A DENSITY-FUNCTIONAL STUDY OF THE RECEPTOR-LIGAND INTERACTION - STABILIZATION ENERGY IN AMMONIUM SALT AROMATIC INTERACTIONS

Amino-aromatic interactions have been well examined in the fields of p rotein structure determination and theoretical calculation. Under phys iological conditions, however, most amines in proteins exist as ammoni um salts, and ammonium salt-aromatic interactions are supposed to be m ore predominant in protein structures than amino-aromatic interactions . A nonlocal density functional theory molecular orbital calculation w as applied to an ammonia-benzene system and gave an interaction energy of 0.9 kcal/mol, which was in good agreement with an experimental val ue (1.4 kcal/mol). A series of calculations also revealed that the int eraction energy was in the range 2.5-6.2 kcal/mol for several ammonium formate-aromatic systems, which could play as important a role in rec eptor-ligand interactions as hydrogen bonding (4.5-6.1 kcal/mol) does.