Study of solvent effects on the stability constant and ionic mobility of the dibenzo‐18‐crown‐6 complex with potassium ion by affinity capillary electrophoresis

The effect of solvent on the strength of noncovalent interactions and ionic mobility of the dibenzo‐18‐crown‐6 complex with K⁺ in water/organic solvents was investigated by using affinity capillary electrophoresis. The proportion of organic solvent (methanol, ethanol, propan‐2‐ol, and acetonitrile) in the mixtures ranged from 0 to 100 vol.%. The stability constant, K_KL, and actual ionic mobility of the dibenzo‐18‐crown‐6‐K⁺ complex were determined by the nonlinear regression analysis of the dependence of the effective electrophoretic mobility of dibenzo‐18‐crown‐6 on the concentration of K⁺ (added as KCl) in the background electrolyte (25 mM lithium acetate, pH 5.5, in the above mixed hydro–organic solvents). Competitive interaction of the dibenzo‐18‐crown‐6 with Li⁺ was observed and quantified in mixtures containing more than 60 vol.% of the organic solvent. However, the stability constant of the dibenzo‐18‐crown‐6‐Li⁺ complex was in all cases lower than 0.5 % of K_KL. The log K_KL increased approximately linearly in the range 1.62–4.98 with the increasing molar fraction of organic solvent in the above mixed solvents and with similar slopes for all four organic solvents used in this study. The ionic mobilities of the dibenzo‐18‐crown‐6‐K⁺ complex were in the range (6.1–43.4) × 10^?9 m² V^?1 s^?1.     

Facilitated Transfer of Alkali and Alkaline‐Earth Metal Ions by a Calix[4]arene Derivative Across Water/1,2‐Dichloroethane Microinterface: Amperometric Detection of Ca2+

The host–guest complexation reactions between 5,11,17,23‐tetra‐tert‐butyl‐25,27‐diethoxycarbonylmethoxy‐26,28‐dimethoxy calix[4]arene (BDDC4) and alkali and alkaline‐earth metal ions were investigated by facilitated ion transfer processes across water/1,2‐dichloroethane microinterface by using steady‐state cyclic voltammetry and differential pulse voltammetry. The obtained facilitated transfers for Li⁺, Na⁺, K⁺, Rb⁺ and Ca²⁺ were evaluated under the different experimental conditions, at the excess concentrations of metal ions with respect to BDDC4 and vice versa. The association constants having 1 : 1 stoichiometry for Li⁺, Na⁺, K⁺ and Rb⁺ in 1,2‐DCE were determined. Also, we demonstrated that BDDC4 can play an important role for the development of highly selective chemical sensor for Ca²⁺ among alkaline‐metal ions in the concentration range of 0.1–1.0 mM in aqueous solution.     

Facilitated Ion‐Transfer of Sodium Cation by (Anthraquinone‐1‐yloxy) methane‐15‐crown‐5 Across the Water/1,2‐Dichloroethane Microinterface

The transfer of sodium cation facilitated by (anthraquinone‐1‐yloxy) methane‐15‐crown‐5 (L) has been investigated at the water/1,2‐dichloroethane microinterface supported at the tip of a micropipette. The diffusion coefficient of (anthraquinone‐1‐yloxy) methane‐15‐crown‐5 obtained was (3.42±0.20)×10^?6 cm² s^?1. The steady‐state voltammograms were observed for forward and backward scans due to sodium ion transfer facilitated by L with 1 : 1 stoichiometry. The mechanism corresponded to an interfacial complexation (TIC) and interfacial dissociation (TID) process. The association constant was calculated to be log β_o=11.08±0.03 in the DCE phase. The association constant of other alkali metals (Li⁺, K⁺, Rb⁺) were also obtained.     

