Thermogravimetric characterization of styrene–divinylbenzene copolymers containing alpha-isopropylaminophosphonic acid groups

A commercial styrene–divinylbenzene copolymer was functionalized by multistep reactions with alpha-isopropylaminophosphonic acid groups. Three different functionalized copolymers were obtained in which the phosphonic groups are in meta (1E), para (2E), and ortho (3E) positions. The thermal behavior was studied using the TG/IR hyphenated technique and kinetic analysis of thermo-oxidation under nonisothermal conditions. The evolved gas analysis confirms the partial thermo-oxidative degradation of polymeric materials, with significant preservation of the aromatic ring. The kinetic analysis was performed by three methods: Friedman, Flynn–Wall–Ozawa, and nonparametric kinetic.     

Complexation in the heptanoic acid–heptylamine system

The complexation between heptylamine and heptanoic acid has been elucidated at 298.15 K using spectroscopic methods and also by measuring macroscopic quantities such as viscosity, conductivity and surface tension. Fourier transform IR and ¹³C NMR measurements point towards the existence of a compound consisting of one amine molecule and one acid molecule in an equimolecular mixing ratio. These suggestions are supported by viscosity and surface tension measurements. This compound is further able to interact with excess acid, but similar behaviour is not observed with excess amine. The equimolecular compound behaves like a catanionic surfactant; this is seen in the phase diagram for the heptylamine–heptanoic acid–water system at 298.15 K, where the dominating phase is the lamellar liquid-crystalline phase. This phase is in equilibrium with almost pure water. At low water content a solution phase extending from the binary heptylamine–heptanoic acid axis and covering all mixing ratios between the amine and the acid is also present. Received: 15 March 1999/Accepted in revised form: 5 July 1999     

The acetylsalicylic acid–bromine system for multicomponent kinetic determinations

When acetylsalicylic acid (ASA) is added to a bromine solution, slow decay of the bromine concentration occurs. Hydrolysis of ASA yields salicylic acid (SA) slowly, and bromine reacts rapidly with SA but not with ASA. Simulated reaction profiles based on a two-step reaction scheme agree closely with the experimental profiles. This behaviour can be used to develop kinetic methods for resolution of mixtures of ASA and a second component that reacts rapidly with bromine. A remarkable practical feature of these methods is that the faster the reaction between bromine and the second component, the simpler and easier the analytical method. The reaction between hydroquinone (HQ) and bromine is rapid and a very simple analytical method is proposed. Mean validation errors of 2.8% for HQ and 7.2% for ASA have been found with concentration ratios [ASA]:[HQ] ranging between 0.32 and 19.4. The reaction between paracetamol (AAP) and bromine is not so fast and more complicated calibration methods are required. After use of a calibration plane mean validation errors of 2.7% for AAP and 8.1% for ASA have been found with concentration ratios ranging between 1.28 and 77.5. Similar kinetic approaches should be possible with many other mixtures of ASA and a second fast-reacting component, because bromine reacts with many inorganic and organic species by oxidation-reduction, substitution, and addition reactions.     

Interaction in the zinc perchlorate–urea–perchloric acid–water system at 25°С

Heterogeneous equilibria in the zinc perchlorate–urea–perchloric acid–water quaternary system at 25°С were studied by investigating solubility. The crystallization regions were found for the initial solid components, eutonic compositions of the ternary systems constituting the quaternary system, binary compounds of urea with zinc perchlorate and perchloric acid, and also two new coordination compounds containing simultaneously zinc perchlorate, urea, and perchloric acid: ZnClO₄ · 4CO(NH₂)₂ · HClO₄ and ZnClO₄ · 2CO(NH₂)₂ · HClO₄.     

Interaction in the nickel perchlorate–acetamide–perchloric acid–water system at 25°С

Heterogeneous equilibria in the nickel perchlorate–acetamide–perchloric acid–water quaternary system at 25°С were studied by studying solubility. The crystallization regions were determined for the initial solid components, eutonic compositions of the ternary systems constituting the quaternary system, binary compounds of acetamide with nickel perchlorate and perchloric acid, and also two new coordination compounds containing simultaneously nickel perchlorate, acetamide, and perchloric acid: Ni(ClO₄)₂ · 4CH₃CONH₂ · HClO₄ and Ni(ClO₄)₂ · 2CH₃CONH₂ · HClO₄.     

