Rapid Binding of Concanavalin A and Maltose−Polyrotaxane Conjugates Due to Mobile Motion of α-Cyclodextrins Threaded onto a Poly(ethylene glycol)

Abstract

Maltose−polyrotaxane conjugates (Mal-PRXs), in which maltose-conjugated α-cyclodextrins (α-CDs) are threaded onto a poly(ethylene glycol) (PEG) chain capped with benzyloxycarbonyl-l-tyrosine, were characterized in terms of their molecular motion and the relation to multivalent interactions between the maltose moiety and concanavalin A from Canavalia ensiformis (Con A). Spin−lattice relaxation time (T₁) and spin−spin relaxation time (T₂) of α-CD C(1), maltosyl C(1), and PEG methylene protons in the Mal-PRXs revealed that the mobile motion of α-CDs in the polyrotaxane governed the molecular motion of maltosyl groups in α-CDs and threading PEG chain. The association constant (K_a) of the Mal-PRXs with 22, 38 and 53% of α-CD threading was 5.7 × 10⁴, 1.1 × 10⁶, and 5.3 × 10⁵ (M^-1-maltose), respectively. The largest K_a value of the Mal-PRX with 38% of α-CD threading was well correlated with the T₁ and T₂ values of maltosyl groups and α-CD, suggesting that the mobile motion of maltose-conjugated α-CDs in the Mal-PRX contributes to the highest affinity with Con A. Initial rate of binding with Con A was also governed by the mobile motion of maltose-conjugated α-CDs. Therefore, we concluded that both highly molecular motion due to the mobile motion of maltose-conjugated α-CDs and multivalency of the Mal-PRXs contributes to inducing rapid Con A binding.