Thermodynamics of Solvation of 18-Crown-6 and Its Alkali-Metal Complexes in Various Solvents

Heats of solution of 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) in acetonitrile, 1,2-dichloroethane, N,N-dimethylformamide, dimethyl sulfoxide, nitromethane, propylene carbonate, pyridine and water were measured at 25 °C and the enthalpies of the transfer of 18-crown-6 from waterto the aprotic solvents were derived. The thermodynamic quantities, G₁°, H₁° and T S₁°, for the formation of the[M(18-crown-6)]⁺ (M⁺ = Na⁺, K⁺, Rb⁺, Cs⁺, NH₄ ⁺) complexeswere determined by titration calorimetry in dimethyl sulfoxide containing0.1 mol dm^-3 (C₂H₅)₄NClO₄ as a constant ionic medium at 25 °C. These thermodynamic quantities suggest that the complexationof 18-crown-6 with the alkali-metal ions mainly reflects the different solvationof 18-crown-6 and also the different degree of solvent structure.     

The effect of cation size (H+, Li+, Na+, and K+) on McLafferty-type rearrangement of even-electron ions in mass spectrometry

Protonation and alkali-metal cation adduction are the most important ionization processes in soft-ionization mass spectrometry.Studies on the fragmentation mechanism of protonated and alkali-metal-cationized compounds in tandem mass spectrometry are essential and helpful for structural analysis.In some cases,it was often observed that a compound attached by different alkali-metal cations(or proton)exhibits similar fragmentation patterns but the relative abundances of product ions are different.This difference was considered to derive from the different electrostatic interactions of alkali-metal cations(or the bonded effect of proton)with the analyte.The alkali-metal cation with a smaller ionic radius shows stronger electrostatic interaction with the molecule because of its higher charge density.In addition,the bonded effect of the proton is stronger than the electrostatic interaction of the alkali-metal cation.In the present study,which used McLafferty-type rearrangements of even-electron ions([M+Cat]+,Cat=H,Li,Na,K)as model reactions,the effect of cation size in mass spectrometric fragmentation reactions is highlighted.These considerations were also successfully applied to interpret the similar but distinct fragmentation behavior of proton and alkali-metal cation adducts of a synthetic compound(2-(acetamido(phenyl)methyl)-3-oxobutanoate)and a drug(entecavir).     

K2CO3-Na2CO3-Li2CO3-H2O四元体系288K的相平衡

水盐体系;碳酸盐;溶解度;盐湖卤水;K2CO3-Na2CO3-Li2CO3-H2O四元体系288K的相平衡     

碱性金属修饰金属有机骨架材料MOF-5吸附位点及其常态下分离二氧化碳/甲烷的应用

利用“一步法”合成并表征了4种碱性金属修饰的金属有机骨架材料MOF-5(记作M-MOF-5,M=Li,Na,K,Mg)。 并应用理想溶液吸附理论(IAST)对样品吸附选择性进行计算比较。 结果表明,碱性金属掺入可以降低MOF-5材料骨架结构的“互穿”程度,同时,在常温常压下,M-MOF-5对CO₂/CH₄的吸附选择性相对MOF-5(选择性为3.79)有着显著提高,尤其是Li-MOF-5(选择性为7.39)。 此外,Li-MOF-5的CO₂捕获能力相对MOF-5也有提高。     

Understanding charge transfer of Li~+ and Na~+ ions scattered from metal surfaces with high work function

For Li~+ and Na~+ ions scattered from high work function metal surfaces, efficient neutralization is observed, and it cannot be explained by the conventional free electron model. In order to explain these experimental data, we investigate the velocity-dependent neutral fraction with the modified Brako–Newns(BN) model. The calculated results are in agreement with the experimental data. We find that the parallel velocity effect plays an important role in neutralizing the Li~+ and Na~+ ions for large angle scattering. The nonmonotonic velocity behavior of neutral fraction is strongly related to the distance-dependent coupling strength between the atomic level and metal states.     

Raman Scattering and X-Ray Diffraction Studies on Alkali-Metal Intercalated Clays

Abstract

Vermiculite and fluor-tetrasilicic mica were intercalated with alkali metals (Na, K and Rb) by vapor transport. X-ray and Raman scattering experiments were conducted to study the structure and lattice dynamics of the new clay compounds. When Rb and K atoms were intercalated to the host materials, superlattices were formed. In Na intercalated compounds, however, no superlattice x-ray diffraction peaks were found. Raman spectra exhibited drastic changes after alkali-metal intercalation, reflecting the structural changes found by our x-ray diffraction.     

Retardation of dibenzo polyether-formaldehyde resin formation by alkali-metal cations

Macrocyclic polyethers are well-known complexing agents for alkali-metal and alkaline earth-metal cations. The influence of alkali-metal cations upon the polycondensation rate of acyclic and cyclic dibenzo polyethers with formaldehyde in formic acid and alkali-metal cation sorption by some of the resultant resins have been investigated. For certain dibenzo polyether and alkali-metal cation combinations, polymer formation is markedly reduced. The alkali-metal cation that provides the best fit for the macrocyclic polyether cavity produces the greatest retardation of polymer formation. It is proposed that metal ion complexation renders the dibenzo polyether monomer inert to polymerization under the reaction conditions. No template effect for alkali-metal cation sorption by dibenzo polyether carboxylic acid resins was observed. © 1995 John Wiley & Sons, Inc.     

Characterization of Extra-framework Cations in Zeolites. A temperature-programmed desorption (TPD) study

We have investigated the interaction of a few 5-ring organic compounds (cyclopentane, cyclopentene, furan, 2-methylfuran, 2,5-dihydrofuran and tetrahydrofuran) with alkali-metal cation-exchanged faujasites (LSX, X and Y types) by means of temperature-programmed desorption (TPD). The desorption behavior at higher temperatures of all probe molecules on the sodium ion containing faujasites with different Si/Al ratios reflects the higher cation content of zeolites with greater aluminum content. Only the desorption profiles of tetrahydrofuran and 2,5-dihydrofuran show, depending on the kind of cation, additional desorption features at higher temperatures. Using a regularization method, desorption energy distribution functions for furan and tetrahydrofuran were calculated. The calculated desorption energy distributions clearly illustrate the very different adsorption behavior of furan and tetrahydrofuran which leads to large differences in the binding energies between the corresponding adsorption complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Momentum densities and Compton profiles of alkali-metal atoms

It is assumed that the dynamics of valence electrons of alkali-metal atoms can be well accounted for by a quantum-defect theoretic model while the core electrons may be supposed to move in a self-consistent field. This model is used to study the momentum properties of atoms from³Li to³⁷Rb. The numerical results obtained for the momentum density, moments of momentum density and Compton profile are found to be in good agreement with the results of more detailed configuration-interaction calculations for the atom³Li. Similar results for¹¹Na,¹⁹K and³⁷Rb are compared with the corresponding Hartree-Fock-Roothaan values only, for want of data from other realistic calculations     

Enhancement of photoinduced intramolecular cross-cycloaddition of α-(9-anthryl)-ω-(1-naphthoyl) end-labeled poly(ethylene glycol) via lipophobic interactions and complexation with metal cations

The fluorescence spectra and photocycloadditions of poly(ethylene glycol) labeled at the chain termini with one 9-anthryl and one 1-naphthoyl group (N-P_n-A) both in non-polar and polar solvents in the presence of alkali-metal cations have been investigated. Lipophobic interactions in non-polar solvents and complexation of the polyether with cations in polar solvents force the two terminal groups of N-P_n-A into proximity, and irradiation of the solutions produces intramolecular photocyclomers to the exclusion of intermolecular products.