Physical properties of microbial polythioesters: characterization of poly(3-mercaptoalkanoates) synthesized by engineered Escherichia coli.
Physical properties of chiral poly(thioesters), PTEs, prepared by engineered Escherichia coli, were examined by GPC, 13C CP/MAS solid-state NMR, X-ray diffraction, and thermal analysis. Microbial homopolymers of PTEs, poly(3-mercaptopropionate), PMP, and poly(3-mercaptovalerate), PMV, showed different solubility characteristics compared to poly(hydroxyalkanoates), PHAs. Generally, PTEs required higher temperatures for dissolution. Poly(3-mercaptobutyrate), PMB, and PMV dissolve in chloroform, and the molecular weight values were revealed by GPC as 176,000 and 165,000, respectively. The density values for PMP and PMB were 1.42 and 1.27 g/cm3, respectively. These values are similar to those for oxygen analogues. The NMR spectra for PTEs showed that carbonyl carbons are greatly shifted downfield by the sulfur atoms in the chain backbone compared to the PHA family. X-ray powder diffraction data indicated that PTEs are crystalline materials, but they do not crystallize as well as in the PHA family. The melting point, Tm, for PMP was 170 degrees C, which is about 100 degrees C higher than the equivalent oxygen analogue, poly(3-hydroxypropionate), PHP, and almost the same as that of bacterial poly(3-hydroxybutyrate), PHB. According to thermal analysis, only the PMP sample had enhanced heat stability, e.g., the decomposition temperature for PMP was 277 degrees C at 5% weight loss, whereas the values for PHP and PHB were 233 and 260 degrees C at the same weight loss, respectively.
Kawada
Jumpei
J
Department of Chemistry, McGill University, 3420 University St., Montreal, QC, H3A 2A7, Canada.
Lütke-Eversloh
Tina
T
Steinbüchel
Alexander
A
Marchessault
Robert H
RH
D004926:Escherichia coli / Q000235:genetics*; D005818:Genetic Engineering; D009682:Magnetic Resonance Spectroscopy; D008970:Molecular Weight; D011091:Polyesters / Q000138:chemical synthesis*; D012995:Solubility; D013438:Sulfhydryl Compounds / Q000138:chemical synthesis; D014961:X-Ray Diffraction
D011091:Polyesters; D013438:Sulfhydryl Compounds