Organic Counterions Research Articles

Removal ofN-butanol from aqueous solutions by ion-exchange membranes containing organic counterions

The pervaporation of aqueous butanol solutions was investigated using thin-film composite membranes composed of a poly(vinylidene fluoride) substrate coated with a sulfonated poly(2,6-dimethyl-1,4-phenelene oxide) polymer. The polymer was ion-exchanged with quaternary ammonium cations having aliphatic substituents of various chain lengths. The pervaporation of aqueous n-butanol solutions using these membranes gave a permeate more concentrated in n-butanol; therefore, they were alcohol-selective. The separation factor increased and the permeate flux decreased as the chain lengths of the aliphatic substituents were increased. Hence, the mass-transport properties of such membranes can be controlled or altered to yield some desired permselectivity by the introduction of a proper counterion. It was observed that the n-butanol flux was small relative to the total flux and, therefore, the water flux dominated the total permeate flux. The degree of swelling of the membranes and its effect on membrane performance was investigated as well. As the n-butanol content was increased, the swelling of the membranes increased greatly. High membrane swelling caused a reduction in the separation factor. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 47–58, 1999

Ion-pair partition of quarternary ammonium drugs: the influence of counter ions of different lipophilicity, size, and flexibility.

The ion-pair partition of quaternary ammonium (QA) pharmacons with organic counter ions of different lipophilicity, size, shape and flexibility was studied to elucidate relationships between ion-pair formation and chemical structure. The apparent partition coefficient (P') of 4 QAs was measured in octanol/pH 7.4 phosphate buffer system by the shake-flask method as a function of molar excess of ten counter ions (Y), namely: mesylate (MES), acetate (AC), pyruvate (PYRU), nicotinate (NIC), hydrogenfumarate (HFUM), hydrogenmaleate (HMAL), p-toluenesulfonate (PTS), caproate (CPR), deoxycholate (DOC) and prostaglandin E1 anion (PGE1). Based on 118 of highly precise logP' values (SD< 0.05), the intrinsic lipophilicity (without external counter ions) and the ion-pair partition of QAs (with different counter ions) were characterized. Linear correlation was found between the logP' of ion-pairs and the size of the counter ions described by the solvent accessible surface area (SASA). The lipophilicity increasing effect of the counter ions were quantified and the following order was established: DOC approximate to PGE1 >> CPR approximate to PTS >> NIC approximate to HMAL >> PYRU approximate to AC approximate to MES approximate to HFUM. Analyzing the lipophilicity/molar ratio (QA:Y) profile, the differences in the ion-pair formation were shown and attributed to the differences in the flexibility/rigidity and size both of QA and Y. Since the largest (in average, 300 X) lipophilicity enhancement was found by the influence of DOC and PGE1 and considerable (on average 40 X) increase was observed by CPR and PTS, it was concluded that bile acids and prostaglandin anions may play a significant role in the ion-pair transport of quaternary ammonium drugs and caproic acid and p-toluenesulfonic acid may be useful salt forming agents to improve the pharmacokinetics of hydrophilic drugs.

Anion interactions with (polypyridyl)ruthenium complexes, and their importance in the cation-exchange chromatographic separation of stereoisomers of dinuclear species †

The separation of the ligand-bridged dinuclear complex cation [{(Me2bpy)2Ru}2(µ-bpm)]4+ (Me2bpy = 4,4′-dimethyl-2,2′-bipyridine; bpm = 2,2′-bipyrimidine) into its two diastereoisomeric forms, meso and rac, by cation-exchange chromatography has been investigated, using a wide range of organic counter anions (aromatic and aliphatic) in the aqueous eluents. 1H NMR titration studies not only confirm association between the complex cation and the counter anions in solution, but also reveal differential associations with the two diastereoisomers of [{(Me2bpy)2Ru}2(µ-bpm)]4+. Analogous interactions are also evident with mononuclear species, [Ru(pp)3]2+, where pp is a bidentate ligand such as Me2bpy, 1,10-phenanthroline (phen) or 2,2′-bipyridine (bpy): from 1H NMR titration studies, the first association with a number of organic anions has a stability constant in the order of 100 dm3 mol–1 in aqueous solution. This association also affects the emission from the MLCT excited state of the monomers, with up to a 10% enhancement in the luminescence.

