Search Results (82)

Plastic pollution poses significant environmental challenges due to its persistence and contribution to the microplastic formation, with polyethylene being among the materials more abundantly found. Understanding how different artificial weathering protocols influence the degradation of plastics is crucial for assessing their environmental impact. This study investigates the effects of three distinct artificial weathering protocols—continuous UV-A irradiation (M_L), cyclic UV-dark exposure (M_C[L→D]), and sequential UV-dark phase (M_L→D)—on the physicochemical properties of plastics, using oxo-low-density polyethylene as the model material. Surface oxidation, measured by quantification of the carbonyl index, was most pronounced under the M_C[L→D] protocol despite the shortest time of overall UV exposure, indicating that oxidative reactions continue during the dark phases. Vinyl group formation, however, required continuous or cyclic UV exposure, highlighting the critical role of light in this chemical process. Alterations in the surface hydrophilicity, measured by contact angle, and changes in molecular weight were quantified and found to closely link to the weathering conditions, with increased oxidations enhancing the surface hydrophilicity and the chain scission balanced by crosslinking with extended UV durations. These findings emphasize the importance of weathering protocols when trying to simulate conditions in the lab that are closer to the ones in the environment to understand plastic degradation mechanisms. Biodegradation experiments with Rhodococcus rhodochrous demonstrated that weathered oxo-LDPE samples with higher surface oxidation levels (ΔCI > 1) supported an increased CO₂ production by Rhodococcus rhodochrous, with the M_C[L→D]—360 h protocol yielding the highest biodegradation rates—31–43% higher than the control. Full article

Sotolon is a chiral furanone derivative featuring three distinct oxygen atoms at carbonyl, hydroxyl, and cyclic ether groups that can serve as hydrogen-bond acceptor sites, making it an ideal model system for probing water’s preferential interactions with competing functional groups. In this study, the rotational spectrum of sotolon and its microsolvated complexes, representing the early stages of hydration, was investigated using chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy. The conformational landscape of sotolon is dominated by a single conformer stabilized by an intramolecular O–H···O=C hydrogen bond. During hydration, water molecules disrupt this interaction by forming closed hydrogen-bonded cycles, resulting in mono- and dihydrated complexes. High-level theoretical calculations underscore the central role of electrostatic interactions in stabilizing these hydrated structures. Furthermore, A/E splittings observed in the rotational spectrum, arising from the internal rotation of one of sotolon’s methyl groups, provide insight into how hydration modulates the methyl internal rotation barrier. Full article

To contribute to the search for effective substances in pest control, this study describes the fumigant and contact toxicity against Tribolium castaneum and Sitophilus zeamais of four essential oils (EOs) and some of their major chemical constituents. The EOs from Tagetes zypaquirensis, Anethum graveolens, Satureja viminea and Minthostachys mollis were obtained by steam distillation and chemically characterized using GC–MS. In the development of research, some monoterpenoids were isolated from the EOs, others were purchased commercially, and some were synthesized from the most active monoterpenoids present in EOs. The main components in the EOs were dill ether (28.56%), α-phellandrene (25.78%) and carvone (23.67%) for A. graveolens, piperitone oxide (30.40%) and pulegone (25.91%) in M. mollis, pulegone (37.40%) and p-menth-3-en-8-ol (11.83%) for S. viminea, and dihydrotagetone (32.13%), myrcene epoxide (19.64%) and β-myrcene (5.30%) for T. zypaquirensis. The results highlight the fumigant action (LC₅₀) and contact toxicity (LD₅₀) of EO from M. mollis against T. castaneum (LC₅₀ of 4.8 µL/L air and LD₅₀ of 6.5 µg/insect) and S. zeamais (LC₅₀ of 7.0 µL/L air and LD₅₀ of 5.81 µg/insect). Among the chemical constituents evaluated, R-carvone 2, piperitone oxide 5 and R-pulegone 6 stand out for their insecticidal potential against S. zeamais (LC₅₀ between 3.0 and 42.4 µL/L, while LD₅₀ between 14.9 and 24.6 µg/insect) and T. castaneum (LC₅₀ between 2.2 and 4.8 µL/L, while LD₅₀ between 4.8 and 13.1 µg/insect). Preliminary structure–activity analysis suggests that the presence of the carbonyl group with conjugated double bonds in cyclic monoterpenes is important for the insecticidal potential exhibited. Full article

