Biopolymers and cell. 2002; 18 (4): 351 - 355

Various point contacts between neutral and deprotonated carboxylic groups of amino acids and 2-aminopurine

A L. Potyahaylo, D. M. Hovorun

The complete family of point contacts between neutral or depro¬tonated acetic acid and 2-aminopurine has been first calculated in vacuum by semi-empirical quantum chemical method MNDO/H. Acetic acid simulated the side chains of glutamic and aspartic acids. It has been found that specific interaction of deprotonated acid with the base transfers the latter from the main N9H tautomeric form to the high energy N3H form with the 0.92 kcal/mol energy advantage and results in the formation of N3H...O , N2H...O point contact. However, the specific interaction of neutral ligand with 2-ami¬nopurine does not cause any tautomeric transformations of the base; the most favourable point contact N9H...O, N3...HO with the 2.3 kcal/mol energy advantage is formed with its main N9H tautomeric form. In all cases carboxylate-ion provides about three times stronger interaction (its energy amounts to SO kcal/mol and higher) than neutral carboxylic group.