Drug-receptor interactions ionic bonds

Electrostatic forces are due to the ionic charges residing on the molecules, which attract or repel each other. The macromolecular structures of the receptors and enzymes mean that there are a number of ionic charges to attract the oppositely charged drug molecules. The forces of electrostatic interactions are weaker than covalent bonding. Electrostatic interactions are more common in drug-receptor interactions. There are two types of electrostatic interactions ... 

Electrostatic bonding is much more common than covalent bonding in drug-receptor interactions. Electrostatic bonds vary from relatively strong linkages between permanently charged ionic molecules to weaker hydrogen bonds and very weak induced dipole interactions such as van der Waals forces and similar phenomena. Electrostatic bonds are weaker than covalent bonds. 

In the broadest sense, these "bonds would include covalent, ionic, hydrogen, dipole-dipole, van der Waals, and hydrophobic interactions. Most drug-receptor interactions constitute a combination of the bond types listed in Table 1.1, most of which are reversible under physiological conditions. 

C=0 C=0, C N C=0, S=0 C=0, C—OH O, and H2O C=0. Because the charge of a dipole is less than that of an ion, charge-dipole and dipole-dipole interactions are weaker than ionic bonds. They are nevertheless key contributors to the overall strengths of drug-receptor interactions, since they occur in any molecule in which electronegativity differences between atoms result in significant bond, group or molecular dipole moments. The key differences between ionic and dipolar interactions relate to their dependence on distance and orientation (Table 21.2). 

Although charge-dipole and dipole-dipole interactions are weaker than ionic bonds, they are nevertheless key contributors to the overall strengths of drug-receptor interactions, since they occur in any molecule in which electronegativity differences between atoms result in significant bond, group or molecular dipole moments. 

The formation of an ionic bond results from the electrostatic attraction that occurs between oppositely charged ions. The strength of this bond is considerably less (5 kcal/mole) than that of the covalent bond and diminishes in proportion to the square of the distance between the ionic species. Most macromolecular receptors have a number of ionizable groups at physiological pH (e.g., carboxyl, hydroxyl, phosphoryl, amino) that are available for interaction with an ionizable drug. 

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