Interactions Of Alkali Metal Cations Research Articles

Solvation of Isoelectronic Halide and Alkali Metal Ions by Argon Atoms.

This work systematically examines the interactions of alkali metal cations and their isoelectronic halide counterparts with up to six solvating Ar atoms (M+Arn and X-Arn, where M = Li, Na, K, and Rb; X = H, F, Cl, and Br; and n = 1-6) via full geometry optimizations with the MP2 method and robust, correlation-consistent quadruple-ζ (QZ) basis sets. 116 unique M+Arn and X-Arn stationary points have been characterized on the MP2/QZ potential energy surface. To the best of our knowledge, approximately two dozen of these stationary points have been reported here for the first time. Some of these new structures are either the lowest-energy stationary point for a particular cluster or energetically competitive with it. The CCSD(T) method was employed to perform additional single-point energy computations upon all MP2/QZ-optimized structures using the same basis set. CCSD(T)/QZ results indicate that internally solvated structures with the ion at/near the geometric center of the cluster have appreciably higher energies than those placing the ion on the periphery. While this study extends the prior investigations of M+Arn clusters found within the literature, it notably provides one of the first thorough characterizations of and comparisons to the corresponding negatively charged X-Arn clusters.

Bonding and Mobility of Alkali Metals in Helicenes.

In this work, we analyze the interactions of alkali metal cations with [6]- and [14]helicene and the cation mobility of therein. We found that the distortion of the carbon skeleton is the reason that some of the structures which are local minima for the smallest cations are not energetically stable for K+ , Rb+ , and Cs+ . Also, the most favorable complexes are those where the cation is interacting with two rings forming a metallocene-like structure, except for the largest cation Cs+ , where the distortion provoked by the size of the cation destabilizes the complex. As far as mobility is concerned, the smallest cations, particularly Na+ , are the ones that can move most efficiently. In [6]helicene, the mobility is limited by the capture of the cation forming the metallocene-like structure. In larger helicenes, the energy barriers for the cation to move are similar both inside and outside the helix. However, complexes with the cation between two layers are more energetically favored so that the movement will be preferred in that region. The bonding analysis reveals that interactions with no less than 50 % of orbital contribution are taking place for the series of E+ -[6]helicene. Particularly, the complexes of Li+ show remarkable orbital character (72.5-81.6 %).

The Relationship of the Energy of Interaction of Alkali Metal Cations with an Aprotic Solvent Molecule with Quantum Topological Electron Density Characteristics

The optimal geometry and wave functions of the complexes [M(Solv)]+ (M = Li, Na, K; Solv is an aprotic solvent molecule) were calculated and the topological characteristics of the electron density distribution at the (3,–1) critical points (CP) of ion–molecule bonds were analyzed by the density functional theory in the B3LYP/6-31+G(d, p) approximation. The parametric dependences for the energy of ion–molecule bonds in terms of the local kinetic and potential electron energy densities at the bond CTs were proposed.

Why oppositely charged ions of equal radii have different heats of hydration?

Looking for the answer to the title question a number of oversimplifications of the Born model of ion hydration are discussed. They involved: ionic radius, dielectric saturation, structure of water molecules around ions and the nature of ion–water interactions. On the basis of recent literature the last factor—pure electrostatic interactions of alkali metal cations with water molecules but hydrogen bonding of halide anions—has been found to decide on the minimum energy of interactions, the charge transferred between interacting species in equilibrium and the distance between them. Thus, different nature of interactions for cations and anions explains difference in their hydration heats as well as the observation that solvent–solvent interactions in hydrogen bond donor solvents give the important contribution to solvation heats only for anions.

Insights into Thiol-Aromatic Interactions: A Stereoelectronic Basis for S-H/π Interactions.

