Search Results (101)

Polystyrene (PS) thermal degradation involves localized molecular bond-cleavage events that are not directly equivalent to the apparent kinetic parameters obtained from bulk thermal analysis. In this study, a finite hydrogen-terminated PS oligomeric model was examined using density functional theory at the M06-2X/LANL2DZ level, whereas the non-isothermal degradation behavior of a PS sample was independently evaluated by thermogravimetric analysis under nitrogen. The computational analysis considered frontier molecular orbital distributions and site-specific thermodynamic descriptors associated with homolytic C–C cleavage and radical-mediated β-scission reactions. The calculated HOMO–LUMO gap of 742.62 kJ mol⁻¹ indicated a comparatively large orbital-energy separation within the selected oligomeric model, while the localization of the frontier orbitals over aromatic and benzylic regions revealed a spatially heterogeneous electronic distribution. Homolytic C–C cleavage exhibited bond dissociation energies ranging from 414.09 to 481.24 kJ mol⁻¹, demonstrating that the thermodynamic requirement for radical generation depends on the local molecular environment of the evaluated structure. The Gibbs free-energy changes calculated for the selected radical β-scission reactions ranged from 55.44 to 189.41 kJ mol⁻¹. These quantities represent model-dependent reaction thermodynamics and should not be interpreted as activation barriers because transition states were not calculated. Thermogravimetric analysis showed systematic increases in Tonset and Tmax with increasing heating rate, consistent with kinetic delay and thermal-lag effects under non-isothermal conditions. The Kissinger method yielded a global apparent activation energy of 186.61 kJ mol⁻¹, whereas the residual-mass-corrected Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods produced average apparent activation energies of 180.81 and 178.49 kJ mol⁻¹, respectively, over α = 0.05–0.95. Across the same conversion interval, the FWO apparent activation energy increased from 143.10 to 221.71 kJ mol⁻¹, while the KAS values increased from 140.10 to 220.23 kJ mol⁻¹, indicating an evolving macroscopic degradation response with greater uncertainty toward high conversion. The computational and experimental datasets were therefore interpreted as complementary but non-equivalent scale-dependent descriptions: DFT compares the relative thermodynamics of selected molecular reactions within a finite isolated oligomer, whereas TGA characterizes the global apparent kinetic behavior of the condensed polymer sample. No direct numerical correspondence was established between the molecular reaction energies and the TGA-derived apparent activation energies, and no individual cleavage reaction was assigned to a specific conversion interval. Extrapolation of these results to high-molecular-weight, polydisperse, additive-containing, cross-linked, or environmentally aged PS microplastics should therefore be made with caution. Full article

Poly(ethylene terephthalate) (PET) waste management faces challenges as mechanical recycling limitations become apparent under strict EU regulations. This review critically evaluates PET glycolysis as a vital chemical recycling method, focusing on overcoming barriers to industrial implementation. While systematizing knowledge on reaction mechanisms and parameters, a significant research gap is identified: the necessity for utilizing a high initial mass fraction of waste PET in the reaction feed. Specifically, exceeding a critical concentration of PET-derived oligomers in the resulting glycolysis reaction mixture (typically when the initial waste PET input is above 40% by mass) inevitably triggers phase instability and secondary crystallization during storage. This instability at high concentrations is fundamentally driven by the altered oligomer molecular-weight distribution and the thermodynamic supersaturation of rigid aromatic segments upon cooling. Traditional laboratory approaches using a high excess of glycolyzing agent fail to meet industrial stability demands for subsequent polyester polyol synthesis. Currently, preventing crystallization relies on costly branched glycols or modifiers to disrupt molecular symmetry. This article highlights the urgent need for alternative, additive-free methods to achieve phase stability, such as the elimination of released ethylene glycol from the reaction environment. By addressing shortcomings in glycolysate shelf-life studies, this review charts innovative directions for developing technologies that convert high concentrations of waste PET into phase-stable glycolysates. Full article

