Search Results (23)

Ultrafine fibers from poly(3-hydroxybutyrate) (PHB) and polyvinylpyrrolidone (PVP) and their blends with different component ratios in the range of 0/100 to 100/0 wt.% were obtained, and their structure and dynamic properties were studied. The polymers were obtained via electrospinning in solution mode. The structure, morphology, and segmental dynamic behavior of the fibers were determined using optical microscopy, SEM, EPR, DSC, and IR spectroscopy. The low-temperature maximum on the DSC endotherms provided information on the state of the PVP hydrogen bond network, which made it possible to determine the enthalpies of thermal destruction of these bonds. The PHB/PVP fiber blend ratio significantly affected the structural and dynamic parameters of the system. Thus, at low concentrations of PVP (up to 9%) in the structure of ultra-fine fibers, the distribution of this polymer occurs in the form of tiny particles, which are crystallization centers, which causes a significant increase in the degree of crystallinity (χ) activation energy (E_act) and slowing down of molecular dynamics (τ). At higher concentrations of PVP, loose interphase layers were formed in the system, which caused a decrease in these parameters. The strongest changes in the concentration of hydrogen bonds occurred when PVP was added to the composition from 17 to 50%, which was due to the formation of intermolecular hydrogen bonds both in PVP and during the interaction of PVP and PHB. The diffusion coefficient of water vapor in the studied systems (D) decreased as the concentration of glassy PVP in the composition increased. The concentration of the radical decreased with an increase in the proportion of PVP, which can be explained by the glassy state of this polymer at room temperature. A characteristic point of the 50/50% mixture component ratio was found in the region where an inversion transition of PHB from a dispersion material to a dispersed medium was assumed. The conducted studies made it possible for the first time to conduct a comprehensive analysis of the effect of the component ratio on the structural and dynamic characteristics of the PHB/PVP fibrous material at the molecular scale. Full article

The adsorption of the drug gemcitabine on nucleobases was investigated using a dispersion-corrected density functional theory (DFT) study. The planar structure of complexes is more stable than those with stacked and buckle-angled configurations. The complexes were found to possess at least two intermolecular hydrogen bonds. The binding energy and interaction energy are both negative, with the highest values observed for the gemcitabine–guanine and the lowest in the gemcitabine–thymine complex. The complex formation was found to be an enthalpy-driven process. Pyrimidine nucleobases have a lower enthalpy of formation than purine nucleobases. The computed HOMA and NICS values on the gemcitabine–nucleobase complexes show a substantial increase compared to the pristine nucleobases. An MESP analysis of the complexes shows a directional interaction and electron density shift between the gemcitabine and the nucleobases. A QTAIM analysis indicates that the intermolecular hydrogen bonds have a partial covalent character. The computed bond energy demonstrates that intermolecular NH⋅⋅⋅N bonds are more potent than other bonds. An energy decomposition analysis using the DLPNO−CCSD(T) method indicates that the complexes exhibit a substantial electrostatic attraction, and dispersion contributes the least towards the system stability. The intermolecular bonds are stronger than the intramolecular bonds in the drug–nucleobase complexes. The strength of intramolecular bonds is determined by the deformation of the gemcitabine ring during the complex formation. Full article

In this paper, a novel mixed Tutton salt (K_0.86Na_0.14)₂Ni(SO₄)₂(H₂O)₆ was successfully synthesized as a single crystal and evaluated as a thermochemical heat storage material. Its thermal and thermochemical properties were correlated with the structure, which was determined by powder X-ray diffraction using the Le Bail and Rietveld methods. The elemental ratio between the K⁺ and Na⁺ monovalent cations was established by energy-dispersive X-ray spectroscopy. Similar compounds such as Na₂Ni(SO₄)₂(H₂O)₄ and K₂Ni(SO₄)₂(H₂O)₆ were also synthesized and used for structural comparisons. The (K_0.86Na_0.14)₂Ni(SO₄)₂(H₂O)₆ salt crystallizes in monoclinic symmetry with the P2₁/c-space group, typical of hexahydrate crystals from the Tutton salt family. The lattice parameters closely resemble those of K₂Ni(SO₄)₂(H₂O)₆. A comprehensive analysis of the intermolecular contacts, based on Hirshfeld surfaces and 2D fingerprint mappings, revealed that the primary interactions are hydrogen bonds (H···O/O···H) and ion-dipole interactions (K/Na···O/O···Na/K). The unit cell exhibits minimal void space, accounting for only 0.2%, indicative of strong atomic packing. The intermolecular molecular and atomic packing are important factors influencing crystal lattice stabilization and thermal energy supplied to release crystallographic H₂O. The thermal stability of mixed Tutton salt ranges from 300 K to 365 K. Under the dehydration of its six H₂O molecules, the dehydration reaction enthalpy reaches 349.8 kJ/mol, yielding a thermochemical energy storage density of 1.79 GJ/m³. With an H₂O desorption temperature ≤393 K and a high energy storage density ≥1.3 GJ/m³ (criteria established for applications at the domestic level), the (K_0.86Na_0.14)₂Ni(SO₄)₂(H₂O)₆ shows potential as a thermochemical material for small-sized heat batteries. Full article

