Chemistry and Materials Science

Abstract: In Mozambique, mining is one of the main drivers of the economy, boosting investment and contributing significantly to public revenue generation. This study aims to evaluate the concentration of tantalum, niobium, and associated elements in tantalite ore. The country hosts significant occurrences of tantalite, the primary source of metals such as tantalum, niobium, iron, oxygen, and manganese. Tantalum is a metal of high technological relevance, widely used in the manufacture of electronic devices. For this investigation, tantalite samples from two distinct references (Reference I and II), as well as from tantaliferous pegmatites, were analyzed. Morphological and elemental characterization was performed using Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-ray Spectroscopy (EDS), enabling the observation of surface morphology, roughness, and chemical heterogeneity through atomic contrast between different mineral phases. The results were complemented by calculations of sample standard deviation and relative standard deviation to assess the precision of the measurements. EDS spectra confirmed the presence of predominant elements such as tantalum, iron, oxygen, aluminum, titanium, silicon, and manganese, consistent with the typical composition of tantalite and associated minerals.

Abstract: The removal of Pb(II) ions from aqueous solution by sorption onto layered double hydroxides (LDHs) is widely documented, yet the reported capacities range from 13 to over 200 mg g⁻¹. The dispersion is usually ascribed to the layer chemistry but cannot be tested because published values come from widely different operating conditions; this work supplies the missing reference member of a single-protocol series. Carbonate-intercalated Mg₂Al–CO₃ was prepared by coprecipitation at constant pH, characterized by XRD, SEM–EDX, N₂ sorption, DSC and pH_PZC, and evaluated as a function of dose, pH, contact time, concentration and temperature. Equilibrium was reached within 60 min, the kinetics were pseudo-first-order, the Redlich–Peterson and Langmuir equations fitted the isotherm best with a monolayer capacity of 59.1 mg g⁻¹, and the uptake was spontaneous and endothermic (ΔH° = 11.1 kJ mol⁻¹). They are then compared with two isostructural phases previously published by our team, Mg₂[FeAl]–CO₃ and Zn₂[FeAl]–CO₃, prepared and tested under strictly identical conditions; no new experiment was performed on these solids, whose values are quoted here for comparison only. Replacing half of the Al(III) by Fe(III) doubles qm to 118.8 mg g⁻¹ and replacing Mg(II) by Zn(II) raises it to 87.9 mg g⁻¹. Normalized to the BET surface area, however, the three capacities converge on 1.55 ± 0.07 mg m⁻²: the layer composition acts on Pb(II) uptake only through the accessible surface area it generates, not through the intrinsic reactivity of the surface. Sorbent design should therefore target textural disorder rather than a particular cation pair.

Abstract: Poly(N-isopropylacrylamide) (PNIPAM)-based hydrogels are “smart” materials of great interest and demand, primarily in a variety of biomedical applications, due to their LCST close to physiological temperature. The basic biomedical applications of PNIPAM-based injectable hydrogels include controlled drug delivery, tissue engineering, wound healing, and cancer therapy. This review summarizes the thermal phase behavior of PNIPAM-based systems in different conditions, including different scenarios of physical gelation in polymer solutions and volume phase transitions in chemically crosslinked hydrogels. The thermodynamics of coil-to-globule phase transition, its relation to the gel formation, and mechanisms underlying the phase transitions in PNIPAM-based hydrogels are discussed, as well as external parameters which may affect these processes. Different types of phase diagrams observed for PNIPAM-based systems are considered, with particular attention paid to the cases in which gelation occurs separately from the coil-to-globule transition. The rational design of injectable platforms should be based upon a thorough understanding of the PNIPAM-based system’s phase behavior to achieve controllable and reproducible properties.

