Study of alkali metal cations binding selectivity of beta-cyclodextrin by ESI-MS

Cyclodextrins (CDs), cyclic oligosaccharides commonly composed of six, seven or eight (alpha, beta, and gamma respectively) D-glucopyranosyl units connected by alpha-(1,4)- glycosidic linkages, have the ability to form inclusion complexes with a wide range of substrates in aqueous solution. This property has led to their applications in different areas such as enzyme mimics, catalysis and the encapsulation. of drugs. ESI-MS has begun to be viewed as a useful tool for investigating the general area of molecular recognition thus providing a powerful mean for the analysis of a wide array of host-guest complexes and other non covalent complexes present in solution. The evaluation of the binding selectivity of beta-cyclodextrin towards the first group alkali cations is reported. The estimation of the affinity degrees has been achieved by competition ESI-MS experiments. In these experiments beta-CD was incubated at the presence of two different cations at the same time, and the ratio of the mass peaks corresponding to the two complexes was calculated. In general, it appears a much larger affinity of the beta-cyclodextrin molecule with sodium with respect to all the other alkaline cations, thus giving evidence that it is the size of the beta-cyclodextrin ring in relation with the cationic radius, which drives the formation of what, at this point, could be defined as an inclusion complex.     

Effect of competing alkali metal cations on neutral Host's anion binding ability

Anion binding by neutral hosts in organic solvents can be inhibited by the presence of alkali metal cations. The binding inhibition is due to salt ion-pairing which increases in the order Cs(+) < K(+) < Na(+). The binding inhibition can be reversed by using heteroditopic hosts that simultaneously bind both the metal cation and the anion. The largest cation-induced enhancements are observed with the less basic anions.     

Organometallic ionophore for alkali metal cations

Complexes of a novel synthetic organometallic ionophore with lithium and sodium cations have been characterized by single-crystal X-ray diffraction. The crystal structure of the lithium complex consists of cation-liganddimers with a tetrahedral coordination around Li. The sodium complex reveals a different structure type consisting of cation-ligandtrimers, with water molecules being included between the trimeric entities. The coordination sphere around the Na ions has a distorted octahedral symmetry. It is anticipated that the observed structures of dinuclear Li and trinuclear Na complexes represent possible modes of aggregation of the cation-ligand entities in lipophilic media.     

Phosphorus-containing cyclodextrin polymers: metal cations and hydroxyapatite affinities

The aim of this study was to highlight the properties of novel phosphorus-containing β-cyclodextrin polymers (CDP) and mainly their dual complexing abilities toward hydrophobic guests and (bio)minerals. Affinity of CDP toward divalent metal cations, calcium, magnesium and zinc, has been investigated by isothermal titration microcalorimetry (ITC). The complexation constants K were around 1.1–6.2 × 10⁴ L mol^?1 and were in the order Ca²⁺ < Mg²⁺ < Zn²⁺. The K regular increase with the CDP molecular weights could be attributed to a cooperative binding of the cations by the monophosphate groups carried by the CDPs. Regarding their CD and phosphorus functionalities, the dual complexing abilities toward amphiphilic guests and divalent cations can occur independently as evidenced from ITC experiments performed in presence of both species. Finally, strong interactions between CDPs and hydroxyapatite have been highlighted by X-ray photoelectron spectrometry with adsorbed amount in the range of 2 mg/m². CDPs are thus promising materials endowed with dual functionalities which could serve in biomaterials to simultaneously entrap bioactive molecules and capture (bio)minerals.     

The interaction of alkali metal cations with oxygen-containing ligands

Ab initio SCF calculations on the interaction of Li⁺ cation with H₂O and H₂CO using two basis sets are presented. Partitioning of SCF energies of interaction into Coulomb-, exchange- and delocalization energies has been performed. Coulomb- and delocalization energies are compared with classical electrostatic and polarization energies. A detailed analysis of the calculated wave functions demonstrates that in the complexes investigated here, charge transfer is of minor importance only. Polarization of the molecules in the strong inhomogeneous field of the cation leads to complicated electron density rearrangements which can be interpreted most easily in terms of polarization of individual localized MO's.     

Synthesis of novel chromogenic azocalix[4]arenemonoquinones and their binding with alkali metal cations

Five new chromogenic azocalix[4]arenemonoquinones have been synthesized, characterized and examined for their interaction with alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) by UV-visible spectroscopic and cyclic voltammetric techniques. It has been determined that 4a selectively exhibits a significant bathochromic shift in its UV-visible spectrum on interaction with potassium ion in comparison to its treatment with other alkali metal cations. The binding stoichiometry of 4a and potassium ion was established to be 1:1 with an association constant of 3.27 × 10⁴ M^?1. Cyclic voltammetric experiments in 4:1 dichloromethane-acetonitrile also revealed a significant anodic shift (ΔE _(1/1′) = 115 mV) of the original redox waves of 4a on interaction with potassium ion.     

