Ammonium Counterions Research Articles

Phase Behavior of Homologous Perfluoropolyether Surfactants: NMR, SAXS, and Optical Microscopy

Self-assembled structures formed by perfluoropolyether (PFPE) carboxylates with hydrophobic chain terminated by Cl−C3F6O, and either sodium or ammonium counterions, have been explored in aqueous binary systems. The focus is on the different counterion-specific micelles and liquid crystals formed. These have been detected and characterized via optical microscopy, SAXS, and NMR. All Cl−PFPE surfactants form lamellar and cubic liquid crystals independently of chain length and counterion. Nonspherical micelles for the shortest PFPE chain surfactants and anomalous swelling of the lamellar phases for almost all surfactants were ascertained.

Influence of ionic specificity on the microstructure and the strength of gelled colloidal silica suspensions.

The dynamic rheological behavior of gelled Ludox suspensions in the presence of the structure-breaker ammonium counterion and the structure-maker sodium counterion has been investigated. Depending on the nature of the electrolyte and its concentration, the results highlight the crucial effect of the network microstructure on the rheological results. Within the same microstructure, the strength of gelled networks has been found to be greater in the presence of the poorly hydrated ammonium counterions at any Ludox volume fraction. The obtained results were discussed with respect to recent contradictory trends reported in the literature concerning the behavior of silica suspensions.

Water-Dispersible FePt Nanoparticles Having ω-Mercapto-α-carboxylic Acid Ligands

ABSTRACTFePt nanoparticles, ∼ 2nm in diameter, were prepared by the polyol reduction of platinum(II) acetylacetonate and iron(III) acetylacetonate in the presence of oleyl amine and oleic acid surfactants. The particles were dispersed in hexane and the dispersion added to a solution of 11-mercaptoundecanoic acid in cyclohexanone. As the 11-mercaptoundecanoic acid ligands replaced the oleic acid ligands, the particles precipitated. The particles could be dispersed in basic water, made basic either with sodium hydroxide or ammonium hydroxide. X-ray photoelectron spectra showed a peak near 164 eV, sulfur (2p) confirming the presence of the thiol ligand. Similarly, the oleic acid ligands were replaced with either 3-mercaptopropionic acid or 16-mercaptohexadecanoic acid to give FePt particles that could be dispersed in water. Dispersions made with FePt nanoparticles having 11-mercaptoundeacnoic acid ligands and ammonium counter ions were dried on TEM grids to give highly ordered films consisting of close-packed arrays of FePt nanoparticles. When the counter ion was sodium, the particles tended to aggregate, instead of forming ordered arrays.

Effect of fluorinated ammonium counterions upon the reversibility in E–Z photoisomerization of azobenzene ion pair films

Alternate light illumination of ion-pairs of (3-perfluorooctanecarboxamido)propyltrimethylammonium azobenzene-4-carboxylate (FOAM–AzoB) at 340 and >440 nm was found to initiate a reversible photoisomerization between the E- and Z-azobenzene chromophores in multi-lamella films. This was in sharp contrast to the case of films involving the corresponding unfluorinated ion-pair, 3-(octanecarboxamidopropyl)trimethylammonium azobenzene-4-carboxylate (HOAM–AzoB) in which no substantial isomerization could take place. These photochemical characteristics are discussed here in terms of the free space surrounding the azobenenzene units of the ion-pairs molecularly packed within the films. Characterization studies using XRD and polarized spectroscopy revealed that the FOAM–AzoB stacked films consist of loosely packed interdigitated monolayers whereas HOAM–AzoB was found to form compactly packed bilayer stacked films.

Counterion and Temperature Effects on Aqueous Ionic Perfluoropolyether Micellar Solutions by Small-Angle Neutron Scattering

