Synthesis of diaza-18-crown-6-functionalized beta-cyclodextrin derivatives at the secondary side and induced circular dichroism studies of their complexes with (2-naphthoxy)alkylammonium ions

Abstract

beta -Cyclodextrin derivatives connected with diaza-18-crown-6 through flexible bridges (R) at the secondary face 1a-c (1a: R = -(CH2)(4)-; 1b: R = -CH2CH2OH2CH2-; 1c: R = -(CH2)(8)-) have been prepared. The association constants of 1 with (2-naphthoxy)alkylammonium ions (2a: alkyl = butyl; 2b: alkyl = octyl) were determined by induced circular dichroism (ICD) spectroscopy and it was found that the derivatization of beta CD with the diazacrown resulted in enhanced binding with 2, compared to the native beta -CD. ICD Characteristics of the host-guest complexes indicate that a part of the alkylammonium moiety of 2 is protruded from the secondary side of the beta -CD cavity, and the guest molecules 2a and 2b move to the secondary and primary side, respectively, to make the binding of the ammonium group with the diaza-18-crown-6 moiety more feasible. The energy accompanied by the relocation of the guest molecules inside beta -CD moiety is compensated by the interaction energy between the ammonium ion and diazacrown ether.