Three novel multicomponent crystals of trimethylglycine with 2-cyanoguanidine, guanidinium and aminoguanidinium chlorides are synthesized and structurally characterized. All three crystal packings are based on the supramolecular synthon formed by two N–H groups of the guanidine species and carboxylate group of trimethylglycine (graph set notation R²₂(8)). Its enthalpy is about 50 kJ/mol. The three-dimensional structure of crystals is stabilized by intermolecular interactions of various types. The energy of C–H∙∙∙X⁻ interactions, where X = O, Cl, reaches 16 kJ/mol due to the acidic nature of methyl hydrogens. The possible structure of the trimethylglycine–urea–2H₂O complex is discussed. Its theoretical metric and spectroscopic parameters are in reasonable agreement with the available literature data on the deep eutectic solvent trimethylglycine–urea. Full article

A new method, based on quantum chemical calculations, is proposed for the thermodynamically consistent reformulation of QSPR-type Linear Free-Energy Relationship (LFER) models. This reformulation permits the extraction of valuable information on intermolecular interactions and its transfer in other LFER-type models, in acidity/basicity scales, or even in equation-of-state models. New molecular descriptors of electrostatic interactions are derived from the distribution of molecular surface charges obtained from COSMO-type quantum chemical calculations. The widely used and very successful Abraham’s Linear Solvation Energy Relationship (LSER) model is selected as the reference LSER model for the calculations in solute–solvent systems as well as in solute self-solvation. Hydrogen-bonding free energies, enthalpies, and entropies are now derived for a variety of common solutes. The capacity of the method to address the role of conformational changes in solvation quantities is discussed. The perspectives of the LSER model with the implementation of the new descriptors are also discussed. Full article

Tutton salts form an isomorphic crystallographic family that has been intensively investigated in recent decades due to their attractive thermal and optical properties. In this work, we report four mixed Tutton crystals (obtained by the slow solvent evaporation method) with novel chemical compositions based on K₂V_1−xM’_x(SO₄)₂(H₂O)₆, where M’ represents Co, Ni, Cu, and Zn, aiming at thermochemical energy storage applications. Their structural and thermal properties were correlated with theoretical studies. The crystal structures were solved by powder X-ray diffraction using the Rietveld method with similar compounds. All of the samples crystallized in monoclinic symmetry with the P2₁/a-space group. A detailed study of the intermolecular interactions based on Hirshfeld surfaces and 2D fingerprint mappings showed that the main interactions arise from hydrogen bonds (H∙∙∙O/O∙∙∙H) and dipole–ion (K∙∙∙O/O∙∙∙K). On the other hand, free space percentages in the unit cells determined by electron density isosurfaces presented low values ranging from 0.53 (V–Ni) to 0.81% (V–Cu). The thermochemical findings from thermogravimetry, a differential thermal analysis, and differential scanning calorimetry indicate that K₂V_0.47Ni_0.53(SO₄)₂(H₂O)₆ salt is the most promising among mixed salts (K₂V_1−xM’_x(SO₄)₂(H₂O)₆) for heat storage potential, achieving a low dehydration temperature (≈85 °C), high dehydration enthalpy (≈360 kJ/mol), and high energy storage density (≈1.84 GJ/m³). Full article

