DSC study of melting and glass transition in gelatins

Abstract

In the range from -50 ~ to +130~ the temperature dependence of the heat capacity for different kinds of gelatins with water contents of from 2 to 95% was studied by the DSC method. It was shown that, in all studied eases, metastable collagen-like structures are formed in gels or crystalline gelatins, with thermodynamic parameters depending on the formation conditions. The characteristic properties of the glass transitions in amorphous gelatins and crystalline gelatins with different melting heats and different contents of the ordered phase were established. Special attention is paid to the structural properties of free and bound water. The dependence of the glass transition temperature Tg on the bound water content was shown to be of general applicability for many denatured biopolymers. Free water in gelatins, in distinction to the bound water, does not act as a plasticizer, but forms a rigid matrix inhibiting the glass transition.

Thermodynamic and dynamic factors involved in the stability of native protein structure in amorphous solids in relation to levels of hydration

“…131 Interestingly, the respective values increased with an increase in the protein ratio, indicating that the T g value of the protein is greater than that of the sugars, and extrapolation of the data to zero sucrose concentration indicates a T g of about 1508C for the native protein state, which is a value similar to those recovered for the unfolded and aggregated proteins described above. 123,128,[132][133][134] That sugars and proteins indeed interact in the amorphous state to form molecular dispersions is also supported by FTIR measurements 135 and by the observation that the presence of protein with sucrose in lyophilized samples prevents crystallization of sucrose, 136 just as has been observed when PVP was mixed with sucrose 121 and other small molecules. 120 If we assume that a lowering of the overall T g in a molecular dispersion, relative to that of the protein alone, would ordinarily increase the molecular mobility of the protein at a given temperature, it would then appear that the sugar would not have the ability to stabilize the system as suggested in the ''vitrification'' model used to explain the stabilizing effects of sugars as lyoprotectants.…”

Drastic effects of fast neutrons and γ-irradiation on the DC conductivity of Co-, Ni-, Mn- and Ag-gelatin doped films

“…The direct effect of c-rays is to excite the carbonyl groups (C=O) of the main polypeptide chain to form other free radicals and carbon monoxide via Norrish reaction [22]. In other words, polymers absorb c-rays in a destructive manner, which is bonds cleavage, either by hydrogen abstractions and its elimination from a chain or by the Table 1 Values of the activation energy (E a ) in (eV) for low (I) and high (II) temperature regions for pure gelatin and that doped with 5, 10, and 15 wt % of CoCl 2 before and after irradiation with different fast neutron fluencies Sample Unirradiated 7.6 · 10 5 n/cm 2 7.6 · 10 6 n/cm 2 3.05 · 10 7 n/cm 2 1.45 · 10 8 n/cm 2 0.5 · 10 9 n/cm 2 I II I II I II I II I II I Table 2 Values of the activation energy (E a ) in (eV) for low (I) and high (II) temperature regions for pure gelatin and that doped with 5 wt% of NiCl 2 , MnCl 2 and AgNO 3 before and after irradiation with different fast neutron fluencies Sample Unirradiated 7.6 · 10 5 n/cm 2 7.6 · 10 6 n/cm 2 3.05 · 10 7 n/cm 2 1.45 · 10 8 n/cm 2 0.5 · 10 9 n/cm 2 I II I II I II I II I II I oxidation reactions may continue with time, resulting in fracture and discoloration usually concentrated at the polymer surface [23].…”

Thermal properties of frozen water in the native and amorphous starches with various hydration degrees

“…This effect has been observed in humid proteins (Tseretely & Smirnova, 1992) and DNA (Mrevlishvili, 1984) as well as in concentrated solutions of carbohydrates of both natural and artificial origin (Slade & Levine, 1991) and starches (Belopolskaya, Tsereteli, Grunina, Smirnova, & Rodriguez, 2010;Belopolskaya, Tsereteli, Grunina, & Smirnova, 2011;Grunina, Tsereteli, Belopolskaya, Smirnova, & Rodriguez Castillo, 2013). The natural assumption arose that the observed effect is caused by the change of the size of small particles, usually referred to as clusters, that are formed in the water surrounding of a biopolymer with low humidity (the socalled size effect).…”