Table 1: Temperatures and Enthalpies of the DSC Transitions for Human -Interfero
ID: 1009840 • Letter: T
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Table 1: Temperatures and Enthalpies of the DSC Transitions for Human -Interferon under Several pH and Buffer Concentration Conditions T,n (°C) H(kJ/mol of dimer) 523 530 600 649 buffer concn 5 mM 4.1 4.3 4.9 6.6* b 53.9 57.5 60.6 3.0* 3.5 3.8 36.0 40.3 44.1 45.9 50.1 51.3 165 310 375 401 460 10 mM 4.1 4.3 45 503 525 547 53.8 54.9 56.0 56.9 58.3 59.5 60.2 4.9 5.3 5.8* 6.6* 7.8* 3.8* 578 606 44.6 47.2 50.8 51.8 54.3 56.8 59.0 60.1 60.2 60.2 20 mM 392 438 4.1 4.3 500 518 4.9 5.8* 6.6* 7.8* 8.8* 560 562 3.9* 45.2 46.7 48.4 54.5 60.0 50 mM 300 332 4.3* 4.9* 6.6* 4.0* 4.3* 5.7* 6.6* 7.6* 44.3 47.7 58.3 59.7 59.1 100 mM 252 401 438 pH values were measured at 25 °C and corrected to the Tm values as indicated under Experimental Procedures. Asterisks indicate that after 2 h ofExplanation / Answer
Enthalpy–entropy compensation is a specific example of the compensation effect. The compensation effect refers to the behavior of a series of closely related chemical reactions (e.g., reactants in different solvents or reactants differing only in a single substituent), which exhibit a linear relationship between one of the following kinetic orthermodynamic parameters for describing the reactions:[1]
(i) between the logarithm of the pre-exponential factors (or prefactors) and the activation energies
lnAi = + Ea,i/R
where the series of closely related reactions are indicated by the index i, Ai are the preexponential factors, Ea,i are the activation energies, R is the gas constant, and and are constants.
(ii) between enthalpies and entropies of activation (enthalpy–entropy compensation)
H‡i = + S‡i
where H‡i are the enthalpies of activation and S‡i are the entropies of activation.
(iii) between the enthalpy and entropy changes of a series of similar reactions (enthalpy–entropy compensation)
Hi = + Si
where Hi are the enthalpy changes and Si are the entropy changes.
When the activation energy is varied in the first instance, we may observe a related change in pre-exponential factors. An increase in A tends to compensate for an increase inEa,i, which is why we call this phenomenon a compensation effect. Similarly, for the second and third instances, in accordance with the Gibbs free energy equation, with which we derive the listed equations, H scales proportionately with S. The enthalpy and entropy compensate for each other because of their opposite algebraic signs in the Gibbs equation.
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