Migration behavior of aromatic amines on alumina thin layers developed with water-in-oil microemulsion

Water-in-oil (w/o) microemulsions consisting of surfactant [sodium dodecyl sulfate (SDS) or N-Cetyl-N,N,N-trimethyl ammonium bromide], water, heptane or hexane, and a cosurfactant (1-pentanol or butanol) have been used as a mobile phase in combination with alumina, microcrystalline cellulose, silica gel G, silica gel H, and Kieselguhr thin layers to study the retention efficiency of amines. The separation of amines from their ternary and binary mixtures is achieved. Thin layers of alumina as the stationary phase and SDS/water/heptane/1-pentanol microemulsion as mobile phase is identified as the best chromatographic system for amine analysis. The limits of identification and dilution are reported for amines. Effects of heavy metals, anions, and phenols on the separation efficacy of diphenylamine-p-chloroaniline-p-nitroaniline have also been examined. The effect of electrolyte in the microemulsion on amine mobility is investigated. The o- and p-isomers move faster compared to the m-isomer of aniline.     

Liquid-phase polymer-based retention and coupled electrocatalytic oxidation to remove Arsenic in the presence of competitive species

The goal was to remove arsenate species in the presence of competitive anions by coupling of liquid-phase polymer-based retention, LPR, a procedure based on the selective As(V) adsorption properties of cationic water-soluble polymers, with an electro-catalytic oxidation process (EO) of As(III) into its more easily removable As(V). The electro-catalytic oxidation of As(III) to As(V) was performed with an organic supporting electrolyte, poly[3-(methacryloylamine)propyl)]trimethyl ammonium chloride, P(ClMPTA), which is recognized as an efficient reagent in removing divalent arsenate species. The bulk electro-catalytic conversion of As(III) to As(V) was carried out with a Pt-gauze electrode, and the resulting mixtures were introduced into a LPR cell to remove the As(V)-polymer adducts. Using P(ClMPTA) and ammonium salts at a 20:1 polymer:As(III) molar ratio at pH 8, complete (100%) Arsenic retention was achieved. For binary mixtures of Arsenic with competitive anions (e.g., SO₄ ²⁻, HPO₄ ²⁻, NO₃ ⁻, and NO₂ ⁻), the retention profile varied in the range 100–70%. In addition, the As(V) retention efficiency was found to be directly related to the consumed charge in the mol ratio As(III) in solution with competitive anionic species.     

Precipitation in solutions containing mixtures of synthetic anionic surfactant and soap. I. Effect of sodium octanoate on hardness tolerance of sodium dodecyl sulfate

The effect of sodium octanoate (SO) and pH on the precipitation of sodium dodecyl sulfate (SDS) with calcium (hardness tolerance) in water was investigated. SO can exist as octanoate anion (O⁻) or as the protonated nonionic fatty acid (HO) with the HO/O⁻ ratio increasing with decreasing pH. At intermediate pH levels, SO or SO/SDS systems are composed of mixtures of anionic and nonionic surfactants, resulting in enhancement of micelle formation due to nonideal mixed micelle formation. Above the critical micelle concentration (CMC), the highest hardness tolerance at each pH level occurs at a mole ratio of 80∶20 SDS/SO due to synergism in the SDS/SO mixtures. This synergism also results in an increase in hardness tolerance of SDS with decreasing pH above the CMC.     

Photoinitiated cationic polymerization of epoxide and vinyl monomers by p-trimethoxytrityl salts

Photoinitiated cationic polymerizations of cyclohexene oxide, tetrahydrofuran and N-vinylcarbazole were investigated in dichloromethane at 25°C, using stable, soluble and nonhygroscopic p-trimethoxytrityl salts having nonnucleophilic anions such as SbF₆ ⁻, AsF₆ ⁻, PF₆ ⁻, BF₄ ⁻, and SbCl₆ ⁻. The effects of anion, polymerization time, concentration of the salt and the intensity of light on the polymerization reaction are presented.     

