Chemical Structure Research Articles

Oxidative Stress Mechanism by Gold Compounds: A Close Look at Total ROS Increase and the Inhibition of Antioxidant Enzymes.

The antitumor activity of various gold compounds is a promising field of investigation, attracting researchers seeking potential clinical candidates. To advance this research, they explore the complex mechanisms of action of these compounds. Since the discovery of the strong inhibition of thioredoxin reductase by auranofin, the primary mechanism explored has been the inhibition of this enzyme. This inhibition disrupts the redox balance in cells, promoting oxidative stress and triggering cell death. In this review, we analyzed studies from the past decade that measured cellular ROS increase and examined the coordination structures of gold compounds. We also correlate ROS increase with the inhibition of redox-regulating enzymes, thioredoxin reductase, and glutathione reductase, to elucidate the relationship between these cellular effects and chemical structures. Our data compilation reveals that different structures exhibit varying efficacy: some significantly increase ROS production and inhibit thioredoxin reductase or glutathione reductase, while others elevate ROS levels without affecting these target enzymes, suggesting alternative mechanisms of action. This review consolidates critical evidence, enhancing our understanding of the mechanisms by which these gold complexes act and providing valuable insights for developing new therapeutic strategies against tumor cells.

Improving the Cellular Internalization of Zr(IV) Nanocages by Tuning Hydrophilicity and Lipophilicity

AbstractNanoscale molecular materials have emerged as a new class of compounds at the nanometer scale with well‐defined chemical structures, remarkable uniformity and high reproducibility. Among these materials, zirconium‐based metal‐organic cages (MOCs) have attracted significant attention due to their exceptional stability and applications in catalysis, recognition and separation and so on. However, their poor water solubility impedes their biomedical applications. In this study, decorating the ligand with Ru(II) complexes can not only improve the water solubility but also endow bright red fluorescence with large Stokes shift (180 nm). Notably, butyl‐modification of the cyclopentadiene rings can significantly enhance the cell uptake (100 folds) of nanocages via actin‐ and dynamin‐mediated endocytosis. The unique advantages and easy modifiability of these nanocages make them highly promising candidates for diverse biological applications.

Impact of molecular configuration on the photoluminescence and electrical characteristics of poly-pyrrol-thiazol-imine polymers films.

The optical, photoluminescence, and electrical properties of Poly(Z)-PTI and Poly(E)-PTI, two Poly-Pyrrol-Thiazol-Imine polymers with comparable chemical structures but distinct configurations, were examined. Using the dip-casting method, polymer films were deposited on ITO substrates. UV-VIS spectroscopy revealed that both polymers diverged between 500 and 800nm, showing the impact of molecular arrangement, but showed similar absorption behavior for wavelengths shorter than 500nm. For Poly(Z)-PTI, the direct optical energy gaps were 2.06eV, while for Poly(E)-PTI, they were 1.78eV. Poly(Z)-PTI displayed an emission peak at 610nm (red) according to laser photoluminescence spectra, while Poly(E)-PTI peaked at 563nm (green-yellow). The capacitance behavior was revealed by electrochemical impedance spectroscopy. Nyquist plots suggested an equivalent circuit model of Rs (CRct)(QR)(CR) for both polymers, and the relaxation times were 15.9 ns for Poly(Z)-PTI and 89.5 ns for Poly(E)-PTI. The Mott-Schottky analysis verified the n-type conductivity, revealing 2.18 × 1016 cm- 3 carrier densities for Poly(Z)-PTI and 1.78 × 1016 cm- 3 for Poly(E)-PTI. At lower frequencies, both polymers exhibited limited conductivity and large dielectric constants. Insights into the possible uses of Poly-Pyrrol-Thiazol-Imine polymers in electrical and optoelectronic devices are provided by this study, which emphasizes the influence of molecular configuration on these polymers' characteristics.