Solvent‐ and counterion‐specific swelling behavior of poly(acrylic acid) gels

The collapse of alkali metal poly(acrylate) (PAAM) gels was investigated for various water/organic solvent mixture systems: methanol (MeOH), ethanol (EtOH), 2‐propanol (2PrOH), t‐butanol (tBuOH), dimethyl sulfoxide (DMSO), acetonitrile (AcN), acetone, tetrahydrofuran (THF), and dioxane. In order to ascertain the counterion specificity in the swelling behavior, four kinds of alkali metal counterions were used: Li⁺, Na⁺, K⁺, and Cs⁺. Remarkable solvent and counterion specificities were observed for every counterion species and every solvent system, respectively. For example, in aqueous EtOH the dielectric constants (D_cr) at which collapse occurred were in the order PAACs < PAALi < PAAK < PAANa. On the other hand, the D_cr at which PAALi gel collapsed increased in the order tBuOH < dioxane < THF < MeOH < 2PrOH < EtOH < acetone < AcN < DMSO, where the D_cr ranged from about 39 to about 67. This was in contrast to our previous observation for a partially quaternized poly(4‐vinyl pyridine) (P4VP) gel, which collapsed in a much narrower D_cr region in similar mixed solvents. The present solvent‐ and counterion‐specific collapses are discussed on the basis of solvent properties such as the dielectric constant and Gutmann's donor number and acceptor number of a pure solvent. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2791–2800, 2000     

Synthesis and Optical Properties of 2,13‐Dibenzothiazol‐2′‐yldibenzo[b,k]‐18‐crown‐6

A new crown ether of 2,13‐dibenzothiazol‐2′‐yldibenzo[b,k]‐18‐crown‐6 was synthesized from 2,13‐diformyl‐ dibenzo[b,k]‐18‐crown‐6 with 2‐aminothiophenol. The binding behavior and the optical properties of the crown ether were examined through UV‐visible spectroscopy and fluorescence spectroscopy. When complexed with Na⁺, K⁺, Rb⁺ and Cs⁺ ions, it led to intramolecular charge transfer and caused the changes of the fluorescence spectra. The protonation of the crown ether was also studied.     

Alkaliisocyanacetate. Synthese und Struktur von [K(18‐Krone‐6)](O2CCH2NC)

Alkali‐isocyanoacetates. Synthesis and Structure of [K(18‐crown‐6)](O₂CCH₂NC) The alkali isocyanoacetates M⁺[O₂CCH₂NC]^? (M = Li,Na,K,Cs) ( 1a ‐ d ) are synthesized by reaction of ethyl isocyanoacetate with the respective alkali hydroxides in ethanol and characterized by IR, NMR (¹H, ¹³C), and mass spectrometry (FAB). In alcoholic solution as well as in the gas phase ion pairs and higher aggregated species are observed. In contrast, [K(18‐crown‐6)][O₂CCH₂NC] ( 2 ) which is obtained from 1c and 18‐crown‐6, turns out to be a 1:1 electrolyte in solution (acetone); in the solid, the isocyanoacetate anion binds to K⁺ via the two carboxylate oxygen atoms resulting in an O₈‐coordinated metal atom.     

Application of affinity capillary electrophoresis and density functional theory to the investigation of benzo-18-crown-6-ether complex with ammonium cation

Affinity capillary electrophoresis (ACE) and quantum mechanical density functional theory (DFT) calculations have been employed for investigation of non-covalent interactions between macrocyclic ligand, benzo-18-crown-6-ether (B18C6) and ammonium cation, NH₄⁺. Firstly, by means of ACE, the strength of the B18C6-NH₄⁺ complex in mixed binary hydro-organic solvent system, methanol–water (50/50, v/v), was determined from the dependence of effective electrophoretic mobility of B18C6 (corrected to reference temperature 25 °C and constant ionic strength, 10 mM) on the concentration of ammonium ion in the background electrolyte (BGE) using non-linear regression analysis. The logarithmic form of the apparent binding (stability) constant (log K_b) of B18C6-NH₄⁺ complex in the above binary solvent system was found to be equal to log K_b = 1.63 ± 0.10. Secondly, the structural characteristics of B18C6-NH₄⁺ complex were described by quantum mechanical density functional theory (DFT) calculations. According to these calculations, in the energetically most favoured form of the B18C6-NH₄⁺ complex, three strong hydrogen bonds are formed between central ammonium ion and B18C6 ligand, one of them is directed to aryl-O-alkyl (Ar–O–CH₂) ethereal oxygen and the other two hydrogen bonds are oriented to alkyl-O-alkyl (CH₂–O–CH₂) ethereal oxygen atoms of the macrocyclic crown ligand.     