Thermochemical depolymerization of polymer mixtures and composite materials is challenging due to non-additive degradation behavior and the emergence of new reaction pathways during pyrolysis. Both polytetrafluoroethylene (PTFE) and silicone rubber (SR) can depolymerize into monomers or low-molecular-weight oligomers when pyrolyzed individually, making them, in principle, suitable candidates for depolymerization-based recycling. Because they are frequently combined in technical applications and composites, their behavior during co-pyrolysis warrants investigation. However, the pyrolysis of PTFE:SR mixtures and composites remains poorly understood. In this study, we examine the pyrolysis behavior of PTFE:SR systems with emphasis on mass balance, product composition, and the formation of new species to address potential limitations for depolymerization-based recycling. Experiments were conducted on virgin PTFE and SR, defined polymer mixtures, and commercially relevant composites, including PTFE-lined silicone tubing and PTFE:SR septa. The results reveal a pronounced, non-linear dependence of product distribution on PTFE content. Product identification by GC-MS, NMR, and FTIR indicates cleavage of Si–O and Si–CH₃ bonds and the formation of fluorinated siloxanes as well as new per- and polyfluoroalkyl substances (PFAS). At low PTFE contents, liquid products are dominated by cyclic siloxanes (D_x). These findings show that depolymerization strategies developed for pure polymers cannot be directly applied to PTFE:SR composites. While systems with low PTFE content may be more amenable to depolymerization, higher PTFE fractions promote the formation of PFAS and difficult-to-valorize fluorinated silicon species. These products complicate selective monomer recovery and could pose significant challenges for the depolymerization-based recycling of PTFE-rich composites. Full article

Detection of nanoplastics in drinking-water systems is only the first analytical step toward exposure interpretation; the next challenge is source attribution. This review examines molecular fingerprinting and transformation pathways that can link nanoscale polymer signals to source waters, drinking-water treatment, distribution infrastructure, packaging materials, laboratory background, or aging processes across the potable-water chain. Nanoplastics are treated here as operationally defined particles below 1 µm, including intentionally manufactured primary nanoplastics and secondary nanoplastics generated by fragmentation, abrasion, weathering, treatment, storage, or packaging stress. The synthesis evaluates how polymer identity, particle morphology, surface oxidation, additive and oligomer profiles, thermal degradation markers, matrix context, and quality assurance/quality control (QA/QC) can be combined into defensible source assignments. Analytical platforms considered include surface-enhanced Raman spectroscopy (SERS), atomic force microscopy–infrared spectroscopy (AFM-IR), optical photothermal infrared spectroscopy (O-PTIR), stimulated Raman scattering microscopy (SRS), pyrolysis–gas chromatography–mass spectrometry (Py-GC/MS), asymmetric flow field-flow fractionation coupled to Py-GC/MS (AF4-Py-GC/MS), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), and chemometric workflows. The central conclusion is that source attribution cannot be inferred from polymer identity alone; robust interpretation requires convergent evidence from particle-level chemistry, polymer-specific mass, additive or marker-ion signatures, aging state, blanks, recovery, and contextual sampling design. Full article

