Determination of Solution Properties of Poly(3-hydroxybutyrate) and Deuterated Poly(3-hydroxybutyrate) by SANS

摘要

Polyhydroxyalkanoates (PHAs) are natural, linear, thermoplastic polyesters synthesized by micro-organisms as intracellular carbon reserves and ion sinks in response to limited nutrient availability and imposed stress conditions. More than 100 different known types of PHA monomers have been reported depending on the number of carbon atoms and functional groups in the precursors. The members of the PHA family encompass a wide range of mechanical properties, from hard and brittle poly(3-hydroxybutyrate) (PHB) to soft and elastomeric poly(3-hydroxyoctanoate) (PHO). The PHB is the most studied polymer from the PHA family, however the proposed single chain conformation of PHB in dilute solutions has been controversial. PHB crystallizes into a left-handed 21-helix with an approximately g+g+tt conformation. Marchessault et al. showed that PHB adopts a helical conformation in solution leading to rigid rod-like particles using optical rotatory dispersion and light scattering measurements. However, the characteristic ratio of unperturbed dimensions, C_∞ = 8, was obtained by both Einaga and Tonelli, using light scattering and computer simulation respectively. The results indicate that PHB chains are randomly coiling in solution rather than forming a helical, rigid conformation. Interestingly, Beaucage et al. reported C_∞ = 40 for deuterated PHB in the amorphous solid phase which is five times larger than those observed for PHB chains in dilute solutions by small-angle neutron scattering (SANS), reflecting a large degree of local persistence in PHB chains.6 Comprehensive SANS analysis has not been applied to dilute solutions of PHB to elucidate the conformation of PHB chain. We bio-synthesized PHB and deuterated PHB (d-PHB) and performed SANS on the dilute solutions of these molecules. In this paper, we report the conformational properties of PHB and d-PHB in d-chloroform and chloroform, respectively.