Natural-synthetic hydrid biomaterials have been isolated from the growth of Alcaligenes latus and Pseudomonas oleovorans in the presence of diethylene glycol (DEG). A. latus could cometabolise DEG with 10 g/L glucose, while DEG was consumed by P. oleovorans with 20 mM sodium octanoate or octanoic acid. The presence of DEG in bioprocessing systems for the production of short chain length (scl-) and medium chain length (mcl-) PHAs consequently lowered cell viability and PHA yield. Cell morphology was slightly changed, but the PHA inclusion bodies apparently were not. DEG affected the composition of the mclPHA which was confirmed to be polyhydroxyoctanoate (PHO) with a significant increase in the C8 component. Gas chromatography-mass spectrometry (GC-MS) was used to quantitatively monitor DEG in the system and revealed its cellular adsorption. Intracellularly, the DEG significantly decreased the molar weight of the mclPHA and sclPHA. P1PH NMR, 2-D COSY and HSQC spectra confirmed that the polymer samples consisted of PHA chains terminated by DEG. Similar to the cultivation of P. oleovorans with DEG, the presence of PEG200 and PEG400 also had an effect on cell growth, PHO yield and cell viability. Furthermore, a hybrid copolymer of PHO-PEG200 was synthesised. The synthesis of these natural-synthetic hybrid copolymers could lead the way for a wide variety of PHA-PEG copolymers with a range of bioactive properties. All thermal properties of PHB were higher than those of PHB-DEG. This may be due to a combination of lower PHB molecular weight and termination of the chains by DEG, i.e. ???DEGylation???. However, PHB-DEG was more elastomeric when compared to PHB, showing properties similar to its copolymer with 20 mol% 3-hydroxyvalerate. Contact angles revealed that the PHB-DEG film was slightly more hydrophilic than PHB. Despite the large difference in their respective proportions, the comparatively small DEG component exerted an influence on chain confirmation, such that solvent casting under humid conditions apparently induced self-assembly and formed a disordered microporous film. DEGylation of PHO also had noticeable effects on the physiochemical properties of the biopolymer. A major decrease in molecular weight, together with the termination of hydrophobic PHO chains with hydrophilic end-groups resulted in changes to its thermal properties when compared to PHO. In comparison to PHO, solvent cast films of PHO-DEG were apparently less flexible, but more hydrophilic.
| Identifer | oai:union.ndltd.org:ADTP/215501 |
| Date | January 2006 |
| Creators | Sanguanchaipaiwong, Vorapat, Biotechnology & Biomolecular Sciences, Faculty of Science, UNSW |
| Publisher | Awarded by:University of New South Wales. School of Biotechnology and Biomolecular Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Vorapat Sanguanchaipaiwong, http://unsworks.unsw.edu.au/copyright |
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