Morphology and crystallization behavior of nascent poly(3-hydroxybutyrate) granules

The structure of poly(3-hydroxybutyrate) (PHB) granules was examined by transmission and scanning electron microscopy (TEM and SEM). They are made of two distinct components: a solid shell (overlapping lamellar crystals) and a non-crystalline core.TEM examination of sections of PHB granules revealed that, upon annealing, the core molecules transform into stacks of lamellar crystals of $ sim$50-70A in thickness. Fourier transform infrared results revealed the presence of bound water in a sample of freeze dried granules. Solid state $ sp{13}$C NMR results showed that the mobility of the granule core molecules was partly retained upon drying. A model for biosynthesis where emerging PHB chains in an extended conformation are simultaneously hydrogen bonded to water molecules is proposed.Hydrolytic degradation of PHB granules in hot HCl proceeds through random scission of the molecules of both the crystalline shell and the non-crystalline core indiscriminately