Ionic selectivity in L-type calcium channels by electrostatics and hard-core repulsion.

The traditional approach to utilizing an ion-relay mechanism for ion transport requires three or more ion-relay stations. Herein, we describe a novel strategy, incorporating a swing action to reali...

Three series of heterocycle substituted calixarenes, derivatized at lower and upper rim, were synthesized and successfully evaluated for metal extraction towards alkali, alkaline, transition and heavy metal ions. The presence and placement of sulfur, heterocycle functionality at upper/lower rim played a crucial role toward the extractability and selectivity of metal ions. The lower rim substituted calixarenes have shown high extractability and poor selectivity. In contrast to this, upper rim substituted calixarenes exhibited good selectivity. Moreover, sulfur functionalized calixarenes have shown better selectivity for heavy metal ions than alkali and alkaline metal ions. Among upper rim substituted calixarenes, 17 and 18 were found to be suitable for Na+, K+ and Ag+, 19,13 for heavy metal ions i.e., Pb2+, Hg+, Hg2+ and Ag+, and 11,12 for Pb2+ and Ag+ only.

Voltammetric studies for cation recognition with thiacalix[4]crown-6s

In the present work, we describe four previously unreported cucurbituril‐based coordination supramolecular self‐assemblies, formed in the presence of alkali metal and cadmium ions. Unexpectedly, in the presence of potassium or rubidium and cadmium cations, cucurbituril prefers to coordinate with cadmium to form three dimensional frameworks. The alkali metal ions seem to play a role of structure inducer in HCl medium and are not present in the final structures. In neutral aqueous solution, cadmium cations also show stronger coordination to cucurbituril and form one‐dimensional supramolecular chains through static electronic interactions. When the alkali metal ion is sodium in HCl solution, sodium ions show stronger coordination to cucurbituril and form one‐dimensional coordination polymers. [CdCl4]2– anions link the linear polymers through static electronic interactions between coordinated chloride anions and sodium cations, which results in the formation of two‐dimensional networks.

Insights into the Ion Selectivity Mechanism of CNG Channels from Mutants of NaK: Structural and Functional Studies

Efficient removal of alkali and alkaline earth metals from biodiesel using Ion-exchange resin: Performance and mechanism

The formation constants (KML+) for 1: 1 complexes of dibenzo-24-crown-8 (DB24C8) with alkali metal ions (Na+, K+, Rb+, and Cs+) in propylene carbonate (PC) and methanol have been determined conductometrically at different temperatures in order to obtain the values of the enthalpy (ΔH) and entropy changes (ΔS). The complexation reactions between DB24C8 and the alkali metal ions in PC and methanol are all exothermic, and the ΔS values of these systems are all negative. In the case of the PC system, there is no considerable difference in ΔS among the alkali metal ions (Na+, K+, Rb+, and Cs+); thus, the KML+ sequences depend entirely on the −ΔH sequences. Since, in methanol, the −ΔH and −ΔS values for K+ are nearly equal to those for Cs+, and since the largest −ΔH value for Rb+ is balanced by the largest −ΔS value, DB24C8 shows no selectivity for the alkali metal ions (K+, Rb+, and Cs+) in methanol.

Removal of alkali metal ions from aqueous solution by foam separation method

In this study, calix[4]arene derivatives (11–14) bearing a single nucleobase (adenine, thymine, cytosine or guanine) were synthesised via click chemistry. The complexation ability of the synthesised derivatives with alkali metal ions was measured using MALDI-TOF mass spectrometry, and their molecular assembly in CDCl3 was determined using 1H NMR. Calix[4]arene derivatives (11–14) formed 1:1 complexes with all alkali metal ions and the rank order for the complexation selectivity was Rb+ > Cs+ > K+ ≅ Na+ > Li+. The attachment of nucleobase at the upper rim of calix[4]arene had little effect on its complexation selectivity for alkali metal ions. Thymine-, adenine- and guanine-calix[4]arenes formed self-assembled structures in CDCl3 via base–base interactions. In addition, adenine-calix[4]arene (11) bound to thymine-calix[4]arene (12) to form a discrete species via Hoogsteen hydrogen bonding.

The first alkali metal transition metal acetylides of general composition A2M0C2 (A = Na − Cs, M0 = Pd, Pt) were obtained by solid state reactions of alkali metal acetylides with palladium and platinum. They are characterized by $^{1}_{\infty}[{\rm M}^{\rm o}({\rm C}_{2})^{2-}_{{2}/{2}}]$ chains, which are separated by alkali metal ions. Analogous $^{1}_{\infty}[{\rm M}^{\rm o}({\rm C}_{2})^{2-}_{{2}/{2}}]$ chains also separated by alkali metal ions are the characteristic structural feature of acetylides of composition AMIC2, which are accessible by reacting AC2H with MII in liquid ammonia (A = Li − Cs, MI = Cu, Ag, Au). Despite their structural similarities they possess different properties, as acetylides of composition A2M0C2 are semiconductors with very small indirect band gaps and slightly extended C–C distances compared to a C–C triple bond, whereas acetylides of composition AMIC2 show a typical salt‐like behavior with C–C distances close to the expected value for a C–C triple bond of 120 pm. But with the help of simple chemical models these differences can be made plausible. Furthermore, it is shown that only by a combination of different methods (powder diffraction with X‐rays and neutrons, solid state NMR spectroscopy, Raman spectroscopy) it was possible to characterize this new class of compounds structurally and chemically.

