Prion protein detection in serum using micromechanical resonator arrays

Prion proteins that have transformed from their normal cellular counterparts (PrP^c) into infectious form (PrP^res) are responsible for causing progressive neurodegenerative diseases in numerous species, such as bovine spongiform encephalopathy (BSE) in cattle (also known as mad cow disease), scrapie in sheep, and Creutzfeldt-Jakob disease (CJD) in humans. Due to a possible link between BSE and CJD it is highly desirable to develop non-invasive and ante mortem tests for the detection of prion proteins in bovine samples. Such ante mortem tests of all cows prior to slaughter will help to prevent the introduction of PrP^res into the human food supply. Furthermore, detection of PrP^res in donated blood will also help to prevent the transmission of CJD among humans through blood transfusion. In this study, we have continued development of a micromechanical resonator array that is capable of detecting PrP^c in bovine blood serum. The sensitivity of the resonators for the detection of PrP^c is further enhanced by the use of secondary mass labels. A pair of antibodies is used in a sandwich immunoassay format to immobilize PrP^c on the surface of resonators and attach nanoparticles as secondary mass labels to PrP^c. Secondary mass labeling is optimized in terms of incubation time to maximize the frequency shifts that correspond to the presence of PrP^c on the surface of resonators. Our results show that a minimum of 200 pg mL⁻¹ of PrP^c in blood serum can be detected using micromechanical resonator arrays.     

Detoxification of antimony by selenium and their interaction in paddy rice under hydroponic conditions

Antimony (Sb) contamination has become a growing concern in recent years. Strategies for reducing Sb contamination and its related health risks are urgently desired. This study was conducted to explore the possibility of selenium (Se) detoxification on Sb toxicity in paddy rice in order to find a feasible method to reduce the health risk of Sb pollution. Seedlings of paddy rice were exposed to 5 mg L⁻¹ Sb (KSbC₄H₄ O₇·1/2H₂O), in the presence of Se (Na₂SeO₃) at 0.1, 1, 5 mg L⁻¹ in culture solution, with no Sb and Se addition as the control. Paddy rice took up Sb greatly and the highest Sb contents measured among all treatments in this experiment in the leaves, stems and roots were 65.5, 298.5 and 195.7 mg kg⁻¹, respectively. Without Sb addition in the solution, single exposure to 0.1 mg L⁻¹ Se remarkably reduced the malondialdehyde (MDA) formation in paddy rice,demonstrating the beneficial effect of Se at low dosages. The addition of 5 mg L⁻¹ Sb was found to generate toxicity to paddy rice, showing as decreased biomass and increased leaf MDA content in paddy rice, while addition of 1 mg L⁻¹ Se mitigated the toxicity of Sb, as seen with the decreased leaf MDA content and increased biomass, indicating antidotal role of Se to Sb. In addition, the presence of 0.1, 1, 5 mg L⁻¹ Se generally decreased the accumulation of Sb in the leaves, stems and roots in paddy rice. Toxicity was also seen when paddy rice was exposed to single Se at 1 and 5 mg L⁻¹ levels, however, 5 mg L⁻¹ Sb addition was found to decrease the contents of Se in the leaves/stems whereas increased them in roots, accompanied with decreased MDA contents and increased biomass in paddy rice, indicating a possible detoxification role of Sb to Se too. Therefore, Sb, although toxic, could also be an antitoxin to Se in paddy rice at certain condition. Our results showed that Se could alleviate Sb toxicity efficiently in paddy rice through two effects as antagonism and antioxidation.     

