Non‐noble transition metal complexes have attracted growing interest as efficient electrocatalysts for oxygen reduction reaction (ORR) while their activities still lack rational and effective ...regulation. Herein, we propose a d–π conjugation strategy for rough and fine tuning of ORR activity of TM‐BTA (TM=Mn/Fe/Co/Ni/Cu, BTA=1,2,4,5‐benzenetetramine) coordination polymers. By first‐principle calculations, we elucidate that the strong d–π conjugation elevates the dxz/dyz orbitals of TM centers to enhance intermediate adsorption and strengthens the electronic modulation effect from substitute groups on ligands. Based on this strategy, Co‐TABQ (tetramino benzoquinone) is found to approach the top of ORR activity volcano. The synthesized Co‐TABQ with atomically distributed Co on carbon nanotubes exhibits a half‐wave potential of 0.85 V and a specific current of 127 mA mgmetal−1 at 0.8 V, outperforming the benchmark Pt/C. The high activity, low peroxide yield, and considerable durability of Co‐BTA and Co‐TABQ promise their application in oxygen electrocatalysis. This study provides mechanistic insight into the rational design of transition metal complex catalysts.
A two‐step strategy was proposed to optimize the ORR activity of TM‐BTA (TM=Mn/Fe/Co/Ni/Cu, BTA=1,2,4,5‐benzenetetramine) analogs by screening preliminarily TM centers and subsequently substituent groups. Strong d–π conjugation in TM‐BTA is found to elevate the dxz/dyz orbitals, which enhances the activity of TM centers, and also enlarges the impact of ligand functional groups on d orbitals of TM centers.
Pt
complexes are commonly used to treat cancer. To reduce their side effects and improve their pharmacological properties, Pt
complexes are being developed as prodrug candidates that are activated by ...reduction in cancer cells. Concomitantly, Ru
polypyridine complexes have gained much attention as photosensitizers for use in photodynamic therapy due to their attractive characteristics. In this article, a novel Pt
-Ru
conjugate, which combines cancer activated chemotherapy with PDT, is presented. Upon entering the cancer cell, the Pt
centre is reduced to Pt
and the axial ligands including the Ru
complex and phenylbutyrate are released. As each component has its individual targets, the conjugate exerts a multi-target and multi-action effect with (photo-)cytotoxicity values upon irradiation up to 595 nm in the low nanomolar range in various (drug resistant) 2D monolayer cancer cells and 3D multicellular tumour spheroids.
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•Coordination Polymers based on calixarene macrocyclic backbones are reviewed.•Chemical modifications of the lower and upper rim of calixarenes are detailed.•The coordination ...abilities of calixarene based ligands towards metals are presented.•The useful properties of the resulting architectures are highlighted.
The solid-state structures of 1D–3D Coordination Polymers based on the macrocyclic calixarene backbone have been reviewed, based on the chemical nature of appended substituents on the macrocycle platform. The coordination propensity of this class of ligands is analysed, taking into account the different coordinating atoms/groups that can be located on the macrocyclic ligand: (1) the unmodified inherently coordinating thiacalix4arene with the S bridges as donor atoms; (2) different conformations of calixnarene units, with appended O donor atoms; (3) the chemical modification of the upper rim of calixnarenes and thiacalixnarenes, with coordinating groups, in particular the use of the sulfonate groups; (4) calix4arenes, thiacalix4arenes and tetramercaptothiacalix4rene that have been modified at their lower rim (mono, di and tetra substitution) with coordinating groups like cyano, carboxylate, pyridyl and pyrazolyl groups. All the formed coordination networks have been described. A special attention has been drawn to the structural and functional properties of these extended networks: magnetic, luminescence, adsorption and catalytic properties. Perspectives and future challenges in this emerging field are also discussed.
Self-assembly of a flexible tritopic aniline and 3-substituted 2-formylpyridine subcomponents around iron(II) templates gave rise to a low-spin Fe
L
capsule, whereas a high-spin Fe
L
sandwich species ...formed when a sterically hindered 6-methyl-2-formylpyridine was used. The Fe
L
cage adopted a new structure type with S
symmetry, having two mer-Δ and two mer-Ʌ metal vertices, as confirmed by NMR and X-ray crystallographic analysis. The flexibility of the face-capping ligand endows the resulting Fe
L
framework with conformational plasticity, enabling it to adapt structurally from S
to T or C
symmetry upon guest binding. The cage also displayed negative allosteric cooperativity in simultaneously binding different guests within its cavity and at the apertures between its faces.
