Search Results (116)

Olive leaves, the main byproducts of olive cultivation, are characterized by a plethora of bioactive metabolites with significant nutritional value. Their main pentacyclic triterpenes, Oleanolic Acid (OA) and Maslinic Acid (MA), are two high added-value compounds with remarkable activities. This study aimed to develop an efficient methodology for extracting and purifying OA and MA, utilizing Supercritical Fluid Extraction (SFE) and Centrifugal Partition Chromatography (CPC)—two modern, scalable, and green techniques. A total of 21 g of olive leaves were subjected to SFE using supercritical CO₂ and ethanol as co-solvent. The extraction employed a step gradient mode, starting with 100% CO₂ and incrementally increasing ethanol (0–10% w/w) every 20 min. Fractions rich in OA and MA (500 mg) were further purified via CPC, utilizing pH zone refining to exploit the protonation and deprotonation properties of acidic triterpenes. The biphasic solvent system consisted of n-hexane, ethyl acetate, ethanol, and water (8:2:5:5 v/v/v/v), with trifluoroacetic acid added to the stationary phase and triethylamine added to the mobile phase. This two-step process yielded 89.5 mg of OA and 28.5 mg of MA with over 95% purity, as confirmed by HPLC-ELSD and ¹H-NMR. Moreover, purified compounds and SFE fractions exhibited promising elastase and collagenase inhibition, highlighting them as dermocosmetic agents. Full article

The effective management of High-Level Liquid Waste (HLLW) is critical for environmental and human health protection. The presence of platinum group metals (PGMs) in HLLW, particularly their refractory nature due to their high melting points, complicates vitrification processes. This study presents a targeted adsorption strategy using COF-42 for Pd²⁺ sequestration in HLLW systems. The comprehensive characterization of COF-42 and its Pd-loaded counterpart (Pd@COF-42) via PXRD, FT-IR, TGA, XPS, and SEM confirms structural robustness and successful Pd²⁺ incorporation. Kinetic and thermodynamic analyses reveal pseudo-second-order adsorption behavior with a maximum capacity of 170.6 mg/g, highlighting the exceptional Pd²⁺ affinity. Systematic optimization identifies HNO₃ concentration (≤3 M) and adsorbent dosage (≤30 mg) as critical parameters governing adsorption efficiency through protonation–deprotonation equilibria. Furthermore, COF-42 exhibits superior selectivity for Pd²⁺ over 13 competing metal ions and maintains ~80% adsorption efficiency after four regeneration cycles. These performance metrics originate from the synergistic interplay of (1) framework flexibility enabling adaptive Pd²⁺ coordination, (2) hierarchical porosity facilitating ion diffusion, and (3) dense –NH/–NH₂ groups acting as electron-rich chelation sites. Full article

The development of alternative energies has become a concern for all countries to ensure domestic energy supply and provide environmental friendliness. One of the providential alternative energies is biodiesel. Biodiesel, commonly stated as fatty acid alkyl ester (FAAE), is a liquid fuel intended to substitute petroleum diesel. Nevertheless, implementation of pure biodiesel is not recommended for conventional diesel engines. It holds poor values of cold flow properties, as the effect of high saturated FAAE content contributes to this constraint. Several processes have been proposed to enhance cold flow properties of biodiesel, but this work focuses on the skeletal isomerization process. This process rearranges the skeletal carbon chain of straight-chain FAAE into branched isomeric products to lower the melting point, related to the good cold flow behavior. This method specifically requires an acid catalyst to elevate the isomerization reaction rate. And then, sulfated tin(IV) oxide emerged as a solid superacid catalyst due to its superiority in acidity. The results of biodiesel isomerization over this catalyst and its modification with iron had not satisfied the expectation of high isomerization yield and significant CFP improvement. However, they emphasized that the skeletal isomers demonstrated minimum impact on biodiesel oxidation stability. They also affirmed the role of an acid catalyst in the reaction mechanism in terms of protonation, isomerization, and deprotonation. Furthermore, the metal promotion was theoretically necessary to boost the catalytic activity of this material. It initiated the dehydrogenation of linear hydrocarbon before protonation and terminated the isomerization by hydrogenating the branched carbon chain after deprotonation. Finally, the overall findings indicated promising prospects for further enhancement of catalyst performance and reusability. Full article