Solid–liquid equilibria in the acetic acid–propanoic acid and propanoic acid–trifluoroacetic acid systems

Solid–liquid equilibria in the binary systems, propanoic acid–acetic acid and propanoic acid–trifluoroacetic acid, were measured by a synthetic method. A solid compound (1:1) was found in the propanoic acid–trifluoroacetic acid system. The obtained activity coefficients were successfully fitted by the Wilson equation.     

Phase state diagram of a poly(amic acid)–solvent–nonsolvent system

Phase behavior and structure formation was studied using optical interferometry, nephelometry, and refractometry in the polymer–solvent–nonsolvent system for DMF solutions of two poly(amic acids): based on 3,3′,4,4′-benzophenonetetracarboxylic acid dianhydride and meta-phenylenediamine (PAA-1) and pyromellitic acid dianhydride and 4,4′-oxydianiline (PAA-2). Distilled water and its mixtures with DMF were used as a nonsolvent. According to the results of the study, isothermal cross sections of the phase state diagram in the threecomponent system were plotted, the position of the critical point, the spinodal, and the conodes were determined, the movement of the figurative points in the system was traced depending on the nonsolvent composition.     

Phase diagram and dissolution studies of the fenofibrate–acetylsalicylic acid system

Enhancement of the dissolution rate of poorly soluble compounds through the formation of drug–drug eutectics was investigated using fenofibrate and acetylsalicylic acid. Solid–liquid equilibria in the system under study were investigated by differential scanning calorimetry (DSC). The phase diagram for the whole range of compositions was constructed. In addition, existence of a metastable polymorph of fenofibrate has been confirmed. The investigation has revealed that acetylsalicylic acid and fenofibrate form a simple eutectic mixture containing 0.958 mol fraction of fenofibrate at the eutectic point. Dissolution rate improvement of fenofibrate correlated with the phase diagram. The amount of fenofibrate released from the solid dispersions that contained fenofibrate as the eutectic mixture with acetylsalicylic acid was at least threefold higher compared to untreated fenofibrate.     

Extraction of triply charged metal cations in aqueous phase-separating system antipyrine–sulfosalicylic acid–water

Extraction of macro amounts of triply charged metal cations (0.01–0.05 mol L^?1) in aqueous phase-separating system antipyrine–sulfosalicylic acid–water containing no organic solvent is studied. Optimum conditions for phase separation are established and the influence of the concentrations of the major components, inorganic acids (H₂SO₄, HCl), salting-out agents, and the volume of the aqueous phase on the process in question is determined. It was found that the optimum antipyrine/sulfosalicylic acid ratio in the system was (1.5–2.0): 1.0. The introduction of inorganic salting-out agents causes the volume of the organic phase (0.8–1.8 mL) to increase to 2 mL and more. The extractability series of triply charged metal ions is as follows: Tl > Fe > Sc > In > Ga. It was shown that inorganic salts and hexamine influence the degree of extraction of metal cations and that inorganic acids and water affect the distribution mechanism and the composition of the complexes. The half-extraction pH values (pH₁/₂) of the cations are calculated and correlations between the pH₁/₂ values, the ionic radii of the cations, and the polarization ability of the metal ions are established.

     

Determination of triadimenol based on the quenching effect on resonance light scattering from the triadimenol–deoxyribonucleic acid–hydrochloric acid system

Analysis of triadimenol was carried out using deoxyribonucleic acids (DNA) via the resonance light scattering (RLS) technique. After adding triadimenol into aqueous medium of pH 1.72, the RLS of DNA was remarkably quenched. A resonance light scattering peak at 310 nm was found, and the quenched intensity of RLS at this wavelength was proportional to the concentration of triadimenol. The linear range of the calibration curve was approximately 0–3 μg mL⁻¹ with a detection limit (S/N = 3) of 0.07 μg mL⁻¹. The triadimenol in samples of water, cucumber and human serum was determined. The results were satisfactory, and the recovery rates were in the range of 96.3–106.0%, 94.8–105.9% and 92.3–100.5%, respectively. The interaction mechanism was also studied.     

