Volume expansion behavior of water–hydrocarbon mixtures at high temperatures and pressures as studied by infrared spectroscopy

Infrared spectra of binary mixtures of water with toluene and ethylbenzene have been measured at temperatures and pressures in the 473–623 K and 100–350 bar ranges, respectively. Concentrations of water and hydrocarbons in the hydrocarbon-rich phase have been estimated from the integrated band intensities, and using these results, densities of the hydrocarbon-rich phase have been obtained as a function of temperature and pressure. In order to characterize the density of the hydrocarbon-rich phase, the experimental densities have been compared with the average densities before mixing, which were calculated from the literature densities of pure water and pure hydrocarbon with the experimental concentrations. All the experimental densities of the mixtures are lower than the average densities before mixing at the same condition. Relative volume change for mixing has been estimated and an anomalously large increase in volume has been found in the vicinity of the critical region of the water–hydrocarbon mixtures. This volumetric behavior is very similar to that previously found for water–benzene mixtures, and may be characteristic of the critical behavior of fluid mixtures of water and hydrocarbons.     

Thermal stability of the extraction system “TODGA in Isopar M with n-decanol” at above atmospheric pressure

Journal of Thermal Analysis and Calorimetry - The gas evolution dynamics has been studied during thermal oxidation of 0.15 and 0.2 mol L?1 solutions of...     

Stereoselective addition of aliphatic thiols to internal alkynes in a catalytic system with palladium “nanosalt” as an active site

An efficient catalytic system based on easily available palladium acetate was developed for the selective addition of aliphatic thiols to the triple bond of internal alkynes. Formed in situ [M(SR)₂] _n nanostructured particles were found to be an active form of the catalyst. It was experimentally confirmed for the first time that the most active form of the catalyst for thiol addition to internal alkynes is formed only in the reaction mixture containing the both reactants, namely, alkyne and thiol.     

Electrophoretic mobility of ester betulin derivatives and their complexation with γ-cyclodextrin studied by capillary electrophoresis in aqueous solutions at different pH values

In this article, capillary electrophoresis was used to measure the effective electrophoretic mobility of ester betulin derivatives as a pH function and to study their complexation with γ-cyclodextrin (γ-CD). The electrophoretic mobility of betulin 3,28-diphthalate (DPhB) and 3,28-disuccinate (DScB) changed unusually with decreasing pH: instead of decreasing, it first increased and then decreased. This fact as well as the turbidity of sample solutions at pH from 2.5 to 6, broadening of electrophoretic peaks and a decrease in the surface tension of the solutions indicates that these betulin derivatives, being amphiphilic compounds and weak acids, exist as micelles in aqueous solutions at pH 6 and below. The inclusion complexation of betulin derivatives with γ-CD at pH 9.18 and 4.5 was studied by mobility shift affinity capillary electrophoresis. At pH 9.18, the apparent binding (stability) constant logarithms for 1:1 γ-CD complexes of DPhB, betulin 3,28-disulfate (DSB) and DScB with 95% confidence interval limits were equal to 7.44 ± 0.02, 7.09 (7.01–7.19), and 6.97 (6.87–7.08) at 25°C, respectively. At pH 4.5, the binding constant for the DSB complex was slightly lower, while the micelle formation did not allow determining the exact values of the constants for the DPhB and DScB complexes.     

The “supercompressed” state of matter as an investigation object in high-pressure chemistry

The prospects of a new line of research in high-pressure chemistry are discussed, which is associated with investigations of chemical reactions accompanied by large volume effects at ambient pressure and, hence, resulting in greater compressibilities of the reaction products. The compounds formed by intercalation of alkali metals in graphite and intermetallic compounds formed between alkali metals and silver or Group V metals (Sb, Bi), which crystallize with the BiF₃ structural type, are considered as examples of “chemical compression”. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1442–1447, August, 1999.     

Stepwise conformational transition of crystalline disodium adenosine 5′-triphosphate with relative humidity as studied by high resolution solid state 13C and 31P NMR

Stepwise conformational transition of disodium adenosine 5′-triphosphate (Na₂ATP) crystals as a function of relative humidity (RH), was examined by means of high resolution solid state NMR spectroscopy. The presence of two types of molecules, A and B, with altered conformations in an asymmetric unit, is evident from both ³¹P and ¹³C NMR spectra, irrespective of the three different crystalline forms, mono-, di- and trihydrates, in which, cell parameters changed linearly with RH. Hydration-dependent conformational transition from the monohydrate (RH 0–10%) through dihydrate (20–40%) to trihydrate (60–90%), was well monitored by stepwise upfield displacements of the C1′ ¹³C signals of ribose moiety (molecule B), although, the corresponding peak for the molecule A, is almost unchanged. This means that, adaptation of stepwise structural transitions to the linear expansion of cell parameters is almost entirely ascribed to the conformational readjustment of the molecule B, together with varying proportion of two types of hydrate forms, at the RH range of 20–40%. We consider that, small clusters or thin layers are formed in the beginning of the transition and subsequently, the number of them, rather than the size or thickness increases, because the phosphorous spin–lattice relaxation times, T₁^P, for the three phosphorous nuclei, including those of mixed state, of the two hydrate forms, turned out to be similar due to sufficient fast spin diffusion rates among them. Since only one direction of the cell parameters is changed, as determined by the previous X-ray diffraction study, we conclude that thin layer type micro crystals might be produced during the stepwise transition. Further, it was found that, these molecules acquired motional flexibility mainly at the bound water molecules, together with increased relative humidity, as determined by a variety of relaxation parameters.     

