Sulfur-bridging the gap: investigating the electrochemistry of novel copper chelating agents for Alzheimer's disease applications

There is currently an unmet demand for multi-functional precision treatments for Alzheimer's disease (AD) after several failed attempts at designing drugs based on the amyloid hypothesis. The focus of this work is to investigate sulfur-bridged quinoline ligands that could potentially be used in chelation therapies for a subpopulation of AD patients presenting with an overload of labile copper ions, which are known to catalyze the production of reactive oxygen species (ROS) and exacerbate other markers of AD progression. The ligands 1-(2'-thiopyridyl)isoquinoline (1TPIQ) and 2-(2'-thiopyridyl)quinoline (2TPQ) were synthesized and characterized before being electrochemically investigated in the presence of different oxidizing and reducing agents in solution with a physiological pH relevant to the brain. The electrochemical response of each compound with copper was studied by employing both hydrogen peroxide (H2O2) as an oxidizing agent and ascorbic acid (AA) as an antioxidant during analysis using cyclic voltammetry (CV). The cyclic voltammograms of each quinoline were compared with similar ligands that contained aromatic N-donor groups but no sulfur groups to provide relative electrochemical properties of each complex in solution. In a dose-dependent manner, it was observed that AA exerted dual-efficacy when combined with these chelating ligands: promoting synergistic metal binding while also scavenging harmful ROS, suggesting AA is an effective adjuvant therapeutic agent. Overall, this study shows how coordination by sulfur-bridged quinoline ligands can alter copper electrochemistry in the presence of AA to limit ROS production in solution.

Buffer Effects in Zirconium-Based UiO Metal-Organic Frameworks (MOFs) That Influence Enzyme Immobilization and Catalytic Activity in Enzyme/MOF Biocatalysts

Novel biocatalysts that feature enzymes immobilized onto solid supports have recently become a major research focus in an effort to create more sustainable and greener chemistries in catalysis. Many of these novel biocatalyst systems feature enzymes immobilized onto metal-organic frameworks (MOFs), which have been shown to increase enzyme activity, stability, and recyclability in industrial processes. While the strategies used for immobilizing enzymes onto MOFs can vary, the conditions always require a buffer to maintain the functionality of the enzymes during immobilization. This report brings attention to critical buffer effects important to consider when developing enzyme/MOF biocatalysts, specifically for buffering systems containing phosphate ions. A comparative analysis of different enzyme/MOF biocatalysts featuring horseradish peroxidase and/or glucose oxidase immobilized onto the MOFs UiO-66, UiO-66-NH₂, and UiO-67 using a noncoordinate buffering system (MOPSO buffer) and a phosphate buffering system (PBS) show that phosphate ions can have an inhibitory effect. Previous studies utilizing phosphate buffers for enzyme immobilization onto MOFs have shown Fourier transform infrared (FT-IR) spectra that have been assigned stretching frequencies associated with enzymes after immobilization. Analyses and characterizations using zeta potential measurements, scanning electron microscopy, Brunauer-Emmett-Teller surface area, powder X-ray diffraction, Energy Dispersive X-ray Spectroscopy, and FT-IR show concerning differences in enzyme loading and activity based on the buffering system used during immobilization.

Interactions of copper and copper chelate compounds with the amyloid beta peptide: An investigation into electrochemistry, reactive oxygen species and peptide aggregation

Alzheimer's disease is a fatal neurological disorder affecting millions of people worldwide with an increasing patient population as average life expectancy increases. Accumulation of amyloid beta (Aβ) plaques is characteristic of the disease and has been the target of numerous failed clinical trials. In light of this, therapeutics that target mechanisms of neuronal death beyond Aβ aggregation are needed. One potential target is the formation of reactive oxygen species (ROS) that are created during an interaction between Aβ and copper ions. This work shows that ROS production can be slowed by disrupting the interaction between Aβ and copper using copper chelating compounds. We demonstrated that ROS are produced in the presence of Aβ and copper in solution by monitoring H₂O₂ production using a fluorescence-based assay, which increased when Cu²⁺ interacted with Aβ. In addition, we were able to show reduced ROS production, without exacerbating the aggregation of Aβ and in some cases alleviating it, by adding copper chelating ligands to the solution. Using cyclic voltammetry, we investigated how these different ligands influenced the electrochemical behavior of copper in solution revealing important insights into the mechanisms of ROS production and chemical interactions that result in decreased ROS rates.

