Linear Configuration of the Spins of a Stable Trinitroxide Radical Based on a Ternary Helical Peptide



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Peptide secondary structure: An octapeptide with three TOAC (2,2,6,6-tetramethyl-1-oxyl-4-amino-4-carboxylic acid) residues forms a 310-helix in the crystal state. The three nitroxide radicals are placed in a linear configuration (see picture). As determined by electron paramagnetic resonance (EPR) spectroscopy, this secondary structure is preserved in solvents of low polarity, while in polar solvents the regularity of the 310-helix is disrupted.