Nature Of Counterion Research Articles

Effect of counterion on the mesomorphic behavior and optical properties of columnar pyridinium ionic liquid crystals derived from 4-hydroxypyridine

A series of 3,4,5-tridodecyloxybenzyl pyridinium salts derived from 4-hydroxypyridine has been designed and prepared. The liquid crystalline properties of these compounds were investigated by polarized optical microscopy, differential scanning calorimetry and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis. The N-3,4,5-tridodecyloxybenzyl-4-pyridone intermediate shows a monotropic columnar hexagonal mesophase ranging from 56°C down to room temperature while the corresponding bromide dodecyl O-alkylated pyridinium salt shows one enantiotropic columnar mesophase and one additional monotropic columnar phase at lower temperatures. Replacing bromide ion (Br−) with other counterions (NO3-,BF4- and PF6-) resulted in mesophase suppression. These luminescent pyridinium salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. Photoluminescent properties of the pyridinium salts do not depend significantly on the nature of counterion employed.

Thermoanalytical study of linkage isomerism in coordination compounds. Part 5: A DSC and DFT study on the linkage isomerization of the dinitrito and dinitro isomers of cis-tetraamminecobalt(III) complexes

The solid-state linkage isomerization of cis-[Co(NH3)4(NO2)2]X (dinitro) and cis-[Co(NH3)4(ONO)2]X (dinitrito) (X=Cl−, NO3−, ClO4−) was investigated by differential scanning calorimetry (DSC). All three salts of the dinitrito isomer show an exothermic peak associated with linkage isomerization, while only the chloride salt of the dinitro isomer exhibits an endothermic DSC peak. The results imply that the chloride salts of both isomers are metastable at ambient temperature and can convert to a stable equilibrium mixture of both isomers at elevated temperatures, but the NO3− and ClO4− salts of the dinitro isomer are in stable state even at high temperatures. The DSC peak temperature and the enthalpy changes of the dinitrito to dinitro isomerization depend upon the nature of counterion as follows: NO3−<Cl−<ClO4−. The stepwise enthalpy changes of the linkage isomerization of the dinitro (only for the Cl− salt) and dinitrito complexes were obtained through mathematical resolution of the observed peak into two peaks, assuming a two-stage reversible isomerization for the Cl− salt and a similar irreversible process for the NO3− and ClO4− salts. The nature of the counterion has little effect on the kinetics of the linkage isomerization. The electronic structures and transition states of the linkage isomers were optimized by DFT and their electronic spectra calculated by TDDFT/PCM methods.

Effects of selected operational parameters on efficacy and selectivity of electromembrane extraction. Chlorophenols as model analytes.

Effects of organic solvent type, pH value, and composition of donor/acceptor solution on the efficacy of electromembrane extraction (EME) were examined. For the first time, a comprehensive quantitative study, based also on measurements of electric charge passed through the EME system, was carried out, which demonstrates that apart from the pH value, also the nature of counter-ions in donor and acceptor solution plays a significant role in the electrically induced transfer of charged analytes across supported liquid membranes (SLMs). The EME transfer of model analytes correlated well with electrophoretic mobilities of inorganic cations, which were added to acceptor solutions during their alkalization with alkali metal hydroxides, and were highest for counter-cations with highest mobilities. Up to a 53-fold improvement of extraction efficiency was achieved for EMEs using optimized composition of donor (alkalized with KOH to pH 7) and acceptor (10 mM CsOH, pH 12) solutions. Six chlorophenols (CPs) were selected as model analytes due to the wide range of pH values that are required for their ionization and due to their high environmental relevance; quantitative measurements were carried out by CE with UV detection. Extraction recoveries of the six CPs ranged between 14 and 25% for 5 min EMEs at 150 V and 750 rpm across SLMs impregnated with 1-ethyl-2-nitrobenzene. Calibration curves were strictly linear (r(2) ≥ 0.999) in 0.01-10 μg/mL range, repeatability values of peak areas were between 0.7 and 5.6% and LODs for standard solutions and environmental samples were better than 5 ng/mL.

