Search Results (952)

Pyrrolidinyl-substituted silacyclopentane (CH₂)₄Si(Pyr)₂ and α-amino isobutyric acid (H₂Aib) react with the release of one equivalent pyrrolidine (HPyr) and the formation of the pentacoordinate silicon bis-chelate (Aib)Si(CH₂)₄(HPyr), which features the di-anion of the amino acid as an (O,N)-chelator and one equivalent of pyrrolidine as an additional lone-pair donor. Crystallographic analyses of the chloroform solvate (Aib)Si(CH₂)₄(HPyr)·(CHCl₃), which undergoes a phase transition at 200 K, and a solvent-free modification (Aib)Si(CH₂)₄(HPyr), which features two crystallographically independent molecules of the complex, revealed that the N atom of the HPyr ligand, as well as the carboxylate of Aib, occupy the axial positions in the trigonal bipyramidal Si coordination sphere; the Si–C bonds of the silacyclopentane rest on equatorial sites. For the isolated molecule in a solvent environment, computational analyses revealed that the energy difference between this configuration and the related isomer with an equatorial HPyr and equatorial–axial positioning of the silacyclopentane motif is marginal. In DMSO solution, the adduct (Aib)Si(CH₂)₄(HPyr) decomposed, forming the hexacoordinate Si complex (HAib)₂Si(CH₂)₄ as one of the decomposition products. In a deliberate manner, this compound was accessible from the diethylamino-substituted silacyclopentane (CH₂)₄Si(NEt₂)₂ and H₂Aib with the liberation of diethylamine. (HAib)₂Si(CH₂)₄ features two mono-anions of the α-amino acid as (O,N)-chelators, their carboxylate O atoms are trans-disposed to silacyclopentane, and their NH₂ groups are mutually trans. Full article

Parkinson’s disease (PD) is a progressive neurodegenerative disorder traditionally defined by dopaminergic neuronal loss and Lewy body pathology; however, increasing evidence indicates that metabolic dysfunction contributes to both motor and non-motor manifestations of disease. While metabolomics studies in PD have largely focused on peripheral biofluids or subcortical brain regions, metabolic remodeling within cortical regions critical for cognition remains poorly characterized. Here, we applied LC-MS/MS-based untargeted metabolomics to post-mortem frontal cortex tissue from PD and neurologically normal control donors, with statistical models adjusted for age, sex, and post-mortem interval. A total of 893 metabolites were quantified, of which 234 exhibited significant differential abundance following false discovery rate correction. Pathway enrichment and network-based integration revealed coordinated metabolic remodeling characterized by predicted inhibition of β-alanine metabolism and pantothenate-dependent coenzyme A biosynthesis alongside activation of amino acid, vitamin B-dependent, cofactor-related, redox-associated, oxidative stress, and inflammatory pathways. Recurrent alterations in pantothenic acid, β-alanine-related intermediates, arginine- and histidine-derived metabolites, lumichrome, and vitamin B₆-associated species may reflect cortical metabolic perturbations associated with mitochondrial bioenergetic vulnerability and oxidative stress. Together, these findings indicate selective metabolic vulnerability in the PD frontal cortex rather than diffuse metabolic collapse. Full article

An efficient catalyst for the reaction of ethanol–acetaldehyde into 1,3-butadiene (EATB) is prepared through the grafting of zirconia into a zeolite Beta lattice. The grafting is achieved through the dealumination of a zeolite framework by acid treatment followed by zirconia impregnation, leading to the substitution of aluminum in the zeolite framework by zirconia. The catalyst with zirconia grafted into the zeolite framework promotes desirable catalyst properties like high zirconium dispersion, stability, and the close proximity of Lewis acid, Bronsted acid, and medium basic sites. The phase, the coordination of zirconia, the location of the active center and the cooperative synergism were elucidated through various characterization techniques, including X-ray diffraction, Raman spectroscopy, N₂ adsorption, UV–vis spectroscopy, XPS, ²⁹Si MAS NMR, NH₃-TPD, Py-IR, CO-IR and CO₂-TPD. The catalytic results show that a suitable phase and content of zirconia were needed to improve the ethanol–acetaldehyde conversion, butadiene selectivity and catalyst stability. Among the catalysts, m+t-ZrO_x-Beta-H₂O-9020 (m = monoclinic, t = tetragonal ZrO₂ phase) achieved the best butadiene selectivity of 82–73% at the conversion of 100–66%, run over 200 h. The results allow us to propose a Lewis acid–medium basic pairing for the Si–O–Zr–O–Si group, where the adjacent Si-OH is the active center for reactions. Full article

