Water desalination across functionalized silicon carbide nanosheet membranes: insights from molecular simulations

Desalination of seawater can be an effective way to access drinking water. In this study, the performance of functionalized silicon carbide nanosheet (SiCNS) membranes for water desalination was investigated using molecular dynamics (MD) simulations. For this purpose, four types of membranes with various functionalized pores were considered to investigate their capabilities in water desalination. The chemical functions of fluorine (–F) (system S1), hydrogen (–H) (systems S2 and S3), and hydrogen (–H) and hydroxyl (–OH) (system S4) were bonded to the pore edge of the SiCNS membranes. Also, the effect of the number of pores in the membrane on the water permeability was studied between systems S2 and S3. The SiCNS membrane was placed at the center of the simulation box and the external pressure was applied to the system in the range of 10–100 MPa. The water permeability, salt rejection, potential of mean force of ions, water density, water density map, and radial distribution function (RDF) of water molecules were calculated in this work. The results demonstrated that the water permeability increases by adding hydrophilic chemical functions such as –F and –OH on the pore edge.

     

Evolution of new narcotic substances and methods of their determination

History of the appearance and evolution of synthetic narcotics in recent years is presented. The main attention is paid to two classes of narcotic substances received the widest distribution in the world, i.e., cannabimetics and synthetic cations. The main classes, problems of identification, and approaches to the determination of new narcotics are considered. Approaches and solutions used in the quantitative analysis and screening of narcotics are discussed along with some aspects of sample preparation to their determination and matrix effects. The specific features of the determination of new narcotics in commercial products and biological samples are considered separately. Present-day methods of chromatography-mass spectrometry are most informative for timely revealing new narcotic substances, studying their metabolism, and developing reliable methods for the screening of native and biological samples.     

Numerical Determination of the Relaxation Parameters of NMR in Complex Heterogeneous Systems

The methods of mathematical processing of the envelopes of spin-echo signals have been considered within the framework of the multiphase relaxation theory. A mathematical model for separation of multiexponential relaxation curves into individual exponential components of spin-spin relaxation times T _2i and amplitudes I _i is described. The multiphase nature of the relaxation of protons in complex heterogeneous systems has been revealed, and the relaxation characteristics of individual components — spin-spin relaxation times and amplitudes — have been determined.     

Determination of some cathinones,tropane alkaloids,and “pharmaceutical narcotics” in urine

A procedure is proposed for determining some narcotic and psychoactive substances (cathinones, tropane alkaloids, derivatives of ?-aminobutyric acid) in urine, including sample preparation and the determination of analytes by HPLC coupled with electrospray ionization tandem mass spectrometry. Sample preparation involved acid hydrolysis or the dilution of the sample. The lower limit of quantification is 200 pg/mL; the limit of detection is 100 pg/mL; and the calibration curves are linear in the range 0.2–50 ng/mL. The procedure was tested on real samples provided by the Toxicological Department of the Krasnodar Regional Narcological Dispensary. The high sensitivity of the analytical system ensures its use for the determination of narcotic preparations within a certain time after their intake, which may be of particular importance for forensic examinations.     

Application of Ranging Analysis to the Quality Assessment of Wines on a Nominal Scale

This work is dedicated to wine quality assessment methods as a problem of considerable current interest. Well-known approaches to wine quality assessment are considered based on the concentrations of volatile substances in wines and on the results of their taste tests. Comparative analysis was carried out for the evaluation of wines on a nominal scale of quality (high, medium, low, and adulterated) by means of discriminant analysis. It was found that the classification of wines based on quality with the use of discriminant analysis as a ranging analysis method with consideration for the concentrations of volatile substances, which are responsible for their organoleptic properties, is highly competitive with their expert (tasting) evaluation. A mathematical model was constructed for the classification of wines into the above categories, and a program module was developed for the automation of calculations.     

Macrocyclic Ionic Liquids with Amino Acid Residues: Synthesis and Influence of Thiacalix[4]arene Conformation on Thermal Stability

Novel thiacalix[4]arene based ammonium ionic liquids (ILs) containing amino acid residues (glycine and L-phenylalanine) in cone, partial cone, and 1,3-alternate conformations were synthesized by alkylation of macrocyclic tertiary amines with N-bromoacetyl-amino acids ethyl ester followed by replacing bromide anions with bis(trifluoromethylsulfonyl)imide ions. The melting temperature of the obtained ILs was found in the range of 50–75 °C. The effect of macrocyclic core conformation on the synthesized ILs’ melting points was shown, i.e., the ILs in partial cone conformation have the lowest melting points. Thermal stability of the obtained macrocyclic ILs was determined via thermogravimetry and differential scanning calorimetry. The onset of decomposition of the synthesized compounds was established at 305–327 °C. The compounds with L-phenylalanine residues are less thermally stable by 3–19 °C than the same glycine-containing derivatives.     

Catalytic test determination of copper on a solid support

A test procedure was developed for the determination of 5 × 10^?7?1 × 10^?3 M copper with the use of the copper-catalyzed reaction of the reduction of molybdophosphoric acid by thiourea on a solid support (paper). The conditions of the indicator reaction and the technique for its conduction were optimized; the pH range in which the acidity of the solution does not affect the time of the reaction was revealed. The calibration plot for the determination of copper was constructed in reaction time-pCu coordinates. The effect of different components on the rate of the indicator reaction was studied. The procedure was approved in the analysis of real and model solutions.     

Separation and identification of phenothiazine compounds by thin-layer chromatography

The chromatographic behavior of phenothiazine derivatives is studied by thin-layer chromatography with the use of Sorbfil silica gel plates in a binary benzene-methanol mixture of solvents. An empirical equation describing the dependence of the retention value (mobility R _f ) of the substance on the physicochemical properties of the eluent is proposed. The effect of interactions of different types on the value of their chromatographic retention is estimated; the relation of the obtained coefficients of equations for the substances under study is analyzed. The obtained empirical dependences are used to calculate the R _f values. The discrepancy between the calculated and experimental data is below 0.07.