Effect of binary extractants and modifier–diluents systems on equilbria of propionic acid extraction

Propionic acid is an important carboxylic acid widely used in chemical industries. The recovery from aqueous waste streams and fermentation broth is of research interest. Extraction of carboxylic acids by reactive extraction using extractant-diluent, mixed extractants in diluents and extractants in mixed diluents etc. are emerging areas of study. With this aim reactive extraction of propionic acid was carried out to study: (i) effect of binary extractants (tri-n-octylamine(TOA):tri-n-butylphosphate (TBP), TOA:Aliquat 336 and TBP:Aliquat 336), (ii) effect of modifier (1-decanol) in different diluents (kerosene, n-octane, n-heptane, petroleum ether, butyl acetate, MIBK, 2-octanol, dodecanol, hexane) and (iii) effect of phase volume. Improved extractions using binary extractants and binary diluents were observed. Since liquid–liquid extraction is dependent on effect of modifier concentration, effect of phase volume, presence of single or binary extractants and binary diluents, the study will be useful in the design of reactive extraction process for propionic acid recovery.     

Determination of glycolic acid in cosmetics by online liquid chromatography–Fourier transform infrared spectrometry

An isocratic online liquid chromatography Fourier transform infrared procedure has been developed for the determination of glycolic acid in cosmetics. The method involves the ultrasound-assisted extraction of glycolic acid from the samples with an acetonitrile:phosphate buffer (25 mM, pH 2.7) (3:97 v/v). The extracts were centrifuged and filtered before their injection into the chromatography system, which was equipped with a C18 column and used a flow rate of 150 microL min(-1). FTIR spectra were acquired using a time-resolved rapid scan mode. To calculate the chromatograms, the spectral area was integrated between 1288 and 1215 cm(-1), with baseline correction established between 1319 and 1150 cm(-1), after correcting for the eluent spectral background. Peak area values of the extracted sample chromatograms were interpolated from an external calibration curve. The method provided a limit of detection of 0.034 mg mL(-1) and a relative standard deviation of 6% for five measurements at the 0.174 mg mL(-1) concentration level. Recovery values obtained by spiking 400 mg of three commercially available samples with amounts of glycolic acid from 3.7 to 9.8 mg ranged between 99.6 and 101%. The results obtained for the commercial samples agree well with their declared concentrations. An attempt to directly determine glycolic acid by attenuated total reflectance measurements using partial least squares calibration showed that results were strongly influenced by compounds coextracted from the matrix.     

FT-IR studies of molecular interactions in formamide–methanol mixtures

FT-IR spectra of formamide (FA)–methanol (MeOH) mixtures have been measured by ATR technique. Factor analysis applied to the spectra has shown two kinds of intermolecular complexes differing in a manner of polarization of component molecules. The composition of the complexes changes monotonically with the composition of the mixtures. The spectra in the CO stretching region have been analyzed separately using both: the factor analysis and the difference spectra method. Four different environments of carbonyl group of formamide has been revealed over the whole range of the mixture composition. The mean number of formamide molecules disturbed by one methanol molecule via carbonyl group in the formamide-rich region has been found as equal to 1.5. Presumable structures for the molecular complexes have been proposed to explain the results of the analyses.     

Phase equilibria in binary subsystems of urea–biuret–water system

Joint results of the differential scanning calorimetry (DSC) and thermogravimetry (TG) experiments were the basis for the fusion enthalpy and temperature determination of the biuret (NH₂CO)₂NH (synthesis by-product of the urea fertilizer (NH₂)₂CO). Recommended values are Δ_m H = (26.1 ± 0.5) kJ mol⁻¹, T _m = (473.8 ± 0.4) K. The DSC method allowed for the phase diagrams of “water–biuret,” “water–urea,” “urea–biuret” binary systems to be studied; as a result, liquidus and solidus curves were precisely defined. Stoichiometry and decomposition temperature of the biuret hydrate identified, composition of the compound in “urea–biuret” system was suggested.     

Oxidation of styrene epoxide–acid binary system and styrene epoxide–acid–amine ternary system catalyzed by Co(II) salts

The Co(II) salt (nitrate, chloride)-induced acceleration of styrene epoxide (SE) consumption and oxidation by molecular oxygen in acetonitrile solutions of three- and four-component systems, SE–acetic acid–cobalt salt and SE–acetic acid–cobalt salt–aniline, was found and investigated. The heterolytic epoxide ring opening in SE and homolysis (oxidation) catalyzed by cobalt salts can be accomplished in the presence of acid co-catalyst. The competition between homolysis and heterolysis processes in the presence of metal-containing catalyst was discovered for the first time for this type of system. The cobalt catalyst is deactivated during the styrene epoxide conversion.     