Crosslinking of viral nanoparticles with “clickable” fluorescent crosslinkers at the interface

Cu (I) catalyzed alkyne-azide cycloaddition (CuAAC) reaction, a typical “click“ reaction, is one of the modular synthetic approaches which has been broadly used in various organic syntheses, medicinal chemistry, materials development and bioconjugation applications. We have for the first time synthesized two dialkyne derivatized fluorescent crosslinkers which could be applied to crosslink two biomolecules using CuAAC reaction. Turnip yellow mosaic virus, a plant virus with unique structural and chemical properties, was used as a prototypical scaffold to form a 2D single layer at the interface of two immiscible liquids and crosslinked with these two linkers by the CuAAC reaction. Upon crosslinking, the fluorescence of both linkers diminished, likely due to the distortion of the polymethylene backbone, which therefore could be used to indicate the completion of the reaction.     

Determination of 16 polycyclic aromatic hydrocarbons in environmental water samples by solid-phase extraction using multi-walled carbon nanotubes as adsorbent coupled with gas chromatography–mass spectrometry

A solid-phase extraction (SPE) using multi-walled carbon nanotubes (MWCNTs) as adsorbent coupled with gas chromatography–mass spectrometry (GC–MS) method was developed for the determination of 16 polycyclic aromatic hydrocarbons (PAHs) in environmental water samples. Several condition parameters, such as extraction adsorbents, elution solvents and volumes, and sample loading flow rate and volume were optimized to obtain high SPE recoveries and extraction efficiency. 150 mg MWCNTs as sorbent presented high extraction efficiency of 16 PAHs due to the large specific surface area and high adsorption capacity of MWCNTs compared with the commercial C18 column (250 mg/2 mL). The calibration curves of 16 PAHs extracted were linear in the range of 20–5000 ng L⁻¹, with the correlation coefficients (r²) between 0.9848 and 0.9991. The method attained good precisions (relative standard deviation, RSD) from 1.2% to 12.1% for standard PAHs aqueous solutions; method recoveries ranged in 76.0–125.5%, 74.5–127.0%, and 70.0–122.0% for real spiked samples from river water, tap water and seawater, respectively. Limits of detection (LODs, S/N = 3) of the method were determined from 2.0 to 8.5 ng L⁻¹. The optimized method was successfully applied to the determination of 16 PAHs in real environmental water samples.     

Erratum on “Complexation of radionuclide 152+154Eu(III) with alumina-bound fulvic acid studied by batch and time-resolved laser fluorescence spectroscopy”

Science China Chemistry - In the above referenced publication [1], the Figure 5 and data in Table 1 are correct, but we ignored to present the final pH values of the system, which is very important...     

Solvent extraction of europium and americium into phenyltrifluoromethyl sulfone by using synergistic mixture of hydrogen dicarbollylcobaltate and “classical” CMPO

Extraction of microamounts of europium and americium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H⁺B⁻) in the presence of tetraisopropyl methylene diphosphonate [T(iPr)MDP, L] has been investigated. The equilibrium data have been explained assuming that the complexes HL⁺, HL₂ ⁺, ML₂ ³⁺, ML₃ ³⁺ and ML₄ ³⁺ (M³⁺ = Eu³⁺, Am³⁺) are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined. It was found that the stability constants of the corresponding complexes EuL _n ³⁺ and AmL _n ³⁺, where n = 2, 3, 4 and L is T(iPr)MDP, in water-saturated nitrobenzene are comparable.     

Preparation of hexagonal MoO3 by “Chimie Douce” reaction with NO2

The metastable hexagonal form of MoO₃ has been successfully prepared starting from the ammonium molybdate, using a “Chimie Douce” reaction with NO₂ gas. The lattice parameters of the as-prepared material were determined by XRD analysis to be: a = 10.633(2) Å and c = 3.719(1) Å. The composition of this material obtained by physical and chemical analysis is MoO₃, 0.09 H₂O, showing that a small amount of water molecules remained while there were no more ammonium ions in this structure. The structural transformation from hexagonal to stable orthorhombic α-MoO₃ phase was observed at 350°C. It was also shown that NO₂ reaction is a very useful method to remove topotactically ammonium ions from a parent structure at low temperature. This “Chimie Douce” process appears to be very promising for obtaining new metastable oxides with large tunnels or interlayer distances.     