Glucose-induced heat production, insulin secretion and lactate production in isolated Wistar rat pancreatic islets

Transplantation of pancreatic islets is efficient in improving the metabolic control and quality of life and in preventing severe hypoglycemia in patients with brittle type 1 diabetes mellitus. More accurate methods to assess islet viability would be extremely useful in designing target interventions for islet cytoprotection and in reducing the number of islets required to achieve insulin independence. Here we report on an application of calorimetry to evaluate the metabolic response of pancreatic islets to glucose stimulation. A significant increase in metabolic heat was produced by islet samples when consecutively subjected to 2.8 and 16.3 mmol L⁻¹ glucose. Under these glucose concentrations, 1000 islets released average heat values of 9.16 ± 0.71 mJ and 14.90 ± 1.21 mJ over 50 min, respectively. Additionally, the glucose stimulation indexes were 1.67 ± 0.30 for insulin, 1.72 ± 0.13 for heat and 2.91 ± 0.50 for lactate, raising the important possibility of substituting the secreted insulin index/ratio by the index/ratio of the heat released in the evaluation of Langerhans islets viability for transplantation. Altogether, our results demonstrate the applicability of calorimetry to assess the quality of isolated pancreatic islets and to study vital islet functions.     

Phosphonobetaine/sulfur dioxide copolymer by Butler’s cyclopolymerization process

The zwitterionic monomer, ethyl 3-(N,N-diallylammonio)propanephosphonate and sulfur dioxide were cyclocopolymerized in DMSO using azobisisobutyronitrile or ammonium persulfate as initiators to afford a pH-responsive polyphosphonobetaine/SO₂ (PPB/SO₂) copolymer. The polymers, on treatment with HCl and NaOH, gave the aqueous solutions of the corresponding cationic polyphosphononic acid (CPP) and anionic polyphosphonate (APP). The solution properties of the PPB having two pH-responsive functionalities were investigated in detail by potentiometric and viscometric techniques. Basicity constants of the amine and phosphonate groups in APP were found to be “apparent” and as such follow the modified Henderson–Hasselbalch equation. The incorporation of SO₂ moiety has resulted in the decrease of basicity constant of the nitrogens in the copolymer by staggering ?2 units of log K in compare to that of the corresponding homopolymer. The basicity difference is expected to have an effect on the chelating properties of the polymers. In contrast to many polycarbo- and -sulfobetaines, the PPB was all found to be soluble in salt-free water as well as in salt (including Ca²⁺ and Li⁺)-added solutions. The PPB demonstrated ‘antipolyelectrolyte’ viscosity behavior and found to have higher viscosity values in LiCl than in NaCl or NaI.     

Thermal stability of solid and aqueous solutions of humic acid

The effects of temperature on the stability of a soil humic acid were studied in the present work. Solid samples of Gohy-573 humic acid (HA) and dissolved ones in aqueous solution (pH 6.0, 0.1 mol L⁻¹ NaClO₄) were investigated in order to understand the impact of temperature on the chemical properties of the material. The methods applied to solid samples in the present investigation were thermogravimetric analysis (TGA), temperature-programmed desorption coupled with mass spectrometry (TPD-MS), and in situ diffuse reflectance infrared Fourier transformed spectroscopy (in situ DRIFTS). Humic acid samples were studied in the 25-800 °C range, with focus on thermal/chemical processes up to 250 °C. The reversibility of the changes observed was investigated by cyclic changes to specified temperature ranges (40-110 °C). All measurements were conducted under inert-gas atmosphere in order to avoid samples combustion at increased temperatures. Aqueous solutions were analyzed by UV-vis absorption spectroscopy after storage at temperatures up to 95 °C, and storage times up to 1 week. For temperatures below 100 °C experiments on solid and aqueous samples have shown results which were consistent to each other. The amount of water desorbed is temperature dependent and up to 70 °C this process was totally reversible. Above 70 °C an irreversible loss of water was also observed, which according to UV-vis spectroscopy corresponds to water produced by condensation leading to more condensed polyaromatic structures. The water released up to 110 °C was about 7 wt% of the total mass of the dried humic acid, where less than 50% corresponded to reversibly adsorbed water. At higher temperatures (>110 °C), gradual decomposition resulting in the formation of carbon dioxide (110-240 °C), and carbon monoxide (140-240 °C) takes place. Hence, thermal treatment of Gohy-573 humic acid above 70 °C results in irreversible structural changes, that could affect chemical properties (e.g., complex formation) of the material.     

