Synthesis and properties of long-chain quaternary ammonium hydroxides

A series of long-chain quaternary ammonium hydroxides were synthesized from tertiary amines and confirmed by ~1H NMR and FTIR.Surface properties and pH of these surfactants were investigated.The critical micelle concentrations(CMC) of the synthesized quaternary ammonium hydroxides are lower than the conventional quaternary ammonium surfactants.The micelles shapes of these long-chain quaternary ammonium hydroxides in aqueous solution are spherical at a concentration of 0.1 mol/L.The pH values of the synthesized quaternary ammonium hydroxides are 12.25-12.51.     

Degradation kinetics and solvent effects of various long-chain quaternary ammonium salts

Surfactants such as quaternary ammonium salts (QAS) have been in increasing demand, for emerging new applications. Recent attempts at process intensification of their production have disclosed the need for a better understanding of QAS thermal stability. This work aims to determine the degradation kinetics of various QASs and the associated solvent effects. The degradation kinetics of four methyl carbonate QASs were determined in various polar solvents in stainless steel batch autoclaves. H NMR spectrometry was employed for offline analysis of the reaction mixtures. The kinetic parameters were then used to compare the thermal stability of the four compounds in the polar solvents. Water showed no degradation, and methanol (MeOH) was the solvent that provided the second-best stability. Water–MeOH mixtures may provide an overall optimum. Moreover, and longer long-chain substituents increased the degradation rate. Thermogravimetric analysis was used to obtain the thermal stability in a solid state, that is, solventless environment. Isoconversional analysis showed that no reliable kinetic parameters could be determined. Nevertheless, the data did allow for a comparison of the thermal stability of 14 different QASs. Furthermore, the relative instability of the compounds in the solid state demonstrated the challenges of solventless QAS production.     

Novel ions of quaternary ammonium halides in FDMS

Field desorption mass spectrometry exhibited novel ions [ Y-n H+n R ]+and [ Y-nH+nX]+as well as cluster ions [nY+(n-1)X-mH+mR]+and [nY+( n-1)X-mH+mX]+(n,m=0-3; X and Y represent the cation and anion moieties of quaternary ammonium halides),whose formation mechanism was discussed.     

Effect of the steric accessibility of the exchange site in long-chain quaternary ammonium salts on the anion-exchange extraction of divalent ions

The constants of anion-exchange extraction of divalent ions by quaternary ammonium salts of various structures were determined. The exchange constants depend significantly on steric accessibility of the exchange site. For the exchange of small-size anions, the affinity of the ion exchanger for divalent ions is higher than for monovalent ions. For large divalent anions, the exchange constant may increase or decrease, depending on the size of a monovalent anion. The obtained results are explained by the specifics of the ion-pair association of monovalent and divalent anions with quaternary ammonium cations.     

Chemical ionization desorption mass spectrometry of some quaternary ammonium salts

The ammonia chemical ionization desorption spectra of N,N-dimethyl quaternary ammonium iodides in addition to high protonated molecular ion [M + H]⁺ intensity, show signals for an ion radical composed of N-methyl abstracted salt cation and ammonia [C + NH₃? CH₃]^+˙. These ions corresponding to the cation +2 show increased importance in the chemical ionization mode, using the same reagent gas. The technique of chemical ionization desorption appears suitable for the analysis of salts, and thus for the determination of the molecular weight of both anion and cation.     

Immobilization of quaternary ammonium salts on silica gel for perchlorate ions removal

Silica surface was modified with quaternary ammonium salts to give three matrices of different chain length. The synthesized supports were characterized by elemental analysis and infrared spectroscopy, as well as scanning electron microscopy and semi-empirical parametric method 5. Their exchange capacities for ClO₄ ⁻, F⁻, NO₃ ⁻ and CH₃COO⁻ ions were investigated by conductometric titration. The amount of exchanged chloride ions from the matrix was studied for different initial anions concentration. The functionalized silica gel showed very good ability of perchlorate ions exchange from the water solution in room temperature. The anion-exchange properties were also studied in comparison to different number of reactive sites in the matrices. The increased number of chloride at the silica surface took effect on increased ability of ClO₄ ⁻ anion exchange      

Electron ionization mass spectral fragmentation of deoxynivalenol and related tricothecenes

Careful analysis of the electron impact (EI) mass spectral data obtained for the trimethylsilyl (TMS) ethers of known trichothecene mycotoxins of the deoxynivalenol group permitted the construction of a database useful for the identification of these mycotoxins directly from a gas chromatography/mass spectrometry (GC/MS) run. Structures of the ions at m/z 103, 117, 147 and 191 were elucidated by high-resolution mass spectrometry (HRMS) and a fragmentation scheme was suggested. The relative abundances of these ions in the mass spectra of the trichothecenes allowed a fast structural diagnosis during analysis of biological matrices. A new mycotoxin of this group, 3-acetylnivalenol, was tentatively identified by using MS data interpretation only.     