First Principles Investigation of Noncovalent Complexation: A [2.2.2]‐Cryptand Ion‐Binding Selectivity Study

A first principles methodology, aimed at understanding the roles of molecular conformation and energetics in host–guest binding interactions, is developed and tested on a system that pushes the practical limits of ab initio methods. The binding behavior between the [2.2.2]‐cryptand host (4,7,13,16,21,24‐hexaoxa‐1,10‐diaza‐bicyclo[8.8.8]hexacosane) and alkali metal cations (Li⁺, Na⁺, and K⁺) in gas, water, methanol, and acetonitrile is characterized. Hartree–Fock and density functional theory methods are used in concert with crystallographic information to identify gas phase, energy‐minimized conformations. Gas phase free energies of binding, with vibrational contributions, are compared to solution‐state binding constants through relative binding selectivity analysis. Calculated relative binding free energies qualitatively correlated with solution state experiments only after gas phase metal desolvation is considered. The B3LYP exchange–correlation functional improves theoretical correlations with experimental relative binding free energies. The relevance of gas phase calculations towards understanding binding in condensed phases is discussed. Natural bond orbital methods highlights previously unidentified intramolecular and intermolecular M⁺(222) chemistries, such as an intramolecular n′_O→σ*_CH hydrogen bond.     

Solvent extraction of univalent and bivalent metal picrates with 1,2-bis[2-(2-methoxyethoxy)ethoxy] benzene (noncyclic crown ether) into CHCl3

The overall extraction equilibrium constants, K_ex, of 1:1:m complexes of 1,2-bis[2-(2-methoxyethoxy)ethoxyjbenzene (AC · B18C6) with uni- and bivalent metal picrates, MA _m were determined at 25°C between CHCl₃ and water, and thereby the ion-pair complex-formation constants,K _MLA,o, of AC · B18C6 with the univalent metal picrates in CHCl₃ were calculated. The AC · B18C6 is an open-chain analog of benzo-18-crown-6 (B18C6). The equilibrium constants of AC · B18C6 were compared with those of B18C6. K_ex sequences of AC · B18C6 for uni- and bivalent metals are Tl⁺ > K⁺ > Rb⁺ > Cs⁺ > Na⁺ > Li⁺ and Pb²⁺ > Ba²⁺ > Sr²⁺, respectively. The same extraction-selectivity was observed for B18C6, but the extractability of AC · B18C6 for the same cation is much lower than that of B18C6; the extraction selectivity of AC · B18C6 for alkali metals is lower than that of B18C6. TheK _MLA,o sequence of AC · B18C6 is K⁺ > Rb⁺ > Tl⁺ > Cs⁺ Na⁺, which is consistent with that of B18C6. ButK _MLA,o of AC · B18C6 is much smaller than the correspondingK _MLA,o of B18C6; the selectivity of AC · B18C6 among alkali metal picrates in CHCl₃ is lower than that of BI8C6. This reflects the difference in the structures between AC · B18C6 (acyclic and flexible) and B18C6 (cyclic and rigid).     

Assembly of a New Cyano‐bridged 4f‐3d Dimer Sm(DMSO)4‐ (H2O)3Cr(CN)6 and Crystal Structure of [K3(18‐crown‐6)3‐(H2O)4]Cr(CN)6·3H2O