Effect of surfactants on the voltammetric response and determination of an antihypertensive drug

The effect of adding surface-active agents to electrolytes containing terazosin, an antihypertensive drug, on the voltammetric response of glassy carbon electrode was studied. The current signal due to the oxidation process was a function of the amount of terazosin, pH of the medium, type of surfactant, and accumulation time at the electrode surface. Two surfactants were used, an anionic type, sodium dodecyl sulfate (SDS) and a cationic type, cetyl trimethyl ammonium bromide (CTAB). Addition of SDS to the terazosin-containing electrolyte was found to enhance the oxidation current signal while CTAB showed an opposite effect. Beside the interfacial interaction of the surfactant with the electrode surface in reference to the bias applied potential and the charge of surfactant, terazosin-surfactant interaction in the electrolytic solution was found to be critical to the magnitude of current signal. Addition of SDS to terazosin-containing buffer solution resulted in a decrease in the drug absorption spectrum both in the ultra-violet and visible (UV-vis) regions. Moreover, NMR measurements showed considerable chemical shifts for the aromatic protons of the quinazolinyl moiety of the terazosin in presence of SDS. The affected aromatic protons are positioned next to the interacting protonated amino-group of the terazosin with the charged sulfonate-group of SDS. On the other hand, addition of CTAB did not cause noticeable changes both to the UV-vis and NMR spectra of the drug. The use of SDS in the electrochemical determination of terazosin using linear sweep voltammetry and differential pulse voltammetry at solid glassy carbon electrode enhanced the detection limit from 6.00 × 10⁻⁷ mol L⁻¹ in absence of surfactant to 4.58 × 10⁻⁹ mol L⁻¹ when present. The validity of using this method in the determination of drug active ingredient in urine samples and tablet formulations was also demonstrated.     

Fluorescence quantification of tetracycline in the presence of quenching matrix effect by means of a four-way model

In this work, a four-way tensor is used to model the quenching effect in fluorescent measurements. By means of the analysis of excitation-emission matrices obtained in the determination of tetracycline in tea, which acts as quencher, it is shown as the impossibility to use a calibration, or an addition standard based on a three-way model. It is analysed the quencher multiplicative effect made on the tetracycline signal by means of an ANOVA. However, by arranging the experimental data in a four-way tensor, it is viable to perform a calibration based on the parallel factor analysis, PARAFAC, decomposition and a four-way partial least squares, 4-PLS, regression to quantify the tetracycline in the presence of the matrix quencher effect. 4-PLS calibration provides better results. In the range from 40 to 220 μg L⁻¹ gives an average of relative errors in absolute value equal to 8.02% in prediction (3.40% in calibration). The repeatability as standard deviation in this range is 5.08 μg L⁻¹ and the method is accurate, slope and intercept being statistically equal to 1 and 0, respectively when a regression calculated versus true concentration is performed. Moreover, it has a decision limit (CCα) of 13.87 μg L⁻¹ for a probability of false positive, α, equal to 0.05 and a capability of detection (CCβ) of 26.63 μg L⁻¹ (for probabilities of false positive, α, false negative, β, equals to 0.05).     

Effect of the rare earth in the perovskite-type mixed oxides AMnO3 (A=Y, La, Pr, Sm, Dy) as catalysts in methanol oxidation

The effect of the rare earth in the perovskite-type mixed oxides AMnO₃ (A=Y, La, Pr, Sm, Dy) on catalytic properties in methanol oxidation was investigated in this work. The perovskites were prepared by reactive grinding in order to enhance the specific surface area in comparison with other classical synthesis procedures. These catalysts were characterized by N₂ adsorption, X-ray diffraction, H₂ temperature-programmed reduction (TPR-H₂), O₂-, CH₃OH- and CO₂-temperature-programmed desorption (TPD). The activity of the five catalysts under study in the methanol oxidation reaction was evaluated. The behaviour of the α-O₂ from the surface of the perovskite was strongly related to the nature of the A-site cation and particularly to its electronegativity but also to its density. Concerning the β-O₂ from the bulk, the rare earth only induces an indirect effect notably due to structural modifications. As suggested in a previous study, the activity in methanol oxidation was directly linked with the surface oxygen density. Under an excess of α-oxygen, the reaction intermediate was found to be a monodentate carbonate that decomposes into CO₂. The stability of monodentate carbonates was also found to be related to the electronegativity of the rare earth during both CH₃OH- and CO₂-temperature-programmed desorption. However, as soon as a lack of α-oxygen was observed in the structure, the dominant reaction intermediate was a bidentate carbonate that induces a consumption of anion vacancies in spite of the production of CO₂. Nevertheless, the accumulation of these carbonates leads to a decrease in the oxidation rate since their desorption requires high temperatures.     