The regulatory effects of bioactive polysaccharides on intestinal function and bile acids: chemical structures, bioactivities, and mechanisms

Polysaccharides are one of the important components of the human diet, offering a wide range of biological activities, especially in improving inflammation in the digestive system and addressing metabolic diseases. Among all the reported bioactivities of polysaccharides, their regulation effects on intestinal function and bile acids (BAs) are gradually attracting the attention of more researchers. Bile acids, the main components of intestinal lipid digestive fluid, are also key signal factors for metabolic homeostasis and impact overall health. Polysaccharides usually interact directly or indirectly with the gut and gut microbiota to participate in the regulation process of reabsorption, metabolism, and excretion of bile acids in humans, thereby exerting their role in the intervention of human diseases. In this review, we comprehensively reviewed the effects of bioactive polysaccharides on the regulation of intestinal function and bile acids. The chemical structures, bioactivities, and potential mechanisms for their activities were also reviewed. This study aimed to provide a comprehensive reference for future research on the activities and mechanisms of polysaccharides, as well as to offer important strategies and insights for the development of bioactive polysaccharides to prevent inflammatory and metabolic diseases.

A Bio-Based Polybenzoxazine Derived from Diphenolic Acid with Intrinsic Flame Retardancy, High Glass Transition Temperature and Dielectric Properties.

A bio-based benzoxazine monomer, diphenolic methyl ester hexafluoro diamino benzoxazine (DPME-HFBz), was successfully synthesized from diphenolic acid (DPA), and the chemical structure was successfully verified. The curing kinetics were studied via non-isothermal differential scanning calorimetry (DSC). The activation energies of DPME-HFBz were calculated by Kissinger and Ozawa methods to be 136.15 and 139.92 kJ/mol, respectively, and the reaction order was calculated to be first order. Owing to the large number of hydrogen bonds after polymerization, poly(DPME-HFBz) presented an ultra-high glass transition temperature of 312 °C and a high initial decomposition temperature (350 °C under air and 345 °C under nitrogen). Because of the excellent charring ability (50.2% residue under nitrogen), the LOI value of poly(DPME-HFBz) was as high as 38%. Poly(DPME-HFBz) also exhibited a very low heat release capacity (HRC) of 90 J/(g·K). In addition, poly(DPME-HFBz) had a dielectric constant (Dk) of 1.88 at 1.5 MHz, which was much lower than the Dk of the reported low-dielectric polymers. This work provides an efficient and sustainable strategy for the synthesis of benzoxazine thermosetting materials with excellent comprehensive properties.

Consumption of Plant-Derived Phenolic Acids Modulates Hunger and Satiety Responses Due to Chemical Interactions with Enteroendocrine Mediators

Energy-dense foods are commonly rich in fat and simple sugars and poor in dietary fiber and micronutrients; regularly consuming them decreases the concentration and/or effect of anorexigenic hormones and may increase that of orexigenic ones, thereby decreasing satiety. In contrast, plant-derived phenolic-rich foods exert positive effects on satiety. In silico, in vitro, and in vivo investigations on some of most representative phenolic acids like chlorogenic acid (CGA), gallic acid (GA), ferulic acid (FA), and protocatechuic acid (PCA) have shown that they are able to modulate various hunger and satiety processes; however, there are few studies that show how their chemical structure contributes to achieve such effects. The objective of this review is to summarize how these phenolic acids can favorably modulate hormones and other satiety mediators, with emphasis on the chemical interactions exerted between the core of these compounds and their biological targets. The evidence suggests that they form interactions with certain hormones, their receptors, and/or enzymes involved in regulating hunger and satiety, which are attributed to their chemical structure (such as the position of hydroxyl groups). Further research is needed to continue understanding these molecular mechanisms of action and to utilize the knowledge in the development of health-promoting foods.

Wybrane aspekty przeciwwirusowej aktywności flawonoidów względem SARS-CoV-2

Coronaviruses cause diseases of the respiratory tract, gastrointestinal tract and central nervous system, which threaten human health and contribute to economic losses. Innovative production technologies make it possible to use bioactive compounds as antiviral agents. Most fruits, vegetables and plant products contain flavonoids. Numerous studies have demonstrated the health-promoting effect of this group of compounds resulting from their antioxidant potential. The activity of an antioxidant in the body is the result of many factors that modulate the reactivity and physicochemical properties, among which the chemical structure is the most important. Bioinformatics tools using molecular modeling often precede research using in vitro and in vivo methods. The aim of this review is to present the mechanism of antiviral action of flavonoids against SARS-CoV-2, responsible for COVID-19. Studies using virtual molecular docking models were collected to test the affinity of flavonoids for key proteins of the SARS-CoV-2 virus replication cycle. Among the flavonoids with antiviral activity, the most active were apigenin, luteolin, isorhamnetin, kaempferol, myricetin, quercetin, hesperetin, naringenin and genistein. Food products with a high content of these compounds are indicated.