Trimethylglycine (glycine betaine, GB) is an important organic osmolyte that accumulates in various plant species in response to environmental stresses and has significant potential as a bioactive agent with low environmental impact. It is assumed that the hydration of GB is playing an important role in the protective mechanism. The hydration and aggregation properties of GB have not yet been studied in detail at the atomistic level. In this work, noncovalent interactions in the GB dimer and its complexes with water and crystalline monohydrate are studied. Depending on the object, periodic and non-periodic DFT calculations are used. Particular attention is paid to the metric parameters and enthalpies of intermolecular hydrogen bonds. The identification of noncovalent interactions is carried out by means of the Bader analysis of periodic or non-periodic electron density. The enthalpy of hydrogen bonds is estimated using the Rosenberg formula (PCCP 2 (2000) 2699). The specific proton donor properties of glycine betaine are due to its ability to form intermolecular C–H∙∙∙O bonds with the oxygen atom of a water molecule or the carboxylate group of a neighboring GB. The enthalpy of these bonds can be significantly greater than 10 kJ/mol. The water molecule that forms a hydrogen bond with the carboxylate group of GB also interacts with its CH groups through lone pairs of electrons. The C–H∙∙∙O bonds contribute up to 40% of the total entropy of the GB–water interaction, which is about 45 kJ/mol. The possibility of identifying C–H∙∙∙O bonds by the proton nuclear magnetic resonance method is discussed. Full article

Lignocellulose is a renewable ubiquitous material that comprises cellulose, hemicellulose, and lignin. Lignin has been isolated from different lignocellulosic biomass via chemical treatments, but there has been little or no investigation carried out on the processing of lignin from brewers’ spent grain (BSG) to the best of authors’ knowledge. This material makes up 85% of the brewery industry’s byproducts. Its high moisture content hastens its deterioration, which has posed a huge challenge to its preservation and transportation; this eventually causes environmental pollution. One of the methods of solving this environmental menace is the extraction of lignin as a precursor for carbon fiber production from this waste. This study considers the viability of sourcing lignin from BSG with the use of acid solutions at 100 °C. Structural and thermal analyses were carried out on extracted samples, and the results were compared with other biomass-soured lignin to assess the proficiency of this isolation technique. Wet BSG sourced from Nigeria Breweries (NB), Lagos, was washed and sun-dried for 7 days. Tetraoxosulphate (VI) (H₂SO₄), hydrochloric (HCl), and acetic acid, each of 10 M, were individually reacted with dried BSG at 100 °C for 3 h and designated as H2, HC, and AC lignin. The residue (lignin) was washed and dried for analysis. Wavenumber shift values from Fourier transform infrared spectroscopy (FTIR) show that intra- and intermolecular OH interactions in H2 lignin are the strongest and possess the highest magnitude of hydrogen-bond enthalpy (5.73 kCal/mol). The thermogravimetric analysis (TGA) results show that a higher lignin yield can be achieved when it is isolated from BSG, as 82.9, 79.3, and 70.2% were realized for H2, HC, and AC lignin. The highest size of ordered domains (0.0299 nm) displayed by H2 lignin from X-ray diffraction (XRD) informs that it has the greatest potential of forming nanofibers via electrospinning. The enthalpy of reaction values of 133.3, 126.6, and 114.1 J/g recorded for H2, HC, and AC lignin, respectively, from differential scanning calorimetry (DSC) results affirm that H2 lignin is the most thermally stable with the highest glass transition temperature (T_g = 107 °C). Full article

Intermolecular interactions, in particular hydrogen bonds, play a key role in crystal engineering. The ability to form hydrogen bonds of various types and strengths causes competition between supramolecular synthons in pharmaceutical multicomponent crystals. In this work, we investigate the influence of positional isomerism on the packing arrangements and the network of hydrogen bonds in multicomponent crystals of the drug riluzole with hydroxyl derivatives of salicylic acid. The supramolecular organization of the riluzole salt containing 2,6-dihydroxybenzoic acid differs from that of the solid forms with 2,4- and 2,5-dihydroxybenzoic acids. Because the second OH group is not at position 6 in the latter crystals, intermolecular charge-assisted hydrogen bonds are formed. According to periodic DFT calculations, the enthalpy of these H-bonds exceeds 30 kJ·mol⁻¹. The positional isomerism appears to have little effect on the enthalpy of the primary supramolecular synthon (65–70 kJ·mol⁻¹), but it does result in the formation of a two-dimensional network of hydrogen bonds and an increase in the overall lattice energy. According to the results of the present study, 2,6-dihydroxybenzoic acid can be treated as a promising counterion for the design of pharmaceutical multicomponent crystals. Full article

