Search Results (120)

Direct hydroxylation of benzene to phenol using hydrogen peroxide is a cornerstone of sustainable green chemistry. This paper presents the results of a stability study of an iron-containing mordenite catalyst in the liquid-phase hydroxylation of benzene to phenol with a 30% aqueous hydrogen peroxide solution. The study utilizes a combination of catalytic activity measurements, dynamic light scattering (DLS), and electron paramagnetic resonance (EPR) spectra. The system is initially shown to exhibit high phenol selectivity; however, over time, DLS measurements indicate aggregation of the catalyst particles with an increase in the average particle diameter from 1.8 to 2.6 μm and the formation of byproducts–dihydroxybenzenes. Iron is present predominantly as magnetite nanoparticles (Fe₃O₄) ~10 nm in diameter, stabilized on the outer surface of mordenite, with minor leaching (<10%) due to the formation of iron ion complexes with ascorbic acid as a result of the latter’s interaction with magnetite particles. Using a thermodynamic approach based on the Ulich formalism (first and second approximations), it is shown that the reaction of benzene hydroxylation H₂O₂ in the liquid phase is thermodynamically quite favorable (ΔG° = −(289–292) kJ·mol⁻¹ in the range of 293–343 K, K = 1044–1052). It is shown that ascorbic acid acts as a redox mediator (reducing Fe³⁺ to Fe²⁺) and a regulator of the catalytic medium activity. The stability of the catalytic system is examined in terms of the Lyapunov criterion: it is shown that the total Gibbs free energy (including the surface contribution) can be considered as a Lyapunov functional describing the evolution of the system toward a steady state. Ultrasonic (US) treatment of the catalytic system is shown to redisperse aggregated particles and restore its activity. It is established that the catalytic activity is due to nanosized Fe₃O₄ particles, which react with H₂O₂ to form hydroxyl radicals responsible for the selective hydroxylation of benzene to phenol. Full article

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by memory loss, cognitive decline, and oxidative stress-driven neuronal damage. Catalase, a key antioxidant enzyme, plays a vital role in decomposing hydrogen peroxide (H₂O₂) into water and oxygen, thereby protecting neurons from reactive oxygen species (ROS)-mediated toxicity. In AD, the catalase function is compromised due to reduced enzymatic activity and aggregation, which not only diminishes its protective role but also contributes to amyloid plaque formation through catalase-Aβ co-oligomers. Hence, therapeutic strategies aimed at simultaneously preventing catalase aggregation and enhancing its enzymatic function are of great interest. In this study, we screened twelve naturally occurring metabolites for their ability to modulate catalase aggregation and activity. Among these, dimethylglycine (DMG) emerged as the most potent candidate. DMG significantly inhibited thermally induced aggregation of catalase and markedly enhanced its enzymatic activity in a concentration-dependent manner. Biophysical analyses revealed that DMG stabilizes catalase by promoting its native folded conformation, as evidenced by increased melting temperature (T_m), higher Gibbs free energy of unfolding (ΔG°), and reduced exposure of hydrophobic residues. TEM imaging and Thioflavin T assays further confirmed that DMG prevented amyloid-like fibril formation. Molecular docking and dynamics simulations indicated that DMG binds to an allosteric site on catalase, providing a structural basis for its dual role in stabilization and activation. These findings highlight DMG as a promising therapeutic molecule for restoring catalase function and mitigating oxidative stress in AD. By maintaining catalase stability and activity, DMG offers potential for slowing AD progression. Full article

