BIOSYNTHESIS OF METHYL-BRANCHED POLY(BETA-HYDROXYALKANOATE)S BY PSEUDOMONAS-OLEOVORANS

Pseudomonas oleovorans was grown on 6-methylnonanoic acid (B-MNA), 7-m ethylnonanoic acid (7-MNA), and methylnonanoic acid (8-MNA), 9-methyld ecanoic acid (9-MDA), 7-methyldecanoic acid (7-MDA), and 2,6-dimethylh ept-5-enoic acid(2,6-DMHA). Poly(beta-hydroxyalkanoate)s (PHAs) were o btained when this bacterium was grown on pure 9-MDA, 8-MNA, 7-MNA, and B-MNA, but not on 7-MDA and 2,6-DMHA. The mixtures of n-nonanoic acid (NA) and either 7-MDA or 2,6-DMHA gave almost pure nonanoic acid homo polymers. For the other branched substrates, H-1 and C-13 NMR studies showed that the polymers obtained contained the type of methyl branchi ng expected from the starting alkanoic acid. The melting points of mos t polymers were similar to that of nonanoic acid except for that of th e polymer from 6-MNA, which was considerably higher. DSC measurements also showed that this polymer crystallized much faster than the others . C-13 NMR spectra of the polymer containing 6-methyl-3-hydroxynonanoa te units showed that equal amounts of the two chiral isomers were pres ent. From the GPC measurements the number-average molecular weights (M (n)) of the polyesters produced were in the range of 70 000-384000 wit h polydispersity indices (M(w)/M(n)) in the range of 1.37-2.55. Wide-a ngle X-ray diffraction measurement revealed that the crystalline struc ture of the polymers obtained from 6-MNA was different from that of th e polymer obtained from n-nonanoic acid.