Interactions solvation-desolvation

The direct ligand-protein interactions and the net solvation-desolvation term together should give an energy contribution that strongly favors formation of the complex (large and negative), since the other two components favor its dissociation. 

Extensive structural characterization of many different -ring heterocycles has not yet been done. Difficulties predicting relative potency of these compounds a priori stem from the lack of understanding of solvation/desolvation effects as well as difficulties in characterizing the low-intensity hydrophobic interactions. Consequently, it seems likely that new structure—activity relationships about the A-ring heterocycle will continue to be determined based on empirical findings. 

Solvation—Desolvation Equilibrium. From the observation of migration of plasticizer from plasticized polymers it is dear that plasticizer molecules, or at least some of them, are not bound permanendy to the polymer as in an internally plasticized resin, but rather an exchange—equilibrium mechanism is present. This implies that there is no stoichiometric relationship between polymer and plasticizer levds, although some quasi-stoichiometric relationships appear to exist (3,4). This idea is extended later in the discussion of specific interactions. 

Electrostatic interactions are considered to be important attractive forces, due to their relative strength, [59, 116—119]. The molecular electrostatic field which surrounds a binding site guides the correct orientation of the drug [59] and is responsible for the first contact. However, the role of electrostatic interactions as being mainly responsible for high affinity has been questioned due to an often unfavorable solvation-desolvation energy balance. It is difficult to express their contribution in a quantitative manner, due to a number of reasons ... 

Solvation to the guest, host, and resulting complex plays a cmcial role in supramolecular chemistry, where several weak interactions work together. Importantly, the seemingly complicated solvation/desolvation behavior as well as the conformational changes upon supramolecular interaction can be rationally and globally understood first by... 

The solvation (hydration) and desolvation of ions is important to the gelation process in AB cement chemistry. The large dipole moment of ion-pairs causes them to interact with polar molecules, including those of the solvent. This interaction can be appreciable. Much depends on whether the solvent molecule or molecules can intrude themselves between the two ions of the ion-pair. Thus, hydration states can affect the magnitude of the interaction. The process leading to separation of ions by solvent molecules was perceived by Winstein et al. (1954) and Grunwald (1954). 

Ion-pair formation (or the formation of triplets, etc.) is a very simple kind of interaction between ions of opposite charge. As the electrolyte concentration increases and the mean distance between ions decreases, electrostatic forces are no longer the only interaction forces. Aggregates within which the ions are held together by chemical forces have certain special features (i.e., shorter interatomic distances and a higher degree of desolvation than found in ion pairs) and can form a common solvation sheath instead of the individual sheaths. These aggregates are seen distinctly in spectra, and in a number of cases their concentrations can be measured spectroscopically. 

The active site of enzymes usually are located in clefts and crevices in the protein. This design effectively excludes bulk solvent (water), which would otherwise reduce the catalytic activity of the enzyme. In other words, the substrate molecule is desolvated upon binding, and shielded from bulk solvent in the enzyme active site. Solvation by water is replaced by specific interactions with the protein (Warshel et al., 1989). 

The sample temperature is increased in a linear fashion, while the property in question is evaluated on a continuous basis. These methods are used to characterize compound purity, polymorphism, solvation, degradation, and excipient compatibility [41], Thermal analysis methods are normally used to monitor endothermic processes (melting, boiling, sublimation, vaporization, desolvation, solid-solid phase transitions, and chemical degradation) as well as exothermic processes (crystallization and oxidative decomposition). Thermal methods can be extremely useful in preformulation studies, since the carefully planned studies can be used to indicate the existence of possible drug-excipient interactions in a prototype formulation [7]. 

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