Abstract: We present a theoretical and numerical study of the Self-Consistent Spectral Potential Mean-Field (SC-SPMF) method for the description of structure and stability of phase transitions in condensed matter. The method extends the original Spectral Potential Mean-Field (SPMF) approach by introducing a fully self-consistent cycle between the Kirkwood relation and the Fisher equation. The SC-SPMF method determines the coordination shell in condensed matter, providing a genuinely predictive framework for the study without requiring approximate functionals or closure relations. The method is applied to the solid-to-liquid and liquid-to-solid phase transitions of argon, a prototypical monatomic system with well-characterized experimental and simulation data. The temperature evolution of key parameters of radial distribution function and potential of mean force clearly identifies the phase transition at approximately 86 K, in agreement with the experimental melting temperature of argon (83.8 K). A central result is the formulation of a spectral criterion for stability: the transition is marked by a change in the curvature of the first eigenvalue of the Fischer equation μ1(T), specifically by the temperature at which the second derivative d2μ1/dT2 becomes positive. This criterion does not rely on the absolute value of μ1, but on a qualitative change in the spectral response of the system, providing a system-independent fingerprint of the onset of the liquid phase. The method captures hysteresis and metastability between heating and cooling paths, with a hysteresis width of approximately 1.6 K, consistent with the first-order nature of the transition. The critical exponent β is found to differ between the two paths: β≈0.36 for the heating (close to the 3D Ising model value of 0.326) and β≈0.51 for the cooling (close to the mean-field value of 0.5). This difference reflects the role of short-range or long-range interactions in determining the effective critical behavior along melting or crystallization paths, respectively. This spectral interpretation offers a new perspective on phase stability, hysteresis, and critical phenomena, making the SC-SPMF method a powerful and original tool for the study of condensed matter.

Abstract:

In this work, we carried out a computational study of the gas-phase thermal decomposition of N‑aryl‑3‑oxobutanamides (β-ketoamides) and the 2‑arylhydrazone derivatives. We performed calculations using density functional theory (DFT) at B97D‑GD3BJ/deft2tzvp level, with multivariant analysis including descriptors of global reactivity, e.g., ionization energy (I), electron affinity (A), molecular hardness (η) and electrophilicity (ω). The objective was to elucidate the reaction mechanism. To this end, we modeled the structures of reactants, transition states and products and studied the effect of substituents on the N-aryl and the 2-aryl aromatic ring on the energy of activation. The synchronicity of the process and the nature of non-covalent interactions were studied to gain insight into the reactivity and selectivity of these molecules. We examined the reactivity of 2-arylhydrazone derivatives, which show reaction rates about three orders of magnitude slower than the parent β-ketoamide. We evaluated two competing mechanisms involving cyclic transition states of six and four members. This study included electronic descriptors, e.g., NBO analysis, IGM/IBSI, Wiberg bond indexes, and intrinsic reaction coordinate calculations (IRC). We introduce a new descriptor, Dynamic Synchronicity, SyD, for mechanistic and kinetic characterization. To the best of our knowledge, this work is the first comprehensive theoretical study of the system ketoamide/aryl hydrazone. Multivariate statistical methods, i.e., principal component analysis (PCA) and hierarchical cluster analysis (HCA), are useful tools for the selection of the atoms involved in the transition states.

Abstract: A SAPT (Symmetry Adapted Perturbation Theory) decomposition analysis was performed for various types of noncovalent interactions (stacking, hydrogen bonds, antiparallel) for various distances of interacting fragments. Although total interaction energy does not significantly change within the small range around the optimal distance, the energy contributions can significantly change in some systems. This is particularly pronounced for stacking interactions, while for hydrogen bonds and antiparallel interaction the energy contributions do not significantly change around the optimal distance. Thus, it is very important to precisely determine the optimal distance between the interacting fragments when performing SAPT analysis of noncovalent interactions, especially for stacking interactions, since the general conclusions about the nature of interactions can differ in the small range of distances between the interacting fragments.

