Search Results (576)

The global demand for biodiesel production is steadily increasing. Conventional homogeneous basic catalysts, while widely used in the industry, face significant drawbacks, such as the requirement for high-quality feedstock, excessive waste generation, and multiple purification steps. In this study, an acidic silane (IM-CPTMS-BS-H₂SO₄) containing imidazolium and sulfonic groups was synthesized. Heterogeneous catalysts were then prepared by anchoring varying proportions of the silane onto SBA-15 mesoporous solids. These materials were characterized by FTIR, ¹³C and ²⁹Si NMR, TGA, XRD, CHNS and acidity measurements. The catalysts were evaluated in the transesterification of methyl acetate with ethanol, with increasing catalytic conversions with the amount of grafted IM-CPTMS-BS-H₂SO₄. Furthermore, increasing the catalyst loading (from 2% to 5% wt.) and the reaction temperature (from 50 °C to 65 °C) led to higher methyl acetate conversion rates. Full article

The persilylated Si₃–Si₇ analogues of the C₃–C₇ aromatic molecules and ions with all hydrogen or all fluorine atoms at silicon have been calculated at high levels of theory, up to MP2/aug-cc-pVTZ for all species and CCSD/6-311++G** for Si₃ and Si₄ species, both in the gas phase and in a polar solvent (water). The aromaticity of the calculated species was estimated using structural, energetic, and NMR criteria. (SiF)₃⁺ cations are more aromatic than (SiH)₃⁺ by the NICS (nuclear-independent chemoical shift) but less aromatic by the ASE (aromatic stabilization energy) criterion. Dications (SiX)₄²⁺ are planar (X = H) or slightly puckered (X = F); the ASE decreases by 4–5 kcal/mol upon going from gas to solution, or from X = H to X = F. Dianions (SiX)₄²⁻are nonplanar and antiaromatic. The ASE for the slightly distorted-from-planarity anion Si₅H₅⁻ is ~53 kcal/mol, vs. 85 kcal/mol for its carbon analogue. The structure of Si₆X₆ molecules strongly depends on the level of calculations. The NICS and ASE values have been calculated for planar Si₆H₆ and (SiH)₇⁺ but not for strongly distorted Si₆F₆ and (SiF)₇⁺ species. Full article

Fly ash is an effective supplementary cementitious material for reducing clinker consumption and carbon emissions, but its low early reactivity often results in delayed hydration and insufficient early-age strength. This study investigated the age-dependent role of graphene oxide (GO) in fly ash-blended cementitious materials by combining compressive strength testing with X-ray diffraction (XRD), thermogravimetric analysis (TG-DTG), ²⁹Si magic-angle spinning nuclear magnetic resonance (²⁹Si MAS NMR), and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS). Fly ash replacement levels of 10%, 20%, and 30% were considered, and 0.07% GO was introduced to evaluate its effect at 3, 7, and 28 days. The results showed that fly ash reduced the 3-day compressive strength, whereas the strength differences became much smaller at 28 days. GO enhanced the compressive strength of all fly ash-blended mixtures. XRD and TG-DTG results showed that GO refined Ca(OH)₂ crystallization and reduced the retained CH content, indicating more effective CH utilization during hydration and pozzolanic reaction. At 28 days, the incorporation of 0.07% GO increased the compressive strength of the 30% fly ash mixture from 47.38 MPa to 56.58 MPa, while reducing the total CH content from 14.20% to 12.89%, indicating enhanced CH utilization and gel development. ²⁹Si MAS NMR further demonstrated that GO promoted a more mature and polymerized silicate gel structure, as evidenced by lower Q⁰ fractions, higher mean chain length, and higher proportions of more polymerized silicate species. SEM-EDS observations confirmed that GO led to a denser matrix, less dominant coarse CH, and lower Ca/Si and Ca/(Si + Al) ratios. Overall, GO improved the mechanical performance of fly ash-blended cementitious materials through coupled regulation of hydration products, silicate gel polymerization, and matrix densification. Full article