Synthesis and characterization of 3-methoxydiphenylamine-4-diazonium salt and its diazoresin

3-Methoxydiphenylamine-4-diazonium salt (MDDS) and its diazoresin were synthesized. The photo- and thermal decomposition of salt and the resins were investigated. The results show that MDDS exhibits excellent thermostability as well as high photosensitivity. A series of diazoresins with different organic counteranions, which dissolve in common solvents and usually were chosen to manufacture the negative presensitized plate, were also synthesized The kinetics of the photo- and thermal decomposition of MDDS in ethanol is reported. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1975–1982, 1998

Linear and non linear rheology of a wormlike micellar system in presence of sodium tosylate

In this experimental work, we investigate the influence of an organic counterion, sodium tosylate, on the rheological properties of an aqueous solution of CTAB at the concentration of 0.05M. With this system we can clearly see shear thickening for small salt concentrations C s and only shear thinning behavior at higher C s characterized by a linear evolution of η=f(γ) in a log-log representation. In these evolutions it is only in a very small domain of concentrations of the salt (near C s =0.035M) that we can observe a nearly constant plateau of the shear stress against shear rate. The values of σ0 (characterizing the stress plateau), G 0 (the plateau modulus) and τR (the relaxation time) obtained by dynamical rheological measurements, allow to compare experimental results obtained to predicted values of the theory of Cates corresponding to the occurrence of shear induced banding structures.

Occurrence of shear thickening in aqueous micellar solutions of CTAB with some added organic counterions

In this experimental work we carefully investigate the influence of some organic counterions (having similarities): sodium salicylate (NaSal), sodium tosylate (NaTos) and sodium benzoate (NaBz) on the rheological properties of two aqueous solutions (0.1 and 0.05 M) of cetyltrimethylammonium bromide (CTAB). Here we are particularly interested in the occurrence of the shear thickening effect corresponding to shear induced structures (SIS). All the rheological measurements presented in this work are realized with the same geometrical device (plan-cone) with controlled imposed shear stress. Conditions of occurrence and evolutions of the characteristics of the obtained shear thickening are given.

Synthesis of organic polymer gels in microemulsions and lyotropic mesophases

AbstractThe synthesis of fine polymer latices and ordered polymer gels by polymerization in microemulsions and lyotropic mesophases is described. For this purpose, a new class of surfactants based on the coupling of cetyl trimethylammonium groups with organic counterions was developed. Interface activity, critical micelle concentration as well as lyotropic liquid crystalline phase behavior of these surfactants were investigated, and very high efficiency and high phase stability was found.Systems optimized such do not only allow the synthesis of very small polymer latices (Rh≥7.5 nm) in reverse systems, but also the generation of gels with lamellar order. Due to the occurrence of phase transitions during polymerization, direct templating of the original lyotropic phase by the polymer gel is prevented, but the final polymer gels are highly ordered and reflect some of the characteristics of the surfactant template.

Stability study of conducting polypyrrole films and polyvinylchloride-polypyrrole composites doped with different counterions

Electrically conducting poiypyrrole and poiyvinylchloride-polypyrrole (PVC-PPY) composite films doped with different counterions were aged in ambient air at room temperature. Polypyrrole and PVC-PPY composite films doped with the organic counterion TsO − (paratoluenesulfonate) show better stability than those doped with inorganic counterions as ClO 4 −, BF 4 −, NO 3 −. We found that the normalized conductivity for air ageing at room temperature for 110 days is between 25 and 30% initial conductivity for pure polypyrrole films doped with C1O 4 − and 10% for BF 4 −-doped polypyrrole. For PVC-PPY composites doped with ClO 4 − the normalized conductivity for air ageing at room temperature is between 15 and 35% initial conductivity. For pure polypyrrole and PVC-PPY composites films doped with TsO −, the normalized conductivity for air ageing for 55 days is between 97 and 128% initial conductivity. It was observed that the conductivity of pure polypyrrole and PVC-PPY composite films doped with inorganic ions decreased drastically in the first days, while that of the films doped with organic ion (TsO −) increased. This different behaviour is attributed to the nature of the doping ions.

