Cation-sensitive fluorescence of anionic polymers bearing naphtho-18-crown-6 units

Changes in the fluorescence intensity of anionic polymers bearing naphtho-18-crown-6 moieties on addition of cations were studied in water at 30 °C. On addition of alkali metal cations, the fluorescence intensity of the polymers decreased sharply for Tl⁺ less for Cs⁺ and little for Li⁺, K⁺ and Rb⁺. On addition of alkaline earth metal cations, Ba²⁺ caused the strongest decrease of the fluorescence intensity of the polymers. The decrease of the fluorescence intensity of the polymers was suggested to be caused by the external heavy-atom effect of the cations bound to the cavity of the crowned naphthalene moiety. The content of the crowned naphthalene units in the polymers affected the cation-dependent fluorescence change. The fluorescence change of the polymers based on the cation complexation competition was also studied.     

Sensing Alkali and Alkaline Earth Metal Cations by Conduction Band Quenching of Dye Photoluminescence

A new luminescence approach for sensing alkali and alkaline earth metal cations in fluid solution at room temperature is described. The approach is to utilize surface-adsorption/desorption–induced energetic shifts of a semiconductor conduction band to alter the electron transfer quenching efficiency of a photoluminescent dye. A proof-of-concept example is described based on TiO₂ nanoparticles with a surface bound Ru(II) coordination compound as the dye, Ru(deeb)(bpy)₂(PF₆)₂ where deeb is 4,4-(CO₂CH₂CH₃)₂-2,2-bipyridine and bpy is 2,2-bipyridine, sensing alkali and alkaline earth metal cations in acetonitrile solution. The Ru(II) compound is highly luminescent with long excited state lifetimes in the absence of the cations but is quenched in their presence. The quenching is found to be reversible. The data demonstrate that this approach yields intensity, lifetime, and wavelength-ratiometric calcium ion sensors that are sensitive to 5 7 × 10^–4 M concentrations.     

Fullerene-C60 and crown ether doped on C60 sensors for high sensitive detection of alkali and alkaline earth cations

Fullerenes are effective acceptor components with high electron affinity for charge transfer. The significant influences of chemical adsorption of the cations on the electrical sensitivity of pristine C₆₀ and 15-(C₂H₄O)₅/C₆₀ nanocages could be the basis of new generation of electronic sensor design. The density functional theory calculation for alkali and alkaline earth cations detection by pristine C₆₀ and 15-(C₂H₄O)₅/C₆₀ nanocages are considered at B3LYP level of theory with 6–31 G(d) basis set. The quantum theory of atoms in molecules analysis have been performed to understand the nature of intermolecular interactions between the cations and nanocages. Also, the natural bond orbital analysis have been performed to assess the intermolecular interactions in detail. Furthermore, the frontier molecular orbital, energy gap, work function, electronegativity, number of transferred electron (∆N), dipole moment as well as the related chemical hardness and softness are investigated and calculated in this study. The results show that the adsorption of cations (M=Na⁺, K⁺, Mg²⁺ and Ca²⁺) are exothermic and the binding energy in pristine C₆₀ nanocage and 15-(C₂H₄O)₅/C₆₀ increases with respect to the cations charge. The results also denote a decrease in the energy gap and an increase in the electrical conductivity upon the adsorption process. In order to validate the obtained results, the density of state calculations are employed and presented in the end as well.     

Nucleophilic substitution reactions promoted by oligoethylene glycols: a mechanistic study of ion‐pair SN2 processes facilitated by Lewis base

We present a mechanistic study for nucleophilic substitution (S_N2) reactions facilitated by multifunctional n‐oligoethylene glycols (n‐oligoEGs) using alkali metal salts MX (M⁺ = Cs⁺, K⁺, X^– = F^–, Br^–, I^–, CN^–) as nucleophilic agents. Density functional theory method is employed to elucidate the underlying mechanism of the S_N2 reaction. We found that the nucleophiles react as ion pairs, whose metal cation is ‘coordinated’ by the oxygen atoms in oligoEGs acting as Lewis base to reduce the unfavorable electrostatic effects of M⁺ on X^–. The two terminal hydroxyl (?OH) function as ‘anchors’ to collect the nucleophile and the substrate in an ideal configuration for the reaction. Calculated barriers of the reactions are in excellent agreement with all experimentally observed trends of S_N2 yields obtained by using various metal cations, nucleophiles and oligoEGs. The reaction barriers are calculated to decrease from triEG to pentaEG, in agreement with the experimentally observed order of efficiency (triEG < tetraEG < pentaEG). The observed relative efficiency of the metal cations Cs⁺ versus K⁺ is also nicely demonstrated (larger [better] barrier [efficiency] for Cs⁺ than for K⁺). We also examine the effects of the nucleophiles (F^–, Br^–, I^–, CN^–), finding that the magnitudes of reaction barriers are F^– > CN^– > Br^– > I^–, elucidating the observation that the yield was lowest for F^–. It is suggested that the role of oxygen atoms in the promoters is equivalent to that of –OH group in bulky alcohols (tert‐butyl or amyl‐alcohol) for S_N2 fluorination reactions previously studied in our lab. Copyright © 2012 John Wiley & Sons, Ltd.     

