Viscosity protein glass transition

Temperature-dependent pure dephasing rates of MbCO in three solvents show identical power law behavior at low temperatures. At intermediate temperatures there is a break in the power law arising from the solvent-influenced protein glass transition. Above this point the data in glassy trehalose are exponentially activated. The other solvents, which at elevated temperatures are liquids, have additional solvent viscosity-dependent contributions to the pure dephasing rate. 

As the temperature is lowered further, the viscosity of the unfrozen solution increases dramatically until molecular mobility effectively ceases. This unfrozen solution will contain the protein, as well as some excipients, and (at most) 50 per cent water. As molecular mobility has effectively stopped, chemical reactivity also all but ceases. The consistency of this solution is that of glass, and the temperature at which this is attained is called the glass transition temperature Tg-. For most protein solutions, Tg- values reside between -40 °C and -60 °C. The primary aim of the initial stages of the freeze-drying process is to decrease the product temperature below that of its Tg- value and as quickly as possible in order to minimize the potential negative effects described above. 

Addition of water to process mixture reduces processing viscosity but does not affect the glass transition temperature which is the same as for dry soy protein (150 C). Addition of 25 wt% of glycerin drastically decreases glass transition temperature to -50 C. Normally brittle polymer loses mechanical strength but gains flexibiUty. 

Many solid polymers are sensitive to heat stimulation and show characteristic REVERSIBLE PHASE TRANSITIONS at the GLASS TRANSITION TEMPERATURE and MELTING TEMPERATURE depending mainly on their own primary structure. This thermal sensitive property is being used in the fabrication of thermoplastic materials into any desired form in a similar means to that of fibers in the case of nylon, polyesters or films and other three dimensional products. In addition to the thermoplastic properties of polymers in the solid state, the molecular motion of polymers in solution is also achieved by thermal stimulation and has extensively been studied after pioneering works of Flory-Huggins. The effects of such thermal stimulation were detected experimantally as "sol-gel transformation", "viscosity changes", "phase separation" and so on. Egg-white and other aqueous solutions of natural proteins such as enzymes and hormones show such detectable behavior in the form of... 

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