Electrocatalytic reduction of nitrite ions by a copper complex attached as SAMs on gold by “self-induced electroclick”: Enhancement of the catalytic rate by surface coverage decrease

A biomimetic copper complex has been attached as SAMs onto an azidoundecanethiol-modified gold electrode by the “self-induced electroclick” procedure. The immobilized complex electrocatalyzes efficiently the reduction of nitrite ions in an acidic medium. The in-situ control of the surface coverage during the grafting process by the electroclick approach has been exploited to rationalize the influence of surface concentration on the electrocatalytic properties of the immobilized Cu complex. The voltammetric analysis shows an enhancement of the catalytic rate when the surface coverage is decreased, as a consequence of steric and electronic effects.     

Application of dispersive liquid–liquid microextraction with alcoholic solvents followed by HPLC–UV as a sensitive and efficient method for the extraction and determination of citalopram in biological samples using an experimental design

A sensitive and rapid method based on alcoholic-assisted dispersive liquid–liquid microextraction followed by high-performance liquid chromatography for determination of citalopram in human plasma and urine samples was developed. The effects of six parameters (extraction time, stirring speed, pH, volume of extraction and disperser solvents, and ionic strength) on the extraction recovery were investigated and optimized utilizing Plackett–Burman design and Box–Behnken design, respectively. According to Plackett–Burman design results, the volume of disperser solvent, stirring speed, and extraction time had no effect on the recovery of citalopram. The optimized condition was a mixture of 172 µL of 1-octanol as extraction solvent and 400 µL of methanol as disperser solvent, pH of 10.3 and 1% w/v of salt in the sample solution. Replicating the experiment in optimized condition for five times, gave the average extraction recoveries equal to 89.42%. The detection limit of citalopram in human plasma was obtained 4 ng/mL, and the linearity was in the range of 10–1200 ng/mL. The corresponding values for human urine were 5.4 ng/mL with the linearity in the range of 10–2000 ng/mL. Relative standard deviations for inter- and intraday extraction of citalopram were less than 7% for five measurements. The proposed method was successfully implemented for the determination of citalopram in human plasma and urine samples.     

Suzuki reaction with aryl bromides at room temperature in the presence of a simple “ligand-free” catalytic system

Possibility was examined of using the simplest catalytic system (palladium salt and NaOH) in ethanol or in a mixture of ethanol and water as a catalyst precursor in order to obtain high product yields in the Suzuki reaction with nonactivated aryl bromides at room temperature without an inert atmosphere or ligand additives.     

The Synthesis of the Trnas Anticodon Loop Fragment (“U-Turn”) with Modified Uridines as the Components

Abstract

To continue studies on dynamics of tRNAs anticodon loop fragments conformation (1) the series of oligomers 1-5 has been synthes ized.     

Synthesis of glycolurils and hydantoins by reaction of urea and 1, 2-dicarbonyl compounds using etidronic acid as a “green catalyst”

Most of the known methods for the synthesis of heterocyclic compounds have disadvantages, such as a long reaction time and aggressive conditions. We have developed a new, rather simple and efficient method for the synthesis of a number of glycoluryls and hydantoins in water using a etidronic acid (HEDP) as “Green catalyst.” So, for the first time, the condensation reaction of ureas with 1, 2-dicarbonyl compounds was carried out in the presence of HEDP. Also based on NMR studies, a chemism of these reactions, which is stepwise, is proposed. It has been established that the optimal conditions for the synthesis of glycoluryls and hydantoins using HEDP are: temperature 80°C-90°C, 40-20 minutes, and the ratio of urea and HEDP is 1:1. In all cases, the remaining aqueous filtrate containing HEDP after the reaction can be reused for other cycles synthesis of glycoluril and other compounds, because HEDP is not converted during the reaction.     

Binuclear complexes with the “Chinese Lantern” geometry as intermediates in the liquid-phase oxidation of dibenzyl ether with atmospheric oxygen in the presence of copper(II) carboxylates

Reactions of copper(II) carboxylates with dibenzyl ether (DBE) gave binuclear complexes of the formula Cu₂(μ-OOCR)₄(DBE)₂ (R = Bu ^t , Ph, and CF₃). The complexes were characterized by X-ray diffraction. The axial positions in the lantern-type dimer are occupied by the coordinated DBE molecules. The complexes seem to be analogs of intermediate catalysts for the oxidation of DBE with atmospheric oxygen in the presence of transition metal complexes. When stored in air, the complex Cu₂(μ-OOCPh)₄(DBE)₂ underwent oxidation into Cu₂(μ-OOCPh)₄(HOOCPh)₂, which was characterized by X-ray diffraction. The geometry of its framework is similar; the structure is stabilized by intramolecular H bonds between the axially oriented benzoic acid molecules and the adjacent bridging benzoate anions.