A straightforward chemical polymerization process was used to create the polyaniline/LiClO₄/CuO nanoparticle (PLC) nanocomposite, which was then exposed to varying doses of electron beam (EB) radiation and studied. The FESEM, XRD, FTIR, DSC, TG/DTA, and electrochemical measurements with higher EB doses showed clear changes. The FTIR spectra of the PLC nanocomposite showed variations in the C-N and carbonyl groups at 1341 cm⁻¹ and 1621 cm⁻¹, respectively. After a 120 kGy EB dose, the shape changed from a smooth, uneven surface to a well-connected, nanofiber-like structure, creating pathways for electricity to flow through the polymer matrix. The EB irradiation improved the thermal stability by decreasing the melting temperature, and the XRD and DSC studies reveal that the decrease in crystallinity is attributed to the dominant chain scission mechanism. The enhanced absorption and red shift in the wavelength (from 374 nm to 400 nm) observed in the UV-Visible spectroscopy were caused by electrons transitioning from a lower to a higher energy state, with a progressive drop in the band gaps (E_g) from 2.15 to 1.77 eV following irradiation. The dielectric parameters increased with the temperature and electron beam doses because of the dissociation of the ion aggregates and the emergence of defects and/or disorders in the polymer band gaps. This was triggered by chain scission, discontinuity, and bond breaking in the molecular chains at elevated levels of radiation energy, leading to an augmented charge carrier density and, subsequently, enhanced conductivity. The cyclic voltammetry study revealed an enhanced electrochemical stability at a high scan rate of about 600 mV/s for the PLC nanocomposite with the increase in the EB doses. The I-V characteristics measured at room temperature exhibited nonohmic behavior with an expanded current range, and the electrical conductivity was estimated, using the I-V curve, to be around 1.05 × 10⁻⁴ S/cm post 20 kGy EB irradiation. Full article

Among the various strategies used to enhance the solvation power of supercritical carbon dioxide (scCO₂), the use of CO₂-philic compounds has been extensively studied over the recent two decades. Given the biocompatibility of this medium, extraction technologies based on scCO₂ are particularly attractive, and a molecular-level understanding of intermolecular interactions is crucial for optimizing processing conditions. Functionalized sugars and cyclic oligosaccharides, such as cyclodextrins, can be rendered soluble in scCO₂, opening new avenues for vectorization strategies and supramolecular chemistry in this medium. To support the exploration of CO₂-philic compounds relevant to these research goals, we conducted a molecular dynamics investigation into the solvation properties of cyclodextrins functionalized with CO₂-philic groups. We thoroughly analyzed the key solute–solvent interactions and their influence on the cavity shape. Additionally, we provided insights into the solvation behavior of peracetylated $\alpha$ and $\beta$-glucose across different regions of the carbon dioxide phase diagram. We were able to confirm the importance of the well-known (acetyl)C–O⋯C(CO₂) interaction, as the most important signature of CO₂-philicity of carbonyl compounds. Depending on the substituent, this interaction can be assisted by a cooperative (methyl)₂HCH⋯O(CO₂) intermolecular bond. In cyclodextrins, conformational flexibility, with a possible change in the conformation of some pyranose units, was observed in the macromolecular structure. On the other hand, these structural modifications were not present for $\alpha$- and $\beta$-glucose. Full article