The development of biomimetic scaffolds requires balancing structural integrity with biological signaling. This study evaluates kefiran, a microbial exopolysaccharide, as a bioactive component in establishing printing feasibility of 3D composite constructs. Kefiran from Romanian artisanal cultures was characterized via ¹H-NMR, HPLC, and SEM/TEM, confirming a high-quality hexasaccharide repeating unit. Three composite inks (K100, K70, and K50) were developed by integrating kefiran, chondroitin sulfate, and Si-substituted hydroxyapatite into an alginate matrix and processed using a Bio X 3D-printer. Results showed that higher kefiran concentrations improved printing feasibility, providing enhanced structural fidelity and stability during the layer-by-layer deposition process. All bioprinted scaffolds demonstrated high cytocompatibility with L929 fibroblasts, maintaining viability above 70%. Notably, kefiran exhibited dual-functional therapeutic potential: concentrations above 500 mg/L showed a concentration-dependent antiproliferative effect against HT-29 cells at 72 h while remaining safe for normal cells. These findings establish kefiran-based biomaterial inks as robust, bioactive platforms for regenerative medicine. By enhancing both the mechanical printability of alginate composites and the biological response of cultured cells, kefiran proves to be a versatile component for advanced tissue engineering and potential biological activity applications. Full article

This work presents the synthesis, characterization, and application of zirconium oxide (ZrO₂)-based catalysts, modified with macro (silica nanospheres, NSP-SiO₂) and mesopore templates (Pluronic 123), impregnated with tungstophosphoric acid (TPA), in the catalytic pyrolysis of tomato agro-industrial residues. The NSP-SiO₂ (SXX) and P123 (PYY) amount mainly influences the ZrO₂SXXPYY-specific surface area (S_BET) and average pore diameter (D_p). ³¹P MAS NMR and FT-IR characterization results show that TPA (H₃PW₁₂O₄₀) was partially transformed into [P₂W₂₁O₇₁]⁶⁻ and [PW₁₁O₃₉]⁷⁻ during the synthesis steps. The acidic properties of ZrO₂SXXPYY samples containing 25 and 50 wt% of TPA (ZrO₂SXXPYYT25 and ZrO₂SXXPYYT50, respectively) are dependent on both the TPA content and the support nature. Bio-oil composition and product selectivity were strongly influenced by the textural and acid-based properties of the catalysts. Notably, non-catalytic pyrolysis favored pathways leading to C2 compounds, with a high content of acetic acid and hydroxyacetone. In contrast, the use of catalysts promoted the formation of higher molecular weight oxygenated compounds (C5–C6), specifically furans, aldehydes, and ketones. Full article

Linear alkylbenzene (LAB) is the main raw material used to make biodegradable detergents, and its production process is based on aromatic alkylation. HY zeolites that have undergone controlled dealumination and desilication have led industrial standards amongst solid acid catalysts because of their controllable acidity and hierarchical pore structure. Coke formation in such systems can assume a dual role, which is dependent on its condition. Though the over-deposition is known to cause deactivation by blocking the micropores, Bronsted acid-site masking, and diffusion collapse, the low-level deposition could also be done to increase the monoalkylate selectivity by the pore mouth catalysis, steric modulation, and selective suppression of secondary alkylation pathways. The critical review is done on the structural-kinetic interaction that determines the coke evolution in HY-based catalysts. In order to moderate the acid-site density and enhance hydrothermal stability, dealumination (Si/Al optimization of about 2.5 to 30–100) occurs, but to reduce deep-pore coke formation, desilication (interconnected mesopores) is created. The bimodal porosity and regulated acidity are found to be synergistic, as hierarchical HY zeolites produced through successive cycles of steam and alkaline treatments not only show LAB selectivity in excess of 90% but also exhibit much longer catalyst lifetimes. Quantitative research on the beneficial coke regime revealed that it was composed of about 36 wt% hydrogen-rich species, which were localized at the pore mouths, hence enhancing monoalkylation selectivity by 15–40%. Beyond a critical transition window (e.g., 8–12 wt.%), coke formation to condensed polyaromatic and graphitic products leads to fast deactivated coke formation, which is due to percolation limits and transport-controlled kinetics. More advanced techniques of characterization of the coke, e.g., temperature-programmed oxidation (TPO), ²⁷Al MAAS NMR, and UV-Raman spectroscopy, indicate how the coke is changed to highly structured graphitic deposits of high oxidation activation energy. Activity recovery of 85–98% is obtained in regeneration processes, including controlled oxidative calcination, microwave-based and plasma-based processes, and thermal management protocols, and it would be determined by the chemistry of the coke, its spatial distribution, and the regeneration protocols. This paper has developed a mechanistic coke control system by cross-tuning the acidity and development of an effective pore network, which led to a sustainable aromatic alkylation reaction with minimal activity loss, high selectivity, and long life. Full article

