Uranyl Photocleavage of Phosphopeptides Yields Truncated C-Terminally Amidated Peptide Products

Towards tailoring hydrophobic interaction with uranyl(VI) oxygen for C-H activation

Bovine serum albumin (BSA) has a uranyl(VI) binding hotspot where uranium is tightly bound by three carboxylates. Uranyl oxygen is "soaked" into the hydrophobic core of BSA. Isopropyl hydrogen of Val is trapped near UO22+ and upon photoexcitation, C-H bond cleavage is initiated. A unique hydrophobic contact with "yl"-oxygen, as observed here, can be used to induce C-H activation.

Ultrasensitive Detection of Aqueous Uranyl Based on Uranyl-Triggered Protein Photocleavage

The detection of environmental uranyl is attracting increasing attention. However, the available detection strategies mainly depend on the selective recognition of uranyl, which is subject to severe interference by coexisting metal ions. Herein, based on the unique uranyl-triggered photocleavage property, the protein BSA is labelled with fluorescent molecules that exhibit an aggregation-induced emission effect for uranyl detection. Uranyl-triggered photocleavage causes the separation of the fluorescent-molecule-labelled protein fragments, leading to attenuation of the emission fluorescence, which is used as a signal for uranyl detection. This detection strategy shows high selectivity for uranyl and an ultralow detection limit of 24 pM with a broad detection range covering five orders of magnitude. The detection method also shows high reliability and stability, making it a promising technique for practical applications in diverse environments.

Perspectives for Uranyl Photoredox Catalysis

The application of uranyl salts as powerful photoredox catalysts in chemical transformations lags behind the advances achieved in thermocatalysis and structural chemistry. In fact, uranyl cations (UO2 2+) have proven to be ideal photoredox catalysts in visible-light-driven chemical reactions. The excited state of uranyl cations (*UO2 2+) that is generated by visible-light irradiation has a long-lived fluorescence lifetime up to microseconds and high oxidizing ability [E o = +2.6 V vs. standard hydrogen electrode (SHE)]. After ligand-to-metal charge transfer (LMCT), quenching occurs with organic substrates via hydrogen-atom transfer (HAT) or single-electron transfer (SET). Interestingly, the ground state and excited state of uranyl cations (UO2 2+) are chemically inert toward oxygen molecules, preventing undesired transformations from active oxygen species. This review summarizes recent advances in photoredox transformations enabled by uranyl salts.

1 Introduction

2 The Application of Uranyl Photoredox Catalysis in HAT Mode

3 The Application of Uranyl Photoredox Catalysis in SET Mode

4 Conclusion and Outlook

Detailed characterization of dioxouranium(vi) complexes with a symmetrical tetradentate N2O2-benzil bis(isonicotinoyl hydrazone) ligand

The reactions of UO2(OAc)2·2H2O with benzil bis(isonicotinoyl hydrazone) ligand (H2L) in varied solvent media resulted in the formation of a series of new dioxouranium(vi) complexes 1-3 of the type UO2(L)(X), [where 1, X = DMF; 2, X = DMSO; 3, X = H2O]. The complexes were systematically characterized by elemental analysis, UV-Visible spectroscopy, TGA, mass spectrometry, cyclic voltammetry, and powder X-ray diffraction study. Among all the complexes, 1 was confirmed by single-crystal X-ray diffraction study. It was found that 1 preferred a distorted pentagonal bipyramidal geometry, in which an equatorial coordination plane was formed by the ONNO-tetradentate cavity of the deprotonated hydrazone ligand along with an additional oxygen atom of the coordinated solvent molecule. Thermal analysis suggested that complexes 1 and 3 undergo weight loss in the temperature range 180-210 °C and 100-120 °C, respectively, due to the ready release of their coordinated solvent molecules. Complexes 1-3 exhibited analogous UV-Visible absorption bands and the intense band between 300-600 nm was assigned to the M ← L and n → π* transitions. Weakly resolved reduction waves assigned to {UO2}2+/{UO2}+ couple were observed for complexes 1 and 2 {1, -1.76 V; 2, -1.75 V; vs. ferrocenium/ferrocene (Fc+/Fc)} in DMSO solution, signifying the feeble electron-donating nature of the L2- ligand. Powder X-ray diffraction study suggested that the crystallite size of all the complexes was in the nanoscale range. Further analysis using density functional theory (DFT) calculations provided structural insights as well as information on the electronic properties of both complex 1 and the ligand.

Excited-State Chemistry: Photocatalytic Methanol Oxidation by Uranyl@Zeolite through Oxygen-Centered Radicals

We have elucidated the complex reaction network of partial methanol oxidation, H₃COH + O₂ → H₂CO + H₂O₂, at a visible-light-activated actinide photocatalyst. The reaction inertness of C-H bonds and O═O diradicals at ambient conditions is overcome through catalysis by photoexcited uranyl units (*UO₂²⁺) anchored on a mesoporous silicate. The electronic ground- and excited-state energy hypersurfaces are investigated with quasirelativistic density-functional and ab initio correlated wave function approaches. Our study suggests that the molecular cluster can react on the excited energy surface due to the longevity of excited uranyl, typical for f-element compounds. The theoretically predicted energy profiles, chemical intermediates, related radicals, and product species are consistent with various experimental findings. The uranyl excitation opens various reaction pathways for the oxidation of volatile organic compounds (VOCs) by "hole-driven hydrogen transfer" (HDHT) through several exothermic steps over low activation barriers toward environmentally clean or chemically interesting products. Quantum-chemical modeling reveals the high efficiency of the uranyl photocatalysis and directs the way to further understanding and improvement of VOC degradation, chemical synthesis, and biologic photochemical interactions between uranyl and the environment.

Uranyl Photocleavage of Phosphopeptides Yields Truncated C-Terminally Amidated Peptide Products

The uranyl ion (UO₂²⁺) binds phosphopeptides with high affinity, and when irradiated with UV‐light, it can cleave the peptide backbone. In this study, high‐accuracy tandem mass spectrometry and enzymatic assays were used to characterise the photocleavage products resulting from the uranyl photocleavage reaction of a tetraphosphorylated β‐casein model peptide. We show that the primary photocleavage products of the uranyl‐catalysed reaction are C‐terminally amidated. This could be of great interest to the pharmaceutical industry, as efficient peptide amidation reactions are one of the top challenges in green pharmaceutical chemistry.