Tetraalkylammonium Cations Research Articles

Tetraalkylammonium cations as templates in the construction of two cadmium(ii) metal–organic frameworks

Hydrothermal reaction of cadmium salts with HATZ in the presence of R4NBr (R = Et, Pr) led to two organic cation templated Cd(II) MOFs, (Et4N)[Cd6Br5(ATZ)8]·H2O (1) and (Pr4N)[Cd4Br5(ATZ)4] (2) (HATZ = 5-amino-tetrazolate, Et = ethyl and Pr = propyl), which are the first examples of tetraalkylammonium cations templated N-heterocyclic ligand based MOFs. These two MOFs have been fully characterized by single crystal X-ray diffraction, XRD, TGA, IR, elemental analysis, photoluminescence spectra and combustion heat measurement. The anionic frameworks of 1 and 2 are three- and two-dimensional, respectively. Topological analyses show that compound 1 exhibits an unprecedented binodal (4,10)-connected network, which is a subnet of the (12,12)-connected tcj net, and compound 2 is a 2-D uninodal four-connected network when the Cd6 clusters in these two MOFs are viewed as nodes. Moreover, compound 1 maybe have potential application as an energetic material due to its high enthalpy of formation.

Relationship between supporting electrolyte bulkiness and dissociative electron transfer at catalytic and non-catalytic electrodes

Dissociative electron transfers (DETs) involving aryl halides in the presence of supporting electrolytes with tetraalkylammonium cations TAA+ of different diameters provide a first model case of rationalized relationship between supporting electrolyte bulkiness effect and DET mechanism.In non-catalytic conditions, with the molecule reacting at the OHP, increasingly bulkier TAA+ cations result in increasing double layer (DL) thickness and consequently in increasingly hindered electron tunnelling, and the reduction peak potentials Ep,DET linearly shift in the negative direction with increasing cation diameter dTAA+. The linear variation of Ep,DET with dTAA+ is consistent with the distance dependence of kET for reagents held at fixed distances from the electrode (lnk=lnk0−βx). The ∂Ep,DET/∂dTAA+ slope is not constant in the investigated model series, but linearly increases with decreasing κ parameter, accounting for the heterogeneous ET step becoming increasingly more determining with respect to the following CX bond cleavage step (as a consequence of decreasing stability of the π* orbital corresponding to the radical anion). Thus the β parameter in the electron tunnelling equation appears to be strictly related to the ET activation barrier (in particular, to its relative weight in the overall DET kinetics).On catalytic Ag electrodes, with the molecule reacting at the IHP, the supporting electrolyte effect is assumed to depend on the increasingly smaller effective potential difference available to the molecule, reacting close to the electrode, with increasing double layer thickness. It appears more conspicuous than in non-catalytic conditions, in spite of the less extreme operating potentials, but consistently with the increased relative importance of the ET activation barrier at a catalytic electrode.

Tetraalkylammonium Uranyl Isothiocyanates

Three tetraalkylammonium uranyl isothiocyanates, [(CH(3))(4)N](3)UO(2)(NCS)(5) (1), [(C(2)H(5))(4)N](3)UO(2)(NCS)(5) (2), and [(C(3)H(7))(4)N](3)UO(2)(NCS)(5) (3), have been synthesized from aqueous solution and their structures determined by single-crystal X-ray diffraction. All of the compounds consist of the uranyl cation equatorially coordinated to five N-bound thiocyanate ligands, UO(2)(NCS)(5)(3-), and charge-balanced by three tetraalkylammonium cations. Raman spectroscopy data have been collected on compounds 1-3, as well as on solutions of uranyl nitrate with increasing levels of sodium thiocyanate. By tracking the Raman signatures of thiocyanate, the presence of both free and bound thiocyanate is confirmed in solution. The shift in the Raman signal of the uranyl symmetric stretching mode suggests the formation of higher-order uranyl thiocyanate complexes in solution, while the solid-state Raman data support homoleptic isothiocyanate coordination about the uranyl cation. Presented here are the syntheses and crystal structures of 1-3, pertinent Raman spectra, and a discussion regarding the relationship of these isothiocyanates to previously described uranyl halide phases, UO(2)X(4)(2-).