Complexation of bis‐crown stilbene with alkali and alkaline‐earth metal cations. Ultrafast excited state dynamics of the stilbene‐viologen analogue charge transfer complex

The complex formation of bis(18‐crown‐6)stilbene ( 1 ) and its supramolecular donor‐acceptor complex with N,N′‐bis(ammonioethyl) 1,2‐di(4‐pyridyl)ethylene derivative ( 2 ) with alkali and alkaline‐earth metal perchlorates has been studied using absorption, steady‐state fluorescence, and femtosecond transient absorption spectroscopy. The formation of 1 ?Mⁿ⁺ and 1 ?(Mⁿ⁺)₂ complexes in acetonitrile was demonstrated. The weak long‐wavelength charge‐transfer absorption band of 1 · 2 completely vanishes upon complexation with metal cations because of disruption of the pseudocyclic structure. The spectroscopic and luminescence parameters, stability constants, and 2‐stage dissociation constants were calculated. The initial stage of a recoordination process was found in the excited complexes 1 ?M⁺ and 1 ?(M⁺)₂ (M = Li, Na). The pronounced fluorescence quenching of 1 · 2 is explained by very fast back electron transfer (τ_et = 0.397 ps). The structure of complex 1 · 2 was studied by X‐ray diffraction; stacked ( 1 · 2 )_m polymer in which the components were connected by hydrogen bonding and stacking was found in the crystal. These compounds can be considered as novel optical molecular sensors for alkali and alkaline‐earth metal cations.     

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.     

Time-resolved response of fluorescent alkali ion indicators and detection of short-lived intermediates upon binding to molecular cavities

Stopped-flow kinetic studies have been performed to determine the kinetic parameters of K⁺ binding to the fluorescent cryptand F222 and of Na⁺binding to F221 at pH 8.O. The results clearly indicate that a comparatively stable intermediate is formed before the rate-limiting binding step occurs with a rate constant around 30 s^–1 under the chosen experimental conditions. The conversion of the intermediate to the final cation complex is assigned to the final penetration of the already bound, but still partially solvated cation into the ligand's cavity. The main fluorescence intensity change found upon cation binding is attributed to the second reaction step, and not to the fast, initial binding reaction. The comparatively slow overall binding reaction is interpreted on the bases of a special solvate substitution mechanism which, in principle, can also account for the 1500 times slower binding of Ca 2⁺ to F221. With regard to time-resolved analytical Na⁺ and K⁺ determinations, the response times under the chosen conditions are around 20 ms. Differentiation between Na⁺ and Ca²⁺, for example, is possible with F221 on the basis of completely different response times.     

Spectroscopic properties, energy transfer and structural analysis of Sr2CeO4:M+ and Sr2CeO4:Eu3+, M+ (M+ = Li+, Na+, K+)

The room-temperature luminescent emission characteristics of Sr₂CeO₄:M⁺ and Sr₂CeO₄:Eu³⁺,M⁺ (M⁺ = Li⁺, Na⁺, K⁺) have been investigated under UV excitation. By introducing appropriate alkali metal cations dopants (Li⁺, Na⁺, K⁺) into the crystalline lattice, not only emission color of the blue-white-emitting Sr₂CeO₄ doped with low Eu³⁺ content can be tuned to green, but also the red emission intensity of Sr₂CeO₄ doped with high Eu³⁺ concentration is strengthened significantly. The relevant mechanisms have been elucidated in detail.     