Thiols can engage favorably with aromatic rings in S-H/π interactions, within abiological systems and within proteins. However, the underlying bases for S-H/π interactions are not well understood. The crystal structure of Boc-l-4-thiolphenylalanine tert-butyl ester revealed crystal organization centered on the interaction of the thiol S-H with the aromatic ring of an adjacent molecule, with a through-space Hthiol···Caromatic distance of 2.71 Å, below the 2.90 Å sum of the van der Waals radii of H and C. The nature of this interaction was further examined by DFT calculations, IR spectroscopy, solid-state NMR spectroscopy, and analysis of the Cambridge Structural Database. The S-H/π interaction was found to be driven significantly by favorable molecular orbital interactions, between an aromatic π donor orbital and the S-H σ* acceptor orbital (a π → σ* interaction). For comparison, a structural analysis of O-H/π interactions and of cation/π interactions of alkali metal cations with aromatic rings was conducted. Na+ and K+ exhibit a significant preference for the centroid of the aromatic ring and distances near the sum of the van der Waals and ionic radii, as expected for predominantly electrostatic interactions. Li+ deviates substantially from Na+ and K+. The S-H/π interaction differs from classical cation/π interactions by the preferential alignment of the S-H σ* toward the ring carbons and an aromatic π orbital rather than toward the aromatic centroid. These results describe a potentially broadly applicable approach to understanding the interactions of weakly polar bonds with π systems.

Association of alkali metal cations with phosphatidylcholine liposomal membrane surface

Interactions of alkali metal cations (Li+, Na+, K+, Cs+) with phosphatidylcholine (PC) liposomal membranes were investigated through experimental studies and theoretical considerations. Using a microelectrophoresis technique, charge densities of experimental membrane surfaces were measured as a function of the pH of electrolyte solutions. Equilibria between the PC liposomal membranes and monovalent ions were mathematically analyzed and described quantitatively through a previously proposed theoretical model. Association constants between functional groups of PC and the studied ions were determined and used to define theoretical curves of membrane surface charge density versus pH. Theoretical and experimental data were compared to verify the model. The PC membrane was found to have the highest affinity for lithium ions, among the ions tested.

Selective Complexation of S‐block Cations with Nanotubular Silk Type Cyclopeptides: A DFT Study

AbstractDensity functional theory (DFT) was used to study the interaction of alkali metal cations (Li+, Na+ and K+) with cyclic peptides constructed from silk type macrocycles (Silk1, Silk2, Silk3, Silk4, Silk5 and Silk6). The calculated binding energies were used as a base for investigating the selectivity of the cyclic peptides in biniding to considered metals ions. The highest cation selectivity for Li+ compared to the other alkali metal ions was observed. The orbital nature of different interactions between the metal cations and the cyclic peptides was analyzed using NBO analysis. The main types of driving force for host‐guest interactions was investigated and it was found that the electron‐donating O offers lone pair electrons to the contacting LP* of alkali metal cations

Theoretical study on supramolecular chemistry of alkali-metal cations with crown ether derivatized thiophenes

This paper describes systemically a theoretical research on the interaction of alkali-metal cations ( Li +, Na +, K + and Rb +) with five different crown ether derivatized thiophenes using density functional theory (DFT). The fully optimized geometries have been performed with real frequencies which indicate the minima states. The optimized structures and electronic properties, such as HOMO and LUMO energies, bandgaps of the free ligands L (L1-L5), the complexes L/M+ ( Li +, Na +, K + and Rb +) have been performed at B3LYP/6-31+G(d,p) and Lanl2DZ level. Natural bond orbital (NBO) and frequency analysis are discussed on the basis of the optimized geometric structures. The main driving forces of the coordination in host–guest molecules are investigated, the electron-donating O offers lone pair electrons to the contacting LP* (1-center valence antibond lone pair) of alkali-metal cations. In addition, the transition energies are calculated by the time-dependent density functional theory (TD-DFT).

Cation···π interactions: QTAIM and NBO studies on the interaction of alkali metal cations with heteroaromatic rings

The cation···π interactions of alkali metal cations (Li+, Na+, and K+) with five-membered heteroaromatic rings [furan(C4H4O), thiophene(C4H4S), pyrrole(C4H5N)] were examined by high level ab initio calculations, to investigate the different roles of C4H4O, C4H4S, and C4H5N as the electron donor, the influential factors that affect these interactions, the nature of this kind of cation···π interaction, and to determine topological and energetical properties to characterize these interactions. The sulfur atom in C4H4S plays a certain role in the cation···π interactions except the C–C π bond, which is different from C4H4O and C4H5N. The size of cation and the character of heteroaromatic ring are two influential factors that affect the cation···π interactions. The studied cation···π interactions can be classified as “closed-shell” and noncovalent interactions. The electron density and its Laplacian at the bond critical points and ring critical points generated upon complexation are useful measurements for the strength of cation···π interactions.

