The mono-μ-hydroxo complex {[Cu(tmpa)]-(μ-OH)} (1) can undergo reversible deprotonation at -30 °C to yield {[Cu(tmpa)]-(μ-O)} (2). This species is basic with a pK of 24.3. 2 is competent for concerted proton-electron transfer from TEMPOH, but is an intrinsically poor hydrogen atom abstractor (BDFE(OH) of 77.2 kcal/mol) based on kinetic and thermodynamic analyses. Nonetheless, DFT calculations experimentally calibrated against 2 reveal that [CuO] is likely thermodynamically viable in copper-dependent methane monoxygenase enzymes.

Endoplasmic reticulum (ER) proteins including protein disulfide isomerase (PDI) are playing crucial roles in maintaining appropriate protein folding. Under nitrosative stress, an excess of nitric oxide (NO) radical species induced the S-nitrosylation of PDI cysteines which eliminate its isomerase and oxidoreductase capabilities. In addition, the S-nitrosylation-PDI complex is the cause of aggregation especially of the α-synuclein (α-syn) protein (accumulation of Lewy-body aggregates). We recently identified a potent antioxidant small molecule, Ferrostatin-1 (Fer-1), that was able to inhibit a non-apoptotic cell death named ferroptosis. Ferroptosis cell death involved the generation of oxidative stress particularly lipid peroxide. In this work, we reported the neuroprotective role of ferrostatin-1 under rotenone-induced oxidative stress in dopaminergic neuroblastoma cells (SH-SY5Y). We first synthesized the Fer-1 and confirmed that it is not toxic toward the SH-SY5Y cells at concentrations up to 12.5 μM. Second, we showed that Fer-1 compound quenched the commercially available stable radical, the 2,2-diphenyl-1-picrylhydrazyl (DPPH), in non-cellular assay at 82 %. Third, Fer-1 inhibited the ROS/RNS generated under rotenone insult in SH-SY5Y cells. Fourth, we revealed the effective role of Fer-1 in ER stress mediated activation of apoptotic pathway. Finally, we reported that Fer-1 mitigated rotenone-induced α-syn aggregation.

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The strength of the relevant bonds in bond-making and bond-breaking processes can directly affect the overall efficiency of the process. Copper–oxygen sites are known to catalyze reactions with some of the most recalcitrant C–H bonds found in nature as quantified by the bond dissociation free energy (BDFE), yet only a handful of copper-bound O–H bond strengths have been defined. Equally important in the design of synthetic catalysts is an understanding of the geometric and electronic structure origins of these thermo­dynamic parameters. In this report, the BDFE­(OH) of two dicopper–hydroxo complexes, {[LCu]2-(μ-OH)}3+ and {[LCu]2-(μ-OH)}4+ (L = tris­(2-pyridylmethyl)­amine), were measured. Two key observations were made: (i) the BDFE­(OH)­s of these complexes were exceptionally high at 103.4 and 91.7 kcal/mol, respectively, which are the highest condensed phase MO-H BDFEs to date and (ii) that the higher oxidation state had a lower BDFE­(OH), which is counter to expectations based on known mononuclear BDFE­(OH)­s which increase with the oxidation state. To understand the origin of these thermo­dynamic values, the BDFE­(OH)­s were measured and analyzed for the mononuclear complexes [LCu­(OH2)]1+ and [LCu­(OH2)]2+ in the same ligand environment. This treatment revealed “dinuclear effects” that include contributions from rehybridization of the oxygen, mixed valency of the metals, magnetic exchange between the metals, and differences in solvation, which are general with respect to [M]2–OH complexes to varying degrees. These analyses are important because they provide a starting point for rationally tuning the thermo­dynamics of catalytic intermediates broadly and for understanding how copper active sites achieve activation of strong C–H bonds.

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