Dehydration Effect on the Recognition of Amphiphiles with Many Pendent Mannose Residues by Concanavalin A†

Abstract

Amphiphiles which carried many pendent mannose residues as side chains were prepared by telomerization of 2-methacryloyloxyethyl d-mannopyranoside (MEMan, α:β = 6.5:3.5) using a lipophilic radical initiator. The mannose-carrying amphiphiles (DODA−PMEMan, DP (degree of polymerization) = 3, 8, 14, and 17) incorporated in liposomes were recognized by a lectin from Canavalia ensiformis (Con A), which was proven by the increase in turbidity of the liposome suspension after mixing with the lectin. The recognition was largely affected by the degree of polymerization and surface density of the amphiphile in the liposomes. The association constant (Kas) between the mannose residue and Con A (2.2 × 105 M-1 for DODA-PMEMan (DP = 17) at 25 °C) was much larger than those for low molecular weight sugars (for example, methyl α-d-mannopyranoside, Kas = 8.2 × 103 M-1) due to the “cluster effect”. Thermodynamic parameters showed a significant contribution of positive entropy change to the effective sugar recognition in the liposome system, which was in contrast to the enthalpy-driven recognition of low molecular weight sugars by Con A. The positive entropy change could be attributed to the “dehydration” of both Con A molecule and the mannose-carrying polymer chains which were fixed to the gigantic and hydrophilic liposome surface.