Molecular Complexes for Catalytic Ammonia Oxidation to Dinitrogen and the Cleavage of N−H Bonds

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Molecular Complexes for Catalytic Ammonia Oxidation to Dinitrogen and the Cleavage of N−H Bonds

Molecular systems, including homogeneous transition metals complexes and those of main group elements, are examined to illustrate the various types of stoichiometric N−H bond cleavage reactions. Molecular complexes that mediate catalytic NH3 oxidation to N2 through chemically or electrochemically driven reactions are described.


Abstract

The molecular complexes described herein use main-group elements or transition metals to control the stoichiometric cleavage of N−H bonds of ammonia (NH3) and/or catalyze chemical and electrochemical NH3 oxidation to dinitrogen (N2). We highlight the phenomenon of coordination-induced bond weakening and a variety of N−H bond cleavage mechanisms of NH3 including H atom abstraction, inter- and intra-molecular deprotonation reactions, oxidative addition, and σ -bond metathesis that have been demonstrated with molecular systems. We provide an overview of the molecular complexes reported for the rapidly developing field of NH3 oxidation catalysis to form N2. These systems exhibit several diverse structure types and innovative ligands to support transition metals capable of activating NH3 and mediating a challenging chemical transformation that requires breaking strong N−H bonds and forming an N−N bond en route to N2 formation.

An Overview of Syntheses of Salvinorin A and its Analogues

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An Overview of Syntheses of Salvinorin A and its Analogues

Salvinorin A, a potent human hallucinogen, uniquely activates the kappa-opioid receptor (κ-OR) with high efficacy and selectivity. Its novel structure lacks nitrogenous components, distinguishing it from other opioids. With a complex trans-decalin core and δ-lactone fused with a furan moiety, synthetic access to Salvinorin A remains challenging due to a sensitive epimerizable center. Despite considerable synthetic efforts, only nine syntheses have been produced. This review aims to offer insights into the primary strategies employed to accomplish the syntheses documented thus far.


Abstract

Salvinorin A is a powerful hallucinogen in humans, and a selective, high efficacy agonist of the kappa-opioid receptor (κ-OR). Salvinorin A is the first plant-derived ligand with high selectivity for κ-OR over other receptors, its structure is unrelated to any known opioid receptor ligands, even lacking any nitrogenous moieties. Mechanistically and pharmacologically, salvinorin A is distinct from other known hallucinogens in humans, making it the only selective κ-OR ligand to gain wide-spread interest outside of research. Structurally, salvinorin A bares a highly functionalized trans-decalin core, containing two quaternary centers, and is fused to a δ-lactone baring a furan moiety. Synthetic access of salvinorin A has been elusive due to a highly sensitive epimerizable center at carbon 8 (C8). All these features make salvinorin A a highly challenging synthetic target. With multiple synthetic efforts from around the world, only nine completed syntheses have been achieved to date. This review is intended to provide a look at the key strategies used to achieve the syntheses reported to date. We will summarize the efforts towards the syntheses of salvinorin A starting from Evans in 2007 to Barriault in 2023.

Dehydrogenative Oxidation of Alcohols by Reusable Iridium Catalysts with a Cooperative Polymer Ligand

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Dehydrogenative Oxidation of Alcohols by Reusable Iridium Catalysts with a Cooperative Polymer Ligand

High catalytic performance of the iridium-polymer complex for the dehydrogenative oxidation of alcohols was demonstrated. Bipyridonate moiety in the polymer structure acts as a cooperative “functional ligand”, realizing the enhancement of dehydrogenation of various alcohols. Further, recovered catalyst could be reused without loss of catalytic efficiency at least ten times.


Abstract

A series of iridium-polymer complexes containing bipyridonate moieties were synthesized. The high catalytic performance of the iridium-polymer complex for the dehydrogenative oxidation of alcohols was demonstrated. Notably, the bipyridonate moiety in the polymer structure acts as a chemically non-innocent “functional ligand”, realizing the enhancement of dehydrogenation process. While numerous metal-polymer catalysts have been reported so far, to our knowledge, introducing a “functional ligand” into a polymer chain that can operate cooperatively with transition metals by changing their structures during the catalytic processes is rare. The iridium-polymer complex could be easily separated from the product and recovered by precipitation upon the addition of methanol after the catalytic reaction. Furthermore, the recovered catalyst could be reused without loss of catalytic efficiency at least ten times.

