Synthesis and Metal-Complexation Ability of Cross-Linking Materials Containing Noria-Templated Cavities with Pendant Carboxylic Acid Groups

We synthesized noria-containing cross-linking materials, Cross(Noria-MA-co-DM[n]m), by radical polymerization of a noria derivative with pendant methacryloyl groups (noria-MA) and α, ω-alkanedimethacrylamides (DM[n], n = 3, 6, 12) at feed ratios of noria-MA/DM[n] = 1/2.4, 1/12, and 1/24 (m = 2.4, 12. and 24). Alkaline hydrolysis reaction of Cross(Noria-MA-co-DM[n]m) removed the noria moieties to give corresponding cross-linking materials, Cross-COOH-DM[n]m, containing noria-templated fixed cavities with pendant carboxylic acid groups. Among the noria-containing cross-linking materials, Cross(Noria-MA-co-DM[6]24) showed the greatest extent of removal of noria upon hydrolysis. Nitrogen and carbon dioxide absorption studies indicated that Cross(Noria-MA-co-DM[6]24) contains fixed cavities, whereas Cross-COOH-DM[6]24 does not in the solid (unswollen) state. Examination of the inclusion-complex-forming ability of the synthesized cross-linking materials using aqueous solutions of metal ions revealed that Cross-COOH-DM[6]24 has the greatest absorption capacity. These results indicate that Cross-COOH-DM[6]24 indeed contains noria-templated cavities that can accommodate metal ions in aqueous solution.exterior and a hydrophobic interior, and form complexes selectively with organic compounds in water[14]. Polyrotaxanes[15-17] and nanotubes[18] also have the ability to form complexes with organic compounds. On the other hand, we synthesized a ladder-type cyclic oligomer, which we called noria (water-wheel in Latin), by means of one-pot reaction using resorcinol and 1,5-pentanedial in high yield.[19] Single-crystal X-ray analysis confirmed that noria has 24 hydroxyl groups, 6 cavities in the side, and a large hydrophobic central hole, i.e., a water-wheel-like structure (Scheme 1). A noria derivative (noria-COOEt) containing carboxylic ester moieties could form a complex with Rb+ ion, which was apparently enclosed in the central hole in the molecule. Other noria derivatives[20 - 27] and noria-like macrocycle compounds [28 - 31] have since been synthesized and their applications have been investigated.This is a product of research which was financially supported (in part) by the Kansai University Fund for Supporting Outlay Research Centers, 2017. “Development of new materials and new processes for establishment of advanced separation system for various metals”