Since 1978, platinum-based drugs have benefited countless cancer patients and come to form the foundation of many cancer pharmacotherapies. These drugs induce apoptosis in cancer cells by forming cross-links between nucleobases in the DNA. Our previous studies have shown that these drugs can also interact with other similar compounds whose structures resemble nucleobases. Therefore, this study analyzed the interactions of Cisplatin, Carboplatin, and Oxaliplatin with Pyridine derivatives (Nicotinic acid, Nicotinamide, Isonicotinic acid, and Picolinic acid). These values were then compared with those for Guanine and Adenine coming from DNA using spectroscopic methods and computational chemistry (B3LYP/6-31G(d,p) and MN15/def2-TZVP methods). Theoretical studies suggest cytostatic affinity, not only for nucleobases but also for Pyridine derivatives. Experimental studies have confirmed these theoretical results. Full article

Plant protease inhibitors (PPI) play a significant role against microbes, insects, and, to a considerable extent, human pathogens. PPIs inactivate hydrolase enzymes or depolarize the plasma membrane of the pathogens, thereby inhibiting their growth, replication, and invasion. Here, an active serine protease inhibitor was isolated and purified from the seeds of Cleome viscosa. The purified inhibitor was homogenous and exhibited a molecular weight of around 12 kDa as a monomer. The secondary structure analysis indicated that the inhibitor was predominantly composed of α-helical content. The kinetics experiments demonstrated a noncompetitive mode of inhibition towards serine protease when casein was used as the enzyme substrate. The inhibitor formed a stable complex with serine protease, having a likely 1:1 stoichiometry, as inferred from ITC, and the dissociation constant was examined to be K_d = 1.9 × 10⁻⁶ M with a Gibbs free energy of ΔG = −8.079 (kcal/mol). The inhibitor exhibits stable protease inhibition up to 90 °C. Further, in vitro preliminary studies revealed its inhibitory effects against HSV-2 function, evidence that it may have a role in the treatment of viral infections. Full article

This study investigates the formation, physicochemical properties, and applicability of surfactant-free microemulsions (SFMEs) as nanoreactors for the synthesis of silicon dioxide nanoparticles. Surfactant-free systems offer a promising and environmentally benign alternative to traditional microemulsions in which particle formation is governed by surfactants, yet their structural behavior and synthesis mechanisms remain insufficiently understood. A ternary system composed of water, ethanol, and n-pentanol was selected as a model, and its structural organization was analyzed through electrical conductivity, surface tension, and dynamic light scattering (DLS) measurements. The results revealed a broad single-phase region, indicating high miscibility of the components and the formation of dynamically connected polar domains. Electrical conductivity data suggested gradual reorganization of the internal structure without a distinct percolation threshold, while surface tension analysis and the corresponding Gibbs free energies of aggregation (ΔG°) reflected a weaker thermodynamic driving force for aggregation compared to systems containing longer-chain alcohols. DLS measurements confirmed the presence of fluctuating aggregates with hydrodynamic radii between 30 and 85 nm, consistent with literature values for surfactant-free systems. Based on these findings, silica nanoparticles were synthesized within selected compositions of the single-phase region. The resulting particles exhibited predominantly spherical morphology and variable dispersity, reflecting the moderate structural stability of the underlying microemulsion. The synthesized silica nanoparticles typically ranged from approximately 0.9 to 1.2 μm in diameter, reflecting the structural characteristics of the selected SFME compositions. Overall, the results demonstrate that water/ethanol/n-pentanol SFMEs provide new insights into surfactant-free aggregation processes and offer a sustainable route for the synthesis of inorganic nanoparticles. Full article