The indole scaffold is common in natural products and bioactive compounds, including anti-cancer and anti-inflammatory medicines. In this work, a series of indole-acrylamide derivatives was synthesized, and their antiproliferative and anti-inflammatory effects were evaluated on COX enzymes and against a panel of cancer cell lines. All the final compounds were characterized via HRMS and (¹H & ¹³C)-NMR. Anticancer and anti-inflammatory activities were evaluated using standard biomedical techniques by SRB, MTS, and COX kit assays. Additionally, the molecular docking analysis was conducted using the AutoDock Vina tool. The results demonstrated that the produced compounds displayed significant inhibitory effects on the COX-2 enzyme, with IC₅₀ values of 128 nM to 1.04 µM. 6a demonstrated significant COX-2 selectivity with an IC₅₀ of 128 nM and an SI of 352, highlighting its preference for COX-2 over COX-1. 6c exhibited potent COX-2 inhibition with an IC₅₀ of 0.215 µM and an SI of 10.6. The assessed compounds exhibited substantial cytotoxic effects on cancer cells, especially against liver cancer cell lines (Huh7, HepG2, Mahlavu, and SNU475), and breast cancer (MCF-7). 6d compound was the most COX-1 selective inhibitor, which observed potent activity against hepatocellular carcinoma, with IC₅₀ values as low as 3.5 µM, and was highly effective against MCF-7. Additionally, COX-2 selective inhibitors, 6a and 6b, exhibited strong antiproliferative effects against both breast cancer (MCF-7) and melanoma (B16F1), with IC₅₀ values ranging from 4.75 to 15.4 µM. Furthermore, the molecular docking of 6a demonstrated a strong affinity for the COX-2 enzyme, with energy scores (S) of −8.392 kcal/mol, comparable to celecoxib’s score of −10.96 kcal/mol. The findings suggest a possible correlation between COX-2 inhibition and anticancer efficacy, especially for compounds 6a and 6c, which demonstrate excellent COX-2 selectivity and notable antiproliferative effects, positioning them as prospective candidates for further advancement in cancer treatment. Full article

Human African Trypanosomiasis (HAT) and Malaria are serious infectious diseases endemic in tropical regions, caused by protozoan parasites, and necessitating an urgent development of new antiprotozoal drugs. As part of our ongoing search for new antiprotozoal steroidal alkaloids from plants, we investigated the methanolic stem bark extract of Holarrhena pubescens (Apocynaceae). H. pubescens is a tropical tree that some Kenyan coastal communities have long used to treat various ailments, including fever and stomach pain. The crude extract, alkaloid fraction, and 16 subfractions acquired through centrifugal partition chromatography (CPC) displayed promising in vitro antiprotozoal activity against Trypanosoma brucei rhodesiense (Tbr) and Plasmodium falciparum (Pf). Partial least squares (PLS) regression modeling of UHPLC/+ESI QqTOF-MS data and the antiprotozoal activity data of the crude extract and its fractions was performed to predict compounds that may be responsible for the observed antiplasmodial activity. Chromatographic separation of the alkaloid fraction afforded one new steroidal alkaloid (5), along with 18 known compounds (1, 2, 4, 6–20), and one artifact (3) that was presumably formed during the acid–base extraction process. The structural characterization of the isolated compounds was accomplished using UHPLC/+ESI-QqTOF-MS/MS and NMR spectroscopy. The isolated compounds were tested for their in vitro antiprotozoal properties against the two aforementioned pathogens, as well as for their cytotoxicity against mammalian cells (L6 cell line). Compounds 2 and 16 (IC₅₀ = 0.2 μmol/L) demonstrated the highest antitrypanosomal activity, with compound 2 showing the highest selectivity (SI = 127). The new compound 5 exhibited the strongest antiplasmodial activity and selectivity against Pf (IC₅₀ = 0.7 μmol/L, SI = 43). Our findings provide further promising antiprotozoal leads for HAT and Malaria. Full article

