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1. Singlet O ₂ from Ultraviolet Excitation of the Quinoline-O ₂ Complex

   https://doi.org/10.1021/acs.jpca.3c02024  

   Parsons, Bradley F.; Rivera, Marcos R.; Freitag, Mark A.; Reardon, Kylie A.; Pappas, Emerson S.; Rausch, Jack T. (June 2023, The Journal of Physical Chemistry A)

   We report results from experiments with the quinoline-O₂ complex, which was photodissociated using light near 312 nm. Photodissociation resulted in formation of the lowest excited state of oxygen, O₂ a ¹Δ_g, which we detected using resonance enhanced multiphoton ionization and velocity map ion imaging. The O₂⁺ ion image allowed for a determination of the center-of-mass translational energy distribution, P(E_T), following complex dissociation. We also report results of electronic structure calculations for the quinoline singlet ground state and lowest energy triplet state. From the CCSD/aug-cc-pVDZ//(U)MP2/cc-pVDZ calculations, we determined the lowest energy triplet state to have ππ* electronic character and to be 2.69 eV above the ground state. We also used electronic structure calculations to determine the geometry and binding energy for several quinoline-O2 complexes. The calculations indicated that the most strongly bound complex has a well depth of about 0.11 eV and places the O₂ moiety above and approximately parallel to the quinoline ring system. By comparing the experimental P(E_T) with the energy for the singlet ground state and the lowest energy triplet state, we concluded that the quinoline product was formed in the lowest energy triplet state. Finally, we found the experimental P(E_T) to be in agreement with a Prior translational energy distribution, which suggests a statistical dissociation for the complex. 

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2. S _N Ar Reaction Toward the Synthesis of Fluorinated Quinolino[2,3,4‐at]porphyrins

   https://doi.org/10.1002/ejoc.202001347  

   Thuita, Damaris; Guberman‐Pfeffer, Matthew_J; Brückner, Christian (December 2020, European Journal of Organic Chemistry)

   Abstract An intramolecular S_NAr displacement of oneo‐fluorine atom of ameso‐pentafluorophenyl‐substituted porphyrin metal complex by a neighboring β‐amino functionality generated the correspondingmeso‐fluorophenyl‐substituted metallo‐quinolino[2,3,4‐at]porphyrins that are not accessible using established quinoline‐annulation methodologies. The Cu(II), Ni(II), and Zn(II) complexes were thus prepared. The parent free base quinolino[2,3,4‐at]porphyrin is accessible only by demetallation of the copper or zinc complexes. A strong through‐space NMR‐spectroscopic coupling between the remainingo‐fluorine atoms on the annulatedmeso‐aryl group and the β‐hydrogen atom on the adjacent pyrrole moiety provide a clear spectroscopic signature for the annulation. Quinoline‐annulation alters the optical properties significantly. On account of the presence of the β‐amino functionality, all quinoline‐annulated porphyrins show strong halochromic responses with Brønsted acids and bases, the prerequisite for their potential use in chemosensing applications. 

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3. Synthesis, structure, properties, and cytotoxicity of a (quinoline)RuCp ⁺ complex

   https://doi.org/10.1039/d2dt03484k  

   Hou, Zhilin; Vanecek, Allison S.; Tepe, Jetze J.; Odom, Aaron L. (January 2023, Dalton Transactions)

   Metal quinoline complexes were prepared using a quinoline-based proteasome inhibitor (Quin1) and an inactive quinoline ligand (Quin2), and their cytotoxicities are reported towards multiple myeloma-related cell lines. 

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4. Crystallographic Evidence for a Sterically Induced Ferryl Tilt in a Non‐Heme Oxoiron(IV) Complex that Makes it a Better Oxidant

   https://doi.org/10.1002/anie.201804836  

   Rasheed, Waqas; Draksharapu, Apparao; Banerjee, Saikat; Young, Jr., Victor G.; Fan, Ruixi; Guo, Yisong; Ozerov, M.; Nehrkorn, Joscha; Krzystek, J.; Telser, Joshua; et al (June 2018, Angewandte Chemie International Edition)

   Abstract Oxoiron(IV) units are often implicated as intermediates in the catalytic cycles of non‐heme iron oxygenases and oxidases. The most reactive synthetic analogues of these intermediates are supported by tetradentate tripodal ligands withN‐methylbenzimidazole or quinoline donors, but their instability precludes structural characterization. Herein we report crystal structures of two [Fe^IV(O)(L)]²⁺complexes supported by pentadentate ligands incorporating these heterocycles, which show longer average Fe–N distances than the complex with only pyridine donors. These longer distances correlate linearly with log k₂′ values for O‐ and H‐atom transfer rates, suggesting that weakening the ligand field increases the electrophilicity of the Fe=O center. The sterically bulkier quinoline donors are also found to tilt the Fe=O unit away from a linear N‐Fe=O arrangement by 10°. 

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5. Natural variation in yeast reveals multiple paths for acquiring higher stress resistance

   https://doi.org/10.1186/s12915-024-01945-7  

   Scholes, Amanda_N; Stuecker, Tara_N; Hood, Stephanie_E; Locke, Cader_J; Stacy, Carson_L; Zhang, Qingyang; Lewis, Jeffrey_A (July 2024, BMC Biology)

   Abstract BackgroundOrganisms frequently experience environmental stresses that occur in predictable patterns and combinations. For wildSaccharomyces cerevisiaeyeast growing in natural environments, cells may experience high osmotic stress when they first enter broken fruit, followed by high ethanol levels during fermentation, and then finally high levels of oxidative stress resulting from respiration of ethanol. Yeast have adapted to these patterns by evolving sophisticated “cross protection” mechanisms, where mild ‘primary’ doses of one stress can enhance tolerance to severe doses of a different ‘secondary’ stress. For example, in many yeast strains, mild osmotic or mild ethanol stresses cross protect against severe oxidative stress, which likely reflects an anticipatory response important for high fitness in nature. ResultsDuring the course of genetic mapping studies aimed at understanding the mechanisms underlying natural variation in ethanol-induced cross protection against H₂O₂, we found that a key H₂O₂scavenging enzyme, cytosolic catalase T (Ctt1p), was absolutely essential for cross protection in a wild oak strain. This suggested the absence of other compensatory mechanisms for acquiring H₂O₂resistance in that strain background under those conditions. In this study, we found surprising heterogeneity across diverse yeast strains in whetherCTT1function was fully necessary for acquired H₂O₂resistance. Some strains exhibited partial dispensability ofCTT1when ethanol and/or salt were used as mild stressors, suggesting that compensatory peroxidases may play a role in acquired stress resistance in certain genetic backgrounds. We leveraged global transcriptional responses to ethanol and salt stresses in strains with different levels ofCTT1dispensability, allowing us to identify possible regulators of these alternative peroxidases and acquired stress resistance in general. ConclusionsUltimately, this study highlights how superficially similar traits can have different underlying molecular foundations and provides a framework for understanding the diversity and regulation of stress defense mechanisms. 

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