The contribution of hydrophobic residues in the pore-forming region of the ryanodine receptor channel to block by large tetraalkylammonium cations and Shaker B inactivation peptides

Although no high-resolution structural information is available for the ryanodine receptor (RyR) channel pore-forming region (PFR), molecular modeling has revealed broad structural similarities between this region and the equivalent region of K+ channels. This study predicts that, as is the case in K+ channels, RyR has a cytosolic vestibule lined with predominantly hydrophobic residues of transmembrane helices (TM10). In K+ channels, this vestibule is the binding site for blocking tetraalkylammonium (TAA) cations and Shaker B inactivation peptides (ShBPs), which are stabilized by hydrophobic interactions involving specific residues of the lining helices. We have tested the hypothesis that the cytosolic vestibule of RyR fulfils a similar role and that TAAs and ShBPs are stabilized by hydrophobic interactions with residues of TM10. Both TAAs and ShBPs block RyR from the cytosolic side of the channel. By varying the composition of TAAs and ShBPs, we demonstrate that the affinity of both species is determined by their hydrophobicity, with variations reflecting alterations in the dissociation rate of the bound blockers. We investigated the role of TM10 residues of RyR by monitoring block by TAAs and ShBPs in channels in which the hydrophobicity of individual TM10 residues was lowered by alanine substitution. Although substitutions changed the kinetics of TAA interaction, they produced no significant changes in ShBP kinetics, indicating the absence of specific hydrophobic sites of interactions between RyR and these peptides. Our investigations (a) provide significant new information on both the mechanisms and structural components of the RyR PFR involved in block by TAAs and ShBPs, (b) highlight important differences in the mechanisms and structures determining TAA and ShBP block in RyR and K+ channels, and (c) demonstrate that although the PFRs of these channels contain analogous structural components, significant differences in structure determine the distinct ion-handling properties of the two species of channel.

Effect of modification of montmorillonite on the cellular structure and mechanical properties of ethylene vinyl acetate/clay nanocomposite foams

Nanocomposite foams, based on ethylene vinyl acetate copolymer, were prepared by melt blending of ethylene vinyl acetate with organically modified montmorillonite and at a high curing pressure of the blends. The organically modified montmorillonites were obtained by the modification of montmorillonite with octadecyl trimethyl ammonium chloride, dimethyl octadecyl hydroxy ethyl ammonium nitrate and dioctadecyl dimethyl ammonium chloride as the intercalating agent. The intercalation effect of montmorillonite layers by the tetraalkylammonium cations was characterized by X-ray diffraction. The state of organically modified montmorillonite in the blends was studied using transmission electron microscopy and the cellular microstructure of the foamed samples was observed by scanning electron microscope. The effects of tetraalkylammonium modification of montmorillonite on the cellular structure and the mechanical properties of the ethylene vinyl acetate-based foams were investigated. It was found that organically modified montmorillonites with different alkyl chains played important role in the formation of the microstructure and the mechanical properties of the ethylene vinyl acetate/organically modified montmorillonite nanocomposite foams. With the alkyl chains, it was possible to obtain ethylene vinyl acetate nanocomposite foams with significantly lowered density and improved mechanical properties.

Transfer of heparin polyion across a polarized water/ionic liquid membrane interface

Cyclic voltammetry is used to investigate the transfer of heparin polyion across the interface between water and the ionic liquid (IL) membrane composed of tridodecylmethylammonium cation (TDMA+) and tetrakis[3,5-bis(trifluoromethyl) phenyl]borate anion (TFPB−). Study reveals a tunable effect of the semihydrophobic tetraalkylammonium cations (TAA+) present at trace concentrations in the aqueous solution containing heparin. Theoretical considerations based on the mixed-potential concept and experimental evidence suggest that the TAA+ cations promote the extraction of heparin into the IL phase, from which heparin can be stripped off by applied potential providing a well-separated current signal. A new method for the amperometric detection of heparin is proposed.

