Thermostabilizers

Poly(vinyl chloride) tends to decompose thermally at common moulding temperatures (175-200°C). To be used in finished articles, the polymer needs stabilization against thermal degradation. The function of the thermal stabilizer is to eliminate the formation of polyconjugated structures (yellowing) and of hydroperoxides during thermal processing. 

The following tin stabilizers of the type RjSnYj have been investigated for their effect on photodegradation of poly(vinyl chloride)  

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Such inorganic compounds as sulphates of heavy metals and calcium [27], sulphites of calcium and potassium, salts of nickel [28] have been reported as thermostabilizers of polyolefins. 

In case of polyethylene potassium hydroxide with an ABC carrier is effective as a thermostabilizer up to the temperature of 440°C. Regarding the thermostabiliz-... 

At present, very few compounds are used as thermostabilizers for cured polyethylene. Among them may be listed I,3-dihydro-2,2,4-trimethylquinoline jS-di-naphtyl, -phenylenediamine, zinc mercaptobenzimida-zole [43-45]. 

Po[yamine disulphides do not inhibit peroxide vulcanization of polyethylene, are stable in air up to 300-350°C, exhibit good compatibility and show no sweating out from the polyethylene mass. Table 8 gives the comparison between the efficiency of polyamine disulphides as thermostabilizers of cured polyethylene. 

A series of polyamine disulphides (polyaniline disulphide, polyamine disulphide, and polyparaphenylenedi-amine disulphide) represent effective thermostabilizers of cured polyethylene, and provide a decrease in gel fraction 2.5-3 times as large as that in case of inhibited thermal destruction. Stabilizers of normal polyethylene (Neozone D , Santonox R ) are inefficient as stabilizers of cured polyethylene, these substances decompose and even initiate thermal destruction of cured polyethylene. 

Polyamine disulphides are effective thermostabilizers of cured polyethylene up to 400°C. In presence of polyamine disulphides a decrease in gel fraction is one half as large as that of nonstabilized cured polyethylene over the temperature range from 350-380°C [46]. 

High thermostabilizing efficiency of polyamine disulphides relative to chemically cross-linked polyethylene is conditioned by the ability to accept macroradicals at the disulphide bridge and imine group. Besides, the presence of paramagnetic centers causes the adherence of macroradicals providing for an extra stabilizing effect [49]. 

Korkegian A, Black ME, Baker D, Stoddard BE. Computational thermostabilization of an enzyme. Science 2005 308 857-60. 

Cline, J., Braman, J.C. and Hogrefe, H.H. (1996) PCR fidelity of Pfu DNA polymerase and other thermostabile DNA polymerases. Nucleic Acids Research 24, 3546-3551. 

Several polyheterocyclic compounds containing a condensed 1,2,4-triazole nucleus, such as 3,5-disubstituted thiazolo [2,3-r][ 1,2,4] triazoles, are thermostabilizers for polypropylene and polycaproamide <2003MI2>. Triazolo[3,4-A][l,3]benzothiazoledicarbonitrile derivatives are used to prepare hexazocyclanes-fluorophores as active media for liquid and solid lasers, scintillators, and for transformation of short-wave radiation to long-wave radiation <2004RUP2238276>. 

F NMR was used to monitor the folding kinetics of TmCsp labelled with 5-fluorotryptophan. It was found that the increased thermostability of TmCsp (rui = 87°C) compared to CspB (ri =52°C) was due to lower unfolding rate constants over a wide temperature range. This suggested that entropic factors play an important role in the thermostabilization of TmCsp. 

The PCR phase of such a study is very similar to PCR amplification of DNA in a reaction tube placed in a thermocycler. Here, however, the specimen is affixed to a slide covered with the reactants (buffer, DNTPs, primers, and a thermostabile DNA polymerase) and placed on the heating block of a traditional or modified (for slides) thermocycler programmed to provide the optimum temperatures for denaturation, primer annealing, and extension. After amplification for 20-30 cycles, the specimen is processed for ISH. 

Mozhaev, V.V. (1993) Mechanism-based strategies for protein thermostabilization. 

