Optical rotatory dispersion and circular dichroism of benzoyl polysaccharides

Measurements of optical rotatory dispersion (ORD) and circular dichroism (CD) were made in the range of 400–205 nm for polysaccharide tribenzoates such as 2,3,6‐tri‐O‐benzoyl amylose (I), 2,3,4‐tri‐O‐benzoyl dextran (II), tri‐O‐benzoyl pullulan (III), 2,3,6‐tri‐O‐benzoyl cellulose (IV), 2,3,6‐tri‐O‐benzoyl mannan (V), and polyglycan dibenzoates such as 2,3,‐di‐O‐benzoyl amylose (VI), cellulose (VII), and mannan (VIII). All compounds exhibit Cotton effects in the region of their UV absorption bands (206–285 nm). Comparison of the corresponding di‐ and tribenzoyl polysaccharides shows a qualitative agreement in number, position and sign of the CD bands but differences in ellipticity magnitude. The disubstituted derivatives exhibit smaller amplitudes than the trisubstituted ones. The contribution of the C(6) chromophore (linked by a CH2‐group to the asymmetric C(5) atom) was determined to be of the same sign as the combined contribution of the C(2) and C(3) substituents. The CD bonds of the individual polysaccharide derivatives, which differ in number, sign, and position, were discussed in terms of the steric position of the single chromophores and the steric arrangement and interaction caused by the configuration of the polysaccharides. The optical behavior of these polysaccharide derivatives was found to be not strongly influenced by a definite chain conformation in solution.