The effect of concentration and temperature on the microstructure of aqueous micelles of carboxylic perfluoropolyether surfactants, with two perfluoroisopropoxy units in the chain (n2) that is chlorine-terminated, are studied by SANS for the ammonium and potassium counterions. The SANS spectra have been analyzed by a two-shell model for the micellar form factor and a screened Coulombic plus steric repulsion potential for the structure factor in the frame of the mean spherical approximation of a multiion system reduced to an effective one component macroions system (OCM). At 28 °C, in the surfactant concentration range 0.05 to 0.12 M, the micelles display spherical shape with inner core radius of 15 Å for both counterions, and interfacial layer thickness of 4 Å. At higher concentration, both counterions provide ellipsoidal micelles, with axial ratio 2 and a limiting dimension of 13 Å. A sharp increase of temperature up to 80 °C enables the ammonium salt at 0.2 M to rearrange its ellipsoidal micelles into spherical ones, while the micelles of the potassium salt remain ellipsoidal. In all cases, the micellar size distribution is extremely narrow and the average aggregation numbers, as well as the surface charge, are found to slightly differ for the two counterions upon variation of concentration and temperature, driving ionization degrees globally spanning from 0.3 to 0.5. The interfacial hydration, the surface potential and the area per polar head at the micellar surface are discussed too.

Evaluation of counterions for electrospray ionization mass spectral analysis of a highly sulfated carbohydrate, sucrose octasulfate.

A systematic approach was used to evaluate the electrospray ionization mass spectral (ESI-MS) analysis of sucrose octasulfate (SOS), an important pharmaceutical agent. SOS represents a model for other suffated carbohydrates, such as heparin and glycosaminoglycan-derived oligosaccharides that also are highly sulfated and pose difficult analytical problems. A survey of ammonium counterions showed that 1 degree, 2 degrees, and 3 degrees ammonium salts of SOS gave substantial fragmentation as a result of sulfate loss. In contrast, quaternary ammonium and phosphonium salts gave excellent ESI spectra, particularly in the positive ion mode. This represents the first report of the ESI-MS analysis of sulfated carbohydrates in the positive ion mode.

The Preparation and Crystal Structure of Ammonium Bismuth(III) Thiosalicylate Dihydrate

The bismuth(III) complex of thiosalicylic acid (2-mercaptobenzoic acid; H2L), ammonium tris(2-mercaptobenzoato-O,S) bismuth(III) dihydrate, {(NH4)3[Bi(L)3]·2 H2O}, has been prepared and its crystal structure determined. The distorted octahedral tris-bidentate complex unit has pseudo-C3 symmetry with the facially related thiolate sulfur donors providing a regular facial cap to the octahedron (Bi–S 2.595, 2.596, 2.596(5) Å) with the Bi–O(carboxylate) distances less regular (2.715, 2.741, 2.785(15) Å). The network polymeric structure is stabilized by hydrogen-bonding associations through both the ammonium counter ions and the lattice water molecules.

Extremely Slow Counterion Dynamics in Xanthan Liquid Crystal through 23Na and 14N NMR

To describe the structure and dynamics in a lyotropic xanthan liquid crystal, we have done 23Na and 14N NMR experiments. The spectra are consistent with a powder average over randomly oriented liquid-crystalline domains. From 14N quadrupolar echo experiments it was concluded that the exchange among the several micron sized domains is slow with residence times in the millisecond range. Conventional spin-lock experiments (14N and 23Na) as well as spin-lock experiments filtered through the quadrupolar spin polarization order (23Na only) revealed the existence of an extremely low frequency, submegahertz dispersion in the spectral densities pertaining to both sodium and ammonium counterions. The corresponding correlation times are on the order of tens of microseconds and agree with a structural correlation length on the order of 500 nm. The latter correlation times reflect the rearrangement of counterions among polymer segments over the same spatial extent as the polymer persistence length.

Separation of plant membrane lipids by multiple solid-phase extraction

Plant membrane lipids were separated by multiple solid-phase extraction (SPE) in a single run. Elution was performed continuously through the modulated stationary phase employing only non-aqueous solvent systems. At the different stages of the glycerolipid separation the SPE manifold combined aminopropyl, aminopropyl/silica gel and silica gel/aminopropyl weak anion exchanger columns. The glycerolipid extract of pigment-containing plant tissues was cleared from the pigments onto the aminopropyl column. The aminopropyl column with the glycerolipid extract was then connected to a silica gel column from which monogalactosyldiacylglycerol, phosphatidylethanolamine, phosphatidylglycerol and digalactosyldiacylglycerol were eluted as individual fractions. The elution was performed under polarity, pH and temperature gradient conditions. To continue the separation, the aminopropyl column was discarded and the silica gel column containing the remaining glycerolipid extract was connected to an aminopropyl anion exchanger column. Individual fractions of sulfoquinovosyldiacylglycerol, phosphatidylcholine and phosphatidylinositol were now eluted. The separation process was supported by ammonium counter ions and by the polarity gradient of the elution systems used. The membrane lipids were isolated from pigment-containing (rice and maize leaves and rice leafy stems) and pigment-free (rice roots) tissues. The repeatability for a standard glycerolipid mixture was 2–6% ( n=7), and for rice leaf lipid extracts, 3–7% ( n=5). Glycerolipid recovery was 87–95%.

