A quantitative method for analysis of mixtures of homologues and stereoisomers of hemicucurbiturils that allows us to follow their formation and stability

Hemicucurbiturils are a sub-group of macrocyclic compounds within the cucurbit[n]uril family. The ability of unsubstituted and substituted hemicucurbiturils to form host-guest complexes allows selective binding of anions, application in catalysis and chiral discrimination between enantiomeric guests. Herein we demonstrate the separation of hemicucurbituril homologues and diastereomers by reverse phase HPLC and the quantitative analysis of hemicucurbit[6]uril, (all-R,R)-cyclohexanohemicucurbit[6]uril, (all-R,S)-cyclohexanohemicucurbit[6]uril and (all-R,R)-cyclohexanohemicucurbit[8]uril. The applicability of the developed quantitative analysis is demonstrated by the estimation of the reaction yields of cyclohexanohemicucurbiturils and by following the depolymerisation of hemicucurbit[6]uril under acidic conditions. Analysis of the studied set of compounds - monomers, oligomers and macrocycles - reveals that the number of repeating units and UV extinction coefficients are not proportional; also, the UV absorbance of a macrocycle is 10-fold higher compared to its linear isomer. The possibility of a drastic difference in the ultraviolet absorbance of oligomeric analogues should also be considered in quantification of other classes of polymeric macrocycles.