Dilute Aqueous Solutions Research Articles

Nanoparticles based on complex of berberine chloride and polymethacrylic or polyacrylic acid with antioxidant and in vitro antitumor activities

Berberine chloride (Brb) is a natural isoquinoline quaternary alkaloid that displayed a set of beneficial biological properties such as antioxidant, antimicrobial, antitumor, anti-inflammatory, and antiviral. Brb is poorly soluble in water and body fluids and its intestinal absorption is very low, which predetermine its low bioavailability. Polymeric nanoparticles seem to be a good platform to overcome these drawbacks. In this study, for the first time, stable aqueous dispersions of nanoparticles (NPs) based on complexes of Brb and poly(methacrylic acid) (PMA) or poly(acrylic acid) (PAA), were successfully prepared by mixing their dilute aqueous solutions as evidenced by the performed dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses. It was found that the mean diameter and zeta potential of NPs depended on the Brb molar fraction. In the case of Brb/PMA and Brb/PAA NPs the encapsulation efficiency was observed to approach a maximum value of 58.9±0.5% and of 78.4±0.9%, respectively, at values of Brb molar fraction at which maximum amount of complexes was obtained. The performed differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses revealed that Brb incorporated in the NPs was in the amorphous state. The Brb release profile was pH-dependent. The Brb-containing NPs displayed good antioxidant capacity close to that of free Brb. In vitro cell viability studies demonstrated that the Brb/PMA (PAA) NPs exerted a higher cytotoxicity against HeLa tumor cell than non-tumor BALB/c 3T3 mouse fibroblast cells. Thus, the obtained NPs are promising candidates in the drug delivery systems in the treatment of cervical tumors.

Kinetic studies on propionic and malic acid reactive extraction using trioctylamine in 1-decanol

The effectiveness and efficiency of the reactive extraction technique for recovery of propionic acid and malic acid from aqueous solution were investigated. Kinetic studies for the solute (acid)–solvent (trioctylamine dissolved in 1-decanol) system were carried out and mass transfer coefficients experimentally determined. These parameters are necessary for the proper design of an extraction unit. The studies were carried out using dilute solutions of the acids with a concentration range of 0.2–0.6 kmol/m3 and trioctylamine (10%v/v) in 1-decanol as extractant at 303.15 K. The effect of stirring speed, acid and extractant concentration at different time intervals was studied. The kinetic process parameters such as reaction order, mass transfer coefficient and rate constant were evaluated using the experimental data. From the results obtained, the reaction was found to be an instantaneous second-order chemical reaction occurring in the organic diffusion film. The values of the rate constants were found to be 0.430 m3/mol s and 0.332 m3/mol s, respectively, for propionic acid and malic acid, while the mass transfer coefficient, km, was also obtained for propionic acid (9 × 10−6 m/s) and malic acid (3 × 10−6 m/s). These are useful for the design of an extraction unit for carboxylic acid recovery from dilute aqueous solutions.

Synthesis and Characterization of a Leucine-Based Block Co-Polypeptide: The Effect of the Leucine Zipper on Self-Assembly.

The self-assembly behavior of an ABC triblock copolypeptide consisting of poly(ethylene oxide-b-(leucine-s-valine)-b-lysine) (PEO-PLV-PK) was examined via dynamic light scattering in dilute aqueous solution. Leucine is a hydrophobic, α-helix forming polypeptide that exhibits a "zipper effect" in coiled-coil dimers. We hypothesize that the specific interaction afforded by the leucine zipper dominates the thermodynamics of self-assembly through the side-by-side ordering of α-helices, which drives vesicle formation in a polymer with only 6 wt % hydrophobic content. Additionally, a multitude of assembly sizes and morphologies were attainable from a single polymer, depending on the solution processing method. Thermodynamic effects of the leucine zipper can be interpreted, in part, from solubility parameters determined from molecular modeling. The combination of synthesis, solvent processing, and computational studies helps to elucidate the thermodynamic effects of this unique assembly motif on classical self-assembly processes.

