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1. Isolable iodosylarene and iodoxyarene adducts of Co and their O-atom transfer and C–H activation reactivity

   https://doi.org/10.1039/C8SC01167B  

   Hill, Ethan A.; Kelty, Margaret L.; Filatov, Alexander S.; Anderson, John S. (January 2018, Chemical Science)

   We report an unusual series of discrete iodosyl- and iodoxyarene adducts of Co. The formation of these adducts was confirmed by a suite of techniques including single crystal X-ray diffraction. The reactivity of these adducts with O-atom acceptors and an H-atom donor has been investigated with particular focus on elucidating mechanistic details. Detailed kinetic analysis allows for discrimination between proposed oxo and adduct mediated mechanisms. In particular, these reactions have been interrogated by competition experiments with isotopically labelled mixtures which shows that all of the studied adducts display a large KIE. These studies suggest different mechanisms may be relevant depending on subtle substituent changes in the adduct complexes. Reactivity data are consistent with the involvement of a transient oxo complex in one case, while the two other systems appear to react with substrates directly as iodosyl- or iodoxyarene adducts. These results support that reactivity typically ascribed to metal-oxo complexes, such as O-atom transfer and C–H activation, can also be mediated by discrete transition metal iodosyl- or iodoxyarene adducts that are frequent intermediates in the generation of oxo complexes. The influence of additional Lewis acids such as Sc 3+ on the reactivity of these systems has also been investigated. 

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2. Redox and Nucleophilic Reactions of Naphthoquinones with Small Thiols and Their Effects on Oxidization of H2S to Inorganic and Organic Hydropolysulfides and Thiosulfate

   https://doi.org/10.3390/ijms24087516  

   Olson, Kenneth R.; Clear, Kasey J.; Gao, Yan; Ma, Zhilin; Cieplik, Nathaniel M.; Fiume, Alyssa R.; Gaziano, Dominic J.; Kasko, Stephen M.; Luu, Jennifer; Pfaff, Ella; et al (April 2023, International Journal of Molecular Sciences)

   Naphthoquinone (1,4-NQ) and its derivatives (NQs, juglone, plumbagin, 2-methoxy-1,4-NQ, and menadione) have a variety of therapeutic applications, many of which are attributed to redox cycling and the production of reactive oxygen species (ROS). We previously demonstrated that NQs also oxidize hydrogen sulfide (H2S) to reactive sulfur species (RSS), potentially conveying identical benefits. Here we use RSS-specific fluorophores, mass spectroscopy, EPR and UV-Vis spectrometry, and oxygen-sensitive optodes to examine the effects of thiols and thiol-NQ adducts on H2S-NQ reactions. In the presence of glutathione (GSH) and cysteine (Cys), 1,4-NQ oxidizes H2S to both inorganic and organic hydroper-/hydropolysulfides (R2Sn, R=H, Cys, GSH; n = 2–4) and organic sulfoxides (GSnOH, n = 1, 2). These reactions reduce NQs and consume oxygen via a semiquinone intermediate. NQs are also reduced as they form adducts with GSH, Cys, protein thiols, and amines. Thiol, but not amine, adducts may increase or decrease H2S oxidation in reactions that are both NQ- and thiol-specific. Amine adducts also inhibit the formation of thiol adducts. These results suggest that NQs may react with endogenous thiols, including GSH, Cys, and protein Cys, and that these adducts may affect both thiol reactions as well as RSS production from H2S. 

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3. Osme Bond: Geometric and Energetic Features in the Adducts between OsO ₄ and Lewis Bases

   https://doi.org/10.1002/chem.202304240  

   Calabrese, Miriam; Pizzi, Andrea; Daolio, Andrea; Beccaria, Roberta; Lo_Iacono, Cristina; Scheiner, Steve; Resnati, Giuseppe (February 2024, Chemistry – A European Journal)

   Abstract Adducts between OsO₄and Lewis bases exert a role in important oxidation processes such as epoxidation and dihydroxylation. It has been shown that the attractive interaction driving the formation of these adducts is a σ‐hole bond involving the metal as the electrophilic species; the term Osme Bond (OmB) was proposed for designating it. Here some new adducts between OsO₄and various bases have been characterized through single crystal x‐ray diffraction (XRD) and computational studies (density functional theory, DFT), confirming the existence of a robust correlation between σ‐hole interaction energy and deformation of the tetrahedral geometry of OsO₄. Also, some adducts formed by RuO₄with nucleophiles were investigated computationally. 

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4. Trigonal Bipyramidal or Square Planar? Density Functional Theory calculations of iron bis(dithiolene) N-heterocyclic carbene complexes

   https://doi.org/10.1039/D4DT02650K  

   Merkel, Katherine; Santos, Alyssa_V B; Simpson, Scott Michael (January 2024, Dalton Transactions)

   Density functional theory (DFT) calculations of 57 iron bis(dithiolene)-N-heterocyclic carbene adducts were conducted to determine what parameters predict, and possibly influence, the coordination of these aforementioned adducts. The parameters considered... 

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5. Base excision repair system targeting DNA adducts of trioxacarcin/LL-D49194 antibiotics for self-resistance

   https://doi.org/10.1093/nar/gkac085  

   Chen, Xiaorong; Bradley, Noah P.; Lu, Wei; Wahl, Katherine L.; Zhang, Mei; Yuan, Hua; Hou, Xian-Feng; Eichman, Brandt F.; Tang, Gong-Li (February 2022, Nucleic Acids Research)

   Abstract Two families of DNA glycosylases (YtkR2/AlkD, AlkZ/YcaQ) have been found to remove bulky and crosslinking DNA adducts produced by bacterial natural products. Whether DNA glycosylases eliminate other types of damage formed by structurally diverse antibiotics is unknown. Here, we identify four DNA glycosylases—TxnU2, TxnU4, LldU1 and LldU5—important for biosynthesis of the aromatic polyketide antibiotics trioxacarcin A (TXNA) and LL-D49194 (LLD), and show that the enzymes provide self-resistance to the producing strains by excising the intercalated guanine adducts of TXNA and LLD. These enzymes are highly specific for TXNA/LLD-DNA lesions and have no activity toward other, less stable alkylguanines as previously described for YtkR2/AlkD and AlkZ/YcaQ. Similarly, TXNA-DNA adducts are not excised by other alkylpurine DNA glycosylases. TxnU4 and LldU1 possess unique active site motifs that provide an explanation for their tight substrate specificity. Moreover, we show that abasic (AP) sites generated from TxnU4 excision of intercalated TXNA-DNA adducts are incised by AP endonuclease less efficiently than those formed by 7mG excision. This work characterizes a distinct class of DNA glycosylase acting on intercalated DNA adducts and furthers our understanding of specific DNA repair self-resistance activities within antibiotic producers of structurally diverse, highly functionalized DNA damaging agents. 

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