In depolymerizing

An enhancement in depolymerization rate after the light was turned off was also observed. This continued enhancement was very obvious after the exposures at 25 and 52 h, and is believed to represent relatively fast depolymerization of small polymer particles which were fragmented from larger particles during illumination. 

Protocol Increase in tubule number concentration Increase in depolymerization rate OfF-rate constant (sec- ) On-rate constant (M- sec" ) Reference... 

Photolytic. Irradiation of styrene in solution forms polystyrene. In a benzene solution, irradiation of polystyrene will result in depolymerization to presumably styrene (Calvert and Pitts, 1966). 

Earlier transition metals, as zirconium and hafnium, are still more active in hydrogenolysis, which allows zirconium hydrides to be used in depolymerization reactions (hydrogenolysis of polyethylene and polypropylene) [89], In this case, the zirconium hydride was supported on silica-alumina. Aluminum hydrides close to [(=SiO)3ZrH] sites would increase their electrophilicity and, thus, their catalytic activity. A catalyst prepared in this way was able to convert low-density polyethylene (MW 125000) into saturated oligomers (after 5h) or lower alkanes at 150°C (100% conversion). It was also able to cleave commercial isotactic polypropylene (MW 250000) under hydrogen at about 190 °C (40% of the starting polypropylene was converted into lower alkanes after 15 h of reaction). 

Scheme 14.8 Comparison and contrast between silica and silsesquioxane alkyls and hydrides, and their activity in depolymerization and hydrogenation.

Backbone chain scission degradation can be divided as occurring via depolymerization, random chain breakage, weak-link or preferential site degradation, or some combination of these general routes. In depolymerization, monomer is split off from an activated end group. This is the opposite of the addition polymerization and is often referred to as unzipping. ... 

Pharmacology The mucolytic action of acetylcysteine is related to the sulfhydryl group in the molecule, which acts directly to split disulfide linkages between mucoprotein molecular complexes, resulting in depolymerization and a decrease in mucus viscosity. The mucolytic activity of acetylcysteine increases with increasing pH. 

The constant awareness that the propellant chemist must keep for small amounts of impurities can be illustrated by the effects of the small quantities of peroxide that can be found in the polyoxide polymers. Small quantities of peroxide lead to chain scission at elevated temperatures and result in depolymerization. 

Ideally, the purpose of delignification is to remove the lignin at least from the middle lamella as selectively as possible. In reality, however, attack on the polysaccharides cannot be avoided and this results in depolymerization of polysaccharides and losses of hemicellulose. 

Melling and Atkinson29 investigated nuclease treatment as a method for the removal of nucleic acids from bacterial suspensions. Two strains of E. coli were used and for both the strains the nuclease treatment was effective in depolymerizing nucleic acids and, hence, in recovery of supernatant after centrifugation to remove cell debris from disrupted cells. The nucleotide content in the supernatant was found to be 15-20% of total proteins and nucleic acids. The nucleotide content in the supernatant was reduced to a very low level by ammonium sulfate precipitation followed by dialysis of the redissolved precipitate. As stated earlier, direct precipitation of nucleotides resulted in significant residual nucleotides in the proteins. 

The enzymes involved in depolymerization of the mannan s consist of /3-mannanase (EC 3.2.1.78), the endo-acting enzyme, and (3-mannosidase (EC 3.2.1.25), which produces... 

A wide range of organic reactions have also been performed in SCW including hydrogenations, eliminations, condensations, hydrations and partial oxidations.It has also been used in depolymerization reactions of natural and synthetic polymers. However, because SCW is more reactive than NCW,... 

All four vinca alkaloids block mitosis with metaphase arrest. Their antitumor activity is based on their high binding affinity to intracellular tubulin, which is the protein subunit of the spindle microtubules. The binding constants of vincristine, vinblastine, and vindesine for tubulin are 8, 6, and 3.3 nmol/1 respectively (9,10). The formation of complexes between the vinca alkaloids and tubulin prevents the polymerization of the tubulin subunits to microtubules, which results in depolymerization of microtubules and inhibition of microtubule assembly. Based on the fact that microtubule assemblies also play a pivotal role in the movement of neurotransmitter substances along neuronal axons, vinca alkaloids can cause neurotoxicity, particularly at higher concentrations (9,10). 

In low-rank coals, particularly in lignites, many of the aliphatic bridges, which participate in depolymerization, may be linked to noncondensed phenolic rings. The reactivity of an aliphatic structure linked to a phenolic ring is suf-... 

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