Monthly Archives: September 2023

Microplastic Pollution in the Gastrointestinal Tract and Gills of Some Teleost and Sturgeon Fish from the Caspian Sea, Northern Iran

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Microplastic Pollution in the Gastrointestinal Tract and Gills of Some Teleost and Sturgeon Fish from the Caspian Sea, Northern Iran

Microplastic pollution was found in the gastrointestinal tract and gills of some commercially important fish species, particularly sturgeon from the Caspian Sea.


Abstract

The increasing microplastic pollution in the marine environment has raised global concern. The main risk of microplastics in aquatic ecosystem is their bioaccumulation in aquatic organisms. A few studies have reported microplastic pollution in the digestive system of Caspian Sea fish species, but there is no research on sturgeon species, nor on fish gills. We investigated the occurrence of microplastics in the gastrointestinal tract (GIT) and gills of 62 specimens belonging to four species including three teleosts (Cyprinus carpio, Rutilus kutum, and Chelon aurata) and one sturgeon (Acipenser persicus, a valuable endangered species) from the Caspian Sea between January and March 2022. Fish tissues were removed, exposed for 24 h to 10% KOH, and then dried on filter paper. Particles were observed under a stereomicroscope and analyzed by Raman microspectrometry, scanning electron microscopy, and energy-dispersive spectroscopy. A total of 91 microplastics were detected in the GIT (average of 1.46 ± 1.17 items/individual) and 63 microplastics in the gills (average of 1.01 ± 0.62 items/individual). A significant correlation was not found between the number of microplastics found in both tissues and fish body length, body weight, GIT weight, and gill weight (p > 0.05), except between microplastics isolated from gills and gill weight in C. carpio (r s = 0.707, p = 0.022). The abundance of microplastics in fish followed the order of A. persicus > C. aurata > R. kutum > C. carpio. The microplastics were in the size range of 45 to 5000 µm, with particles of 300 to 1000 µm being the most prevalent; 74.68% of the particles were shaped like fibers, 30.53% were red, and 70.6% were composed of nylon polymer. Environ Toxicol Chem 2023;00:1–13. © 2023 SETAC

On the aromaticity and stability of benzynes in the ground and lowest‐lying triplet excited states

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On the aromaticity and stability of benzynes in the ground and lowest-lying triplet excited states

The aromaticity and stability of benzynes in the ground and first triplet states have been studied using unrestricted DFT methods. The results using multiple aromaticity criteria and CCSD(T) calculations show that aromaticity is conserved while stability is reversed from the ground to the excited state.


Abstract

In this work, we have revisited the aromaticity of benzyne isomers at the unrestricted density functional theory level (UDFT) using the energetic, magnetic, and delocalization criteria. In addition, this last criterion has also been analyzed employing complete active space (CASSCF) calculations. The results show conservation of aromaticity in these monocycles. Additionally it is observed that this trend is maintained in polycyclic aromatic hydrocarbon derivatives such as biradical didehydrophenanthrenes. Do these results imply a violation of Baird's rule? The answer is No, because this conservation in aromaticity is due to the loss of hydrogen atoms affects only the electronic σ skeleton and exerts a minor influence on the π cloud. Additionally, we have analyzed the relative stability of benzyne isomers and their relationship with experimental ΔE S-T values. According to the literature, the stability of the benzynes in the singlet state is due to an effective interaction between the electrons of the biradical centers; however, this effect is completely reversed in the triplet state, which explains why the para isomer has the lowest ΔE S-T gap.

Silver Supported Nanoparticles on [Mg4Al‐LDH] as an Efficient Catalyst for the α‐Alkylation of Nitriles, Oxindoles and Other Carboxylic Acid Derivatives with Alcohols

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Silver Supported Nanoparticles on [Mg4Al-LDH] as an Efficient Catalyst for the α-Alkylation of Nitriles, Oxindoles and Other Carboxylic Acid Derivatives with Alcohols

Alcohols are used as accessible and safe C-alkylation agents to produce α-functionalized nitriles or oxindoles and 2-quinolinones via borrowing hydrogen strategy mediated by a [Mg4Al-LDH]-supported silver nanoparticle catalyst. Combination of a suitable basic LDH support together with homogeneously distributed silver metallic centers are the key elements for the success of the protocol.


