Precursor control over the self-assembly of [2]catenanesviahydrazone condensation in water

Abstract

By means of hydrazone condensation, a series of homo-[2]catenanes were self-assembled in high yields in water. The properties of the precursors have a great impact on the self-assembly pathway, as well as the stability and co-conformations of the products.

Dynamic Covalent Self‐Assembly Based on Oxime Condensation

“…In addition, both 3 4+ ·4 Cl À and 3 4+ ·4 PF 6 À seem to be remarkably stable in solid state.For example,after keeping the solid-state sample of 3 4+ ·4 Cl À for no less than four months,werecorded its 1 HNMR spectrum ( Figure S27) in [D 6 ]DMSO,w hich were almost identical as that of the freshly prepared samples.T hese observations are in contrast to our previously reported [18,19] catenanes obtained by hydrazone condensation, which underwent remarkable decomposition during counteranion exchange and in solid state.T he enhanced stability of 3 4+ compared to its hydrazone-based counterpart is even more remarkable in solution. No observable decomposition of 3 4+ occurred during counteranion exchange as inferred from the 1 HNMR spectra of both 3 4+ ·4 PF 6 À and 3 4+ ·4 Cl À ,i ndicating that 3 4+ is remarkably chemically inert.…”

“…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 + -. 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. 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. 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. 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.…”

“…Tw op recursors for oxime condensation, namely ab ishydroxylamino linker 1 [31] and aw ater-soluble bisaldehyde compound 2 2+ ·2 Cl À , [19] are synthesized from commercially available compounds in two and one-step procedures,respectively.Compound 1 is soluble in acidic water, because it exists predominantly in its dicationic protonated form, namely 1·2 H 2+ .W ef irst combined 1 and 2 2+ ·2 Cl À in D 2 Oo rw eakly acidic aqueous solution (e.g.,0 .001m of HCl in D 2 O). The corresponding solutions were heated at 80 8 8Cfor no less than 3days until the corresponding 1 HNMR spectrum no longer changed.…”