For sustainable soil management, the link between carbon amendment structure and soil health is paramount, yet how the particle size of carbon governs hydrolase activity through kinetic and thermodynamic mechanisms remains poorly understood. A three-year field experiment with four treatments, including Control, Straw, Biochar, and Nanocarbon, was conducted in black soil. After harvest, the activities of invertase (INV), urease (URE), and acid phosphatase (ACP) were assayed from 15 to 55 °C. Kinetic parameters—including half-saturation constant (K_m), maximal reaction rate (V_max) and catalytic efficiency (K_a)—and thermodynamic parameters—including Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS)—were determined. INV and ACP activities increased with temperature, peaking at 55 °C, whereas URE peaked at 45 °C. The V_max, K_a, and ΔG of the enzymes also increased with temperature. With straw, INV activity remained stable, whereas INV-K_a, INV-ΔH, and INV-ΔS increased with decreased INV-K_m. URE activity declined with thermodynamic elevation. For ACP, ACP-K_m and ACP-V_max increased, whereas ACP-K_a and ACP-ΔG decreased. With biochar or nanocarbon, the enzyme activities, V_max, and K_a decreased, whereas ∆G increased, with stronger inhibition by nanocarbon. Correlation analysis revealed ∆G as the dominant factor for activity after carbon addition, while redundancy analysis identified organic carbon (OC) and total phosphorus (TP) as the key regulators. Overall, straw, biochar, and nanocarbon had different sustainable values on hydrolase systems, with thermodynamic parameters, especially ∆G, better reflecting system shifts than kinetic traits. Full article

Compost amendments are widely recognized as an effective strategy for improving soil quality, modulating enzyme activities, and enhancing nitrogen cycling. Urease, a key enzyme in nitrogen transformation, is characterized by kinetic parameters such as the maximum reaction rate (V_max) and Michaelis constant (K_m), as well as thermodynamic attributes including temperature sensitivity (Q₁₀), activation energy (E_a), enthalpy change (ΔH), Gibbs free energy change (ΔG), and entropy change (ΔS). However, how different compost sources regulate urease kinetics, thermodynamics, and nitrogen availability remains poorly understood. In this study, we evaluated the effects of three compost amendments—mushroom residue (MR), mushroom residue–straw mixture (MSM), and leaf litter (LL)—on urease kinetics and thermodynamics in a temperate agroecosystem. The MSM treatment significantly enhanced urea hydrolysis capacity and catalytic efficiency. In contrast, LL treatment resulted in the highest Km value, indicating a substantially lower enzyme-substrate affinity. Furthermore, MSM reduced the E_a and increased the thermal stability of urease, thereby supporting enzymatic performance under fluctuating temperatures. Collectively, our findings highlight that compost composition is a critical determinant of urease function and nitrogen turnover. By elucidating the coupled kinetic and thermodynamic responses of urease to compost inputs, this study provides mechanistic insights to guide optimized soil management and sustainable nitrogen utilization in temperate agricultural systems. Full article

An intracellular α-glucosidase was isolated and purified from a Pseudanabaena sp. cyanobacterial strain. Before the enzyme purification, the optimal cultural conditions were determined. Optimal culture conditions (15 g/L maltose, 2 g/L yeast extract, 23 ± 1 °C) yielded 3.3 g/L of biomass and 2186 U/L of α-glucosidase in a lab-scale bioreactor. The purified enzyme displayed a molecular mass of 52 kDa with optimum activity at 40 °C and pH 7.0, and maintained stability within an acidic and neutral range of pH 4.0 to 7.0. Enzyme activity was affected by both the concentration and interaction time of the metal ions and chelator. Kinetic constants of K_m, V_max, and k_cat for the hydrolysis of pNPG were determined as 2.0 Mm, 2.9 μmol min⁻¹, and 14.86 min⁻¹, respectively. The activation energy (E_a) was 24.2 kJ mol⁻¹ and the thermodynamic parameters of enthalpy (ΔH^*), entropy (ΔS^*) of activation, Gibbs free energy (ΔG^*), free energy of substrate binding (ΔG^*_E-S), and transition state formation (ΔG^*_Ε-Τ) were 21.6, −116, 57.8, −22.2, and −41.2 kJ mol⁻¹, respectively. Moreover, the thermodynamic parameters for thermal inactivation of the enzyme were ΔH^*= 131 kJ mol⁻¹, 105 ≤ ΔS^* ≤ 108 kJ mol⁻¹, and 96 ≤ ΔG^* ≤ 98 kJ mol⁻¹, while the thermal inactivation energy (E_(a)d) was determined to be 133 kJ mol⁻¹. This is the first detailed investigation concerning the characterization of α-glucosidase derived from cyanobacteria. The presented enzymatic characteristics provide a valuable predictive model for identifying suitable applications. Full article