The selective conversion of high-molecular-weight paraffins (C₂₀–C₄₀) into linear alpha-olefins is often hindered by severe diffusion limitations and secondary over-cracking. This study addresses these challenges by transforming low-value natural minerals into sophisticated catalytic systems. We present a “top-down” engineering strategy for designing hierarchical catalysts based on natural Kazakhstani clinoptilolite. The multi-stage modification involves synergistic demineralization and precision chelation (EDTA, sulfosalicylic acid) to generate a tailored mesoporous architecture. This framework serves as a host for the sub-nanometric immobilization of Keggin-type heteropolyacids (PW₁₂, PMo₁₂), ensuring optimal active-phase dispersion. The innovative dual-step modification successfully bypassed the “micropore barrier”, creating a high-surface-area hierarchical network that facilitates the transport of bulky paraffinic molecules. Precise localization of heteropolyacid clusters within the created mesopores resulted in the formation of superstrong Lewis acid sites, as confirmed via temperature-programmed ammonia desorption. These sites triggered a highly efficient monomolecular beta-scission mechanism, suppressing undesirable hydrogen transfer reactions. The resulting catalysts achieved a breakthrough in technical paraffin cracking, delivering a 70% liquid product yield with an unprecedented >50% selectivity toward the C₇–C₁₄ α-olefin fraction. This work demonstrates a sustainable pathway for upgrading natural zeolites into high-performance, green catalysts that rival expensive analogs in precision and efficiency. Full article

Zeolites, both natural (e.g., clinoptilolite) and synthetic (e.g., FAU, ZSM-5), provide robust, tunable platforms for the removal of air pollutants and process-stream contaminants via adsorption and catalysis. This author-led article integrates experimental and theoretical insights on the adsorption of odorous compounds and ammonia (NH₃) and the catalytic abatement of nitrogen oxides (NOx) and nitrous oxide (N₂O), highlighting how topology, acidity, and metal speciation jointly control performance. Representative theoretical results show that adsorption on Brønsted acid sites is significantly more favorable (≈−1.1 eV for NH₃ and −0.37 eV for acetaldehyde) than on Na⁺ sites (≈0.02 eV and 1.22 eV, respectively), demonstrating the critical role of acid site distribution in adsorption selectivity. We dissect structure–function relationships encompassing pore size and connectivity, Si/Al ratio, Brønsted/Lewis site distribution, hydrophilicity/hydrophobicity, and the role of water, with emphasis on hierarchical porosity to alleviate transport limitations. Metal exchange and surface functionalization are discussed as levers to tailor adsorption strength and redox activity, supported by density functional theory (DFT) analyses and reaction pathways. We propose practical design descriptors (acid strength metrics, metal nuclearity, and confinement factors) that enable faster iteration of zeolite architecture for targeted separations and reactions. Sustainability considerations include the use of abundant natural zeolites, low-energy regeneration, stability under humid, mixed-stream conditions that minimize pressure drop and waste. The article closes with a forward look at data-guided optimization to accelerate “engineering zeolites” for durable, selective, and energy-efficient clean-air and process-intensification applications. Full article

In this work, the activity of vanadium-doped and undoped phosphomolybdic acids with general formulae H_3+nPMo_12−nV_nO₄₀ (n = 0, 1, 2, and 3) was evaluated in the acetalization of furfural with alkyl alcohols. The main focus was to assess how vanadium charge affects the catalytic activity of phosphomolybdic acid and to link these effects to changes in structural properties. The main reaction parameters, such as charge and concentration of the catalyst, temperature, time, type of alcohol and aldehyde, and charges of vanadium and of H⁺ ions, were studied. Various Brønsted acids (sulfuric, p-toluenesulfonic, undoped, and doped phosphomolybdic acids) were evaluated on the condensation reactions of furfural with methyl alcohol. Notably, H₄PMo₁₁VO₄₀ was the most active and selective catalyst for the formation of methyl acetal furfural. Water has a leveling effect on the strength of these acids. Nonetheless, under reaction conditions, the presence of vanadium affected their acidity strength, and it was possible to verify that the vanadium-monosubstituted phosphomolybdic acid was the strongest. The superior performance of H₄PMo₁₁VO₄₀ was attributed to its additional acidity, resulting from the presence of very strong Brønsted acid sites (H⁺) and Lewis acid sites, due to the inclusion of V⁵⁺ ions in its structure. The novelty of this work is the assessment of vanadium-doped phosphomolybdic acids in the homogeneous phase in the condensation reactions of furfural with various alcohols and of methyl alcohol with various aldehydes. Full article

