Melting temperature biopolymer

Schildkraut, C. (1965) Dependence of the melting temperature of DNA on salt concentration. Biopolymers, 3, 195-208. 

The melting temperature (Tm) of the biopolymer was determined from differential scanning calorimetry thermograms. The Tm value of the P (3HB) homopolymer was about 177°C and P (3HB) with 10% P(3HV) was about 150°C (Table l),but the Tm values of biopolymer extracted from E. coli HMS174 were about 166°C. The Tm of the sample was lower than that of the P (3HB) homopolymer, but higher than that of the P (3HB) with 10% P (3HV), because the P (3HV) content in the sample is only about 4.5% of the biopolymer produced. The PHV content in extracted biopolymer was low, the flexibility of extracted biopolymer was low, and different fermentation conditions should be investigated. 

Fig. 221. Phase diagram of kappa carrageenan based on the melting temperature, T , and the total ftee potassium concentration, Cy. Reproduced from Biopolymers [Ref. 569] by the courtesy of the authors and of John Wiley Sons, Inc...

In fact all of the biopolymers are injection-mouldable in practice and can even be blown into film quite successfully provided that care is taken to minimize melt temperatures and residence times. It is also possible to adopt inverted temperature profiles along extruders such that the polymer is first melted at a relatively high temperature and then conveyed to the die through much cooler zones. This further reduces thermal degradation. 

Biopolymers satisfy environmental concerns, but they may have some limitations in terms of performance, such as heat resistance, barrier properties and mechanical properties associated with costs. Some PHA/PHB films may have increased fragility (due to high glass transition temperatures and melting temperatures), greater stiffness, less impact resistance and less heat resistance. All these factors are limiting the application of these films in food packaging. 

Clarinval AM. Engineer, biopolymer glass transition and melt temperatures. Brussels, Belgium CRIF-WTCM 2001. 

PHB has a melting temperature (Tm) of 180"C, a glass transition temperature (Tg) of 5 "C and a high molecular weight. It is naturally not crystalline, and is converted in a more crystalline form during the extraction process. Research has been undertaken to avoid this transformation step that causes a decrease in the mechanical properties. The properties of PHB are similar to those of polypropylene, except for its biodegradability. It is also more rigid, more brittle and denser than PP. It resists oxidation but presents low chemical resistance. PHB is insoluble in water and relatively resistant to hydrolysis, the opposite of most biopolymers. 

One of results of the binding of such compounds onto DNA chains is that the so called melting-temperature of the biopolymer is markedly increased. We have found that the stabilizing influence of spermine and spermidine against thermal denaturation of DNA and of t-RNA is, qualitatively, very similar. The results of equilibrium dialysis measurements have shown that also the free energy of binding of... 

Both the denaturation process in proteins and the melting transition (also referred to as the helix-to-coil transition) in nucleic acids have been modeled as a two-state transition, often referred to as the all-or-none or cooperative model. That is, the protein exists either in a completely folded or completely unfolded state, and the nucleic acid exists either as a fully ordered duplex or a fully dissociated monoplex. In both systems, the conformational flexibility, particularly in the high-temperature form, is great, so that numerous microstates associated with different conformers of the biopolymer are expected. However, the distinctions between the microstates are ignored and only the macrostates described earlier are considered. For small globular proteins and for some nucleic acid dissociation processes,11 the equilibrium between the two states can be represented as... 

Y. A. Chen and E. W. Prohofsky, Sequence and temperature dependence of the interbase hydrogen-bond breathing modes in B-DNA polymers comparison with low-frequency Raman peaks and their role in helix melting. Biopolymers, 35(6), 573-582 (1995). 

FIGURE 6.25 Differential scanning calorimetry (DSC) as applied to potato starch-water mixtures % water (w/w) indicated near the curves. In DSC, the differential amount of heat (or more precisely, enthalpy, H) needed to increase the temperature (dHjdT) is registered as a function of temperature (T), and any melting (or similar transition) causes a peak in the heat uptake. The peak area is proportional to the melting enthalpy. In the figure, the specific heat capacity of the material has been subtracted, providing horizontal base lines. (After results by J. W. Donovan. Biopolymers 18 (1979) 263.)... 

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