Raman spectroscopic investigation on the microenvironment of the liver tissues of Zebrafish (Danio rerio) due to titanium dioxide exposure

Nano titanium dioxide (nTiO₂), generally considered to be toxicologically inert, is manufactured in large quantities and extensively applied in consumer products. The small size and large surface area endow them with an active group or intrinsic toxicity. Advances in instrumentation are making Raman spectroscopy the tool of choice for an increasing number of (bio) chemical applications. One of the great advantages of this technique is its ability to provide information on the concentration, structure and interaction of biochemical molecules in their microenvironments within intact cells and tissues, non-destructively. Zebrafish (Danio rerio), one of the most important vertebrate model organisms used in developmental biology, are increasingly used in biomedical research, particularly as a model of human disease. In the present work, an attempt is made to study the effect of titanium dioxide, both nano and bulk, on the microenvironment of the liver tissues of Zebrafish using FT-Raman spectroscopy. The results of the present study suggest that TiO₂ exposure demonstrate a marked influence on the microenvironments of the liver tissues of Zebrafish. A shift to a higher wavenumber and an increase in the intensity of the band at ∼1087 cm⁻¹ in the TiO₂ exposed tissues suggest that some of the conformational changes resulting from the alkali recovery process takes place due to TiO₂ exposure. The decreased intensity ratio (I₃₂₂₀/I₃₄₀₀) observed in the titanium-exposed tissues suggests a decreased water domain size, which could be interpreted in terms of weaker hydrogen-bonded molecular species of water in the TiO₂ exposed tissues. The observed shift of COO⁻ bands to higher frequencies shows the disruption of salt bridges as a result of a change in the oppositely charged partners and due to the enhanced random coil conformation. The variation in the intensity ratio of the tyrosyl doublet (I₈₅₈/I₈₂₅) indicates variation in the hydrogen bonding of the phenolic hydroxyl group due to TiO₂ exposure. The results further suggest that the microenvironments are greatly altered due to titanium nano exposure when compared to titanium bulk. In conclusion, the results indicate that FT-Raman spectroscopy might be a useful tool for rapid assessment of nano particle biological interactions.     

Diels-Alder reaction volumes in the solid state and solution

The densities of anthracene, tetracyanoethylene, maleic anhydride, N-phenylmaleineimide, trans, trans-1,4-diphenylbuta-1,3-diene, and their Diels-Alder adducts were measured in the solid state and in solution at 25 °C. The reaction volumes in the solid state were calculated from the difference in molar volumes. They turned out to be low, close to each other (–4 to –11 cm³ mol^–1), and slightly different from the reaction volumes (–8±1 cm³ mol^–1) calculated from the van der Waals radii. The reaction volumes in solutions (–15 to –32 cm³ mol^–1) were found from the difference in partial molar volumes of the reactants in dioxane, acetonitrile, and 1,2-dichloroethane, The experimental Diels-Alder reaction volumes in solution are determined not only by the formation of new bonds in an adduct: a considerably higher contribution (to 75%) is made by a change in the volume of intermolecular empty spaces in solution on going from reactants to adducts.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2386–2390, November, 2004.     

Effect of the Heating Rate on Crystallization Kinetics of Mg84Ni12.5Y3.5 Amorphous Ribbons

Crystallization kinetics of Mg₈₄Ni_12.5Y_3.5 amorphous ribbons produced by the melt-spinning method, was studied by DSC analysis and X-ray diffraction. The effect of heating rate (from 2 to 240 K min^–1) was investigated in the temperature range from 298 to 673 K. The results showed that the crystallization process took place in two stages: a) crystallization of part of the amorphous matrix to an intermediate phase and hcp-Mg, and b) transformation of the intermediate phase and the remaining amorphous material to Mg₂Ni+Mg (solid solution of Y in Mg). Increasing the heating rate from 2 to 240 K min^–1 results in increases of the temperature difference between the two-step crystallization of the first stage transformation processes from 33 to 56 K and in increases of the temperature difference between the two-stage transformation from 62 to 97 K.This revised version was published online in November 2005 with corrections to the Cover Date.     

