V. N. Karazin Kharkiv National University Bulletin. Chemical series

Carbon Nanotubes in Liquid Media: Influence of Solvation on the Colloidal Stability

Vladislav Haidar — 2026-05-29

This article presents the results of a study of the colloidal properties of multiwalled carbon nanotubes (MWCNTs) in water and two organic solvents. This work continues the systematic study of the aggregation stability and coagulation of carbon nanoparticles in various solvents with the aim of identifying the contribution of solvation to the colloidal properties of these widely used systems. The samples were characterized by EDS and XPS methods. The suspension was prepared using ultrasonic treatment in N-methyl-pyrrolidin-2-one and diluted 100-fold with water, acetonitrile, or dimethyl sulfoxide. The working concentration of MWCNTs carbon nanotubes was 5×10^–4 g L^–1. The size of negatively charged particles in water, 95 vol% aqueous CH₃CN, and 95 vol% DMSO was determined by dynamic light scattering: the Z_aver values are 249±15, 265±42 and 146±8 nm, respectively, which corresponds to the diameter of the equivalent sphere. TEM images show that the CNT diameter in aqueous suspension is approximately 9–11 nm and the length is approximately 40–170 nm. Critical coagulation concentrations (CCC) of NaCl were determined using the Fuchs function. These values differ significantly in water and 95% acetonitrile: CCC = 230 and 1.0 mM, respectively. In 95% DMSO, coagulation is less pronounced. The effects were discussed in terms of Gutmann’s Donor Numbers for organic solvents and the specificity of hydration of non-polar materials in water. The CCC of HCl in water is 1.5 mM, which suggests the role of acid-base properties in the formation of the negative charge of the MWCNT colloidal particles.

A New Synthetic Strategy for the Synthesis of 2-amino-6-R-[1,3]thiazolo[5,4-b]pyridines

Andrii Tolkunov — 2026-05-29

Derivatives of 1,3-thiazolopyridine are synthetically available compounds that are actively studied due to their potential antibacterial and anti-tumor activity.

Recently [1,3]thiazolo[5,4-b]pyridine alkaloid, janthinedine A, was isolated from Taxus wallichiana var. chinensis (Pilger) Florin as a secondary metabolite, which demonstrated high antimicrobial and antifungal activities.

The article discusses the new approach to the synthesis of 2-aminothiazolo[5,4-b]pyridine derivatives that is based on the nucleophilic substitution in 2-chloro-3-nitropyridines by the action of KSH with simultaneous reduction of nitro group. 3-Aminopyridine-2(1H)-thiones obtained in this way react with cyanogen bromide in anhydrous MeOH to form the target products in good yields. According to LCMS data, the purity of the target products obtained by the proposed method exceeds 95%.

The structures of the compounds were proved using ¹H NMR, ¹³C NMR and mass-spectra.

Analysis of Volumetric Properties of Liquid Mixtures. II Aqueous-Organic Solvent Systems

Pavel Efimov — 2026-05-29

An extended model of binary additive quasi-solvates (BAQS) is proposed to describe the properties of binary liquid systems. The model incorporates two additional parameters: the limiting partial molar quantities of the solution components. Notably, these parameters are determined a priori, typically from independent experimental data. Concurrently, within the model framework, the effective limiting partial molar quantities are derived from the dependence of the studied property on the mixture composition. The discrepancy between the a priori and effective values is attributed to a shift in the equilibrium between homogeneous and heterogeneous quasi-solvates, as well as a redistribution of the solvent-solute roles within heterogeneous quasi-solvates. For each component, a parameter ξ is introduced, representing the ratio of the effective excess limiting partial molar quantity to its corresponding a priori value. Based on these parameters, the excess functions of heterogeneity α^E and role asymmetry β^E are defined.

Using molar volume dependencies for 12 binary aqueous systems (with methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, tetrahydrofuran, 1,4-dioxane, acetonitrile, acetone, dimethylformamide, dimethylacetamide, and dimethyl sulfoxide) at 298.15 K, along with literature data, the functions α^E and β^E were calculated. The study determined the compositions and function values at extrema, average function values, and quasi-solvate weighting factors for equimolar mixtures. The results demonstrate that the calculated parameters can effectively characterize structural features of aqueous-organic solutions. Despite the model's apparent simplicity, this approach is suitable for the rapid analysis of large sets of binary liquid systems.