Terpinen-4-ol (TP4O) is a key monoterpene alcohol commonly used as a quality and authenticity marker in essential oils, cosmetics, herbal products, and pharmaceutical formulations. However, reliable and comparable quantification of TP4O across laboratories is challenged by variability in natural matrices and the limited availability of well-characterized, traceable reference materials. In this study, a high-purity certified reference material (CRM) of TP4O was developed and characterized by the National Institute of Metrology (Thailand). The material’s purity was determined using two independent and complementary approaches: a mass balance method (MB) method based on gas chromatography with flame ionization detection (GC-FID), Karl Fischer coulometric titration (KFT), and thermogravimetric analysis (TGA), and a quantitative ¹H NMR (qNMR) method employing DSS-d₆ as an internal standard. The purity values obtained using the MB (98.41 ± 0.09%) and qNMR (99.13 ± 0.94%) methods were statistically equivalent (p > 0.05). Based on the combined evaluation, a certified purity value of 98.77% with an expanded uncertainty of 3.05% (k = 2) was assigned. Homogeneity and short- and long-term stability assessments confirmed the suitability of the material for its intended use. This TP4O CRM provides an SI-traceable, high-purity reference to support calibration, method validation, and quality assurance in analytical applications involving essential oil components. Full article

Michael acceptors, such as chalcones and benzylidenes, are privileged scaffolds for the development of anticancer agents. Taking this into account, we developed a selective Claisen–Schmidt condensation of the dammarane-type triterpenoid hollongdione with pyridine-2-carbaldehyde, enabling controlled synthesis of mono- and bis-substituted triterpenes depending on the reaction conditions. The reaction demonstrated high temperature-dependent regioselectivity, providing C2-mono- 2 or 2,21-bis-substituted 3 triterpenes with yields up to 96% and 95%, respectively. The structures of the newly synthesized triterpene chalcones were elucidated by 1D and 2D NMR spectroscopy and unambiguously confirmed by a single-crystal X-ray diffraction, which established the E configuration of the exocyclic double bond. In biological studies, the bis-2-pyridylidene derivative 3 exhibited a pronounced and broad-spectrum antitumor activity in the NCI-60 panel, inducing cell death in 58 of 59 cancer cell lines. High selectivity toward melanoma, renal, and prostate cancer cell lines was observed, with selectivity indices (SI) of up to 18.82 for melanoma LOX IMVI. In MTT assays, compound 3 displayed a submicromolar cytotoxicity, particularly against the KRAS-mutant PANC-1 cell line (IC₅₀ = 0.22 µM). Anticancer activity was further confirmed in a zebrafish (Danio rerio) xenograft model of human HCT116 colon cancer, where tumor growth inhibition reached 72% without pronounced embryotoxicity (LC₅₀ = 1.4 µM). We have developed an efficient approach for the site-selective modification of hollongdione, providing access to potent anticancer dammarane-type chalcones. The bis-2-pyridylidene derivative 3 emerged as a promising lead compound, demonstrating submicromolar potency, high selectivity towards melanoma, and significant in vivo efficacy in a zebrafish xenograft model. Full article

