Binuclear and Mononuclear Aluminum Complexes as Quick and Controlled Initiators of Well‐ordered ROP of Cyclic Esters

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Binuclear and Mononuclear Aluminum Complexes as Quick and Controlled Initiators of Well-ordered ROP of Cyclic Esters

A simple and efficient route to achieve excellent yield and well-ordered PLAs and PCLs through the ROP of cyclic esters using bimetallic and monometallic aluminum complexes supported by functionalized P−N ligands under mild conditions.


Abstract

Described herein is an efficient ring-opening polymerization (ROP) of rac-lactide and ϵ-caprolactone (ϵ-CL) using novel bimetallic and monometallic aluminum complexes supported by functionalized P−N ligands. All the aluminum complexes were seen to be active catalysts in the ROP of both rac-lactide and ϵ-CL in toluene at 60 °C. Bimetallic aluminum complex, [Al(Me)2{Ph2P(Se)N(CH2)2N−(CH2CH2)2O}(AlMe3)] containing an uncoordinated Se atom and an auxiliary Al atom within the proximity of another central Al cation was observed to exhibit the highest catalytic activity among all the catalysts studied. Kinetic experiments, comparing bimetallic and related monometallic complexes revealed that bimetallic cooperativity among the two metallic centers in bimetallic complex plays an essential role in driving such superior reactivity. We synthesized several isoselective polylactides (PLAs) and polycaprolactones (PCLs) with controlled molecular weights and narrow molecular weight distributions and characterized by 1H, 13C NMR, DSC and TGA.

Double Hydroamination of Terminal Alkynes over Beta Zeolite‐Supported CuO Catalyst

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Double Hydroamination of Terminal Alkynes over Beta Zeolite-Supported CuO Catalyst

An efficient heterogeneous 1 % Cuβ zeolite catalyzed double hydroamination of terminal alkynes for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones is achieved in a solvent-free environment. This method offers an appealing approach to a number of di-substituted quinazolinones with decent to excellent yields.


Abstract

An effective and novel heterogeneous beta zeolite supported CuO (Cuβ) catalyzed double hydroamination of alkynes for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones has been achieved in a solvent-free condition. Cuβ zeolite was synthesized by impregnation method. The synthesized Cuβ was characterized by X-ray diffraction, Fourier transformation infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Pure Hβ (18 % yield) or Nano CuO (44 % yield) displayed poor catalytic activity, whereas 1 % Cuβ (96 % yield) showed higher catalytic activity for double hydroamination of alkynes due to the synergistic effect of CuO and Hβ zeolite in the reaction. The new protocol offers an appealing approach to a number of di-substituted quinazolinones with decent to excellent yields. The catalyst has been successfully recycled for up to 5 consecutive cycles.

Synthesis of Alkynyl Sulfides: Alkynyl Trifluoromethyl Sulfides and Thiocyanates

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Synthesis of Alkynyl Sulfides: Alkynyl Trifluoromethyl Sulfides and Thiocyanates

Various synthetic methodologies towards sulfur-containing alkynes are developed including C(sp)−S coupling, thiolation, S-alkynylation, trifluoromethylthiolation, and so on. In this review, the approaches to synthesize alkynyl sulfides over the last three years, as well as to form alkynyl trifluoromethyl sulfides and alkynylthiocyanates, are highlighted.


Abstract

Sulfur-containing alkynes, are important starting materials and intermediates in organic reactions. Some of sulfur-containing alkynes display interesting bioactivities and are potentially applied as drugs. Various synthetic methodologies towards sulfur-containing alkynes have been developed, including C(sp)−S coupling, thiolation, S-alkynylation, trifluoromethylthiolation, etc. In this review, the approaches towards alkynyl sulfides in recent 3 years, as well as to form alkynyl trifluoromethyl sulfides and alkynylthiocyanates were highlighted. Firstly, the property and application of alkynes were introduced. After presenting the superiority of sulfur-containing alkynes, their synthetic methods were classified and presented in details. According to different kinds of sulfur-containing alkynes, synthetic methodologies for alkynyl sulfides, alkynyl trifluoromethyl sulfides and alkynylthiocyanates were summarized and the proposed reaction mechanisms were demonstrated if available.

Industrially Promising β‐Ni(OH)2 Nanosheets Self‐Supported Electrode for Highly Efficient Electrooxidation of 5‐Hydroxymethylfurfural

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Industrially Promising β-Ni(OH)2 Nanosheets Self-Supported Electrode for Highly Efficient Electrooxidation of 5-Hydroxymethylfurfural

Electrooxidation: β-Ni(OH)2 petal-like nanosheets was synthesized by facile stepwise electrodeposition. It was found that the β- Ni(OH)2 has superior ability to electrooxidize 5-hydroxymethylfurfural (HMF) due to its better lattice matching with substrate intrinsic electrocatalytic activity, as well as the adsorption of HMF. It achieves a 2,5-furandicarboxylic acid (FDCA) yield of 80.6 % under 30 mA/cm2 in industrial electrolysis mode.


