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, τ_1/2 = 49 h (ΔH^‡ = 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 (τ_1/2 = 48 s, ΔH^‡ = 10.0 ± 0.3 kcal mol^-1). Aminyl radical 2 aggregates at ambient conditions in water and has a half-life, τ_1/2 = 2 h.