High molecular weight PHB

High molecular weight PHB (>12,000 units), which was first described more than 75 years ago is a microbial storage material (intracellular carbon source, en-... 

In this research, commercially available PHB/PET copolyester LCP, PEN and PET were mechanically blended to form the LC phase of the blends. The critical composition of PHB in the PEN and PET forming an LC ternary blend was investigated, and the miscibility and thermal behavior were studied using thermal analysis. The PHB content in the ternary blend was controlled by the amount of PHB/PET copolyester, as a high-molecular-weight PHB homopolyester does... 

This may be demonstrated by extruding two identical pieces of pure, high molecular weight PHB homopolymer lace from the melt into air at ambient conditions using, for example, a simple MFI grader. If one piece is left to crystallize isotropically as a control, while the other is stretched immediately by 50-100%, then the latter will remain elastic for several minutes after the former has fully crystallized. Both samples, however, eventually harden to the same isotropically crystalline and very brittle condition. 

A completely new type of ROP catalyst was recently reported by Rieger and coworkers. Chromium salphen complexes (Fig. 32) convert racemic (3-BL to slightly isotactic-enriched PHB (0.60 < Pm < 0. 70) with a molecular weight of up to 800,000 g/mol (PD up to 8.5). These catalysts combine high activity and high molecular weight products, featuring the desired stereocontrol at moderate reaction conditions [13]. 

Poly-(3-hydroxybutanoic acid) (PHB), belongs to the large family of poly-(hydroxyalkanoates) (PHAs), high molecular weight natural polymers produced by various microorganisms and stored in cell cytoplasm (200). Low molecular weight PHB, also present in bacteria and are primarily involved in transport of ions and DNA across inner bacterial membrane (201). PHB could be developed as a valuable biocompatible material with possible applications in gene delivery after cytotoxic, safety, and efficacy evaluations. 

PolyPs and PHB have been found to be associated with ion-conducting proteins such as the human erythrocyte Ca2+-ATPase pump (Reush et al, 1997) and the Streptomyces lividans potassium channel (Reusch, 1999b). Some enzymes of PolyP metabolism, such as polyphosphate glucokinase (Phillips et al, 1999) and yeast high-molecular-weight exopolyphosphatase (Andreeva et al, 2001, 2004), can contain tightly bound PolyP. 

Figure 2. Biosynthesis and biodegradation of high-molecular-weight storage PHB (sPHB) by the most common mechanism. Microorganisms store PHB (acetate and NADH precursor ) as a survival measure, when glucose or other acetate precursors are available in the environment and when, at the same time, essential conditions for growth and multiplication are not met (cf. limitation of nitrogen, oxygen, phosphorous, trace element(s)) [2],...

Ultra-high-molecular-weight P(3HB) samples (UHMW-P(3HB), M = 1.3-16 X 10 ) were produced by E. coli XLl-Blue (pSYL105)" containing a stable plasmid harboring the R. eutropha H16 (ATCC 17699) PHB biosynthesis genes operon phbCAB. Two-step cultivation of the recombinant E. coli... 

---