In prior SAMPL challenges, the Isaacs group provided unpublished experimental binding thermodynamic values (free energy and enthalpy) of guests towards cucurbituril[n] type receptors (i.e. CB[n] (n=7,8), acycylic CB[n] (trimer trip), and glycoluril based molecular clips). Like the macrocyclic cucurbiturils, WP6 (a derivative of pillar [6]arene) is a macrocyclic molecular container used as a sequestration agent that has shown high affinity for hydrophobic cationic guests and were sought after for SAMPL. Thus, for SAMPL9, the guest dataset consisted of thirteen hydrophobic cationic guests (Figure ) like, but not limited to, adamantanes and viologens . WP6 is composed of six phenylene groups containing CH2 linkers. Each phenylene group contains two anioinic carboxylate arms, for a total of twelve arms (Figure and). This potentially gives WP6 twelve negatively charged groups at pH 7.4.