Alkali Metal Cation Interactions with 15-Crown-5 in the Gas Phase: Revisited

Quantitative interactions of the alkali metal cations with the cyclic 15-crown-5 polyether ligand (15C5) are studied. In this work, Rb(+)(15C5) and Cs(+)(15C5) complexes are formed using electrospray ionization and studied using threshold collision-induced dissociation with xenon in a guided ion beam tandem mass spectrometer. The energy-dependent cross sections thus obtained are interpreted to yield bond dissociation energies (BDEs) using an analysis that includes consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion-neutral collisions. 0 K BDEs of 175.0 ± 9.7 and 159.4 ± 9.6 kJ/mol, respectively, are determined and exceed those previously measured [J. Am. Chem. Soc. 1999, 121, 417-423] by 68 and 57 kJ/mol, respectively, consistent with the hypothesis proposed there that excited conformers had been studied. Because the analysis techniques have advanced since this early study, we also reanalyze the published data for the Na(+)(15C5) and K(+)(15C5) systems to ensure a self-consistent interpretation of all four systems. Revised BDEs for these systems are 296.1 ± 15.5 and 215.6 ± 10.6 kJ/mol, respectively, which are within experimental uncertainty of the previously reported values. In addition, quantum chemical calculations are conducted at the B3LYP/def2-TZVPPD level of theory with theoretical BDEs in reasonable agreement with experiment. Computations are also used to explore features of the potential energy surfaces for isomerization of the M(+)(15C5) complexes.

Metal Cation Dependence of Interactions with Amino Acids: Bond Dissociation Energies of Rb+ and Cs+ to the Acidic Amino Acids and Their Amide Derivatives

Metal cation-amino acid interactions are key components controlling the secondary structure and biological function of proteins, enzymes, and macromolecular complexes comprising these species. Determination of pairwise interactions of alkali metal cations with amino acids provides a thermodynamic vocabulary that begins to quantify these fundamental processes. In the present work, we expand a systematic study of such interactions by examining rubidium and cesium cations binding with the acidic amino acids (AA), aspartic acid (Asp) and glutamic acid (Glu), and their amide derivatives, asparagine (Asn) and glutamine (Gln). These eight complexes are formed using electrospray ionization and their bond dissociation energies (BDEs) are determined experimentally using threshold collision-induced dissociation with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy-dependent cross sections include consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion-neutral collisions. Quantum chemical calculations are conducted at the B3LYP, MP2(full), and M06 levels of theory using def2-TZVPPD basis sets, with results showing reasonable agreement with experiment. At 0 and 298 K, most levels of theory predict that the ground-state conformers for M(+)(Asp) and M(+)(Asn) involve tridentate binding of the metal cation to the backbone carbonyl, amino, and side-chain carbonyl groups, although tridentate binding to the carboxylic acid group and side-chain carbonyl is competitive for M(+)(Asn). For the two longer side-chain amino acids, Glu and Gln, multiple structures are competitive. A comparison of these results to those for the smaller alkali cations, Na(+) and K(+), provides insight into the trends in binding energies associated with the molecular polarizability and dipole moment of the side chain. For all four metal cations, the BDEs are inversely correlated with the size of the metal cation and follow the order Asp < Glu < Asn < Gln.

