Editing ChargeCalculator:Motivation (section)

=Chemical reactivity=

Many reaction mechanisms rely on a surplus of positive or negative charge at a certain site in the molecule. For instance, a nucleophylic attack happens at a positively charged site. In simple molecules like tert-butyl bromide, such sites are easy to identify by electron induction effects. However, as molecules become more complex, it is difficult to distinguish potential reaction sites based solely on concepts like induction and conjugation, because they are not quantitative. A simple atomic charge calculation can easily identify potential reaction sites.

Such a concept can be extended to biochemically interesting sites. Due to charge transfer and polarizability, total residue charges will deviate from the expected formal values (-1,0,1). Specific residues which are significantly more positive or negative than their surroundings are more likely to be the site of post translational modifications. Some salt bridges are stronger than others, and it is possible to predict which salt bridges can be more easily disrupted.