Antibody-free nucleic acid lateral flow assays (AF-NALFA) are an established approach for rapid detection of amplified pathogens DNA but can yield inconsistent signals across targets. Since AF-NALFA depends on dual hybridization of probes to single-stranded amplicons (ssDNA), site-specific thermodynamic (Gibbs free energy-ΔG) at probe-binding regions may be crucial for performance. This study investigated how site-specific-ΔG and sequence complementarity at probe-binding regions determine Test-line signal generation, comparing native and synthetic amplicons and assessing the effects of local secondary structures and mismatches. Asymmetric PCR-generated ssDNA amplicons of Listeria monocytogenes, Mycobacterium leprae, and Leishmania amazonensis were analyzed in silico and tested in AF-NALFA prototypes with gold-labeled thiol probes and biotinylated capture probes. T-line signals were photographed, quantified (ImageJ version 1.4k), and statistically correlated with site-specific-ΔG. While native ssDNA from M. leprae and L. amazonensis failed to produce AF-NALFA T-line signals, L. monocytogenes yielded strong detection. Site-specific-ΔG below −10 kcal/mol correlated with reduced hybridization. Synthetic oligos preserved signals despite structural constraints, whereas ~3–4 mismatches, especially at capture probe regions, markedly impaired T-line intensity. The performance of AF-NALFA depends on the synergism between thermodynamic accessibility, site-specific-ΔG-induced site constraints, and sequence complementarity. Because genomic context affects hybridization, target-specific thermodynamic in silico evaluation is necessary for reliable pathogen DNA detection. Full article

The oxalic acid leachate of vanadium-bearing shale (OALS) is a complex system in which the ion states and coordination mechanisms of the primary metallic elements—vanadium, iron, and aluminum—are not fully understood. This study investigated the ionic speciation and coordination mechanisms of vanadium, iron, and aluminum in OALS. The results indicate that vanadium predominantly existed as VO(C₂O₄)₂²⁻ anions, iron as Fe(C₂O₄)₂⁻ and Fe(C₂O₄)₃³⁻ anions, and aluminum as Al(C₂O₄)₂⁻ and Al(C₂O₄)₃³⁻ anions. The coordination reaction processes and equations of various oxalate complexes were examined. Regardless of whether the molar ratio was 1:1 or 1:2, the iron–oxalate complex exhibited the lowest reaction Gibbs free energy (ΔG), with values of −5343.69 and −1470.72 kJ/mol, respectively. The aluminum–oxalate complex followed, with ΔG values of −5169.23 and −1318.87 kJ/mol, respectively. The vanadium–oxalate complex displayed the highest reaction ΔG, at −2760.65 and −714.12 kJ/mol, respectively. Therefore, the coordination mechanism of vanadium, iron, and aluminum with oxalate ions in OALS is such that iron coordinated with oxalate first, followed by aluminum, and finally vanadium. The research results have important guiding significance for the purification, enrichment, and coordination mechanisms of complex solutions. Full article

