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Summary: The emergence of multidrug resistance in cancer cells necessitates the development of new therapeutic modalities. One way cancer cells orchestrate energy metabolism and redox homeostasis is through overloaded iron pools directed by iron regulatory proteins, including transferrin. Here, we demonstrate that targeting redox homeostasis using nitrogen-based heterocyclic iron chelators and their iron complexes efficiently prevents the proliferation of liver cancer cells (EC50: 340 nM for IITK4003) and liver cancer 3D spheroids. These iron complexes generate highly reactive Fe(IV)=O species and accumulate lipid peroxides to promote oxidative stress in cells that impair mitochondrial function. Subsequent leakage of mitochondrial cytochrome c activates the caspase cascade to trigger the intrinsic apoptosis pathway in cancer cells. This strategy could be applied to leverage the inherent iron overload in cancer cells to selectively promote intrinsic cellular apoptosis for the development of unique iron-complex-based anticancer therapeutics.

Various metalloenzymes employ O2 for oxidative reactions, which is crucial in catalysis and biological processes involving high-valent metal–oxygen species. This study introduces novel high-valent Co(III)–(μ-1,2-O2)–Co(IV) and Co(III)–(μ-1,2-O2˙−)–Co(III) complexes, stabilized by an electron-donating TPA* ligand. This study advances our understanding of Co–oxygen intermediates, which are key for water oxidation catalysis. [ABSTRACT FROM AUTHOR]

The exceptional reactivity observed in non‐heme iron enzymes can be attributed to their capability to access high‐valent iron oxygen species in their active site. Numerous inorganic model complexes have been reported to date, providing insights into the intricate structural and spectroscopic features of many iron‐containing enzymes and advancing our understanding of their enzymatic reaction pathways. While the reactivities of synthetic iron complexes have been evaluated using various oxidants, the investigation into the formation of reactive intermediates has primarily focused on acetonitrile. However, water, which serves as the medium in biological systems, has been less frequently employed in these studies. Motivated by this, we conducted a comprehensive study on the generation of key reactive species using various oxidants with a model complex, [(BnTPEN)Fe(II)(OTf)]+ (1) (where BnTPEN=N‐benzyl‐N,N,N‐tris(2‐pyridylmethyl)‐1,2‐diaminoethane) in water, which yielded important findings. In water, a quantitative yield of Fe(IV)=O species was achieved with the oxidant NaIO4. Additionally, we observed an equilibrium between side‐on Fe(III)−OO and Fe(III)−OOH, with the latter eventually converting to Fe(IV)=O. The insights gained from this study are likely to be relevant in the chemistry of other Fe(II) complexes with polypyridyl pentadentate ligands. [ABSTRACT FROM AUTHOR]

In this study, we developed a nitrate-coordinated iron–nickel hydroxide [NC–FeNi(OH)2] catalyst for hydrazine oxidation-assisted seawater splitting. Replacement of O2 evolution by hydrazine oxidation in a two-electrode setup resulted in a cell voltage of 1.20 V at 100 mA cm−2. This represents a voltage reduction of 470 mV compared to conventional seawater splitting. Additionally, NC–FeNi(OH)2 demonstrated remarkable stability over a period of 60 hours. [ABSTRACT FROM AUTHOR]

Electrocatalytic alcohol assisted water splitting has attained immense interest to improve the energy efficiency of water splitting. A series of metal–organic frameworks (MOFs) have been employed to replace the anodic oxygen evolution reaction with electrocatalytic alcohol oxidation. In this work, we have developed a multimetallic Prussian blue analogue (MnFeCoNiCu-PBA) nanoparticles using a room temperature method and utilized it for anodic oxygen evolution reaction (OER) and benzyl alcohol (BA) oxidation. The multimetallic composition resulted in the enhanced synergistic effect and increased the electrochemical surface area and electronic conductivity to improve the catalytic performance. Interestingly, MnFeCoNiCu-PBA nanoparticles exhibited a 100 mA cm–2 current density for BA oxidation at 1.57 V vs RHE, which was lower than that of OER (1.67 V vs RHE), with 98.9% Faradaic efficiency and 100% selectivity for benzoic acid production. Besides, the hydrogen production was improved by 2.2 times with the BA oxidation compared to the OER. During the electrocatalytic BA oxidation, multimetallic PBA was electrochemically reconstructed into an active metal hydroxide-(oxy)-hydroxide catalyst with high valent metal ions, further improving the activity. [ABSTRACT FROM AUTHOR]

Adding HClO4 to [(BnTPEN)MnIII–OO]+ in MeOH generates a short-lived MnIII–OOH species, which converts to a putative MnV＝O species. The potent MnV＝O species in MeCN oxidizes the pendant phenyl ring of the ligand in an intramolecular fashion. The addition of benzene causes the formation of (BnTPEN)MnIII-phenolate. These findings suggest that high valent Mn species have the potential to catalyze challenging aromatic hydroxylation reactions. [ABSTRACT FROM AUTHOR]

Lewis acid‐bound high valent Mn‐oxo species are of great importance due to their relevance to photosystem II. Here, we report the synthesis of a unique [(BnTPEN)Mn(III)−O−Ce(IV)(NO3)4]+ adduct (2) by the reaction of (BnTPEN)Mn(II) (1) with 4 eq. ceric ammonium nitrate. 2 has been characterized using UV/Vis, NMR, resonance Raman spectroscopy, as well as by mass spectrometry. Treatment of 2 with Sc(III)(OTf)3 results in the formation of (BnTPEN)Mn(IV)−O−Sc(III) (3), while HClO4 addition to 2 forms (BnTPEN)Mn(IV)−OH (4), reverting to 2 upon Ce(III)(NO3)3 addition. 2 can also be prepared by the oxidation of 1 eq. Ce(III)(NO3)3 with [(BnTPEN)Mn(IV)=O]2+ (5). In addition, the EPR spectroscopy revealed the elegant temperature‐dependent equilibria between 2 and Mn(IV) species. The binding of redox‐active Ce(IV) boosts electron transfer efficiency of 2 towards ferrocenes. Remarkably, the newly characterized Mn(III)−O−Ce(IV) species can carry out O‐atom and H‐atom transfer reactions. [ABSTRACT FROM AUTHOR]

