The Hg−C bond of MeHgCl, a ubiquitous environmental toxicant, is notoriously inert and exceedingly difficult to cleave. The cleavage of the Hg−C bond of MeHgCl at low temperature, therefore, is of significant importance for human health. Among various bis(imidazole)-2-selones LnSe (n=1–4, or 6), the three-spacer L3Se shows extraordinarily high reactivity in the degradation of various mercury alkyls including MeHgCl because of its unique ability to coordinate through κ2-fashion, in which both the Se atoms simultaneously attack the Hg center of mercury alkyls for facile Hg−C bond cleavage. It has the highest softness (σ) parameter and the lowest HOMO(LnSe)-LUMO(MeHgX) energy gap and, thus, L3Se is the most reactive among LnSe towards MeHgX (X=Cl or I). L3Se is highly efficient, more than L1Se, in restoring the activity of antioxidant enzyme glutathione reductase (GR) that is completely inhibited by MeHgCl; 80 \% GR activity is recovered by L3Se relative to 50 \% by L1Se. It shows an excellent cytoprotective effect in liver cells against MeHgCl-induced oxidative stress by protecting vital antioxidant enzymes from inhibition caused by MeHgCl and, thus, does not allow to increase the intracellular reactive oxygen species (ROS) levels. Furthermore, it protects the mitochondrial membrane potential (ΔΨm) from perturbation by MeHgCl. Major Hg-responsive genes analyses demonstrate that L3Se plays a significant role in MeHg+ detoxification in liver cells. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Karri R.

Chalana A.

Kumar B.

Jayadev S.K.

Roy G.

<p>Shiv Nadar University is a comprehensive, multidisciplinary, research-focused, and student-centric University offering a full range of academic programs at the undergraduate, postgraduate and doctoral level. With state-of-the-art infrastructure, the University comprises of academic wings, sophisticated labs, international standard sports facilities, amphitheaters, auditorium, conference rooms and smart classrooms. The University&rsquo;s goal is to become internationally recognized for the quality of its research and creative endeavors and their applicability to improving quality of life, generating new insights and expanding the boundaries of human knowledge creativity. Committed to excellence in teaching, research and service, the University aims to serve the higher education needs of India and the world beyond.</p>

Shiv Nadar University

Chemistry - A European Journal

<p>Two new arene ruthenium(II) complexes with chemical formula [Ru2(η6-p-cymene)2(μ-L1)(μ-Cl)Cl2] [Ru]-1 and [Ru(η6-p-cymene)(L2)Cl2] [Ru]-2 (L1 = 5-phenyl-2H-tetrazole and L2 = 2-(2H-tetrazol-5-yl)pyridine) were synthesized by the reaction of [{(η6-p-cymene)RuCl2}2] with two bidentate ligands L1 and L2. Both the complexes were structurally characterized using single-crystal X-ray diffraction and other analytical techniques. The X-ray crystal structures of both the complexes revealed the coordination of tetrazolate ligands to two Ru(II) centres in bridging mode in [Ru]-1, whereas one Ru(II) centre in [Ru]-2 in chelating fashion, with overall pseudo-octahedral geometry. The resulted complexes were screened for their cytotoxic activity against three different cancer cell lines, HCT116 (colon cancer), HepG2 (liver cancer) and MCF7 (breast cancer) under in vitro conditions. Interestingly, [Ru]-1 showed much higher cytotoxicity with respect to [Ru]-2 against all the screened cancer cell lines and even better than cisplatin. For exploring the mechanism of action of [Ru]-1, reactive oxygen species (ROS) production, alterations in mitochondrial membrane potential and gene expression profiling of apoptosis related genes (Bcl2, caspase-3 and caspase-9) were also evaluated. The cancerous cells treated with [Ru]-1 showed an increase in intracellular ROS levels, disruption of mitochondrial membrane potential, up-regulation of proapoptotic caspase-3 and caspase-9 and down-regulation of antiapoptotic Bcl2. The results concluded that [Ru]-1 induced apoptosis through oxidative stress mediated activation of intrinsic pathway by generating intracellular ROS, loss of MMP and alteration of expression of apoptosis related genes. In addition, antimetastatic activity of [Ru]-1 was observed by wound healing assay showing anti-migratory property. The dual properties, antimetastatic activity and high cytotoxicity make [Ru]-1 potent platform for the development of new anticancer agents. © 2021 John Wiley &amp; Sons, Ltd.</p>