Uric acid (UA) detection is critical for human health monitoring, necessitating the development of electrochemical sensing electrodes suitable for physiological environments. This study evaluated four 2D conductive metal–organic frameworks (2D c-MOFs), namely Cu-HHTP, Ni-HHTP, Cu-HAB, and Ni-HAB, which share identical graphene-like 2D sheet structures but differ in π-conjugation extent and catalytic active centers [MX₄] (M = Cu or Ni; X = O or NH) as electrosensing electrodes. Electrochemical sensing performance was compared by detecting UA in phosphate-buffered saline (PBS). Herein, the Ni-HHTP electrode demonstrated superior sensitivity (6.79 μA·μM⁻¹·cm⁻²), the lowest oxidation potential (0.272 V), and the lowest detection limit (0.44 μM). Langmuir adsorption isotherm analysis revealed that the Ni-HHTP electrode possesses the highest surface coverage (Γ_A) (5061.16 pmol cm⁻²) and the most favorable Gibbs adsorption free energy (ΔG°) (−18.775 kJ mol⁻¹), indicating its strongest UA adsorption capacity and molecular interaction. This enhanced performance is attributed to the optimal synergy between [NiO₄] catalytic centers and extended ligand π-conjugation, facilitating greater analyte adsorption and electron transfer efficiency. This work establishes clear structure–performance relationships for 2D c-MOF electrodes in UA detection, providing key insights for designing advanced electrosensing materials. Full article

Tryptophan hydroxylase 2 (TPH2) hydroxylates L-tryptophan to L-5-hydroxytryptophan (5-HTP) the first and rate-limiting step of serotonin (5-HT) synthesis in the mammalian brain. Some mutations in the Tph2 gene reducing TPH2 activity are associated with hereditary depressive disorders. The P447R substitution in the mouse TPH2 molecule reduces its thermal stability in vitro and its activity in the brain. The effects of iron ions on thermal stability in vitro and the activity in the brain of the mutant TPH2 were investigated. In the in vitro experiment effects of 0.01, 0.05, and 0.2 mM of FeSO₄ and FeCl₃ on the enthalpy (ΔH) and Gibbs free energy (ΔG) of thermal denaturation of the mutant TPH2 extracted from the midbrain of Balb/c mice were assayed. All FeSO₄ concentrations and 0.05 and 0.2 mM concentrations of FeCl₃ increased these thermodynamic characteristics of the mutant TPH2. Repeated (for 7 days) intramuscular administration of Fe(III) hydroxide dextran complex (15 and 30 mg/kg/day) increased TPH2 activity in the hippocampus, but not in the midbrain in Balb/c mice. Repeated (for 7 days) intramuscular administration of Fe(III) hydroxide dextran complex (15 and 30 mg/kg/day) together with thiamine (8 mg/kg/day) and cyanocobalamin (0.8 mg/kg/day) increased TPH2 activity in the hippocampus, while 30 mg/kg of Fe(III) hydroxide dextran also increased the enzyme activity in the midbrain in Balb/c mice. These results are the first evidence for chaperone-like effects of iron ions on thermal stability in vitro and activity in the brain of the mutant TPH2. Full article

The escalating crisis of multidrug resistance, together with the persistence of antibiotic residues in clinical and environmental matrices, demands integrated strategies that couple sensitive detection, efficient decontamination, and controlled delivery. However, current techniques for quantifying avibactam (AVI)—a broad-spectrum β-lactamase inhibitor—such as HPLC-UV lack the sensitivity and specificity required for both therapeutic drug monitoring and environmental surveillance. Encapsulation of AVI within cyclodextrins (CDs) may simultaneously enhance its stability, bioavailability, and detectability, while the high binding affinities of CDs position them as molecular traps capable of scavenging residual AVI. In this study, the inclusion complexation of AVI with various CDs was examined through molecular dynamics (MD) simulations, experimental isothermal titration calorimetry (ITC), and non-covalent interaction (NCI) analysis. Stable 1:1 inclusion complexes were observed between AVI and β-cyclodextrin (β-CD), 2,6-dimethyl-β-cyclodextrin (DM-β-CD), and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), with standard Gibbs free energies of binding (ΔG°) of –3.64, –3.24, and –3.11 kcal/mol, respectively. In contrast, γ-cyclodextrin (γ-CD) exhibited significantly weaker binding (ΔG° = –2.25 kcal/mol). DFT-based NCI analysis revealed that cooperative interaction topology and cavity complementarity, rather than the sheer number of localized contacts, govern complex stability. Combined computational and experimental data establish β-CD derivatives as effective supramolecular hosts for AVI, despite an entropic penalty in the DM-β-CD/AVI complex. These CD–AVI affinities support the development of improved analytical methodologies and pharmaceutical formulations, and they also open avenues for decontamination strategies based on molecular trapping of AVI. Full article

