Effect of molecular mass on the optical activity of chitosan

The optical activity of chitosan has been examined by the optical rotary dispersion method in a wide molecular mass range, beginning from low-molecular analogs of the monomer unit and oligomers. In the spectral range from 300 to 710 nm, all samples demonstrate smooth curves of the optical rotary dispersion. For the polymers and oligomers, these curves lie in the region of negative values of specific optical rotation α], while for monosaccharides, these curves are in the positive region. High-molecular-mass samples are characterized by maximal ?α] values that are practically independent of molecular mass. For partially depolymerized samples with M < 2 × 10⁵ and for oligomers, the smaller the molecular mass of the sample, the greater the decrease in the modulus of ?α]. The passage to D-glucosamine chlorohydrate and to N-acetyl-D-glucosamine is characterized by inversion of the sign of rotation and achievement of high +α] values.