Chelating ionophores based electrochemical sensor for Hg(II) ions

Poly(vinyl chloride) (PVC)-based membranes of pyrimidines, 1-(2′-aminoaryl)-4, 4, 6-trimethyl-1, 4, 5, 6-tetrahydro-6-hydroxypyrimidine-2-thiol (HPT) (R = −H, −CH₃, −OCH₃) with sodium tetraphenylborate (NaTPB) as an anion inhibitor and dibutylphthalate (DBP), dioctylphthalate (DOP), dibutyl (butyl) phosphonate (DBBP) and 1-chloro naphthalene (CN) as plasticizing solvent mediators were prepared and used as Hg²⁺ selective electrodes. Optimum performance was observed with the membrane having HPT(−OCH₃)−PVC−NaTPB−DOP in the ratio 1:33:1:65 (w/w). The electrode works well over a wide concentration range 5.0 × 10⁻⁶−1.0 × 10⁻¹ M (detection limit 1.0 ppm) with Nernstian compliance (29.5 mV decade⁻¹) between pH 2.5 and 4.0 with a fast response time of about 20 s. The selectivity coefficient values of the order of 0.001 for mono-, bi- and trivalent cations, indicate high selectivity for Hg²⁺ ions over these cations. Further, anions such as Cl⁻ and SO ₄ ²⁻ do not interfere in the functioning of Hg²⁺ sensor. The electrodes were used over a period of five months with good reproducibility (std. dev. ±0.2 mV) and the performance of the electrodes was found satisfactory even up to 10% nonaqueous medium. The electrode assembly was also evaluated for potentiometric determination of Hg²⁺.     

Chlorinated long chain fatty acids—their properties and reactions: III. Solvent effects in the dehydrohalogenation of sodium 9,10-dichlorooctadecanoate in dilute alkaline solutions

The first stage of the alkaline dehydrohalogenation of sodium 9,10-dichlorooctadecanoate (DCO) has been studied in ethylene glycol-water mixtures and in pure water at 90 C. The rate of the reaction was found to decrease rapidly with increasing water concentration. The rate of removal of the first chlorine from sodium 9,10-dichlorooctadecanoate was determined as a function of the water concentration in various ethylene glycol-water mixtures. The rate coefficient (k_OH) in pure water solution was 1.4·10⁻⁴ kg·mole⁻¹·min⁻¹ as compared to the maximum value of 2.7·10⁻² kg·mole⁻¹·min⁻¹ in 19 wt % solution. The effects of temperature and base concentration on the reaction rate were also investigated.     

Use of an Aqueous Methionine Mobile Phase in Identification of Cetylpyridinium Chloride on a Kieselguhr Layer with Preliminary Separation from Nonionic Surfactants

Thin layer chromatography of cationic and nonionic surfactants was performed on kieselguhr ‘G’ layers. Eight amino acids at three different concentration levels were used as aqueous mobile phase systems to examine the chromatographic behavior of cationic and nonionic surfactants. Among mobile phases used, a 0.01% methionine solution was found most suitable for the separation of cetylpyridinium chloride (CPC) from the mixture of nonionic surfactants on kieselguhr layers. The separation is not influenced by the presence of metal cations as impurities in the sample. None of the dyes, except ammonium purpurate and malachite green, hamper the separation. The exposure of the sample to UV radiation (λ = 254 nm) also does not have any adverse effect on the separation of CPC from TritonX-100 and Brij-35. The R _F values of surfactants were found to vary marginally on substitution of l-methionine by its d-isomer in the mobile phase or by the change in pH of the mobile phase (0.01% l-methionine) from 2.9 to 8.8. The proposed method can also be used for preparative thin layer chromatography.