Irbesartan (IRB) is a commonly used BCS Class II antihypertensive drug requiring dissolving capacity enhancement to address oral bioavailability limitations. In this work, seven new IRB salts were successfully synthesized, including one carboxylate (IRB-MAL) and six sulfonate salts (IRB-TOSA, IRB-BSA, IRB-4-CBSA, IRB-2, 5-CBSA, IRB-MSA, and IRB-CPSA). Their vitro dissolution, intrinsic dissolution rates (IDRs), thermal/hygroscopic stability (via thermal analysis, dynamic vapor sorption, and accelerated stability tests), and phase transition process (monitored by in situ Raman spectroscopy) were evaluated. The results revealed that IRB-TOSA, IRB-MAL, IRB-BSA, IRB-4-CBSA, and IRB-MSA salts exhibited IDRs of 0.3194–0.7383 mg/(cm²·min), all significantly higher than IRB, with dissolution concentrations increased by 14.9–113.6%. IRB-TOSA and IRB-4-CBSA salts demonstrated excellent hydrothermal stability. Single crystal structure analysis confirmed proton transfer from coformers’ sulfonic/carboxylic acids (deprotonation site, H-out) to IRB’s diazaheterocycles (protonation site, H-in) in IRB salts. Six sulfonate salts exhibited N_H-in–H···O_H-out and N_non-H-in–H···O_H-out hydrogen bonds, with the former absent in IRB-MAL. Furthermore, supramolecular synthon studies revealed distinct hydrogen-bonding patterns (e.g., bifurcated bonds in 2,5-CBSA and CPSA salts) that correlate with moisture resistance. Quantitative analysis of IRB salts suggested hydrogen bond strengths may influence their melting points (decomposition temperatures). This study demonstrates that IRB salts hold promise for advanced pharmaceutical applications. Full article

In the field of sustainable energy conversion and storage technologies, copper-based complexes have become a research hotspot due to their efficient and stable catalytic performance. The development of bifunctional catalysts that can simplify catalytic steps, enhance efficiency, and reduce catalyst usage has become an important research area. In this study, we successfully synthesized two copper complexes with different geometries utilizing di(2-pyridyl) ketone as the ligand, [Cu^II₂L₂Cl₂]·0.5H₂O (1) and [Cu₄^IIL₄(OCH₃)₂](NO₃)₂ (2) (L = deprotonated methoxy-di-pyridin-2-yl-methanol), which can serve as homogeneous electrocatalysts for water oxidation and CO₂ reduction simultaneously. The turnover frequency (TOF) of complexes 1 and 2 for electrocatalytic water oxidation are 7.23 s⁻¹ and 0.31 s⁻¹ under almost neutral condition (pH = 8.22), respectively. Meanwhile, the TOF of complexes 1 and 2 for the catalytic reduction of CO₂ to CO are 4.27 s⁻¹ and 8.9 s⁻¹, respectively. In addition, both complexes remain essentially unchanged during the electrocatalytic water oxidation and electrocatalytic CO₂ reduction processes, demonstrating good stability. Structural analysis reveals that the distinct catalytic efficiencies originate from their geometric configurations: the binuclear structure of complex 1 facilitates proton-coupled electron transfer during water oxidation, whereas the tetranuclear architecture of complex 2 enhances CO₂ activation. Complexes 1 and 2 represent the first two copper molecular electrocatalysts capable of catalyzing both water oxidation and CO₂ reduction. The findings in this work can open up new avenues for the advancement of artificial photosynthesis simulation and the development of bifunctional catalysts for water oxidation and CO₂ reduction. Full article

Aramid nanofiber (ANF), a nanoscale building block with a prominently complex structure, can be prepared by splitting poly(p-phenylene terephthalamide) (PPTA) fibers into negatively charged ANFs in a deprotonating manner in a DMSO/KOH solvent system, followed by a subsequent re-protonation process using a proton-donor reagent. There are rare reports regarding the utilization of an aprotic donor reagent to convert deprotonated ANF dispersion into film or gel with a controllable structure and high mechanical properties. In this work, dichloromethane, as an anhydrous aprotic donor solvent, has been introduced into the deprotonated ANF dispersion to replace DMSO, containing PPTA molecules and hydroxyl ions, leading to the gelation of deprotonated ANF dispersions, forming a film (ANF_DCM) possessing a surprisingly highly entangled and oriented structure, as proven by SEM results. Due to the attenuation of electrostatic repulsion in the dispersion, partially deprotonated ANFs intertwined and cross-linked through π–π conjugation among a large number of benzene rings in PPTA molecules. After treating ANF_DCM with water for re-protonation, the as-prepared film (ANF_DCM-W) exhibited high tensile strength (307.7 MPa) and toughness (74.7 MJ m⁻³). Full article