Abstract: This study investigates the resistance responses of polypyrrole (PPy), titanium dioxide (TiO₂) single layers, and PPy/TiO₂ bilayer, a heterostructure, to rectangular pulses of monochromatic LED illumination under controlled humidity. Exposure to moisture increases the resistance of TiO₂ while rapidly decreasing that of PPy, reflecting opposite influences of electron donation from hydroxyl groups in adsorbed H₂O on the intrinsic carrier densities of the two materials. Under monochromatic illumination, PPy exhibits a simple decrease in resistance, whereas TiO₂ displays a resistance increase accompanied by a brief transient at excitation wavelengths near its optical edge (367 nm and 398 nm). This behavior is assigned to photoinduced carrier density modification through two oposite processes; photogeneration releasing while H₂O photodesorption eliminating charge carriers. The PPy/TiO₂ heterostructure demonstrates a mixed photoresponse arising from the contrasting behaviors of its p‑type PPy and n‑type TiO₂ components, together with charge exchange across the p–n junction. When subjected simultaneously to moisture and monochromatic light, differences in photoinduced carrier generation in two components dynamically modulate the depletion region, producing a wavelength‑dependent resistance response. This complementary “push–pull” interaction results in a synergistic enhancement of photocatalytic and sensing performance in the PPy/TiO₂ heterostructure.

Abstract: A In this study, the combustion behavior of Çayırhan coal under an oxygen atmosphere was investigated, and its combustion kinetics and thermodynamic parameters were determined. Thermal analyses (TGA, DTG, and DSC) revealed that the combustion process occurs in two consecutive steps. The first step, where 85% of the total weight loss takes place, requires a relatively low activation energy. Conversely, the second step, corresponding to the remaining 15% of the combustion, demands a significantly higher activation energy. Both combustion stages were analyzed using model-free isoconver-sional methods. The average activation energies were calculated as 139.65 ± 9.66 kJ/mol for the first stage and 402.27 ± 65.53 kJ/mol for the second stage. Subsequent kinetic modeling studies demonstrated that both combustion reactions are highly compatible with the diffusion mechanism. Following the determination of the most suitable reaction model, the Arrhenius pre-exponential factor (A) and other thermodynamic parameters of the activated complex (ΔS‡, ΔH‡ and ΔG‡) were successfully evaluated.

Abstract: Nonlamellar liquid crystalline nanodispersions produced from single monoacylglycerols or from their combinations with fatty acids or other amphiphiles have attracted interest owing to their structural versatility and tunability. In this study, we investigated the effect of dilinolein (DLO) incorporation on the structural features of Pluronic F127-stabilized monolinolein (MLO) nanodispersions using small-angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (cryo-TEM), and dynamic light scattering (DLS). We report on a lipid composition-dependent direct colloidal transformation from hexosomes, defined as nanoparticles with an ordered internal inverse hexagonal (H₂) phase, to emulsified L₂ phases (ELPs), which are nanoparticles with a more disordered internal inverse micellar (L₂) phase) upon the partial replacement of MLO by DLO. Small-angle X-ray scattering (SAXS) measurements showed that, at relatively low DLO content, the MLO-rich MLO:DLO 90:10 (w/w) nanodispersion ) retained an ordered internal H₂ phase, with three well-defined characteristic Bragg peaks; whereas the SAXS patterns recorded for all nanodispersions containing ≥ 20 wt% DLO displayed broad correlation peaks consistent with internal L₂ nanostructures. Similarly, the control nanodispersion prepared from DLO alone, displayed a single broad correlation peak, supporting its assignment as an internal L₂ phase. For the assigned internal L₂ phases, the SAXS-derived characteristic distance decreased monotonically from 4.53 to 2.87 nm as the DLO fraction increased. The experimental findings show that DLO modifies lipid packing at the MLO-water interface and promotes more negative spontaneous curvature, driving the direct H₂-to-L₂ phase transition. The ability to tune the internal nanostructure by lipid composition while maintaining nanoscale particle size and low dispersity makes these nanodispersions attractive platforms for drug nanocarrier development.