Effect of Electrolytes and Correlations for Salinities at the Optimum Formulation of Sodium Dodecyl Benzene Sulfonate Microemulsions

The influences of different kinds of electrolytes on sodium dodecyl benzene sulfonate microemulsions were investigated in this work. Electrolyte cations had a strong influence on the microemulsion phase behavior. The higher the valence of the cation was, the stronger the influence of the electrolyte on the microemulsion phase inversion and the higher the optimum solubilization parameters, ordered as AlCl₃ > MgCl₂ > NH₄Cl > KCl > NaCl. The anion in electrolytes showed a relatively weak influence. The influences of anions with equal valence are almost the same for sodium salts, and a lower valence had a stronger impact on microemulsion phase inversion, ordered as Cl^? > CO₃^2? = SO₄^2? > PO₄^3?. The change of anions in sodium salts had little influence on the optimum solubilization parameters , all in the range of 5.301 ± 0.105 g_oil/g_surfactant. The efficiency ratio of electrolytes was defined based on the cationic charge concentration in mol/l. The efficiency ratios for electrolytes with monovalent cations were inversely proportional to (1 + Z_i), where Z_i is the anion valence, but this was not true for electrolytes with higher valence cations. For a microemulsion using electrolyte mixtures, the efficiency ratio shows a linear relationship with that of the component salts and the composition of the mixture.     

Optimization of synthesizing leucine-binding nano-sized magnetite by a two-step transformation

The optimum conditions for synthesizing leucine (Leu)-binding nano-sized magnetite (NSM) particles by a two-step transformation (TST) process were studied. The formation and magnetization of as-synthesized NSM particles were investigated through variation of the acidity, the type of surface modifier, and the nature of the acid for pH adjustment. With increased acidity, the saturation magnetization of the NSM particles decreased, but the amount of Leu coated on the surface of NSM particles increased. After the influence of hydroxyl (OH⁻) groups on the surface of NSM particles was removed by using the dicarboxyl anion (C₂O₄²⁻) as a ligand in the first step, Leu was successfully bound with NSM particles in the second step. However, when polyethylene glycol (PEG) was used as a surface modifier, it was difficult to form the Leu-to-NSM particle complex. In terms of the acid used to modify pH, H₂SO₄ was slightly less effective than HCl in achieving saturation magnetization because the coordination for SO₄²⁻ anions is stronger than that of Cl⁻ anions. The preparation of other amino acid-binding NSM particles can be optimized in an analogous manner.     

Synthesis of Indium Nanowires by Galvanic Displacement and Their Optical Properties

Single crystalline indium nanowires were prepared on Zn substrate which had been treated in concentrated sulphuric acid by galvanic displacement in the 0.002 mol L⁻¹ In₂(SO₄)₃-0.002 mol L⁻¹ SeO₂-0.02 mol L⁻¹ SDS-0.01 mol L⁻¹ citric acid aqueous solution. The typical diameter of indium nanowires is 30 nm and most of the nanowires are over 30 μm in length. XRD, HRTEM, SAED and structural simulation clearly demonstrate that indium nanowires are single-crystalline with the tetragonal structure, the growth direction of the nanowires is along [100] facet. The UV-Vis absorption spectra showed that indium nanowires display typical transverse resonance of SPR properties. The surfactant (SDS) and the pretreatment of Zn substrate play an important role in the growth process. The mechanism of indium nanowires growth is the synergic effect of treated Zn substrate (hard template) and SDS (soft template).     

Synthesis of Manganese Oxide Embedded Carbon Nanofibers as Effective Biomimetic Enzymes for Sensitive Detection of Superoxide Anions Released from Living Cells

Carbon nanofiber/manganese oxide (CNF‐MnO) hybrid nanofibers are synthesized by calcination of potassium permanganate (KMnO₄) loaded bacterial cellulose (BC) hydrogels. The chemical structure, morphology, performance, and application of CNF‐MnO aerogels are characterized and studied. The results revealed that MnO nanoparticles are uniformly deposited on the surface of CNF which derived from BC hydrogels. An amperometric superoxide anions (O₂^??) sensor is fabricated by the immobilization of the CNF‐MnO aerogels on a glassy carbon electrode, which displays a linear amperometric response with a high sensitivity of 76.2 µA cm^?2 × 10^?3m ^?1 and a low detection limit of 1.2 × 10^?9m in the concentration range of 5.0 × 10^?9m – 2.5 × 10^?6m . The successful detection of O₂^?? released from cancer cells verifies the potential application in biomedical field.     

