Andrej Krzan | PubMed Health

PubMed2006

Sequence distribution in microbial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) co-polyesters determined by NMR and MS.

The microstructure of bacterial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolyesters (PHBV) as well as a mixture of two PHBV copolyesters of different comonomer composition and sequence distribution was studied by 13C NMR based on dyad and triad analysis and multistage electrospray ionization mass spectrometry (ESI-MSn). Both techniques gave results that were in good agreement for all investigated samples. The effect of microstructure on PHBV thermal properties was investigated from the melting behavior of samples. A PHBV copolyester with randomly distributed hydroxyvalerate units (12.0 mol % HV) showed a single melting peak, whereas samples with nonrandom composition distribution showed multiple melting peaks in their thermograms. Such complex melting behavior suggested that the 12.9 and 27.1 mol % PHBV copolyesters were actually blends of several copolymers with widely different comonomer-unit composition.

Calorimetry, Differential Scanning↗

PubMedDate not supplied

SEC-MALS characterization of microbial polyhydroxyalkanoates.

Characterization of poly-3-hydroxybutyric acid (PHB) and poly-3-hydroxybutyric-co-valeric acid (PHBV, 13% valerate) in chloroform was performed using size exclusion chromatography coupled to a multi-angle light scattering detector (SEC-MALS). Absolute molar mass averages, molar mass distribution, and the radius of gyration were determined. Three sample preparation methods were examined: dissolution in chloroform (1) at room temperature, (2) at 60 degrees C, and (3) after thermal pretreatment of samples (annealing at 180 degrees C with subsequent quenching in liquid nitrogen). Dissolution at 60 degrees C and dissolution of thermally pretreated samples gave molecularly dissolved PHB and PHBV. At 60 degrees C using acid free chloroform, there was no indication of degradation for up to 120 min dissolution time, whereas thermal degradation of polymers did take place during annealing at 180 degrees C. The degradation rate constants for number and weight average degree of polymerization at 180 degrees C were slightly higher for PHB (5.19 x 10(-5) min(-1), 4.95 x 10(-5) min(-1)) than for PHBV (4.99 x 10(-5) min(-1), 4.54 x 10(-5) min(-1)). The dependence of the radii of gyration on molar mass showed that both polymers form random coils in chloroform. The relationship between the absolute molar masses and relative SEC results was determined. DSC and NMR characterization also gave evidence of the progress of degradation.

Biodegradation, Environmental↗