Pure CB[10] was isolated by Isaacs and coworkers in 2005 by introducing a more strongly binding melamine diamine guest that is capable of displacing the CB[5].[8] The melamine diamine guest was then separated from the CB[10] by reaction with acetic anhydride that converted the positively charged amine groups to neutrally charged amides. Cucurbiturils strongly bind cationic guests, but by removing the positive charge from the melamine diamine guest reduces the association constant to the point it can be removed by washing with methanol, DMSO, and water. The CB[10] has an unusually large cavity (870 Å3) that's free and capable of binding extraordinarily large guests including a cationic calix[4]arene.