Protolytic reactions on the surface of a titania photocatalyst (TiO₂ P25 containing chlorine impurities) were studied using potentiometric and calorimetric acid-base titration. The impurity was removed by either washing or heat treatment. The efficiency of purification was tested by chlorine (TOX) analysis and acid-base titration. Common intersection points of −0.023 and −0.021 mmol/g were obtained for the original and 400 °C heat-treated samples, which are in good agreement with the measured TOX value of 28 mmol/kg. The point of zero charge of the purified sample was determined to be 6.50. Titration data were fitted to simulate protolytic reactions during isothermal calorimetric titrations of purified titania. The evolved heat was measured, and data points were corrected with the heat of mixing and neutralization. The quantity of charged surface species formed in each step of titration was calculated using the parameters from the constant capacitance model fit. The partial molar enthalpy values of the exothermic and endothermic processes of surface protonation (ΔH_pr, −17.47 to −16.10 kJ/mol) and deprotonation (ΔH_depr, 32.53 to 27.08 kJ/mol) depend slightly on the ionic strength of suspensions. The average standard enthalpy of one proton transfer reaction is −23.54 ± 1.75 kJ/mol, which is consistent with the literature. Full article

The pursuit of electrochemical carbon dioxide reduction reaction (CO₂RR) as a means of energy generation and mitigation of global warming is of considerable interest. In this study, a novel RuO₂-incorporated SnO₂-fabricated glassy carbon electrode (GCE) with a Nafion binder was used for the electrochemical reduction of CO₂ in an aqueous alkaline imidazole medium. The electrode fabrication process involved the drop-casting method, where RuO₂.SnO₂ was incorporated onto the surface of the GCE. Electrochemical studies demonstrated that the GCE-RuO₂.SnO₂ electrode facilitated CO₂ reduction at −0.58 V vs. the reversible hydrogen electrode (RHE) via a diffusion-controlled pathway with the transfer of two electrons. Importantly, the first electron transfer step was identified as the rate-determining step (RDS). A Tafel slope of 144 mV dec⁻¹ confirmed the association of two-electron transfer kinetics with CO₂RR. Moreover, the standard rate constant (k_o) and formal potential (E°′) were evaluated as 2.89 × 10⁻⁵ cm s⁻¹ and 0.0998 V vs. RHE, respectively. Kinetic investigations also reveal that the deprotonation and electron release steps took place simultaneously in the CO₂RR. Based on the reported results, the GCE-RuO₂.SnO₂ electrode could be a promising candidate for CO₂ reduction, applicable in renewable energy generation. Full article

Prototropic conversion (prototropy) for heterocyclic nucleobases was already signaled by Watson and Crick about seventy years ago as one of the reasons for nucleic acids mutations. This isomeric phenomenon has been investigated for neutral derivatives by means of both experimental and theoretical procedures, and their favored tautomers discussed in numerous articles published in the last fifty years. Protonation/deprotonation reactions in the gas phase have also been studied using both quantum-chemical calculations and experimental techniques. Some thermochemical parameters of these processes have been documented. However, prototropy has not always been taken into account in protonation/deprotonation reactions. Most frequently, tautomeric heterocycles have been treated as simple polyfunctional compounds without possible intramolecular protontransfers. Taking into account the lack of data for the complete tautomeric mixtures, quantum-chemical investigations have been undertaken by us about twenty-five years ago for prototropic heterosystems. In this work, the pyrimidine base uracil (U) was chosen. It possesses two identical exo groups (=O/OH) at the 2- and 4-positions, two labile (tautomeric) protons, and five conjugated sites (N1, N3, C5, O7, and O8). Different types of isomerism, prototropy and OH-rotation, were considered for the neutral, protonated, and deprotonated forms. Using quantum-chemical methods, thermochemical stabilities of all possible tautomers-rotamers were examined in vacuo and the potential isomers selected. The selected isomeric mixtures for the neutral and ionic forms were applied for the determination of the thermochemical parameters in the four-step acid/base equilibria: B²⁻ BH⁻ BH₂ BH₃⁺ BH₄²⁺, where BH₂ indicates U. For each step, the microscopic (kinetic) and macroscopic (thermodynamic) acid/base parameters were estimated, and sites of the proton gain and proton loss examined. The similarities and differences between the acid/base equilibria for uracil and other pyrimidine nucleobases were discussed. Full article

