Long-Lived C60 Radical Anion Stabilized Inside an Electron-Deficient Coordination Cage.

Fullerene C60 and its derivatives are widely used in molecular electronics, photovoltaics, and battery materials, because of their exceptional suitability as electron acceptors. In this context, single-electron transfer on C60 generates the C60• - radical anion. However, the short lifetime of free C60• - hampers its investigation and application. In this work, we dramatically stabilize the usually short-lived C60• - species within a self-assembled M2L4 coordination cage consisting of a triptycene-based ligand and Pd(II) cations. The electron-deficient cage strongly binds C60 by providing a curved inner π-surface complementary to the fullerene's globular shape. Cyclic voltammetry revealed a positive potential shift for the first reduction of encapsulated C60, which is indicative of a strong interaction between confined C60• - and the cationic cage. Photochemical one-electron reduction with 1-benzyl-1,4-dihydronicotinamide allows selective and quantitative conversion of the confined C60 molecule in millimolar acetonitrile solution at room temperature. Radical generation was confirmed by nuclear magnetic resonance, electron paramagnetic resonance, ultraviolet-visible-near-infrared spectroscopy and electrospray ionization mass spectrometry. The lifetime of C60• - within the cage was determined to be so large that it could still be detected after one month under an inert atmosphere.

In-Cell Characterization of the Stable Tyrosyl Radical in E. coli Ribonucleotide Reductase Using Advanced EPR Spectroscopy.

The E. coli ribonucleotide reductase (RNR), a paradigm for class Ia enzymes including human RNR, catalyzes the biosynthesis of DNA building blocks and requires a di-iron tyrosyl radical (Y122. ) cofactor for activity. The knowledge on the in vitro Y122. structure and its radical distribution within the ß2 subunit has accumulated over the years; yet little information exists on the in vivo Y122. . Here, we characterize this essential radical in whole cells. Multi-frequency EPR and electron-nuclear double resonance (ENDOR) demonstrate that the structure and electrostatic environment of Y122. are identical under in vivo and in vitro conditions. Pulsed dipolar EPR experiments shed light on a distinct in vivo Y122. per ß2 distribution, supporting the key role of Y. concentrations in regulating RNR activity. Additionally, we spectroscopically verify the generation of an unnatural amino acid radical, F3 Y122. , in whole cells, providing a crucial step towards unique insights into the RNR catalysis under physiological conditions.