The exclusion mutants behavior has been readily and adequately determined by biochemical and crystallographic means [91,92]. The mutations occur within the hydrophobic pocket of VP1 and thermostabilization studies have shown that these mutations preclude the binding of drug in the VP1 pocket. One mutation site in HRV14 has been located at position 1188, which is on the side of the pocket closest to the viral interior, away from the canyon. Mutations at this site that convey resistance... 

With the di-sodium salt of 1,2-dicarbomethoxyethylphosphonic acid as modifier the diethylene glycol content and the carboxyl group content is very low (Table III). These results indicate that the used modifier has also thermostabilizing properties. The integral and differential curves (Fig.2) of molecular mass distribution show that the polydispersity of modified resin is comparable to that of the un-modified. 

Biopharmaceuticals may be subjected to heat treatment as a means of viral inactivation. Protein damage is prevented by the addition of high concentrations of a thermostabilizing excipient such as sugars or polyhyd-ric alcohols. The non-reducing polyhydric additives increase thermostability of the protein by the formation of a hydrogen-bonded solvent shell. The typical treatment for factor VIII consists of heat treatment at 60°C for... 

Fig. 2. Different thermodynamic strategies for increasing the denaturation temperature of a protein, (a) Free energy curve for a mesophilic enzyme, (b) Thermostabilization by broadening the free energy curve, (c) Thermostabilization by shifting the curve to higher temperatures, (d) Thermostabilization by increasing the free energy of stabilization at all temperatures.

If the enzyme of interest is essential for growth or survival, then it may be thermostabilized by selection in a thermophilic host (Oshima, 1994). The host growth temperature must be higher than the denaturation temperature of the enzyme to select for thermostable mutants. However, if the lower limit for growth is too far above the enzyme s... 

The plot of the stabilities and activities of clones from the first generation S41 random mutant library shows once again that most mutations are detrimental to stability and activity (Fig. 14). However, compared to the esterase library (Fig. 7), there are more mutants with improvements in both properties, suggesting that the two enzymes have different adaptive potentials. This may be due to the relatively poor stability of S41, or it may reflect constraints intrinsic to the three-dimensional structures of the two proteins. Evidence for the former can be found by comparing the results for the first generations of the psychrophilic sub-tilisin S41 and the mesophilic subtilisin E. Screening 864 mutants of S41 yielded nine thermostabilized variants (a hit rate of approximately 1%) (Miyazaki and Arnold, 1999) in contrast, screening 5000 subtilisin E mutants identified five thermostable variants (a hit rate of only 0.1%) (Zhao and Arnold, 1999). 

Of the nine thermostabilized S41 variants identified in the first generation, three had substitutions at residue 211, and one contained a substitution at 212. Saturation mutagenesis was performed at both sites in order to explore a greater sequence diversity than that accessible through error-prone PCR (Miyazaki and Arnold, 1999). One hundred and five of the clones from the library that showed reasonable activity were assayed... 

Characteristics of Thermostabilizing Mutations in pNB Esterase, Subtilisin E, and Subtilisin S41... 

PospfSil J, NeSpurek S and Zweifel H (1996) The role of quinone methides in thermostabilization of hydrocarbon polymers, Part I, Formation and reactivity of quinone methides, Polym Degrad Stab 54 ... 

Y. M. Drozdowicz, Y. P. Lu, V. Patel, S. Fitz-Gibbon, J. H. Miller and P. A. Rea (1999). A thermostabile vacuolar-type membrane pyrophosphatase from the archaeon Pyrobaculum aerophilum implications for the origins of pyrophosphate-energized pumps. FEES Lett., 460, 505-512. 

Due to the high polymerization temperature, only thermostabile materials can be used therefore the incorporation of biomacromolecules is not possible. 

The proposed block catalysts of honeycomb structure are characterized by the following component ratio, mass. % perovskite - 50-95, the oxides of aluminium or silicon, zirconium, chromium 5-50. A distinguishing feature of the catalyst is the use of perovskites CaMeOj and Ca,Lai.jMe03, where Me=Fe, Co, Ni, Mn and x=0.9-0.1, and of active components with structure-forming and thermostabilizing properties, such as aluminium, silicon, zirconium, chromium compounds. 

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