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

Abstract

The chiral amines (R,R and S,S)‐1‐amino‐2‐benzyloxycyclopentane and (R and S)‐α‐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 α‐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. 1H 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.

Tiara[n]uril: A Glycoluril-Based Macrocyclic Host with Cationic Walls

“…As a preliminary exploration of association of an organic molecule through ion–ion and H-bond interaction, an aqueous buffered solution of Me 10 Tu­[3] 2+ (pH 6.6) was added to L-glutamine in the same buffer. The sensitivity of circular dichroism (CD) and a potential for induced chirality through association was expected. , CD spectra showed a significant maximum red shifted (4 nm) to 210 nm and a positive increase in molar ellipticity ([θ] = 1.2 and 2.9) following the addition of 2 and 2.25 mol equiv of Me 10 Tu­[3] 2+ , respectively. This was an interesting result though we remain cognizant of the other competing ions of Cl – from Me 10 Tu­[3]­Cl 2 and the phosphate in the buffer.…”