This study investigated the influence of parameters such as pH condition, polyelectrolyte concentration, polymer ratio, and order of addition of the commercial polyelectrolytes chitosan and iota-carrageenan (ι-carrageenan) on the formation of polymeric nanoparticles in suspension (coacervates). A preliminary purification step of the polymers was essential for obtaining stable nanoparticles with small sizes as impurities, particularly metal ions that interfere with complexation, are removed by dialysis. Microparticles (13.5 μm in dry diameter) are obtained when aliquots of chitosan solution are poured into the ι-carrageenan solution. In general, an excess of chitosan results in the formation of agglomerated particles. The addition of an aliquot of ι-carrageenan solution (30 mL at 0.6 mg/mL and pH 4.0) to the chitosan solution (6.0 mL at 0.3 mg/mL and pH 4.0) leads to dispersed nanoparticles with a hydrodynamic radius of 278 ± 5 nm, a zeta potential of −31 ± 3 mV, and an average dry diameter of 45 ± 11 nm. The hydrodynamic radius increases as the pH rises. The partial deprotonation of ι-carrageenan chains enhances the interaction with water molecules, causing the particles to swell. These findings contribute to the fundamental understanding of polyelectrolyte complexation processes in aqueous suspension and provide insights for developing stable nanomaterials for potential practical applications. Full article

The adsorption of As(V) and As(III) (0.01–1 mM) on a calcined oxidic lithologic material substrate with pH-dependent surface variable charges, chemically modifiable, was investigated. The substrate was prepared via thermal treatment using a natural lithologic material rich in amphoteric oxides of Fe, Al, Mn and Ti. The calcined substrate was treated with acid media (HCl 0.1) to homogenize the positive charge density on the oxide surface via oxide protonation so that anion adsorption would be favored. A batch experiment was performed on the acid-treated substrate (activated) and non-activated substrate. L-type isotherms were obtained, which fit the Freundlich model. Isotherm constants showed that there was a greater affinity between the activated substrate and As(V) (K = 10.58) compared to As(III) (K = 5.45). The adsorption capacity of the activated substrate was two times greater than that of the non-activated substrate, As(V) (K_act = 10.58 and K_noact = 5.45) vs. As(III) (K_act = 5.45 y K_noact = 2.44), which was due to the greater positive charge density on the activated surface, created by the protonation of the surface oxides. Protons were liberated during the adsorption reaction (As(V): 2.17 × 10⁻³ and As(III): 0.96 × 10⁻³ mmol/mL). The forms H₂AsO₄⁻ and H₃AsO₃ deprotonated when adsorbed by the surface groups $\mathrm{M}-\mathrm{O}{\mathrm{H}}_2^{+}$ (M: Fe, Al). Kinetic data showed a second-order process for As(V) adsorption and a first-order process for As(III) adsorption. The adsorption rate on the activated substrate was two times greater compared with the non-activated substrate: As(V) (k_act = 3.78 × 10⁻⁵ L/mg·min and k_noact = 2.16 × 10⁻⁵ L/mg·min) vs. As(III) (k_act = 0.055 h⁻¹ and k_noact = 0.027 h⁻¹). The tested substrate is potentially useful as a low-cost natural material for arsenic removal from contaminated water. Full article

The action of abscisic acid (ABA) is closely related to its level in plant tissues. Uridine diphosphate-glycosyltransferase71c5 (UGT71C5) was characterized as a major UGT enzyme to catalyze the formation of the ABA-glucose ester (ABA-GE), a reversible inactive form of free ABA in Arabidopsis thaliana (thale cress). UGTs function in a mode where the catalytic base deprotonates an acceptor to allow a nucleophilic attack at the anomeric center of the donor, achieving the transfer of a glucose moiety. The proteomic data revealed that UGT71C5 can be persulfidated. Herein, an experimental method was employed to detect the persulfidation site of UGT71C5, and the computational methods were further used to identify the yet unknown molecular basis of ABA glycosylation as well as the regulatory role of persulfidation in this process. Our results suggest that the linker and the U-shaped loop are regulatory structural elements: the linker is associated with the binding of uridine diphosphate glucose (UPG) and the U-shaped loop is involved in binding both UPG and ABA.It was also found that it is through tuning the dynamics of the U-shaped loop that is accompanied by the movement of tyrosine (Y388) that the persulfidation of cysteine (C311) leads to the catalytic residue histidine (H16) being in place, preparing for the deprotonation of ABA, and then reorientates UPG and deprotonated ABA closer to the ‘Michaelis’ complex, facilitating the transfer of a glucose moiety. Ultimately, the persulfidation of UGT71C5 is in favor of ABA glycosylation. Our results provide insights into the molecular details of UGT71C5 recognizing substrates and insights concerning persulfidation as a possible mechanism for hydrogen sulfide (H₂S) to modulate the content of ABA, which helps us understand how modulating ABA level strengthens plant tolerance. Full article