Applied Organometallic Chemistry

In vitro evaluation of cytotoxicity and antimetastatic properties of novel arene ruthenium(II)-tetrazolato compounds on human cancer cell lines

We show that the N-methylimidazole-based selone ImOHSe having an N-CH2CH2OH substituent has the remarkable ability to degrade methylmercury by two distinct pathways. Under basic conditions, ImOHSe converts MeHgCl into biologically inert HgSe nanoparticles and Me2Hg via the formation of an unstable intermediate (MeHg)2Se (pathway I). However, under neutral conditions, in the absence of any base, ImOHSe facilitates the cleavage of the Hg-C bond of MeHgCl at room temperature (23 °C), leading to the formation of a stable cleaved product, the tetracoordinated mononuclear mercury compound (ImOHSe)2HgCl2 and Me2Hg (pathway II). The initial rate of Hg-C bond cleavage of MeHgCl induced by ImOHSe is almost 2-fold higher than the initial rate observed by ImMeSe. Moreover, we show that ImYSe (Y = OH, Me) has an excellent ability to dealkylate Me2Hg at room temperature. Under acidic conditions, in the presence of excess ImYSe, the volatile and toxic Me2Hg further decomposes to the tetracoordinated mononuclear mercury compound [(ImYSe)4Hg]2+. In addition, the treatment of ImOHSe with MeHgCys or MeHgSG in phosphate buffer (pH 8.5) afforded water-soluble Hg(SeS) nanoparticles via unusual ligand exchange reactions, whereas its derivative ImOMeSe or ImMeSe, lacking the N-CH2CH2OH substituent, failed to produce Hg(SeS) nanoparticles under identical reaction conditions. © 2017 American Chemical Society.

Inorganic Chemistry

Cleavage of Hg-C Bonds of Organomercurials Induced by ImOHSe via Two Distinct Pathways

Here we report that [S2]-donor ligands BmmOH, BmmMe, and BmeMe bind rapidly and reversibly to the mercury centers of organomercurials, RHgX, and facilitate the cleavage of Hg-C bonds of RHgX to produce stable tetracoordinated Hg(II) complexes and R2Hg. Significantly, the rate of cleavage of Hg-C bonds depends critically on the X group of RHgX (X = BF4-, Cl-, I-) and the [S2]-donor ligands used to induce the Hg-C bonds. For instance, the initial rate of cleavage of the Hg-C bond of MeHgI induced by BmeMe is almost 2-fold higher than the initial rate obtained by BmmOH or BmmMe, indicating that the spacer between the two imidazole rings of [S2]-donor ligands plays a significant role here in the cleavage of Hg-C bonds. Surprisingly, we noticed that the initial rate of cleavage of the Hg-C bond of MeHgI induced by BmeMe (or BmmMe) is almost 10-fold and 100-fold faster than the cleavage of Hg-C bonds of MeHgCl and [MeHg]BF4 respectively, under identical reaction conditions, suggesting that the Hg-C bond of [MeHg]BF4 is highly inert at room temperature (21 °C). We also show here that the nature of the final stable cleaved products, i.e. Hg(II) complexes, depends on the X group of RHgX and the [S2]-donor ligands. For instance, the reaction of BmmMe with MeHgCl (1:1 molar ratio) afforded the formation of the 16-membered metallacyclic dinuclear mercury compound (BmmMe)2Hg2Cl4, in which the two Cl atoms are located inside the ring, whereas due to the large size of the I atom, a similar reaction with MeHgI yielded polymeric [(BmmMe)2HgI2]m·(MeHgI)n. However, the treatment of BmmMe with ionic [RHg]BF4 led to the formation of the tetrathione-coordinated mononuclear mercury compound [(BmmMe)2Hg](BF4)2, where BF4- serves as a counteranion. © 2017 American Chemical Society.