Microstructure of colloidal dispersions in the ionic liquid ethylammonium nitrate: influence of the nature of the nanoparticles' counterion

In order to better identify the key parameters governing colloidal stability in ionic liquids we probe the influence of the nature of the initial counterion of citrate-coated maghemite nanoparticles (NP), with Na+, Li+ and ethylammonium (EA+) on their dispersions in ethylammonium nitrate (EAN). Chemical analysis shows that sodium and lithium counterions remain at the nanoparticle surface after their transfer from water to EAN, despite their low concentration compared with EA+. Macroscopically, all suspensions are stable over the range of volume fractions ΦNP tested (∼ 1% to 8%). A microstructural study coupling small angle scattering and magneto-optic birefringence measurements shows that nanoparticles are perfectly dispersed with sodium counterions and interact through weak repulsions. Conversely, small clusters of a few nanoparticles are formed with lithium counterions, with the aggregation number increasing with ΦNP. However, such clusters are fragile; evidence that the attractions responsible for aggregation are of weak amplitude. Suspensions with EA+ counterions show an intermediate behaviour. Our results demonstrate the determining role of initial counterions of the nanoparticles on the microstructure of colloidal dispersions in ionic liquids and therefore, the essential role of the interfacial zone between the solid and the liquid.

Removal of EDDS and copper from waters by TiO2 photocatalysis under simulated UV–solar conditions

Abstract The TiO 2 photocatalytic oxidation of the N , N ′-ethylenediamine-disuccinic acid and Cu(II) ions photoreduction were investigated in acidic solutions. The experimental results indicated a conversion of 100% for both EEDS and Cu(II) species whereas the mineralization degree was quite small (24%). The influence of several experimental variables, like purging gas, counter ion nature, pH, TiO 2 type, photocatalyst load, initial concentration of cupric ions, radiation source (natural or artificial), was investigated. For almost equimolar feed ratios of reactants, EDDS was not totally removed whereas Cu(II) species were completely reduced. An analysis of the data collected indicated a Cu(II)/EDDS molar consumption ratio close to two. The presence of oxygen decreased the photoreduction process of Cu(II) species, whereas the initial concentration of Cu(II) ions and the counter ion (excepted for the chloride ions) did not affect the photocatalytic process. Ecotoxicity tests ( Pseudokirchneriella subcapitata and Lemna minor ) on treated samples indicated a marked decrease of the ecotoxicity for very prolonged reaction times.

Electrochemical characterization of the CMX cation exchange membrane in buffered solutions: Effect on concentration polarization and counterions transport properties

In the present work, the combination of both properties of buffer and weak electrolyte solutions and their effects on concentration polarization phenomena, particularly on the limiting current density and the ohmic region resistance (Rohm) is investigated. Acetic acid (pKa=4.75) plays the role of weak electrolyte while at the same time buffers the pH of the system with acetate co-ions. In order to better understand the effect of the counterion nature and the pKa of the buffer acid/base pair, different electrolyte solutions are studied. The current–voltage curve characteristic values such as the limiting current density, the ohmic resistance (Rohm) and the polarization plateau resistance (Rpol) are determined and discussed according to the classical concentration polarization theory. However, it remains insufficient to explain the most important result obtained: The addition of acetic acid increases linearly the limiting current density while the ohmic resistance remains constant whatever the acetic acid concentration is.

Tuning the colloidal stability in ionic liquids by controlling the nanoparticles/liquid interface.

To shed light on the origin of colloidal stability in ionic liquids,we focus on a model colloidal system (maghemite nanoparticles) in which surface charge and counterion nature can be controlled at will. We thus evidence the crucial role of interfacial features on dispersion quality in a standard ionic liquid, ethylammonium nitrate.