Salt forms of sulfadiazine with alkali metal and organic cations

The structures of four salt forms of sulfadiazine (SDH) with alkali metal cations are presented. Three contain the deprotonated SD anion (C₁₀H₉N₄O₂S). These are the discrete complex diaqua{4‐[(pyrimidin‐2‐ylazanidyl‐κN¹)sulfonyl‐κO]aniline}lithium(I), [Li(SD)(H₂O)₂], (I), and the coordination polymers poly[{μ₃‐4‐[(pyrimidin‐2‐ylazanidyl)sulfonyl]aniline}sodium(I)], [Na(SD)]_n, (II), and poly[diaqua{μ₃‐4‐[(pyrimidin‐2‐ylazanidyl)sulfonyl]aniline}potassium(I)], [K(SD)(H₂O)₂]_n, (III). Na complex (II) is a three‐dimensional coordination polymer, whilst K complex (III) has two crystallographically independent [K(SD)(H₂O)₂] units per asymmetric unit (Z′ = 2) and gives a two‐dimensional coordination polymer whose layers propagate parallel to the crystallographic ab plane. The different bonding modes of the SD anion in these three complexes is discussed. Structure (IV) contains protonated SDH₂ cations {4‐[(pyrimidin‐2‐yl)sulfamoyl]anilinium, C₁₀H₁₁N₄O₂S} and the Orange G dianion [OG, 7‐oxo‐8‐(phenylhydrazinylidene)naphthalene‐1,3‐disulfonate, C₁₆H₁₀N₂O₇S₂], namely, 4‐[(pyrimidin‐2‐yl)sulfamoyl]anilinium tetraaqua[7‐oxo‐8‐(phenylhydrazinylidene)naphthalene‐1,3‐disulfonato]sodium(I) sesquihydrate, (SDH₂)[Na(OG)(H₂O)₄]·1.5H₂O. The [Na(OG)(H₂O)₄]₂ dimers have antiparallel naphthyl ring structures joined through two Na centres that bond to the hydrazone anions through the O atoms of the ketone and sulfonate substituents. The structures of the salts formed on reaction of SDH with 2‐aminopyridine and ethanolamine are also presented as 2‐aminopyridinium 4‐[(pyrimidin‐2‐ylazanidyl)sulfonyl]aniline, [C₅H₇N₂][SD], (V), and ethanolaminium 4‐[(pyrimidin‐2‐ylazanidyl)sulfonyl]aniline monohydrate, [HOCH₂CH₂NH₃][SD]·H₂O, (VI), respectively. Structure (V) features a heterodimeric R₂²(8) hydrogen‐bond motif between the cation and the anion, whilst structure (VI) has a tetrameric core of two cations linked by a central R₂²(10) hydrogen‐bonded motif which supports two anions linked to this core by R₃³(8) motifs.     

Selectivity of alkali metal cations adsorption on controlled porous glasses

Alkali metal ions are adsorbed on controlled porous glasses from basic solutions. Narrow porous glasses show a relatively high selectivity with adsorption decreasing in the series Cs, K, Na, Li.     

Relative binding affinities of molecular capsules investigated by ESI-mass spectrometry

ESI-MS(/MS) has been used as a method which allows the fast, unambiguous and sensitive simultaneous detection and relative stability approximation of supramolecular assemblies in mixtures. In spite of the obvious fundamental differences between solution and gas phase, ESI-MS in the case of self-assembled molecular capsules has been shown to produce very similar results to single binding experiments monitored by NMR titrations as well as conformational searches performed by Monte-Carlo simulations. MS/MS experiments reveal the same relative order of gas phase stabilities as previously found in solution. Moreover, proton transfer reactions which lead to new molecular capsules, are not detectable in the time-averaged NMR spectrum. However, the newly produced species are found in the complex mixtures by ESI-MS and can be conveniently characterized by subsequent MS/MS experiments: in a collision-induced dissociation the single half-spheres are easily discovered and structurally assigned. Thus, ESI-MS has worked as a valuable tool for the rapid screening of complex supramolecular mixtures and in combination with MS/MS experiments elucidated both the path of unexpected side reactions as well as the thermodynamic gas-phase stabilities of all components in the mixture.     