A new force field for the adsorption of H2, O2, N2, CO,H2O,and H2S gases on alkali doped carbon nanotubes

The main goal of this work is the generation of a new force field data set to the interaction of several gases such as H₂, O₂, N₂, CO, H₂O, and H₂S with alkali cation-doped carbon nanotubes (CNTs) using ab initio calculations at the MP2(full)/6-311++G(d,p) level of theory. Different alkali cations including Li⁺, Na⁺_, K⁺ and Cs⁺ were used to dope in the CNT. The calculated potential energy curve for the interaction of each gas molecule with each alkali cation-doped CNTs was fitted to an analytical potential function to obtain the parameters of the potential function. A modified Morse potential function was selected for the fitting in which the electrostatic interactions has been accounted by adding the β/r term to the Morse potential. The accuracy of the calculated force field was checked via Grand Canonical Monte Carlo (GCMC) simulation of the H₂ adsorption on Li-doped graphite and Li-doped CNT. The results of these simulations were compared with the experimental measurements and the closeness of the simulation results with the experimental data indicated the accuracy of the proposed force field. The main merit of this work is the derivation of a specific force field for interaction of each of six gases with four alkali cation-doped CNT, which can be used in molecular simulation of these 24 of systems. The simulation results showed the increase of the H₂ adsorption capacity of nanotube and graphite up to 50% and 10%, respectively, due to the insertion of Li ions.     

Complexation and DFT studies of lower rim hexahomotrioxacalix[3]arene derivatives bearing pyridyl groups with transition and heavy metal cations. Cone versus partial cone conformation

The binding of representative alkali, alkaline earth, transition and heavy metal cations by 2‐pyridylmethoxy derivatives (1b, in cone and partial cone conformations) of p‐tert‐butylhexahomotrioxacalix[3]arene was studied. Binding was assessed by extraction studies of the metal picrates from water into dichloromethane and by stability constant measurements in acetonitrile and methanol, using spectrophotometric and potentiometric techniques. Microcalorimetric studies of some selected complexes in acetonitrile were performed, as well as proton NMR titrations. Computational methods (density functional theory calculations) were also employed to complement the NMR data. The results are compared with those obtained with the dihomooxacalix[4]arene 2b and the calix[4]arene 3b derivative analogues. Partial cone‐1b is the best extractant for transition and heavy metal cations. Both conformers of 1b exhibit very high stability constants for soft and intermediate cations Pb²⁺, Cd²⁺, Hg²⁺, Zn²⁺ and Ni²⁺, with cone‐1b the strongest binder (ML, log β ≥ 7) and partial cone‐1b the most selective. Both derivatives show a slight preference for Na⁺. Besides the formation of ML complexes, ML₂ and M₂L species were also observed. The former complexes were, in general, formed with the transition and heavy metal cations, whereas the latter were obtained with Ag⁺ and Hg²⁺ and partial cone‐1b. In most cases, these species were corroborated by the proton NMR and density functional theory studies. Copyright © 2013 John Wiley & Sons, Ltd.     

Density functional theory study of the bis‐3‐benzo‐crown ethers and their complexes with alkali metal cations Na+, K+, Rb+ and Cs+

The binding interactions of bis‐3‐benzo‐15‐crown‐5 ethers and bis‐3‐benzo‐18‐crown‐6 ethers (neutral hosts) with a series of alkali metal cations Na⁺, K⁺, Rb⁺ and Cs⁺ (charged guests) were investigated using quantum chemical density functional theory. Different optimized structures, binding energies and various thermodynamic parameters of free crown ethers and their metal cation complexes were obtained based on the Becke, three‐parameter, Lee–Yang–Parr functional using mixed basis set (C, H, O, Na⁺ and K⁺ using 6‐31 g, and the heavier cation Rb⁺ and Cs⁺ using effective core potentials). Natural bond orbital analysis is conducted on the optimized geometric structures. The main types of driving force host–guest interactions are investigated. The electron donating O offers a lone pair of electrons to the contacting LP* (1‐center valence antibond lone pair) orbitals of metal cations. The bis‐3‐benzocrown ethers are assumed to have sandwich‐like conformations, considering the binding energies to gauge the exact interactions with alkali cations. It is found that there are two different types of complexes: one is a tight ion pair and the other is a separated ion pair. Copyright © 2011 John Wiley & Sons, Ltd.     

Neutral beam sputtering of positive ion clusters from alkali halides

Neutral argon atom beams of 15 keV energy have been used to sputter alkali halides and the ejected positive ions have been analysed in energy, mass and angular distribution.

The use of a neutral beam, rather than an ion beam, minimizes surface charge and the deflection of ejected ions by electrostatic interaction with a charged incident beam.

A cluster component of the form K₂Cl⁺, K₃Cl⁺ ₂ and higher members of the series is found for all alkali halides studied.     

