Blue-colored tert-butylamine clathrate hydrate.

Clathrate hydrates preserve active species more stably than the other icy materials and investigation of the behavior of the active species elucidates the physicochemical properties of clathrate hydrates like guest-guest interaction. Color of the tert-butylamine clathrate hydrate changes to blue after gamma irradiation and is bleachable with visible light. The electron spin resonance (ESR) spectrum at 120 K mainly consists of a triplet signal of the C-centered radical NH2C(CH3)2CH2• together with a single signal at g = 2.0008. The latter signal disappears after light exposure. These results indicate that both the blue color and the single ESR signal are derived from trapped electrons in the hydrate. They thermally decay around 140-160 K by the first-order reaction, and the activation energy is 27 kJ/mol. Since tert-butylamine molecules can capture protons due to the high proton affinity, electrons may remain in the hydrate without reacting with protons, making the hydrate blue after gamma irradiation. The long-lived trapped electrons in the tert-butylamine hydrate have an advantage to investigate those in icy materials because tert-butylamine hydrate is nonionic and has a tetra-coordinated host water network like crystalline ice without any substitution for water molecules.