Definitions of Drug-Receptor Binding Interactions

Bond type Example Total interaction energy, -A (kJ/mol) Electrostatic energy, (kJ/mol) Charge-transfer energy, (kJ/mol) 

Ionic bonds are formed between ions of opposite charge. Their electrostatic interaction is very strong  

Ion-dipole interactions are even more powerful, with energies that can reach 100-150 kJ/mol. The energy of such an interaction can be calculated from 

The term charge tranter refers to a succession of interactions between two molecules, ranging from very weak donor-acceptor dipolar interactions to interactions that result in the formation of an ion pair, depending on the extent of electron delocalization. Charge transfer (CT) complexes are formed between electron-rich donor molecules and electron-deficient acceptors. Typically, donor molecules are p-electron-rich heterocycles (e.g., furan, pyrrole, thiophene), aromatics with electron-donating substiments, or compounds 

A classic example of CT complex formation occurs in the solution of iodine (an acceptor) in cyclohexene (a donor), when the solution assumes a brown color due to a shift in its absorption spectrum. The brown is not a color in the physical sense, but rather the result of a very broad absorption band encompassing about 200 nm in the visible spectrum and evolving as a result of electronic changes in the CT complex. In contrast, a solution of iodine in CCI4—an inert solvent—is purple. 

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