Biaxial Q-shearing of 27Al 3QMAS NMR spectra: Insight into the structural disorder of framework aluminosilicates

In this contribution, we present the application potentiality of biaxial Q-shearing of 27Al 3QMAS NMR spectra in the analysis of structural defects of aluminium units in aluminosilicates. This study demonstrates that the combination of various shearing transformations of the recorded 27Al 3QMAS NMR spectra enables an understanding of the broadening processes of the correlation signals of disordered framework aluminosilicates, for which a wide distribution of 27Al MAS NMR chemical shifts and quadrupolar parameters (i.e., second-order quadrupolar splitting and quadrupole-induced chemical shifts) can be expected. By combining the suitably selected shearing transformation procedures, the mechanisms of the formation of local defects in aluminosilicate frameworks, including Al/Si substitution effects in the next-nearest neighbouring T-sites, variations in bond angles, and/or variations in the physicochemical nature of charge-balancing counter-ions, can be identified. The proposed procedure has been extensively tested on a range of model aluminosilicate materials (kyanite, γ-alumina, metakaolin, analcime, chabazite, natrolite, phillipsite, mordenite, zeolite A, and zeolite Y).

Oxidation Products of Doubly Trimethylene-Bridged Tetrabenzylp-Phenylenediamine Paracyclophane

We report synthesis and investigation of doubly trimethylene-bridged tetrabenzyl-p-phenylenediamine 1(Bz) in its singly and doubly charged redox states. The singly oxidized monoradical cation, which is a mixed-valence (MV) system with directly interacting charge-bearing units, shows broad and solvent-sensitive intervalence bands consistent with class II compounds according to the Robin-Day classification. The doubly oxidized diradical dication of 1(Bz) exists in the spin-paired singlet state with thermally accessible triplet state. It has similar conformations as the other dimeric p-phenylenediamines, such as derivatives 1(Me) and 1(Et), in both the solid-state and solution phases. The successful isolation of the single-crystalline 1(Bz)(2+) diradical dications with two different in nature counteranions, relatively highly coordinating SbF6(-) and weakly coordinating carborane [undecamethylcarborane HCB11Me11(-) (CB(-))], reveals the distinct effect of the nature of counterions on the structural features of diradical dication. Cyclic voltammetry measurements of 1(Bz) in dichloromethane reveal separation of the first and second oxidation potential by 0.12 V (2.8 kcal/mol), indicating relatively stable mixed-valence state in the dichloromethane, whereas in the acetonitrile both the first and second oxidation potentials overlap into one unresolved redox peak with minimal separation.

Efficient Near-UV Emitters Based on Cationic Bis-Pincer Iridium(III) Carbene Complexes

We report on the photophysical studies of two cationic near-UV emitters based on bis-pincer Ir(III) carbene complexes: [Ir(nBu)(C(NHC)(Me)CC(NHC))2]X, where Ir(nBu)(C(NHC)(Me)CC(NHC)) is (4,6-dimethyl-1,3-phenylene-κC(2))bis(1-butylimidazol-2-ylidene) and X = I(-) or PF6(-)). The compounds are highly emitting in deaerated CH3CN solution with emission maxima at 384 and 406 nm, and photoluminescence quantum yields of 0.41 and 0.38, for [Ir(nBu)(C(NHC)(Me)CC(NHC))2]I and Ir(nBu)(C(NHC)(Me)CC(NHC))2]PF6, respectively. In order to gain deeper understandings into their structural and electronic features, as well as to ascertain the nature of the excited states involved into the electronic absorption processes, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been performed on the ground and excited states of the closely related complex [Ir(Me)(C(NHC)(Me)CC(NHC))2](+). In the solid state, an emission at low energy is observed (λ(max) = 500 nm) for both complexes. However, the intensity of the emission at high energy versus the intensity of the new emission at low energy is dependent on the nature of counterions. The origin of this emission is not completely clear, but the experimental data point to the formation of trapping sites induced by aggregation processes involving the interaction between the cationic emitter and the counterion.