Comprehensive Overview of the Amide Linker Modification in the Succinate Dehydrogenase Inhibitors.

Succinate dehydrogenase inhibitors (SDHIs) have become one of the most important classes of agrochemical fungicides. According to the data from FRAC, the resistance risk for SDHIs had reached up to medium and even to high. In general, the chemical structure of SDHIs mainly contained three fragments: an acid core, a hydrophobic tail, and an amide linker, corresponding to three modification directions for each fragment. Among them, amide linker modification (ALM) has become a research hotspot for the design of novel SDHIs fungicides in recent years. We presented here a detailed review on the ALM strategy in the past decade, and some of them had entered the market. According to their chemical structures, ALM strategy were classified into four parts: (1) linked aliphatic chain between amide bond and hydrophobic tail, (2) introducing substituents to replacing hydrogen atom in the amide bond, (3) reverse extending the amide linker, and (4) changed with other bioisosteres. Moreover, the structure-activity relationship and the interaction mechanism of ALM-SDHI with SDH were discussed. This review aims to provide a global perspective on research and development of novel SDHIs, as well as suggestions for food safety management.

The Underrepresented Quinolinone Alkaloids in Genera Penicillium and Aspergillus: Structure, Biology, and Biosynthetic Machinery.

Quinolone alkaloids are N-heterocycles with extensive structural diversity, mainly derived from in fungi from anthranilic acid and amino acids as precursors with a wide range of biological activities as antifungal, antimicrobial, anti-inflammatory, and insecticidal activities. The quinolone basic skeleton comprised of either 2-quinolones or 4-quinolones generated more than one hundred compounds. Several reviews discussed quinolones; particularly, the fluoroquinolones, yet few studies tackled natural quinolones. Many of these quinolones were not assayed for their antimicrobial potential despite their unique stereospecificity, which can supersede synthetic quinolones if their discovery is coupled with OMICS techniques, biochemical and molecular strategies as heterologous expression to maximize their yield. Herein, we conducted a comprehensive review of the quinolone's family in Aspergillus and Penicillium species, the exclusive producers of quinolones whether they are soil, endophytic or marine derived highlighting their isolation, chemical structures, pharmacological effects, structure activity relationships if any, and biosynthetic machinery. We believe that our initiative will pave the way for further development of natural quinolones as future antimicrobial agents.

Nanodomains and Their Temperature Dependence in a Phosphonium-Based Ionic Liquid: A Single-Molecule Tracking Study.

Ionic liquids (ILs) exhibit a unique nanoscale structure (i.e., nanodomains) characterized by their organization into distinct domains. We present evidence of nanodomains in trihexyl(tetradecyl)phosphonium chloride, [P66614][Cl], using single-molecule tracking (SMT) and the maximum entropy method (MEM) to analyze single-molecule trajectories. The diffusion properties of ATTO 647N were assessed as the temperature of [P66614][Cl] increased from 20 °C (4020 cP), 35 °C (1239 cP), 45 °C (599 cP) to 50 °C (439 cP). The MEM analysis revealed a distinct two-population distribution of diffusion coefficients representing nanodomains in [P66614][Cl] at 20 °C (4020 cP). The slow population accounts for 16%, with a diffusion coefficient of 0.104 μm2/s, while the fast population constitutes 84% with a diffusion coefficient of 0.634 μm2/s. Two diffusing populations were also measured for the chemically different probes ATTO 647N, DiD, and Nile Blue chloride in [P66614][Cl] at 20 °C. In contrast, only a single fast population was measured in [P66614][Cl] at 50 °C. At a similar viscosity (640 cP) but a lower temperature of 20 °C, trihexyl(tetradecyl)phosphonium bis[(trifluoromethyl)-sulfonyl]imide, [P66614][NTf2], also showed only a single diffusing population. The elimination of the slow population and the presence of a single diffusing population in [P66614][Cl] as the temperature increases and the viscosity decreases is consistent with liquid-liquid phase separation (LLPS) as a mechanism of nanodomain formation. In addition, the measurement of two diffusing populations for three fluorophores with different chemical structures is also consistent with a physical mechanism, and not a chemical mechanism, for nanodomain formation.