In this study, sweet potato β-amylase (SPA) was modified by methoxy polyethylene glycol maleimide (molecular weight 5000, Mal-mPEG5000) to obtain the Mal-mPEG5000-SPA modified β-amylase and the interaction mechanism between SPA and Mal-mPEG5000 was investigated. the changes in the functional groups of different amide bands and modifications in the secondary structure of enzyme protein were analyzed using infrared spectroscopy and circular dichroism spectroscopy. The addition of Mal-mPEG5000 transformed the random curl in the SPA secondary structure into a helix structure, forming a folded structure. The Mal-mPEG5000 improved the thermal stability of SPA and protected the structure of the protein from breaking by the surrounding. The thermodynamic analysis further implied that the intermolecular forces between SPA and Mal-mPEG5000 were hydrophobic interactions and hydrogen bonds due to the positive values of ΔH^θ and ΔS^θ. Furthermore, the calorie titration data showed that the binding stoichiometry for the complexation of Mal-mPEG5000 to SPA was 1.26, and the binding constant was 1.256 × 10⁷ mol/L. The binding reaction resulted from negative enthalpy, indicating that the interaction of SPA and Mal-mPEG5000 was induced by the van der Waals force and hydrogen bonding. The UV results showed the formation of non-luminescent material during the interaction, the Fluorescence results confirmed that the mechanism between SPA and Mal-mPEG5000 was static quenching. According to the fluorescence quenching measurement, the binding constant (K_A) values were 4.65 × 10⁴ L·mol⁻¹ (298K), 5.56 × 10⁴ L·mol⁻¹ (308K), and 6.91 × 10⁴ L·mol⁻¹ (318K), respectively. Full article

In this study, the adsorption of aromatic organic pollutants such as hexachlorobenzene, decachlorobiphenyl, benzene, and biphenyl by 2D nanomaterials was investigated using quantum chemical methods. The calculation results include reaction enthalpies, non-covalent intermolecular and intramolecular interactions, optimized structures, hydrogen bonds, and molecular electrostatic potentials. Fukui’s FMO electrophile sensitivity is used to predict the most reactive positions on the chemical species for both nucleophilic and electrophilic roles. The results of hard–soft acid-base reactivity descriptors show that the electronic structures of BN-doped graphene and C-doped hexagonal boron nitride depend on the degree of doping and the modification of β-cyclodextrin. C doping helps to significantly improve the conductivity of h-BN, and β-cyclodextrin enhances the binding stability of aromatic organic pollutants. Hydrogen bonding between β-cyclodextrin and chlorine-substituted compounds can enhance non-covalent interactions. In particular, the high adsorption capacity and electron transfer capacity of decachlorobiphenyl laid the foundation for the development of new sensors. Full article

In order to broaden the study of energetic cations, a cation 3,5-diamino-4H-pyrazol-4-one oxime (DAPO) with good thermal stability was proposed, and its three salts were synthesized by a simple and efficient method. The structures of the three salts were verified by infrared spectroscopy, mass spectrometry, elemental analysis, and single crystal X-ray diffraction. The thermal stabilities of the three salts were verified by differential scanning calorimetry and thermos-gravimetric analysis. DAPO-based energetic salts are analysed using a variety of theoretical techniques, such as 2D fingerprint, Hirshfeld surface, and non-covalent interaction. Among them, the energy properties of perchlorate (DAPOP) and picrate (DAPOT) were determined by EXPLO5 program combined with the measured density and enthalpy of formation. These compounds have high density, acceptable detonation performance, good thermal stability, and satisfactory sensitivity. The intermolecular interactions of the four compounds were studied by Hirshfeld surface and non-covalent interactions, indicating that hydrogen bonds and π–π stacking interactions are the reasons for the extracellular properties of perchlorate (DAPOP) and picrate (DAPOT), indicating that DAPO is an optional nitrogen-rich cation for the design and synthesis of novel energetic materials with excellent properties. Full article

