Enthalpy property-parameter curves

The enthalpies of transfer of BE (0.025 mol kg" -) from water to NaDec solutions are shown In Figure 5. With no adjustable parameters curve A Is predicted with the model of Roux et al (. The relation Is analogous to Equation 3. By adjusting Kp and AH3 a nearly quantitative fit can again be obtained as shown In curve B of Figure 5. The value of Kp used In this simulation Is about twice as large as the one used for volumes and heat capacities. If was fixed as the same value as that used for other properties the maximum In Figure 5 Is then underestimated. 

In brief, a DSC instrument comprises two cells fixed in an adiabatic chamber. One cell contains the sample to be tested, the second cell contains a reference solution or an empty DSC pan. The adiabatic chamber is maintained under pressure to avoid the evaporation of the sample (Plum, 2009). A DSC-thermogram represents the plot of heat capacity difference ACp (between the sample and the reference) as a function of temperature. Thermodynamic parameters, such as T, AH and AS, could be determined by the DSC curve analysis. T is the temperature at which the concentration of denatured and native forms of the protein are equal. This specific temperature is also called the midpoint of the thermal transition. AH represents the enthalpy of thermal transition determined from the integration of the DSC curve. The entropy (AS) of the thermodynamic transition of the protein may be calculated from the integrated area under the curve of AC /T vs. T. The free energy (AG), which gives an indication of the protein stability, can also be determined at any temperature from the values of AH and AS (O Brien and Haq, 2004 Plum, 2009). Thermal and thermodynamic properties of proteins analyzed by DSC are greatly affected by the experimental conditions used, such as pH, salts, alcohols, and the presence of other food components (e.g., lipids, polysaccharides) (Grinberg et al, 2009). 

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