Consideration of dipole–quadrupole interactions in molecular based equations of state

The thermodynamic behaviour of a number of real substances is determined by dipolar as well as quadrupolar interactions of the molecules. In equations of state (EOS) like, e.g. BACKONE separate contributions to the Helmholtz energy for the dipolar and the quadrupolar interactions are considered but no cross contributions. Here, the concept of effective dipole and quadrupole contributions is suggested in which the effective dipole strength μ_e is influenced by the quadrupole cross interaction. Similarily, the effective quadrupole strength Q_e takes into account the dipole cross interaction. In order to arrive at these effective dipolar and quadrupolar strengths, molecular simulations are performed. From the simulation results correlation equations are derived which are used in combination with BACKONE for the calculation of vapour–liquid equilibria (VLE) of real mixtures. By using these effective moments, the only required binary mixing rule parameter k_ij tends to small values of about 0.01 and becomes temperature-independent. Moreover, the VLE pressures are predicted now considerably better than without consideration of the cross contributions.     

Electrochemical investigations of baicalin and DNA–baicalin interactions

Baicalin is an anti-HIV drug purified from the traditional Chinese medicinal plant Scutellaria Baicalensis Georgi. Baicalin has proven to be electroactive at pyrolytic graphite (PG) electrodes. We thus studied its interaction with DNA via the electrochemical approach. We observed that the peak currents corresponding to the baicalin reduction–oxidation (redox) reaction significantly decrease upon the addition of DNA. With complementary ultraviolet/visible (UV/Vis) spectroscopic evidence, we suggest that baicalin binds to DNA through intercalation. This feature has enabled baicalin to discriminate between double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA).Electronic Supplementary Material Supplementary material is available in the online version of this article at . A link in the frame on the left on that page takes you directly to the supplementary material.     

The shear hysteresis in lamellar structure of surfactant–water binary system

We study the shear effect on the lamellar structure of surfactants in water using dissipative particle dynamics simulations. Starting from a lamellar structure without shear flow, we increase the shear rate and then decrease it stepwisely. A weak shear changes the lamellar plane to be parallel to the shear direction though the lamellar normal has no specific direction on the plane normal to the shear direction. By increasing the shear rate, the lamellar normal eventually flips to the vorticity direction regardless of the initial configuration. Lamellar normal would stay along the vorticity direction on decreasing the shear rate. The hysteresis is also found in shear-stress. By varying the shear rate, the time needed to reach the final unique state is significantly shortened compared with that observed with a constant shear rate. We find a correlation between the excess shear-stress and the tilt angle of surfactant in lamellar.     

Crystal and molecular structure of β-(N-benzoxazoline-2-thione) propionic acid and its salts

The crystal and molecular structures of β-(N-benzoxazoline-2-thione)propionic acid, its monoethanolammonium (NН₂(CH₂)₂OH) and ethylenediammonium (NН₂(CH₂)₂NH₂) salts are studied. In the salts the monoethyleneamine amine group participates in the deprotonation of one ethylenediamine–two β-(N-benzthiazolin-2-one)propionic acid molecules. The geometry of the molecules and intermolecular hydrogen and donor-acceptor bonds in crystals are analyzed. In the crystal structures weak interactions form a two-dimensional layer whose thickness corresponds to unit cell sizes.     

Phases of the K2TaF7–TaF5 binary system

The phase equilibria in the K₂TaF₇–TaF₅ binary system were determined up to x _TaF5 = 0.5 by means of differential scanning calorimetry. XRD diffraction analysis of solidified mixtures was performed. Besides the K₂TaF₇ and KTaF₆ phases, the presence of a third phase was observed, as well. It was suggested that the last phase melts incongruently. Correspondence: B. Kubikova, Institute of Inorganic Chemistry SAS, Dúbravská cesta 9, Bratislava, 845 36, Slovakia.     

The devitrification of glasses in the binary system SiO2TiO2

The solid solutions series in the system SiO₂TiOP₂ in the vitreous as well as in the devitrified state were investigated by various methods up to 10% by weight TiO₂. The relative intensities of the characteristics infrared absorption bands and of the respective Raman scattering bands about 950 cm⁻¹ reach their maximum at about 4% TiO₂ (by weight).These and other effects observed at this concentration of TiO₂ are discussed in connection with the linking of [SiO₄] and [TiO₄] tetrahedra and with the observed separation of rutile and anatase in small quantities in the devitrification process. A possible sequence of events during the devitrification process in this system is suggested.     

