Attachment of 1,5,9-Triazacyclododecane and β-Cyclodextrin to Poly(ethylenimine) in Proximity by Site-Directed Functionalization

A novel methodology for the site-directed introduction of a functional group in the vicinity of β-cyclodextrin (CD) on the backbone of branched poly(ethylenimine) (PEI) is developed. Site-directed or random attachment of 1,5,9-triazacyclododecane (TC) to CD-containing PEI followed by acetylation of the primary and secondary amines of the polymer backbone produced [TC–CD]SDAcPEI or [TC–CD]RanAcPEI, respectively. By the addition of Ni(II), Cu(II), or Zn(II) ion, [M(II)TC–CD]SDAcPEI or [M(II)TC–CD]RanAcPEI was obtained. The formation constant for the complexation of a hydrophobic ester revealed that the TC portion was indeed positioned in the vicinity of the CD cavity in [M(II)TC–CD]SDAcPEI. Compared with [M(II)TC–CD]RanAcPEI, [M(II)TC–CD]SDAcPEI appears to exert an extra stabilization effect (−ΔΔG° = 1.0–1.3 kcal/mol) on the complexed ester by hydrogen bonding between the metal-bound water of the polymer and the carbonyl group of the ester.