A new cyano‐bridged binuclear 4f‐3d complex Sm(DMSO)₄‐(H₂O)₃Cr(CN)₆ was synthesized and characterized by single crystal structure analysis. It crystallizes in monoclinic, space group P2₁ with a=0.9367(2) nm, b = 1.3917(3) nm, c = 1.1212(2) run, β = 99.88(3)° and Z = 2. In this binuclear complex, Sm atom is eight coordinated and linked to the Cr atom by a cyano bridge. The molecules packs to form 3D structure due to the hydrogen bonds among them. [K₃(18‐C‐6)₃(H₂O)₄]Cr(CN)₆·3H₂O (18‐C‐6 represents 18‐crown‐6‐ether) that was synthesized as a byproduct in the preparation of a Gd—Cr complex is also structurally characterized. Crystal data: triclinic, space group P‐l with a = 1.0496(7) nm, b= 1.1567(14) nm, c = 1.3530(13) nm, a = 94.15(9)°, β = 96.04(8)°, γ = 95.25(9)° and Z = l. [K₃(18‐C‐6)₃(H₂O)₄]‐Cr(CN)₆·3H₂O consists of ionic [K₃(18‐C‐6)₃(H₂O)₄]³⁺ and [Cr(CN)₆]^3‐ pairs, of which the [K₃(18‐C‐6)₃(H₂O)₄]³⁺ ion is a trinuclear duster connected by water, and K atoms are eight coordinated by eight oxygen atoms of one 18‐C‐6 and two water molecules.     

[N‐(6‐Amino‐3,4‐di­hydro‐3‐methyl‐5‐nitroso‐4‐oxopyrimidin‐2‐yl)glycylglycinato]aquapotassium,a three‐dimensional coordination polymer

In the title compound, polymeric potassium N‐(6‐amino‐3,4‐di­hydro‐3‐methyl‐5‐nitro­so‐4‐oxopyrimidin‐2‐yl)­glycyl­gly­cinate hydrate, (K⁺·C₉H₁₁N₆O₅^?·H₂O)_n, the hexacoordinate K⁺ cation is linked to five different anions as well as to the water mol­ecule, with K—O distances in the range 2.617 (2)–2.850 (2) Å. Four of the O atoms in each anion coordinate to K centres, one of them acting as a bridging ligand, leading to the formation of nearly square centrosymmetric K₂O₂ rings. The structure is analysed in terms of (010) metal–ligand sheets linked by [010] chains of fused rings.     

K+‐Responsive Block Copolymer Micelles for Targeted Intracellular Drug Delivery

In this work, a novel type of block copolymer micelles with K⁺‐responsive characteristics for targeted intracellular drug delivery is developed. The proposed smart micelles are prepared by self‐assembly of poly(ethylene glycol)‐b‐poly(N‐isopropylacry‐lamide‐co‐benzo‐18‐crown‐6‐acrylamide) (PEG‐b‐P(NIPAM‐co‐B18C6Am)) block copolymers. Prednisolone acetate (PA) is successfully loaded into the micelles as the model drug, with loading content of 4.7 wt%. The PA‐loaded micelles display a significantly boosted drug release in simulated intracellular fluid with a high K⁺ concentration of 150 × 10⁻³m , as compared with that in simulated extracellular fluid. Moreover, the in vitro cell experiments indicate that the fluorescent molecules encapsulated in the micelles can be delivered and specifically released inside the HSC‐T6 and HepG2 cells responding to the increase of K⁺ concentration in intracellular compartments, which confirms the successful endocytosis and efficient K⁺‐induced intracellular release. Such K⁺‐responsive block copolymer micelles are highly potential as new‐generation of smart nanocarriers for targeted intracellular delivery of drugs.     

Alkali‐Metal Ion Catalysis and Inhibition in SNAr Displacement: Relative Stabilization of Ground State and Transition State Determines Catalysis and Inhibition in SNAr Reactivity

We report here the first observation of alkali‐metal ion catalysis and inhibition in S_NAr reactions. The plot of k_obsd versus [alkali‐metal ethoxide] exhibits downward curvature for the reactions of 1‐(4‐nitrophenoxy)‐2,4‐dinitrobenzene with EtOLi, EtONa, and EtOK, but upward curvature for the corresponding reaction with EtOK in the presence of 18‐crown‐6‐ether (18C6). Dissection of k_obsd into the second‐order rate constants for the reactions with the dissociated EtO^? and the ion‐paired EtOM (i.e., k and k_EtOM, respectively) has revealed that the reactivity increases in the order EtOLi<EtONa<EtOK<EtO^?<EtOK/18C6. This indicates that the reaction is inhibited by Li⁺, Na⁺, and K⁺ ions but is catalyzed by 18C6 K⁺ ion. The reactions of 1‐(Y‐substituted‐phenoxy)‐2,4‐dinitrobenzenes have been proposed to proceed through a stepwise mechanism, in which expulsion of the leaving group occurs after the rate‐determining step based on the kinetic result that σ^o constants exhibit a much better Hammett correlation than σ^? constants. Alkali‐metal ion catalysis or inhibition has been discussed in terms of differential stabilization of ground‐state and transition‐state complexes through a qualitative energy profile. A π‐complexed transition‐state structure is proposed to account for the kinetic results.     

