Facile synthesis of 5A zeolite from attapulgite clay for adsorption of <Emphasis Type="Italic">n</Emphasis>-paraffins

5A zeolites were facilely synthesized from attapulgite clay and sodium aluminate precursors. The optimum synthesis condition for 4A zeolite (Na-form) were H₂O/attapulgite ratio of 40:1 volume/mass, NaOH/attapulgite mass ratio of 2.35:1, the crystallization time was 4 h at 80–85 °C. The 4A zeolite was converted to related 5A zeolite (Ca-form) through ionic exchanges using calcium chloride solution with the Si/Al mole ratio of 1.3. SEM images demonstrated that as-synthesized 5A zeolites are ordered cubic crystals, average crystals length dimension is 1–2 μm. And the zeolites product had a specific surface area of 482 m² g^?1 and total pore volume of 0.274 cm³ g^?1. The static adsorption experiments showed that the equilibrium adsorption capacities of n-decane and n-pentadecane on produced 5A zeolite were 0.253 and 0.510 g g^?1, respectively. And the adsorption equilibrium time of n-decane and n-pentadecane on 5A zeolite were 45 and 60 min, respectively. The experimental adsorption data of n-decane and n-pentadecane on three zeolites could be properly fitted by the Langmuir–Freundlich isotherm model.     

Electrophoretic and spectrophotometric determination of triiodides of sulfur-containing organic cations

Trimethylsulfonium triiodide (I) and p-xylylene-bis-(tetrahydrothiophenium) triiodide (II) were identified and determined by capillary electrophoresis with the resolution R _s = 4.86 using an unmodified quartz capillary. The procedure ensures the determination of sulfur-containing organic compounds in a concentration range of 1.0 × 10^?5–5.0 × 10^?4 M RSD ≤ 5%). The high stability of trimethylsulfonium triiodide and p-xylylene-bis-(tetrahydrothiophenium) triiodide in chloroform and acetonitrile solutions was found by spectrophotometry. A procedure was proposed for the spectrophotometric determination of compounds I and II as ion associates of sulfur-containing cations with a sulfophthalein dye, Bromocresol Purple (c _min (I) = 1.32 × 10^?5 M, c _min (II) = 7.1 × 10^?6 M, RSD = 5%), and by the characteristic absorption of the triiodide anion in acetonitrile (c _min (I) = 3.18 × 10^?6 M, c _min (II) = 2.76 × 10^?6 M, RSD <-3%).     

Determination of migrated phthalic acid residues into edible oils using a green mode of air-assisted liquid–liquid microextraction followed by high-performance liquid chromatography–diode array detector

In this study, for the first time, an organic solvent-free air-assisted liquid–liquid microextraction method has been reported for the extraction and preconcentration of phthalic acids (o-phthalic acid, m-phthalic acid, and p-phthalic acid) from edible oil samples. The method is based on the repeated aspirating/injection of an alkaline aqueous solution and the oil sample mixture in a conical bottom centrifuge tube to form a cloudy solution. After phase separation by centrifuging, the sedimented phase is directly analyzed by high-performance liquid chromatography–diode array detection. Under the optimum extraction conditions, the method showed low limits of detection and quantification between 0.11–0.29 and 0.28–0.91 ng mL^?1, respectively. Extraction recoveries and enrichment factors were from 81 to 97% and 406 to 489, respectively. The relative standard deviations for the analysis of 5 ng mL^?1 of each analyte were less than 5.9% for intraday (n = 6) and interday (n = 5) precisions. Finally, different oil samples were successfully analyzed using the proposed method and m-phthalic acid, and p-phthalic acid were determined in some of them at ng mL^?1 level.     

