Designing catalysts that are not based on precious metals remains a major research priority worldwide, particularly for the feasible production of hydrogen gas. Given the increasing interest in metallocorroles as electrocatalysts, three nickel corroles were explored as catalysts for the hydrogen evolution reaction (HER) in the current study. The precatalysts were fully characterized as square planar d8 nickel­(II) coordination compounds in which the extra negative charge is stabilized by electron-withdrawing substituents on the corrole and a robust countercation. This unique feature leads to an about 0.8 V shift in redox potentials and different reaction pathways compared to trivalent and hence neutral metallocorroles, as well as increased reactivity toward weak acid relative to a neutral nickel­(II) porphyrin analogue. Only singly reduced and singly oxidized reaction intermediates are shown to be involved in the catalytic cycle for the conversion of protons to hydrogen, by both experimental and computational analyses; the nickel corroles were prepared and characterized in all of the corresponding oxidation states. The nickel corrole with two sulfonamido groups on its skeleton catalyzes the HER with an onset potential of about −1 V vs Fc+/0 and thousands of turnovers per second.

Electrocatalysis by first-row transition metals chelated by porphyrins, corroles, and related macrocycles gains increased attention due to the need of developing approaches for clean and renewable energy. While some of the above complexes display good catalytic activity, their performance often suffers from much larger overpotentials than the extremely efficient, but not sustainable metal, platinum. Intrigued by the report of copper corroles as catalysts for the electrochemical conversion of protons to hydrogen gas, we hypothesized that trifluoromethylation of corroles would be most effective for inducing a positive shift of the potentials required for reduction of the copper chelated thereby. A combination of methodologies allowed for full characterization of the trisand tetra-CF 3 -substituted complexes and elucidation of their unique structural, physical, and chemical properties. The desired outcome was also achieved, as the potential required for reduction to the copper(I) oxidation state, postulated to be the catalytically active species, was the least negative. The tris-substituted complex was found to be a particularly good electrocatalyst for production of hydrogen from protons, with a remarkably early catalytic onset potential.

Recent work has highlighted the potential of metallocorroles as versatile platforms for the development of drugs and imaging agents, since the bioavailability, physicochemical properties and therapeutic activity can be dramatically altered by metal ion substitution and/or functional group replacement. Significant advances in cancer treatment and imaging have been reported based on work with a water-soluble bis-sulfonated gallium corrole in both cellular and rodent-based models. We now show that cytotoxicities increase in the order Ga < Fe < Al < Mn < Sb < Au for bis-sulfonated corroles; and, importantly, that they correlate with metallocorrole affinities for very low density lipoprotein (VLDL), the main carrier of lipophilic drugs. As chemotherapeutic potential is predicted to be enhanced by increased lipophilicity, we have developed a novel method for the preparation of cell-penetrating lipophilic metallocorrole/serum-protein nanoparticles (NPs). Cryo-TEM revealed an average core metallocorrole particle size of 32 nm, with protein tendrils extending from the core (conjugate size is ~100 nm). Optical imaging of DU-145 prostate cancer cells treated with corrole NPs (≤100 nM) revealed fast cellular uptake, very slow release, and distribution into the endoplasmic reticulum (ER) and lysosomes. The physical properties of corrole NPs prepared in combination with transferrin and albumin were alike, but the former were internalized to a greater extent by the transferrin-receptor-rich DU-145 cells. Our method of preparation of corrole/protein NPs may be generalizable to many bioactive hydrophobic molecules to enhance their bioavailability and target affinity.

Development of novel therapeutic strategies to eradicate malignant tumors is of paramount importance in cancer research. In a recent study, we have introduced a facile protocol for the preparation of corrole-protein nanoparticles (NPs). These NPs consist of a corrole-core coated with protein. We now report that a novel lipophilic corrole, (2)Ga, delivered as human serum albumin (HSA)-coated NPs, displayed antineoplastic activity towards human prostate cancer DU-145 cells. Cryo-TEM analysis of these NPs revealed an average diameter of 50.2 ± 8.1 nm with a spherical architecture exhibiting low polydispersity. In vitro cellular uptake of (2)Ga/albumin NPs was attributable to rapid internalization of the corrole through ligand binding-dependent extracellular release and intercalation of the corrole cargo into the lipid bilayer of the plasma membrane. This finding is in contrast with a previously reported study on corrole-protein NPs that displayed cellular uptake via endocytosis. Investigation of the non-light-induced mechanism of action of (2)Ga suggested the induction of necrosis through plasma membrane destabilization, impairment of calcium homeostasis, lysosomal stress and rupture, as well as formation of reactive oxygen species (ROS). (2)Ga also exhibited potent light-induced cytotoxicity through ROS generation. These findings demonstrate a rapid cellular uptake of (2)Ga/protein NPs along with targeted induction of tumor cell necrosis.

A series of tetranuclear copper iodide clusters supported by zwitterionic ligands were prepared, which display hypsochromic luminescence upon cooling.