Branched-chain Analogues of Linear Polysaccharides. A Spectroscopic and Conformational Investigation on Chitosan Derivatives

The solution properties and conformational features of 2-substituted propanoic acid (I) and 2-substituted pentanedioic acid (II) derivatives of chitosan were investigated over a wide range of pH by potentiometric, optical and chiroptical measurements, and by theoretical conformational analysis. No significant change is observed in the solution properties of I upon pH variations, in agreement with computational results showing that the conformational features of the polymer do not vary with respect to the charge state of the ionizable groups. In contrast, spectroscopic titration and preliminary 1H-n.m.r. data indicate that conformational equilibria in II are pH-dependent. Consistently, computed models show that both the charge state of the ionizable groups and the chirality of the carbon atom in the side chain control the structural features of the polymer.