Dynamic Assemblies of Molecular Motor Amphiphiles Control Macroscopic Foam Properties.

Stimuli-responsive supramolecular assemblies controlling macroscopic transformations with high structural fluidity, i.e., foam properties, have attractive prospects for applications in soft materials ranging from biomedical systems to industrial processes, e.g., textile coloring. However, identifying the key processes for the amplification of molecular motion to a macroscopic level response is of fundamental importance for exerting the full potential of macroscopic structural transformations by external stimuli. Herein, we demonstrate the control of dynamic supramolecular assemblies in aqueous media and as a consequence their macroscopic foam properties, e.g., foamability and foam stability, by large geometrical transformations of dual light/heat stimuli-responsive molecular motor amphiphiles. Detailed insight into the reversible photoisomerization and thermal helix inversion at the molecular level, supramolecular assembly transformations at the microscopic level, and the stimuli-responsive foam properties at the macroscopic level, as determined by UV–vis absorption and NMR spectroscopies, electron microscopy, and foamability and in situ surface tension measurements, is presented. By selective use of external stimuli, e.g., light or heat, multiple states and properties of macroscopic foams can be controlled with very dilute aqueous solutions of the motor amphiphiles (0.2 weight%), demonstrating the potential of multiple stimuli-responsive supramolecular systems based on an identical molecular amphiphile and providing opportunities for future soft materials.

Acidic ionic liquid grafted PPF membrane reactor and its catalytic esterification kinetics

Electrospun polypropylene fibrous (PPF) membrane was selected as a substrate to graft ionic liquids (ILs) and avoid tedious ILs separation and recovery. A catalytic membrane, BILs-g-PPF, was prepared by long-distance and dynamic low-temperature Ar plasma flow activation and subsequent grafting with dual -SO3H imidazole Brönsted acidic ILs (BILs), [(CH2)3SO3HVIm]HSO4. A novel multistage membrane series reactor was first developed by employing the BILs-g-PPF membrane to catalyze esterification of acetic acid with ethyl alcohol. The BILs, which supplied strong active H+ and benefited to overcome the chemical equilibrium due to its high hydrophilic groups, was chosen as a catalyst. The three-dimensional porous network architecture of PPF membrane provided a high specific surface area to graft considerable BILs and enhanced mass transfer in membrane. The optimization of reaction conditions was studied and the results were as followed: BILs grafting degree of 213.5 mol/m3, reaction temperature 70 °C, molar ratio of acid to alcohol 1:5, membrane flux of 21.36 L/(m2·h). In single-stage catalytic membrane system, the acid conversion achieved 66.24% in 8 h. The multistage membrane series reactor can improve the reaction conversion efficiency. For the used membrane which lost some anions, its catalytic properties could be largely restored by soaking activation using a dilute sulfuric acid aqueous solution with a mass concentration of 10%. The proposed reaction kinetic models which related the feed volume and membrane structure parameters predict the esterification process well at different conditions.

Molecular dynamics simulation on Na+−F− ion-pair association from ambient to supercritical water

Constrained classical molecular dynamics simulations were carried out to investigate the sodium fluoride associations in dilute aqueous solutions from ambient to supercritical thermodynamic condition. Solvent mediated potential of mean force (PMF) of Na+−F− ions pair was calculated by thermodynamic integration with five different force fields and the SPC/E water model. The corresponding association constants were also calculated from the PMFs. The structure and dynamics of Na+ and F− in water calculated from these force fields were compared with the results from ab initio molecular dynamics at 298 K. The results show Na+−F− ion-pair tends to associate with increasing temperature and dissociate with increasing pressure. The association constants of the ion-pairs (Kall) including contact ion-pair (CIP), solvent shared ion-pair (SShIP) and solvent separated ion-pair (SSIP) from different force fields agreed well with each other within 0.4 log unit in the whole thermodynamic condition, and they are also in accordance with the recently published data at 298 K. But in the sub-supercritical region, significant deviations occurred between the contact ion-pair association constants (KCIP) and Kall for each force field and also between KCIP from different force fields. These two kinds of deviations decreased at higher temperature when CIP became the predominated configuration. Comparison of radial distribution functions (RDFs) characteristics from the five force fields with that from AIMD calculation shows that the force field parameters developed by combing single ion properties with mineral lattice energy or ion-pair interaction properties is better.