Ester derivatives of hexahomotrioxacalix[3]naphthalenes: conformational and binding properties with alkali metal cations

The syntheses of the triesters formed between ethyl bromoacetate and hexahomotrioxacalix[3]naphthalene 8, and its tert-butyl analogue 11, are described. Depending on the conditions employed, cone or partial cone conformers are produced. The conformations appear to have some influence on their complexation in neutral medium, with alkali metal cations. The X-ray structure of the partial cone triester 10 is presented.     

Tetraphenylborate salts of alkali and alkaline earth metal complex cations

An introductory review summarises complex formation between poly(alkyleneoxy) adducts and inorganic salts. This is followed by preparative and IR and NMR spectroscopic features of the tetraphenylborates of complexes of polyethylene glycols, nonylphenoxy(polyethyleneoxy)ethanols and polypropylene glycols with sodium, magnesium, calcium, strontium and barium ions. Generally, an alkylene oxide:cation ratio of 8.5:1 is indicated for the complexes with sodium, and 12:1 (∼10.5:1 for the polyethylene glycols)_for the complexes with the alkaline earth metals.     

Influence of alkali metal cations upon the Kolbe-Schmitt reaction mechanism

The mechanisms of the carboxylations of lithium, potassium, rubidium, and cesium phenoxides are investigated by means of the DFT method with the LANL2DZ basis set. It is shown that the reactions of all alkali metal phenoxides with carbon dioxide occur via very similar reaction mechanisms. The reactions can proceed in the ortho and para positions. The exception is lithium phenoxide which yields only salicylic acid in the Kolbe-Schmitt reaction. It is found that the yield of the para substituted product increases with increasing the ionic radius of the alkali metal used. An explanation for this experimental and theoretical observation is proposed.     

Relative metal ion affinities of organic nitriles in the gas phase

The relative metal ion (Ni⁺ and Co⁺) affinities of 14 alkanenitriles, alkenenitriles and benzonitrile were estimated using Cooks' kinetic method in a fast atom bombardment mass spectrometer. The results are compared with proton affinities, affinities for other metal ions, two-ligand dissociation enthalpies and the dipole moments of the nitriles. The RCN? Co⁺ bond is found to be close to the RCN? Ni⁺ bond but weaker than the RCN? Al⁺ bond. The effective temperature (T) of the metal-bound dimer ions falls in the range 298 K < T < 400 K.     

Complex-forming and selectivity properties of substituted tetraphenylethylenediphosphine dioxides with respect to alkali metal cations

The complex-forming reactivity of mono- and disubstituted ethylenediphosphine dioxides of the general formula Ph₂P(O)CH₂C(R¹R²)P(O)Ph₂, and of a tetraphosphorylated monopodand, ortho-bis[4,5-bis(diphenylphosphinyl)-pentoxy]benzene, relative to alkali metal cations have been determined conductometrically in THF-CHCl₃ medium (4:1). Introduction of alkyl substituants in the ethylene bridge of tetraphenylethylenediphosphine dioxide increases its Li/Na selectivity; maximum Li/Na selectivity equal to 40 is observed for the dimethyl-substituted tetraphenylethylenediphosphine dioxide derivative. Among the ligands examined herein the hexadentate tetraphosphoryl-containing monopodand ortho-bis[4,5-bis(diphenylphosphinyl)pentoxy]benzene was found to be the most effective complex-forming agent with respect to lithium (log=6.0), with a high Li/Na selectivity value equal to 40. The syntheses of 1,1-dimethyltetraphenylethylenediphosphine dioxide and of ortho-bis[4,5-bis(diphenylphosphinyl)pentoxy]benzene are described.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 873–877, April, 1990.The authors wish to thank Z. N. Vostroknutovii for carrying out the stability constant measurements in anhydrous acetonitrile.     

Thermal characterization of Flemion® membranes substituted by alkali metal cations

The thermal behavior of perfluorosulfonated membranes of three equivalent mass (EW=910, 1000 and 1100 g eq⁻¹) has been studied for membranes in acid form and in the alkali metal countercations substituted samples. The water contents of the membranes decrease progressively with increasing EW and the countercations charge density. The monovalent cations substitutions increase the membranes thermal stability. DSC curves show a single endothermic peak around 120°C that give low peak temperature for low EW and high peak temperature for large cations size. The membrane mechanical properties changed for different EW and temperatures of membranes. Stress-strain analysis showed that K⁺ substituted membranes at both temperatures present a highest YM compared to the other alkali cation substitutions. The thermal properties of perfluorosulfonated membranes depend on the water contents, cation size, temperature and also on EW value.     

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.