The Saunders-Bell Analysis of Tunnel Effects in Reactions with Kinetic Isotope Effects

The primary kinetic isotope effects of deuterium were investigated in 22 hydrogen and deuterium transfer reactions, including enzymatic and nonenzymatic hydride transfer reactions, elimination reactions, and reactions catalyzed by enzymes lipooxygenase, amine dehydrogenase, and methylmalonyl-CoA mutase. In each case, the Saunders-Bell analysis was applied to calculate the tunnel effects and the corresponding thermodynamic parameters. The Saunders-Bell analysis was effective in 14 cases out of 22. A high degree of correlation was found between the barrier factor, the tunnel factor, and the entropy factor among all reactions studied. From this, a general relationship between the three factors was derived, based on the Saunders-Bell analysis of the Bell equation; the Saunders-Bell analysis is valid within certain limits of the barrier factor. This general relationship is universally valid for all hydrogen/deuterium transfer reactions in nature with moderate tunneling, when the Saunders-Bell analysis applies.