Polymers accumulation

NAWRATH, C POIRIER, Y., SOMERVILLE C., Targeting of the polyhydroxybutyrate biosynthetic pathway to the plastids of Arabidopsis thaliana results in high levels of polymer accumulation, Proc. Natl. Acad. Sci. USA, 1994, 91, 12760-12764. 

Thus, 0 = Rate of monomer loss through reaction + Rate of polymer accumulation... 

SAFETY. Only a small amount of solvent is needed. The adsorbed solutes are eluted under gentle column flow conditions. In solvent extraction, larger volumes of solvent are needed and violent agitation is usually necessary. Thus, the fire and toxic hazards are much less for polymer accumulation. This safety feature compliments the decreased analytical costs and the lower solvent blanks associated with the use of smaller amounts of solvent. 

High-surface-area polymers can be used to accumulate large amounts of relatively insoluble organic compounds from very large volumes of water. In the adsorption step of the accumulation, the more soluble components are not recovered efficiently so that the accumulated solutes do not accurately reflect the proportions of different compounds present at trace levels in the water. Nevertheless, the very simple polymer approach can be used for many studies because the mutagenicity appears to reside in the hydrophobic fraction that the polymers accumulate efficiently. This conclusion is based on favorable bioassay comparison of the extracts accumulated by the XAD-2 method and the extracts collected by the more complicated and expensive freeze concentration method (216, 233). 

Stone, P.J., Nicholas, M.E. 1996. Varietal differences in mature protein composition of wheat resulted from different rates of polymer accumulation during grain filling. Aust J Plant Physiol 23 727-737. 

This is obviously due to the aggregation of hydroperoxides formed in local microdomains of the polymer. Accumulation of hydroperoxides in a certain microregion brings about their faster decomposition by an assisted bimolecular reaction and the domain increases its sizes. 

The behavior of the reaction rate as a function of temperature dispels any notion that the reaction is simple. Figure 3 shows that there is a maximum in the first-order rate constant-temperature curve at approximately 80 °C. At such a low temperature, the rate-temperature maximum cannot be explained by depolymerization, nor can it be explained by deactivation of the catalyst as a result of more rapid polymer accumulation on the catalyst at higher temperatures since the maximum is obtained for initial rates measured as a function of temperature. Theoretical considerations predict that a maximum in the rate-temperature curve may be expected from the Langmuir-Hinshelwood model for polymerization on solid surfaces but not from the Rideal model (5). The rate of reaction for the Langmuir-Hinshelwood model is given by ... 

Griffith, M., Huner, N. P. A., Espelie, K. E., Kolattukudy, P. E.. 1985. Lipid polymers accumulate in the epidermis and mestome sheath cell walls during low temperature development of winter rye leaves. Protoplasma 125 53-64. 

The next two types of mass transport, through the polymer surrounding each fragment, and then through the polymer aggregate, raise the question of how porous is that polymer accumulation. Should ethylene transport through the polymer be considered as travel through a porous solid, or as dissolution into semisolid reaction solvent Both views have been used to make model calculations. 

Some other catalysts, such as Cr /aluminophosphate, exhibit polymerization rates that do decay with time. In these systems, at least, polymer accumulation over time might cause the declining activity, because of increasing resistance to mass transport. However, this interpretation would mean that the polymerization rate would be a function, not of time itself, but of the amount of polymer accumulation. Investigation of the kinetics variables makes it clear that the rate is dependent not on polymer build up but on the reaction time. Similar rate-decay kinetics can be obtained with a high or a low polymer yield, by variation of ethylene concentration and other variables. In one experiment, the ethylene in the reactor was removed just as the peak reaction rate was reached, and not... 

A limitation of mass transport is another possible explanation for this behavior. Polymer accumulation could generate concentration gradients... 

FIGURE 170 Stopped flow kinetics experiment conducted at 95 °C using Cr/AlP04 catalyst (P/AI atomic ratio of 0.8, 600 °C). The reactivity decayed normally even in the absence of polymerization, which rules out polymer accumulation as the cause. 

U., Staiger, D., Lockau, W., Pistorius, E.K., and Broer, I. (2008) Plastid targeting strategies for cyanophycin synthetase to achieve high-level polymer accumulation in Nicotiana tabacum. Plant Eiotechnol. J., 6, 321-336. 

This fermentation was carried out with glucose as sole carbon source. In order to obtain 3-hydroxybutyrate-co-3-hydroxyvalerate copolymer, valerate was added when polymer accumulation phase began. Results are presented in Fig. 1 and 2 and Table 1. 

Taidi, B., Mansfield, D. and Anderson, A., 1995, Turnover of poly(3-hydroxybutyrate) (PHB) and its influence on the molecular mass of the polymer accumulated by Alcaligenes eutrophus during batch culture. FEMS Microbiol Lett., 120 201-206. 

Regardless of the production process chosen, a thin film of non conducting polymer accumulated at the interface during the molding or stamping process needs to be removed before further use of the bipolar plates. 

As poly(ethylenimine) (PEI) is one of the most widely studied non-viral vectors due to its high transfection ability, and much effort has been contributed to decrease its toxicity, we mainly focus on the current progress of PEI and its derivatives as the gene carrier. In addition, biodegradable polymers, which have gained increasing attention during the past decade for their reduced toxicity and prevention of polymer accumulation in the body, are also discussed. 

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