Effects of Charge Separation, Effective Concentration, and Aggregate Formation on the Phase Transfer Catalyzed Alkylation of Phenol

The factors that influence the rate of alkylation of phenol under phase transfer catalysis (PTC) have been investigated in detail. Six linear, symmetrical tetraalkylammonium cations, Me(4)N(+), Et(4)N(+), (n-Pr)(4)N(+), (n-Bu)(4)N(+), (n-Hex)(4)N(+), and (n-Oct)(4)N(+), were examined to compare the effects of cationic radius and lipophilicity on the rate of alkylation. Tetraalkylammonium phenoxide·phenol salts were prepared, and their intrinsic reactivity was determined from initial alkylation rates with n-butyl bromide in homogeneous solution. The catalytic activity of the same tetraalkylammonium phenoxides was determined under PTC conditions (under an extraction mechanism) employing quaternary ammonium bromide catalysts. In homogeneous solution the range in reactivity was small (6.8-fold) for Me(4)N(+) to (n-Oct)(4)N(+). In contrast, under PTC conditions a larger range in reactivity was observed (663-fold). The effective concentration of the tetraalkylammonium phenoxides in the organic phase was identified as the primary factor influencing catalyst activity. Additionally, titration of active phenoxide in the organic phase confirmed the presence of both phenol and potassium phenoxide aggregates with (n-Bu)(4)N(+), (n-Hex)(4)N(+), and (n-Oct)(4)N(+), each with a unique aggregate stoichiometry. The aggregate stoichiometry did not affect the PTC initial alkylation rates.

Electrical Conductivity Studies of Tetraalkylammonium Bromides in Aqueous Solutions at Several Temperatures

The molar electrical conductivities of tetramethylammonium, tetraethylamonium, tetra-n-propylammonium, and tetra-n-butylammomium bromides in aqueous solutions at (278.15, 283.15, 288.15, 293.15, and 298.15) K have been measured in the concentration range from (0.002 to 0.04) mol·kg–1. The data were analyzed according to the low-concentration chemical model (lcCM) of Barthel. Values of the limiting molar conductivities, Λ∞, and association constants, KA, were evaluated. Using known values for the limiting molar conductivity of bromide ion, the limiting molar conductivities of the tetraalkylammonium cations were evaluated at all temperatures. The Walden product and the Eyring activation enthalpy were calculated. The results are discussed in terms of solute–solvent interactions.

Preparation and Characterization of Graphene Nanoplatelets from Natural Graphite via Intercalation and Exfoliation with Tetraalkylammoniumbromide

A new method for the preparation of graphene nanoplatelets (GNP) from graphite intercalation compounds (GICs) was investigated. Donor-type ternary GICs of natural graphites, lithium ions and tetrahydrofurane (NG-Li-THF) were synthesized via a solution process, with the lithium ions in the GICs then exchanged with different tetra alkyl ammonium cations to expand the interlayer distance (d-spacing) of these GICs. Microwave irradiation of these GICs resulted in the exfoliation of GICs, forming so-called 'worm-like exfoliated graphites.' Sonication of the worm-like exfoliated graphites in acetone resulted in GNPs with different aspect ratios. Powder X-ray diffractometry, scanning electron microscopy and transmission electron microscopy were employed to characterize the GICs and GNPs. It was found that the ion-exchange of NG-Li-THF increased the volume expansion ratios, and the molecular structure of the tetra alkyl ammonium cations affected the aspect ratios of the GNPs after exfoliation.

Ubiquinone-10 in gold-immobilized lipid membrane structures acts as a sensor for acetylcholine and other tetraalkylammonium cations

It is reported that the reduction of ubiquinone incorporated into supported lipid bilayers and into immobilized liposome layers on gold electrodes is kinetically and thermodynamically enhanced by the presence of acetylcholine and tetrabutylammonium (TBA+) in solution. The reduction peak and the mid-peak potentials of the redox reactions, determined by cyclic voltammetry, are displaced towards more positive potentials by approximately 500 and 250mV, respectively, in the case of TBA+; and by approximately 750 and 530mV, respectively, in the case of acetylcholine. The intensity of the signal varies with the cation concentration, allowing for quantitative determinations in the millimolar range. It is proposed that the enhanced reduction of ubiquinone arises from the formation of tetraalkylammonium cation–ubiquinone radical anion ion-pairs. Electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) measurements confirmed that the potential shift and the intensity of the redox signal are coupled with the adsorption of the tetraalkylammonium cations on the lipid membrane. The Langmuir adsorption equilibrium constant (K) of TBA+ on lipid membranes at physiological pH is determined. In supported lipid bilayers K=440.7±160M−1, while in an immobilized liposome layer K=35.53±3.53M−1.