Electrokinetic characterization of superparamagnetic nanoparticle–aptamer conjugates: design of new highly specific probes for miniaturized molecular diagnostics

With the view of designing new nanoparticle (NP)-aptamer conjugates and proving their suitability as biorecognition tools for miniaturized molecular diagnostics, new maghemite-silica core-shell NP-aptamer conjugates were characterized for the first time in terms of grafting rate and colloidal stability under electrophoretic conditions using capillary electrophoresis. After the grafting rate (on the order of six to 50) of the lysozyme-binding aptamer had been estimated, the electrophoretic stability and peak dispersion of the resulting oligonucleotide-NP conjugates were estimated so as to determine the optimal separation conditions in terms of buffer pH, ionic strength and nature, as well as temperature and electric field strength. The effective surface charge density of the NPs was close to zero for pH lower than 5, which led to some aggregation. The NPs were stable in the pH range from 5 to 9, and an increase in electrophoretic mobility was evidenced with increasing pH. Colloidal stability was preserved at physiological pH for both non-grafted NPs and grafted NPs in the 10-100 mM ionic strength range and in the 15-60 °C temperature range. A strong influence of the nature of the buffer counterion on NP electrophoretic mobility and peak dispersion was evidenced, thus indicating some interactions between buffer components and NP-aptamer conjugates. Whereas an electric field effect (50-900 V cm(-1)) on NP electrophoretic mobility was evidenced, probably linked to counterion dissociation, temperature seems to have an appreciable effect on the zeta potential and aptamer configuration as well. This information is crucial for estimating the potentialities of such biorecognition tools in electrophoretic systems.

Nickel complexes with cyclic ligands containing P and N atoms as coordination sites: novel biomimetic catalysts for hydrogen oxidation

Nickel complexes with new cyclic ligands containing phosphorus and nitrogen atoms as coordination sites are novel efficient catalysts for hydrogen oxidation. A systematic study of their electrochemical properties made it possible to classify the nickel systems in question into four groups according to the sequence of electron transfer processes in the reduction (MII-MI-M0) and to the nature of solvents and counterions. Regularities of catalytic transformations involving nickel complexes with P,N-cyclic ligands in the H2 oxidation reaction in the coordination sphere of the catalyst and a correlation between the structure of the complex and its redox properties were established. The most efficient catalysts contain phenyl and 2-pyridyl substituents at the phosphorus atom and benzyl or 2-pyridyl substituents at the nitrogen atom.

Association and colloid-chemical properties of humic acids in aqueous solutions

Colloid-chemical properties of humic acids in aqueous solutions have been studied as functions of their concentration, medium pH, and counterion nature. It has been established that, at pH 4, the state of humic acids depends on the solution concentration. At low concentrations, they exist as individual molecules; as the concentration is increased, they associate to form supramolecular structures at 5 mg/dm3 and micelles at 8 g/dm3. An increase in the counterion charge has been shown to decrease the critical concentration of supramolecular structuring. Supramolecular structures have increased adsorbability on clay minerals and promote the manifestation of solubilizing properties of humic acids in solutions even at a concentration of 5 mg/dm3, which is three orders of magnitude lower than the critical micelle concentration (8 g/dm3).

A critical study on efficiency of different materials for fluoride removal from aqueous media

Fluoride is a persistent and non-biodegradable pollutant that accumulates in soil, plants, wildlife and in human beings. Therefore, knowledge of its removal, using best technique with optimum efficiency is needed. The present survey highlights on efficacy of different materials for the removal of fluoride from water. The most important results of extensive studies on various key factors (pH, agitation time, initial fluoride concentration, temperature, particle size, surface area, presence and nature of counter ions and solvent dose) fluctuate fluoride removal capacity of materials are reviewed.

Noise spectra of K+ and NH4+ ions at over-limiting current in an electrochemical system with a cation exchange membrane

The present work investigates the effect of the counter ion nature on the noise of the over-limiting current (Iov). Moreover, the electrochemical methods, current voltage curve (I–V) and the chronopotentiometry (V–t) measurements are applied. The over-limiting current is always accompanied by a neat electrical noise. It is a well accepted experimental phenomenon. The study of this noise may contribute to a better understanding of the Iov and the feasibility of electrodialysis operation at this current in terms of energy consumption. The electrical noise depends directly on the counter ion nature. The power spectral density of the membrane's potential fluctuation was obtained via Fourier analysis of the time series recorded during the transport of counter ions (K+ and NH4+). The spectra are evaluated above the limiting current indicating the differences between the K+ and the NH4+. It is found that the cation NH4+ presents a singular behaviour and the noise is minimal.