Abstract: Water exhibits anomalous thermodynamic and structural behavior as it approaches and crosses below its melting point. Modelling this behaviour computationally remains challenging: as temperature decreases, nuclear quantum effects (NQE) become increasingly significant, sampling efficiency deteriorates dramatically, and the choice of computational method critically impacts the accuracy of predicted structural and dynamical properties. This review aims to provide practitioners with a comprehensive guide to performing reliable molecular dynamics simulations of water at low temperatures, with particular emphasis on the supercooled regime (200--273 K). We examine commonly used methods in ab initio molecular dynamics (AIMD) approaches, and critically evaluate strategies for incorporating nuclear quantum effects through path-integral molecular dynamics (PIMD), ring-polymer MD (RPMD), and centroid MD (CMD); below approximately 250 K the magnitude of nuclear quantum effects, and the sensitivity of structural and dynamical properties to them, grows to the point where classical treatment of the nuclei is no longer adequate. The known limitations of density functional approximations for water structure are assessed in the context of their interplay with NQE treatment, rather than in isolation. By discussing practical considerations, including sampling efficiency and the temperature scaling of path-integral bead counts, alongside the methods themselves, this review is intended to serve as a practical reference for reliable AIMD studies of supercooled water.

Abstract: The prevailing scientific consensus on the origin of primordial water on Earth identifies two main possibilities: the Interstellar Origin, where primordial water was sourced from external bodies, and the Common Origin, which suggests that water formed alongside the planet. This paper supports the idea that primordial water may have formed during Earth’s formation. Nevertheless, it proposes a scenario in which the interplay of the primordial multilayered atmosphere, the primordial planetesimal crust, and, most importantly, various chemical reactions contributed to the global cycles of chlorate and ammonia. Within these cycles, a series of thermodynamically favorable chemical reactions and the conditions under which they occur are examined and discussed to substantiate the development of Earth’s primordial saline ocean water and nitrogen-rich atmosphere.

Abstract: A series of novel complexes with the general formula [RuNO(L)Cl₃], where L is a bidentate ligand (bpym, bpy, phen), was synthesized and characterized. The photochemical activity of fac-[RuNO(bpym)Cl₃] (1), fac-[RuNO(phen)Cl₃] (2), mer-[RuNO(phen)Cl₃] (3), fac-[RuNO(bpy)Cl₃] (4), mer-[RuNO(bpy)Cl₃] (5) in DMSO was quantified under 450 nm irradiation using a flow-through system, allowing simultaneous IR and UV-Vis spectral monitoring. Quantum yields for photoinduced release of NO were determined as follows: 5.4 ± 0.5 % for fac-[RuNO(bpym)Cl₃] (1); 0.8±0.1 % for fac-[RuNO(phen)Cl₃] (2); 0.6±0.1 % for mer-[RuNO(phen)Cl₃] (3); 3.7±0.1 % for fac-[RuNO(bpy)Cl₃] (4); 2.1±0.1 % for mer-[RuNO(bpy)Cl₃] (5). The product of photolysis of compound 5 in acetonitrile solution was isolated and structurally characterized as mer-[Ru(CH₃CN)(bpy)Cl₃] (6). Taking into account the presence of typical DNA intercalating ligands the complexes can be potentially exploited as photoNORMs.

Abstract: In mathematical chemistry, topological indices are frequently employed to link numerical descriptors related to chemical and biological aspects with molecular graph structures. The Sombor index is one of these indicators that has attracted a lot of interest lately because of its remarkable structural sensitivity and predictive power. In this study, we extend the conventional Sombor index to fuzzy graph situations by introducing a fuzzy graph-based Sombor index, represented by SO(Fη). Under basic graph operations, such as the union, join, composition, and Cartesian product of fuzzy graphs, several constraints for SO(Fη) are found. Additionally, a comparison analysis is carried out to examine the connection between the Sombor index and other well-known topological indices, emphasizing its usefulness in chemical graph theory. A modified fuzzy Sombor index is created and used to analyze cancer diagnosis data in China, where uncertainty in risk factors including nutrition, obesity, diabetes, and air pollution plays a critical role in disease progression, in order to show the practical applicability of the suggested index. The promise of the fuzzy Sombor index as a flexible tool connecting theoretical graph invariants and practical data analysis is demonstrated by this application.