Bifunctional Ion‐Selective Electrode Based on C60‐Cryptand 22 for Silver and Iodine Ions

Fullerence C60‐cryptand 22 was prepared and successfully applied as the electric carrier in the PVC electrode membrane of a bifunctional ion‐selective electrode for cations, e.g., Ag⁺ ions as well as anions, e.g., I^? ions. The bifunctional ion‐selective electrode based on C60‐cryptand 22 can be applied as a Silver (Ag⁺) ion selective electrode with an internal electrode solution of 10^?3 M AgNO₃ in water (pH = 6.3), or as an Iodide (I^?) ion selective electrode with an acidic internal electrode solution of 10^?4 M KI_(aq) (pH = 2) in which the cryptand 22 is protonated, and the C60‐cryptand 22 is changed to C60‐Cryptand22–H⁺ and becomes an anionic electro‐carrier to absorb the I^? ion. The Ag⁺ ion selective electrode based on C60‐cryptand 22 gave a linear response with a near‐Nernstian slope (59.5 mV decade^?1) within the concentration range 10^?1‐10^?3 M Ag⁺_(aq). The Ag⁺ ion electrode exhibited comparatively good selectivity for silver ions, over other transition‐metal ions, alkali and alkaline earth metal ions. The Ag⁺ ion selective electrode with good stability and reproducibility was successfully used for the titration of Ag⁺_(aq) with Cl^? ions. The Iodide (I^?) Ion selective electrode based on protonated C60–cryptand22‐H⁺ also showed a linear response with a nearly Nernstian slope (58.5 mV decade^?1) within 10^?1 ‐ 10^?3 M I^? _(aq) and exhibited good selectivity for I^? ions and had small selectivity coefficients (10^?2–10^?3) for most of other anions, e.g., F^? , OH^?, CH₃COO^?, SO₄^2?, CO₃^2?, CrO₄^2?, Cr₂O₇^2? and PO₄^3? ions.     

Kristallstrukturen „supramolekularer”︁ (Benzo‐18‐krone‐6)kaliumtetrathiocyanatometallate: Ein dimerer Komplex {[K(Benzo‐18‐krone‐6)]2[Hg(SCN)4]}2 und zwei isomere Komplexe [K(Benzo‐18‐krone‐6)][Cd(SCN)3] mit kettenförmigen Trithiocyanatocadmat‐Anionen

Crystal Structures of „Supramolecular”︁ Benzo‐18‐crown‐6 Potassium Tetrathiocyanato Metallates: A Dimeric Complex {[K(Benzo‐18‐crown‐6)]₂[Hg(SCN)₄]}₂ and Two Isomeric Complexes [K(Benzo‐18‐crown‐6)][Cd(SCN)₃] Containing Trithiocyanato Cadmate Anions with Chain Structures By reaction of potassium thiocyanatomercurate(II) complexes with benzo‐18‐crown‐6 (2,3‐benzo‐1,4,7,10,13,16‐hexaoxacyclooctadec‐2‐ene) crystals of {[K(benzo‐18‐crown‐6)]₂[Hg(SCN₄)]}₂ ( 1 ) were obtained. 1 crystallizes monoclinic, space group P2₁/n (non‐standard setting of P2₁/c), a = 1737.35(2), b = 1377.16(2), c = 1984.12(3) pm, β = 100.637(1)°, Z = 2. With potassium tetrathiocyanatocadmate(II) two modifications of a complex [K(benzo‐18‐crown‐6)][Cd(SCN)₃] ( 2 , 3 ), of different symmetry were formed. 2 crystallizes monoclinic, P2₁/c, a = 1158,31(3), b = 1096,55(2), c = 2028,46(2) pm, β = 99,5261(2)°, Z = 4, 3  orthorhombic, P2₁cn, a = 1105,95(3), b = 1413,07(4), c = 1617,10(5) pm, Z = 4. 1 has a dimeric structure, built up from a dication K₂(benzo‐18‐crown‐6)₂]²⁺ and two [K(benzo‐18‐crown‐6)]⁺ cations, which are bridged by two [Hg(SCN)₄]^2– anions. In 2 and 3 triply bridged infinite [{Cd(SCN)₃^–}_n] zigzag chains, stretching along screw axes, are to be found as anions. In 2 these chains exist in two conformations related by inversion symmetry, whereas in 3 only one form can be found. [K(benzo‐18‐crown‐6)]⁺ cations are linked to the anion chains via K · · · S interactions of different lengths.     