PANI@UiO-66 and PANI@UiO-66-NH2 Polymer-MOF Hybrid Composites as Tunable Semiconducting Materials

This investigation explores optimum synthetic conditions for novel polymer-metal organic framework hybrid composites composed of Zr-terephthalate-based MOF UiO-66 and conductive polyaniline (PANI) nanofibers in an effort to optimize conductivity while minimizing MOF structural deformation. Successful syntheses of self-assembled PANI nanofibers in PANI@UiO-66 and PANI@UiO-66-NH₂ composites were confirmed using scanning electron microscopy, infrared spectroscopy, and powder X-ray diffraction. The polymer-MOF composites show different bonding synergies to the PANI nanofibers depending on the organic linker used. Electronic properties of the post-synthetically modified PANI@UiO-66 and PANI@UiO-66-NH₂ were investigated using UV-vis diffuse reflectance spectroscopy. Sheet resistivity of the self-assembled polymer-MOF composites was determined under an inert atmosphere at room temperature using four-point probe measurements to confirm tunable semiconductivity ranging from 40 to 2 mS/sq. Furthermore, the effects of aniline oxidation on the crystallinity and coordination of UiO-66 and UiO-66-NH₂ were determined through analysis of these results.

Crystal structure of {2,2'-[N,N'-bis-(pyridin-2-yl-meth-yl)cyclo-hexane-trans-1,2-diyldi(nitrilo)]di-acetato}-cobalt(III) hexa-fluorido-phosphate

In the title compound, a Co^III center is coordinated by four N atoms and two O atoms, with the monodentate acetate groups of the ligand oriented trans with respect to each other, whereas the pyridine N atoms are coordinated in a cis configuration.

The title compound [Co(C₂₂H₂₆N₄O₄)]PF₆, commonly known as [Co(bpcd)]PF₆, where bpcd²⁻ is derived from the historical ligand name N,N′-bis­(2-pyridyl­meth­yl)-trans-1,2-di­amino­cyclo­hexane-N,N′-di­acetate, crystallized by slow evaporation of a saturated aceto­nitrile solution in air. The cation of the hexa­fluorido­phosphate salt has the Co^III atom in a distorted octa­hedral coordination geometry provided by an N₄O₂ donor atom set. The acetate groups, which are oriented trans with respect to each other, exhibit monodentate coordination whereas the pyridyl N atoms are coordinating in a cis configuration. The geometry of the cation is compared to the geometries of other di­amino di­acetate complexes with Co^III.

{2,2'-[N,N'-Bis(pyridin-2-ylmeth-yl)propane-1,3-diyldi(nitrilo)]di-acetato}-cobalt(III) hexa-fluoridophosphate aceto-nitrile 0.064-solvate

In the title compound, [Co(C₁₉H₂₂N₄O₄)]PF₆·0.064CH₃CN, commonly known as [Co(bppd)]PF₆·0.064CH₃CN, where bppd represents the historical ligand name N,N′-bis(2-pyridylmethyl)-1,3-diaminopropane-N,N′-diacetate, the Co^III atom is coordinated in a distorted octa­hedral geometry with an N₄O₂ donor atom set. The acetate O atoms, which exhibit monodentate coordination, are oriented in a trans configuration with respect to each other, whereas the pyridyl N atoms are coordinated in a cis configuration. The compound crystallizes with two crystallographically unique cations and two anions per asymmetric unit along with a disordered, partially occupied (occupancy = 0.128) aceto­nitrile solvent mol­ecule. Crystals of the title complex were found to be twinned by pseudomerohedry with a 180° rotation around [10-1] and a refined contribution of 90.5 (3)% of the major twin component.