Self-association and self-assembly of molecular clips in water

Molecular clips functionalized with two sodium or ammonium benzoate groups self-assemble in water by means of a hydrophobically driven dimerization reaction. Depending on the counter ions, this self-assembly stops at the stage of the dimer (sodium) or continues to generate largenanometer-sized aggregates (ammonium). The molecules in the latteraggregates are proposed to be `glued' together by multiplehydrogen bonds between the ammonium counter ions and the benzoategroups of the clips.

Manganese citrate chemistry: syntheses, spectroscopic studies, and structural characterizations of novel mononuclear, water-soluble manganese citrate complexes.

The first two mononuclear manganese citrate complexes, (NH4)4[MnII(C6H5O7)2] (1) and (NH4)5[MnIII(C6H4O7)2].2H2O (2) were synthesized in aqueous solutions near physiological pH values. They were isolated in their pure crystalline forms and characterized by elemental analyses and spectroscopic techniques, including UV/visible, electron paramagnetic resonance, Fourier transformed infrared, and magnetic susceptibility measurements. Compound 1 crystallizes in the monoclinic space group P2(1)/c, with a = 8.777(1) A, b = 13.656(3) A, c = 9.162(2) A, beta = 113.62(2) degrees, V = 1006.2(6) A3, and Z = 2. Compound 2 crystallizes in the triclinic space group P1, with a = 9.606(3) A, b = 9.914(3) A, c = 7.247(3) A, alpha = 91.05(1) degrees, beta = 105.60(1) degrees, gamma = 119.16(1) degrees, V = 571.3(3) A3, and Z = 1. The X-ray crystal structures of 1 and 2 revealed that, in both cases, the manganese ion is six-coordinate and is bound by two citrate ligands in a distorted octahedral fashion. In the case of complex 1, the citrate ion binds to Mn2+ as a triply deprotonated ligand, retaining the central carbon hydroxyl hydrogen, whereas, in the case of compound 2, the citrate ligand coordinates to Mn3+ as a fully deprotonated entity. Compound 2 contains water molecules of crystallization in the unit cell which, through extensive hydrogen-bonding interactions, bestow considerable stability upon the Mn(3+)-citrate assembly. There are significant contributions to the stabilities of the assembled lattices in 1 and 2 arising from the ammonium counterions neutralizing the high anionic charges of the complexes. The EPR spectra attest to the presence of paramagnetic Mn2+ and Mn3+ species in the solid state. Corroborative evidence is obtained from the magnetic susceptibility measurements in the range 5-300 K. Complexes 1 and 2 present clear cases of mononuclear manganese citrate species relevant to manganese speciation in biological media and potentially related to the beneficial as well as toxic effects of manganese on humans.

Linear chains in polymeric dicyclohexylammonium tributyl(4-oxo-4H-pyran-2,6-dicarboxylato)stannate and methylphenylammonium tributyl(pyridine-2,6-dicarboxylato)stannate containing trigonal bipyramidal tin.

catena-Poly[dicyclohexylammonium [tributyltin-mu-(4-oxo-4H-pyran-2,6-dicarboxylato-O(2):O( 6))]], (C(12)H(24)N)[Sn(C(7)H(2)O(6))(C(4)H(9))(3)], consists of 4-oxo-4H-pyran-2,6-dicarboxylato groups that axially link adjacent tributyltin units into a linear polyanionic chain. The ammonium counter-ions surround the chain, and each cation forms a pair of hydrogen bonds to the double-bond carbonyl O atoms of the same dianionic group. The chain propagates in a zigzag manner along the c axis of the monoclinic cell. In catena-poly[methyl(phenyl)ammonium [tributyltin-mu-(pyridine-2,6-dicarboxylato-O(2):O(6))]], (C(7)H(10)N)[Sn(C(7)H(3)NO(4))(C(4)H(9))(3)], the pyridine-2, 6-dicarboxylato groups also link the tributyltin groups into a chain, but the hydrogen-bonded chain propagates linearly on the ac face of the monoclinic cell.