The origin of life is commonly framed within the RNA World hypothesis, yet increasing evidence suggests that early evolution may have involved a broader diversity of hereditary systems than those preserved in modern biology. Alternative informational polymers, compositional inheritance, autocatalytic networks, and compartmentalized molecular communities have all been proposed as mechanisms that may have preceded modern genome-based heredity. Building upon these concepts, we propose that the fundamental unit of early evolution may have been neither the gene nor the organism, but persistent molecular networks capable of maintaining organizational continuity through time. We define Stable Molecular Networks (SMNs) as interacting systems of informational polymers, catalytic oligomers, metabolites, compartments, and environmental feedback processes that maintain continuity despite continual molecular turnover. We further propose that compartmentalized SMNs could form molecular ecosystems termed Precellular Polymer Consortia (PPCs), in which heredity emerges from network organization rather than genome replication alone. Within PPCs, selective interactions, molecular memory, ecological feedback, and distributed information exchange may generate lineage-like evolutionary processes that we term precellular speciation. To connect these concepts to extant biology, we examine archaeal and bacterial systems that preserve organizational principles potentially relevant to early evolution, including CRISPR-Cas adaptive memory systems, ancient RNA-based molecular machines such as the ribosome and RNase P, hydrothermal vent archaea, chemolithotrophic microorganisms, syntrophic consortia, and complex microbial communities. Although these systems are not direct descendants of precellular networks, they provide experimentally accessible examples of molecular memory, distributed information processing, protometabolism, ecological cooperation, and system-level organization. Finally, we propose PLURIBUS (Planetary Liquid Universal Polymer Identification By Ultrasensitive Sequencing) as a framework for discovering noncanonical informational polymers, novel RNA modifications, and alternative hereditary systems within Earth’s microbial biosphere, particularly among poorly characterized archaeal and extremophile communities. Knowledge gained from these environments may ultimately support the development of more general life-detection strategies for planetary exploration. Together, these perspectives suggest that extant microbial ecosystems provide valuable experimental windows into evolutionary processes that may have preceded modern cells, genomes, and the Last Universal Common Ancestor (LUCA). Full article

Pulmonaria rubra (Boraginaceae) is a widely distributed plant in Bulgaria, yet its phytochemical profile and therapeutic potential have remained unexplored. P. rubra methanol extract (PRE) was evaluated through phytochemical profiling and in vitro neuroprotective and antioxidant assays. Rat brain synaptosomes, mitochondria and microsomes were treated with PRE alone, and in combination with 6-hydroxydopamine and tert-butyl hydroperoxide as toxic agents. The extract exhibited concentration-dependent protective effects in all subcellular models. Additionally, it was tested on hMAOA/B and different isoforms of CYP450 enzymes, but it did not show any activity in the tested conditions. In the UHPLC-HRESIMS analysis, 26 secondary metabolites were identified, mainly hydroxycinnamic acids and caffeoyl oligomers, flavonoids, a lignan (globoidnan A), and the terpenoid glycoside roseoside. Seven compounds were identified via UHPLC-UV method using reference compounds: rosmarinic acid, rutin, quercetin-3-O-glucoside, astragalin, apigenin-7-O-glucoside, apigenin-7-O-glucuronide and alcesefoliside, with the latter two being reported for the first time in genus Pulmonaria. The quantity of rosmarinic acid in PRE was 4.35%, distinguishing the compound as the main bioactive molecule in the species. Characterized by its high content of rosmarinic acid, P. rubra represents a highly viable candidate for subsequent development into standardized phytopharmaceuticals targeting oxidative stress-related neurodegenerative diseases. Full article

Mg–La mixed metal oxides derived from layered double hydroxide (LDH) precursors were synthesized via coprecipitation and evaluated as heterogeneous catalysts for solventless glycerol etherification to short-chain polyglycerols. The influence of Mg/La molar ratio on the structural, textural, and catalytic properties of the catalysts was systematically investigated using XRD, BET, SEM-EDX, FTIR, TPD-CO₂, TPD-NH₃ and ICP-OES analyses. XRD confirmed the formation of La₂O₂CO₃ phases, while CO₂-TPD analysis revealed the presence of abundant medium-to-strong basic sites. Among the synthesized catalysts, Mg_0.25La_0.75O₂ exhibited the highest basic site concentration (6830 µmol g⁻¹) and superior catalytic performance due to the possible cooperative interaction between Mg- and La-derived sites. Under optimum reaction conditions of 220 °C, 8 h, and 2 wt% catalyst loading, the catalyst achieved 90% glycerol conversion with 70% diglycerol selectivity, 23% triglycerol selectivity, and 84% combined diglycerol and triglycerol yield. Reaction temperature, catalyst loading, and reaction duration significantly influenced oligomer distribution and catalyst performance. Reusability studies demonstrated acceptable catalyst stability for up to four cycles before gradual deactivation caused by oligomer deposition and metal leaching. The results highlight Mg–La mixed oxides as promising catalysts for sustainable solvent-free glycerol valorization, while demonstrating a scalable and environmentally benign strategy for maximizing lower-degree polyglycerol production within shorter reaction durations and reduced processing cost. Full article