Selective complexation of alkali metal ions and nanotubular cyclopeptides: a DFT study

A density functional theory based on interaction of alkali metal cations (Li+, Na+, K+, Rb+ and Cs+) with cyclic peptides constructed from 3 or 4 alanine molecule (CyAla3 and CyAla4), has been investigated using mixed basis set (C, H, O, Li+, Na+ and K+ using 6-31+G(d), and the heavier cations: Rb+ and Cs+ using LANL2DZ). The minimum energy structures, binding energies, and various thermodynamic parameters of free ligands and their metal cations complexes have been determined with B3LYP and CAM-B3LYP functionals. The order of interaction energies were found to be Li+ > K+ > Na+ > Rb+ > Cs+ and Li+ > Na+ > K+ ≫ Rb+ > Cs+, calculated at CAM-B3LYP level for the M/CyAla3 and M/CyAla4 complexes, respectively. Their selectivity trend shows that the highest cation selectivity for Li+ over other alkali metal ions has been achieved on the basis of thermodynamic analysis. The main types of driving force host–guest interactions are investigated, the electron-donating O offers lone pair electrons to the contacting LP* of alkali metal cations.

Selectivity of ion exchangers in extracting cesium and rubidium from alkaline solutions

We compare the ion exchange selectivity of phenol-type sorbents based on phenol formaldehyde resins, products of condensation of diatomic phenols with formaldehyde, and crosslinked polymer based on C-phenyl[4]resorcinarene resin, for cesium and rubidium ions. It is shown that phenol formaldehyde sorbents are the ones most selective. The interaction of alkali metal cations with the anion of calix[4]arene is investigated via quantum-chemical modeling. It is shown that the selectivity toward cesium and rubidium ions in ion exchangers of the phenolic type is not due to specific interactions of ions with phenolic groups.

Thermochemistry of Alkali Metal Cation Interactions with Histidine: Influence of the Side Chain

The interactions of alkali metal cations (M(+) = Na(+), K(+), Rb(+), Cs(+)) with the amino acid histidine (His) are examined in detail. Experimentally, bond energies are determined using threshold collision-induced dissociation of the M(+)(His) complexes with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy dependent cross sections provide 0 K bond energies of 2.31 ± 0.11, 1.70 ± 0.08, 1.42 ± 0.06, and 1.22 ± 0.06 eV for complexes of His with Na(+), K(+), Rb(+), and Cs(+), respectively. All bond dissociation energy (BDE) determinations include consideration of unimolecular decay rates, internal energy of reactant ions, and multiple ion-neutral collisions. These experimental results are compared to values obtained from quantum chemical calculations conducted previously at the MP2(full)/6-311+G(2d,2p), B3LYP/6-311+G(2d,2p), and B3P86/6-311+G(2d,2p) levels with geometries and zero point energies calculated at the B3LYP/6-311+G(d,p) level where Rb and Cs use the Hay-Wadt effective core potential and basis set augmented with additional polarization functions (HW*). Additional calculations using the def2-TZVPPD basis set with B3LYP geometries were conducted here at all three levels of theory. Either basis set yields similar results for Na(+)(His) and K(+)(His), which are in reasonable agreement with the experimental BDEs. For Rb(+)(His) and Cs(+)(His), the HW* basis set and ECP underestimate the experimental BDEs, whereas the def2-TZVPPD basis set yields results in good agreement. The effect of the imidazole side chain on the BDEs is examined by comparing the present results with previous thermochemistry for other amino acids. Both polarizability and the local dipole moment of the side chain are influential in the energetics.