Nanostructured cupric oxide electrode: An alternative to amperometric detection of carbohydrates in anion-exchange chromatography

In this paper, a new and low cost copper/cupric oxide nanostructured electrode is presented as an alternative to the amperometric detection of carbohydrates in high-performance anion exchange chromatography. The modified copper electrodes were prepared by a simple and fast method which resulted in the obtainment of homogeneously distributed nanostructures adhered to the surface with controlled chemical nature. The results, when compared to conventional copper electrodes, exhibited considerable improvements in analytical results, including: 1) Better repeatability in consecutive glucose detections, in which the percent relative standard deviation improved from 15.1% to 0.279%. 2) Significant improvements in the stability of the baseline and a decrease of the stabilization time, going from several hours to approximately 15 min. 3) Considerable increase in the sensitivity towards glucose, from 5.02 nA min mg L⁻¹ to 25.5 nA min mg L⁻¹. 4) Improvements in the detectability with limits as low as 1.09 pmol. 5) Wide working range of concentrations (1 × 10⁻² to 1 × 10⁴ mg L⁻¹). 6) Good linearity with correlation coefficients greater than 0.998. 7) Possibility of detecting different molecules of carbohydrates (lactose, maltose, sucrose cellobiose, sorbitol, fructose, glucose, galactose, manose, arabitol, xylose, ribose and arabnose). In comparison to the electrode that is more employed for this type of application (gold electrode), the low cost, the possibility of detection at constant potential and the equivalent detection limits presented by the new electrode material introduced in this work emerge as characteristics that make this material a powerful alternative considering the detection of carbohydrates in anion exchange chromatography.     

Development and Validation of Liquid Chromatography-Tandem Mass Spectrometry Methods for the Quantification of Cefquinome,Ceftiofur, and Desfuroylceftiofuracetamide in Porcine Feces with Emphasis on Analyte Stability

Cefquinome and ceftiofur are β-lactam antibiotics used for the treatment of bacterial infections in swine. Although these antimicrobials are administered intramuscularly, the exposure of the gut microbiota to these cephalosporins is not well described. This exposure can contribute to the emergence and spread of antimicrobials in the environment and to the possible spread of antimicrobial resistance genes. To assess the impact of drug administration on the intestinal excretion of these antimicrobials it is essential to measure the amounts of native compound and metabolites in feces. Two (ultra)-high-performance liquid chromatography-tandem mass spectrometry ((U)HPLC–MS/MS) methods were developed and validated, one for the determination of cefquinome and ceftiofur and the other for the determination of ceftiofur residues, measured as desfuroylceftiofuracetamide, in porcine feces. The matrix-based calibration curve was linear from 5 ng g⁻¹ to 1000 ng g⁻¹ for cefquinome (correlation coefficient (r) = 0.9990 ± 0.0007; goodness of fit (gof) = 3.70 ± 1.43) and ceftiofur (r = 0.9979 ± 0.0009; gof = 5.51 ± 1.14) and quadratic from 30 ng g⁻¹ to 2000 ng g⁻¹ for desfuroylceftiofuracetamide (r = 0.9960 ± 0.0020; gof = 7.31 ± 1.76). The within-day and between-day precision and accuracy fell within the specified ranges. Since β-lactam antibiotics are known to be unstable in feces, additional experiments were conducted to adjust the sampling protocol in order to minimize the impact of the matrix constituents on the stability of the analytes. Immediately after sampling, 500 µL of an 8 µg mL⁻¹ tazobactam solution in water was added to 0.5 g feces, to reduce the degradation in matrix.     

