Monthly Archives: March 2024

Synthesis, Structure and Antiferromagnetic Large‐Distance Long‐Range Coupling of the Ruthenate(V) Sr3(Ag2/3Sr1/6)RuO6

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Synthesis, Structure and Antiferromagnetic Large-Distance Long-Range Coupling of the Ruthenate(V) Sr3(Ag2/3Sr1/6)RuO6

Despite a wide spatial separation of the magnetic cations, the oxide Sr3(Ag2/3Sr1/6)RuO6 shows robust antiferromagnetic order below the relatively high Néel temperature of 79 Kelvin in magnetic fields up to at least 9 Tesla. The new oxido-ruthenate(V) was synthesized in a reactive potassium superoxide flux at high temperature.


Abstract

Black, air-stable crystals of the new ruthenate(V) Sr3(Ag2/3Sr1/6)RuO6 were grown in a silver ampoule using KO2 as oxidative flux. X-ray diffraction on single-crystals revealed a rhombohedral structure with the space group R c. Sr3(Ag2/3Sr1/6)RuO6 crystallizes isostructural to Sr4PtO6 in the K4CdCl6 structure type. By sharing trigonal faces, alternating [RuO6] octahedra and [(Ag2/3Sr1/6□1/6)O6 trigonal prisms form segmented chains running parallel to the crystallographic c-axis. Eightfold coordinated strontium cations are located between the rods. Regardless of the wide spatial separation of the magnetic cations (588 and 594 pm), Sr3(Ag2/3Sr1/6)RuO6 shows long-range antiferromagnetic order below the relatively high Néel temperature of 79 K in magnetic fields up to at least 9 T, as measurements of the magnetic susceptibility and heat capacity show. Despite the pseudo one-dimensional character of the structure, the characteristic of the susceptibility indicates a three-dimensional coupling of magnetic ions.

Unprecedented Pyrazine‐Bridged Guanidinate Rare Earth Complexes Through a Bridge Splitting Reaction Path

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Unprecedented Pyrazine-Bridged Guanidinate Rare Earth Complexes Through a Bridge Splitting Reaction Path

Two dinuclear pyrazine-bridged rare earth complexes were synthesized through a bridge splitting reaction, and unambiguously characterized by X-ray crystallography, spectroscopy, and computations. The cyclic voltammograms reveal multiple redox features which are attributed to the bridging pyrazine ligand. These materials represent promising building blocks for the development of supramolecular systems.


Abstract

The development of reaction pathways and ancillary ligand scaffolds is essential in the pursuit of higher nuclearity rare earth metal clusters that are relevant in storage materials and catalysis. Guanidinate anions represent attractive ligands due to their high degree of customizability allowing for facile alterations of both their steric and electronic properties. Here, we demonstrate an unprecedented bridge splitting reaction that shifts chloride anions in favor of a bridging neutral pyrazine to give pyrazine-bridged dinuclear guanidinate rare earth complexes, [{(Me3Si)2NC(NiPr)2}2RECl]2(μ-pyz) (RE =Y (1) and Er (2), pyz=pyrazine). Each six-coordinate metal center is ligated by two guanidinates, one chloride ligand, and one nitrogen atom from the bridging pyrazine unit. The molecules were characterized by X-ray crystallography, IR, NMR, and UV-Vis spectroscopy. DFT calculations conducted on 1 provide insight into both the bonding picture and the mechanism of complex formation. This type of reaction constitutes a seminal application of a bridge splitting mechanism to the rare earth metals.

Mechanistic Studies of Continuous Partial Methane Oxidation on Cu‐Zeolites Using Kinetic and Spectroscopic Methods

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Over the past few decades, a significant amount of research effort has focused on investigating the active site requirements and reaction mechanisms for partial methane oxidation (PMO) to methanol over copper-exchanged zeolites during stoichiometric and stepwise chemical looping routes. More recently, research efforts have expanded to include investigating the PMO reaction in a continuous catalytic regime, primarily focusing on determining the influence of catalyst composition on Cu speciation and structure and, in turn, on PMO rate and selectivity. The structures of candidate Cu active sites are commonly studied using a combination of ex situ and in situ spectroscopic approaches. In this perspective, we critically examine the prior literature on catalytic PMO over Cu-zeolites to identify key knowledge gaps that remain in our understanding as motivation for future research efforts. We identify opportunities for future research to address these gaps by adapting analogous interrogation techniques that have been successfully used to elucidate the active site requirements and mechanistic details of another catalytic redox reaction cycle on Cu-zeolites, the selective catalytic reduction (SCR) of nitrogen oxides (NOx).