Simultaneous determination of trace aluminum (III), copper (II) and cadmium (II) in water samples by square-wave adsorptive cathodic stripping voltammetry in the presence of oxine

A validated adsorptive cathodic stripping voltammetry method is described for simultaneous determination of Al(III), Cu(II) and Cd(II) in water samples. In acetate buffer (pH 5) containing 10 μM oxine, these metal ions were determined as oxine complexes following adsorptive accumulation onto the HMDE at −0.05 V versus Ag/AgCl/KCl_s. The best signal to noise ratio was obtained using a square wave of scan increment 10 mV, frequency 120 Hz, and pulse-amplitude 25 mV. Limits of detection as low as 0.020 μg L⁻¹ Al(III), 0.012 μg L⁻¹ Cu(II) and 0.028 μg L⁻¹ Cd(II) were achieved. Interference due to various cations (K(I), Na(I), Mg(II), Ca(II), Mn(II), Fe(III), Bi(III), Sb(III), Se(IV), Pb(II), Zn(II), Ni(II), Co(II)), anions (Cl⁻, NO³⁻, SO₄ ²⁻, PO₄ ³⁻) and ascorbic acid was minimal as the measured signals change by 4% at the maximum. The stripping voltammetry method was successfully applied for simultaneous determination of Al(III), Cu(II) and Cd(II) in tap and natural bottled water samples.     

Removal of phosphate from aqueous solutions by iron nano-particle resin Lewatit (FO36)

Lewatit FO36 resin was covered with Fe (III) nano-particles, and it was used as a new way to eliminate phosphate. Column experiments were carried out in 11 stages in fixed bed columns with constant flow rate of 9 ml/min and the empty bed contact time (EBCT) of 2.1 min. The adsorption capacity was calculated for different concentration of phosphate solutions. After resin was regenerated by using NaOH and NaCl solutions, the adsorption capacity of resin was computed for 6mg/L of phosphate, typically. The adsorption capacity of resin was checked again a typical concentration of phosphate. The adsorption capacity measurements of regenerated resin show that the concentration of phosphate reached to 1.6mg/g after an 8.5% decrease when the initial concentration of phosphate is 6 mg/L. Competition of anions with phosphate was analyzed using chloride, sulfate, bicarbonate and a combination of these anions. Finally the effect of resin in phosphate removal was studied for a typical real sample, and the data was analyzed using statistical software (SPSS 13). The statistical results indicated that Cl⁻, SO₄³⁻, HCO₃⁻ and combined competing anions did not have a strong influence on the phosphate removal efficiency.     

Chemical fixation of carbon dioxide to dimethyl carbonate from propylene carbonate and methanol using ionic liquid catalysts

The synthesis of dimethyl carbonate (DMC) through the transesterification of propylene carbonate (PC) with methanol was investigated by using imidazolium salt ionic liquid catalysts. 1-alkyl-3-methyl imidazolium salts of different alkyl group (C₂, C₄, C₆, C₈) and anions (Cl⁻, Br⁻, BF₄⁻, PF₆⁻) were used for catalysts. The reaction was carried out in an autoclave at 140–180°C under carbon dioxide pressure of 1.48–5.61 MPa. The imidazolium salts of shorter alkyl group, and more nucleophilic counter anion exhibited higher catalytic activity. The conversion of PC increased as CO₂ pressure and reaction temperature increased. Kinetic studies were also performed to better understand the reaction mechanism. This paper was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Extraction and separation of D/L-lactic acid in simulated fermentation broth

The recovery of lactic acid from fermentation broth plays an important part in production of lactic acid. In this case, the extraction of lactic acid from simulated fermentation broth was processed by tri-n-octylamine dissolved in oleyl alcohol. The extraction efficiency was investigated with several variables, and the optimal condition of extraction of lactic acid (10 mg mL⁻¹) from aqueous solution was tri-n-octylamine/oleyl alcohol (30/70, v/v) and solvent phase/ fermentation (1/2, v/v) stirred for 60 min under room temperature. The optimal back extraction of lactic acid was obtained by hot water (∼90 °C) with solvent phase/water (1/4, v/v). The back extracted racemic lactic acid was direct enantiomeric analyzed and separated by chiral ligand chromatography due to strict requirement of absolute configuration in pharmaceutical field and food science. The effect of various parameters on enantioselectivity was discussed and the (L)-phenylalaninamide·HCl (6.0 mmol L⁻¹) and CuSO⁴·5H₂O (3.0 mmol L⁻¹) dissolved in methanol/water (5/95, v/v) at pH=6.0 was the suitable mobile phase for chiral ligand exchange separation of (D, L)-lactic acids. By the investigations, a convenient systemic method was established for extraction and separation of (D, L)-lactic acid.     

