An Exploration of Induced Supramolecular Chirality Through Association of Chiral Ammonium Ions and Tartrates with the Achiral Host Cucurbit[7]uril

The chiral amines (R,R and S,S)-1-amino-2-benzyloxycyclopentane and (R and S)--methylbenzylamine were converted to ammonium (D and L) hydrogen tartrate salts and induced chiroptic effects were investigated following encapsulation in Q[7]. Significant chiroptic differences were observed in ORD and CD spectra for the two amines. The optical spectra were performed as a precursor study to a potential method for enantiomer separation, utilising Q[7] encapsulation in conjunction with enantio-pure hydrogen tartrates. An enantiomeric excess was achieved for the two antipodes of 1-amino-2-benzyoxycyclopentane but not for those of -methylbenzylamine. However, material differences of crystallinity or the formation of a glass were observed for the latter amine induced by the different antipodes of hydrogen tartrate. H-1 NMR spectra of aminobenzyloxycyclopentane showed back-folding of the two rings with complete encapsulation in Q[7], leading to a secondary helical structure observed in CD spectra.