Kinetic and Mechanistic Aspects of Photocatalysis by Polyoxotungstates: A Laser Flash Photolysis, Pulse Radiolysis, and Continuous Photolysis Study

Illumination of polyoxotungstates generates a short-lived excited state which decays to form the reactive intermediate wO that is responsible for subsequent transformation of organic substrates. It is shown by laser flash photolysis that wO is formed with a quantum yield of 0.6 and that it survives for ca. 55 ns in deoxygenated acetonitrile. In the presence of a substrate such as propan-2-ol wO reacts to produce the one-electron-reduced species, as characterized by transient spectroscopy and as confirmed by pulse radiolysis. Oxygen intercepts the initially-formed radicals so that this methodology may be used to follow the course of the reaction. Under continuous photolysis, propan-2-ol is converted into acetone and hydrogen peroxide but with adamantane as substrate the corresponding hydroperoxides are formed. Quantum yields of oxygen consumption have been measured for a variety of other substrates and range from ca. 0.05 for pure acetonitrile to ca. 0.5 for propan-2-ol. In the absence of other substrates, reaction of organic counterions may be observed. All these observations are consistent with hydrogen-atom abstraction from an organic substrate by wO, followed by rapid deprotonation of •wOH and/or trapping by O2. A concise reaction scheme involving coupling between oxyradicals is proposed that adequately describes the overall chemistry.

Determination of organic acid drug counter-ions by capillary electrophoresis

A capillary electrophoresis method is described for the novel application of quantifying levels of the simple organic acid counter-ions of a variety of basic drugs. These counter-ions are organic acids such as succinic and maleic. The method uses indirect UV detection and an electroosmotic flow modifier. Acceptable precision and detector linearity were obtained using internal standards. Method validation was completed and acceptable data was generated. The method is now in routine use for this type of testing.

Imaging of Dihexadecylphosphate Vesicles by AFM and Counterion Effect on Their Size and Stability

The effect of counterions on vesicles prepared from dihexadecylphosphate is investigated. Alkali metal ions as well as an organic guanidinium counterion have been employed and it has been found that the size of the vesicles is dependent on the size of the counterions. Specifically, the bigger the counterion the smaller are the vesicles that are formed. The vesicles exhibited very good stability which was not significantly affected by the nature of the counterion. It is interesting to note that a subtle chemical modification, viz., in the nature of the counterion, can have a significant bearing on the size and morphology of the vesicles. The implications in self-assembly occurring in biological systems are therefore easy to appreciate.

Biphasic polystyrene ionomers neutralized by bifunctional organic counterions

AbstractThe evidence for biphasic morphology in lightly sulfonated polystyrene (PS‐SSA) ionomers neutralized by bifunctional organic cations (namely, 1,6‐hexanediamine or HDA) is established by comparing their dynamic mechanical behavior, as a function of ion content and degree of neutralization, with that for metal‐neutralized biphasic ionomers. The trends as a function of ion content regarding the transition temperatures and intensities of the HDA‐neutralized ionomers parallel what is observed for metal‐neutralized ionomers, in particular polystyrene‐based ones. A small‐angle X‐ray scattering peak, identified as an “ionomer peak”, is observed in the PS‐SSA‐HDA ionomer of the highest ion content studied. Furthermore, it was observed that partial neutralization affects the cluster phase more strongly than the matrix phase. This can be explained by the contribution of the acid groups to the matrix Tg, and their ability, when present in large amounts, to affect the ionic interaction strength or facilitate ion hopping, which influences primarily the cluster Tg.