Concentrating water-soluble ionic liquids from aqueous solutions: Osmotic distillation with hydrophobic membranes

Ionic liquids (ILs) show a wide range of applications as “green” solvents in the new era and the recovery of water-soluble ILs has become an urgent issue. Herein, for the first time, osmotic distillation is applied to concentrate and recover water-soluble ILs with a series of hydrophobic membranes. Poly(vinylidene fluoride) membrane with vertically oriented pores and stainless steel mesh were hydrophobically modified and then compared with commercial membranes to demonstrate the influence of different pore structures on the osmotic distillation concentration process. With the vapor pressure difference between two sides of the membrane being the driving force, the dilute aqueous solutions of ILs can be concentrated to about 84 wt% after 24 h with a water flux of 7.8 kg m−2 h−1. It is also able to achieve ultra-high rejections to ILs and MgCl2 (>99.99%) by this osmotic distillation process. Although there exists a limitation for dewatering the ILs solutions with very high concentrations and thus the final ILs purity cannot reach 100%, this method is promising for practical applications benefiting from its high rejection to ions, easy operability at ambient temperature and remarkable universality in terms of hydrophobic membranes used.

Arsenic removal from water by starch functionalized maghemite nano-adsorbents: Thermodynamics and kinetics investigations

Arsenic is a highly toxic element present in water which needs to be removed from the water to eliminate its adverse health effects on human beings. But the concentration in most natural sources of water is deficient. Therefore investigations for its elimination from dilute aqueous solutions were carried out for obtaining potable water. Fabrication of As(III) specific magnetically recyclable stable nano-adsorbents would be an effective way of solving this tricky problem. The present study investigated the As(III) removal from low concentration aqueous solutions by magnetically recyclable superparamagnetic starch functionalized maghemite nano-adsorbents. For the sake of comparison, arsenic removal from its dilute aqueous solution was carried using both starch functionalized and non-functionalized maghemite nanoparticles as adsorbents. Functionalization by starch led to a significant increase in the As(III) adsorption capacity of the maghemite. The data obtained for arsenite adsorption was found to fit the Freundlich isotherm model, while the kinetics of the adsorption followed the pseudo-second-order model. The maximum Langmuir adsorption capacities achieved for virgin maghemite and functionalized maghemite were 7.14, 7.46, and 7.35 mg/g, and 8.57, 8.88, and 8.67 mg/g at 27, 35 and 45 °C, respectively. The negative value of ∆G (−7.13, −7.21, and −7.50 kJ/mol, for γ-Fe2O3; and −5.50, −5.45 and −5.98 kJ/mol for γ-Fe2O3@starch, at 27, 35 and 45 °C, respectively) indicated the feasibility and spontaneity of the As(III) adsorption on both adsorbents. The negative values of ∆H (−0.0016 kJ/mol for γ-Fe2O3; and −0.00022 kJ/mol for γ-Fe2O3@starch) showed that the adsorption process was exothermic.

Amphiphilic Copolymers of Acrylic Acid and n-Butyl Acrylate with the Predetermined Microstructure: Synthesis and Properties

