1 and 2 complexes (except 1-Cs+ and 2-Na+) decrease as compared with those for the corresponding [2.2.2] complexes. Formation of six-membered chelate ring(s) by the propyleneoxy unit(s) of 1 and 2 with a cation stabilizes the cryptate complexes of the small Na+ and destabilizes the complexes of large alkali metal cations. Thermodynamic data indicate that the stabilities of the cryptate complexes studied are dominated mostly by the enthalpy change. In most cases, both stabilization of Na+ complexes and destabilization of the complexes of large alkali metal cations by six-membered chelate ring(s) also result from an enthalpic effect. Cryptand [3.3.1] shows a selectivity for K+ over Cs+, despite its two long CH2(CH2OCH2)3CH2 bridges. The [3.1] macroring portion of [3.3.1]may be too small to effectively bind the Cs+, resulting in the low stability of the Cs+ complex.

Physicochemical properties of alkali-metal exchanged type X zeolites

The changes in the physicochemical properties of a series of faujasite type X zeolites cation exchanged with K+, Rb+ and Cs+ have been studied by XRD, IR, thermoanalytical methods and sorption measurements. As a consequence of the enhanced scattering of X-rays by larger alkali metal cations, the percent relative intensity of the XRD peaks of cation exchanged zeolites was found to have decreased considerably. The framework IR spectra also showed analogous changes. The alkali metal exchange was found to enhance the thermal stability of the parent zeolite. The available void volume and specific surface area (obtained by low temperature nitrogen sorption) also decreased with the increase in the degree of exchange and cationic size. Equilibrium sorption capacities (298 K andP/P0=0.5) for water,n-hexane, cyclohexane and 1,3,5-trimethylbenzene also exhibited the same trend.

Molecular Design of Crown Ethers. VII. Syntheses and Cation Selectivities of Unsubstituted 12- to 16-Crown-4

Abstract Solvent extraction of aqueous alkali and some heavy metal picrates with the title compounds showed that, with most cations except for Li+, Na+, and Ag+, the extractability decreases monotonically as the ring size increases from 12 to 16. However, 14-crown-4 showed the highest extractability and selectivity for Li+ over the larger alkali metals, while 15-crown-4 exhibited the highest Ag+/TI+ selectivity.

Caesium-selective poly(vinyl chloride) membrane electrodes based on calix[6]arene esters

Hexameric calix[6]arene ester compounds have shown an ability to extract large alkali metal ions such as caesium and rubidium in phase transfer studies. A potentiometric selectivity study has been made using two ester containing hexameric calix[6]arenes, p-tert-butyl hexaethyl ester (1a) and the unsubstituted hexaethyl ester (1b), as the ionophores for caesium ions. Six electrodes were prepared with 2-nitrophenyl octyl ether as the solvent mediator and various amounts of potassium tetrakis(p-chlorophenyl)borate as the ion exchanger in a poly(vinyl chloride) matrix. The ligands examined produced electrodes with near-Nernstian slopes; the selectivity coefficients for caesium with respect to rubidium, potassium, sodium, lithium, calcium, magnesium, hydrogen and ammonium were determined. Lifetimes of at least 1 month were estimated.

Reflectance spectra for sodium and potassium doped ammonia frosts: Implications for Io's surface

This paper reports measurements of the reflection spectra of sodium- and potassium-doped ammonia frosts as a function of alkali metal concentration for the wavelength range 0.35-2.5 microns. The purpose of the measurements was to determine whether or not the reflection spectra for such a solid was compatible with the spectra albedo of Io. The data show that, with a sufficiently large alkali metal concentration, the reflection spectra of the doped ammonia frosts do not display the characteristic ammonia features at 2.0 and 2.25 micron. The high reflectance of the more concentrated samples and the character of the observed reflection spectrum make it difficult to rule out sodium-doped ammonia frost as a surface constituent on Io on the basis of existing data.

Conductivities of alkali metal perchlorates in ethylene glycol at 25°C

The conductivities of NaClO4, KClO4, RbClO4 and CsClO4 in ethylene glycol at 25°C were determined and the temperature coefficients of their mobilities estimated. These data, together with those for other electrolytes in the same solvent, were analysed to obtain the association constants and the limiting molar conductivities of the electrolytes. The analysis shows that alkali metal ions are strongly solvated in ethylene glycol. The salts of the large tetra-alkylammonium ions are definitely associated, and the values of the association constants are larger than expected for purely electrostatic ion-pairing. This type of behaviour, which has been observed in other protic solvents, depends on the intermolecular hydrogen bonding of the solvent molecules. Large alkali metal ions appear to be structure-breaking ions in ethylene glycol as well as in water.