Counterions Br Research Articles

Self-Assembly of Amphiphilic Copper Nanoclusters Driven by Cationic Surfactants.

Amphiphilicity is an excellent physicochemical property, which is yet to be explored from traditional surfactants to nanoparticles. This article shows that the amphiphilicity of copper nanoclusters (CuNCs) can be readily tuned by electrostatic interactions with cationic surfactants and cetyltrimethylammonium cations (CTA+) with counterions Br-, Cl-, and C7H8O3S-. Due to the role of surface ligands, the complexes of glutathione-capped CuNCs (GSH-CuNCs) and the surfactants exhibit good amphiphilicity, which enables them to self-assemble like a molecular amphiphile. This could significantly increase the utility of metal nanoclusters in basic and applied research. As the concentration of the surfactant changes, the aggregates change from nanoparticles to network-like structures. After the formation of supramolecular self-assemblies by hydrophobic interactions, the enhancement of fluorescence intensity was observed, which can be ascribed to the suppression of intramolecular vibrations based on aggregation-induced emission (AIE) and combined with the compactness of GSH-CuNCs in self-assemblies. Our study provides a facile way to generate solid fluorescent materials with excellent fluorescence performance, which may find applications in light-emitting diodes (LEDs).

High capacity ethidium bromide removal by montmorillonites

Ethidium bromide (EtBr) is commonly used as a reagent to investigate DNA and RNA bonding in biochemistry. However, it is mutagenic and toxic; thus, its removal from the waste solution is of the top priority in lab safety practice. Although many products with high EtBr removal capacities are available on the market, developing new products with low material costs and high removal capacities is still an urgent priority. As the EtBr is in a cationic form Et+ balanced by counterion Br in aqueous solution, materials with high cation exchange capacity and large specific surface area may have great potential for efficient EtBr removal, Thus, several montmorillonites (MMTs) were evaluated for their EtBr removal capacity and methods of regeneration in this study. Results showed that both external and internal surfaces of MMTs were effective sorption sites for EtBr with a capacity up to 600mg/g. And the waste-laden materials could be regenerated or safely disposed after incineration at 500 °C for 2 h. As such, further tests on optimization and manufacturing kits or devices for practical EtBr removal in routine lab practice is of engineering priority, should MMTs be further explored as an effective material for EtBr removal.

Enhanced removal of ethidium bromide (EtBr) from aqueous solution using rectorite

Ethidium bromide (EtBr) is an intercalating agent commonly used as nucleic acid fluorescent tag in various techniques of life science field. It is considered as a serious biohazard due to its mutagenicity and carcinogenicity. As such, developing high efficiency and low cost materials as cleanup kits is in urgent need although many methods have already been developed. In this study we take use of the affinity of organic cations for clay minerals of high cation exchange capacity (CEC) and large specific surface area (SSA) and tested the removal of EtBr using rectorite, a type of clay mineral made of 1:1 regularly mixed layers of illite and montmorillonite. Our results showed that the uptake of Et+ on rectorite could be as high as 400 mmol/kg and the removal of Et+ was extremely fast. Desorption of inorganic cation Ca2+ and sorption of counterion Br− revealed that cation exchange was the dominating mechanism of Et+ removal using rectorite. Thermal analyses revealed that the EtBr could be thermally destructed inside the interlayer of rectorite and the material could be thermally regenerated. Thus, clay minerals could have a great potential to be fabricated into cleanup kits for the removal of EtBr in case of spill.

Effect of the nature of counterion on the micellar properties of cationic surfactants: a conductometric study

ABSTRACTInteraction of cationic surfactants, tetradecyltrimethylammium bromide (TTAB) and tetradecyltrimethylammonium chloride (TTAC) with anionic dye, tartrazine in aqueous solution has been investigated employing conductometric technique. The free energy of transfer of hydrophobic chain, , surface contribution, and their transfer values, and , free energy, , enthalpy, , and entropy, of micellisation have been calculated. A marked decrease in the critical micelle concentration for TTAB compared to TTAC indicates dramatic role of the smaller counterion Br− over the bigger counterion Cl−. Formation of dye–surfactant ion-pairs which behave as nonionic surfactant has been proposed. Higher negative and positive values for TTAB than TTAC are attributed to difference in the size and nature of the counterions Br− and Cl−. Negative and values clearly suggest that micellisation of TTAB and TTAC is thermodynamically spontaneous and exothermic in nature. As ), it suggests that the process of micellisation is entropy dominated for the two surfactants.