The effect of substitution of phenyl and naphthyl rings to benzene was examined to elucidate the cation-π interactions involving alkali metal ions with 1,3,5-tri(phenyl)benzene (TPB) and 1,3,5-tri(naphthyl)benzene (TNB). Benzene, TPB, and four TNB isomers (with ααα, ααβ, αββ, and βββ types of fusion) and their complexes with Li+, Na+, K+, Rb+, and Cs+ were optimized using DFT approach with B3LYP and M06-2X functionals in conjunction with the def2-QZVP basis set. Higher relative stability of β,β,β-TNB over α,α,α-TNB can be attributed to peri repulsion, which is defined as the nonbonding repulsive interaction between substituents in the 1- and the 8-positions on the naphthalene core. Binding energies, distances between ring centroid and the metal ions, and the distance to metal ions from the center of other six-membered rings were compared for all complexes. Our computational study reveals that the binding affinity of alkali metal cations increases significantly with the 1,3,5-trisubstitution of phenyl and naphthyl rings to benzene. The detailed computational analyses of geometries, partial charges, binding energies, and ligand organization energies reveal the possibility of favorable C-H···M+ interactions when a α-naphthyl group exists in complexes of TNB structures. Like benzene-alkali metal ion complexes, the binding affinity of metal ions follows the order: Li+ > Na+ > K+ > Rb+ > Cs+ for any considered 1,3,5-trisubstituted benzene systems. In case of TNB, we found that the strength of interactions increases as the fusion point changes from α to β position of naphthalene.

Natural macrocvclic compounds, such as valinomycin, are attractive to analysts who have interest in the high selectivity of potassium ion as compared to sodium ion. This selectivity in alkali metal ions was not found in other ligands. Pedersen synthesized many crown ethers [1] and published his result that dibenzo-18-crown-6 (DB18C6) had a larger affinity to potassium than other alkali metals. Since then, these ligands and related compounds have held great interest for physical, inorganic and biochemists.

Metal ions widely exist in biological systems and participate in many vital biochemical processes. Monitoring and analyzing metal ions in biological systems can help reveal physiological processes and understand disease causes. There are various detection methods for metal ions, among which organic small-molecule fluorescent probes have significant advantages, such as high fluorescence quantum yield, easy modification, good biocompatibility, high sensitivity, and fast real-time detection. This review presents recent studies on fluorescent probes for alkali and alkaline earth metal ions (including Na+, K+, Ca2+, and Mg2+) in biological systems. All the candidates are organized according to their structures, and the sensing mechanisms of fluorescent probes are also highly taken into account. Finally, the challenges, trends and prospects of fluorescent probes in metal ion detection are discussed. We hope that this review can provide guidance for the development of fluorescent molecular probe-based alkali and alkaline earth metal ion detection methods in the future.

A combination of density functional theory calculations, hydrogen/deuterium exchange (HDX) reactions, ion mobility-mass spectrometry, and isotope labeling tandem mass spectrometry was used to study gas-phase "host-guest" type interactions of a benzyloxycarbonyl (Z)-capped proline (P) glycine (G) model dipeptide (i.e., Z-PG) and its various structural analogues with ND3. It is shown that in a solvent-free environment, structural differences between protonated and alkali metal ion (Na(+), K(+), or Cs(+))-complexed species of Z-PG affect ND3 adduct formation. Specifically, [Z-PG + H](+) and [Z-PG-OCH3 + H](+) formed gas-phase ND3 adducts ([Z-PG (or Z-PG-OCH3) + H + ND3](+)) but no ND3 adducts were observed for [Z-PG + alkali metal](+) or [Z-PG + H - CO2](+). Experimentally measured and theoretically calculated collision cross sections (CCSs) of protonated and alkali metal ion-complexed Z-PG species showed similar trends that agreed with the observed structural differences from molecular modeling results. Moreover, results from theoretical ND3 affinity calculations were consistent with experimental HDX observations, indicating a more stable ND3 adduct for [Z-PG + H](+) compared to [Z-PG + alkali metal](+) species. Molecular modeling and experimental MS results for [Z-PG + H](+) and [Z-PG + alkali metal](+) suggest that optimized cation-π and hydrogen bonding interactions of carbonyl groups in final products are important for ND3 adduct formation. Graphical Abstract ᅟ.

The complexation abilities of 5,11,17,23,29,35-hexacarboxy-37,38,39,40,41,42- hexa-methoxy-hydroxamic calix[6]arene extraction of metal ions (Cu2+, Ni2+, Na+, Fe3+, Cd3+, Mn2+, Pb2+) were studied. And the complexation ration of Cu2+ and Pb2+ were obtained by Job's method. The selective removal of Cu2+ (Pb2+) coexisting with alkali metals ions (Na+, K+) and alkaline earth metal ions (Ca2+, Mg2+), heavy metal ions (Zn2+, Mn2+, Pb2+(Cu2+), Ni2+) and anions (CO32-, C2O42-, SO42-, NO3-) were studied separately . The results revealed that the percent of Cu2+(Pb2+) removal in the presence of alkali metals ions and alkaline earth metal ions was over 83.8% (90%) and in the presence of anions was over 90.1% (81.3%) while the percent of Cu2+(Pb2+) removal in the presence of heavy metal ions was lower than 70.6% (70.0%), and the minimum percent of Cu2+(Pb2+) removal in the presence of heavy metal ions was 32.7% (61.2%).