Size‐Dependent Carbon Dioxide Reduction Activity of Copper Nanoparticle and Nanocluster Electrocatalysts

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The electrochemical carbon dioxide (CO2) reduction reaction (CRR, which can convert CO2 into useful compounds at room temperature and ambient pressure by using electricity derived from renewable energy source), has been attracting attention in recent years. This is because it can convert CO2 into useful compounds, which is pertinent to establishing a next-generation recycling-oriented energy society. However, further improvement of the electrocatalyst is required to improve its activity, selectivity, and durability. Among these, copper (Cu) can synthesize various hydrocarbons from CO2 and has been the most studied electrocatalyst for the CRR over many years. In particular, regarding ligand-protected Cu particles for the CRR, the size, shape, and ligands of Cu particles prepared by chemical reduction can be precisely controlled. In this review, we summarize previous research on the size-dependence of the CRR by using Cu particles (nanoparticles and nanoclusters) prepared by liquid-phase reduction, and discuss the current status of these studies for researchers on the electrochemical CRR.

Development and Characterization of Plant‐derived Aristatoside C and Davisianoside B Saponin‐loaded Phytosomes with Suppressed Hemolytic Activity

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Development and Characterization of Plant-derived Aristatoside C and Davisianoside B Saponin-loaded Phytosomes with Suppressed Hemolytic Activity

Phytosomal formulations of aristatoside C and davisianoside B compounds isolated from Cephalaria Aristata and Cephalaria davisina plants were prepared using the thin film hydration method. Physical characterization studies of the prepared phytosomal saponin formulation were carried out. The cytotoxic activity of phytosomal formulations was examined. The suppression of hemolytic activity of phytosomal formulations on erythrocytes caused by free saponins was investigated.


Abstract

Saponins are glycosides widely distributed in the plant kingdom and have many pharmacological activities. However, their tendency to bind to cell membranes can cause cell rupture, limiting their clinical use. In the previous study, aristatoside C and davisianoside B were isolated from Cephalaria species. Cytotoxicity assays showed that they are more active on A-549 cell lines than doxorubicin but caused hemolysis. In the current research, aristatoside C and davisianoside B were loaded to phytosomes called ALPs and DLPs respectively, and characterized for particle size, zeta potential, encapsulation efficiency, release kinetic, hemolytic activity, and cytotoxicity on A-549 cell line. DLPs maintained the cytotoxic activity of the free saponins against A-549 cells with IC50 of 9,64±0,02 μg/ml but dramatically reduced their hemolytic activity. Furthermore, temperature and time-dependent stability studies based on the size and zeta potential of ALPs and DLPs revealed that the phytosomes have sustained release properties over 2 weeks. Overall, DLPs displayed cytotoxicity against A-549 cells with minimal hemolysis and sustained release, highlighting their potential as nanotherapeutics for clinical applications.

Water‐Soluble μ‐oxo triruthenium Compound of Biological Interest: H‐Bonds Network and Interaction with HSA

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Water-Soluble μ-oxo triruthenium Compound of Biological Interest: H-Bonds Network and Interaction with HSA

The fully water-soluble compound [Ru3O(CH3COO)6(4-ampy)3]Cl (1) engages in a hydrogen-bonds network involving the 4-ampy ligands and methanol, Cl-, and the π-cloud of neighboring 4-ampy molecules. 1 has pKa=2.25 and logP=−0.86, showing its high hydrophilicity. 1 interacts with HSA by static mechanism through hydrogen-bonds formation, which was confirmed by molecular docking calculations.


Abstract

The water-soluble compound [Ru3O(CH3COO)6(4-ampy)3]Cl (1, 4-ampy=4-aminopyridine) was evaluated in terms of its biologically relevant properties. Compound 1 participates in a hydrogen bonding network which includes the NH2 substituents of the ancillary ligands, methanol molecules, the Cl− counter-ion, and a non-conventional hydrogen bond with the neighboring 4-ampy molecules′ π-cloud, as determined by X-ray measurements. One protonation equilibrium was observed at pH values below 2.3. Additionally, the compound exhibited a partition coefficient value of −0.86 (±0.07), indicating that it is highly hydrophilic. At 37 0C and pH=7.4 (phosphate buffer), compound 1 shows moderate (Ksv=2.4 104 M−1) and spontaneous (ΔG=−26.4 kJ mol−1) binding to human serum albumin (HSA) through ground-state association, which involves formation of hydrogen bonds (ΔH=−35.7 kJ mol−1 and, ΔS=−29.8 J mol−1 K−1). Molecular docking calculations support the formation of hydrogen bonds between 1 and HSA, and suggest subdomain IIA (site I), which contains the Trp-214 residue, as the primary interactive pocket, in agreement with the experimental static fluorescence quenching mechanism. Furthermore, a preliminary assay reveals that 1 has low cytotoxicity towards human glioblastoma U87-MG cells.