Kinetics of the Stepwise Hydrolysis of Mononitrofluorescein Diacetates in Organized Solutions

Daria Kharchenko — 2026-05-29

The kinetics of the stepwise alkaline hydrolysis of three isomeric mononitrofluorescein diacetates, containing the nitro group in the residue of the phthalic acid, were investigated in water and organized aqueous solutions of cationic surfactants and a cationic calix[4]arene. The reaction follows a consecutive two-stage mechanism involving the formation of a spectroscopically distinguishable monoacetate intermediate. UV-visible spectrophotometric monitoring allowed for the separate determination of the pseudo-first-order rate constants for both hydrolytic steps. The catalytic efficiency of the organized systems was found to increase in the order: cetyltrimethylammonium bromide (CTAB) < N,N-dimethyl-N-hydroxyethyl-4-dodecyloxybenzylammonium chloride (C₁₂-Bn-Ch) < 5,11,17,23-Tetra(N,N-dimethyl-N-hydroxyethylammonium)methylene-25,26,27,28-tetradodecyloxy calix[4]arene tetrachloride (C₁₂-C4A-Ch), with acceleration factors reaching nearly three orders of magnitude for the 3'-nitro derivative. The positioning of the nitro substituent markedly influenced the relative rates of the two hydrolysis stages, with the k₂’/k₁' ratio being governed by the interplay between intrinsic electronic effects and the nature of the organized environment. These results suggest that supramolecular assemblies based on calixarene derivatives provide a highly efficient microenvironment for ester hydrolysis, likely through a synergy between specific host-guest recognition within the macrocyclic cavity and collective electrostatic effects at the aggregate interface.

Binding Free Energies of Divalent Cations to Functional Groups of Amino Acids with OPLS-AA Force Field

Volodymyr Farafonov — 2026-05-29

Purification of water from heavy metal ions is an urgent environmental problem. An actively studied method for this is the binding of metal ions by means of natural materials like plant proteins, as well as engineered materials like functionalized carbon allotropes. Carboxyl, thiol, amino groups are capable of complexing with metal cations, which leads to the removal of pollutants from water. Computational chemistry methods including classical molecular dynamics modeling are actively used in search of suitable materials. The paper evaluates the correctness of reproducing binding free energies of a number of divalent metal cations with functional groups found in amino acids using OPLS-AA force field. Both standard built-in and recently used potential models of cations are considered. Comparisons are made with respect to experimentally measured stability constants of modeled complexes or their structural analogues. Calculations of free energies are performed by the method of alchemical transformation. It is shown that despite the validity of the potential models, the binding free energies to functional groups of amino acids are generally poorly reproduced: strongly overestimated for the carboxylate group, underestimated for the thiolate and amino groups, and incorrect for imidazole. This indicates that OPLS-AA force field should be used with caution for calculation of the energy characteristics of metal binding. The way to fix potential models in order to accurately reproduce experimental values is outlined and applied to four cation – ligand complexes.

Solvatochromic Effects of Reichardt’s Dyes and 4-[[(2,4-dinitrophenyl)methylene]imino-2,6-diphenyl]phenol in Individual Solvents and Aqueous-Organic Mixtures: Structural Features of Aqueous Solvents of Non-Electrolytes

Yevgeniya Serhieieva — 2026-05-29

The solvatochromic effects of 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl) phenolate (Ind 1) and 4-[[2,4-dinitrophenyl)methylene]imino-2,6-diphenyl]phenol (Ind 2) were studied in 28 individual solvents and in 16 binary aqueous-organic mixtures.

It was found that in individual solvents, Ind 1 and Ind 2 show approximately the same nature in of the change in the solvatochromic effects when passing from one solvent to another, with the exception of water, in which Ind 2 shows an anomalously small solvatochromic effect, as compared with Ind 1. This anomaly is due to the fact that water can stabilize the excited state of Ind 2 because of hydration, while in Ind 1, only the ground state is stabilized.

It was found that in binary aqueous-organic mixtures, Ind 1 is not very suitable for studying their solvating ability, while Ind 2 shows a specific feature – a sharp drop in Е_Т at a certain concentration to values characteristic of pure water. It was assumed that the constant value of Е_Т after a sharp drop is associated with the possible existence of a micro-heterogeneous structure of a binary mixture at these compositions with micro-areas of water, in which both the structural (H-bonds) and hydration properties of pure water are preserved.

The shard drop of Е_Т can be explained by the change in the hydration shell around the phenolate oxygen atom in the ground state at the maximum dependence on the hydration shell around the nitro fragment in the excited state, which is characteristic of pure water.