This study investigates the impact of oxygen-containing functional groups (COO-Li, CO-Li, and O-Li) on the electronic and optical properties of graphene, with a focus on hydrogen sensing applications. Using density functional theory (DFT) calculations, we evaluated the thermodynamic feasibility of the functionalization and hydrogen adsorption processes. The Gibbs free energy changes (ΔG) for the functionalization of pristine graphene were calculated as −1233, −1157, and −1119 atomic units (a.u.) for COO-Li, CO-Li, and O-Li, respectively. These negative values indicate that the functionalization processes are spontaneous (ΔG < 0), with COO-Li being the most thermodynamically favorable. Furthermore, hydrogen adsorption on the functionalized graphene surfaces also exhibited spontaneous behavior, with ΔG values of −1269, −1204, and −1175 a.u., respectively. These results confirm that both functionalization and subsequent hydrogen adsorption are energetically favorable, enhancing the potential of these materials for hydrogen sensing applications. Among the functional groups we simulated, COO-Li exhibited the largest surface area and volume, which were attributed to the high electronegativity and steric influence of the carboxylate moiety. Based on the previously described results, we analyzed the interaction of these functionalized graphene systems with molecular hydrogen. The adsorption of two H₂ molecules per system demonstrated favorable thermodynamics, with lithium atoms serving as active sites for external adsorption. The presence of lithium atoms significantly enhanced hydrogen affinity, suggesting strong potential for sensing applications. Further, electronic structure analysis revealed that all functionalized systems exhibit semiconducting behavior, with band gap values modulated by the nature of the functional group. FTIR (Fourier-Transform Infrared Spectroscopy) and Raman spectroscopy confirmed the presence of characteristic vibrational modes associated with Li-H interactions, particularly in the 659–500 cm⁻¹ range. These findings underscore the promise of lithium-functionalized graphene, especially with COO-Li, as a tunable platform for hydrogen detection, combining favorable thermodynamics, tailored electronic properties, and spectroscopic detectability. Full article

This study systematically investigates the effects of demineralization on the pyrolysis characteristics, kinetics, and thermodynamics of three biomass types (eucalyptus, straw, and miscanthus) using thermogravimetric analysis (TGA) combined with multiple kinetic approaches. The Coats–Redfern integral model was employed to determine the reaction mechanisms. The results indicate that the primary weight-loss temperature ranges for eucalyptus, straw, and miscanthus were 222.02~500.23 °C, 205.43~500.13 °C, and 202.30~490.52 °C, respectively. Demineralization increased the initial pyrolysis temperature and significantly enhanced the reaction rates. Kinetics analysis revealed that the ash content significantly influences the activation energy of the pyrolysis reaction. The average activation energies follow the trend eucalyptus (193.48 kJ/mol) < miscanthus (245.66 kJ/mol) < straw (290.13 kJ/mol). After demineralization, the activation energies of both straw and miscanthus pyrolysis decreased, with the largest reduction observed in straw, which dropped by 77.53 kJ/mol. However, the activation energy for eucalyptus pyrolysis increased by 12.52 kJ/mol after demineralization. The Coats–Redfern model and thermodynamic analysis demonstrated that each type of biomass followed distinct reaction mechanisms at different stages, which were altered after demineralization. Additionally, demineralization leads to higher ΔH and Gibbs free energy ΔG for eucalyptus, but lower values for straw and miscanthus, which indicate that the ash content has a significant impact on the biomass pyrolysis reaction. These findings provide fundamental insights into the role of ash in biomass pyrolysis kinetics and offer theoretical support for the design of pyrolysis reactors. Full article