The effect of CTAB on Na2SO4 nucleation in mixed Na2SO4/CTAB aerosols by FTIR-ATR technology

Abstract FTIR-ATR technology is used to study the efflorescence kinetic of Na2SO4 and mixed Na2SO4/CTAB aerosols. As the RH decreased linearly, the ν3 SO42− band shifts from 1094 cm−1 to 1132 cm−1, suggesting the phase transition of Na2SO4 from solution to crystal phase (III). For pure Na2SO4 aerosols, the ERH is 75.1% RH, whereas the efflorescence point of mixed Na2SO4/CTAB aerosols (74.2%) is lower. By further analysis of IR differential spectra, the ratio of Na2SO4 crystals in mixed aerosols is only 62.7% and the heterogeneous nucleation rate of Na2SO4 in Na2SO4/CTAB mixed aerosols is lower than that in pure Na2SO4 aerosols. They showed that CTAB assembled into reversed micelle and part Na2SO4 droplets are in the core to form core-shell structure, and CTAB shell prevents core Na2SO4 solutions from crystallizing. However, the counter ion Br− for CTAB reversed micelle can interact with Na+ ions, which decreases the crystallization rate of free Na2SO4 droplets and ERH is delayed.

Counter ions and constituents combination affect DODAX : MO nanocarriers toxicity in vitro and in vivo.

Liposomes have received extensive attention as nanocarriers for bioactive compounds due to their good biocompatibility, possibility of targeting and incorporation of hydrophilic and hydrophobic compounds. Although generally considered as safe, detailed knowledge of the effects induced in cells and tissues with which they interact is still underexplored. The aim of this study is to gain insight into the toxicity profile of dioctadecyldimethylammonium (DODAX) : monoolein(MO) liposomes (X is bromide or chloride), previously validated for gene therapy, by evaluating the effect of the counter ions Br- or Cl-, and of the cationic : neutral lipid molar fraction, both in vitro and in vivo. Effects on cellular metabolism and proliferation, plasma membrane integrity, oxidative stress, mitochondrial membrane potential dysfunction and ability to trigger apoptosis and necrosis were evaluated in a dose-/time-dependent manner in normal human skin fibroblasts. Also, newly fertilized zebrafish zygotes were exposed to liposomes, permitting a fast-track evaluation of the morphophysiological modifications. In vitro data showed that only very high doses of DODAX : MO induce apoptosis and necrosis, inhibit cell proliferation, and affect the metabolism and plasma membrane integrity of fibroblasts in a dose-/time-dependent manner. Furthermore, liposomes affected mitochondrial function, increasing ROS accumulation and disturbing mitochondrial membrane potential. DODAC-based liposomes were consistently more toxic when compared to DODAB-based formulations; furthermore, the inclusion of MO was found to reduce toxicity, in contrast to liposomes with cationic DODAX only, especially in DODAB : MO (1 : 2) nanocarriers. These results were corroborated, in a holistic approach, by cytotoxicity profiling in five additional human cell lines, and also with the zebrafish embryotoxicity testing, which constitutes a sensitive and informative tool and accurately extends cell-based assays.

Counter-ion and solvent effects in electrospray ionization of solutions of alkali metal and quaternary ammonium salts

Despite the wide use of electrospray ionization (ESI) mass spectrometry, the factors determining the relative signal intensities of different analytes are not yet fully understood. We have performed a systematic study to assess the influence of selected counter-ions (Br−, ClO4−, BF4−, BPh4−) on the ESI response of alkali-metal (Li+, Cs+) and quaternary ammonium ions (NEt4+, NBu4+) over a concentration range of 0.025–2.5mmolL−1. Specifically, we have subjected solutions containing equimolar mixtures of these analytes in H2O, CH3OH, CH3CN, and tetrahydrofuran, respectively, to ESI and determined the relative signal intensities of the ions thus produced. Especially in the aprotic solvents, variation of the counter-ion can significantly change the outcome of the ESI process, which we ascribe to ion pairing. The smaller counter-ions Br−, ClO4−, and BF4− undergo more selective ion pairing in that their tendencies to pair up with the cations strongly decrease in the order Li+>Cs+>NEt4+>NBu4+. In contrast, ion pairing of the larger BPh4− counter-ion with the different cations is much less selective. As a result, the smaller counter-ions Br−, ClO4−, and BF4− suppress the ESI response of Li+ and Cs+ ions significantly more strongly than does BPh4−. Additional evidence for selective ion pairing comes from the observation of ionic aggregates enriched in the alkali-metal ions relative to the quaternary ammonium ions.