RNA-based therapeutics are reshaping the treatment landscape for skeletal muscle disorders by enabling modulation of RNA processing or direct correction of disease-causing alleles. In Duchenne muscular dystrophy (DMD), four antisense oligonucleotides—eteplirsen, golodirsen, viltolarsen, and casimersen—have received FDA approval; these phosphorodiamidate morpholino oligomers (PMOs) induce exon skipping to restore the reading frame and enable expression of internally truncated dystrophin. Beyond splice switching, RNA therapeutics include RNase H-active gapmers and steric-blocking antisense oligonucleotides (ASOs), small interfering RNAs (siRNAs) that mediate post-transcriptional gene silencing, and RNA-guided gene-modifying technologies such as CRISPR systems that can reframe or repair endogenous alleles. Despite major progress in DMD, broader clinical impact remains constrained by inefficient delivery to skeletal and especially cardiac muscle, the need for repeat administration for most modalities, and safety considerations that limit dose escalation and durability. Next-generation approaches aim to overcome these barriers through peptide- or antibody-conjugated oligonucleotides that enhance cellular uptake and tissue distribution, alternative chemistries with improved stability and potency, and viral or non-viral platforms for durable splice modulation. In parallel, CRISPR-based strategies—including base and prime editing—offer the prospect of one-time correction, while raising important questions regarding delivery, immunogenicity, editing specificity, and long-term safety. This review synthesizes recent advances in antisense and gene-modifying strategies for skeletal muscle and highlights practical priorities for translation, including improved muscle/heart delivery, controllable safety mechanisms, scalable manufacturing, and standardized biomarker-to-clinical outcome relationships. Full article

The enzymatic saccharification of cellulose remains a key step in biomass conversion processes, often influenced by enzyme stability, distribution, and accessibility at solid–liquid interfaces. Immobilization of cellulolytic enzymes on nanostructured supports has been proposed as a strategy to modulate catalytic behavior; however, the relationship between enzyme loading and catalytic response remains insufficiently understood. In this study, CuO-based nanobiocatalysts were prepared through controlled cellulase immobilization and systematically evaluated under defined experimental conditions. Structural and physicochemical characterization was performed using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and integrated thermal analysis (TGA–DTG–DSC), enabling a comparative assessment of the analyzed systems. SEM analysis showed that the average particle diameter increased from 39.5 ± 14.8 nm (CuO nanoparticles) to 95.6 ± 21.8 nm (NPI10), 106.6 ± 27.7 nm (NPI15), and 113.5 ± 23.1 nm (NPI20), indicating progressive variations in particle organization with increasing enzyme loading. Catalytic performance was evaluated through enzymatic hydrolysis of cellulose filter paper as a model substrate, with products quantified by HPLC at a representative reaction time. The system prepared at lower enzyme loading (NPI10) exhibited product formation comparable to that of the free enzyme, with apparent average glucose formation values of 1.054 and 1.047 mg·mL⁻¹·h⁻¹, respectively. In contrast, higher immobilization levels were associated with reduced catalytic output. Across all systems, glucose was the predominant product, with negligible accumulation of intermediate oligomers under the evaluated conditions. These results indicate that increasing enzyme loading does not correspond to proportional increases in product formation and highlight the influence of enzyme distribution and accessibility within the system. The combined structural and catalytic observations provide a controlled framework for evaluating how immobilization conditions influence system behavior in nanobiocatalytic systems. Full article

