Chain Depolymerization Research Articles

Induction and the Regulation of Production of Cellulase by Fungi

SYNTHESIS of cellulases by fungi is considered to be induced by cellulose substrates, or more specifically by their water soluble short chain depolymerization products such as cellobiose1, and occasionally by other disaccharides such as sophorose2 or lactose3. Glucose is considered to invoke an inducer-represser mechanism of regulation of enzyme production when added to cellulose, for it represses the induction of cellulase unless present in extremely small amounts4. But fungi which grow on cellulose alone must also utilize glucose, for the monomer is often reported to be the final product of cellulose depolymerization5,6. The production of cellulase would not be expected to be repressed in these conditions because the organism's rate of glucose utilization would usually be restricted by the relatively slow rate of release of monomer from cellulose. Thus, if glucose were supplied to laboratory cultures as their sole source of carbohydrate at a limited rate, comparable with its slow rate of release from cellulose, then production of the enzyme might well be promoted. We have experimental support for this hypothesis, showing that the production of cellulase is controlled by the organismapos;s rate of metabolism when regulated, for example, by carbohydrate uptake. We have also found that neither cellulose, cellobiose, nor any other sugar is required per se for production of the enzyme.

Study of molten isotactic polystyrene. II. The kinetics of thermal degradation from melt viscosity data

AbstractStarting from the established relation: log η = A + 3.4 log M̄v, the kinetics of thermal degradation of isotactic polystyrene has been investigated in terms of melt viscosities measured as a function of melting time at constant temperatures between 265 and 320°C. Random chain scission predominates over radical chain depolymerization and can be described by a zero‐order reaction with an activation energy E of about 39 kcal./mole. At the same time, the kinetic plots permit evaluation of the temperature dependence of melt viscosity without interference by degradation. This leads to an activation energy for viscous flow E′ of 20 ± 2 kcal./mole. As the same value holds for atactic polystyrene; viscous flow seems not to be influenced by the stereoregularity of polystyrene. In addition to the above activation energies only a single run of melt viscometry with 1–2 g. of a new sample of isotactic polystyrene is needed for a quantitative prediction of its melt viscosity at any practical melting time and temperature.

Thermogravimetric Analysis of Polyoxymethylene

Abstract The character of the thermal decomposition of polyoxymethylene, acetylated polyoxymethylene and Delrin in air and in nitrogen has been studied by thermogravimetric analysis. Two peaks have been observed in each atmosphere in the derivative thermogravimetric analysis curves for these samples. It has been confirmed that the feature of doublet peaks is related to the concentration of oxygen during the decomposition and, thus, that the first stage is due to the chain depolymerization as well as to the oxidative decomposition, and that the second stage is to be attributed to the random degradation of a stable fragment formed during the first stage decomposition. An increase of carbonyl groups in the polymer molecule with the degradation was confirmed by infrared spectroscopy.

A comparison of the effects of ultra-violet and gamma radiation in polymethylmethacrylate

The exposure of polymethylmethacrylate ( PMM ) and many other macromolecules to high-energy y- or electron radiation produces a degradation of the molecular chains. This may result from either ionization or excitation. Ultra-violet light results in excitation only. This paper compares the effects of these forms of radiation. The degradation of PMM has been studied in thick or thin films, and in solutions in benzene. It is found that at room temperature degradation (random main chain fracture) occurs with ultra-violet radiation, whereas at higher temperatures the reaction is one of chain depolymerization. The energy absorbed per main chain fracture is about 550 eV with ultra ­ violet radiation, so that less than 1 % of the quanta absorbed are effective; this compares with about 65 eV of γ-energy absorbed per fracture. Apart from this difference in efficiency, the two reactions are very similar. In both cases the number of fractures is proportional to dose and the radicals formed (as seen by e.s.r.) are identical in character. Somewhat similar changes also appear in the optical spectrum, although these may be modified by surface oxygen. These results show no significant contribution from any ionization produced by high-energy radiation.

The thermal depolymerization of polystyrene. IV—Depolymerization in naphthalene and tetralin solutions

The rapid decrease in molecular weight which occurs in the initial stages of the thermal degradation of polystyrene at 325°C occurs at the same rate whether the reaction is carried out in bulk polymer or in solution in naphthalene or tetralin. On the other hand, the radical chain depolymerization process which occurs in bulk polymer and in naphthalene solution, and results in the evolution of volatile products, principally monomer, dimer and trimer, is completely inhibited in tetralin solution. Thus it is deduced that volatilization and molecular weight decrease are manifestations of two distinct processes and this together with previous evidence is taken as proof that the decrease in molecular weight is due to scission of weak links rather than to an intermolecular process involving the depolymerizing free radicals.

Kinetics of Chain Depolymerization

Kinetics of Chain Depolymerization

Loss of power in steam engines

Five amide derivatives of Hyaluronic Acid (HA) were synthesized with C8, C12, C15, C16 and C18 linear alkyl-amines. These polymers (Hyadd) were tested against thermal, oxidative and hyaluronidase degradation by means of rheological experiments and SEC analysis and compared to non-modified HA. First of all, no free hexadecylamine was detected in the treated samples, meaning that under these stressing conditions only cleavage of glycosidic bonds occurs. Then, viscoelastic properties were assessed during thermal degradation and their variation as a function of time was expressed by means of a decay constant kG′: while no significant difference in the decrease rate was observed between Hyadd-C8 and Hyadd-C12, a marked stabilization of viscoelastic properties during thermal treatment was detected for Hyadd-C15, Hyadd-C16 and Hyadd-C18. On the other hand, no difference was observed between the MW decrease rate (kMW decay constant) of HA and Hyadd-C12 to-C18; the depolymerization takes place on the backbone of the polymers independently whether they are derivatized or not, but longer alkyl chains lead to higher viscoelasticity in the depolymerized products. Finally, both oxidative and enzymatic degradation were carried out analyzing the changes in elastic modulus and in dynamic viscosity: once again, the amide side chain came out with similar behavior to chemical cross-linked HA (HBC) and with improved performances respect to linear HA in terms of preservation of viscoelasticity after chain depolymerization.