Abstract

The electrocatalytic selective oxidation of 5-hydroxymethylfurfural (HMF) presents a highly efficient and eco-friendly method for biomass utilization. Herein, we synthesized pure β-Ni(OH)2 and amorphous Ni(OH)2 on nickel foam (NF) using a facile stepwise electrodeposition technique and evaluated their catalytic performances for the oxidation of HMF to 2,5-furan dicarboxylic acid (FDCA). The β-Ni(OH)2 nanosheets-decorated electrode (β-NiNS/NF) exhibited excellent interfacial lattice matching with the substrate nickel, resulting in enhanced electron transfer at the catalyst-substrate interface, as confirmed by electrochemical analysis. Consequently, the β-NiNS/NF electrode displayed improved intrinsic electrocatalytic activity and interfacial stability. Additionally, it demonstrated effective HMF adsorption capability. These advantageous properties led to enhanced HMF conversion, selectivity, and structural stability. Notably, the β-NiNS/NF electrode achieved an unprecedented FDCA yield of 80.6 % under relatively large current density galvanostatic electrolysis commonly used in industry. Moreover, our investigation identified a novel possible oxidation pathway during HMF electrocatalysis. This study not only showcases an efficient and scalable synthetic approach but also highlights the potential of the β-NiNS/NF electrode for industrial HMF electrocatalytic oxidation under conditions involving relatively large applied currents.

PNP‐Pincer Ligands Armed With Methyls: New Tools To Control Sterics and Non‐Innocence

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PNP-Pincer Ligands Armed With Methyls: New Tools To Control Sterics and Non-Innocence

Methylation of PNP pincer arms has emerged as a new versatile tool to control steric hindrance and disable metal-ligand cooperative or ligand-centered reactivity. This Concept describes applications of the methylation approach in the control of catalytic activity and selectivity in hydrogenation, hydroboration and semihydrogenation, with Ru and Fe complexes.


Abstract

The widespread use of pyridine-based PNP pincer ligands has inspired the concept of metal-ligand cooperation (MLC), in which the reactivity at the deprotonated CH2 (or NH) arm of the ligand is proposed to play an important role. Several groups developed a family of PNP-type pincer ligands with methylated arms which were initially introduced to test the effect of blocking MLC in catalysis, but eventually led to unexpected consequences such as stabilization of unusual oxidation states, beneficial catalytic activity, or selectivity. Analysis of the sterics imposed by introducing Me groups revealed that arm protection can be an efficient tool to control sterics around the metal as an alternative to phosphine substitution, leading to much greater steric hinderance above and below pincer's coordination plane. This Concept will describe several illustrative examples which contrast the reactivity of classical CH2/NH-arm PNP pincers with their CMe2/NMe-armed counterparts, in particular related to Ru-catalyzed alcohol dehydrogenative coupling, Fe-catalyzed hydrogenation, hydroboration, and alkyne semihydrogenation.

Structural Diversity in Cyclometalated Diiridium(III) Complexes with Bridging syn and anti μ2‐Oxamidato and μ2‐Dithioxamidato Ligands

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Structural Diversity in Cyclometalated Diiridium(III) Complexes with Bridging syn and anti μ2-Oxamidato and μ2-Dithioxamidato Ligands

X-ray crystallography, NMR spectroscopy and computations reveal a remarkable diversity of structures in a series of diiridium complexes bridged by μ2-oxamidato and μ2-dithioxamidato ligands.


Abstract

Six new diiridium complexes containing 2-methyl-6-phenylpyridyl as the cyclometalating ligand with a μ2-oxamidato or a μ2-dithioxamidato ligand as the bridge have been synthesized in 60–73 % yields. These complexes were revealed by multinuclear NMR spectroscopy to contain inseparable mixtures of diastereomers (rac, ΔΔ/ΛΛ and meso, ΔΛ) with bridges in anti and syn configurations. The remarkable variety of isomers present was confirmed by X-ray crystallography on single crystals grown from mixtures of each complex. In one complex with a N,N’-bis(4-trifluoromethylphenyl)-μ2-oxamidato bridge, two single crystals of anti and syn isomers were structurally determined. Two single crystals of the μ2-dithioxamidato bridge complex were found to contain rac and meso forms of the syn isomer. Hybrid DFT computations on the four isomers of each diiridium complex revealed negligible energetic preferences for one isomer despite the methyl groups in the 2-methyl-6-phenylpyridyl cyclometalating ligands being close to the neighboring methyl groups and the bridge, thus supporting the experimental findings of isomer mixtures. Two distinct broad emissions with maxima at 522–529 nm and at 689–701 nm observed in these complexes in dichloromethane are attributed to mixed metal-ligand to ligand charge transfer (MLLCT) excited states involving the pyridyl and bridge moieties respectively with the aid of electronic structure computations.