Synthesis of Mono‐, Di‐, Tri‐, and Tetra‐cationic Pyridinium and Vinylpyridinium Modified [2.2]Paracyclophanes: Modular Receptors for Supramolecular Systems

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Synthesis of Mono-, Di-, Tri-, and Tetra-cationic Pyridinium and Vinylpyridinium Modified [2.2]Paracyclophanes: Modular Receptors for Supramolecular Systems

Modular Scaffolds for Supramolecular Systems: In this report, a new series of mono-, di-, tri-, and tetra-cationic pyridinium and vinylpyridinium modified [2.2]paracyclophanes (PCPs) is described. On N-methylation, the 3D PCPs bearing (cationic) pyridyl and vinylpyridinium functionalities have been demonstrated as efficient molecular receptors for application in supramolecular systems. The PCPs on grafting with light-responsive azobenzene (−N=N−) functional core as side-groups impart photosensitivity that can be remotely transformed on irradiation, offering photo-controlled smart molecular functions.


Abstract

In this report, a new series of mono-, di-, tri-, and tetra-cationic pyridinium and vinyl pyridinium-modified [2.2]paracyclophanes as useful molecular tectons for supramolecular systems are described. Regioselective functionalization at specific positions, followed by resolution step and successive transformations through Pd-catalyzed Suzuki-Miyaura and Mizoroki-Heck cross-coupling chemistry furnish a series of modular PCP scaffolds. In our proof-of-concept study, on N-methylation, the PCPs bearing (cationic) pyridyl functionalities were demonstrated as useful molecular receptors in host-guest supramolecular assays. The PCPs on grafting with light-responsive azobenzene (−N=N−) functional core as side-groups impart photosensitivity that can be remotely transformed on irradiation, offering photo-controlled smart molecular functions. Furthermore, the symmetrical PCPs bearing bi-, and tetra-pyridyl functionalities at the peripheries have enormous potential to serve as ditopic and tetratopic 3D molecular tectons for engineering non-covalent supramolecular assemblies with new structural and functional attributes.

Cross‐linked Triblock Peptide Capsules as Potential Oxygen Carriers

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Cross-linked Triblock Peptide Capsules as Potential Oxygen Carriers

We report the synthesis of perfluorodecalin (PFD)-filled triblock peptide capsules. The capsules exhibit a suitable diameter, a certain mechanical strength, a large diffusion constant, fast gas exchange rates, and little cytotoxicity. Given the above advantages, these PFD-filled peptide capsules are very promising as potential artificial oxygen carriers.


Abstract

Perfluorodecalin (PFD)-filled capsules have been studied for over 15 years as artificial oxygen carriers. However, none of these capsules combines good biocompatibility, good mechanical stability and dispersion stability. Here we propose to use synthetic triblock peptides containing a central block of cysteine units as a cross-linking shell material for capsules with both good biocompatibility and stability. Together with outer aspartate units and inner phenylalanine units, the resulting amphiphilic triblock peptides can encapsulate PFD efficiently to prepare capsules with a suitable diameter, a certain mechanical strength, a large diffusion constant, fast gas exchange rates, and little cytotoxicity. Given the above advantages, these PFD-filled peptide capsules are very promising as potential artificial oxygen carriers.

Amino Acid Modified Hyper‐Cross‐Linked Polymer Enabling High‐efficient Photocatalytic Amines Oxidation Coupled with H2O2 Production

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Amino Acid Modified Hyper-Cross-Linked Polymer Enabling High-efficient Photocatalytic Amines Oxidation Coupled with H2O2 Production

The introduction of L-phenylalanine resulting in a notable optimization of the bandgap structure, the utilization of photocarriers and the generation of ROS of HCPs H3LP-HCPs, and achieving close to 100 % conversion efficiency and 100 % selectivity toward benzylamine oxidation with a high yield of H2O2 (9.2 mmol ⋅ gcat −1 ⋅ h−1) under 455 nm LED lamp in air.