Structural comparison of three N‐(4‐halogenophenyl)‐N′‐[1‐(2‐pyridyl)ethylidene]hydrazine hydrochlorides

2‐{1‐[(4‐Chloroanilino)methylidene]ethyl}pyridinium chloride methanol solvate, C₁₃H₁₃ClN₃⁺·Cl⁻·CH₃OH, (I), crystallizes as discrete cations and anions, with one molecule of methanol as solvent in the asymmetric unit. The N—C—C—N torsion angle in the cation indicates a cis conformation. The cations are located parallel to the (02) plane and are connected through hydrogen bonds by a methanol solvent molecule and a chloride anion, forming zigzag chains in the direction of the b axis. The crystal structure of 2‐{1‐[(4‐fluoroanilino)methylidene]ethyl}pyridinium chloride, C₁₃H₁₃FN₃⁺·Cl⁻, (II), contains just one anion and one cation in the asymmetric unit but no solvent. In contrast with (I), the N—C—C—N torsion angle in the cation corresponds with a trans conformation. The cations are located parallel to the (100) plane and are connected by hydrogen bonds to the chloride anions, forming zigzag chains in the direction of the b axis. In addition, the crystal packing is stabilized by weak π–π interactions between the pyridinium and benzene rings. The crystal of (II) is a nonmerohedral monoclinic twin which emulates an orthorhombic diffraction pattern. Twinning occurs via a twofold rotation about the c axis and the fractional contribution of the minor twin component refined to 0.324 (3). 2‐{1‐[(4‐Fluoroanilino)methylidene]ethyl}pyridinium chloride methanol disolvate, C₁₃H₁₃FN₃⁺·Cl⁻·2CH₃OH, (III), is a pseudopolymorph of (II). It crystallizes with two anions, two cations and four molecules of methanol in the asymmetric unit. Two symmetry‐equivalent cations are connected by hydrogen bonds to a chloride anion and a methanol solvent molecule, forming a centrosymmetric dimer. A further methanol molecule is hydrogen bonded to each chloride anion. These aggregates are connected by C—H...O contacts to form infinite chains. It is remarkable that the geometric structures of two compounds having two different formula units in their asymmetric units are essentially the same.     

Stabilization of Substituted Triazenide Oxides: Synthesis and X‐ray Structural Features of Polymeric Potassium 3‐(4‐carboxylatophenyl)‐1‐methyltriazene N‐oxide‐hydrate, {K[O2C‐C6H4‐N(H)NN(CH3)O]·4H2O}n

3‐(4‐carboxyphenyl)‐1‐methyltriazene N‐oxide reacts with KOH in methanol/pyridine to give {K[O₂C‐C₆H₄‐N(H)NN(CH₃)O]·4H₂O}_n, Potassium‐3‐(4‐carboxylatophenyl)‐1‐methyltriazene N‐oxide). The terminal carboxylato group of the anion does not interact with the cation. In the crystal lattice of {K(C₈H₈N₃O₃)·4H₂O}_n each three of the four water molecules interact with two potassium cations, every K⁺ ion being the centre of six bridging K···O interactions. Potassium cations interact further with the terminal N‐oxigen atom of single [C₈H₈N₃O₃]^? anions achieving two parallel {C₈H₈N₃O₃^?K⁺}_n chains, which are linked through water molecules. The resulting polymeric, one‐dimensional chain, is operated by a screw axis 2₁ parallel to the crystallographic direction [010], along and equidistant to the K⁺ centres. The coordination of the K⁺ centres involves a distortion of the boat conformation of elementary sulfur (S₈) with the ideal C_2v symmetry.     

