TABLE OF CONTENTS Life depends on reversible molecular interactions. The covalent bonds that bind the molecules of life together are generally too strong to participate in these reversible interactions. Not surprisingly, the weaker bonds that we discussed earlier, the hydrogen and the van der Waals bonds, are very important. Interestingly, the ionic or electrostatic bond is also important. These three bonds differ in strength, geometry, and specificity. All biomolecular processes depend on the interplay between all bond types and the structures that they form and stabilize.
The simplest bond is the ionic bond. In biological and biochemical literature, this bond has a number of other names including salt bridge, electrostatic bond, salt linkage, and ion pair. An ionic bond forms between two charges of opposite sign. Furthermore, the charges are usually on different chemical groups and entities. Recall that the force between two charges is along the line joining the two charges and has a magnitude F given by Coulomb s Law:
In this equation, k is a constant, q 1 and q 2 are the two charges, r is the center-to-center distance between the two charges, and ? is the dielectric constant. The inclusion of the dielectric constant ? is significant because ? in water is about 80 compared to ?=1 in vacuum. Thus, the magnitude of an ionic bond in water is significantly reduced compared to that obtained when the same two charges are in...