The complex of hypofluorous acid with acetonitrile—HOF•CH₃CN—is the only substance possessing a truly electrophilic oxygen. This fact makes it the only tool suitable for transferring oxygen atoms to sites that are not accessible to this vital element. We will review here most of the known organic reactions with this complex, which is easily made by bubbling dilute fluorine through aqueous acetonitrile. The reactions of HOF•CH₃CN with double bonds produce epoxides in a matter of minutes at room temperature, even when the olefin is electron-depleted and cannot be epoxidized by any other means. The electrophilic oxygen can also substitute deactivated tertiary C-H bonds via electrophilic substitution, proceeding with full retention of configuration. Using this complex enables transferring oxygen atoms to a carbonyl and oxidizing alcohols and ethers to ketones. The latter could be oxidized to esters via the Baeyer–Villiger reaction, proving once again the validity of the original Baeyer mechanism. Azines are usually avoided as protecting groups for carbonyl since their removal is problematic. HOF•CH₃CN solves this problem, as it is very effective in recreating carbonyls from the respective azines. A bonus of the last reaction is the ability to replace the common ¹⁶O isotope of the carbonyl with the heavier ¹⁷O or ¹⁸O in the simplest and cheapest possible way. The reagent can transfer oxygen to most nitrogen-containing molecules. Thus, it turns practically any azide or amine into nitro compounds, including amino acids. This helps to produce novel α-alkylamino acids. It also attaches oxygen atoms to most tertiary nitrogen atoms, including certain aromatic ones, which could not be obtained before. HOF•CH₃CN was also used to make five-member cyclic poly-NO derivatives, many of them intended to be highly energetic materials. The nucleophilic sulfur atom also reacts very smoothly with the reagent in a wide range of compounds to form sulfone derivatives. While common sulfides are easily converted to sulfones by many orthodox reagents, electron-depleted ones, such as R_f-S-Ar, can be oxidized to R_f-SO₂-Ar only with this reagent. The mild reaction conditions also make it possible to synthesize a whole range of novel episulfones and offer, as a bonus, a very easy way to make S^xO₂, x being any isotope variation of oxygen. These mild conditions also helped to oxidize thiophene to thiophen-S,S-dioxide without the Diels–Alder dimerizations, which usually follow such dioxide formation. The latter reaction was a prelude to a series of preparations of [all]-S,S-dioxo-oligothiophenes, which are important for the efficient preparation of active layers in field-effect transistors (FETs), as such oligomers are considered to be important for organic semiconductors for light-emitting diodes (LEDs). Several types of these oligothiophenes were prepared, including partly or fully oxygenated ones, star-oligothiophenes, and fused ones. Several [all]-S,S-dioxo-oligo-thienylenevinylenes were also successfully prepared despite the fact that they also possess carbon–carbon p centers in their molecules. All oxygenated derivatives have been prepared for the first time and have lower HOMO-LUMO gaps compared to their parent compounds. HOF•CH₃CN was also used to oxidize the surface of the nanoparticles of oligothiophenes, leaving the core of the nanoparticle unchanged. Several highly interesting features have been detected, including their ability to photostimulate the retinal neurons, especially the inner retinal ones. HOF•CH₃CN was also used on elements other than carbon, such as selenium and phosphor. Various selenides were oxidized to the respective selenodioxide derivatives (not a trivial task), while various phosphines were converted efficiently to the corresponding phosphine oxides. Full article

We have synthesized novel cobalt(II) and nickel(II) pincer ligand complexes containing novel tridentate ligand precursors that coordinate via oxygen, nitrogen, and oxygen donor atoms. The novel tridentate ONO ligands, which are neutral, incorporate a carbonyl-substituted imidazole functionality and contain R groups of ethyl, isopropyl, or tert-butyl. The ligand precursors were thoroughly characterized using NMR spectroscopy, ESI-MS, and IR spectroscopy. The metal complexes were thoroughly characterized using single crystal X-ray diffraction, elemental analysis, ESI-MS, and cyclic voltammetry. The nickel(II) and cobalt(II) complexes with ethyl, isopropyl, and t-butyl wingtip groups had a pseudo-octahedral geometry about the metal center. The nickel(II) complex with R = isopropyl had a monoclinic lattice with C121 space group (a = 21.7639(8); b = 11.0649(5); c = 10.9225(4); alpha = 90.0 degrees; beta = 90.609(3) degrees; gamma = 90.0 degrees). The cobalt(II) complex with R = ethyl had a monoclinic lattice with P2₁/n space group (a = 17.7907(7); b = 21.5278(6); c = 21.8597(7); alpha = 90.0 degrees; beta = 95.063(3) degrees; gamma = 90.0 degrees). The cobalt(II) complexes were paramagnetic with μ_eff = 1.59 BM (R = ethyl) and 6.67 BM (R = t-butyl). The nickel(II) complex was paramagnetic with μ_eff = 2.59 BM. The ligand precursors and metal complexes are redox-active. Full article

Peroxymonosulfate-based advanced oxidation processes (PMS-AOPs) relying on non-radical pathways offer advantages such as resistance to interference, efficient oxidant utilization, and selective degradation of pollutants. In this study, an Fe, N co-doped activator (Fe-N-C_1.5) was synthesized using a simple mixed solvent pyrolysis method. The Fe-N-C_1.5 exhibited excellent PMS activation activity. A total of 100% of paracetamol (PCT, 10 ppm) was degraded in the Fe-N-C_1.5/PMS system in 7 min. Furthermore, this oxidation system maintained effective PCT removal even in the presence of background ions and in real water matrices. In addition, the leached Fe concentration after 60 min was only 0.084 mg/L, and 94% of PCT could still be removed during the fourth cyclic use of the catalyst. Quenching experiments, electron paramagnetic resonance (EPR), and electrochemical analysis revealed that the Fe-N-C_1.5/PMS/PCT system predominantly relies on non-radical pathways, including singlet oxygen (¹O₂) and catalyst-interface-mediated electron transfer process (ETP). X-ray photoelectron spectroscopy (XPS) analysis and KSCN toxicity experiment confirmed that the graphitic N, carbonyl (C=O), and Fe-N_x were the main PMS activation sites. This study provides an understanding of degradation mechanisms of the Fe-N-C_1.5/PMS/PCT system and offers insights into the design of iron–carbon composite catalysts that carry out non-radical PMS activation. Full article