Phase Diagrams of the <Emphasis Type="Italic">n</Emphasis>-Decane–<Emphasis Type="Italic">n</Emphasis>-Hexadecane–Cyclododecane, <Emphasis Type="Italic">n</Emphasis>-Decane–Cyclododecane,and <Emphasis Type="Italic">n</Emphasis>-Hexadecane–Cyclododecane Systems

The n-decane–n-hexadecane–cyclododecane, n-decane–cyclododecane, and n-hexadecane–cyclododecane systems are studied by means of low-temperature differential thermal analysis using a differential scanning heat flow calorimeter. It is noted that all studied systems belong to the eutectic type. It is concluded that in the n-decane–n-hexadecane–cyclododecane system, the eutectic composition contains 85.0 wt % n-С₁₀Н₂₂, 4.0 wt % n-С₁₆Н₃₄, and 11.0 wt % С₁₂Н₂₄. It has a melting point of ?35.0°C.     

Use of adsorptive square-wave anodic stripping voltammetry at carbon paste electrode for the determination of amlodipine besylate in pharmaceutical preparations

The antihypertensive drug amlodipine has been characterized voltammetrically in a carbon paste electrode by means of anodic stripping voltammetry. An adsorptive stripping method in a carbon paste electrode for trace determination of amlodipine has been described. Cyclic voltammetric studies indicated the oxidation of amlodipine besylate at the electrode surface through a single two-electron irreversible step fundamentally controlled by adsorption. A study of the variation in the peak current with solution variables such as pH, ionic strength, concentration of amlodipine, possible interference, and instrumental variables, such as preconcentration time and accumulation potential, has resulted in the optimization of the oxidation signal for analytical purposes. By anodic adsorptive anodic stripping voltammetry, the calibration plot was linear in the range 9.9 × 10^?9 ? 1.4 × 10^?7 M with a detection limit of 2 × 10^?10 M in a carbon paste electrode at pH 11.0. The procedure was successfully applied to the assay of amlodipine besylate in some commercial products in the market (Amlopres®, Amlodipine, and Norvasc®). The percentage recoveries were in agreement with those obtained by the reference method.     

Determination of <Emphasis Type="Italic">o</Emphasis>-phthalic acid esters in water by chromatography–mass spectrometry with emulsion dispersive liquid–liquid microextraction preconcentration

Using emulsion dispersive liquid–liquid microextraction preconcentration and injection of a large volume of an extract (10 μL), the limits of chromatographic–mass spectrometric detection of o-phthalic acid esters in water have been attained at the level 4 × 10^–6–1 × 10^–5 mg/L. The main source of the systemic error of the determination of impurities was found to be the release of o-phthalates from microparticles of chromatographic septum to the carrier gas. The extractant (n-octane) was purified by Rayleigh distillation. The independence of the concentration coefficient of the studied o-phthalates of concentration in the range (0.4–30) × 10^–4 mg/L has been demonstrated. The relative expanded uncertainty of the determination of o-phthalates has been calculated and equals 12–39%.     

Phase diagrams of a condensed decane–eicosane–cyclododecane system

An n-eicosane–cyclododecane–n-decane system related to eutectic-type systems is investigated by means of differential thermal analysis. The eutectic alloy with melting point of–33.8°C contains 2.8 wt % of n-eicosane, 89.2 wt % of n-decane, and 8.0 wt % of cyclododecane.     

Antimicrobial Property of Nanosilver Colloid Prepared by Electrical Spark Discharge Method on <Emphasis Type="Italic">Aspergillus niger</Emphasis>

This study employed an electrical spark discharge method (ESDM) to prepare a nano-Ag colloid as an antifungal solution. The solution was diluted to two concentrations, and the fungal medium prepared in this study was coated with Aspergillus niger. The nano-Ag colloid solution was mixed with A. niger in various concentrations and dripped onto 3M Petrifilm plates. Inhibited growth observed after several days confirmed the antifungal effect of the nano-Ag colloid on A. niger. Because direct washing produced inaccurate quantitation and yielded A. niger in an excessively high concentration, this study employed an inoculation loop method for A. niger quantitation. The concentrations of A. niger ranged from 10^?2 to 10^?7%. The optimal colony count was observed on day 2. During an experiment regarding the antifungal effect of the ESDM-prepared nano-Ag colloid on A. niger, 3M Petrifilm plates were employed to observe the growth of A. niger. The colony count of 10^?2% A. niger without nano-Ag colloid was approximately 60. After the nano-Ag colloid was added, the colony count substantially decreased to approximately 10. The colony count of 10^?7% A. niger was reduced to 11 or lower after the nano-Ag colloid was added. The results confirmed the antifungal effect of the nano-Ag colloid on the growth of A. niger.     