A novel bio-capable method has been implemented for the synthesis of newly substituted derivatives of perimidine using Fe₃O₄@nano-cellulose/Ti(IV) as a magnetic, sustainable, and eco-friendly Lewis acid nanocatalyst. The catalyst was thoroughly characterized by XRD, FESEM, and TGA analyses, confirming its crystalline structure, uniform nanoscale morphology, and high thermal stability. The reaction proceeded smoothly in eco-friendly solvents, providing outstanding yields under mild and rapid conditions, especially with ultrasonics. The catalyst, derived from renewable materials, exhibited remarkable activity, easy magnetic recovery, and excellent reusability over several cycles without significant loss of efficiency. Spectral characterization, IR, ¹H NMR, ¹³C NMR, ¹⁹F NMR, and HRMS analyses verified that perimidine derivatives were synthesized properly. This sustainable and efficient approach demonstrates the prospect of green Lewis acid nanocatalysts for the sustainable synthesis of valuable heterocyclic compounds. Full article

A comprehensive thermodynamic and molecular-level investigation of adsorption on MgY and NH₄Y zeolites is presented using inverse gas chromatography at infinite dilution (IGC-ID), combined with a Hamaker-based formalism and an extended five-parameter Lewis acid–base model. The study introduces a unified framework that integrates dispersive, polar, and donor–acceptor interactions while explicitly accounting for temperature-dependent intermolecular geometry. The results demonstrate that the London dispersive free energy exhibits a highly linear temperature dependence (R² > 0.999), while the corresponding surface energy decreases linearly with temperature (e.g., ${\gamma }_s^d\left(T\right)=-0.297T+189.48$ mJ·m⁻² for MgY), reflecting the progressive weakening of dispersion forces. Simultaneously, the intermolecular separation distance follows a linear relation $r\left(T\right)=r_0+{\alpha }_{\mathrm{eff}}T$, with ${\alpha }_{\mathrm{eff}}$ values on the order of (2–3) × 10⁻³ Å·K⁻¹ for MgY, enabling the determination of intrinsic contact distances $r_0$ at 0 K, varying between 4.00 Å and 6.60 Å. A major finding is that the molecular surface area of adsorbed probes is not constant but follows a quadratic temperature dependence with excellent accuracy (R² > 0.999), establishing adsorption cross-section as a thermodynamic variable. The comparison between MgY and NH₄Y reveals two distinct adsorption regimes: MgY exhibits a structured and strongly dispersive interaction field associated with Mg²⁺ cations, whereas NH₄Y displays enhanced polarity, stronger specific interactions, and greater molecular flexibility driven by hydrogen bonding and protonic effects. Thermodynamic analysis of Lewis acid–base interactions shows that classical linear models are insufficient. Statistical evaluation (R² ≈ 0.986, minimum AIC/BIC, lowest RMSE) demonstrates that the five-parameter Hamieh model provides the most accurate and physically meaningful description, capturing nonlinear donor–acceptor interactions and amphoteric coupling effects. Overall, this work establishes a novel thermodynamic methodology that quantitatively links macroscopic surface energetics to microscopic interaction parameters, providing new insight into adsorption mechanisms and a robust framework for the rational design of porous materials in catalysis, separation, and energy applications. Full article

CO₂ adsorption on subnanometric metal clusters is highly sensitive to the computational protocol used to describe the potential energy surface, particularly when several low-lying geometries and spin states are accessible. In this work, CO₂ adsorption on Cu₄ and Sc₄ clusters was investigated using density functional theory (DFT) to evaluate how the choice of functional/basis-set protocol, spin multiplicity, initial geometry, and vibrational stability affects the predicted adsorption behavior. Four representative computational protocols (TPSSh, r²SCAN-3c, PBE-D4/def2-TZVP, and PBE0-SDD) were assessed for isolated clusters and cluster–CO₂ complexes. The lowest harmonic vibrational frequency, ω_min, was used as a diagnostic criterion to distinguish true minima from unstable or weakly defined stationary points. Selected cases were also cross-checked using the ORCA and Gaussian quantum-chemistry packages to assess whether comparable computational settings yielded consistent stationary-point character. The results show that Cu₄ generally exhibits weak CO₂ binding, whereas Sc₄ displays stronger but more protocol-dependent adsorption, consistent with its higher structural flexibility and more pronounced Lewis-acid character. Low-frequency and imaginary modes were found in several optimized structures, indicating that adsorption energies should not be interpreted without prior vibrational validation. The comparison also shows that variations in functional/basis-set treatment and spin multiplicity can alter both the optimized geometry and the predicted adsorption strength. Therefore, CO₂ adsorption on small metal clusters should be discussed using combined structural, vibrational, and energetic criteria rather than electronic adsorption energies alone. Overall, this study provides a protocol-oriented framework for evaluating the reliability of DFT predictions in CO₂ adsorption on Cu₄ and Sc₄ clusters. Full article

