Ling, Siew Chen
(2012)
Biosynthesis Of
Poly(3-Hydroxybutyrate-Co-3-
Hydroxy-4-Methylvalerate)
Copolymer By Chromobacterium sp. USM2.
Masters thesis, Universiti Sains Malaysia.
Abstract
Polyhydroxyalkanoate (PHA) with enhanced physicochemical properties will
be ideal for a wide range of practical applications. The incorporation of 3-hydroxy-
4-methylvalerate (3H4MV), a branched C6-monomeric unit into the polymer
backbone is known to improve the overall properties of the resulting polymer.
However, the most suitable microorganism and PHA synthase that can synthesize
and polymerize this monomer efficiently still remain unknown at present. In this
study, the ability of Chromobacterium sp. USM2 to synthesize poly(3-
hydroxybutyrate-co-3-hydroxy-4-methylvalerate) [P(3HB-co-3H4MV)] was
evaluated under different culture conditions. It was found that Chromobacterium sp.
USM2 can synthesize P(3HB-co-3H4MV) when glucose and isocaproic acid were
fed as carbon sources. However, the highest molar fraction of 3H4MV, 22 mol%
was detected in Chromobacterium sp. USM2 when isocaproic acid was provided as
the sole carbon source. In addition, dissolved oxygen concentration was identified as
a crucial factor in initiating the accumulation of high 3H4MV molar fractions. The
structural configuration of the resulting P(3HB-co-3H4MV) was confirmed by FTIR,
1D and 2D NMR spectroscopy analysis. Subsequently, the thermal and tensile
properties of P(3HB-co-3H4MV) copolymer was characterized. P(3HB-co-3H4MV)
copolymer with Mw in the range of 5.4 x 105–9.3 x 105 Da were produced. TGA
analysis and tensile test further revealed that the incorporation of small amounts of
3H4MV into 3HB polymer chain resulted in greater flexibility and thermal stability
compared to P(3HB) homopolymer.
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