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Abstract Here, we report CdS quantum dot (QD) gels, a three‐dimensional network of interconnected CdS QDs, as a new type of direct hydrogen atom transfer (d‐HAT) photocatalyst for C−H activation. We discovered that the photoexcited CdS QD gel could generate various neutral radicals, including α‐amido, heterocyclic, acyl, and benzylic radicals, from their corresponding stable molecular substrates, including amides, thio/ethers, aldehydes, and benzylic compounds. Its C−H activation ability imparts a broad substrate and reaction scope. The mechanistic study reveals that this reactivity is intrinsic to CdS materials, and the neutral radical generation did not proceed via the conventional sequential electron transfer and proton transfer pathway. Instead, the C−H bonds are activated by the photoexcited CdS QD gel via a d‐HAT mechanism. This d‐HAT mechanism is supported by the linear correlation between the logarithm of the C−H bond activation rate constant and the C−H bond dissociation energy (BDE) with a Brønsted slopeα=0.5. Our findings expand the currently limited direct hydrogen atom transfer photocatalysis toolbox and provide new possibilities for photocatalytic C−H activation.
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What Is the Catalytic Mechanism of Enzymatic Histone N‐Methyl Arginine Demethylation and Can It Be Influenced by an External Electric Field?
Abstract Arginine methylation is an important mechanism of epigenetic regulation. Some Fe(II) and 2‐oxoglutarate dependent Jumonji‐C (JmjC) Nϵ‐methyl lysine histone demethylases also have N‐methyl arginine demethylase activity. We report combined molecular dynamic (MD) and Quantum Mechanical/Molecular Mechanical (QM/MM) studies on the mechanism of N‐methyl arginine demethylation by human KDM4E and compare the results with those reported for N‐methyl lysine demethylation by KDM4A. At the KDM4E active site, Glu191, Asn291, and Ser197 form a conserved scaffold that restricts substrate dynamics; substrate binding is also mediated by an out of active site hydrogen‐bond between the substrate Ser1 and Tyr178. The calculations imply that in either C−H or N−H potential bond cleaving pathways for hydrogen atom transfer (HAT) during N‐methyl arginine demethylation, electron transfer occurs via a σ‐channel; the transition state for the N−H pathway is ∼10 kcal/mol higher than for the C−H pathway due to the higher bond dissociation energy of the N−H bond. The results of applying external electric fields (EEFs) reveal EEFs with positive field strengths parallel to the Fe=O bond have a significant barrier‐lowering effect on the C−H pathway, by contrast, such EEFs inhibit the N−H activation rate. The overall results imply that KDM4 catalyzed N‐methyl arginine demethylation and N‐methyl lysine demethylation occur via similar C−H abstraction and rebound mechanisms leading to methyl group hydroxylation, though there are differences in the interactions leading to productive binding of intermediates.
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- Award ID(s):
- 1904215
- PAR ID:
- 10237372
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 27
- Issue:
- 46
- ISSN:
- 0947-6539
- Format(s):
- Medium: X Size: p. 11827-11836
- Size(s):
- p. 11827-11836
- Sponsoring Org:
- National Science Foundation
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