The participation of both ligand and the metal center in the redox events has been recognized as one of the ways to attain the formal high valent complexes for the late 3d metals, such as Ni and Cu. Such an approach has been employed successfully to stabilize a Ni(III) bisphenoxyl diradical species in which there exist an equilibrium between the ligand and the Ni localized resultant spin. The present work, however, broadens the scope of the previously reported three oxidized equivalent species by conveying the approaches that tend to affect the reported equilibrium in CH3CN at 233 K. Various spectroscopic characterization revealed that employing exogenous N‐donor ligands like 1‐methyl imidazole and pyridine favors the formation of the Ni centered localized spin though axial binding. In contrast, due to its steric hinderance, quinoline favors an exclusive ligand localized radical species. DFT studies shed light on the novel intermediates′ complex electronic structure. Further, the three oxidized equivalent species with the Ni centered spin was examined for its hydrogen atom abstraction ability stressing their key role in alike reactions. [ABSTRACT FROM AUTHOR]

Non‐isothermal thermogravimetric tests of Terminalia chebula (Helikha) were conducted under inert N2 gas environment for temperatures (25–900°C) at heating rates of 10, 20, 35, and 55°C min−1. Kinetic triplet approximated employing five iso‐conversional methods namely, differential Friedman method (DFM), distributed activation method (DAEM), Ozawa–Flynn–Wall (OFW), Kissinger–Akahira–Sunose (KAS), and Starink (STK). Average values of activation energy (kJ mol−1) and frequency factor (min−1) calculated by the five models were 227.11, 2.98 × 1021 for DFM; 229.21, 4.63 × 1021 for KAS; 227.11, 3.81 × 1020 for OFW; 225.54, 1.15 × 1018 for STK; and 227.33, 3.02 × 1020 for DAEM respectively over the conversion range up to 0.8. In the kinetics study, correlation coefficient (R2) of greater than 0.97 is noticed in the conversion range of α = 0.1–0.8 for all models. From thermodynamic analysis, average values of ΔH (kJ mol−1), ΔG (kJ mol−1), and ΔS (kJ mol−1 K−1) for DAEM: 221.8, 179.69, and 0.065; for DFM: 236.40, 179.37, and 0.089; for KAS: 221.8, 179.69, and 0.065; for OFW: 220.22, 179.72, and 0.063; and for STK: 222.02, 179.68, and 0.066 were estimated to assess viability and reactivity of the process. Criado's master plots revealed that the data obtained from pyrolysis of selected biomass was followed a multistep reaction pathway. [ABSTRACT FROM AUTHOR]

The reaction of [(L)MnII]2+ (L = neutral polypyridine ligand framework) in the presence of mCPBA (mCPBA = m‐Chloroperoxybenzoic acid) generates a putative MnV=O species at RT. The proposed MnV=O species is capable of performing the aromatic hydroxylation of Cl‐benzoic acid derived from mCPBA to give [(L)MnIII(m‐Cl‐salicylate)]+, which in the presence of excess mCPBA generates a metastable [(L)MnV(O)(m‐Cl‐salicylate)]+, characterized by UV/Vis absorption, EPR, resonance Raman spectroscopy, and ESI‐MS studies. The current study highlights the fact that [(L)MnIII(m‐Cl‐salicylate)]+ formation may not be a dead end for catalysis. Further, a plausible mechanism has been proposed for the formation of [(L)MnV(O)‐m‐Cl‐salicylate)]+ from [(L)MnIII(m‐Cl‐salicylate)]+. The characterized transient [(L)MnV(O)‐m‐Cl‐salicylate)]+ reported in the current work exhibits high reactivity for oxygen atom transfer reactions, supported by the electrophilic character depicted from Hammett studies using a series of para‐substituted thioanisoles. The unprecedented study starting from a non‐heme neutral polypyridine ligand framework paves a path for mimicking the natural active site of photosystem II under ambient conditions. Finally, evaluating the intracellular effect of Mn(II) complexes revealed an enhanced intracellular ROS and mitochondrial dysfunction to prevent the proliferation of hepatocellular carcinoma and breast cancer cells. [ABSTRACT FROM AUTHOR]

Inspired by copper-based metalloenzymes, we aim to incorporate amino acids into our ligands to facilitate active copper intermediates that serve as functional and structural models for these enzymes. Herein, we report the synthesis of a Cu(II) complex with a C2 symmetric proline-based pseudopeptide LH2 (N,N′-(ethane-1,2-diyl)bis(pyrrolidine-2-carboxamide)), which is capable of supporting an [(L)Cu(III)]+ (3) intermediate in MeOH : CH3CN (1 : 20) at −30 °C. From comparative studies with the pyridine analog Cu(II) complex, it was demonstrated that the incorporation of amino acid in the ligand framework decreased the Cu(III)/Cu(II) redox potential significantly to react readily with mCPBA and CAN. The newly generated [(L)Cu(III)]+ can promote hydrogen atom abstraction reactions with phenolic substrates. [ABSTRACT FROM AUTHOR]