Influence of the hydrophobic groups and the nature of counterions on ion-binding in aliphatic ionene solutions

Transport and binding capabilities in aqueous solutions of 3,3-, 6,6-, and 6,9-ionene fluorides and bromides at 25°C were explored through the experimentally determined values for transport numbers of counterions and polyion constituents, along with the data for electrical conductivity in these solutions. Within the association theory, the fractions of free counterions and the effective linear charge densities of polyions were calculated. Experimental data were compared with the predictions of the Manning theory of polyelectrolyte solutions. It was determined that binding of the counterions to the polyion critically depends (i) on charge density of the polyion and (ii) on the chemical nature of the counterion in question. The effects of the charge density are the strongest in solutions of ionene bromides. Differences in the behavior of solutions of ionene fluorides and bromides are the consequence of different hydration capabilities of these ions. The effective linear charge density was found to be much lower than the one predicted from structural parameters of ionenes. The study addresses questions important to the biomedical field, in particular that of binding of ligands to charged macromolecules.

Catecholase activity investigations using in situ copper complexes with pyrazole and pyridine based ligands

The in situ copper (II) complexes of six pyrazole and pyridine based ligands: 1-[5-methyl-1-pyridin-2-yl-1H-pyrazol-3-yl] methanol L1, 2-(3,5-dimethyl-pyrazol-1-yl)-pyridine L2, (5-methyl-3-pyridin-2-yl-1H-pyrazol-1-yl) ethyl acetate L3, 1′,5,5′-trimethyl-1′H-1,3′-bipyrazol-3-ethyl carboxylat L4, (1′,5,5′-trimethyl-1′H-1,3′-bipyrazol-3-yl) methanol L5, and 5,5′-diphenyl-3,3′-bipyrazole L6, are reported and studied for their catecholase activities at ambient conditions, the reaction rate depends on four parameters: The nature of the carbonic chain bounded to the pyrazole ring, the nature of counter anion, the concentration of ligand and the nature of solvent. The highest rate activity is given by complex resulting from one equivalent of ligand L4 and two equivalents of Cu(CH3COO)2 in methanol, which equal to 4.440μmolL−1min−1.

Effect of novel antibacterial gallium-carboxymethyl cellulose on Pseudomonas aeruginosa

Gallium has emerged as a new therapeutic agent due partly to the scarcity in development of new antibiotics. In this study, a novel antibacterial gallium exchanged carboxymethyl cellulose (Ga-CMC) has been developed and tested for the susceptibility on a common bacteria, Pseudomonas aeruginosa. The results show that an increase in average molecular weight (MW) from 90 k, 250 k to 700 k of Ga-CMC caused a decrease in antimicrobial activity against planktonic P. aeruginosa. Gallium loading of the Ga-CMC (250 k) samples was altered by varying the amount of functionality (0.7, 0.9 and 1.2 acid groups per mole of carbohydrate) which affected also its antimicrobial activity against planktonic P. aeruginosa. Further, the ability to prevent the growth of biofilms of P. aeruginosa was tested on MW = 250 k samples with 0.9 acid groups per mole of carbohydrate as this sample showed the most promising activity against planktonic P. aeruginosa. Gallium was found to reduce biofilm growth of P. aeruginosa with a maximum effect (0.85 log(10) CFU reduction compared to sodium-carboxymethyl cellulose, Na-CMC) after 24 h. Results of the solubility and ion exchange studies show that this compound is suitable for the controlled release of Ga(3+) upon their breakdown in the presence of bacteria. SEM EDX analysis confirmed that Ga(3+) ions are evenly exchanged on the cellulose surface and systematic controls were carried out to ensure that antibacterial activity is solely due to the presence of gallium as samples intrinsic acidity or nature of counterion did not affect the activity. The results presented here highlight that Ga-CMC may be useful in controlled drug delivery applications, to deliver gallium ions in order to prevent infections due to P. aeruginosa biofilms.