Abstract: This work investigates the photo-Fenton degradation of azo dyes in an aqueous medium rich in sodium dodecyl sulfate (SDS), using methyl orange (MO) as a model contaminant. Chemometric modeling was integrated with mechanistic analysis to elucidate the role of the micellar pseudophase in radical distribution, dye partitioning, and overall reaction efficiency. A sequential experimental design strategy was applied, combining fractional factorial design and response surface methodology (RSM) to evaluate the individual and interactive effects of key operational variables and determine the optimal operating conditions for maximum degradation efficiency. Under optimized conditions (pH 2.85, [H₂O₂] = 100 mM, [Fe²⁺] = 0.5 mM, [SDS] = 13 mM, [MO] = 0.01 mM), MO degradation reached 98.4% in 5 minutes. Spectroscopic and partitioning studies revealed a strong affinity of MO for the micellar interface, indicating preferential localization in a microheterogeneous environment. Radical scavenging experiments confirmed that hydroxyl radicals are the dominant oxidizing species in water, while the reduction observed in the presence of SDS suggested secondary radical pathways derived from the surfactant under micellar conditions. Kinetic analyses highlighted the role of intermolecular interactions and micellar compartmentalization in radical generation. The optimized system was successfully extended to other azo dyes, underscoring the potential of surfactant-rich organized media to enhance photo-Fenton reactions in complex aqueous environments.

Abstract: Antimicrobial peptides are promising agents for combating resistant infections. They exhibit bactericidal activity against a wide range of microbes, primarily by disrupting the permeability of the bacterial membrane and ultimately causing cell death. Effective bacterial killing requires a high number of membrane-bound peptide molecules. Therefore, it is conceivable that peptide accumulation on the membrane could also interfere with essential cellular processes by altering bilayer dynamics, a hypothesis referred to as the “sand in the gearbox” model. In this work, we systematically investigated how membrane dynamics is affected by a set of well-characterized yet highly diverse peptides: the natural AMP magainin 2, the toxin melittin, the synthetic peptides LAH4 and Killer-FLIP, and small membrane-active peptidomimetics with bactericidal activity. These effects were examined using fluorescence spectroscopy techniques, by measuring anisotropy, generalized polarization, and excimer formation of specific probes inserted at different depths within the lipid bilayer. Our results show that the activity of all compounds extends beyond membrane permeabilization, and that perturbation of membrane dynamics is a common feature among all systems analyzed. The membrane-active compounds induced a stiffening of the phospholipid bilayer by reducing lipid lateral mobility and decreasing water penetration, at least on the nanosecond timescale accessible to fluorescence measurements. Interestingly, when accounting for differences in the resulting membrane surface area coverage, the concentration range in which this behavior occurred was the same for all compounds studied. This threshold is, generally, higher than that required for membrane permeabilization and reflects near-complete coverage of the bilayer surface.

Abstract: In this paper, we present new methods for the synthesis of picrylamino derivatives. Improvements over existing methods are demonstrated, including significantly reduced reaction times and the use of less hazardous reagents. One of these methods is recommended for the synthesis of 3-picrylamino-1H-1,2,4-triazole due to its slightly higher yield and reduced use of harmful picryl chloride. The proposed methods provide a practical approach for producing insensitive high-energy materials with good yields and high purity. The purity of the synthesized materials was confirmed by LC-MS or FT-IR spectra analysis. It is also shown that introducing substitutions into the benzene or triazole ring does not require additional synthetic steps, while the resulting compounds exhibit improved stability and/or detonation performance. The proposed methods provide a practical approach for producing insensitive high-energy materials with good yields and high purity. The stability of the picrylamino derivatives was confirmed by bullet impact tests. In addition, the structure of picrylamino-1,2,4-triazole is analyzed to provide insight into its stability. The results establish a practical and scalable approach to the development of safer, more stable, and high-performance energetic materials.

Abstract: The calculation of gas properties from the gas composition is an activity that occurs frequently in gas analysis. Such calculations play an important role in the transmission and distribution of energy gases, carbon dioxide and other commodities. They also occur in monitoring air quality. Applications include the calculation of compressibility factors of natural gas to convert metered gas volumes from actual to reference conditions, the conversion of amount fractions into mass concentrations and calculations in process design and optimisation. Evaluating measurement uncertainty is important, as usually there are legislative, regulatory and commercial requirements to be met. Assessing and demonstrating compliance with such requirements requires knowledge about the uncertainty of the measurement result. It is shown how the well-known law of propagation of uncertainty can be used with models from which it is not evident how to calculate partial derivatives, such as equations of state, which are used to calculate, e.g., compressibility factors, densities and energies. Furthermore, it is shown how to calculate time averages from measurement data in grids and networks.

