Iron-Catalyzed C(sp3)–H Alkylation through Ligand-to-Metal Charge Transfer

We report the FeCl3-catalyzed alkylation of nonactivated C(sp3)–H bonds. Photoinduced ligand-to-metal charge transfer at the iron center generates chlorine radicals that then preferentially abstract hydrogen atoms from electron-rich C(sp3)–H bonds distal to electron-withdrawing functional groups. The resultant alkyl radicals are trapped by electron-deficient olefins, and the catalytic cycle is closed by Fe(II) recombination and protodemetalation.

Main-Chain Ferrocene-Containing Polymers Prepared by Acyclic Diene Metathesis Polymerization: A Review

Ferrocene, the crown of metallocene family, is widely studied as a functional unit in electrochemical and catalytic applications due to its sandwich structure. Ferrocene moieties can be embedded into the polymer backbone, leading to main-chain ferrocenecontaining polymers. These polymeric materials combine the unique functionalities of iron center with the processabilities of polymers. As one of the choice polymerization techniques, acyclic diene metathesis (ADMET) polymerization serves as a versatile method to prepare main-chain ferrocene-containing polymers under mild conditions using α,ω-dienes as monomers. This paper overviews main-chain ferrocene-containing polymers prepared by ADMET polymerization. Advances in the design, synthesis and applications of this class of organometallic monomers and polymers are detailed.

Characterization of the nonheme iron center of cysteamine dioxygenase and its interaction with substrates

Cysteamine dioxygenase (ADO) has been reported to exhibit two distinct biological functions with a nonheme iron center. It catalyzes oxidation of both cysteamine in sulfur metabolism and N-terminal cysteine-containing proteins or peptides, such as regulator of G protein signaling 5 (RGS5). It thereby preserves oxygen homeostasis in a variety of physiological processes. However, little is known about its catalytic center and how it interacts with these two types of primary substrates in addition to O2. Here, using electron paramagnetic resonance (EPR), Mössbauer, and UV-visible spectroscopies, we explored the binding mode of cysteamine and RGS5 to human and mouse ADO proteins in their physiologically relevant ferrous form. This characterization revealed that in the presence of nitric oxide as a spin probe and oxygen surrogate, both the small molecule and the peptide substrates coordinate the iron center with their free thiols in a monodentate binding mode, in sharp contrast to binding behaviors observed in other thiol dioxygenases. We observed a substrate-bound B-type dinitrosyl iron center complex in ADO, suggesting the possibility of dioxygen binding to the iron ion in a side-on mode. Moreover, we observed substrate-mediated reduction of the iron center from ferric to the ferrous oxidation state. Subsequent MS analysis indicated corresponding disulfide formation of the substrates, suggesting that the presence of the substrate could reactivate ADO to defend against oxidative stress. The findings of this work contribute to the understanding of the substrate interaction in ADO and fill a gap in our knowledge of the substrate specificity of thiol dioxygenases.

Pseudomonas aeruginosa lasR mutant fitness in microoxia is supported by an Anr-regulated oxygen-binding hemerythrin

Pseudomonas aeruginosa strains with loss-of-function mutations in the transcription factor LasR are frequently encountered in the clinic and the environment. Among the characteristics common to LasR-defective (LasR−) strains is increased activity of the transcription factor Anr, relative to their LasR+ counterparts, in low-oxygen conditions. One of the Anr-regulated genes found to be highly induced in LasR− strains was PA14_42860 (PA1673), which we named mhr for microoxic hemerythrin. Purified P. aeruginosa Mhr protein contained the predicted di-iron center and bound molecular oxygen with an apparent Kd of ∼1 µM. Both Anr and Mhr were necessary for fitness in lasR+ and lasR mutant strains in colony biofilms grown in microoxic conditions, and the effects were more striking in the lasR mutant. Among genes in the Anr regulon, mhr was most closely coregulated with the Anr-controlled high-affinity cytochrome c oxidase genes. In the absence of high-affinity cytochrome c oxidases, deletion of mhr no longer caused a fitness disadvantage, suggesting that Mhr works in concert with microoxic respiration. We demonstrate that Anr and Mhr contribute to LasR− strain fitness even in biofilms grown in normoxic conditions. Furthermore, metabolomics data indicate that, in a lasR mutant, expression of Anr-regulated mhr leads to differences in metabolism in cells grown on lysogeny broth or artificial sputum medium. We propose that increased Anr activity leads to higher levels of the oxygen-binding protein Mhr, which confers an advantage to lasR mutants in microoxic conditions.