Laser flash photolysis study of the mechanism of photooxidation ofalkanes catalysed by decatungstate anion

Generated during light excitation, the O(2p) → W(5d) ligand-to-metal charge transfer (LMCT) excited state of decatungstate anion (W10O324-) relaxes for t < 30 ps to a transient X which persists for 5 ns. In the nanosecond time domain, it reacts with all components of the photocatalytic system (substrate, organic counter-ion and solvent) to give a one-electron reduced decatungstate species HW10O324- and an organic radical R˙. The latter is quenched by dioxygen at a near diffusion-controlled rate, forming a peroxyl radical ROO˙. In the solvent cage, the peroxyl radical ROO˙ reoxidizes HW10O324- to give the hydroperoxide ROOH and W10O324-, thus closing the catalytic cycle. The catalyst reoxidation is the rate-limiting step of the alkane oxidation.

Microemulsion polymerization: New surfactant systems by counterion variation

Novel surfactant systems that allow the formation of polymerizable microemulsions are required for the synthesis of ultrafine polymer latices. The work reported here extends the ability to formulate new microemulsion “recipes” by means of a new approach: the geometry and polarity of a given surfactant can be adjusted by electrostatic coupling with an appropriate organic counterion, e.g., the generation of a very bulky hydrophobic head group. It is demonstrated that counterion variation of classical surfactants leads to a significant improvement of classical microemulsions.

Competition between Monovalent and Divalent Counterions in Surfactant Systems

Competition between mono- and divalent ions in the association of counterions to the headgroups of amphiphiles was studied in one surfactant system with organic counterions (piperidine+/piperazine2+octanesulfonate) and one with inorganic counterions (Na+/Ca2+octyl sulfate). By conductivity and13C NMR chemical shift measurements the critical micelle concentration (CMC) was found to decrease drastically when small amounts of divalent counterions were present in the system. Self-diffusion coefficients of surfactant ions and organic counterions were measured in the micellar phase by the Fourier transform pulsed-gradient spin-echo (FT-PGSE) NMR method. The degree of counterion binding in the micellar system with piperidine+/piperazine2+counterions was obtained from FT-PGSE NMR measurements. It was observed that the divalent counterions were more strongly bound than the monovalent counterions. The experimental results were compared with theoretical Poisson–Boltzmann calculations. The cell model was used to study the electrostatic effects. Good agreement between electrostatic theory and experiment was observed; however, an attractive force exists between the monovalent piperidine counterions and the micelle, probably because of hydrophobic interactions.

Calcium uptake and release modulated by counter‐ion conductances in the sarcoplasmic reticulum of skeletal muscle

The sarcoplasmic reticulum (SR) plays the central role in regulating the free myoplasmic Ca2+ level for the contractile activation of skeletal muscle. The initial stages of the voltage-controlled Ca2+ release mechanism are known in molecular detail. However, there is still very little known about the later stages of Ca2+ uptake and total Ca2+ turnover in the contraction-relaxation cycle under normal physiological conditions or under conditions influenced by fatigue or disease. Ca2+ uptake and release are both accompanied by "counter-ion' movements across the SR membrane which prevent or reduce the generation of SR membrane potentials and balance for electroneutrality in the SR lumen. The SR membrane is permeable for the cations K+, Na+, H+ and Mg2+ and the anion Cl-. Using electron-probe X-ray microanalysis. It has been shown that during tetanic stimulation the Ca2+ release was mainly balanced by uptake of K+ and Mg2+ leaving a charge deficit that was assumed to be neutralized via H+ ion or organic counter-ion movement. The low time resolution of electron-probe X-ray microanalysis leaves the possibility of other transient concentration changes in the SR, e.g. for Cl- ions. Possible physiological roles of the SR counter-ion conductances can be tested using skinned muscle fibre preparations with intact sarcoplasmic reticulum and removed or chemically permeabilized outer sarcolemma. In skinned fibres, the SR K+ conductance can be effectively reduced with SR K+ channel blockers such as 4-aminopyridine, tetraethylammonium and decamethonium. Interestingly, these blockers increase Ca2+ loading as well as Ca2+ release, whereas other less specific blockers, such as 1.10-bis-quanidino-n-decane, seem to reduce Ca2+ release, possibly also via blocking Ca2+ release channels. Thus, it seems very important also to test the effects of counter-currents carried by K+, Mg2+, H+ or Cl- ions on intact and voltage-clamped single-fibre preparations.