Abstract: In this study, hydantoin (C₃H₄N₂O₂) was selected to investigate the photoluminescence mechanism of non-typical luminescent compounds. The emission spectra of single crystals were examined using a laser confocal microscope. Within the same crystal, the peak shape and position were consistent across different regions, while the intensity varied; this phenomenon is attributed to confinement-induced emission. For different crystal blocks, variations in molecular packing modes led to changes in both peak shape and position. Combined with theoretical calculations and analyses, the results show that: as the molecular number increases, the energy gap decreases and the excitation wavelength increases (lower excitation energy); the hole-electron attraction energy, delocalization index, and overlap degree all decrease, with the hole delocalization index decreasing faster than that of the electron; the spin-orbit coupling coefficients for high-lying triplet states are more sensitive to the molecular count; and the intersystem crossing rate increases sharply with increasing energy level. In summary, the number and mode of molecular packing in the crystal influence the excited-state electronic structure and hole-electron interactions, thereby determining the luminescence behavior of non-typical luminescent compounds.

Abstract: In protein solutions, an additive that increases protein-protein attractive interactions is expected to decrease protein crystal solubility and raise temperature of liquid-liquid phase separation (LLPS). In contrast, addition of 0.10-M 4-(2-hydroxyethyl)-1-piperazineethanesulfonate (HEPES) to lysozyme-NaCl aqueous solutions at constant pH (7.4) and ionic strength (0.20 M) decreases solubility but lowers LLPS temperature. This leads to a broadening of LLPS metastability gap in the phase diagram and an enhancement of protein crystallization yield from LLPS. We theoretically examine the effect of HEPES on both solubility and LLPS boundaries using a colloid model. Under the hypothesis that HEPES stabilizes protein-protein contacts in the crystal lattice by physical cross-linking, we apply cell theory to describe the thermodynamic behavior of the crystalline phase and use solubility data to show that HEPES increases protein-protein attraction energy by 2.7%. Since an increase in attraction incorrectly predicts a raise in LLPS temperature, we consider that HEPES also enhances the anisotropic character of protein-protein interactions. To describe the thermodynamic behavior of the solution phase, we start from Barker-Henderson second-order perturbation theory on the hard-sphere reference fluid with square-well potential and local-compressibility approximation. We modify this model so that it can reproduce the correct mathematical expression of the second virial coefficient. This also leads to a better agreement with Monte Carlo simulations. We then approximately incorporate anisotropy by assuming that the square-well attraction energy is a temperature-dependent average over all particle surface with a given fractional coverage of attractive spots. The attraction energy of the attractive spots is set to be the same as that of protein-protein contacts in the crystal. Only fractional coverage (anisotropy) was varied to successfully fit the effect of HEPES on the LLPS boundary.

Abstract: Heparin is a highly sulfated polyelectrolyte, and its properties depend a lot on its shape in solution. In this study, we closely examined the structural behaviour of UVC-irradiated low-molecular-weight heparin. By using controlled photodegradation, we created native, small, and ultra-small molar mass fractions, which allowed us to study how structural properties change with molecular weight. We examined how molar mass, radius of gyration, second virial coefficient, and critical overlap concentration are related to one another to understand different conformational states. Our results showed that as molar mass decreased, the chain diameter and persistence length also dropped, while the overlap concentration increased. This means the hydrodynamic volume went down and the chains became more flexible. The positive second virial coefficient values showed that polymer–solvent interactions remained favourable after photo-tailing. The scaling exponents suggest that degraded heparin behaves as a semi-flexible polyelectrolyte and adopts an extended-coil shape in water with electrolytes. Further analysis showed that the characteristic ratio and stiffness of the chains decreased as the chains were broken by irradiation. Overall, UVC phototailing provides a reliable way to modify the structure of these molecules while maintaining solution stability. These findings show a clear link between reduced molecular weight and changes in shape, which is useful for developing better low-molecular-weight heparins for pharmaceutical and medical use.