Effect of tri-n-butyl phosphate on physical properties of dodecane–nitric acid system

Extraction power of solvent depends upon the physical properties of the system. Tri-n-butyl phosphate (TBP) in dodecane is a versatile solvent used in the nuclear fuel reprocessing like PUREX process. The study of physical properties like density, viscosity, interfacial tension and solubility for TBP–nitric acid–dodecane system will be helpful in carrying out different extraction studies during PUREX process. Thus, physical properties like density, viscosity, interfacial tension and solubility have been measured for TBP–nitric acid–dodecane system using pycnometer, viscometer, pendant drop method and high performance liquid chromatography respectively. It has been observed that density and viscosity increases but interfacial tension and solubility decreases with the concentration of TBP in dodecane–nitric acid system. Physical properties of 30 % TBP–nitric acid–dodecane system have also been studied in detail. All these studies will also be useful in stripping out dissolved TBP from the nuclear waste.     

Rapid automatic nucleic acid purification system based on gas–liquid immiscible phase

The continuous expansion of nucleic acid detection applications has resulted in constant developments in rapid, low-consumption, and highly automated nucleic acid extraction methods. Nucleic acid extraction using magnetic beads across an immiscible phase interface offers significant simplification and parallelization potential. The gas–liquid immiscible phase valve eliminates the requirement for complicated cassettes and is suitable for automation applications. By analyzing the process of magnetic beads crossing the gas-liquid interface, we utilized a low magnetic field strength to drive large magnetic bead packages to cross the gas-liquid interface, providing a solution of high magnetic bead recovery rate for solid-phase extraction with a low-surfactant system based on gas-liquid immiscible phase valve. The recovery rate of magnetic beads was further improved to 90%–95% and the carryover of the reagents was below 1%. Consequently, a chip and an automatic system were developed to verify the applicability of this method for nucleic acid extraction. The Hepatitis B virus serum standard was used for the extraction test. The extraction of four samples was performed within 7 minutes, with nucleic acid recovery maintained above 80% and good purity. Thus, through analysis and experiments, a fast, highly automated, and low-consumption nucleic acid recovery method was proposed in this study.     

Lanthanide–actinide separation by bis-2-ethylhexylphosphoric acid from citric acid–nitric acid medium

Phosphate rock (Pho-ore) is the starting raw material used in manufacturing of most phosphate products. This material contains phosphorous, natural uranium, thorium potassium radionuclide and other trace elements. Single super phosphate powder (SSPho-P), single super phosphate granules (SSPho-G), and triple super phosphate (TSPho) are the common phosphate products produced along with phosphogypsym (CaSO₄) as a waste product. Since these materials are industrially manufactured by the reaction of the phosphate ore with phosphoric and sulphuric acids, these products and the waste product are extremely acidic. Pho-ore, SSPho-P, SSPho-G, TSPho and CaSO₄ samples were used in our study. Chemical analyses showed that these phosphate samples contain phosphorous, iron, aluminum ions and traces of uranium ions. Accumulation of the fertilizers on soils usually transfers some of these ions from the fertilizer materials to the soil/water interfaces. The migration of uranium U(VI), P, Al and Fe in subsurface soils was found to be strongly influenced by the sorption/desorption reaction at the solid/water interfaces. Thus, dissolution of these ions in soil/water phases is very important. Speciation of U(VI), P, Al and Fe in soil/water phases were calculated using a geochemical code (MINTEQA2). This study was conducted to determine sorption properties and the surface electrical properties of these ions at the soil samples.     