TXRF determination of mercury(II) in water in combination with liquid–liquid microextraction

A highly selective hybrid way of TXRF determination of mercury(II) in drinking water at the level of n(10^–2–10⁰) μg/L is developed. The technique of preconcentration of mercury(II) ions includes directly suspended droplet microextraction with benzene in the form of an iodide molecular complex. The proposed method of determination is characterized by its high degree of sensitivity and reproducibility (c _min = 8 ng/L, s _r = 0.12 (100 ng/L)). The accuracy of the analysis results is confirmed by the introduced–found method.     

Thermodynamic characteristics of the dissolution of glycine,glycylglycine, and glycylglycylglycine in aqueous solutions of sodium dodecyl sulfate at <Emphasis Type="Italic">Т</Emphasis> = 298.15 K

the enthalpies of dissolution of glycine (Gly), glycylglycine (GlyGly), and glycylglycylglycine (GlyGlyGly) are measured in aqueous solutions of sodium dodecyl sulfate (SDS) at SDS concentrations m = 0–0.7 mol kg^?1 and Т = 298.15 K by means of calorimetry. The obtained data are used to calculate the standard values of enthalpies of dissolution (Δ_sol H ^m ) and enthalpies of transfer (Δ_tr H ^m ) of glycine and its oligomers from water to SDS aqueous solutions. The dependences of Δ_sol H ^m and Δ_tr H ^m on SDS concentration in an aqueous solution at a constant concentration of glycine and its oligomers are determined. A comparative analysis of the thermodynamic characteristics of Gly, GlyGly, and GlyGlyGly transfer within the studied range of SDS concentrations is performed. The results are interpreted in terms of ion–ion, ion–polar, and hydrophobic interactions between SDS and molecules of glycine and its oligomers.     

Polarographic Determination of Pb(II) and Cd(II) with Selective Removal of Se(IV) Using Ionic Poly(<Emphasis Type="Italic">N,N</Emphasis>-dimethylacrylamide-co-allylthiourea)

Hydrogels based on N,N-dimethylacrylamide (DMAAm), allylthiourea (ATU), and maleic acid (MA) were synthesized by free-radical cross-linking copolymerization in water with N,N-methylene-bis(acrylamide) (BAAm) as the cross-linker, ammonium persulfate (APS) as the initiator, and N,N,N′,N′-tetramethylenediamine (TEMED) as the activator. Since Se(IV) is the most serious interfering element in the electroanalytical (polarographic or voltammetric) determination of lead and cadmium, a new method for their correct determination after selective separation of the interfering ion (selenite) was developed by using poly(N,N-dimethylacrylamide-co-allylthiourea) [P(DMAAm-co-ATU)] hydrogels containing reducing pedant groups like allylthiourea. The proposed method showed good reproducibility and accuracy with relative standard deviations of 8.5 and 3.4% and relative errors of ?6.0 and ?5.4% for the determination of 5.0 × 10^?5 M Pb(II) and Cd(II), respectively, next to 3.0 × 10^?5 M Se(IV).     

Thermochemistry of the Dissolution of Dipeptides Containing DL-α-Alanine in Aqueous Solutions of Sodium Dodecyl Sulfate at 298.15 K

Enthalpies of the dissolution of DL-α-alanylglycine (AlaGly), DL-α-alanyl-DL-α-alanine (AlaAla), DL-α-alanyl-DL-α-valine (AlaVal), and DL-α-alanyl-DL-norleucine (AlaNln) in an aqueous solution of sodium dodecyl sulfate (SDS) at SDS concentration of m = 0–0.07 mol kg^?1 and temperature Т = 298.15 K are measured via calorimetry. The standard values of the enthalpy of dissolution (Δ_solH ^m ) and the transfer of dipeptides (Δ_trH ^m ) from water to aqueous SDS solutions are calculated using the experimental data. The dependences of Δ_solH ^m and Δ_trH ^m the SDS concentration at a constant concentration of dipeptide are established. Thermochemical characteristics of the transfer of AlaGly, AlaAla, AlaVal, and AlaNln in the investigated range of SDS concentrations are compared. The results are interpreted by considering ion–ion, ion–polar, and hydrophobic–hydrophobic interactions between SDS and dipeptide molecules.     

