THE CHEMISTRY OF FUNCTIONAL-GROUP ARRAYS - ELECTROSTATIC CATALYSIS AND THE INTRAMOLECULAR SALT EFFECT

Ionic groups and salt bridges in the active sites of enzymes are thought to have important effects upon substrate reactivity. This paper describes the evaluation of an ion pair as an intramolecular effector of reaction rate for an addition reaction. The results reveal that in chloroform the intramolecular salt effect can lead to very large rate enhancements. It is proposed that in this case the local effect of the ion pair probably depends upon two factors: the electrostatic effects of the salt pair and, to a lesser extent, an intramolecular hydrogen bond. This observation of large rate enhancements in nonpolar solvents provides evidence of the substantial effects that ion pairs within the active sites of enzymes could have on reaction rates. The most specific and strongest synthetic molecular associations have been reported for host-guest systems in chloroform, and it is foreseen that hydrogen bond based host-guest systems will be combined with the intramolecular salt effect to bring within reach a large class of new shape selective specific synthetic catalysts and molecular effectors.