ABSTRACT
Enzymes are central to biology because they catalyze breakage and re-formation of chemical bonds at physiological conditions, not only during the interconversion of isomers but for many other metabolic transformations. Covalent or bonded interactions occur between atoms that are connected by chemical bonds. Non-covalent or non-bonded interactions include all other types of interactions, including electrostatic attraction or repulsion between ions and dipoles, and steric repulsions. Non-covalent or non-bonded interactions are through-space interactions between atoms that are not directly connected to each other by chemical bonds. Both polar and nonpolar interactions are affected by the dielectric constant er of the medium and by the relative orientation of the dipoles involved. The halogen bond is an attractive electrostatic interaction between a halogen atom and a lone pair from another atom. The geometric restraints for van der Waals interactions are less strict than those for dipolar interactions. Favorable geometries between aromatic systems are the face-to-face and the edge-to-face orientations.