The antioxidant properties of lycopene concentrate extracted from tomato paste

Lycopene concentrate (LC) containing 50 wt% lycopene was extracted from tomato paste. The antioxidant properties of LC were evaluated by means of chemiluminescence in four models. The four models were superoxide anions generated from pyrogallol autoxidation, hydroxyl radicals from Fenton reaction, singlet oxygens from OH⁻−NaClO−H₂O₂, and lipid peroxidation from 2,2′-azobis(2-amidinopropane)dihydrochloride-induced γ-linolenic acid. LC was an effective scavenger toward superoxide anions, hydroxyl radicals, and singlet oxygens, and also it could effectively reduce lipid peroxidation. The 50% efficient concentrations (EC₅₀) toward superoxide anions, hydroxyl radicals, lipid peroxidation and singlet oxygen were 0.75, 0.05, 0.1, and 1 mg/mL, respectively. In addition, changes of antioxidant behaviors with time were investigated. The time requirements of LC for effectively scavenging superoxide anions, hydroxyl radicals, and inhibiting lipid peroxidation were not higher than 6, 6, and 18 s, respectively.     

Nonoxidative dehydrogenation and aromatization of methane over W/HZSM‐5‐based catalysts

Highly active and heat‐resisting W/HZSM‐5‐based catalysts for nonoxidative dehydro‐aromatization of methane (DHAM) have been developed and studied. It was found from the experiments that the W−H₂SO₄/HZSM−5 catalyst prepared from a H₂SO₄‐acidified solution of ammonium tungstate (with a pH value at 2–3) displayed rather high DHAM activity at 973–1023 K, whereas the W/HZSM‐5 catalyst prepared from an alkaline or neutral solution of (NH₄)₂WO₄ showed very little DHAM activity at the same temperatures. Laser Raman spectra provided evidence for existence of (WO₆)^n- groups constructing polytungstate ions in the acidified solution of ammonium tungstate. The H₂‐TPR results showed that the reduction of precursor of the 3% W–H₂SO₄/HZSM‐5 catalyst may occur at temperatures below 900 K, producing W species with mixed valence states, W⁵⁺ and W⁴⁺, whereas the reduction of the 3% W/HZSM‐5 occurred mainly at temperatures above 1023 K, producing only one type of dominant W species, W⁵⁺. The results seem to imply that the observed high DHAM activity on the W–H₂SO₄/HZSM‐5 catalyst was closely correlated with (WO₆)^n- groups with octahedral coordination as the precursor of catalytically active species. Incorporation of Zn (or La) into the W–H₂SO₄/HZSM‐5 catalyst has been found to pronouncedly improve the activity and stability of the catalyst for DHAM reaction. Over a 2.5% W–1.5% Zn–H₂SO₄/HZSM‐5 catalyst and under reaction conditions of 1123 K, 0.1 MPa, and GHSV=1500 ml/(h g−cat.), methane conversion (XCH₄) reached 23% with the selectivity to benzene at ∼96% and an amount of coke for 3 h of operation at 0.02% of the catalyst weight used. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular Spin Ladders Constructed from [Ni(dmit)2]− Building Blocks: Synthesis, Structure and Physical Properties