Features of the synthesis of n-butyl acrylate copolymers with acrylic acid in 1,4-dioxane by free radical reversible addition-fragmentation chain transfer (RAFT) polymerization mediated by symmetric trithiocarbonates are considered. It is shown that the living mechanism of polymerization is realized in the studied systems. The chemical nature of the RAFT agent dictates different chain microstructures (random block or random) of the copolymers. The effect of chain microstructure on the properties of the copolymers containing about 90 mol % of acrylic acid units is studied by differential scanning calorimetry, contact angle measurements, turbidimetry, potentiometric titration, and dynamic light scattering. It is demonstrated that all the copolymers in the solid phase have similar properties: a single glass transition temperature close to the glass transition temperature of polyacid and a good water wettability. In dilute aqueous solutions, the properties of the copolymers are different: at the inherent pH, random copolymer macromolecules form large associates, while random block copolymers are dispersed into individual coils or micelles. All the copolymers are weaker polyacids compared with PAA; the random block copolymers are characterized by the compaction of macromolecules at small degrees of ionization. Our studies provide evidence that reversible addition-fragmentation chain transfer polymerization is an efficient tool for the targeted insertion of nonpolar units into a polyelectrolyte chain and it can be used for the fine-tuning of its properties.

A Highly Water-Stable meta-Carborane-Based Copper Metal-Organic Framework for Efficient High-Temperature Butanol Separation.

Biofuels are considered sustainable and renewable alternatives to conventional fossil fuels. Biobutanol has recently emerged as an attractive option compared to bioethanol and biodiesel, but a significant challenge in its production lies in the separation stage. The current industrial process for the production of biobutanol includes the ABE (acetone-butanol-ethanol) fermentation process from biomass; the resulting fermentation broth has a butanol concentration of no more than 2 wt% (the rest is essentially water). Therefore, the development of a cost-effective process for separation of butanol from dilute aqueous solutions is highly desirable. The use of porous materials for the adsorptive separation of ABE mixtures is considered a highly promising route, as these materials can potentially have high affinities for alcohols and low affinities for water. To date, zeolites have been tested toward this separation, but their hydrophilic nature makes them highly incompetent for this application. The use of metal-organic frameworks (MOFs) is an apparent solution; however, their low hydrolytic stabilities hinder their implementation in this application. So far, a few nanoporous zeolitic imidazolate frameworks (ZIFs) have shown excellent potential for butanol separation due to their good hydrolytic and thermal stabilities. Herein, we present a novel, porous, and hydrophobic MOF based on copper ions and carborane-carboxylate ligands, mCB-MOF-1, for butanol recovery. mCB-MOF-1 exhibits excellent stability when immersed in organic solvents, water at 90 °C for at least two months, and acidic and basic aqueous solutions. We found that, like ZIF-8, mCB-MOF-1 is non-porous to water (type II isotherm), but it has higher affinity for ethanol, butanol, and acetone compared to ZIF-8, as suggested by the shape of the vapor isotherms at the crucial low-pressure region. This is reflected in the separation of a realistic ABE mixture in which mCB-MOF-1 recovers butanol more efficiently compared to ZIF-8 at 333 K.

Swelling mechanism of PEBA-2533 membrane for pervaporation separation of high boiling point organic compounds: Experiment and molecular dynamics simulation

High boiling point organic compounds (HBOCs) with aromaticity can be recovered by poly(ether block amide) (PEBA-2533) membrane from dilute aqueous solutions as the products with high-purity using a pervaporation-fractional condensation (PVFC) coupling system. The swelling mechanism of the PEBA-2533 membrane is the decisive factor for the separation and recovery of HBOCs, however, it has not yet been clearly understood. In this study, the swelling behaviors of PEBA-2533 membrane in phenol, aniline, and furfural aqueous solutions were investigated by experiments and molecular dynamics (MD) simulation. The effect of the non-bond interaction energy and the number of hydrogen bonds between water and HBOC molecules on the swelling degree of PEBA-2533 was analyzed. The results show that the number of hydrogen bonds should be the dominant factor to determine the swelling degree of membrane. Furthermore, the structures of phenol, aniline and furfural were evaluated for their abilities to form hydrogen bonds through the molecular electrostatic potential (MESP) analysis. Besides, by investigating the feed-membrane surface affinity, it is found that the absorption concentration was related to the proportion of organic compound on the membrane surface. Based on the MD simulation results, the swelling mechanism of PEBA-2533 in dilute aqueous solutions was proposed and illustrated, which provided a way to promote the industrialization of PV technology.

