Radiation stability of alkylated pillar[5]arenes

Abstract

Radiation stability of methoxypillar[5]arene (1) and n-butoxypillar[5]arene (2) was studied by an electron accelerator with dose up to 14 MGy in air at room temperature. The radiolysis products and the possible radiolytic mechanism were also proposed. The structures of both irradiated and unirradiated pillar[5]arenes samples were comparatively characterized by Micro-FTIR NMR, UV-vis, MALDI-TOF-MS and HPLC measurement. The results showed that the skeleton of the pillar[5]arenes was stable to a great extent when the dose was lower than 100 kGy, indicating excellent radiation stability of alkylated pillar[5]arenes. When the dose was more than 300 kGy, all compounds showed different degrees of radiation damage, leading to the radiolysis products via breakage of appending arms and the bond between α-carbon and β-carbon of appending arms of pillar[5]arenes. With increasing the dose, the degree of radiation damage from electron beam irradiation to pillar[5]arenes skeleton experienced a gradual rise. As the dose reached 2000 kGy, the compounds 1 and 2 decomposed by 21% and 33%, respectively, as a result of radiolytic degradation. Furthermore, the side chain length of alkyl groups will also significantly affect the irradiation stability of pillar[5]arenes, particularly at the dose beyond 2000 kGy. These results provide reliable data support for the radiation stability of alkylated pillar[5]arenes in a wide range of irradiation dose.