Alkali metal cation interactions with 12-crown-4 in the gas phase: Revisited

Quantitative interactions of alkali metal cations with the cyclic 12-crown-4 polyether ligand (12C4) are studied. Experimentally, Rb+(12C4) and Cs+(12C4) complexes are formed using electrospray ionization and their bond dissociation energies (BDEs) determined using threshold collision-induced dissociation of these complexes with xenon in a guided ion beam tandem mass spectrometer. The energy-dependent cross sections thus obtained are interpreted using an analysis that includes consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion-neutral collisions. 0K BDEs of 151.5±9.7 and 137.0±8.7kJ/mol, respectively, are determined and exceed those previously measured by 60 and 54kJ/mol, respectively, consistent with the hypothesis proposed there that excited conformers had been studied. In order to provide comparable thermochemical results for the Na+(12C4) and K+(12C4) systems, the published data for these systems are reinterpreted using the same analysis techniques, which have advanced since the original data were acquired. Revised BDEs for these systems are obtained as 243.9±12.6 and 182.0±17.3kJ/mol, respectively, which are within experimental uncertainty of the previously reported values. In addition, quantum chemical calculations are conducted at the B3LYP and MP2(full) levels of theory with geometries and zero point energies calculated at the B3LYP level using both HW*/6-311+G(2d,2p) and def2-TZVPPD basis sets. The theoretical results are in reasonable agreement with experiment, with B3LYP/def2-TZVPPD values being in particularly good agreement. Computations also allow the potential energy surfaces for dissociation of the M+(12C4) complexes to be elucidated. These are used to help explain why the previous studies formed excited conformers of Rb+(12C4) and Cs+(12C4) but apparently not of Na+(12C4) and K+(12C4).

Adsorption of Carbon Dioxide on Sodium and Potassium Forms of STI Zeolite

AbstractSodium and potassium forms of STI zeolite synthesized with Si/Al ratios 15, 25, and 35 were characterized using X‐ray powder diffraction and nitrogen adsorption at 77 K. To obtain detailed information on the effect of alkali metal cations on CO2 adsorption, the temperature dependence of CO2 isotherms was investigated in the temperature range from 273 to 333 K. Based on these data, isosteric heats of adsorption of CO2 were determined. It was found that the isosteric heat of CO2 adsorption attains the highest values on the sodium form of STI zeolite with a Si/Al ratio of 15. The lowest values were found with both sodium and potassium forms of STI zeolite having a Si/Al ratio of 35. Heats of adsorption of CO2 obtained for STI zeolites were discussed in detail and compared with those of FER, MFI, MEL, TUN, and IMF structural types. This comparison revealed that isosteric heats of adsorption of CO2 on STI zeolites are lower by approximately 8 kJ mol−1 compared with heats of adsorption for FER, MFI, MEL, TUN, and IMF zeolites composed of the eight‐ or/and ten‐ring channel systems as well as STI zeolites. This effect was explained on the basis of stronger interaction of alkali metal cations with oxygen atoms of the zeolitic framework.

DFT study of crown ether-bridged Z-stilbenes and their complexes with alkali metal cations

A density functional theory (DFT) based on the interaction of alkali metal cations (Li+, Na+, K+, Rb+ and Cs+) with crown ether-bridged Z-stilbene has been investigated. The minimum energy structures, binding energies, and various thermodynamic parameters of free ligands and their metal cations complexes have been determined with B3LYP functional using mixed basis set (C, H, O, Li+, Na+ and K+ using 6-31+G(d), and the heavier cations: Rb+ and Cs+ using LANL2DZ). The optimized geometric structures are performed natural bond orbital (NBO) analysis. The main types of driving force host–guest interactions are investigated, the electron-donating O offers lone pair electrons to the contacting LP* (1-center valence lone pair) of alkali metal cations. In addition, the maximum absorption wavelength is studied on the time-dependent density functional theory (TD-DFT), the calculated results indicate that the wavelength is blue shifted when alkali cations incorporating into the ether rings. It is found that the crown ether-bridged Z-stilbene is good candidate for moderate alkali metal cations’ recognition regent.

Non-covalent interactions of alkali metal cations with singly charged tryptic peptides