Activation of the Hg-C Bond of Methylmercury by [S2]-Donor Ligands

Organomercurials including methylmercury are ubiquitous environmental pollutants and highly toxic to humans. Now it could be shown that N-methylimidazole based thiones/selones having an N-CH2CH2OH substituent are remarkably effective in detoxifying various organomercurials to produce less toxic HgE (E=S, Se) nanoparticles. Compounds lacking the N-CH2CH2OH substituent failed to produce HgE nanoparticles upon treatment with organomercurials, suggesting that this moiety plays a crucial role in the detoxification by facilitating the desulfurization and deselenization processes. This novel way of detoxifying organomercurials may lead to the discovery of new compounds to treat patients suffering from methylmercury poisoning. Getting rid of mercury: Insoluble HgE (E=S, Se) nanoparticles (NPs) are formed under physiologically relevant conditions when organomercurials are treated with N-methylimidazole-based thiones/selones having an N-CH2CH2OH substituent. Compounds lacking the N-CH2CH2OH substituent failed to produce HgE NPs upon treatment with organomercurials under identical reaction conditions. A novel pathway of detoxifying various organomercurials is described. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Angewandte Chemie - International Edition

Chemical Detoxification of Organomercurials

Herein, we describe the synthesis and biomimetic activity of a series of N,N-disubstituted thiones and selones that contain an imidazole pharmacophore. The N,N-disubstituted thiones do not show any inhibitory activity towards LPO-catalyzed oxidation reactions, but their corresponding N,N-disubstituted selones exhibit inhibitory activity towards LPO-catalyzed oxidation reactions. Substituents on the N atom of the imidazole ring appear to have a significant effect on the inhibition of LPO-catalyzed oxidation and iodination reactions. Selones 16, 17, and 19, which contain methyl, ethyl, and benzyl substituents, exhibit similar inhibition activities towards LPO-catalyzed oxidation reactions with IC50 values of 24.4, 22.5, and 22.5 μM, respectively. However, their activities are almost three-fold lower than that of the commonly used anti-thyroid drug methimazole (MMI). In contrast, selone 21, which contains a N-CH2CH2OH substituent, exhibits high inhibitory activity, with an IC50 value of 7.2 μM, which is similar to that of MMI. The inhibitory activity of these selones towards LPO-catalyzed oxidation/iodination reactions is due to their ability to decrease the concentrations of the co-substrates (H2O2 and I 2), either by catalytically reducing H2O2 (anti-oxidant activity) or by forming stable charge-transfer complexes with oxidized iodide species. The inhibition of LPO-catalyzed oxidation/iodination reactions by N,N-disubstituted selones can be reversed by increasing the concentration of H2O2. Interestingly, all of the N,N-disubstituted selones exhibit high anti-oxidant activities and their glutathione peroxidase (GPx)-like activity is 4-12-fold higher than that of the well-known GPx-mimic ebselen. These experimental and theoretical studies suggest that the selones exist as zwitterions, in which the imidazole ring contains a positive charge and the selenium atom carries a large negative charge. Therefore, the selenium moieties of these selones possess highly nucleophilic character. The 77Se NMR chemical shifts for the selones show large upfield shift, thus confirming the zwitterionic structure in solution. Stop, in the name of love: The inhibition of lactoperoxidase (LPO)-catalyzed reactions by a series of N,N-disubstituted thiones and selones that contain an imidazole pharmacophore is described. The inhibitory activity not only depends on the substituent that is attached to the nitrogen atom, but also on the nature of the chalcogen atom. The inhibition of LPO activity by selones is due to their ability to scavenge the substrate, hydrogen peroxide. Copyright © 2013 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Chemistry - An Asian Journal

Inhibition of lactoperoxidase-catalyzed oxidation by imidazole-based thiones and selones: A mechanistic study

Metallomics

Disruption of selenium transport and function is a major contributor to mercury toxicity in zebrafish larvae

Exploiting the κ2-Fashioned Coordination of [Se2]-Donor Ligand L3Se for Facile Hg−C Bond Cleavage of Mercury Alkyls and Cytoprotection against Methylmercury-Induced Toxicity