Alkali-activated cementitious materials are environmentally friendly alternatives to traditional cement. The structure of their core product, sodium aluminosilicate hydrate (N-A-S-H) gel, is regulated by the silicon-to-aluminum (Si/Al) ratio; however, the atomic-scale mechanism underlying this influence remains unclear. Integrating reactive force field molecular dynamics simulations and experiments, this study systematically reveals the regulation mechanism of the Si/Al ratio (1.0–2.0) on the microstructure and macroscopic properties of N-A-S-H gels. Starting from well-defined PS and PSS oligomers, the simulation results demonstrate that the Si/Al ratio governs the polymerization pathway, aluminum coordination environment (especially the content of pentacoordinate aluminum), and evolution of nanoporosity. When the Si/Al ratio is approximately 1.8, the system exhibits the highest silicate polymerization degree, lowest nanoporosity, and densest three-dimensional (3D) network structure; deviation from this ratio leads to structural degradation due to charge imbalance or excessive polymerization. These computational findings are validated by experiments on fly ash-based geopolymers: the material achieves the highest compressive strength at a Si/Al ratio of 1.8. The consistency between simulations and experiments collectively reveals a cross-scale action mechanism: the Si/Al ratio determines the macroscopic mechanical properties by regulating the nanoscale packing density and defect distribution of the gel. This study provides critical atomic-scale insights for the rational design of high-performance geopolymers. Full article

Effective metabolic waste clearance and maintaining ionic homeostasis are essential for the health and normal function of the central nervous system (CNS). To understand its mechanism and the role of fluid flow, we develop a multidomain electro-osmotic model of optic-nerve microcirculation (as a part of the CNS) that couples hydrostatic and osmotic fluid transport with electro-diffusive solute movement across axons, glia, the extracellular space (ECS), and arterial/venous/capillary perivascular spaces (PVS). Cerebrospinal fluid enters the optic nerve via the arterial parivascular space (PVS-A) and passes both the glial and ECS before exiting through the venous parivascular space (PVS-V). Exchanges across astrocytic endfeet are essential and they occur in two distinct and coupled paths: through AQP4 on glial membranes and gaps between glial endfeet, thus establishing a mechanistic substrate for two modes of glymphatic transport, at rest and during stimulus-evoked perturbations. Parameter sweeps show that lowering AQP4-mediated fluid permeability or PVS permeability elevates pressure, suppresses radial exchange (due mainly to hydrostatic pressure difference at the lateral surface and the center of the optic nerve), and slows clearance, effects most pronounced for solutes reliant on PVS–V export. The model reproduces baseline and stimulus-evoked flow and demonstrates that PVS-mediated export is the primary clearance route for both small and moderate solutes. Small molecules (e.g., A$\beta$) clear faster because rapid ECS diffusion broadens their distribution and enhances ECS–PVS exchange, whereas moderate species (e.g., tau monomers/oligomers) have low ECS diffusivity, depend on trans-endfoot transfer, and clear more slowly via PVS–V convection. Our framework can also be used to explain the sleep–wake effect mechanistically: enlarging ECS volume (as occurs in sleep) or permeability increases trans-interface flux and accelerates waste removal. Together, these results provide a unified physical picture of glymphatic transport in the optic nerve, yield testable predictions for how AQP4 function, PVS patency, and sleep modulate size-dependent clearance, and offer guidance for targeting impaired waste removal in neurological disease. Full article

Heterogeneous catalysts comprising immobilized nickel(II) complexes bearing a fluorine- or trifluoromethyl-substituted iminopyridine ligand (X_n-C₆H_5–n-N=C (CH₃)-C₅H₅N, X = F or CF₃) in fluorotetrasilicic mica interlayers were prepared by reacting Ni²⁺-exchange fluorotetrasilicic mica with the appropriate ligand. Upon activating the precatalyst with triethylaluminum or triisobutylaluminum, the generated active species showed catalytic activity for ethylene oligomerization, yielding low-molecular-weight polyethylene (PE), ethylene oligomers, and wax-like PE. The oligomer distribution almost agreed with what we expected according to the Schultz–Flory distribution. However, the amount of solid products was much higher than the theoretical value, indicating that at least two active species were formed, i.e., the oligomer and low-molecular-weight PE. The precatalyst with a 2,4-F₂C₆H₃ group on the imino nitrogen atom activated by triethylaluminum showed the highest catalytic activity for ethylene oligomerization (408 g-C₂ g-cat⁻¹ h⁻¹), with selectivities to the liquid and solid products of 51.0% and 11.5%, respectively, with the rest of the product corresponding to wax-like PE. Meanwhile, the highest selectivity to the liquid product (66.7% at 233 g-C₂ g-cat⁻¹ h⁻¹) was obtained using the precatalyst with a 2-FPh group on the imino nitrogen atom activated by triisobutylaluminum. Full article