Effect of metal cations [Li+, Na+, K+, Be2+, Mg2+, and Ca2+] on the structure of 2‐(3′‐hydroxy‐2′‐pyridyl)benzoxazole: A theoretical investigation

Density functional theory calculations were performed at the B3LYP/6‐311++G(d,p) level to systematically explore the geometrical multiplicity and binding strength for the complexes formed by alkaline and alkaline earth metal cations, viz. Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, and Ca²⁺ (Mⁿ⁺, hereinafter), with 2‐(3′‐hydroxy‐2′‐pyridyl)benzoxazole. A total of 60 initial structures were designed and optimized, of which 51 optimized structures were found, which could be divided into two different types: monodentate complexes and bidentate complexes. In the cation‐heteroatom complex, bidentate binding is generally stronger than monodentate binding, and of which the bidentate binding with five‐membered ring structure has the strongest interaction. Energy decomposition revealed that the total binding energies mainly come from electrostatic interaction for alkaline metal ion complexes and orbital interaction energy for alkaline earth metal ion complex. In addition, the electron localization function analysis show that only the Be? O and Be? N bond are covalent character, and others are ionic character. © 2012 Wiley Periodicals, Inc.     

Fine‐tuning of electromembrane extraction selectivity using 18‐crown‐6 ethers as supported liquid membrane modifiers

Selectivity of electromembrane extractions (EMEs) was fine‐tuned by modifications of supported liquid membrane (SLM) composition using additions of various 18‐crown‐6 ethers into 1‐ethyl‐2‐nitrobenzene. Gradually increased transfer of K⁺, the cation that perfectly fits the cavity of 18‐crown‐6 ethers, was observed for EMEs across SLMs modified with increasing concentrations of 18‐crown‐6 ethers. A SLM containing 1% w/v of dibenzo‐18‐crown‐6 in 1‐ethyl‐2‐nitrobenzene exhibited excellent selectivity for EMEs of K⁺. The established host–guest interactions between crown ether cavities in the SLM and potassium ions in donor solution ensured their almost exhaustive transfer into acceptor solution (extraction recovery ～92%) within 30 min of EME at 50 V. Other inorganic cations were not transferred across the SLM (Ca²⁺ and Mg²⁺) or were transferred negligibly (NH₄⁺, Na⁺; extraction recovery < 2%) and had only subtle effect on EMEs of K⁺. The high selectivity of the tailor‐made SLM holds a great promise for future applications in EMEs since the range of similar selective modifiers is very broad and may be applied in various fields of analytical chemistry.     

A Black Phosphorus–Graphite Composite Anode for Li‐/Na‐/K‐Ion Batteries

Black phosphorus (BP) is a desirable anode material for alkali metal ion storage owing to its high electronic/ionic conductivity and theoretical capacity. In‐depth understanding of the redox reactions between BP and the alkali metal ions is key to reveal the potential and limitations of BP, and thus to guide the design of BP‐based composites for high‐performance alkali metal ion batteries. Comparative studies of the electrochemical reactions of Li⁺, Na⁺, and K⁺ with BP were performed. Ex situ X‐ray absorption near‐edge spectroscopy combined with theoretical calculation reveal the lowest utilization of BP for K⁺ storage than for Na⁺ and Li⁺, which is ascribed to the highest formation energy and the lowest ion diffusion coefficient of the final potassiation product K₃P, compared with Li₃P and Na₃P. As a result, restricting the formation of K₃P by limiting the discharge voltage achieves a gravimetric capacity of 1300 mAh g^?1 which retains at 600 mAh g^?1 after 50 cycles at 0.25 A g^?1.