Influence of Alkyl Chain Length and Temperature on Thermophysical Properties of Ammonium-Based Ionic Liquids with Molecular Solvent

Mixing of ionic liquids (ILs) with molecular solvent can expand the range of structural properties and the scope of molecular interactions between the molecules of the solvents. Exploiting of these phenomena essentially require a basic fundamental understanding of mixing behavior of ILs with molecular solvents. In this context, a series of protic ILs possessing tetra-alkyl ammonium cation [R(4)N](+) with commonly used anion hydroxide [OH](-) were synthesized and characterized by temperature dependent thermophysical properties. The ILs [R(4)N](+)[OH](-) are varying only in the length of alkyl chain (R is methyl, ethyl, propyl, or butyl) of tetra-alkyl ammonium on the cationic part. The ILs used for the present study included tetramethyl ammonium hydroxide [(CH(3))(4)N](+)[OH](-) (TMAH), tetraethyl ammonium hydroxide [(C(2)H(5))(4)N](+)[OH](-) (TEAH), tetrapropyl ammonium hydroxide [(C(3)H(7))(4)N](+)[OH](-) (TPAH) and tetrabutyl ammonium hydroxide [(C(4)H(9))(4)N](+)[OH](-) (TBAH). The alkyl chain length effect has been analyzed by precise measurements such as densities (ρ), ultrasonic sound velocity (u), and viscosity (η) of these ILs with polar solvent, N-methyl-2-pyrrolidone (NMP), over the full composition range as a function of temperature. The excess molar volume (V(E)), the deviation in isentropic compressibility (Δκ(s)) and deviation in viscosity (Δη) were predicted using these properties as a function of the concentration of ILs. Redlich-Kister polynomial was used to correlate the results. A qualitative analysis of the results is discussed in terms of the ion-dipole, ion-pair interactions, and hydrogen bonding between ILs and NMP molecules. Later, the hydrogen bonding features between ILs and NMP were also analyzed using a molecular modeling program with the help of HyperChem 7.

Charge-Based Assemblies Comprising Planar Receptor-Anion Complexes with Bulky Alkylammonium Cations

Charge-by-charge assembly: On the basis of a planar receptor-anion complex, bulky tetraalkylammonium cations were found to construct charge-by-charge assemblies comprising alternately stacked positively and negatively charged species. The number and length of long alkyl chains in the cations determine the states of assembled structures, resulting in the formation of a library of charge-based materials (see scheme).

Potentiometric sensors based on organic ion exchangers of tetraalkylammonium and silver complexes with ampicillin, oxacillin, and cefazolin

Potentiometric sensors with plasticized polymer membranes based on tetraalkylammonium organic ion exchangers and silver(I) complexes with ampicillin, oxacillin, and cefazolin are proposed for the quantification of antibiotics in model mixtures. The quantitative parameters of complex species of silver with β-lactam antibiotics (β-lac) are established. The complexes (β-lac)2Ag are shown applicable as electroactive components of membranes of potentiometric sensors with tetraalkylammonium cations as counterions. For the information on potentiometric selectivity coefficients and the parameters of cross-sensitivity of sensors in solutions of β-lactam antibiotics they might be used in multisensor systems of the electronic tongue type. The analytical signals are processed by the method of neural network. The average relative error of the individual quantification of β-lactam antibiotics in three-component model mixtures was 4–6%.

Ion-pair induced self-assembly of molecular barrels with encapsulated tetraalkylammonium cations based on a bis–trisurea stave

A bis-trisurea ligand assembles with the tetraalkylammonium halides to form the flat 'stave' structures or 'barrels' that encapsulate multiple R(4)N(+) guests, depending on the size of the halide anion (Cl(-) or Br(-)) and the R(4)N(+) cation.

Novel Method for Grafting Alkyl Chains onto Glassy Carbon. Application to the Easy Immobilization of Ferrocene Used as Redox Probe

Primary alkyl iodides (RI) have been found to react with a cathodically charged glassy carbon surface at potentials more negative than -1.7 V vs Ag/AgCl. In aprotic solvents, this reaction results in grafting of the alkyl chains onto carbon. It is proposed that the process corresponds to the cathodic charge of graphitized and fullerenized zones present in carbon followed by a displacement reaction (analogous to a nucleophilic attack) toward alkyl iodides. This new mode of grafting is applied to the immobilization of ferrocene used as an electrochemical probe. The present work points out the reaction of ω-iodoalkylferrocenes and quantifies the level of grafting of alkyl chains via this promising method for modification of carbon surfaces. Coverage levels were found to be high, reaching the apparent surface concentrations of 8 × 10(-9) mol cm(-2). These large values are explained on the basis of swelling of the interface provoked by progressive charging of the carbon surface via insertion of tetraalkylammonium cations concomitantly with the substitution process. Alkylferrocene layers deposited onto carbon were found to be chemically and electrochemically stable.

