Polyhydroxyalkanoates (PHAs) are biodegradable aliphatic polyesters, known to be produced by many common microorganisms. Nodax is a recently introduced family of PHA copolymers comprising 3-hydroxybutyrate units and a relatively small amount of other medium chain length 3-hydroxyalkanoate (mcl-3HA) comonomers with side groups of at least three carbon units or more. There are several different grades of copolymers available, depending on the average molecular weight, average mcl-3HA content within the copolymer, and side group chain length of the chosen mcl-3HA unit. PHA copolymers with different mcl-3HA types and contents can be made either by bacterial fermentation or by chemical synthesis. The incorporation of mcl-3HA units into PHAs effectively lowers the crystallinity and T(m) in a manner similar to the effect of alpha-olefins in linear low-density polyethylene. The T(m) can be lowered well below the thermal decomposition temperature of PHAs to make this material much easier to process. The reduced crystallinity provides the ductility and toughness required for many practical applications. The mcl-3HA content regulates the T(m) and crystallinity of copolymer almost independently of the branch size, as long as more than three carbons are present in the side group. On the other hand, the side group chain length of the mcl-3HA has a profound effect on the flexibility of copolymer.
The synthesis, spectral characterization, and electrochemical behavior of bis(tri-n-hexylsiloxy)(2,3-phthalocyaninato)silicon [SiPc(OR)2], its dimer [RO(SiPcO)2R], and its naphthalocyanine analogue [SiNc(OR)2] are described. All compounds show near-UV absorption corresponding to Soret and N bands and intense absorption in the visible-near-IR region corresponding to Q bands. In CH2C12, within the solvent stability limit, there are two reductions and one oxidation for SiPc(OR)2 and two reductions and two oxidations for RO(SiPcO)2R and SiNc(OR)2; all appear as reversible one-electron waves, although = 2 for the dimer. The difference in the peak potentials of the first oxidation and first reduction waves agrees well with the excitation energy and fluorescence (corresponding to Q bands) of SiPc(OR)2 and SiNc(OR)2. Both compounds emit upon electrochemical generation of reduced and oxidized forms (electrogenerated chemiluminescence, eel). The corrected eel maxima are near 684 nm for SiPc(OR)2 and 792 nm for SiNc(OR)2; the latter corresponds to the longest wavelength eel emission reported so far. The phthalocyanine dimer, RO(SiPcO)2R, is easier to reduce and easier to oxidize than the monomer.The voltammetric waves in this case involve two-electron transfers with peak splittings characteristic of le waves, suggesting that the two phthalocyanine rings in the dimer do not strongly interact. No fluorescence or eel was observed from the dimer.Phthalocyanine compounds often show high thermal and chemical stability and interesting optical and electrical properties.1"5 67We and others have been interested in the conductivities
The persistence length of isotactic poly(hydroxy butyrate) was measured using small-angle neutron scattering. The value obtained from these measurements reflects a high degree of local chain persistence. If this local persistence is accounted for, scattering from these chains can be globally fit with Gaussian scaling. A global scattering function, the unified equation, is used, which decomposes the chain structure into two levels, one corresponding to the Gaussian regime and one to the persistence regime. The persistence length obtained using this global scattering function is compared to that obtained using the graphical approach of Kratky and Porod with good agreement. Additionally, the global fitting approach of Sharp and Bloomfield is also considered. The Kratky and the Sharp and Bloomfield approaches appear to yield different values for the persistence length. Additionally, the Sharp and Bloomfield function does not allow inspection of the component parts of the fit. One advantage of both global functions is that the level of statistical confidence in the persistence length can be determined in a least-squares fit. Another advantage is the removal of ambiguity concerning an apparent regime of non-Gaussian scaling between the persistence scaling regime and the Gaussian regime.
Introduction Experimental Chemical Synthesis Biological Production Molecular Weight Determination NMR Thermal Analysis X‐ray Analysis Crystallization Kinetics Mechanical Analysis Rheological Measurements Properties Breaking Down Isodimorphism Increasing Flexibility, Ductility Crystallization Rate Melt Properties Melt Stability Deformation Properties and Morphology Conclusions Acknowledgements
Ralstonia eutropha has been considered as a bacterium, incorporating hydroxyalkanoates of less than six carbons only into polyhydroxyalkanoates (PHAs). Cells of the wild type cultivated with sodium octanoate as the carbon source in the presence of the fatty acid beta-oxidation inhibitor sodium acrylate synthesized PHAs composed of the medium chain length hydroxyalkanoates (3HA(MCL)) 3-hydroxyhexanoate (3HHx) and 3-hydroxyoctanoate (3HO) as well as of 3-hydroxybutyrate and 3-hydroxyproprionate as revealed by gas chromatography, (1)H NMR spectroscopy, and mass spectroscopy. The characterization of the polymer as a tetrapolymer was confirmed by differential solvent extraction and measurement of melting and glass transition temperature depression in the purified polymer compared to PHB. These data suggested that the R. eutropha PHA synthase is capable of incorporating longer chain substrates than suggested by previous in vitro studies. Furthermore, expression of the class II PHA synthase gene phaC1 from P. aeruginosa in R. eutropha resulted in the accumulation of PHAs consisting of 3HA(MCL) contributing about 3-5% to cellular dry weight. These PHAs were composed of nearly equal molar fractions of 3HO and 3-hydroxydecanoate (3HD) with traces of 3HHx. These data indicated that 3HA(MCL)-CoA thioesters were diverted from the fatty acid beta-oxidation pathway towards PHA biosynthesis in recombinant R. eutropha.
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