The reactivity of the benzenedithiolate (bdt)-bridged complex [Fe₂(CO)₆(µ-bdt)] with arsine, stibine and phosphine ligands has been studied. The new mono- and disubstituted complexes [Fe₂(CO)₅(EPh₃)(µ-bdt)] (E = As, 1; E = Sb 3) and [Fe₂(CO)₄(EPh₃)₂(µ-bdt)] (E = As, 2; E = Sb, 4) and the previously reported [Fe₂(CO)₄(PPh₂H)₂(µ-bdt)] (5) have been prepared by Me₃NO-initiated carbonyl substitution reactions of [Fe₂(CO)₆(µ-bdt)] with appropriate ligands at 80 °C. Spectroscopic and single-crystal X-ray diffraction studies reveal that in all cases the introduced ligands occupy apical coordination site(s) lying trans to the iron–iron bond. Their electrochemistry has been probed by cyclic voltammetry and selected complexes have been tested as proton reduction catalysts. Monosubstituted complexes 1 and 3 show two irreversible reductions at ca. −1.7 V and −2.0 V, respectively, relative to Fc⁺/Fc, while the disubstituted complexes 2 and 5 show a single irreversible reduction at ca. −2.2 V and −1.84 V, respectively. Complexes 1, 3 and 5 can catalyse electrocatalytic proton reduction in the presence of either p-toluene sulfonic acid (TsOH) or trifluoroacetic acid (CF₃CO₂H). Full article

Background: Melanoma is the most aggressive and lethal skin cancer that affects thousands of people worldwide. Ruthenium complexes have shown promising results as cancer chemotherapeutics, offering several advantages over platinum drugs, such as potent efficacy, low toxicity, and less drug resistance. Additionally, anthraquinone derivatives have broad therapeutic applications, including melanoma. Objectives: Thus, two new ruthenium complexes with 1-hydroxy-9,10-anthraquinone were obtained: trans-[Ru(HQ)(PPh₃)₂(bipy)]PF₆ (1) and cis-[RuCl₂(HQ)(dppb)] (2), where HQ = 1-hydroxy-9,10-anthraquinone, PPh₃ = triphenylphospine, bipy = 2,2′-bipyridine, PF₆ = hexafluorophosphate, and dppb = 1,4-bis(diphenylphosphine)butane. Methods: The complexes were characterized by infrared (IR), UV–vis, ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopies, molar conductivity, cyclic voltammetry, and elemental analysis. Furthermore, density functional theory (DFT) calculations were performed. Results: Compound (2) was determined by single-crystal X-ray diffraction, which confirms the bidentate coordination mode of HQ through the carbonyl and phenolate oxygens. Additionally, DNA-binding experiments yielded constants of 10⁵ M⁻¹ (Kb = 6.93 × 10⁵ for (1) and 1.60 × 10⁵ for (2)) and demonstrate that both complexes can interact with DNA through intercalation, electrostatic attraction, or hydrogen bonding. Conclusions: The cytotoxicity profiles of the compounds were evaluated in human melanoma cell lines (SK-MEL-147, CHL-1, and WM1366), revealing greater cytotoxic activity for (1) on the CHL-1 cell line with an IC₅₀ of 14.50 ± 1.09 µM. Subsequent studies showed that (1) inhibits the proliferation of CHL-1 cells and induces apoptosis, associated at least in part with the pro-oxidant effect and cell cycle arrest at the G1/S transition. Full article