Abstract

An efficient heterogeneous silver-catalyzed α-alkylation of nitriles and oxindoles using alcohols via borrowing hydrogen strategy has been developed for the first time. The active nanostructured material, namely [Ag/Mg4Al-LDH], composed by silver nanoparticles (3-4 nm average particle size) homogeneously stabilized onto a [Mg4Al-LDH] support with suitable Brønsted basic properties, constitutes a stable catalyst for the sustainable building of novel C−C bonds from alcohols and C-nucleophiles. By applying this catalyst, a broad range of α-functionalized nitriles and oxindoles has been accessed with good to excellent isolated yields and without the addition of external bases. Moreover, the novel silver nanocatalyst has also demonstrated its successful application to the cyclization of N-[2-(hydroxymethyl)phenyl]-2-phenylacetamides to afford 3-arylquinolin-2(1H)-ones, through a one-pot dehydrogenation and intramolecular α-alkylation. Control experiments, kinetic studies, and characterization data of a variety of [Ag/LDH]-type materials confirmed the silver role in the dehydrogenation and hydrogenation steps, while [Mg4Al-LDH] matrix is able to catalyze condensation. Interestingly, these studies suggest as key point for the successful activity of [Ag/Mg4Al-LDH], in comparison with other [Ag/LDH]-type nanocatalysts, the suitable acid-base properties of this material.

Selective Conversion of Propane by Electrothermal Catalysis in Proton Exchange Membrane Fuel Cell

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Selective Conversion of Propane by Electrothermal Catalysis in Proton Exchange Membrane Fuel Cell

Combining electrosynthesis with thermocatalysis: A strategy for efficient conversion of propane to high value-added C3 oxygenated products is developed by coupling the electrosynthesis of H2O2 on oxygen-doped carbon electrocatalyst for 2e− oxygen reduction reaction with thermocatalysis of propane oxidation over MIL-53 (Al, Fe) active sites in the proton exchange membrane fuel cell.


Abstract

Electrochemical conversion of alkanes to high value-added oxygenated products under a mild condition is of significance. Herein, we effectively couple the electrocatalysis of H2O2 with the thermo-catalysis of propane oxidation in the cathode of proton exchange membrane fuel cell. Specifically, H2O2 is in-situ generated on the nitric acid-treated carbon black (C-acid) via 2e− process of oxygen reduction reaction, and then transports to the Fe active sites of MIL-53 (Al, Fe) metal–organic frameworks for propane oxidation. Based on this strategy, the space-time yield of C3 oxygenated products of propane oxidation reaches 2.65 μmol h−1 cm−2, which represents a new benchmark for electrochemical alkane oxidation in the fuel-cell-type electrolyzer. This study highlights the importance of multifunctional composite catalysts in the field of electrosynthesis.

Merging Organocatalysis and Photocatalysis: A New Momentum in Covalent Radical Catalysis

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Merging Organocatalysis and Photocatalysis: A New Momentum in Covalent Radical Catalysis

This Concept article describes the contribution of photocatalysis in the field of covalent radical catalysis to control the generation and reactivity of radical catalysts. The synthetic perspectives offered by such catalytic combinations are discussed from a mechanistic point of view.


Abstract

The use of free radicals as organocatalysts constitutes a powerful strategy to activate and functionalize unsaturated carbon chains. Indeed, the unique affinity of open-shell species for alkenes and alkynes can be rerouted to achieve the catalytic covalent activation of the substrate and control a subsequent radical cascade. However, the field of covalent radical catalysis has remained challenging for decades due to important issues in terms of catalyst handling, reaction design and viability. Recently, these pitfalls have been addressed one by one by the use of photocatalysis to control the generation and the reactivity of radical catalysts. This Concept article aims to highlight recent achievements in the field of photocatalyzed covalent radical catalysis and the perspectives offered by such catalytic combinations. The reaction mechanisms and the interconnection between the catalytic cycles are reviewed with the hope of demonstrating the synthetic potential of this approach and foster a rapid growth of this nascent topic.