Strategies for the Construction of Multicyclic Phage Display Libraries

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Peptide therapeutics have gained great interest due to their multiple advantages over small molecule and antibody-based drugs. Peptide drugs are easier to synthesize, have the potential for oral bioavailability, and are large enough to target protein-protein interactions that are undruggable by small molecules. However, two major limitations have made it difficult to develop novel peptide therapeutics not derived from natural products, including the metabolic instability of peptides and the difficulty of reaching antibody-like potencies and specificities. Compared to linear and disulfide-monocyclized peptides, multicyclic peptides can provide increased conformational rigidity, enhanced metabolic stability, and higher potency in inhibiting protein-protein interactions. The identification of novel multicyclic peptide binders can be difficult, however, recent advancements in the construction of multicyclic phage libraries have greatly advanced the process of identifying novel multicyclic peptide binders for therapeutically relevant protein targets. This review will describe the current approaches used to create multicyclic peptide libraries, highlighting the novel chemistries developed and the proof-of-concept work done on validating these libraries against different protein targets.

First‐Principles Study of Carbon‐Substituted ZnO Monolayer for Adjusting Lithium Adsorption in Battery Application

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First-Principles Study of Carbon-Substituted ZnO Monolayer for Adjusting Lithium Adsorption in Battery Application

We investigate the structural stability, local density of states, bonding information, and charge distribution differences of C-substituted ZnO (C/VZnxOy ) monolayer structures, as well as their interactions with lithium atoms, using the density functional theory (DFT) method. The results indicate that all C/VZnxOy structures are stable. They bind as well as turn Li3 to Li3 + with varying binding strengths.


Abstract

Structural stability, local density of states, bonding information, and charge distribution differences of C-substituted ZnO (C/VZnxOy ) monolayer structures, as well as their interactions with lithium atoms, are investigated using the density functional theory (DFT) method. The energy required to generate vacancies in pristine ZnO monolayers is considerably high, but since the C atoms are strongly adsorbed in the vacant sites, the energy required to form C/VZnxOy structures is reduced. These lattice substitutions cause an alteration of the Zn d-states. The bonding analysis shows that the C−O interaction is stronger than the C−Zn interaction. So, it generates high stability for these structures. Furthermore, because the development of C/VZnxOy is aimed at lithium battery electrode applications, the most fundamental thing that needs to be examined initially is the interaction between the C/VZnxOy surfaces and the lithium atoms. Li3 strongly binds on all C/VZnxOy surfaces, and it turns to Li3 + based on a simple analysis of charge distribution differences. These findings will have a substantial impact on the future development of ZnO monolayers, and their potential as lithium battery electrodes can be studied further.

Visible Light‐Induced Metal‐free Arylation of Coumarin‐3‐carboxylates with Arylboronic Acids

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Visible Light-Induced Metal-free Arylation of Coumarin-3-carboxylates with Arylboronic Acids

A metal free photoredox strategy for alkenyl C−H arylation has been developed for the first time to synthesize a diverse range of 4-aryl coumarin-2-oxo-3-carboxylate derivatives.


Abstract

The present work represents a novel methodology for the selective arylation of coumarin-3-carboxylates with arylboronic acids via a photochemical route, marking the first-ever attempt for the direct alkenyl C−H arylation using rose bengal as a photocatalyst, which is a readily available and cost-effective alternative to transition metal catalysis. The reaction proceeds smoothly in MeOH/H2O solvent media in the presence of radical initiator affording the arylated products in good yields (60–80 %). The reaction parameters such as visible light, radical initiator, oxidant, anhydrous solvent, and inert atmosphere play a crucial role for the success of this methodology. The substituents present on the substrate show a significant effect on the conversion. This study provides a valuable contribution to the field of organic synthesis offering a new and efficient approach to the arylation of coumarin-3-carboxylic acid esters with a broad substrate scope and high functional group tolerance. It is a versatile method and provides a direct access to biologically relevant 4-arylcoumarin-3-carboxylates.