The high environmental impact associated with ordinary Portland cement production has driven increasing interest in alternative low-carbon binder systems based on alkali-activated materials. In this context, geopolymers synthesized from metakaolin and supplemented with natural or industrial by-products represent a promising route toward more sustainable construction materials. In this study, the partial substitution of metakaolin (MK) with stainless steel slag (SSS, calcium rich) or volcanic ash (VA, silica-rich) in alkali-activated cements (AACs) synthesis was investigated by analyzing their physical, mechanical, and thermal properties. The structural evolution associated with alkali activation was assessed using X-ray diffraction (XRD) and ²⁹Si and ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR). Fourier transform infrared spectroscopy (FTIR) revealed a shift in the main Si–O–T (T = Si, Al) asymmetric stretching band toward lower wavenumbers (≈1000 cm⁻¹), indicating changes in the aluminosilicate network consistent with geopolymer formation. Scanning electron microscopy (SEM) was used to examine the microstructural features of the hardened matrices. The results showed that samples containing 50 wt.% MK and 50 wt.% VA achieved the highest mechanical performance, with compressive and flexural strengths of 46.29 MPa and 16.2 MPa at 7 days, increasing to 56.66 MPa and 17.58 MPa at 28 days of curing, respectively. In contrast, the samples containing 50 wt.% MK and 50 wt.% SSS displayed lower strength development, reaching compressive and flexural strengths of 27.7 MPa and 9.6 MPa at 7 days and 41.01 MPa and 13.68 MPa at 28 days. Additionally, thermal conductivity decreased with increasing porosity and decreasing bulk density, highlighting the potential of these AACs as structurally efficient materials with improved thermal insulation performance. Full article

Cement stabilization is widely used to improve the mechanical performance of bentonite-rich soils; however, the behavior of cement-stabilized bentonite under highly alkaline conditions remains unclear. This study aims to elucidate the degradation mechanisms of the mechanical properties of cement-stabilized bentonite exposed to NaOH solutions with concentrations ranging from 1 to 8 mol/L. Unconfined compressive strength (UCS) tests were combined with XRD, ²⁹Si NMR, and MIP to characterize mineral phases, silicate structure, and pore structure of the stabilized soils. Increasing alkalinity led to pronounced strength deterioration, with the 90 d UCS decreasing from 2.56 MPa to 0.25 MPa, corresponding to a reduction of approximately 90%. Microstructural analyses indicate that elevated alkali content inhibits cement clinker hydration, promotes the formation of zeolitic crystalline phases, induces depolymerization of the silicate network with the mean chain length decreasing from 6.4 to 3.5, partially transforms montmorillonite from a 2:1 to a 1:1 layer structure, and results in significant pore coarsening, as reflected by an increase in the most probable pore size from 62.53 to 1054.52 nm. These coupled effects weaken the integrity of the gel network and account for the continuous reduction in mechanical strength with increasing alkali concentration, providing a mechanistic basis for understanding the alkali-induced weakening behavior of cement-stabilized bentonite and offering guidance for its engineering application in alkaline environments. Full article

Zirconia (ZrO₂) containing bioactive glasses (BG’s) have been synthesized to determine their influence on the structure of a 0.56SiO_2–0.15Na₂O-0.25CaO-0.04P₂O₅ glass and the resulting solubility within a hydrated environment. In this study, the SiO₂ content was directly substituted with 0.04 ZrO₄ (Mol. Fr.) and structural analysis of the Control and Zr-Glasses was conducted using X-ray Photoelectron Spectroscopy (XPS) and Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR). These techniques indicate that the overall network connectivity (NC) of the glass increases with ZrO₂/SiO₂ substitution, suggesting that ZrO₂ acts predominantly as a network former in the glass structure. The ion release profiles of the glasses incubated in de-ionized water from 1 to 1000 h showed decreased dissolution rates for the Zr-containing glasses. The in vitro bioactivity of glasses tested in Simulated Body Fluid (SBF) showed calcium phosphate (CaP) formation on the surface of all glasses after 100–1000 h incubation; however, the Zr-glass experienced delayed CaP precipitation compared to the Zr-free Control. Full article

