Microstructure and 13c-nuclear magnetic relaxation of bacterial poly (b-hydroxyalkanoates)

Abstract

A new method for the determination of the composition of poly($beta$-hydroxybutyrate-co-$beta$-hydroxyvalerate) (P(HB-co-HV)) copolyesters, by using optical rotation dispersion (ORD) spectra, was proposed. A linear equation based on the "optical superposition principle" has been shown to relate the specific rotation ($alpha$) of P(HB-co-HV) samples with their content of $beta$-hydroxyvalerate determined by $sp1$H NMR.The microstructure of P(HB-co-HV) copolymers, based on fast atom bombardment mass spectrometry (FAB-MS) analysis of the partial methanolysis or ammonolysis products, is described. The interpretation of the data indicated that the sequence distribution of all samples were statistically random (Bernoullian model), and permitted the detection in one sample of traces of pure poly($beta$-hydroxybutyrate), PHB.$sp{13}$C spin-lattice relaxation times and NOE were measured as a function of temperature in two magnetic fields, for poly ($beta$-hydroxybutyrate) in chloroform-d and 1,1,2,2,-tetrachloroethane-d$sb2$ (TCE). Among the various dynamic models used for the interpretation of the data, the Dejean-Laupretre-Monnerie (DLM) model offered the best description of the segmental motion along the PHB chain