The effect of ultrasonication (25 kHz for 10 min) on physical, thermal, and structural properties and storage stability of palm oil-based oleogels prepared using different concentrations of carnauba wax (CW) (5% or 10%) were investigated and compared with oleogels prepared with a homogenizer (2000 rpm for 10 min). Overall, this study found that applying an ultrasonication process with higher CW concentration (10%) effectively improved the properties and stability of palm oil-based oleogel (p < 0.05). Oleogels processed with ultrasonication had higher lightness (L*), higher yellowness (b*), and lower redness (a*) than those processed with homogenizer (p < 0.05), irrespective of CW concentrations. However, a higher CW concentration (10%) increased the textural properties of oleogels such as hardness, stickiness, and tackiness as compared to oleogels with a lower CW concentration (5%) (p < 0.05). Thermal properties including melting onset temperature, melting peak temperature, and melting enthalpy were found to be significantly higher in ultrasonication-processed oleogels with high CW concentration (p < 0.05). Furthermore, the microscopic examination of the oleogels exhibited a strong gel network when prepared using a high concentration of CW and processed with ultrasonication. Fourier Transform Infrared (FTIR) spectra of oleogels revealed that strong intra- and intermolecular interactions were formed by hydrogen bonding between CW and palm oil. X-ray diffraction (XRD) showed a smooth and fine structural network of oleogels and proved that ultrasonication increased the structural properties of oleogel. Moreover, oil loss and peroxide value of oleogels were increased during 90 days of storage (p < 0.05). However, oleogels processed with the ultrasonication had reduced oil loss and increased peroxidation stability during storage (p < 0.05). Overall, this study showed that application of ultrasonication with a higher CW concentration could improve properties and storage stability of palm oil-based oleogel. Full article

We investigated the modification of wheat starch with Ligustrum robustum (Rxob.) Blume extract (LRE) and determined the action mechanism. Based on differential scanning calorimetry, LRE decreased the gelatinization enthalpy of wheat starch from 19.14 to 7.15 J/g and changed gelatinization temperatures (including the variation in gelatinization onset temperature, peak temperature and conclusion temperature in different degrees). Moreover, LRE affected the pasting viscosity curve of wheat starch, and changed its rheological parameters (including the decrease in storage modulus and loss modulus, as well as the increase in loss tangent). Based on the analysis of scanning electron microscopy and wide-angle X-ray diffraction, LRE increased the hole size and the roughness of the gel microstructure, and decreased the crystallinity of wheat starch. Meanwhile, the evaluation results of the texture analyzer and the colorimeter showed that LRE could change the quality properties (including decrease hardness, fracturability and L* values, as well as increase a* and b* values) of wheat starch biscuits after hot air baking (170 °C). Furthermore, with molecular dynamics simulation analysis, phenolic compounds of LRE combined with starch molecules via H-bonds and affected the formation of molecular bonds (including intra- and intermolecular hydrogen bonds), so as to change the spatial conformation and properties of wheat starch during gelatinization and retrogradation. The present results suggest that LRE can modify the physicochemical properties of wheat starch and further improve its processing properties, indicating its potential in the design and development of starch foods (such as steamed buns, bread, biscuits, etc.). Full article

The [3+2] cycloaddition (32CA) reaction of an azomethine ylide (AY) with an electrophilic ethylene linked to triazole and ferrocene units has been studied within the Molecular Electron Density Theory (MEDT) at the ωB97X-D/6-311G(d,p) level. The topology of the electron localization function (ELF) of this AY allows classifying it as a pseudo(mono)radical species characterized by the presence of two monosynaptic basins, integrating a total of 0.76 e, at the C1 carbon. While the ferrocene ethylene has a strong electrophilic character, the AY is a supernucleophile, suggesting that the corresponding 32CA reaction has a high polar character and a low activation energy. The most favorable ortho/endo reaction path presents an activation enthalpy of 8.7 kcal·mol⁻¹, with the 32CA reaction being exergonic by −42.1 kcal·mol⁻¹. This reaction presents a total endo stereoselectivity and a total ortho regioselectivity. Analysis of the global electron density transfer (GEDT) at the most favorable TS-on (0.23 e) accounts for the high polar character of this 32CA reaction, classified as forward electron density flux (FEDF). The formation of two intermolecular hydrogen bonds between the two interacting frameworks at the most favorable TS-on accounts for the unexpected ortho regioselectivity experimentally observed. Full article