This study examined the chemoselectivity and diastereoselectivity of silyl nitronate alkenyn-nitroethers in Intramolecular Silyl Nitronate Cycloadditions (ISNCs) to produce isoxazole derivatives with interesting medicinal properties. These reactions resulted in the formation of either dihydrofuro[3,4-c]isoxazolines/isoxazolidines and/or alkynyl moieties attached to 2,5-dihydrofuryl carbonyls. This study also discerned the diastereoselectivities of the resulting cyclic adducts and compared them to previous findings. The reactions were also investigated with Spartan molecular modeling computations to aid in the understanding of any displayed chemo- and/or stereoselectivity. These [3+2]-cycloaddition reactions demonstrated excellent to complete chemospecificity. The cycloadditions also demonstrated remarkable diastereospecificity in that each diastereomer of the nitroethers resulted in the formation of only one of four possible diastereomeric outcomes. The stereochemistry of the major diastereomers did not agree with previously published findings. Full article

Herein we describe the synthesis and rearrangement of 1,3-diamino-2,7-naphthyridines and 1-amino-3-oxo-2,7-naphthyridines. In the case of 1,3-diamino-2,7-naphthyridines, it was found that the rearrangement reaction was influenced by both the substituent at the 7th position of the 2,7-naphthyridine ring and by the nature of the cyclic amine at the 1st position. The influence was mainly steric. The reaction of 1-amino-3-oxo-2,7-naphthyridines with amines was studied for the first time. It was revealed that for these substrates, the rearrangement occurs faster and without any influence of the alkyl and cyclic amine groups. We also observed the nucleophilic addition of the amine to the carbonyl group of the rearranged product with the formation of a Schiff base. The calculation of the ESP charges on these substrates indicates a considerable increase in the positive charge on the cyano group that suffers the nucleophilic attack during the rearrangement process, possibly explaining its increased tendency to react and to have a higher reaction velocity. Full article

The present article describes the successful performance of crossed aldol reactions of the CF₃-containing pseudo-C₂ symmetric cyclic imide with various aldehydes. The utilization of HMPA as an additive attained the preferential formation of the anti-products in good to excellent yields, which contrasts with our previous method without this additive, proceeding to furnish the corresponding syn-isomers. The effective participation of ketones and α,β-unsaturated carbonyl compounds in reactions with this imide was also demonstrated to expand the application of this imide. Full article

Macrocycles bridge the gap between conventional small molecules and polymers. Drawing inspiration from successful carbon heteroatom-containing macrocycles, peroxide-containing macrocycles are gaining attention for enhanced bioactivity, potential chelating properties, and applications in energetic materials. This review presents the following strategies for the construction of cyclic peroxides with 10- to 36-membered frameworks: (1) the intramolecular iodocyclization of hydroperoxides, (2) the intermolecular cyclization of hydroperoxides with alkyl dihalides or carbonyls, (3) the acid-catalyzed rearrangements of ozonides or 11-membered cyclic triperoxides via oxy- or peroxycarbenium ions, and (4) the peroxidation of carbonyls targeting macrocyclic peroxides. The specific agents that allow for the selective construction of the medium and large cycles are also analyzed. Full article

Redox-active porous organic polymers (POPs) demonstrate significant potential in supercapacitors. However, their intrinsic low electrical conductivity and stacking tendencies often lead to low utilization rates of redox-active sites within their structural units. Herein, polyimide POPs (donated as PMTA) are synthesized in situ on multi-walled carbon nanotubes (MWCNTs) from tetramino-benzoquinone (TABQ) and 1,4,5,8-naphthalene tetracarboxylic dianhydride (PMDA) monomers. The strong π–π stacking interactions drive the PMTA POPs and the MWCNTs together to form a PMTA/MWCNT composite. With the assistance of MWCNTs, the stacking issue and low conductivity of PMTA POPs are well addressed, leading to the obvious activation and enhanced utilization of the redox-active groups in the PMTA POPs. PMTA/MWCNT then achieves a high capacitance of 375.2 F g⁻¹ at 1 A g⁻¹ as compared to the pristine PMTA POPs (5.7 F g⁻¹) and excellent cycling stability of 89.7% after 8000 cycles at 5 A g⁻¹. Cyclic voltammetry (CV) and in situ Fourier-Transform Infrared (FT-IR) results reveal that the electrode reactions involve the reversible structural evolution of carbonyl groups, which are activated to provide rich pseudocapacitance. Asymmetric supercapacitors (ASCs) assembled with PMTA/MWCNTs and activated carbon (AC) offer a high energy density of 15.4 Wh kg⁻¹ at 980.4 W kg⁻¹ and maintain a capacitance retention of 125% after 10,000 cycles at 5 A g⁻¹, indicating their good potential for practical applications. Full article