Bioactive Three-Dimensional Chitosan-Based Scaffolds Modified with Poly(dopamine)/CBD@Pt/Au/PVP Nanoparticles as Potential NGCs Applicable in Nervous Tissue Regeneration—Preparation and Characterization

Tissue engineering of nervous tissue is a promising direction in the treatment of neurological diseases such as spinal cord injuries or neuropathies. Thanks to technological progress and scientific achievements; the use of cells; artificial scaffolds; and growth factors are becoming increasingly common. Despite challenges such as the complex structure of this tissue, regenerative medicine appears as a promising future approach to improve the quality of life of patients with nervous injuries. Until now; most functional biomaterials used for this purpose were based on decellularized extra cellular matrix (ECM) or nanofibrous materials, whereas current clinically verified ones in most cases do not exhibit bioactivity or the possibility for external stimulation. The aim of this research was to develop a new type of bioactive, chitosan-based 3D materials applicable as nerve guide conduits (NGCs) modified with poly(dopamine), Au/Pt coated with PVP nanoparticles, and cannabidiol. The NGCs were prepared under microwave-assisted conditions and their chemical structure was studied using the FT-IR method. Next, this study will discuss novel biomaterials for morphology and swelling abilities as well as susceptibility to biodegradation in the presence of collagenase and lysozyme. Finally, their potential in the field of nervous tissue engineering has been verified via a cytotoxicity study using the 1321N1 human astrocytoma cell line, which confirmed their biocompatibility in direct contact studies.

Design, synthesis and biological studies of new isoxazole compounds as potent Hsp90 inhibitors.

Heat shock protein 90 (Hsp90), a molecular chaperone, contributes to the preservation of folding, structure, stability, and function proteins. In this study, novel compounds comprising isoxazole structure were designed, synthesized and their potential ability as Hsp90 inhibitors was validated through docking studies. The active site-based compounds were prepared through a multi-step synthesis process and their chemical structures were characterized employing FT-IR, NMR, and mass spectrometry analysis. Cytotoxic and Hsp90 inhibition activities of synthesized compounds were assessed by MTT assay and ELISA kit, respectively. Based on the obtained results, compound 5 exhibited the highest cytotoxicity (IC50; 14 µM) against cancer cells and reduced Hsp90 expression from 5.54 ng/mL in untreated (normal cells) to 1.56 ng/mL in cancer cells. Moreover, molecular dynamics (MD) simulation results indicated its high affinity to target protein and approved its excellent stability which is essential for exerting an inhibitory effect on cancer cell proliferation.

Surface Plasmons in Two-Dimensional MXenes.

MXenes, a class of layered two-dimensional transition metal carbides and nitrides, exhibit excellent optoelectronic properties and show promise for fields ranging from photonics and communications to energy storage and catalysis. Some members of the MXene family are metallic and exhibit large in-plane conductivity, making them possibly suited for 2D plasmonics. The highly variable chemical structure of MXenes offers a broad chemical space to tune material properties for plasmonic applications, including plasmon-enhanced catalysis, surface-enhanced Raman spectroscopy (SERS), and electromagnetic shielding. However, this synthetic complexity has also presented several roadblocks in the process of moving MXene plasmonics into applications. For example, in the prototypical MXene Ti3C2Tx, there remains disagreement over the bulk plasmon energy and the assignment of a prominent resonance around 1.7 eV. We discuss fundamental models and theories of plasmon physics and apply these models to MXenes in order to clarify some of these problems. We outline the potential for hyperbolic plasmons in MXenes and propose new avenues for MXene photonics research.

Capsaicin-Loaded Melanin Nanoparticles for Long-Lasting Nociceptive-Selective Nerve Blockade.