Molar volumes and ion pairing of lithium halides in alcohols

The concentration dependence of the apparent molar volumes of lithium halides (and electrolytes in general) in alcohols (and solvents permitting association in general) is, in the first instance, due to changes in the degree of association and to the inherent difference between the apparent molar volumes of the ions and of the ion pairs. Previous publications on the molar volumes of electrolytes in organic solvents, disregarding altogether ion pairing, appear to be incorrect. Data from the literature for lithium chloride and lithium bromide in normal primary alcohols and several branched alcohols from C₁ to C₈ and data from our laboratory for lithium halides in 1-hexanol and 2-ethyl-1-hexanol served for the determination of φ _V and φ _E . Electrical and structural contributions to the values of these functions for the ions and for the ion pairs are discussed.     

Fibrillation Tendency of Cellulosic Fibers. Part 2: Effects of Temperature

The influences of temperature, concentration of swelling agents and fiber materials on the fibrillation tendency in various cellulosic fibers in aqueous solutions were investigated in terms of fibrillation stability and fibrillation sensitivities to alkali and heat. The fibrillation stability and the fibrillation sensitivity to swelling agents were evaluated with a critical point of fibrillation (CPF_conc.) that is the concentration of the swelling agents where fibrillation begins, and the ratio of initial increase in fibril number to increase in concentration of swelling agent (I_i). The fibrillation sensitivity to heat was estimated with the increase in I_i against temperature. The CPF_conc. of lyocell fiber was 16.7 mol/l water in ethanol/water mixture at 25 °C and decreased to 0 mol/l at 80 °C, indicating acceleration of the fibrillation at higher temperatures. The I_i of lyocell was enhanced from 3.50 to 7.57 count l/mol. The CPF_conc. increased in the order of viscose > cross-linked lyocell > modal > lyocell while the I_i decreased in the order of viscose < modal < cross-linked lyocell < lyocell at 40 °C. The I_i of lyocell fiber increased to the greatest extent with increase in temperature as compared with the other cellulosic fibers. Lyocell fiber has the lowest fibrillation stability and the highest fibrillation sensitivities to alkali and to heat resulting in the highest fibrillation tendency.     

Determination of arsenate in natural pH seawater using a manganese-coated gold microwire electrode

Direct electrochemical determination of arsenate (As^V) in neutral pH waters is considered impossible due to electro-inactivity of As^V. As^III on the other hand is readily plated as As⁰ on a gold electrode and quantified by anodic stripping voltammetry (ASV). We found that the reduction of As^V to As^III was mediated by elemental Mn on the electrode surface in a novel redox couple in which 2 electrons are exchanged causing the Mn to be oxidised to Mn^II. Advantage is taken of this redox couple to enable for the first time the electrochemical determination of As^V in natural waters of neutral pH including seawater by ASV using a manganese-coated gold microwire electrode. Thereto Mn is added to excess (∼1 μM Mn) to the water leading to a Mn coating during the deposition of As on the electrode at a deposition potential of −1.3 V. Deposition of As⁰ from dissolved As^V caused elemental Mn to be re-oxidised to Mn^II in a 1:1 molar ratio providing evidence for the reaction mechanism. The deposited As^V is subsequently quantified using an ASV scan. As^III interferes and should be quantified separately at a more positive deposition potential of −0.9 V. Combined inorganic As is quantified after oxidation of As^III to As^V using hypochlorite. The microwire electrode was vibrated during the deposition step to improve the sensitivity. The detection limit was 0.2 nM As^V using a deposition time of 180 s.     

Highly stereoselective anti-aldol reactions catalyzed by simple chiral diamines and their unique application in configuration switch of aldol products

Chiral derivatives of trans-1,2-diaminocyclohexane with different N,N-dialkyl groups in well-defined orientations have been synthesized, and applied as catalysts for the asymmetric aldol reaction between a variety of aldehydes and ketones. Enantiomeric catalyst 1j catalyzed the reaction in ethanol and provided excellent diastereoselectivity and enantioselectivity. Significantly, simple replacement of organic solvents with water switched the products of the aldol reactions from anti to syn configuration. Such catalytic reactions led to the products with anti to syn diastereoselectivity up to 99:1 in ethanol, while in water gave the products with syn to anti diastereoselectivity up to 99:1.     