Making 1 $\mathrm{k}$$\mathrm{t}$ of cheese produces 9 $\mathrm{k}$$\mathrm{t}$ of cheese whey permeate, a waste with 5% lactose, which is either discarded or dried for animal feed. One pathway to add value to this waste is to convert it to lactic acid (LA), a monomer for polylactic acid, the largest bioplastic produced in the world. Lactose hydrolyses to glucose and galactose. While Brønsted acidity enhances lactose hydrolysis, Lewis acidity favours the formation of lactic acid. For the first time, we tested both industrial whey permeate and purified lactose as feedstocks for LA over a heterogeneous catalyst–Er₂O₃/Al₂O₃. LA Yield from whey permeate reached 14%, while the maximum yield with purified lactose was 22%. LA yield was invariant with respect to mixing speed while increasing temperature accelerates the time it takes to reach quasi-equilibrium. Yield was also independent of pressure with either air, He, N₂, or H₂ in the vapour space above the liquid phase in the autoclave. LA yield over spent catalyst with fresh lactose was only 11%, which indicates that the catalyst deactivates. Based on XRF analyses, the Er₂O₃ mass fraction dropped from 15% to 5%, with 6.4% leaching into the aqueous phase after the first step but only 0.8% after the second test. Full article

Considering the expanded interest in reducing organic solvents in synthesis, surfactants and surfactant-based catalysis have been used to carry out various organic transformations in water. In recent years, the integration of Lewis and Brønsted acid catalysis with micellar systems has gained considerable attention as a powerful approach to enhance reaction efficiency while minimizing the environmental impact of synthetic processes. In this article, we depict the most recent advances in the water-interceded synthesis of different organic systems by utilizing different surfactant-type catalysts, which are important structural motifs in pharmaceuticals, agrochemicals and functional materials. Further, these methods incorporate green reaction media, mild reaction conditions, and a great yield of product with high purity in a shorter interval of time. Understanding the scope and impact of this area, authors have made efforts to collect and compile the data that indicates many named reactions, such as Friedlander annulation, aldol condensation, the Biginelli reaction, the Mannich reaction, Suzuki–Miyaura cross-coupling, etc., now take place using surfactant-based catalysts. Full article

The ethylene aromatization (ETA) reaction is a pivotal route for non-petroleum-based aromatics production, yet a systematic understanding of its thermodynamic constraints and kinetic modulation remains elusive. Herein, an integrated thermodynamic and kinetic study is presented to elucidate the temperature-dependent reaction pathways over metal oxide-modified HZSM-5 catalysts. Thermodynamic calculations reveal that while oligomerization, cyclization, and the hydrogen transfer (HT) pathway are exothermic, the aromatics-generating dehydrogenation (DH) pathway is endothermic. Crucially, despite the general thermodynamic penalty imposed by elevated temperatures on most elementary steps, the overall ethylene aromatization reaction retains a strong driving force, underscoring the dehydrogenation pathway as the thermodynamic and kinetic key to aromatic selectivity. Experimentally, it is demonstrated that modifying HZSM-5 with ZnO, Ga₂O₃, and ZnGa₂O₄ effectively tunes the Lewis-to-Brønsted acid (L/B) ratio. A strong linear correlation is established between the L/B ratio and the apparent activation energy, with a higher L/B ratio significantly lowering the activation barrier. This synergistic effect optimally promotes the dehydrogenation pathway, suppresses alkane by-product formation, and maximizes aromatic yield within an optimal temperature window of 470–520 °C. The findings provide a fundamental and practical framework for the rational design of high-efficiency ethylene aromatization catalysts and the optimization of process conditions via targeted acid site engineering. Full article