The complexes formed by alkali metal cations (Cat(+) = Li(+), Na(+), K(+), Rb(+)) and singly charged tryptic peptides were investigated by combining results from the low-energy collision-induced dissociation (CID) and ion mobility experiments with molecular dynamics and density functional theory calculations. The structure and reactivity of [M + H + Cat](2+) tryptic peptides is greatly influenced by charge repulsion as well as the ability of the peptide to solvate charge points. Charge separation between fragment ions occurs upon dissociation, i.e. b ions tend to be alkali metal cationised while y ions are protonated, suggesting the location of the cation towards the peptide N-terminus. The low-energy dissociation channels were found to be strongly dependant on the cation size. Complexes containing smaller cations (Li(+) or Na(+)) dissociate predominantly by sequence-specific cleavages, whereas the main process for complexes containing larger cations (Rb(+)) is cation expulsion and formation of [M + H](+). The obtained structural data might suggest a relationship between the peptide primary structure and the nature of the cation coordination shell. Peptides with a significant number of side chain carbonyl oxygens provide good charge solvation without the need for involving peptide bond carbonyl groups and thus forming a tight globular structure. However, due to the lack of the conformational flexibility which would allow effective solvation of both charges (the cation and the proton) peptides with seven or less amino acids are unable to form sufficiently abundant [M + H + Cat](2+) ion. Finally, the fact that [M + H + Cat](2+) peptides dissociate similarly as [M + H](+) (via sequence-specific cleavages, however, with the additional formation of alkali metal cationised b ions) offers a way for generating the low-energy CID spectra of 'singly charged' tryptic peptides.

An Experimental and Theoretical Study of Alkali Metal Cation Interactions with Cysteine

The interactions of alkali metal cations (M(+) = Li(+), Na(+), K(+), Rb(+)) with the amino acid cysteine (Cys) are examined in detail. Experimentally, bond energies are determined using threshold collision-induced dissociation of the M(+)(Cys) complexes with xenon in a guided ion beam mass spectrometer. Analyses of the energy dependent cross sections provide 0 K bond energies of 2.65 +/- 0.12, 1.83 +/- 0.05, 1.25 +/- 0.03, and 1.06 +/- 0.03 eV for complexes of Cys with Li(+), Na(+), K(+), and Rb(+), respectively. All bond energy determinations include consideration of unimolecular decay rates, internal energy of reactant ions, and multiple ion-molecule collisions. Ab initio calculations at the MP2(full)/6-311+G(2d,2p), B3LYP/6-311+G(2d,2p), and B3P86/6-311+G(2d,2p) levels with geometries and zero-point energies calculated at the B3LYP/6-311G(d,p) level for the lighter metals show good agreement with the experimental bond energies. For Rb(+)(Cys), similar calculations using the HW* basis set and ECP underestimate the experimental bond energies, whereas the Def2TZVP basis set yields results in good agreement. Ground state conformers are tridentate for Li(+) and Na(+), and subtle changes in the Cys side-chain orientation are found to cause noticeable changes in the alkali metal binding energy. For K(+) and Rb(+), tridentate and carboxylic acid bound (both charge-solvated and zwitterionic) structures are nearly isoenergetic, with different levels of theory predicting different ground conformers. The combination of this series of experiments and calculations allows the influence of the sulfur functional group of Cys on the overall binding strength to be explored. Comparison to previous results for serine elucidates the influence of sulfur for oxygen substitution.

An experimental and theoretical study of alkali metal cation/methionine interactions

The interactions of alkali metal cations (M + = Li +, Na +, K +) with the amino acid methionine (Met) are examined in detail. Experimentally, the bond energies are determined using threshold collision-induced dissociation of the M +(Met) complexes with xenon in a guided ion beam mass spectrometer. Analyses of the energy dependent cross sections provide 0 K bond energies of 3.03 ± 0.13 eV, 2.09 ± 0.11 eV, and 1.47 ± 0.11 eV for complexes of Met with Li +, Na +, and K +, respectively. All bond energy determinations include consideration of unimolecular decay rates, internal energy of reactant ions, and multiple ion-molecule collisions. Ab initio calculations at the MP2(full)/6-311 + G(2d,2p), B3LYP/6-311 + G(2d,2p), and B3P86/6-311 + G(2d,2p) levels with geometries and zero point energies calculated at the B3LYP/6-311G(d,p) level show good agreement with the experimental bond energies, especially for the sodium and potassium complexes. Ground state conformers are tridentate for Li + and Na +, and subtle changes in the Met side-chain orientation are found to cause noticeable changes in the alkali metal binding energy. For K +, tridentate and zwitterionic structures are nearly isoenergetic, with different levels of theory predicting different ground conformers. The combination of this series of experiments and calculations allows the influence of the functional groups of Met on the overall binding strength to be thoroughly explored.