Shape-Controlled Synthesis of Palladium Nanorods and Their Magnetic Properties

A simple method for the controlled growth of single crystalline palladium nanorods is presented. Through tuning the molar ratio of two surfactants, cetyltrimethylammonium bromide (CTAB) and poly(vinyl pyrrolidone) (PVP), single crystalline palladium nanorods with different aspect ratios can be synthesized in large quantities. The introduction of cosurfactant CTAB is critical to the growth of palladium nanorods. Its headgroup CTA+ and counterion Br− anion act as stabilizing species and etchant, respectively. Compared with PVP-capped Pd nanoparticles, the Pd nanorods show a ferromagnetism behavior at 5 and 300 K, respectively.

X-ray diffraction study of mesophase bitemplate-containing silicas

The effect of the composition of a bitemplate (solubilization) mixture on the formation of a spatially organized structure of mesophase siliceous systems has been investigated by X-ray diffraction. Alkylpyridinium halides (CnPyHal with n = 8−16 (counterion Cl) and 18 (counterion Br)) were used a solubilizator, and monoethanolamides (EACm) of saturated n-aliphatic acids (m = 10−16) and trialkylphosphine oxides (H2e + 1Ce)3PO, where e = 8, 10, or 12, were used as solubilizates. Differences in the mesophase structure of template-containing silicas synthesized in aqueous and aqueous salt (NaCl) solutions have been revealed. It is shown that the type and degree of ordering of the silica mesophase structure depends on the nature, spatial organization, and the solubilizator and solubilizate concentrations.

Transport of micelles of cationic surfactants through clinoptilolite zeolite

Natural clinoptilolite is capable of removing metal cations from water due to its high cation exchange capacity. The affinity of the zeolite for cations makes it a good candidate to remove cationic surfactants from water. The transport of hexadecyltrimethylammonium (HDTMA), at a solution concentration greater than its critical micelle concentration (CMC), through zeolite columns of different particle sizes resulted in a retardation factor of 50–60. The capacities of HDTMA sorption at the breakthrough point C B are 82–83 mmol kg −1 at 20–25 PVs and 140–160 mmol kg −1 at 40–45 PVs for the 1.4–2.4 mm and 0.4–1.4 mm zeolite, respectively. While, the capacities of HDTMA sorption at the exhaustion point C E are 185–187 mmol kg −1 at 110–120 PVs and 195–210 mmol kg −1 at 90–100 PVs, for the 1.4–2.4 mm and 0.4–1.4 mm zeolite, respectively. In the early stage of the transport experiment, the HDTMA effluent concentration was close to zero while the counterion Br − concentration was about 50% of the input concentration, indicating a complete removal of HDTMA but only a partial removal of bromide. At any given time, the amount of surfactant removed is about twice that of counterion Br − removed and twice that of metal cations released. The concurrent removal of counterion accompanying surfactant sorption was attributed to HDTMA admicellar sorption by the zeolite, indicating that both cation exchange and hydrophobic bonding are dominant mechanisms for HDTMA removal when its input concentration is greater than the CMC. Therefore, when designing an adsorption bed to remove surfactant from aqueous solutions with concentrations greater than the CMC, partially release of counterion needs to be taken into consideration.

Adsorption of a cationic gemini surfactant from aqueous solution onto aluminosilicate powders of the MCM-41 type: effect of pore size and co-adsorption of phenol