Chemiluminescence Determination of Cyanide Ions

It was found that alkaline solutions of luminol exhibit chemiluminescence in the presence of p-nitrobenzaldehyde (p-NBA), hemin, and cyanide ions. Air oxygen dissolved in the solutions is an essential component of the process. The kinetics of luminol chemiluminescence in the presence of p-NBA, hemin, and cyanide ions indicates the catalytic nature of the process. A scheme was proposed for the series of reactions resulting in chemiluminescence and generated by superoxide radicals formed in the p-NBA-catalyzed reaction between hemin-activated air oxygen and hydrated p-NBA species. A procedure was developed with a determination limit of (1.0 ± 0.3) × 10^?7 mg/mL (n = 5, P = 0.95) for cyanide ions.     

Potentiometric study of the kinetics and equilibria of formation of chloroglycinate palladium(II) complexes from bis-glycinato palladium(II) complexes

The equilibria and kinetics of the reaction of Pd(gly)₂ complexes with hydrogen ions and chloride ions has been studied by a potentiometric method. The underlying idea of the method is the measurement of solution pH as a function of reaction time t using a glass electrode. The solutions used had the following initial compositions: xM Pd(gly)₂, xM Hgly, and 1 M NaCl with x = 1 × 10^?4, 5 × 10^?4, and 1 × 10^?3; initial pH₀ was from ～3.5 to ～4.4. The experimentally determined pH versus t dependences and the rate equation for a pseudo-second-order reaction were used to determine the equilibrium constant of formation of Pd(gly)(Hgly)Cl complexes from Pd(gly)₂ complexes and the observed rate constant for this reaction, k _obs. The dependence of k _obs on the pH of the acid solutions studied was assigned to a change in the sequence of the reactions of addition of a hydrogen ion and a chloride ion to the complex Pd(gly)₂.     

Elastic properties of a nematic in a tetrapalladium organyl-pentadecane system

The temperature dependences of birefringence Δn, anisotropy of permittivity ?_a, and elastic constants K ₁₁ and K ₃₃ in the nematic phase of a tetrapalladium organyl-pentadecane system with a pentadecane content of 55 wt % have been investigated experimentally. It has been shown that, as temperature is elevated, ?_a, K ₁₁, and K ₃₃ values decrease and Δn remains unchanged. Elastic constants K ₁₁ and K ₃₃ have been established to vary from 3.4 × 10^?7 to 5.6 × 10^?6 dyn and from 1.3 × 10^?6 to 27.4 × 10^?5 dyn, respectively. The value of ?_a has been revealed to vary over the range 0.2–0.5. It has been found that, at temperatures above the N₂ → Cr phase transition by 6°C, an imposed electric field induces the growth of tetrapalladium organyl crystals.     

Structure and location of proton hydrates in Triton N-42 reverse micelles during injection solubilization of HCl solutions

A Fourier IR spectroscopic study has shown that during injection solubilization* of HCl solutions (V _s/V _o = 1.0-3.5 vol.%) at a concentration of 1-4 M by Triton N-42 reverse micelles in n-decane, the number of water molecules bound to protons is equal to 2.7±0.1. Protons form H₇O₃ ⁺ (70%) and H₅O₂ ⁺ (30%) cations in equilibrium, which are localized in the aqueous cores of the micelles.     

