Temperature-dependent self-assembly of a purely organic cage in water

Abstract

Using a novel dynamic covalent approach relying on reversible hydrazone formation, a purely organic 3-dimensional prismatic cage was developed in water at elevated temperatures. By lowering the temperature, the hydrazone bond becomes kinetically inert. This self-assembled cage acts as an effective receptor for donor-acceptor pairs, whose interactions are weak in the absence of the cage.

Dynamic Covalent Self‐Assembly Based on Oxime Condensation

“…As ac onsequence, avariety of complex molecules [9][10][11][12][13] are obtained in high yields, especially when these self-assembled molecules are sophisticatedly designed to represent the most thermodynamically favoured products.One of the major disadvantages of iminebased DCC is that, this dynamic bond is apt to undergo hydrolysis in aqueous solution. Avariety of macrocycles, [15,16] cages, [17] catenanes [18,19] as well as knots [20] were obtained in water based on hydrazone condensation in pure water. Thepartially negatively-charged carbon atom is therefore less electrophilic,p rotecting the C=Nb ond from nucleophilic attack by water molecules or other nucleophiles.…”

“…Therefore,the self-assembled products containing imine can hardly realize their functions in water, the medium of life.H ydrazone (-C=NÀN-), [14] am ore robust counterpart of imine,w as thus employed to develop water-compatible DCC approaches.T he higher stability of hydrazone results from the delocalization of the lone electron pair in the adjacent nitrogen atom onto to the C = Nd ouble bond, resulting in acharge-separated resonance form, namely -C À ÀN=N + -. Avariety of macrocycles, [15,16] cages, [17] catenanes [18,19] as well as knots [20] were obtained in water based on hydrazone condensation in pure water. Avariety of macrocycles, [15,16] cages, [17] catenanes [18,19] as well as knots [20] were obtained in water based on hydrazone condensation in pure water.…”

“…Thepartially negatively-charged carbon atom is therefore less electrophilic,p rotecting the C=Nb ond from nucleophilic attack by water molecules or other nucleophiles. Avariety of macrocycles, [15,16] cages, [17] catenanes [18,19] as well as knots [20] were obtained in water based on hydrazone condensation in pure water. Thed ynamic nature of hydra-zone,however, jeopardizes the inherent stabilities of the selfassembled products.F or example,w eo bserved that the catenanes [18,19] containing hydrazone undergo decomposition via hydrazone exchange during counteranion exchange or solvent removal, even in the condition of low temperature and/or in the absence of acid catalyst.…”

Self‐Assembly in Water with N‐Substituted Imines

“…In 2018, Li and co‐workers employed this novel dynamic approach for synthesizing a cage and a macrocycle . The cage 6 6+ ⋅6 Cl − was self‐assembled in high yields by the [3+2] condensation of carbonohydrazide 5 with the trialdehyde 1 3+ ⋅3 Cl − in water (Figure ).…”

Dynamic Behavior of Covalent Organic Cages

“…The disassembly process is also important dynamic behavior of covalent organic cages and can be controlled by stimuli, depending on the kind of dynamic covalent bond. For example, imine, hydrazone, boronic ester, and boroxine formation are controlled by hydration/dehydration and disulfide formation is controlled by oxidation/reduction . A study of the disassembly process of covalent organic cages gives insights into the stability of the cages and uptake/release of guest molecules.…”