The positive halochromism of phenolate dyes in hydroxylic solutions of tetraalkylammonium cations

By contrast with the negative halochromic behaviour shown by phenolate betaines in the presence of alkaline and alkaline-earth cations, the addition of tetraalkylammonium salts to hydroxylic solutions of these dyes generate bathochromic shifts of their charge-transfer band. This positive halochromic behaviour by organic cations was examined systematically and its origin rationalized by nonspecific changes of the medium permittivity, and by specific dye–cation interactions in solution.

Study of ion transfer through liquid membrane systems by Current Reversal Chronopotentiometric techniques

General analytical equations are given for the E–t and dt/dE–E responses for the uptake and stripping of a target ion when Current Reversal Chronopotentiometry and Cyclic Reciprocal Derivative Chronopotentiometry with constant current are applied to liquid membrane systems of one and two polarized interfaces. Theoretical expressions for the peak coordinates of both uptake and stripping processes are quantitatively related to the half-wave potential of the ion transfer and to the transition times of the uptake and stripping processes. The predicted behavior has been experimentally verified through the study of the transfer of a series of tetraalkylammonium cations from water to a solvent polymeric membrane.

Application of Current Fluxes to the Characterization of Ion Transfer at Solvent Polymeric Membranes with One and Two Polarized Interfaces

AbstractChronopotentiometric and reciprocal derivative chronopotentiometric E–t, dt/dE–E and dI/dE–E responses are analyzed for the ion transfer of a series of tetraalkylammonium cations and tricyclic catamphiphilic drugs, driven by an exponential and a constant current flux in a liquid membrane system of one and two polarized interfaces. Reciprocal derivative chronopotentiometry shows a strong resolving power, since the dt/dE–E and dI/dE–E responses obtained with this technique are narrower than those provided by some of the more powerful voltammetric techniques, like square wave voltammetry and differential pulse voltammetry. From the experimental results we have obtained the standard ion transfer potential of the different ions assayed.

Oligoether Carboxylates: Task-Specific Room-Temperature Ionic Liquids

Recently, a new family of ionic liquids based on oligoether carboxylates was introduced. 2,5,8,11-Tetraoxatridecan-13-oate (TOTO) was shown to form room-temperature ionic liquids (RTILs) even with small alkali ions such as lithium and sodium. However, the alkali TOTO salts suffer from their extremely high viscosities and relatively low conductivities. Therefore, we replaced the alkali cations by tetraalkylammonium (TAA) ions and studied the TOTO salts of tetraethyl- (TEA), tetrapropyl- (TPA), and tetrabutylammonium (TBA). In addition, the environmentally benign quaternary ammonium ion choline (Ch) was included in the series. All salts were found to be ionic liquids at ambient temperatures with a glass transition typically at around -60 °C. Viscosities, conductivities, solvent polarities, and Kamlet-Taft parameters were determined as a function of temperature. When using quaternary ammonium ions, the viscosities of the resulting TOTO ionic liquids are >600 times lower, whereas conductivities increase by a factor of up to 1000 compared with their alkali counterparts. Solvent polarities further reveal that choline and TAA cations yield TOTO ionic liquids that are more polar than those obtained with the, per se, highly polar sodium ion. Results are discussed in terms of ion-pairing and structure-breaking concepts with regard to a possible complexation ability of the TOTO anion.

Structure of NR4BR-H2O and CoBr2-NR4BR-H2O solutions according to electronic and IR spectroscopy data

Absorption spectra of NR4Br-H2O and CoBr2-NR4Br-H2O (R = Et, Bu) aqueous solutions were measured within the range of 1000–25000 cm−1, and the influence of tetraalkylammonium cations on the equilibrium between cobalt octahedral and tetrahedral complexes was revealed. The specificity of hydration interactions in solutions under study in various concentration ranges and resulting from them difference in spectral characteristics were analyzed. Variously directed changes in positions of bands in the region of stretching vibrations, a composite frequency of 5200 cm−1, and the first water overtone occurring due to the concentration variation were found.