Equilibrium and dynamic surface properties of long-chain quaternary ammonium hydroxides with different chain length and number

The equilibrium and dynamic surface tensions of five long-chain alkyl ammonium hydroxides (AAH) at the air/aqueous solution interface were investigated, and the effects of the length and number of alkyl chain on surface tensions had been discussed. With the increase of the length, the equilibrium surface tension (EST) increased from 28.65 to 40.52?mN/m. While, for the double chains at the critical micelle concentration (CMC), the EST decreased from 32.71 to 26.61?mN/m with the length increasing. In addition, the adsorption behaviors of the AAH were analyzed and the effective diffusion coefficients (D_eff) were calculated on basis of the Ward–Tordai equation. Moreover, the time required to attain the EST decreases with the increase of surfactant concentration. The longer the C–H chain is, the lower surface tension at initial concentration is. What’s more, the diffusion processing of the AAH to air/water interface mainly depends on the surfactant concentration, and the adsorption is controlled by diffusion mechanism in a dilute concentration, while under a high concentration the adsorption is controlled by mixed diffusion–kinetic mechanism.     

Interaction between quaternary ammonium ions and dipeptides: positive anion allosteric effect

The binding properties of dipeptides possessing aromatic residues towards quaternary ammonium ions have been investigated by 1H-NMR spectroscopy. The intermolecular hydrogen bonding between exchangeable protons (OH and NH) of aromatic residues of dipeptides and the counter anion of ammonium ion is the primary force. After the formation of the intermolecular hydrogen bonding, two aromatic residues of dipeptides can provide pi-base cavity to interact with the quaternary ammonium moiety.     

Stereochemistry of retro-diel-salder fragmentation in gas-phase ions formed by chemical ionization

Retro Diels Alder fragmentation is highly stereospecific in the diones 1 under chemical ionization conditions, both with methane and isobutane as the reagent gases. Only the cis-isomers yield abundant protonated diene and quinone ions. The isotope effect indicates preferential protonation on a CO oxygen, and a subsequent H-migration prior to the formation of the protonated diene cations in the cis isomers.     

Exploring fluorescence and fragmentation of ions produced by electrospray ionization in ultrahigh vacuum

An instrument for fluorescence spectrometry and FTICR-MS has been developed to study ions produced by a commercial ESI source.

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The determination of free long-chain quaternary ammonium species with an ion-selective electrode based on a cetyltrimethylammonium ion pair

The cetyitrimethylammonium ion-selective electrode described is based on a tetrazole ion-pair and silicone-rubber membranes. The electrode is almost Nernstian in response from 10^-6 M to the critical micelle concentration. The electrode responds little to dodecyland decyltrimethylammonium ions and inorganic ions. Selectivity coefficients for numerous compounds are given. The uses of the ion-selective electrode are discussed in terms of the ability to monitor free quaternary ammonium ions in the presence of electrolyte and complexing additives. The electrode described can be useful in developing certain pharmaceutical formulations.     

Simultaneous determination of bromide and iodide ions by capillary isotachophoresis using quaternary ammonium salts

Bromide and iodide ions were determined simultaneously by capillary isotachophoresis using an aqueous electrolyte system; the separation principle was based on the ion-pairing equilibria between tetradecyldimethylbenzylammonium ion and these anions in the leading electrolyte. The interaction between iodide ion and tetradecyldimethylbenzylammonium ion was stronger than that for bromide ion. Thus complete separation of bromide and iodide ions could be obtained by using a leading electrolyte containing 1.5 mM tetradecyldimethylbenzylammonium ion. The pH of the leading electrolyte was adjusted to 5.0. The relative standard deviations of the zone length for bromide and iodide ions were 1.1 and 1.2%, respectively, when mixture of 3.0 mM of these ions was analysed. A 150-μl volume could be injected for the simultaneous determination of low concentrations of bromide and iodide ions.     