Cation Selectivity at Air/Anionic Surfactant Solution Interfaces

The selective binding of alkali metal and quaternary ammonium ions to anionic surfactant films at the air/solution interface has been investigated using the ion flotation technique. Surfactant anions studied were the dodecyl phosphate monoanion, the hexadecyl phosphate dianion, bis(2-ethylhexyl) phosphate, dodecanoate, and dodecyl sulfate. Alkali metal ions display only weak selectivity at adsorbed films of all surfactants studied. The binding strength increases in the order Na+ < K+ < Rb+ < Cs+, with the exception of films of dodecanoate, for which the ions have equal affinity, and the hexadecyl phosphate dianion, for which the selectivity sequence is Cs+ < Rb+ < K+ < Na+. By contrast, the binding of quaternary ammonium counterions to adsorbed films of anionic surfactants has a striking dependence on the surfactant headgroup. Results are interpreted using a model which includes solvation of the headgroups and competing counterions and is compared with competitive binding of phosphate, sulfate, and acetat...

Counterion effect on the phase behavior of perfluoropolyether carboxylates: micelles and liquid crystals in water

Perfluoropolyether carboxylates having sodium, potassium or ammonium counterions, and hydrophobic chains, mostly ClC 3F 6O terminated, have been investigated in aqueous binary systems, with the focus laid upon the counterion effect on the major self-assembly features. Micellization and liquid crystal formation have been detected via surface tension, conductivity, optical microscopy and NMR.

Liquid–liquid distribution of ion associates of hexabromotellurate (IV) with quaternary ammonium counter ions

The distribution behavior of ion associates (Q +) 2. TeBr 6 2− of TeBr 6 2− with quaternary ammonium cations (Q +) between aqueous phase and two organic phases (1,2-dichloroethane (DCE) and chloroform (CF)) was examined, and the extraction constants (log K ex) were determined. The extractability with long-chain alkyltrimethylammonium cations (group I) is greater than that with symmetrical tetraalkylammonium cations (group II) in the 1,2-dichloroethane extraction system and the difference in log K ex for two cations (one of each type) with the same number of carbon atoms was about 3 on the average. The contributions of a methylene group in the cations of groups I and II to log K ex were found to be 0.43∼1.10 and about 0.74 on the average. Among the ion associates examined, the extractability of the extracting solvent was in the DCE>CF; the difference in log K ex was about 5 on the average.

The Primary Electroviscous Effect in Polystyrene Latices of Small Particle Size Range Prepared with the Addition of Anionic Surfactant as Emulsifier. Effect of Increasing Concentrations of Quaternary Ammonium Counterions of Different Ionic Sizes and Stability Characteristic of the Latices and the Latex–Electrolyte Mixtures

Polystyrene latices were prepared by the emulsion polymerization method using hydrogen peroxide as an initiator and sodium dodecyl sulfate as the emulsifying agent. Latices of different particle sizes were prepared by the seeded growth technique. The particle size and its frequency distribution were determined by electron microscope. The viscosities and electrophoretic mobilities of the latex and latex:added electrolyte mixtures were measured in the presence of gradually increasing concentrations of quaternary ammonium counterions of different ionic sizes. The ζ-potentials were calculated by the computational method of Wiersema–Loeb– Overbeek (WLO); the surface charge densities σ were calculated by the method of Loeb–Wiersema–Overbeek (LWO). The primary electroviscous effects were calculated by using the Booth equation. The free energies of adsorption ΔḠadsof the counterions on the particle surface were calculated. The stability characteristic of the latices and latex–added electrolyte mixtures has been studied on the basis of the DLVO theory.

