Crystal structures of four host–guest inclusion complexes of α,α′,δ,δ′-tetramethylcucurbit[6]uril and cucurbit[8]uril with some l-amino acids

Four crystal structures of inclusion complexes of amino acid and cucurbit[n]uril have been synthesized and characterized by X-ray diffractions. The used four amino acids are l-Glutamate (l-Glu), l-Tyrosine (l-Tyr), l-Hisdine (l-His), l-Leucine (l-Leu) and the hosts are α,α′,δ,δ′-tetramethylcucurbit[6]uril (TMeQ[6]), the normal cucurbit[8]uril (Q[8]). The corresponding compounds based on the inclusion complexes of amino acid and cucurbit[n]uril have stoichiometry of {l-Glu@TMeQ[6]}+·Cl−·13H2O (1), {(l-Tyr)2@Q[8]}·27H2O (2), {(l-His)2@Q[8]}·19H2O (3) and {(l-Leu)2@Q[8]}2+·2Cl−·32H2O (4). The crystal structure of the compound 1 reveals that a l-Glu molecule is captured by a host TMeQ[6] with a 1:1 host:guest ratio. The crystal structures of compounds 2, 3 and 4 show that all three inclusion complexes of l-Tyr@Q[8], l-His@Q[8] and l-Leu@Q[8] are in 1:2 host:guest ratio. The host Q[8] can include not only two aromatic moieties from two same guests (such as in the cases of 2 and 3) but also two alkyl chains of two l-Leu molecules (the case of 4).