Abstract

The simultaneous production of imine and hydrogen peroxide (H2O2) via photocatalytic aerobic amine oxidation is a bright way to obtain value added products, however, rapid recombination of photogenerated charge leads to low conversion efficiency and selectivity. Herein, a metal-free amino acid modified hyper-cross-linked polymer (H3LP-HCPs) photocatalyst was synthesized for photocatalytic amines oxidation by regulating the ratio of L-phenylalanine (L-Phe) and hexaphenylbenzene (Hex). The results showed that the H3LP-HCPs photocatalyst with 1 : 3 molar ratio of L-Phe and Hex achieves close to 100 % conversion efficiency and 100 % selectivity toward benzylamine oxidation under 455 nm blue LED lamp irradiation. Furthermore, a high yield of H2O2 (9.2 mmol ⋅ gcat −1 ⋅ h−1) was synchronously obtained in benzylamine oxidation. Experiments and time-dependent density functional theory calculation results revealed that the N-functional groups in H3LP-HCPs photocatalyst not only remarkably broadens light-response range, but also facilitates electrons transfer from L-Phe to the Hex, thus accelerating photogenerated charge separation efficiency and the formation of reactive oxygen species (ROS).

Zinc selenide quantum dots as fluorescent labels for biomedical imaging

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Zinc selenide quantum dots as fluorescent labels for biomedical imaging

A facile, gram-scale synthesis of high-quality zinc selenide quantum dots using selenourea as the selenium source at a relatively low temperature is reported. The synthesized dots exhibit intense green emission due to donor-acceptor pair recombination of photogenerated carriers. ZnSe QDs show significant potential as nanoscale flourescent labels for biomedical imaging.


We, herein, report a facile green synthetic route for the gram-scale synthesis of high-quality thiol-derivatized zinc selenide quantum dots (QDs) using selenourea as the source of selenium at a relatively low temperature. The one-pot synthesis of colloidal dots has been achieved by selenizing zinc (II) acetate in a non-coordinating solvent medium. The structural, microstructural, optical, thermal, textural and electronic properties of the as-synthesized monodisperse ZnSe dots have been investigated in detail. We attribute the observed green emission from the dots to the donor-acceptor pair (DAP) recombination of photoexcited charge carriers. All the findings of the investigation indicate that ZnSe QDs hold great promise as a nanoscale emissive probe to unveil cellular dynamics beyond the capabilities of conventional imaging techniques.

Electrochemical studies: Biological evaluation of the homometallic‐binuclear complexes of malonate‐derived tetradentate O2N2 ligand

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Electrochemical studies: Biological evaluation of the homometallic-binuclear complexes of malonate-derived tetradentate O2N2 ligand

Different metal complexes through mixing N 1,N 3-bis(4-phenylthiazol-2-yl)malonamide with Cr(III), Fe(III), Cu(II), and Zn(II) nitrates in a 1:2 ratio in excellent yield and spectral analysis investigation were synthesized and showed change of SEM of surface of ligand and Cu(II) complex. Furthermore, antimicrobial activities and docking simulation also showed electrochemical behavior and Cr complex acts as a conducting material that can be used in supercapacitor. Additionally, computational investigation was made with basis set DFT/B3LYP/LANL2DZ to find the theoretical stability and FMO orbitals and evaluate physical parameter.


Novel metal complexes were synthesized by mixing N 1 ,N 3 -bis(4-phenylthiazol-2-yl)malonamide with Cr (III), Fe (III), Cu (II), and Zn (II) nitrates in a 1:2 (L: metal) ratio. Through the use of several analytical and spectral methods, the structures of all compounds were determined. It was determined that the novel ligand functions through O2N2 sites as a neutral tetradentate. The thermal stability and the thermodynamic parameters were evaluated using thermal gravimetric analysis and the Coats-Redfern equations. Powder X-ray diffraction investigation revealed the type of unit cell and the degree of crystallinity. The complexes were further tested for their antibacterial efficacy, with molecular simulation using several proteins demonstrating the strongest action against a range of pathogens. Optimization for all compounds were made through the basis set DFT/B3LYP/LANL2DZ to find the theoretical stability, FMO orbitals, energy gaps, molecular electrostatic potentials (MEPs), and evaluate physical parameter. Here, the electrochemical properties of the metal complexes were investigated using cyclic voltammetry and electrochemical impedance spectroscopy methods. Additionally, [Cr2(L)(NO3)4(H2O)4](NO3)2 complex has been authorized that has high electrocatalytic characteristics, making it attractive for use in supercapacitor applications.