Effect of Organic Additives or Counterions on the Supramolecular Assembly Structures Constructed by Amphiphiles. A Small-Angle Neutron Scattering Investigation

Small-angle neutron scattering (SANS) was measured for aqueous solutions of amphiphiles with organic additives or counterions such as 2-indenecarboxylic acid, cinnamic acid, and salicylic acid or their ions. The effect of organic species on the supramolecular assembly structure was investigated. Equimolar mixtures of dodecyldimethylamine oxides and aromatic carboxylic acids constructed vesicles. The vesicular bilayer thicknesses were 29−30 A, independent of organic species. On the other hand, hexadecyltrimethylammoniums with aromatic carboxylate counterions always formed rodlike micelles with axial ratios 8−10. Aqueous solutions of tetradecyltrimethylammonium salicylate displayed a strong interparticle interference effect on SANS profiles at concentrations above 0.8 × 10-2 g cm-3, although such an effect disappeared with addition of more than 5/mM sodium salicylate.

Aerobic photocatalysed oxidation of alkanes in the presence of decatungstates: products and effects of solvent and counter-ion of the catalyst

The aerobic photocatalysed oxidation of alkanes in the presence of decatungstates Q4W10O32(Q = Na, Me4N, Pr4N, Bu4N, Hex4N) leads to hydroperoxides as primary products. Nitrile solvents and organic counter-ions of the catalyst compete in this photooxidation with alkane substrate. The influence of this competition on quantum yield, rate and selectivity for the oxidation of adamantane is quantitatively evaluated. A catalytic cycle, describing the formation of primary and secondary oxidation products, is proposed.

Carrier-mediated, thermal energy-coupled, non-isothermal membrane transport. II. A gaseous system

The non-isothermal facilitated transport of CO 2 through a sulfonic cation exchange membrane (Permion 5010) containing organic diamine counter-ion carrier (EDA) has been studied experimentally and confronted with a theoretical model based on the Nernst-Planck flux equation, with good agreement between the two approaches. Discussions also took into account measurements at different temperatures of isothermal passive and facilitated transports, membrane conductivity and corresponding Arrhenius plots, the stability constant of the permeant-carrier complex determined with a new technique and of heat of reaction (Δ H) obtained from Van't Hoff plots. Steady state fluxes of carbon dioxide were measured at different temperature gradients (Δ T) and partial pressures in mixtures with N 2. A permeability of 7.4×10 −7 mmol/cm/s/atm was obtained for a Δ T of 8 K around 295 K at a steady state flux of 4 × 10 −7 mmol/cm/s for 1% CO 2 in the mixture. Facilitation factors as well as thermal gradient amplification factors are presented. It is concluded that the effect of the thermal gradient on the flux is mediated by the modification of the concentration gradient inside the membrane. Stimulation or hindering are dependent on the sign of Δ H and of the orientation of Δ T relative to the gradient of partial pressure.

Main chain liquid crystalline ionic polymers with thermotropic and lyotropic mesophases

AbstractAn ionogenic main chain liquid crystalline polymer was synthesized. In contrast to previous studies the charged sites were incorporated into the flexible spacer and not into the mesogenic group. This was done through quaternization of 1,2‐bis(4‐pyridylethane) with a biphenyl‐4,4′‐nonanoxytoluenesulphonate. The polymer displayed thermotropic and lyotropic me‐sophases. The thermotropic mesophase was smectic. Organic counterions such as meth‐ylsulfonates and p‐toluenesulfonates were found to be favorable to the development of mesophases, due to the increased solubility and lower isotropisation temperatures, when compared to bromide counterion containing polymers. Easy supercooling, dependence on thermal history, and the development of batonnet textures on cooling from the melt were also observed. © 1995 John Wiley &amp; Sons, Inc.