PEGylated, Water-Soluble, Stable Aminyl Radical

We report the synthesis and kinetic study of PEGylated, water-soluble aminyl radical 2. The radical possesses four mPEG-3 groups replacing four methyl groups in the tert-butyl groups at the 3 and 6-positions of 1,3,6,8-tetra-tert-butyl carbazyl (TTBC). This structure is designed to mitigate the rapid decomposition of the radical via intramolecular 1,5-hydrogen atom transfer (1,5-HAT) that was observed in its constitutional isomer 1-H with four mPEG-3 groups in the vicinity of the nitrogen-centered radical (1- and 8-positions of TTBC). In dry, degassed acetone at 295 K, the radical 2 has a half-life, tau(1/2) = 49 h (Delta H-double dagger = 17.9 +/- 0.8 kcal mol(-1)), which is 3 orders of magnitude longer than that for 1-H, which decays via 1,5-HAT (tau(1/2) = 48 s, Delta H-double dagger = 10.0 +/- 0.3 kcal mol(-1)). Aminyl radical 2 aggregates at ambient conditions in water and has a half-life, tau(1/2) = 2 h.