Supramolecular design of biocompatible nanocontainers based on amphiphilic derivatives of a natural compound isosteviol

Two diterpenoid surfactants with ammonium head groups and bromide (S1) or tosylate (S2) counterions have been synthesized. Exploration of these biomimetic species made it possible to demonstrate that even minor structural changes beyond their chemical nature may dramatically affect their solution behavior. While their aggregation thresholds differ inconsiderably, morphological behavior and affinity to lipid bilayer are strongly dependent on the counterion nature. Compound S2 demonstrates properties of typical surfactants and forms small micelle-like aggregates above critical micelle concentration. For surfactant S1, two critical concentrations and two types of aggregates occur. Structural transitions have been observed between small micelles and aggregates with higher aggregation numbers and hydrodynamic diameter of ca. 150 nm. Unlike S2, surfactant S1 is shown to integrate with liposomes based on dipalmitoylphosphatidylcholine, resulting in a decrease of the temperature of the main phase transition. Both surfactants demonstrate an effective complexation capacity toward oligonucleotide (ONu), which is supported by recharging the surfactant-ONu complexes and the ethidium bromide exclusion at a low N/P ratio. Meanwhile, a very weak complexation of plasmid DNA with the surfactants has been revealed in the gel electrophoresis experiment. The DNA transfer to bacterial cells mediated by the surfactant S1 is shown to depend on the protocol used. In the case of the electroporation, the inhibition of the cell transformation occurs in the presence of the surfactant, while upon the chemical treatment no surfactant effect has been observed. The variability in the morphology, the biocompatibility, the nanoscale dimension and the high binding capacity toward the DNA decamer make it possible to nominate the designed surfactants as promising carriers for biosubstrates or as a helper surfactant for the mixed liposome-surfactant nanocontainers.

Influence of Counterions on Lauric Acid Vesicles and Theoretical Consideration of Vesicle Stability

The counterions, including inorganic cations, Na(+) and Cs(+), and organic cation, (C(2)H(5))(4)N(+), influence the phase behavior and self-assembled structures of the lauric acid (LA) in water. Dissolving LA in NaOH, CsOH, and (C(2)H(5))(4)NOH (tetraethylammonium hydroxide, TeAOH) solutions, respectively, we observed that the three systems totally exhibited the same phase behavior, from birefringent L(α) phase/precipitates (P) → L(α) phase → L(α) phase/L(1) (micelles) → L(1). The temperature influence on phase behavior was investigated, and with an increase of temperature, we observed that less phase behavior change occurred in the systems of LA/CsOH/H(2)O and LA/TeAOH/H(2)O, while the phase behavior of the LA/NaOH/H(2)O system exhibited an obvious change. Cryogenic transmission electron microscopy (cryo-TEM) images demonstrated that the different microstructures of L(α) phase samples in the three systems existed. For the systems of LA/NaOH/H(2)O and LA/TeAOH/H(2)O, uni- and multilamellar vesicles coexist for L(α) phase samples, as both the morphology and size of these vesicles are polydisperse. The curvatures of the bilayer membranes of the two systems are considered to vary from positive, zero, and even negative. However, only spherically unilamellar vesicles exist in the system of LA/CsOH/H(2)O, indicating that the bilayers are more rigid than those in the LA/NaOH/H(2)O and LA/TeAOH/H(2)O systems. Through the combination of the Helfrich curvature energy theory and the mass-action model, the effective bending constant K = 0.5 k(B)T in the LA/CsOH/H(2)O system was obtained, demonstrating that the unilamellar vesicles are stabilized by thermal fluctuations. A primary discussion for the effect of the nature of counterions on the stability and deformation of the vesicles is presented.