Upgrading Waste Polylactide via Catalyst‐Controlled Tandem Hydrolysis‐Oxidation

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Upgrading Waste Polylactide via Catalyst-Controlled Tandem Hydrolysis-Oxidation

Highly selective degradation of polylactide (PLA) waste can be achieved through the use of supported-metal catalysts and molecular oxygen in water, process, known as “catalyst-controlled tandem hydrolysis-oxidation”, that offers a high flexibility and pathway-specific control. It is also scalable and operationally efficient, enabling complete conversion of PLA waste into valuable feedstocks such as pyruvic acid, acetic acid, or a mixture of acetic acid and formaldehyde through carbon upcycling.


Abstract

As plastic waste pollution continues to pose significant challenges to our environment, it is crucial to develop eco-friendly processes that can transform plastic waste into valuable chemical products in line with the principles of green chemistry. One major challenge is breaking down plastic waste into economically valuable carbon resources. This however presents an opportunity for sustainable circular economies. In this regard, a flexible approach is presented that involves the use of supported-metal catalysts to selectively degrade polylactide waste using molecular oxygen. This protocol has several advantages, including its operation under organic solvent-free and mild conditions, simplicity of implementation, and high atom efficiency, resulting in minimal waste. This approach enables the chemical upcycling of polylactide waste into valuable chemicals such as pyruvic acid, acetic acid, or a mixture containing equimolar amounts of acetic acid and formaldehyde, providing a viable alternative for accessing key value-added feedstocks from waste and spent plastics.

α‐Synuclein Drives Tau’s Cytotoxic Aggregates Formation through Hydrophobic Interactions

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α-Synuclein Drives Tau's Cytotoxic Aggregates Formation through Hydrophobic Interactions

Hydrophobic α-peptide induces fibrillization of tau and these hetero-aggregates are toxic in cell culture. ITC experiments showed the interaction of the α-peptide with tau full-length (441),4R (244-369), and both hexapeptides 275VQIINK280 and 306VQIVYK311 through hydrophobic interactions. Raman spectroscopy spectra showed conformational changes in the Amide region in the aggregates formed with full-length tau and α-syn peptide. The incubation of different types of aggregates in cell culture provokes the release of Lactate dehydrogenase (LDH), a cytoplasmic enzyme whose release is linked to membrane damage Altogether, the data suggest that α-synuclein peptide can drive the aggregation of full-length tau-provoking morphological and structural changes evoking cytotoxic effects.


Abstract

Tau and α-synuclein are proteins involved in pathologies known as tauopathies and synucleinopathies, respectively. Moreover, evidence shows that there is a crosstalk between them as is seen in the brains of individuals with sporadic neurodegenerative disorders. Based on that, we present data showing that the hydrophobic α-peptide 71VTGVTAVAQKTV82 induces the aggregation of the full-length tau fragment in the absence of heparin assessed by ThT. Moreover, AFM images reveal the presence of straight filaments and amorphous aggregates of full-length tau in the presence of the α-peptide. Additionally, ITC experiments showed the interaction of the α-peptide with tau full-length (441 amino acids),4R (amino acids from 244 to 369), and both hexapeptides 275VQIINK280 and 306VQIVYK311 through hydrophobic interactions. The Raman spectroscopy spectra showed conformational changes in the Amide region in the aggregates formed with full-length tau and α-syn peptide. Furthermore, the incubation of extracellular aggregates with N2a cells showed morphological differences in the cellular body and the nucleus suggesting cell death. Moreover,, the incubation of different types of aggregates in cell culture provokes the release of Lactate dehydrogenase (LDH). Altogether, we found that α-synuclein peptide can drive the aggregation of full-length tau-provoking morphological and structural changes evoking cytotoxic effects.

A Physical Impedance Model of Lithium Intercalation into Graphite Electrodes for a Coin‐Cell Assembly

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A Physical Impedance Model of Lithium Intercalation into Graphite Electrodes for a Coin-Cell Assembly

Electrochemical impedance spectroscopy is a sensitive research technique for gaining insights into the underlying mechanisms of battery systems. The authors present a physical impedance model that explains the three-stage mechanism of lithium-ion intercalation into graphite electrodes, using a two-electrode coin cell configuration across two initial lithiation and delithiation cycles. Important electrochemical parameters are provided and validated through these cycles. The results provide valuable insights and can serve as a benchmark for the future research.


Abstract

Graphite electrodes are widely used in commercial metal-ion batteries as anodes. Electrochemical impedance spectroscopy serves as one of the primary non-destructive techniques to obtain key information about various batteries during their operation. However, interpretation of the impedance response of graphite electrodes in contact with common organic electrolytes can be complicated. It is especially challenging, particularly when utilizing the 2-electrode configuration that is common in battery research. In this work, we elaborate on a physical impedance model capable of accurately describing the impedance spectra of a graphite|electrolyte|metallic Li system in a coin-cell assembly during two initial charge/discharge cycles. We analyze the dependencies of the model parameters for graphite and metallic lithium as a function of the state of charge to verify the model. Additionally, we suggest that the double layer capacitance values obtained during specific intercalation stages could help to determine if the area-normalized values align with the expected range. The data and the procedure necessary for calibration are provided.