Clinically used amino-ester and amino-amide local anesthetics, such as bupivacaine and lidocaine, face two primary challenges: inadequate duration of action and nonselective action on both sensory and motor neurons, resulting in motor function loss alongside pain relief. In this work, we developed capsaicin-loaded melanin nanoparticles (Cap-MNPs) to address these two challenges. Capsaicin selectively acts on sensory neurons without affecting motor neurons, thereby achieving nociceptive-selective nerve blockade. Melanin is known for its exceptional biocompatibility, biodegradability, and abundance in pigmented human tissue. Melanin's inherent chemical structure and hydrophobic nature enable the encapsulation and sustained release of amino-ester and amino-amide local anesthetics with aromatic rings through π-π interactions and hydrophobic interactions. The drug loading efficiency of Cap-MNPs was 82.99 ± 1.55%, the drug loading capacity was 67.47 ± 4.24%, and capsaicin was continuously released for more than 360 h. In rats, a single injection of Cap-MNPs containing 8.04 mg of capsaicin produced a sciatic sensory nerve block lasting for 6 h without causing any local toxicity and capsaicin-related systemic toxicity. Cap-MNPs show promise as clinically useful therapeutics for pain management.

Synthesis and evaluation of vanillin Schiff bases as potential antimicrobial agents against ESBL-producing bacteria: towards novel interventions in antimicrobial stewardship.

The escalating challenge of antimicrobial resistance necessitates the development of novel antibacterial agents. In this study, a series of five vanillin Schiff bases (SB-1 to SB-5) were synthesized from vanillin and various aromatic amines. The chemical structures of these compounds were characterized using Thin Layer Chromatography (TLC), Fourier Transform Infrared Spectroscopy (FT-IR), proton nuclear magnetic resonance ( -NMR), carbon-13 NMR ( -NMR), and mass spectrometry techniques. Antibacterial efficacy was evaluated against strains of bacteria producing extended-spectrum beta-lactamases (ESBL), including Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae using the disc diffusion method. Cytotoxic effects were assessed through haemocompatibility and brine shrimp lethality assays. The Schiff bases demonstrated notable antibacterial activities, with SB-1, SB-2, SB-4, and SB-5 exhibiting zones of inhibition up to 16.0, 16.5, 16.6, and 15.5 mm against ESBL E. coli, respectively. SB-3 showed a maximum inhibition zone of 15.0 mm against ESBL K. pneumoniae. In cytotoxicity assays, the compounds exhibited IC values against red blood cells (RBCs) greater than 200 μg/mL and ranging from 45.7 to 50.5 μg/mL for the brine shrimp assay. While demonstrating potent antibacterial properties, the toxicity towards human RBCs suggests that further toxicity evaluations and structural modifications are essential for developing safer therapeutic agents based on vanillin Schiff bases.

Effect of pore solution alkalinity on alkali–silica reaction (ASR) in metakaolin‐based geopolymer

AbstractGeopolymer concretes have shown better resistance against alkali–silica reaction (ASR) than ordinary Portland cement concretes, which was attributed to the low pore solution alkalinity of the geopolymer. However, the alkalinity of the geopolymer pore solution depends on the concentration and volume of the activating solutions used and age of the geopolymer. The main objective of this study was to investigate the effects of pore solution alkalinity on the ASR expansion of the metakaolin‐based geopolymer concrete. The chemistry of the pore solution of metakaolin‐based geopolymer was studied, and its reaction with reactive and non‐reactive aggregates was investigated. The concrete prism expansion tests showed no ASR‐induced expansion in geopolymer despite sufficient pore solution alkalinity to attack the reactive aggregates. The SEM and XRD characterizations confirmed that no ASR‐related gel was formed during the reaction between reactive aggregates and extracted pore solution. The chemical structure of the reaction product between aggregates and pore solution was characterized using MAS NMR and revealed no difference in the reaction products with reactive and non‐reactive aggregates. The results suggest that the pore solution alkalinity is not the sole governing parameter for ASR expansion in the geopolymer.