Abstract  A new ion-pair complex [1-(4-bromobenzyl)-3-methylpyridinium][Ni(dmit)₂] (1), in which dmit = 4,5-dimercapto-1,3-dithiole-2-thione, has been synthesized and structurally characterized. The anions of [Ni(dmit)₂]⁻ stack into dimers, which further construct into a two-leg ladder through lateral S···S interactions. The weak H-bonding interactions of C–H···S and van de Waals interactions between anion and cations were observed. The magnetic susceptibilities measured from 2–300 K indicate an AFM exchange interaction domination and an AFM ordering below ~8 K. The best fit to magnetic susceptibility above 40 K, using a dimer model with s = ?, gives rise to Δ/k_B = 29.8 K, zJ′ = −0.72 K, C = 3.40 × 10⁻³ emu K mol⁻¹ and χ ₀ = −5.8 × 10⁻⁶ emu mol⁻¹ with a fixed g = 2.0. Cyclovoltammetry revealed two quasi-reversible one-electron steps, which are attributed to Ni(IV/III) and Ni(III/II) redox couples. Graphical Abstract  [A novel complex [1-(4-bromobenzyl)-3-methylpyridinium][Ni(dmit)₂] has been synthesized and structurally characterized. The anions of [Ni(dmit)₂]⁻ stack into dimers, which further construct into two-leg ladder through lateral S···S interactions. The weak H–bonding interactions of C–H···S and van de Waals interactions between anion and cations were observed. Moreover, its magnetic property and electrochemical property have been investigated] .     

Kinetic characterization of Prussian Blue-modified graphite electrodes for amperometric detection of hydrogen peroxide

Prussian Blue-modified graphite electrodes (G/PB) with electrocatalytic activity toward H₂O₂ reduction were obtained by PB potentiostatic electrodeposition from a mixture containing 2.5 mm FeCl₃ + 2.5 mm K₃[Fe(CN)₆] + 0.1 m KCl + 0.1 m HCl. From cyclic voltammetric measurements, performed in KCl aqueous solutions of different concentrations (5 × 10⁻²–1 m), the rate constant for the heterogeneous electron transfer (k _s) was estimated by using the Laviron treatment. The highest k_s value (10.7 s⁻¹) was found for 1 m KCl solution. The differences between the electrochemical parameters of the voltammetric response, as well as the shift of the formal potential, observed in the presence of Cl⁻ and NO₃⁻ compared to those observed in the presence of SO₄²⁻ ions, points to the involvement of anions in the redox reactions of PB. The G/PB electrodes showed a good electrochemical stability proved by a low deactivation rate constant (0.8 × 10⁻¹² mol cm² s⁻¹). The electrocatalytic efficiency, estimated as the ratio , was found to be 3.6 (at an applied potential of 0 mV vs. SCE; Γ = 5 × 10⁻⁸ mol cm⁻²) for a H₂O₂ concentration of 5 mm, thus indicating G/PB electrodes as possible H₂O₂ sensors.     

Fast atom bombardment and tandem mass spectrometry of phosphatidylserine and phosphatidylcholine

Fast atom bombardment (FAB) desorption of phosphatidylserine and various phosphatidylcholines produces a limited number of very informative negative ions. Especially significant is the formation of (M-H)⁻ ions for phosphatidylserine, a compound which does not yield informative high mass ions by other ionization methods. Phosphatidylcholines of not yield (M-H)⁻ ions but instead produce three characteristic high mass ions, (M-CH ₃ ⁺ _⁻, [M-HN(CH₃) ₃ ⁺ ]⁻ and [M-HN(CH_{3 3} ⁺ -C₂H₂]⁻. Both classes of lipids also yield anions attributed to the carboxylate components of these complex lipids. FAB desorption in combination with collisional activation allows for characterization of fragmentation and determination of structural features. Collisional activation of the carboxylate anion fragments from the complex lipids is especially informative. Structural characterization of the fatty acid chain can be achieved as the released saturated carboxylate anions undergo a highly specific 1,4-elimination of H₂, which results in the losses of the elements of CH₄, C₂H₆, C₃H₈...in a fashion entirely consistent with the chemistry of carboxylate anions desorbed from free fatty acids. These C_nH_2n+2 losses begin at the alkyl terminus and progress along the entire alkyl chain. Modified fatty acids undergo a similar fragmentation; however, the modification affects the series of C_nH_2n+2 losses in a manner which permits determining the type of modification and its location on the fatty acid chain.