Cation-mediated sandwich formation between benzene and pillar[5]arene: a DFT study

Cation–π interactions in alkali metal ion (Li⁺, Na⁺ and K⁺)–pillar[5]arene complexes and sandwiches of pillar[5]arene and benzene formed via alkali metal ions are studied in the light of density functional theory. Several possible modes of interaction between metal ions and pillar[5]arene have been studied. Results suggest that interaction is stronger in the complexes with the metal ion present inside the cavity of the pillar[5]arene as compared to that where the metal ion is outside the cavity. The calculated interaction energy further reveals that though cation–π complexes with larger number of alkali metal ions are unstable, however, corresponding sandwiches are stable, which further support the fact that pillar[5]arene–metal ion complexes can interact with other π–electron-rich species. Absorption spectra of the complexes formed undergo both blue and red shifts as compared to the pillar[5]arene.     

Raman analysis of perrhenate and pertechnetate in alkali salts and borosilicate glasses

Sodium borosilicate glasses containing rhenium or technetium were fabricated and their vibrational spectra studied using confocal Raman microscopy. Glass spectra were interpreted relative to new high‐resolution spectra of pure crystalline NaReO₄, KReO₄, NaTcO₄, and KTcO₄ salts. Spectra of perrhenate and pertechnetate glasses exhibited sharp Raman bands, characteristic of crystalline salt species, superimposed on spectral features of the borosilicate matrix. At low concentrations of added KReO₄ or KTcO_4, the characteristic pertechnetate and perrhenate features are weak, whereas at high additions, sharp peaks from crystal field‐splitting and C_4h symmetry dominate glass spectra, clearly indicating ReO₄⁻ or TcO₄⁻ is locally coordinated with K and/or Na. Peaks indicative of both K and Na salts are evident in many Raman spectra, with the Na form being favored at high concentrations of the source chemicals, where more K⁺ is available for ion exchange with Na⁺ from the base glass. The observed ion exchange likely occurred within depolymerized channels where nonbridging oxygens create segregation from the glass network in regions containing anions such as ReO₄⁻ and TcO₄⁻ as well as excess alkali cations. Although this anion exchange provides evidence of chemical mixing in the glass, it does not prove the added salts were homogeneously incorporated in the glass. The susceptibility to ion exchange from the base glass indicates that long‐term immobilization of Tc in borosilicate glass must account for excess charge compensating alkali cations in melt glass formulations. Published 2014. This article is a U. S. Government work and is in the public domain in the USA.     

Characterizing Protein Conformational Transitions of Na,K-ATPase with Antibodies by Fluorescence Spectroscopy

Stationary and time-resolved fluorescence of FITC–Na,K-ATPase is investigated as a function of pH in the presence of different ligands, cations, and the monoclonal anti-FITC antibody 4-4-20. The binding of K⁺ and of the antibody leads to the same decreased fluorescence intensity level. Antibody binding is observed only under conditions where the enzyme exists in the conformational state F₁, and not in the form of the Na⁺ or K⁺ complex or when it is phosphorylated with inorganic phosphate in the presence of Mg²⁺. For the interpretation of the results it is shown that the fluorophore is not essentially affected by an acidity change of the bound dye, so that pK variations responsible for the observed intensity changes can be excluded in favor of a static quenching process     

Cation disorder in NaW2O6+δ·nH2−zO post-ion exchange with K, Rb, Sr, and Cs

The structure of the defect pyrochlore NaW₂O_6+δ·nH_2−zO after ion exchange with K, Rb, Sr or Cs for Na has been investigated using thermal analysis, solid-state nuclear magnetic resonance, laboratory X-ray and neutron diffraction methods. Neutron diffraction studies show that both the A-type cations (Na⁺, K⁺, Rb⁺, and/or Cs⁺) and the water molecules reside within the channels that form in the 111 direction of the W₂O₆ framework and that these strongly interact. The analytical results suggest that the water and A-type cations compete for space in the tunnels within the W₂O₆ pyrochlore framework, with the total number of water molecules and cations being approximately constant in the six samples investigated. The interplay between the cations and water explains the non-linear dependence of the a lattice parameter on the choice of cation. It appears that the ion-exchange capacity of the material will be controlled by the amount of water initially present in the sample.     