Green synthesis and characterization of zeolite silicalite-1 from recycled mother liquor

Researches on zeolite silicalite-1 have focused mainly on improving its performance, with little attention paid on green and economic synthesis. Herein, a novel route for green synthesis of pure silicalite-1 from the recycled mother liquor has been developed. This route starts from the hydrothermal reaction of natural quartz with NaOH to form a sodium silicate solution, which is then transformed into a silicic acid (H2SiO3) gel by hydrochloric acid titration. Then the solid silicic acid (H2SiO3) gel and fumed silica (SiO2) are mixed with water under stirring to form a highly active slurry, which can be hydrothermally “dissolved” in a dilute NaOH aqueous solution. Using this slurry with a high SiO2/Na2O molar ratio of 5 : 1 as the silica source as well as tetrapropylammonium bromide (TPABr) as the organic template, MFI-type pure silicalite-1 has been successfully synthesized. After each synthesis, the mother liquor of centrifuged supernatant was recovered and recycled. The silica source and organic template were added to the recycled mother liquors for the synthesis of pure silicalite-1. The minimum TPABr/SiO2 molar ratio needed to synthesize pure silicalite-1 in the initial run is 0.04 : 1. In comparison, only half the amount of the organic template is needed in subsequent runs with the recovered mother liquors. Through recycling, all reactants in the mother liquors were ultimately utilized without any waste, leading to not only effectively reducing the cost of silicalite-1 synthesis but also minimizing its environmental impact.

Quantitative Structure-Based Prediction of Electron Spin Decoherence in Organic Radicals.

The decoherence, or dephasing, of electron spins in paramagnetic molecules limits sensitivity and resolution in electron paramagnetic resonance spectroscopy, and it represents a challenge for utilizing paramagnetic molecules as qubit units in quantum information devices. For organic radicals in dilute frozen aqueous solution at cryogenic temperatures, electron spin decoherence is driven by neighboring nuclear spins. Here, we show that this nuclear-spin-driven decoherence can be quantitatively predicted from the molecular structure and solvation geometry of the radicals. We use a fully deterministic quantum model of the electron spin and up to 2000 neighboring protons with a static spin Hamiltonian that includes nucleus-nucleus couplings. We present experiments and simulations of two nitroxide radicals and one trityl radical, which have decoherence time scales of 4-5 μs below 60 K. We show that nuclei within 12 Å of the electron spin contribute to decoherence, with the strongest impact from protons 4-8 Å away.

Non-segregated crystalline state of dilute glycerol aqueous solution.

When a dilute aqueous solution freezes at 1 atm, it is segregated into water-rich ice Ih and solute-rich freeze-concentrated glassy solution. A similar segregation is observed at the crystallization of homogeneous glassy aqueous solutions by heating. The influence of solutes on the nucleation of solvent water and the solute discharge process from the crystalline ice are not clear. In this study, I made a homogeneous dilute glassy glycerol aqueous solution (0.07 mol fraction) using pressure liquid cooling vitrification (PLCV), measured the specific volume and the sample temperature during the compression and decompression processes, and examined the polyamorphic and crystallization behaviors. It is found that the sample crystallized slightly above the crystallization temperature is amorphized homogeneously under pressure, and that the amorphized sample is equivalent to the homogeneous glassy sample made by PLCV. This indicates that glycerol solutes in the crystalline sample are dispersed homogeneously and the crystalline sample does not segregate. These experimental results suggest that nucleation does not involve segregation and that crystal growth induces segregation. The discovery of the non-segregated crystalline state has an implication in not only the understanding of crystallization of glassy ice in meteorology and planetary physics but also the application to cell thawing techniques in cryobiology and food engineering.

Quantitative Prediction of the Structure and Viscosity of Aqueous Micellar Solutions of Ionic Surfactants: A Combined Approach Based on Coarse-Grained MARTINI Simulations Followed by Reverse-Mapped All-Atom Molecular Dynamics Simulations.

