The biological and physical chemistry of polyhydroxyalkanoates as seen by NMR spectroscopy

Abstract

The use of 13C NMR spectroscopy to study the biosynthesis, degradation and physical properties of polyhydroxyallkanoates (PHAs) is described. Solution-state NMR of whole cells allows direct observation of biosynthetic pathways within the cell and demonstrates that the bulk of the polymer is in a remarkably fluid, amorphous state. A new model is proposed for the maintenance of this state in vivo: the known rate of crystal nucleation combined with the physical dimensions of the native PHA granule lead naturally to the conclusion that polymer morphology is under kinetic rather than thermodynamic control. Finally solid-state NMR studies of isolated PHAs allow observation of separate crystalline regions based on hydroxybutyrate and hydroxyvalerate and measurement of the HB and HV contents of these and amorphous domains.