Conducting materials prepared by the oxidation of <Emphasis Type="Italic">p</Emphasis>-phenylenediamine with <Emphasis Type="Italic">p</Emphasis>-benzoquinone

p-Phenylenediamine was oxidized with p-benzoquinone in the aqueous solutions of methanesulfonic acid (MSA). The conductivity of the products increased with increasing concentration of MSA from 1.5?×?10^?12 S cm^?1 in 0.1 M MSA up to 3.4?×?10^?4 S cm^?1 in 5 M MSA. The low-molecular-weight products are basically composed of one p-benzoquinone and two p-phenylenediamine molecules. Their molecular structure is discussed on the basis of mass, Fourier-transform infrared, Raman, NMR and electron paramagnetic resonance (EPR) spectroscopies. The formation of 2,5-di(p-phenylenediamine)-p-benzoquinone protonated with methanesulfonic acid best complies with the information provided by spectroscopic techniques. Its conversion to hydroquinone tautomer explains the formation of unpaired spins observed by EPR and their potential contribution to the conduction.     

Electronic Structure and Relative Stabilities of 10- and 12-Vertex. <Emphasis Type="Italic">Closo</Emphasis>and <Emphasis Type="Italic">Nido</Emphasis>-Heteroborane Clusters of Ga,Ge, and As Elements

A DFT method with the B3LYP functional and the 6-311++G(d,p) diffuse basis set is used to predict geometries, relative stabilities, electronic structures, and the bonding of closo- and nido-Ga_mB_n–mH _n ^2? , Ge_mB_n–mH _n ^m?2 , and As_mB_n–mH _n ^{2 m?2} (n = 10, 12 and m = 1, 2) Clusters are obtained by replacing BH with isolobal GaH, GeH⁺, and AsH²⁺ fragments, keeping the same skeleton electron pairs (SEP). Based on the polyhedral skeletal electron pairs theory (PSEPT), closo and nido structures are predicted and can be of significant interest for experimentalists working in the field of heteroboranes. Different cluster stabilities are studied according to Gimarc′s and Williams′ rules, where our calculations show that the monosubstituted clusters deviate from these rules, giving rise to open structures. As₂B₈H _n ²⁺ as 10-vertex structures lead to nido-type clusters, however, Ge_mB_n–mH _n ^m?2 (n = 10, 12 and m = 1, 2) give rise to closo isomers with close energies. All optimized structures exhibit large HOMO–LUMO gaps suggesting a good kinetic stability, thus predicting their isolation and characterization.     

The inductive effect of a radical center and transferability of the properties of functional groups in <Emphasis Type="Italic">n</Emphasis>-alkyl radicals

Electron density distribution in n-alkyl radicals (from ethyl to n-octyl) was studied by the B3LYP/6-311++G(3df,3pd) DFT method. The theory of atoms in molecules was used to show that the inductive effect of a free valence extends to two neighboring CH₂ groups. The electronegativities χ(C^?H₂) > χ(CH₃) > χ(CH₂) of groups and χ(C^?) > χ(H) > χ(C) atoms were qualitatively determined. The group method for calculating the enthalpies of formation of n-alkyl radicals Δ_f H°(n-C _n H_{2n+ 1}, n > 5) was substantiated.     

Probing Structure,Thermochemistry, Electron Affinity and Magnetic Moment of Erbium-Doped Silicon Clusters ErSi<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 3–10) and Their Anions with Density Functional Theory

The lowest energy structures and electronic properties of ErSi _n (n = 3–10) and their anions were probed using the ABCluster global search technique combined with the PBE, TPSSh and B3LYP schemes. The lowest energy energies of neutral ErSi _n (n = 3–10) can be regarded as substituting a Si atom of the lowest energy structure of Si_n+1 with a Er atom. The additional electron effects on the geometries are very strong, resulting the lowest energy structures of ErSi _n ^? with n > 6 are different from their neutral counterparts. Starting from n = 7, the potential energy surfaces of ErSi _n ^? are very flat, resulting isomeric arrangements occur and functional dependence of the predicted most stable structures exist. The AEAs, VDEs and simulated PES of ErSi _n (n = 3–10) are reported. Introducing Er to Si cluster can significantly improve photochemical reactivity of the cluster. The 4f electron of Er atom in ErSi₄, ErSi _n ^? (n = 4, 7–10) prefers to take part in bonding. The total magnetic moments of ErSi _n and their anions are mainly provided by the 4f electrons of Er atom. The dissociation energies of Er from ErSi _n and their anions were evaluated to inspect relative stability.