Cellular organisms store heritable information in two forms, genetic and epigenetic, the latter being largely dependent on cytosine methylation (5mC). Chargaff’s Second Parity Rule (CSPR) describes the nucleotide composition of cellular genomes in terms of intra-strand DNA symmetry. However, it remains unknown whether DNA methylation patterns display intra-strand DNA symmetry. Computational analysis was conducted of the DNA methylation patterns observed in human cell lines and in tissue samples from healthy donors. Analysis of 5mC marks in mutually reverse-complementary pairs of short oligomers, containing CpG dinucleotide in the middle, revealed deviations from CSPR and methylation asymmetry that can be observed for two non-overlapping mirror groups defined by CpG methylation values. Deviations from CSPR, together with combinatorial probabilities of pattern distributions and computer simulations, highlight the non-random nature of methylation processes and enabled us to identify specific cell types as outliers. Further analysis revealed a compensatory methylation asymmetry that reduces deviations from intra-strand symmetry and implies the existence of strand-specific methylation during cell differentiation. Among six pairs of reverse-complementary tetranucleotides, four pairs with specific sequence motifs display pronounced methylation asymmetry. This mirror asymmetry may be associated with chromosome folding and the formation of a complex three-dimensional landscape. Full article

Furfural is a fascinating bio-based platform molecule that can be converted into useful cyclic compounds, among others. In this work, the hydrogenative rearrangement-dehydration of furfural towards cyclopentanone using a commercially available Pt/C catalyst was investigated in terms of its reaction performance to assess its feasibility as an industrial process. However, acquiring an acceptable cyclopentanone yield proved very difficult, and the reaction was constrained by unforeseen parameters, such as the relative liquid volume in the reactor and the substrate concentration. Most strikingly, the sacrificial formation of furanoic oligomers that precipitated onto the catalyst’s surface was a troublesome key factor that mediated the product’s selectivity versus the carbon mass balance. By applying a biphasic water–toluene solvent system, the yield of cyclopentanone was somewhat improved to a middling 59%, while tentatively positive distributions of reaction components over these solvent phases were observed, which could be advantageous for anticipated down-stream processing. Overall, the sheer difficulty of controlling this one-pot cascade transformation towards a satisfactory product output under rather unfavorable reaction parameters renders it unsuitable for industrial process development, and a multi-step procedure for this chemical transformation might be considered instead. Full article

Recent advances in designing multinuclear late transition metal catalysts for the oligo-/polymerization of olefins emphasize the great interest and promising approaches in the preparation and application of these catalytic systems. Accordingly, in this study, two dinuclear macrocyclic bis(iminopyridine) Fe- and Co-based complexes (FC and CC) were prepared at moderate yields through a one-pot template reaction. Upon activation by MMAO, not only did the catalysts show reasonable activities for the oligomerization of ethylene but also showed high selectivity for the production of tetramers (α-C₈). With respect to the catalyst structure, FC demonstrated higher catalyst activity (9.45 g mol⁻¹ Fe h⁻¹ × 10⁵ vs. 8.75 × 10⁵ g mol⁻¹ Co h⁻¹) along with higher selectivity for α-C₈ production compared to CC (96.6 vs. 96.1%). Both catalysts had thermal stability up to 70 °C, with FC being much more active and stable than CC under identical conditions. On the other hand, polymerization parameters had an influence on the catalyst performance and oligomer distribution. Moreover, molecular calculations were employed for geometry optimization and structural determination, which was consistent with the experimental results. Full article