In this work, various types of organosilanes were introduced into Sn-Si oxide through a simple aerosol process to yield synthesis precursors. Then, a series of Sn-Beta zeolites were successfully synthesized using a hydrothermal method in the presence of fluoride. The influence of amine groups (A, 2A, and 3A), the length of branched chains present in the organosilanes, as well as the use of dipodal silanization agents (B2A) on the morphology, pore structure, acidic properties, coordination state, and content of Sn species in the obtained Sn-Beta zeolite samples was investigated. Compared to the organosilane-free Sn-Beta (crystal size: 1.3 μm; Si/Sn = 119; Lewis acid density: 77 μmol·g⁻¹), all monopodal organosilane-doped samples (Sn-Beta-A, -2A, and -3A) exhibited reduced crystal sizes (~0.9 μm) and increased specific surface areas (up to 502 m²·g⁻¹ for Sn-Beta-2A). UV–Vis spectroscopy showed that Sn-Beta-2A (containing two amine groups) achieved the highest optical bandgap (4.68 eV) and the strongest suppression of extra-framework SnO_x species (peak at ~269 nm), indicating the most isolated tetrahedral framework Sn⁴⁺ sites. This sample also delivered the highest Lewis acid density (225 μmol·g⁻¹) and the best catalytic performance in the Baeyer–Villiger oxidation of cyclohexanone (39% conversion, TON = 106) and 2-adamantanone (37% conversion, TON = 101). By contrast, the dipodal organosilane (B₂A) caused severe steric hindrance, yielding the lowest crystallinity (relative crystallinity 64%), Si/Sn ratio (158), Lewis acid density (38 μmol·g⁻¹), and catalytic activity, despite forming a nanoaggregate morphology with high mesoporosity (V meso = 0.20 cm³·g⁻¹). These quantitative results demonstrate that monopodal organosilanes with two amine groups optimally balance Sn incorporation and textural properties, whereas dipodal silanes hinder framework Sn entry. This study provides clear, numerically grounded guidelines for selecting organosilane functional groups to design high-performance Sn-Beta zeolites. Full article

Ammonia decomposition represents a promising route for CO₂-free hydrogen production; however, the development of efficient and stable catalysts remains a critical challenge. In this work, a series of Al-based mixed-oxide catalysts (AlM, where M = Ni, Co, Ce) were synthesized via co-precipitation and systematically investigated to elucidate the relationship between physicochemical properties and catalytic performance in ammonia decomposition. Comprehensive characterization by X-ray diffraction (XRD), N₂ physisorption (BET), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDX), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and pyridine-adsorbed Fourier transform infrared spectroscopy (FTIR-Py) revealed significant variations in surface area, morphology, dispersion, and acidity as a function of the incorporated metal. Among the investigated catalysts, the AlNi system exhibited superior activity, achieving the highest ammonia conversion over the studied temperature range. This enhanced performance is attributed to its high specific surface area, homogeneous mesoporous structure, and a balanced distribution of Lewis/Brønsted acid sites, which promote effective ammonia adsorption, activation and decomposition. Kinetic analysis further confirmed the favorable reaction pathway on AlNi, as evidenced by its lower apparent activation energy and higher pre-exponential factor compared to the other materials. The results demonstrate a clear correlation between surface acidity, textural properties, and catalytic performance, highlighting the pivotal role of AlM interactions in governing ammonia decomposition. These findings provide valuable insights for the rational design of efficient catalysts for hydrogen production from ammonia. Full article

Boron (B) is increasingly recognized as more than a trace dietary element, emerging as a context-dependent organizer of molecular interactions at the host–microbiome interface. B exhibits reversible covalent chemistry driven by Lewis’ acidity and selective affinity for cis-diol-rich biomolecules, enabling dynamic complexation with polyols, glycans, and phenolic ligands that dominate the intestinal mucus environment and shape microbial ecology. We synthesize evidence supporting an architecture-based framework in which B modulates biological function by conditioning the physicochemical context of microbial communication rather than acting as a single-pathway effector. Central to this model is spatial bioavailability, distinguishing plasma-accessible boron from microbiota-accessible boron (MAB), species that persist in the lumen and mucus layer long enough to influence interface-level processes. We propose that insufficient or altered MAB availability may contribute to dysbiosis (DYS) by destabilizing quorum-associated coordination, signal persistence, and mucosal microstructure, thereby promoting barrier dysfunction and inflammaging. Particular attention is given to B-mediated symbiotaxis, a hypothesis-driven concept describing how B-containing molecular assemblies may bias microbial communities toward cooperative, barrier-supportive configurations and reduce ecological volatility. We identify key knowledge gaps and experimental priorities (speciation-aware measurements, signal-centric readouts) necessary to determine when, where, and how B-mediated molecular architecture may counteract DYS and support healthspan. Full article