A Spectral Approach to Study Interaction between Chitosan Modified with Mannose and Concavalin A for the Creation of Address Delivery Systems of Antituberculosis Drugs

We present a comprehensive study of the receptor–ligand interaction by spectral methods on the example of Concanavalin A lectin and 5 kDa chitosan modified with D-mannose. An improved method for the modification of chitosan with D-mannose and purification of these conjugates is developed. A novel approach to calculate the constants of the Concavalin A binding with the mannose-containing ligand is proposed. The calculation is based on the intensity reduction of the Amide II absorption band in the IR spectra normalized by Amide I during the receptor binding with the modified chitosan-mannose polymer. The linearization of the binding curves in Scatchard coordinates allows finding the complex dissociation constants whose value constituted (5.5 ± 0.3) × 10–5 M. These results are confirmed by fluorescence polarization analysis. IR spectroscopy is found to be the most suitable and precise method for the calculation of dissociation constants, which does not require preliminary protein modification.