Ion-beam irradiation effects on polyimide-UV–vis and infrared spectroscopic study

Ion-beam irradiation effects on polyimide, Kapton™, were studied with respect to optical and electronic properties. Stack films of Kapton™ (12.5 μm thick) were irradiated to various ion beams in air or vacuo at room temperature and subjected to ultraviolet–visible (UV–vis) spectroscopy, and change in absorbance and energy gap is discussed. The UV–vis absorption spectrum, which is assigned to the transition of electrons in benzene rings from π to π* orbital, upon He²⁺ (6 MeV/u) irradiation in air, shifted towards longer wavelength direction for all cases, and the shift was more obvious for higher linear energy transfer (LET) ion beams. The energy gap of the transition was estimated, and the H⁺ and He²⁺ ion beams caused little change in the transition energy gap Eg, while the heavier ions such as C⁶⁺ and Si¹⁴⁺ caused more significant decrease. This decrease is assumed to the structural changes around benzene rings, and the infrared spectroscopy revealed breakage in imide groups next to benzene ring in the repeating unit of polyimide.     

Solubility of β-carotene in ethanol- and triolein-modified CO2

Modification of an experimental device and methodology improved speed and reproducibility of measurement of solubility of β-carotene in pure and modified SuperCritical (SC) CO₂ at (313 to 333) K. Solubilities of β-carotene in pure CO₂ at (17 to 34) MPa ranged (0.17 to 1.06) μmol/mol and agreed with values reported in literature. The solubility of β-carotene in CO₂ modified with (1.2 to 1.6) % mol ethanol increased by a factor of 1.7 to 3.0 as compared to its solubility in pure CO₂ under equivalent conditions. The concentration of triolein in equilibrated ternary (CO₂ + β-carotene + triolein) mixtures having excess triolein reached values (0.01 to 0.39) mmol/mol corresponding to its solubility in pure SC CO₂ under equivalent conditions. Under these conditions, the solubility of β-carotene in triolein-modified CO₂ increased by a factor of up to 4.0 in relation with its solubility in pure CO₂ at comparable system temperature and pressure, reaching an uppermost value of 3.3 μmol/mol at 333 K and 32 MPa. Unlike in the case of ethanol, where enhancements in solubility where relatively independent on system conditions, solubility enhancements using triolein as co-solvent increased markedly with system pressure, being larger than using (1.2 to 1.6) % mol ethanol at about (24 to 28) MPa, depending on system temperature. The increase in the solubility β-carotene in SC CO₂ as a result of using ethanol or triolein as co-solvent apparently does not depend on the increase in density associated with the dissolution of the co-solvent in CO₂. Enhancements may be due to an increase in the polarizability of SC CO₂, which possibly growths markedly as triolein dissolves in it when the system pressure becomes higher.     

Coupled transport of Ag(I) ions through triethanolamine–cyclohexanone-based supported liquid membranes

Facilitated transport of silver(I) ions in acidic medium, across a supported liquid membrane (SLM) by using triethanolamine (TEA) as carrier, dissolved in cyclohexanone, has been investigated. The parameters studied are HNO₃ concentration variation in the feed, pH of the feed solution, carrier concentration in the membrane phase, silver(I) ions concentration in the feed phase and KCN concentration in the stripping phase. Increase in H⁺ concentration by increasing HNO₃ concentration from 0.5 to 1 M results into an increase in silver ions flux but a decrease in flux has been found beyond 1 M HNO₃ concentration in the feed, providing a maximum flux of 3.21 × 10⁻⁷ mol/m² s at 1 M HNO₃. Increase in TEA concentration inside the membrane enhances flux with its maximum value at 2.25 M TEA. Further increase in the concentration of TEA leads to a decreased rate of transport due to the increase in viscosity of membrane liquid. The optimum conditions for Ag(I) ions transport are 1 M HNO₃ (feed), 2.25 M TEA (membrane) and 1.5 M KCN in the stripping phase. It has been observed that Ag(I) flux across the membrane tends to increase with increase in Ag(I) ions concentration in the feed phase. Applying the studied conditions to silver plating waste solutions, Ag ions have been removed up to 99% in a time interval of 5 h.