Electron-Deficient Organic Molecules Based on B←N Unit: A N-Type Room-Temperature Chemiresistive Sensors with Moisture Resistance.

Organic molecules with tailorable chemical structures, high stability, and solution processability have great potential in the sensing field. Compared with p-type organic small molecules (OSMs), the electron-dominated n-type analogs show superior conductivity when exposed to reducing gases, which can achieve outstanding sensor signal-to-noise ratios. However, inadequate humidity resistance at room temperature hinders the development of such molecules. Herein, an A-D-π-D-A molecular design strategy is proposed based on electron-deficient B←N units, which results in effective intramolecular charge transport and sensitive responses by extending the π-conjugation bridge. As a result, the ST-2BP with A-D-π-D-A configuration shows a prominent sensitivity of 787 (Ra/Rg) in 20ppm NH3 at room temperature and an almost initial and stable response under different relative humidity conditions, which is the highest among currently reported OSM sensors. Supported by theoretical calculations and in situ FTIR spectra, it is revealed that B←N units, which function as the active centers mediate the specific ammonia adsorption. This study provides a new understanding of the design of high-performance room temperature gas sensing materials by decorating B←N units.

Highly prevalent geriatric medications and their effect on β-amyloid fibril formation.

The unprecedented increase in the older population and ever-increasing incidence of dementia are leading to a "silver tsunami" in upcoming decades. To combat multimorbidity and maintain daily activities, elderly people face a high prevalence of polypharmacy. However, how these medications affect dementia-related pathology, such as Alzheimer's β-amyloid (Aβ) fibrils formation, remains unknown. In the present study, we aimed to analyze the medication profiles of Alzheimer's disease (AD; n = 124), mild cognitive impairment (MCI; n = 114), and non-demented (ND; n = 228) patients to identify highly prevalent drugs and to determine the effects of those drugs on Aβ fibrils formation. Study subjects (≥ 65 years) were recruited from an academic geriatric practice that heavily focuses on memory disorders. The disease state was defined based on the score of multiple cognitive assessments. Individual medications for each subject were listed and categorized into 10 major drug classes. Statistical analysis was performed to determine the frequency of individual and collective drug classes, which are expressed as percentages of the respective cohorts. 10 µM monomeric β-amyloid (Aβ) 42 and fibrillar Aβ (fAβ) were incubated for 6-48h in the presence of 25 µM drugs. fAβ was prepared with a 1:10 ratio of Aβ42 to Aβ40. The amount of Aβ fibrils was monitored using a thioflavin T (Th-T) assay. Neuronal cells (N2A and SHSY-5Y) were treated with 25 µM drugs, and cell death was measured using a lactose dehydrogenase (LDH) assay. We noticed a high prevalence (82-90%) of polypharmacy and diverse medication profiles including anti-inflammatory (65-77%), vitamin and mineral (64-72%), anti-cholesterol (33-41%), anti-hypersensitive (35-39%), proton pump inhibitor (23-34%), anti-thyroid (9-21%), anti-diabetic (5-13%), anti-constipation (9-11%), anti-coagulant (10-13%), and anti-insomnia (9-20%) drugs in the three cohorts. Our LDH assay with 18 highly prevalent drug components showed toxic effects of Norvasc, Tylenol, Colace, and Plavix on N2A cells, and of vitamin D and Novasc on SH-SY5Y cells. All these drugs except Colace significantly reduced the amount of Aβ fibril when incubated with Aβ42 for a short period (6h). However, Lipitor, vitamin D, Levothyroxine, Prilosec, Flomax, and Norvasc prominently reduce the amount of fibrils when incubated with monomeric Aβ42 for a longer period (48h). Furthermore, our disaggregation study with fAβ showed consistent results for cholecalciferol (vitamin D), omeprazole (Prilosec), clopidogrel hydrogensulfate (Flomax), levothyroxine, and amlodipine (Norvasc). The chemical structures of these four efficient molecules contain polyphenol components, a characteristic feature of the structures of polyphenolic inhibitors of Aβ fibrillation. A higher polypharmacy incidence was observed in an elderly population of 228 ND, 114 MCI, and 124 AD patients. We found that several highly recommended drug components, including vitamin D3, Levothyroxine, Prilosec, Flomax, and Norvasc, efficiently reduce the amount of fibrils formed by monomeric Aβ42 and existing preformed Aβ fibrils in vitro. However, only Levothyroxine was able to prevent Aβ-mediated toxicity to SH-SY5Y cells. Our study suggested that these drugs likely function as polyphenolic inhibitors of Aβ.