Aluminum Incorporation and Interfacial Structures in MCM-41 Mesoporous Molecular Sieves

Two-dimensional (2D) solid-state NMR spectroscopy has been used to identify interfacial species and establish framework locations of aluminum atoms incorporated in aluminosilicate MCM-41 mesophases and mesoporous solids. In these experiments, chemical shifts of protons in the material are correlated with the chemical shifts of nearby (ca. 1 nm) 13C, 27Al, or 29Si species via their respective heteronuclear dipole−dipole couplings. For aluminosilicate MCM-41 mesophases prepared at room temperature, 2D heteronuclear chemical shift correlation NMR spectra show that tetrahedrally coordinated aluminum and silicon species are in close spatial proximity to the trimethylammonium head groups of the cationic surfactant species in the as-synthesized materials and to ammonium cations following calcination and ion exchange. For MCM-41 materials synthesized under hydrothermal conditions, 2D heteronuclear correlation NMR measurements show that the appearance of six-coordinate aluminum species results from strongly bound water molecules coordinated to aluminum atoms that are also proximate to the surfactant species. The detection of couplings between 27Al or 29Si species and protons associated with the structure-directing surfactant molecules or exchangeable ammonium counterions establishes that a significant fraction of the aluminum atoms are present in the inorganic frameworks of these materials.

Liquid-liquid distribution of ion associates of tetrabromoindate(III) with quaternary ammonium counter ions

The solvent extraction of an ion associate of tetrabromoindate(III) ion, InBr − 4, with quaternary ammonium cations (Q +) has been studied. The extraction constant ( K ex) were determined for the ion associates of InBr − 4 with Q + between an aqueous phase and several organic phases (chloroform, chlorobenzene, benzene and toluene). A linear relationship was found between log K ex and the total number of carbon atoms in Q +; from the slope of the lines, the contribution of a methylene group to log K ex was calculated to be 0.91 for the chloroform extraction system and 0.52 for the other extraction systems. The extractability with alkyltrimethylammonium cations was larger than that with symmetrical tetraalkylammonium cations and the mean difference in log K ex for two cations (one of each type) with the same number of carbon atoms was about 1.3. From the extraction constant obtained, the extractability of InBr − 4 among metal-halogeno complex anions was in the order TlBr − 4 > BiI − 4 > AuBr − 4 > AuCl − 4 > TlCl − 4 > InBr − 4 > CuCl − 2.

Crown Ether Complexation in Electrical Double Layer of Anion-Exchange Resin

The complex formation of crown ethers with ammonium ions chemically bonded on the silica gel surface is affected by the nature of a counteranion and by the concentration of an anion in solution. Equations based on the Gouy−Chapman−Stern model for electrical double layers are derived to describe the adsorption isotherms of crown ethers and to elucidate effects of anion concentration on their chromatographic behaviors. Although the derived equations are not analytically solved, numerical solutions well describe experimental results. In the present case, the various types of interaction between the ammonium ion and counterions, i.e., the ion-pair (and triple ion) formation between the ammonium ion and a counteranion and the ion-pair formation between the ammonium ion complexed by a crown ether and a counteranion, are important and essential factors governing the overall adsorption of crown ethers. These constants are evaluated on the basis of the derived equation.

RNA hydration: three nanoseconds of multiple molecular dynamics simulations of the solvated tRNAAsp anticodon hairpin

The hydration of the tRNAAsp anticodon hairpin was investigated through the analysis of six 500 ps multiple molecular dynamics (MMD) trajectories generated by using the particle mesh Ewald method for the treatment of the long-range electrostatic interactions. Although similar in their dynamical characteristics, these six trajectories display different local hydration patterns reflecting the landscape of the “theoretical” conformational space being explored. The statistical view gained through the MMD strategy allowed us to characterize the hydration patterns around important RNA structural motifs such as a G-U base-pair, the anticodon U-turn, and two modified bases: pseudouridine and 1-methylguanine. The binding of ammonium counterions to the hairpin has also been investigated. No long-lived hydrogen bond between water and a 2′-hydroxyl has been observed. Water molecules with long-residence times are found bridging adjacent pro-Rp phosphate atoms. The conformation of the pseudouridine is stiffened by a water-mediated base-backbone interaction and the 1-methylguanine is additionally stabilized by long-lived hydration patterns. Such long-lived hydration patterns are essential to ensure the structural integrity of this hairpin motif. Consequently, our simulations confirm the conclusion reached from an analysis of X-ray crystal structures according to which water molecules form an integral part of nucleic acid structure. The fact that the same conclusion is reached from a static and a dynamic point of view suggests that RNA and water together constitute the biologically relevant functional entity.