The valorization of dredged sediments represents a major environmental and logistical challenge, particularly in the context of forthcoming regulations restricting their marine disposal. This study investigates the potential of untreated dredged sediments as sustainable raw materials for geopolymer binder development, with the dual objective of sustainable sediment management and reduction in cement-related environmental impact. Dredged sediments from the Grand Port Maritime de Bordeaux (GPMB) were activated with sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃), both alone and in combination, with supplementary aluminosilicate and calcium-rich co-products, to assess their reactivity and effect on binder performance. A multi-scale experimental approach combining mechanical testing, calorimetry, porosity analysis, Scanning Electron Microscopy and Energy-Dispersive Spectroscopy (SEM–EDS), X-ray diffraction (XRD), Thermogravimetric Analysis (TGA), and solid-state Nuclear Magnetic Resonance (NMR) was employed to challenge the commonly assumed inert behavior of sediments within geopolymer matrices, to elucidate gel formation mechanisms, and to optimize binder formulation. The results show that untreated sediments actively participate in alkali activation, reaching compressive strengths of up to 5.16 MPa at 90 days without thermal pre-treatment. Calcium-poor systems exhibited progressive long-term strength development associated with the formation of homogeneous aluminosilicate gels and refined microporosity, whereas calcium-rich systems showed higher early age strength but more limited long-term performance, linked to heterogeneous gel coexistence and increased total porosity. These findings provide direct evidence of the intrinsic reactivity of untreated dredged sediments and highlight the critical role of gel chemistry and calcium content in controlling long-term performance. The proposed approach offers a viable pathway for low-impact, on-site sediment valorization in civil engineering applications. Full article

Organophilic acidic magadiites were prepared after an acidic magadiite (A-Mgd) reaction with cetyltrimethylammonium solutions containing different anions, such as cetyltrimethylammonium bromide (C16TMABr), cetyltrimethylammonium chloride (C16TMACl), and cetyltrimethylammonium hydroxide (C16TMAOH). The resulting materials were studied as adsorbents for Eosin Y removal from artificially contaminated solution. Successful preparation of oganophilic A-Mgd was achieved using C16TMAOH solution with an increased basal spacing from 1.21 nm to 3.15 nm and uptake C16TMA amount of 1.16 mmol/g. Meanwhile, no variation in the basal spacing of 1.20 nm occurred using C16TMACl and C16TMA Br solutions with an uptake mount of 0.07 to 0.09 mmol/g, respectively. Other techniques supported the behavior of the counteranion of surfactant solution on the synthesis of organophilic A-Mgd samples. 13C CP/MAS NMR data revealed that C16TMA cations displayed all-trans conformation comparable to C16TMABr solid, and ²⁹Si MAS NMR confirmed the stability of the host silicate layers during the reaction. The specific surface area of A-Mgd was reduced after the intercalation of C16TMA cations from 38 m²/g to 11 m²/g. The removal properties of organophilic samples were investigated under different conditions, including the Eosin Y pH solution, initial concentration, dosage mass, and content of C16TMA cations. The maximum removal amount was 70 mg/g at acidic pH and using A-Mgd prepared from C16TMAOH solution, while the other organophilic A-Mgds exhibited low removal amounts of 3 to 5 mg/g. The regeneration tests indicated that the efficiency was maintained after four reuse tests with a drop of 30 to 50% from the initial value after seven cycles. The adsorber batch design was employed to estimate theoretically the required masses of used samples to treat an effluent volume of 10 L at a removal percentage of 95% at a fixed initial concentration of 200 mg/L. In total, 20 g of organophilic prepared from A-Mgd and C16TMAOH solution was needed, while 243 g of sample prepared from C16TMABr solution was required. This study proposes the development of a cost-effective, sustainable solution for dye-contaminated wastewater treatment. Full article