Differentiation of isomeric photomodified oligodeoxynucleotides by fragmentation of ions produced by matrix-assisted laser desorption ionization and electrospray ionization

UV irradiation of oligodeoxynucleotides at 254 nm generates several different types of DNA photoproducts, including cis-syn cyclobutane pyrimidine dimers, pyrimidine[6-4] pyrimidone photoproducts and their Dewar valence isomers, and thymine-adenine photoproducts (TA*). Studies of photoproducts in oligodeoxynucleotides require the development of suitable structure determination methods such as mass spectrometry. In an earlier study (Vollmer et al. Int. J. Mass Spectrom. Ion Processes 1997, 165/166, 487-496), we showed that fast atom bombardment and tandem sector mass spectrometry can be used to locate the site of photomodification and identify most of the photoproducts of d(TATTAT). One goal of the present research was to expand the method to the more sensitive electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) methods. A second goal was to test the generality of the methods by investigating not only the photoproducts of d(TATTAT) but also those of three other oligodeoxynucleotides, d(GTATTAT), d(GGCTATAA), and d(AATTAA). The photoproducts of these sequences were separated by HPLC and gave characteristic fragment ions in postsource decompositions of MALDI-produced ions and collisionally activated decompositions of ESI-produced ions.     

Ring-opening reactions of 1,4-diazabicyclo[2.2.2]octane (DABCO) derived quaternary ammonium salts with phenols and related nucleophiles

1,4-Diazabicyclo[2.2.2]octane (DABCO) has been evaluated as a starting material for the synthesis of 1-alkyl-4-(2-phenoxyethyl)piperazines and related derivatives. We found that 1-alkyl-1,4-diazabicyclo[2.2.2]octan-1-ium salts, resulting from the alkylation of DABCO, efficiently react with a variety of nucleophiles in polyethyleneglycol (PEG) or diglyme at high temperatures to give piperazine products resulting from the nucleophilic ring-opening reaction. The benzylation side reaction was found to be relevant with softer nucleophiles when using 1-benzyl-1,4-diazabicyclo[2.2.2]octan-1-ium salts, while other types of alkylations were not observed. One-pot methodologies allow for the synthesis of piperazines directly from primary alcohols, alkyl halides or sulfonates, using phenols, or other nucleophile sources, and DABCO.     

Ion-pair liquid chromatography--atmospheric pressure ionization mass spectrometry for the determination of quaternary ammonium herbicides

High-performance liquid chromatography coupled with atmospheric pressure ionization mass spectrometry (electrospray and atmospheric pressure chemical ionization) has been used to characterize some quaternary ammonium herbicides (quats). The separation of these compounds was carried out using ion-pair chromatography with heptafluorobutyric acid (15 mM, pH 3.3) and acetonitrile gradient elution for successful coupling to mass spectrometry. Detection limits down to 0.1-4 micrograms l-1 were obtained for spiked tap water following a preconcentration step. Good reproducibilities (day-to-day and run-to-run) were also obtained.     

Production and fragmentation of multiply charged ions in 'electron-free' matrix-assisted laser desorption/ionization

An unusually large fraction of multiply charged ions is observed in 'electron-free' matrix-assisted laser desorption/ionization (MALDI). Here we investigate how the yield of multiply charged ions depends on experimental parameters in MALDI. It is found to increase if measures are taken to limit the number of electrons in the plume, for example, by using non-metallic MALDI targets or low laser pulse energies. The ionization energy of the matrix is another important parameter that affects the yield of multiply charged ions: matrices with high ionization energies lead to greater intensities of multiply charged ions. It is furthermore proposed that some of the fragment ions observed in MALDI are due to reactions of analyte with electrons in the plume. The possibility of electron capture dissociation of multiply charged ions produced by MALDI is shown.     

Peptides derivatized with bicyclic quaternary ammonium ionization tags. Sequencing via tandem mass spectrometry

Improving the sensitivity of detection and fragmentation of peptides to provide reliable sequencing of peptides is an important goal of mass spectrometric analysis. Peptides derivatized by bicyclic quaternary ammonium ionization tags: 1‐azabicyclo[2.2.2]octane (ABCO) or 1,4‐diazabicyclo[2.2.2]octane (DABCO), are characterized by an increased detection sensitivity in electrospray ionization mass spectrometry (ESI‐MS) and longer retention times on the reverse‐phase (RP) chromatography columns. The improvement of the detection limit was observed even for peptides dissolved in 10 mM NaCl. Collision‐induced dissociation tandem mass spectrometry of quaternary ammonium salts derivatives of peptides showed dominant a‐ and b‐type ions, allowing facile sequencing of peptides. The bicyclic ionization tags are stable in collision‐induced dissociation experiments, and the resulted fragmentation pattern is not significantly influenced by either acidic or basic amino acid residues in the peptide sequence. Obtained results indicate the general usefulness of the bicyclic quaternary ammonium ionization tags for ESI‐MS/MS sequencing of peptides. Copyright © 2014 John Wiley & Sons, Ltd.