Experimental and Theoretical Structure Elucidation of the [2 : 1] Complex Ion of Carbo[n]helicene with n=6, 7 and 8 and Ag+

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Experimental and Theoretical Structure Elucidation of the [2 : 1] Complex Ion of Carbo[n]helicene with n=6, 7 and 8 and Ag+

Gas-phase complexes of [n]helicenes with n=6, 7 and 8 and silver(I) cation are generated. Besides the well-established [1 : 1] helicene/Ag+-complex in which the helicene provides a tweezer-like surrounding for the Ag+, there is also a [2 : 1] complex formed. The second helicene attaches via π-π stacking to the first helicene of the [1 : 1] tweezer complex. Using [n]helicene mixtures, tweezer complexes of Ag+ are preferably formed with the larger helicenes.


Abstract

Gas-phase complexes of [n]helicenes with n=6, 7 and 8 and the silver(I) cation are generated utilizing electrospray ionization mass spectrometry (ESI-MS). Besides the well-established [1 : 1] helicene/Ag+-complex in which the helicene provides a tweezer-like surrounding for the Ag+, there is also a [2 : 1] complex formed. Density functional theory (DFT) calculations in conjunction with energy-resolved collision-induced dissociation (ER-CID) experiments reveal that the second helicene attaches via π-π stacking to the first helicene, which is part of the pre-formed [1 : 1] tweezer complex with Ag+. For polycyclic aromatic hydrocarbons (PAHs) of planar structure, the [2 : 1] complex with silver(I) is typically structured as an Ag+-bound dimer in which the Ag+ would bind to both PAHs as the central metal ion (PAH–Ag+–PAH). For helicenes, the Ag+-bound dimer is of similar thermochemical stability as the π-π stacked dimer, however, it is kinetically inaccessible. Coronene (Cor) is investigated in comparison to the helicenes as an essentially planar PAH. In analogy to the π-π stacked dimer of the helicenes, the Cor−Ag+−Cor−Cor complex is also observed. Competition experiments using [n]helicene mixtures reveal that the tweezer complexes of Ag+ are preferably formed with the larger helicenes, with n=6 being entirely ignored as the host for Ag+ in the presence of n=7 or 8.

Fabrication of Hyperbranched Photomechanical Crystals Composed of a Photochromic Diarylethene

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Fabrication of Hyperbranched Photomechanical Crystals Composed of a Photochromic Diarylethene

The sublimation process where the thin films of 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene are formed on a concave surface of the spherical glass substrate, accompanying the movement of boundaries between the thin film domains under the higher relative humidity condition, leads to the fabrication of the hollow crystals having the highly branched shapes.


Abstract

We report the fabrication of hyperbranched hollow crystals of 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene on a concave surface of the spherical glass substrate by sublimation and their practical photomechanical behaviors. The number of units of the branched structure of the hollow crystals composed of this compound is proportional to the substrate curvature of the substrate. Compared with the sublimation process of the same compound on the flat glass substrate, two kinds of the thin film domains are generated separately in the center and around the edge of the spherical glass substrate. Especially under the high relative humidity condition, the boundaries between these thin film domains move gradually around the edge through the center during as long as 6 h of sublimation time so that the hyperbranched hollow crystals are densely produced on the entire surface of the substrate. These hyperbranched hollow crystals can be prepared with the highly ordered molecular packing due to the very slow formation process of the crystalline walls of the hollow structures. Furthermore, the photo-induced bending behaviors in the few- and highly-branched hollow crystals have the practical roles in moving and bending the minute objects according to their characteristics of these branched shapes.