We address the problem of the quantitative prediction of micelle formation in dilute aqueous solutions of ionic surfactants using sodium dodecyl sulfate (SDS) as a model system through a computational approach that involves three steps: (a) execution of coarse-grained simulations based on the MARTINI force field (with slightly modified parameters to afford the formation of large micelles); (b) reverse mapping of the final self-assembled coarse-grained configuration into an all-atom configuration; and (c) final relaxation of this all-atom configuration through short-time (on the order of a few tens of nanoseconds), detailed isothermal-isobaric molecular dynamics simulations using the CHARMM36 force field. For a given concentration of the solution in SDS molecules, the modified MARTINI-based coarse-grained simulations lead to the formation of large micelles characterized by mean aggregation numbers above the experimentally observed ones. However, by reintroducing the detailed chemical structure through a strategy that solves a well-defined geometric problem and re-equilibrating, these large micellar aggregates quickly dissolve to smaller ones and equilibrate to sizes that perfectly match the average micelle size measured experimentally at the given surfactant concentration. From the all-atom molecular dynamics simulations, we also deduce the surfactant diffusivity DSDS and the zero-shear rate viscosity, η0, of the solution, which are observed to compare very favorably with the few experimental values that we were able to find in the literature.

Dissolution of highly molecular weight cellulose isolated from wheat straw in deep eutectic solvent of Choline/l-Lysine hydrochloride

Green solvents for cellulose dissolution is a key topic for green chemistry, especially natural cellulose with high molecular weight, and there are scarce solvents reported. Deep eutectic solvent (DES) is a typical kind of green solvent that has been attracted much attention recently. Here, high molecular weight natural cellulose (DP > 3000) was first isolated from wheat straw and then be directly dissolved in the choline/l-lysine (Ch/Lys) DES. The solution owns excellent stability, and the solubility reaches ∼5%. Rheological studies revealed that the natural cellulose can be well dispersed in the DES solution and showed gelation at high concentrations. The dissolved cellulose can be regenerated when the dilute acid aqueous solution was added into the solution. It provides an energy conversation and an environmentally friendly route to prepare a cellulose solution, which makes it possible to convert cellulose to valuable chemicals and materials in its homogeneous solution.

Lennard-Jones Parameters Determined to Reproduce the Solubility of NaCl and KCl in SPC/E, TIP3P, and TIP4P/2005 Water.

Most classical nonpolarizable ion potential models underestimate the solubility values of NaCl and KCl in water significantly. We determine Lennard-Jones parameters of Na+, K+, and Cl- that reproduce the solubility as well as the hydration free energy in dilute aqueous solutions for three water potential models, SPC/E, TIP3P, and TIP4P/2005. The ion-oxygen distance in the solution and the cation-anion distance in salt are also considered in the parametrization. In addition to the target properties, the hydration enthalpy, hydration entropy, self-diffusion coefficient, coordination number, lattice energy, enthalpy of solution, density, viscosity, and number of contact ion pairs are calculated for comparison with 17 frequently used or recently developed ion potential models. The overall performance of each ion model is represented by a global score using a scheme that was originally developed for comparison of water potential models. The global score is better for our models than for the other 17 models not only because of the quite good prediction for the solubility but also because of the relatively small deviation from the experimental value for many of the other properties.

Physicochemical properties of dilute aqueous solutions of 1-Ethyl-3-Methylimidazolium Ethylsulfate, 1-Ethyl-3-Methylimidazolium Methylsulfate, 1-Ethyl-3-Methylimidazolium Tosylate and 1, 3-Dimethylimidazolium Methylsulfate at different temperatures and at atmospheric pressure