The principal reactions that maintain redox homeostasis in living systems are the deprotonation of thiols, followed by the oxidative conversion of the produced thiolates into disulfides, which thus reduce the harmful oxidizing agents. The various biological thiols have different molecule-specific propensities to carry on the co-dependent deprotonation and redox processes. This study utilizes the known correlation between thiolate basicities and oxidizabilities, to quantify antioxidant or reducing capacities and pH-dependences of thiol–disulfide antioxidant systems, as a tool to find adequate molecules against oxidative stress. Full article

Degumming is a critical process in the purification of natural fibers, essential for enhancing their quality and usability across various applications. Traditional degumming methods employed for natural fibers encounter inherent limitations, encompassing prolonged procedures, excessive energy consumption, adverse environmental impact, and subpar efficiency. To address these challenges, a groundbreaking wave of degumming technique has emerged, transcending these constraints and heralding a new era of efficiency, sustainability, and eco-friendly techniques. This study represents the Firmiana simplex bark (FSB) fiber’s delignification by using deep eutectic solvents (DESs). The study explores the application of deep eutectic solvents, by synthesizing different types of DES using a hydrogen bond acceptor (HBA) and four representative hydrogen bond donors (HBDs) for FSB fiber degumming. This study investigates the morphologies, chemical compositions, crystallinities, and physical properties of Firmiana simplex bark fibers before and after the treatment. Furthermore, the effects and mechanisms of different DESs on dispersing FSB fibers were examined. The experimental results showed that choline chloride-urea (CU)-based DES initiates the degumming process by effectively disrupting the hydrogen bond interaction within FSB fibers, primarily by outcompeting chloride ions. Following this initial step, the DES acts by deprotonating phenolic hydroxyl groups and cleaving β-O-4 bonds present in diverse lignin units, thereby facilitating the efficient removal of lignin from the fibers. This innovative approach resulted in significantly higher degumming efficiency and ecofriendly as compared to traditional methods. Additionally, the results revealed that CU-based DES exhibits the utmost effectiveness in degumming FSB fibers. The optimal degumming conditions involve a precise processing temperature of 160 °C and a carefully controlled reaction time of 2 h yielding the most favorable outcomes. The present study presents a novel straightforward and environmentally friendly degumming method for Firmiana simplex bark, offering a substantial potential for enhancing the overall quality and usability of the resulting fibers. Our findings open new pathways for sustainable fiber-processing technologies. Full article

Utilizing Density Functional Theory (DFT) calculations at the B3LYP/QZVP level and incorporating the Conductor-like Polarizable Continuum Model (C-PCM) for solvation, the thermodynamic and chemical activity properties of 21-(hydroxymethoxy)henicosadecaenal, identified in cultured freshwater pearls from the mollusk Hyriopsis cumingii, have been elucidated. The study demonstrates that this compound releases formaldehyde, a potent antimicrobial agent, through dehydrogenation and deprotonation processes in both hydrophilic and lipophilic environments. Moreover, this polyenal exhibits strong anti-reductant properties, effectively scavenging free radicals. These critical properties classify the pearl-derived ingredient as a natural multi-functional compound, serving as a coloring, antiradical, and antimicrobial agent. The 2-(hydroxymethoxy)vinyl (HMV) moiety responsible for the formaldehyde release can be transferred to other compounds, thereby enhancing their biological activity. For instance, tyrosol (4-(2-hydroxyethyl)phenol) can be modified by substituting the less active 2-hydroxyethyl group with the active HMV one, and hinokitiol (4-isopropylotropolone) can be functionalized by attaching this moiety to the tropolone ring. A new type of meso-carrier, structurally modeled on pearls, with active substances loaded both in the layers and the mineral part, has been proposed. Full article