Deracemization of (±)-mandelic acid using a lipase–mandelate racemase two-enzyme system

Deracemization of (±)-mandelic acid was achieved by using a novel two-enzyme process consisting of: (i) Pseudomonas sp. lipase catalyzed O-acylation of (±)-mandelic acid in diisopropyl ether; followed by (ii) mandelate racemase catalyzed racemization of the remaining unreacted (R)-mandelic acid in aqueous buffer. When this one-pot sequence was repeated four times, (S)-O-acetylmandelic acid was obtained in 80% isolated yield and >98% ee as the sole product.     

Thermal stability and flammability of butadiene–styrene rubber nanocomposites

Heterobimetallic oxalato complex precursors, manganese(II)tetraaquatris(oxalato)lanthanate(III)hexahydrate (MnOLa), cobalt(II)pentaaquatris(oxalato)lanthanate(III)trihydrate (CoOLa), nickel(II)pentaaquatris(oxalato)lanthanate(III)hexahydrate (NiOLa) and copper(II)diaaquatris(oxalato)lanthanate(III)monohydrate (CuOLa) of the type, M₃[La(C₂O₄)₃(H₂O) _m ]₂·nH₂O have been synthesized in aqueous medium. The precursors were characterized by elemental analysis, IR, electronic spectral and powder X-ray diffraction studies. The good crystalline nature with monoclinic structures predominates in MnOLa and NiOLa whereas triclinic structures were found in CoOLa and CuOLa. The solid-state thermal behaviour of the precursors was explored using TG, DTG and DTA in air. The MnOLa generated a mixture species consisting mainly of MnO₂, Mn₃O₄, Mn₅O₈, La₂O₃ and LaMn₇O₁₂ at 1000 °C through the formation of several intermediate species at 380 and 570 °C. The studies revealed that CoOLa led mainly to LaCoO₃ and La₂CoO₄ along with some oxides of both the cobalt and lanthanum at 1000 °C. In case of nickel analogue the mixture species identified at 1000 °C are mainly of La₂NiO₄, La₂O₃, Ni₂O₃ and NiO_2. In case of CuOLa the product at 1000 °C consisted of La₂CuO₄, La₂Cu₂O₅ and oxides of copper and lanthanum. The nature of decomposition of the precursors in nitrogen were seen from DSC study and the kinetic parameters i.e., E ^* , lnk ₀, ΔH ^# , ΔS ^# and order of reaction of all the steps were evaluated and discussed.     

Catalytical oxidation of styrene by molecularly imprinted polymer with phenylacetic acid as template

This letter used the molecular imprinting technology to build up the microenvironment around co-monomer bemin to mimic the cytochrome P450 catalyzing the epoxidation of styrene. The results showed that the conversion rates of products were obviously enhanced by molecularly imprinted polymers, compared to free heroin solution, using three kinds of oxidants. The used axial ligand in polymers synthesis also improved the total conversion rates.     

Alkaline methanol–air system

Methanol is a promising fuel for power devices such as fuel cells because it has a high theoretical capacity per volume and weight, is relatively easy to handle and is easy to store. Many studies on the alkaline methanol fuel cell system were made in the 1960s and 1970s. The article gives a brief summary of these studies and shows some results of the new work started recently at the TU Graz, AustriaDedicated to Prof. Wolf Vielstich on the occasion of his 80th birthday in recogniton of his numerous contributions to interfacial electrochemistry.     

Fourier transformed infrared spectral investigations of molecular interactions in propionic acid–2-propanol binary system

FTIR spectra of propionic acid (PA), 2-propanol (PROH) and its binary mixtures with varying molefraction of the PA were recorded in the region 500–3500 cm^?1, to investigate the formation of hydrogen bonded complexes in a mixed system. The observed features in ν(CO), ν(CO) and δ(COH) of PA, ν(CO) of PROH and δ(COH) of PA + PROH have been explained in terms of the hydrogen bonding interactions between PROH and PA and dipole–dipole interaction. The dipole moment derivative for the above mentioned vibrational modes have also been predicted from the integrated absorbance. The intrinsic linewidth for the vibrational modes ν(CO) and δ(COH) of PA has been elucidated using Bondarev and Mardaeva model.