This work presents the experimental data on thermophysical properties of aqueous solutions of imidazolium-based ionic liquids (ILs) such as 1-Ethyl-3-Methylimidazolium Ethylsulfate [EMIM][EtSO4], 1-Ethyl-3-Methylimidazolium Methylsulfate [EMIM][MeSO4], 1-Ethyl-3-Methylimidazolium Tosylate [EMIM][Tos], and 1,3-Dimethylimidazolium Methylsulfate [MMIM][MeSO4] in water at different temperatures. Many researchers have studied imidazolium based ILs in different solvents but there is scarcity of data in dilute region. So the aim of this work is to understand the interactions between imidazolium based ILs and water in dilute region. To understand the ion-ion and ion–solvent interactions between IL and water, the thermophysical properties such as density (ρ), speed of sound (u), and viscosity (η) have been measured at temperatures T = (298.15, 303.15, 308.15 and 313.15) K and at atmospheric pressure. The properties like apparent molar volume, limiting apparent molar volume and coefficient of thermal expansion have been derived from the density data. The speeds of sound and density data were combined to evaluate isentropic and isothermal compressibilities. Using Jones-Dole equation, the viscosity A and B coefficients have been determined. The influence of IL cation chain length, different anions and temperature on the sign, magnitude of BV (the deviation parameter from Debye-Hückel theory) and on viscosity B-coefficient has been discussed.

Effect of ZIF-71 ligand-exchange surface modification on biofuel recovery through pervaporation

In this paper, zeolitic imidazolate framework-71 (ZIF-71) particles (~500 nm diameter) were modified with four different ligands through the solvent-assisted linker exchange (SALE) method. The objective of this was to assess the effect of ligand exchanged ZIF-71 on the performance of ZIF-71/polydimethylsiloxane (PDMS) mixed matrix membranes (MMMs) for removal of alcohol from dilute aqueous solutions. Both Fourier-transform infrared spectroscopy (ATR-FTIR) and proton nuclear magnetic resonance (1H NMR) spectroscopy confirmed the exchange of the new ligands into the ZIF-71 material. The 1H NMR spectra demonstrated the molar ratios of the ligand-exchange into the ZIF-71 particles. X-ray diffraction and scanning electron microscopy results showed that the crystal structure and the morphology of ZIF-71 were maintained after the ligand-exchange modification process. Modified ZIF-71/PDMS composite membranes were synthesized to study the effect of ligand modification on alcohol/water separation performance. Ligand-modified ZIFs dispersed more evenly in the condensation cure PDMS polymer matrix than the unmodified ZIFs. The alcohol permeability and alcohol/water selectivity for ethanol and 1-butanol remained the same or decreased for membranes made with ligand-exchanged ZIF-71 particles.

High-energy ionizing radiation-induced degradation of amodiaquine in dilute aqueous solution: radical reactions and kinetics

The widely used antimalarial drug amodiaquine (AQ) contains a 7-Cl-quinoline unit, a substituted 4-aminophenol part connected through the amino group and a tertiary amine part. The 4-aminophenol unit can be easily oxidized through radical intermediates to iminoquinone. This reaction also takes place in vitro and in vivo enzymatic reactions. The reaction is expected to have an important role in degradation of AQ in surface waters and also during degradation in advanced oxidation processes. In this paper by means of radiation chemical techniques the one-electron oxidation and reduction of AQ were studied using transient kinetics, kinetics of AQ degradation, formation and decay of end-products of radical reactions. The hydroxyl radicals were shown to add both to the quinoline (∼ 38%) and aminophenol (∼ 50%) parts via formation of hydroxycyclohexadienyl radicals and by H-abstraction or by an electron removal from the tertiary amine part of the molecule (∼ 12%). The dihydroxycyclohexadienyl radical formed on the aminophenol part is suggested to transform to aminophenoxy radical. The hydrated electrons can also effectively contribute to AQ degradation. Chemical oxygen demand and total organic carbon content investigations were also made in order to characterize the ionizing radiation-induced oxidation and mineralization. In aerated 0.1 mmol dm−3 solution, at 2.5 kGy absorbed dose AQ and its higher molecular mass degradation products demolished completely. Ionizing irradiation is a capable technique for degradation of AQ under both oxidative and reductive circumstances.