The adsorption of cationic gemini dodecanediyl- α, ω-bis(dodecyldimethylammonium) bromide (i.e., C 12C 12C 12) from aqueous solution onto aluminosilicate powders of the MCM-41 type (referred to as SiAl32 dx, where x is the mean pore diameter in Å) has been studied at 298 K under the conditions of free pH of the aqueous phase. Macroporous silica gel XO15M was used for comparative purposes. The discussion was based on the interpretation of experimental adsorption isotherms and differential enthalpies of displacement obtained on various solid samples. For the hydrogen-exchanged SiAl32 d28 sample (i.e., H +–SiAl32 d28), the adsorption of bromide counterions Br − at the solid–solution interface, the isotherm of the pH evolution in the equilibrated supernatant liquid, and the electrophoretic mobility of the solid particles coated with the adsorbed C 12C 12C 12 were additionally measured. The uptake of phenol (PhOH) by a surfactant–solid system from a 1.5 mmol kg −1 PhOH solution and the related thermal effect of displacement onto SiAl32 d50 were quantified with the use of the solution depletion technique combined with UV spectrophotometry and the titration calorimetry technique. Titration calorimetry was also used to determine the molar enthalpy change accompanying micellization of C 12C 12C 12 in pure deionized water and in a 1.5 mmol kg −1 PhOH solution at 298 K. The adsorption of C 12C 12C 12 occurs simultaneously on the external surface and on the pore walls and it is a strongly co-operative phenomenon. Surfactant aggregates forming at adsorption saturation are thought to be composed of the adsorbed surfactant units having their cationic head groups mostly oriented outward with respect to the solid surface. Therefore, they can provide co-adsorption sites for polarisable phenol molecules. On average, there is one phenol molecule retained for one gemini cation adsorbed. Transfer of phenol from the aqueous phase to either the bulk micelles or to the interfacial aggregates is enthalpically favourable.

Adsorption and Interfacial Aggregation of a Cationic Quaternary Ammonium Surfactant on Powdered Mesoporous MCM-41 Aluminosilicates from Dilute Aqueous Solutions

The adsorption of cationic tetradecyltrimethylammonium bromide (TTAB) from aqueous solution on two series of powdered MCM-41 aluminosilicates (referred to as SiAlxCn, where x is the mole Si:Al ratio and n the chain length of the surfactant template) has been studied at 298 K under the conditions of free pH of the aqueous phase. Potentiometric acid−base titrations of SiAl32C14 in NaNO3 and TTAB solutions were performed. The results of the previous study on the adsorption of ionic surfactants and the new proton-balance data indicate that the MCM-41 surface acquires a negative charge under the experimental conditions employed. The influence of the pore size and the surface charge density on the adsorption mechanism was evidenced by comparing adsorption isotherms of the surface-active ions TTA+, electrophoretic mobilities of solid particles, and differential molar enthalpies of displacement obtained on various solid samples. For the hydrogen-exchanged SiAl32C14 sample (H+−SiAl32C14), the adsorption of bromide counterions Br- at the solid−solution interface and the isotherm of the pH evolution in the equilibrated supernatant liquid were additionally measured. Titration microcalorimetry was also used to determine the molar enthalpy of micellization and the critical micelle concentration of TTAB in deionized water at 298 K. Surfactant adsorption appears to occur simultaneously on the external surface area and the pore walls. Monolayered aggregates consisting of “head-on” oriented surfactant units are expected to form on hydrophilic, highly charged surface zones of Na+-derived samples at low bulk molalities. It is postulated that displacing and destructuring of vicinal water induced by the growth of compact aggregates are responsible for the positive enthalpy of displacement in this adsorption range. The endothermic domain broadens with decreasing pore size and increasing aluminum content in the silica matrix. The displacement process is exothermic over the whole experimental range on H+−SiAl32C14 because water structuring is not significant for this sample. The aggregates formed on solid samples at higher surface densities are very heterogeneous in size and shape, depending on the surface charge density and the pore space available to the adsorbate.

Photophysics of 3- and 4-phenyl pyridyl ketones in submicellar and micellar solutions of ionic and non-ionic surfactants

The photophysics of the 3- and 4-phenyl pyridyl ketones has been studied in submicellar and micellar solutions of sodium dodecyl sulfate (SLS), Triton X-100 (TX-100) and hexadecyltrimethylammonium bromide (CTAB) by stationary techniques and nanosecond laser flash photolysis. In the presence of CTAB, the main effect is that of the counter-ion Br–, in SLS and TX-100, the photochemical behaviour is dominated by hydrogen abstraction from the surfactants by the triplet ketones. The rate parameters of this interaction were determined by phosphorescence quenching measurements and the ketyl radicals produced were identified by laser flash photolysis at submicellar concentration. The dynamics of the spin-correlated radical pairs formed in micellar solution were studied; transient absorption spectra and lifetime were determined. By using quenchers that are solubilised in the micelle (biphenyl) or in the bulk water (CuCl2), intra- and extra-micellar processes were characterised.