Thermal transitions thermodynamics

Privalov, P.L., N.N. Khechinashvili, and B.P. Atanasov. 1971. Thermodynamic analysis of thermal transitions in globular proteins. I. Calorimetric study of chy-motrypsinogen, ribonuclease and myoglobin. Biopolymers 10 1865-1890. 

Application to Macromolecular Interactions. Chun describes how one can analyze the thermodynamics of a particular biological system as well as the thermal transition taking place. Briefly, it is necessary to extrapolate thermodynamic parameters over a broad temperature range. Enthalpy, entropy, and heat capacity terms are evaluated as partial derivatives of the Gibbs free energy function defined by Helmholtz-Kelvin s expression, assuming that the heat capacities integral is a continuous function. 

Hen egg-white lysozyme, lyophilized from aqueous solutions of different pH from pH 2.5 to 10.0 and then dissolved in water and in anhydrous glycerol, exhibits a cooperative conformational transition in both solvents occurring between 10 and 100°C (Burova, 2000). The thermal transition in glycerol is reversible and equilibrium follows the classical two-state mechanism. The transition enthalpies AHm in glycerol are substantially lower than in water, while transition temperatures Tm are similar to values in water, but follow similar pH dependences. The transition heat capacity increment ACp in glycerol does not depend on the pH and is 1.25 0.31 kj (mol K) 1 compared to 6.72 0.23 kj (mol K)-1 in water. Thermodynamic analysis of the calorimetric data reveals that the stability of the folded conformation of lysozyme in glycerol is similar to that in water at 20-80°C but exceeds it at lower and higher temperatures. 

A significant part of medical and pharmacological research is conducted on the biochemical level. Calorimetric work on such systems usually has the character of thermodynamic measurements and can be considered as part of biophysical chemistry. Two types of experiments currently seem to be the most important studies of binding processes using titration microcalorimetry and investigations of thermal transitions involving high sensitivity DSCs. 

The thermal and thermodynamic properties of LC polymers make it clear that the flexible spacer has a great influence on both the transition temperatures and transition entropies. This conclusion is again evidence of the vital part played by the flexible spacer in determining the organization and degree of order in the mesophase, and it also points out the critical interplay which occurs between the mesogenic unit and the flexible spacer. 

Thermal transitions were performed with the CD instrument above. Proteins were monitored at 222 run over a temperature range of 5-80°C. Data were collected in 1°C increments with a slope of 10°C/min. Initially, data were fit to a simple sigmoidal mathematical relationship for comparison. The half-point of the thermal transition, Tm, was determined by iterative fitting using the Boltzmann equation. Data were also fit to the following thermodynamic model ... 

Polarimetric (or indeed, any optical) data alone can yield only two thermodynamic parameters describing the thermal transition, Tc and AH. To proceed further, it becomes desirable to use one of the statistical mechanical treatments of one-dimensional cooperative transitions which have been recently formulated to treat this and more generalized problems (S, 15). In the present work we use the theory of Zimm and Bragg (18, 19) and extensions of this by Applequist (2). The theory predicts all the major features of the transition found experimentally in terms of a parameter, <7, which in our nomenclature is given by... 

Figure 10-2. Schematic representation of various thermal transitions the melting process as a first-order thermodynamic process, a rotational transition as a second-order thermodynamic process, and a glass transition 1, liquid cr, crystal am, amorphous state (after G. Rehage and W. Borchard).

DSC measures heat as a function of changing temperature. It is typically used to discern a wide range of thermal transitions in biological systems and the thermodynamic parameters associated with these changes. ITC is typically used for monitoring a chemical reaction initiated by the addition of a binding component and has become the method of choice for characterizing biomolecular interactions. 

With respect to polymeric materials, it is important to have applicability, which is defined by the intrinsic characteristics of specific polymeric materials. These inherent characteristics are related to all of the following but not limited to molecular weight, thermal transitions, structure type formed, physical state, thermodynamic equilibrium, kinetic mechanisms, heat and mass transfer phenomena, type of initiator utilized, presence of catalyst (when appropriate), particle size, nucleation process, medium viscosity, inorganic fillers, and others. Several of these properties may be controlled that is, specific materials may be obtained through specific variations and combinations of any of polymerization processes previously mentioned [3-5],... 

Chapter 1 is devoted to introductory concepts and de nitions, while Chapter 2 deals with physical and molecular aspects of polymers, that is, those relating to molecular shape and size, distinctive characteristics, conformational and con gurational behavior, structural features, morphology, thermal transitional phenomena, and relaxation properties. Chapter 3 discusses polymer solution behavior, the emphasis being on thermodynamics, phase equilibria, solubility, swelling, frictional properties, and viscosity. Molecnlar weight determination, which is one of the rst steps of polymer characterization and a centrally important topic of polymer science, mostly involves... 

In general, the enthalpy and temperature of thermal transitions are directly determined from DSC thermograms. However, other thermodynamic properties, such as heat capacity, can also be obtained from these experiments. 

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