Increasing the C3 concentration from 50 mM to 300 mM increased the selectivity from 12% to 38% (Figure ). Notably, the effect tended to wear off as the concentration C3 increased. Taken together, increasing the C3 concentration increases the likelihood of forming the wanted anhydride, but the effect wears off. Besides, decreasing the yield of the N-acylurea product to 30% is insufficient for supramolecular machinery-it would imply that less than 1% of the catalyst is present after as little as four cycles.