Abstract
In this paper, the objective is to point out some characteristics of stereoregular biopolymers, especially concerning their behaviour in aqueous solutions. Firstly, stereoregular polymers such as DNA, polypeptides and some polysaccharides adopt helical conformations at given thermodynamic conditions. This conformation is semi-rigid forming liquid cristalline phases and/or cooperative interactions stabilizing physical gels. Secondly, they are often charged and have positive or more frequently negative sites distributed regularly along the main chain, becoming polyelectrolytes. An unique viscometric behaviour is observed, but in the presence of slight amount of external salt (preferably ≥ 0.05M NaCl), their behaviour reaches that of a polymer having the same chemical structure and the same contour length but no ionic sites allowing their macromolecular characterization. Thirdly, the semi-rigid character gives an unique hydrodynamic behaviour: a model of worm like chain must be adopted, giving a quite different behaviour compared with the flexible chain model. Especially, even in specific thermodynamic conditions (the θ-conditions), the chains are not gaussian but they are expanded due to the local stiffness (expressed by the persistence length) with free draining behaviour and a Mark Houwink exponent larger than 0.5.
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