A bidentate chiral dithiol (diBINAS) is utilised to bridge Au
nanoclusters to form oligomers. Separation by size allows the isolation of fractions that are stable thanks to the bidentate nature of ...the linker. The structure of the products is elucidated by small-angle X-ray scattering and calculated using density functional theory. Additional structural details are studied by diffusion-ordered nuclear magnetic resonance spectroscopy, transmission electron microscopy and matrix-assisted laser desorption/ionization time of flight mass spectrometry. Significant changes in the optical properties are analysed by UV/Vis and fluorescence spectroscopies, with the latter demonstrating a strong emission enhancement. Furthermore, the emergent chiral characteristics are studied by circular dichroism. Due to the geometry constraints of the nanocluster assemblies, diBINAS can be regarded as a templating molecule, taking a step towards the directed self-assembly of metal clusters.
Sepsis, characterized by immoderate production of multiple reactive oxygen and nitrogen species (RONS), causes high morbidity and mortality. Despite progress made with nanozymes, efficient ...antioxidant therapy to eliminate these RONS remains challenging, owing largely to the specificity and low activity of exploited nanozymes. Herein, an enzyme‐mimicking single‐atom catalyst, Co/PMCS, features atomically dispersed coordinatively unsaturated active Co‐porphyrin centers, which can rapidly obliterate multiple RONS to alleviate sepsis. Co/PMCS can eliminate O2.− and H2O2 by mimicking superoxide dismutase, catalase, and glutathione peroxidase, while removing .OH via the oxidative‐reduction cycle, with markedly higher activity than nanozymes. It can also scavenge .NO through formation of a nitrosyl–metal complex. Eventually, it can reduce proinflammatory cytokine levels, protect organs from damage, and confer a distinct survival advantage to the infected sepsis mice.
Better than nanozymes: By mimicking triple antioxidant enzymes, conducting an oxidative‐reduction cycle, and formation of a nitrosyl–metal complex, an enzyme‐mimicking single‐atom catalyst (SAzyme) can quickly obliterate multiple reactive oxygen and nitrogen species (RONS) and reduce proinflammatory cytokine levels to alleviate sepsis.
Metal complexes have shown promise as photosensitizers for cancer diagnosis and therapeutics. However, the vast majority of metal photosensitizers are not ideal and associated with several ...limitations including pharmacokinetic limitations, off-target toxicity, fast systemic clearance, poor membrane permeability, and hypoxic tumour microenvironments. Metal complex functionalized nanomaterials have the potential to construct multifunctional systems, which not only overcome the above defects of metal complexes but are also conducive to modulating the tumour microenvironment (TME) and employing combination therapies to boost photodynamic therapy (PDT) efficacy. In this review, we first introduce the current challenges of photodynamic therapy and summarize the recent research strategies (such as metal coordination bonds, self-assembly, π-π stacking, physisorption, and so on) used for preparing metal complexes functionalized nanomaterials in the application of PDT.
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•Centered and non-centered coordination in smaller fullerenes.•Interplay between bonding and steric effects.•Ti, offers a loose fit, in contrast to Zr.•Centered coordination modes, ...involves contribution from the overall cage.•Dynamic features are described.
The endohedral metallic fullerenes (EMF), exhibit the interplay between stabilizing interaction and steric hindrance effects owing to the internal size provided by the fullerene cage. The small C28 fullerene, offers the smallest cavity realized to encapsulate metal ions. The characterized energy minima structure for Ti@C28 exhibits a non-centered disposition of the Ti atom in a spherical cage, in contrast to Zr@C28, where Zr atom is located at the very center. Here, we explore variations of the 3d-Ti-π-C28 bonding interaction from a centered conformation towards the non-centered disposition in comparison to Zr@C28. Our results show that in such structures, a variation of both electrostatic and orbital character of the metal-cage interaction can be observed. Interestingly, the orbital term is largely favored underlying the more effective bonding in the latter conformation, playing a crucial role in the determination of the coordination mode. In addition, molecular dynamics simulations were employed to determine the endohedral atom variation at 300°K, denoting that Zr@C28 cage exhibits more structural variation in comparison to Ti@C28, owing to the movement of a more fitted metal center induces larger variations to the cage distance.
Agents inducing both apoptosis and autophagic death can be effective chemotherapeutic drugs. In our present work, we synthesized two organometallic gold(III) complexes harboring C^N ligands that ...structurally resemble tetrahydroisoquinoline (THIQ): Cyc-Au-1 (AuL
Cl
, L
= 3,4-dimethoxyphenethylamine) and Cyc-Au-2 (AuL
Cl
, L
= methylenedioxyphenethylamine). In screening their in vitro activity, we found both gold complexes exhibited lower toxicity, lower resistance factors, and better anticancer activity than those of cisplatin. The organometallic gold(III) complexes accumulate in mitochondria and induce elevated ROS and an ER stress response through mitochondrial dysfunction. These effects ultimately result in simultaneous apoptosis and autophagy. Importantly, compared to cisplatin, Cyc-Au-2 exhibits lower toxicity and better anticancer activity in a murine tumor model. To the best of our knowledge, Cyc-Au-2 is the first organometallic Au(III) compound that induces apoptosis and autophagic death. On the basis of our results, we believe Cyc-Au-2 to be a promising anticancer agent or lead compound for further anticancer drug development.
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