Kinetics of Threading α-Cyclodextrin onto Cationic and Zwitterionic Poly(bola-amphiphiles)

Abstract

The amphiphilic polymers, poly(iminoundecamethylene), poly((N-methylimino)undecamethylene), poly((N,N-dimethylammonio)undecamethylene), and poly((N-methylimino)undecamethylene-N-oxide) were synthesized from nylon-11 by BH3 reduction of amide groups to amino groups and subsequent methylations. The poly(N-oxide) was obtained by H2O2 oxidation of the polymeric tertiary amine. Since the polymers and their inclusion compounds were water-soluble, threading kinetics of α-cyclodextrin rings onto these polymers could be investigated by 1H NMR. Kinetics were fitted by an empirical root exponential association function Y = Y∞(1 − exp(−sqrt(5.3t/t90))). The time t90, necessary to reach 90% completion of the threading process, was taken as a measure of the steric hindrance exerted by the hydrophilic groups along the polymer chain. The vaIues of t90 decreased by more than 3 orders of magnitude as the diameters of the hydrophilic groups decreased from 5.5 to 4.3 Å.