Enthalpy-driven processes

A large negative AH and a near zero AS were found for the complex. This result would suggest that inclusion of the adamantyl moiety in (3 - CD is an enthalpy-driven process and that Ka decreases when the temperature increases. 

The determination of the association constant K values can be done either graphically or numerically (Kertes and Gutmann, 1976). The K values can be used to estimate thermodynamic quantities such as AG°, AH° and AS0. The interactions of polar substances, such as methanol, ethanol and acetone, with Aerosol OT in toluene systems were examined (Kon-no, 1993). The negative AG° value was found in the decreased order methanol > ethanol > acetone and the contribution to AG° was AH° > TAS°. This result indicates that the solubilization of three solutes with Aerosol OT micelle is an enthalpy driven process. 

The consequences are seen in Figure 17.1, the agonists ( ) are binding to the (3-receptors by an enthalpy-driven process, whereas the antagonists (O) are binding with entropy and/or enthalpy-entropy driven processes. 

Notable Type C CBMs are the CBM Family 9 (p-sandwich folded),one member of which has been shown rigorously to bind the reducing end of oligo-and polysaccharides in an enthalpy-driven process." ... 

Another enthalpy driven process in polymer HPLC is the distribution of solute molecules between the volume of the mobile phase and the volume of the chromatographic stationary phase. The accepted terminology designates the processes of this kind absorption or the partition, which is driven by enthalpy and therefore it is the enthalpic partition. To prevent confusion between processes of adsorption and absorption, the term enthalpic partition is preferred in present chapter - also as the opposite to entropic partition, exclusion. Surprisingly, in many works the processes of adsorption and enthalpic partition are confused though the principal differences in their qualities are evident. 

The thermodynamic parameters (AG , A77 , and -FAS ) estimated by this procedure are plotted in Figure 3.3b as a function of temperature. The contribution of entropy term (-FAS ) to negative AG is superior to that of enthalpy term (Aff°) at low temperatures, whereas this relationship becomes opposite at high temperatures. This indicates that the micelle formation results from an entropy-driven process at low temperatures, whereas from an enthalpy-driven process at high... 

Enthalpy-Driven Processes in Weak Poly electrolytes and Poly electrolyte Complexes... 

A chiral CE separation method was developed for ephe-drine, norephedrine, synephrine, and epinephrine using a 20-mM phosphate buffer with pH 3.0 containing 0.4% w/v S-P-CD as CS. Peng et al. performed the separation in 50-pm i.d. capillaries with total and effective lengths of 60 and 50 cm, respectively. The effect of the temperature (20-60°C) on the CD enantioselectivity was investigated. An increase in temperature decreased the enantioselectivity toward ephedrine and norephedrine but increased that toward synephedrine and epinephrine. This observation suggests that the enantioseparation of ephedrine and norephedrine was an enthalpy-driven process, while for synephrine and epinephrine, it was entropy-driven. 

---