The migration of alkali metal (Na+, Li+, and K+) ions in single crystalline vanadate nanowires: Rasch-Hinrichsen resistivity

We report the synthesis of single crystalline alkali metal vanadate nanowires, Li-vanadate (Li₄V₁₀O₂₇), Na-vanadate (NaV₆O₁₅), and K-vanadate (KV₄O₁₀) and their electrical properties in a single nanowire configuration. Alkali metal vanadate nanowires were obtained by a simple thermal annealing process with vanadium hydroxides(V(OH)₃) nanoparticles containing Li⁺, Na⁺, and K⁺ ions and further the analysis of the migration of charged particles (Li⁺, Na⁺, and K⁺) in vanadate by measuring the conductivity of them. We found that their ionic conductivities can be empirically explained by the Rasch-Hinrichsen resistivity and interpreted on the basis of transition state theory. Our results thus indicate that the Li ion shows the lowest potential barrier of ionic conduction due to its small ionic size. Additionally, Na-vanadate has the lowest ion number per unit V₂O₅, resulting in increased distance to move without collision, and ultimately in low resistivity at room temperature.     

Characterization of polycrystalline (Na,K)β/β′- alumina ceramics

K β′-alumina is unstable at >1300°C. Mixed alkali β′-alumina has a variable stability depending on the alkali ratio, [K⁺]/([Na⁺]+[K⁺]). For f(β)<[K⁺]/([Na⁺]+[K⁺]), the β′-Al₂O₃ phase decomposes to Kβ-Al₂O₃ 0997 0815 V 3 and a solid solution of Na β′-Al₂O₃ and K β′-Al₂O₃. For f(β)=[K⁺]/([Na⁺]+[K⁺], the ceramic consists of K β-Al₂O₃ and Naβ′-Al₂O₃ and for f(β)>[K⁺]/([Na⁺]+[K⁺]), the excess Na⁺ after Na β′-Al₂O₃ dissolves in the β phase, giving Na β-Al₂O₃/K β-Al₂O₃ solid solution and Na β′-Al₂O₃. These sequences were confirmed by measuring the dependence of the c-axis lattice parameters of β- and β′-Al₂O₃ phases on the f(β), and the change of these parameters during the ion-exchange of Na⁺ and K⁺ ions.     

Shrinking of anionic polyacrylate coils induced by Ca2+, Sr2+ and Ba2+: A combined light scattering and ASAXS study

Anionic polyacrylate chains (NaPA) form precipitates if alkaline earth cations are added in stoichiometric amounts. Accordingly, precipitation thresholds were established for three different alkaline earth cations Ca²⁺, Sr²⁺ and Ba²⁺. Close to the precipitation threshold, the NaPA chains significantly decrease in size. This shrinking process was followed by means of combined static and dynamic light scattering. Intermediates were generated by varying the ratio [MCl₂]/[NaPA] with M denoting the respective alkaline earth cation. All experiments were performed at an inert salt level of 0.01M NaCl. Similar coil-to-sphere transitions could be observed with all three alkaline earth cations Ca²⁺, Sr²⁺ and Ba²⁺. Based on these findings, supplementary conventional and anomalous small-angle X-ray scattering experiments using selected intermediates close to the precipitation threshold of SrPA were performed. The distribution of Sr counterions around the polyacrylate chains in aqueous solution provided the desired scattering contrast. Energy-dependent scattering experiments enabled successful separation of the pure-resonant terms, which solely stem from the counterions. The Sr²⁺ scattering roughly reflects the monomer distribution of the polyacrylate chains. Different ratios of the concentrations of [ SrCl₂]/[NaPA] revealed dramatic changes in the scattering curves. The scattering curve at the lowest ratio indicated an almost coil-like behaviour, while at the higher ratios the scattering curves supported the model of highly contracted polymer chains. Most of X-ray scattering experiments on intermediate states revealed compact structural elements which were significantly smaller than the respective overall size of the NaPA particles.     

Colorimetric quantitative sensing of alkali metal ions based on reversible assembly and disassembly of gold nanoparticles

A novel and simple method for the colorimetric quantitative sensing of individual alkali metal ions (Li⁺, Na⁺, K⁺, and Rb⁺) based on the reversible properties of self-assembled aggregates and individual gold nanoparticles (Au NPs) is described. This paper demonstrates reversible self-assembly processes where the degree of assembly and disassembly is dependent on the individual alkali metal ion concentration, nanoparticle size, and alkali metal ionic radii. The color changes of the colloidal Au NPs with metal ion concentrations in colloidal NP solutions occur reversibly. Below a certain concentration of alkali metal ions, the aggregates of Au NPs are redispersed. As the Au NP diameters and the alkali metal ionic radii increase, the critical concentration decreases.