Electron–phonon interactions in atomic and molecular devices

Electron–phonon interactions are extremely important for understanding charge transport, inelastic processes, heating, and heat dissipation in nanoscale molecular and atomic devices. In molecular electronics Inelastic Electron Tunneling Spectroscopy (IETS) has recently emerged as one of the premier methods for characterizing molecular-scale junctions and devices. This method provides a distinct chemical fingerprint for identifying molecules within a junction, and has allowed for clear demonstrations of single molecule devices, the effects of electric field on molecular orbitals, the importance of molecular configuration on conductance, as well as information about the charge transport mechanism. In this review we will discuss the use of Point Contact (PC) and IET spectroscopies on molecular and atomic systems, discuss the basic principles involved in inelastic transport for these spectroscopic methods to function, and focus on the experimental techniques involved and the important conclusions drawn from the experiments performed to date.     

Thermodynamic reassessment of the Al–Zr binary system

Journal of Thermal Analysis and Calorimetry - Based on the data of the literature reports, the Al–Zr binary system has been re-assessed thermodynamically through the CALPHAD (CALculations of...     

Solvation model for acetic acid in binary mixtures of cyclohexane–1,2-dichloroethane

The partition of acetic acid between aqueous solutions and various binary mixtures of 1,2-dichloroethane and cyclohexane were studied at 30.0 °C. The observed nonlinearities of both monomer partition coefficient and dimerization constant in the organic phase with the mole fraction of 1,2-dichloroethane are interpreted in terms of the preferential solvation of various solvation sites of the involved species. Two polar sites were identified for the monomer each with a solvation preference by 1,2-dichloroethane seven times that by cyclohexane. This preference decreases to about two upon dimerization.     

Excess properties and spectroscopic studies of binary system of 1-methoxy-2-propanol + dimethyl sulfoxide at T = (298.15–318.15) K

Thermophysical property data for the binary system of 1-methoxy-2-propanol (PGME) + dimethyl sulfoxide (DMSO), a potential candidate for use as the scrubbing liquid for the absorption of SO₂, are lacking in the literature. This paper presents experimental data at 0.1 MPa on the density and viscosity for this binary system measured over the whole composition range at T = (298.15, 303.15, 308.15, 313.15 and 318.15) K. The extended combined uncertainty U_c with a 0.95 level of confidence for the pycnometer method and Ubbelohde viscometer used in this study is 0.002 g·cm^?3 and 0.028 cm²·s^?1, respectively. The PGME + DMSO system shows negative values of the excess molar volume at all temperatures and compositions. Based on UV-Vis and FTIR, the intermolecular interaction of PGME with DMSO was confirmed as hydrogen bonding between the hydroxyl hydrogen atom in PGME and the oxygen atom in DMSO.     

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     

Solid–solvent molecular interactions observed in crystal structures of β-chitin complexes

Three β-chitin structures [anhydrous, di-hydrate, mono-ethylenediamine (EDA)] recently determined by synchrotron X-ray and neutron fiber diffraction were reviewed from the viewpoint of molecular interactions. Both water and EDA molecules interact with the chitin chains through multiple hydrogen bonds. When water complexes with chitin, the hydrogen bonding pattern rearranges with the replacement of an intrachain chitin hydrogen bond by a stronger hydrogen bond between chitin and water, with an associated reduction in the degrees of freedom; the water oxygen is a much stronger acceptor than the O5 ring atom. The behavior of hydrogen exchange by deuterium supports this interpretation. EDA-molecules change the conformation of hydroxymethyl group from gg to gt, accompanied by changes in hydrogen bonds due to the strong accepting ability of the EDA nitrogen atoms. Some important interactions are in common with experimental crystallographic results of cellulosic crystals and of molecular dynamics studies. These new insights into solid–solvent interactions are valuable in understanding molecular interactions in other polysaccharides-solvents system in solution or on surface.     

Thermodynamic properties of alloys of the binary In–Yb system

The thermochemical properties of melts of the binary In–Yb system were studied by the calorimetry method at 1160–1380 K over the whole concentration interval. It was shown that significant negative heat effects of mixing are characteristic features for these melts. Using the ideal associated solution (IAS) model, the activities of components, Gibbs energies and the entropies of mixing in the alloys, and the phase diagram of this system were calculated. They agree with the data from literature.