Investigation of the mechanism of [M-H]+ ion formation in photoionized N-alkyl-substituted thieno[3,4-c]-pyrrole-4,6-dione derivatives during higher order MSn high-resolution mass spectrometry.

The mechanism underlying dopant-assisted atmospheric pressure photoionization's (APPI) formation of ions is unclear and still under debate for many chemical classes. In this study, we reexamined the gas-phase reaction mechanisms responsible for the generation of [M-H]+ precursor ions, resulting from the loss of a single hydrogen atom, in a series of N-alkyl-substituted thieno[3,4-c]-pyrrole-4,6-dione (TPD) derivatives. Atmospheric pressure photoionization combined with higher order MS/MSn using high-resolution mass spectrometry (APPI-HR-CID-MSn) and electronic structure calculations using density functional theory were used to determine the chemical structure of observed [M-H]+ ions. As a result, the higher order MSn (n = 3) experiments revealed a reversed Diels-Alder fragmentation mechanism, leading to a common fragment ion at m/z 322 from the studied [M1-5-H]+ ion species. In addition, the calculation for two chemical structure models (N-alkyl-TPD1 and N-alkyl-TPD5) showed that the fragment structure, resulting from the removal of the hydrogen atom connected to the third carbon atom of the N-alkyl side chain, has a more stable cyclic form compared with the linear one. The proposed chemical structure of the N-alkyl TPD ion species, following the loss of a single hydrogen atom, was revealed during APPI-HR-CID-MSn (n= 3) experiments on the [M-H]+ species. Hydrogen radical (H•) abstraction from the alkyl side chain (e.g., hexyl, heptyl, octyl, 2-ethylhexyl, and nonyl) triggered a rearrangement in the radical cation structure of the N-alkyl-TPD derivatives, initiating cyclization and forming a six-membered ring that connects the oxygen atom to the third carbon atom in the alkyl chain. In addition, theoretical calculations supported the APPI-HR-CID-MSn (n = 3) experiments by demonstrating that the proposed chemical structure, resulting from the intramolecular cyclization of the N-alkyl-TPD ion species, was stable in the presence of chlorobenzene. These findings will aid the structural determination and elucidation of molecules with similar core structures.

Characterizing the chemistry of artificially degraded Scots pine wood serving as a model of naturally degraded waterlogged wood using1H–13C HSQC NMR

AbstractChemically and biologically degraded Scots pine wood was prepared as a model material for the research on new conservation agents for waterlogged archeological wood. In this study, the model wood was characterized using a 2D1H–13C solution-state NMR technique without derivatization, isolation, or extraction to assess the effect of applied degradation processes on its chemical composition and structure. The results clearly show how the two artificially degraded model wood types are chemically different. Biological decay by the brown-rot fungus Coniophora puteana caused degradation of wood polysaccharides, with heavy depletion in arabinan, mannan, and galactan, along with an increase in the cellulose's reducing ends (i.e., lowering the degree of polymerization) and partial deacetylation of mannan. The fungus cleaved roughly one-fifth of the β-aryl ethers in lignin, leading to a broadening effect on the lignin aromatic unit contours; other lignin sidechains were left untouched. Chemical degradation by NaOH hydrolysis resulted in a depletion in mannan, galactan, and glucan, as well as efficient deacetylation of mannan. It also decreased lignin content, causing changes in its structure; minor β-aryl ether cleavage along with substantial phenylcoumaran cleavage were evident. Detailed knowledge about the chemical composition and structure of artificially degraded model pine wood obtained in this research is necessary to understand the reactivity of these wood types with chemicals used for their conservation. This research will help explain the differences in the stabilization effectiveness observed between these wood types treated during conservation and understand the stabilization mechanisms, thus contributing to developing new, more effective conservation agents for wooden artifacts of Cultural Heritage.