A general nuclear magnetic resonance analysis of hetero-association of aromatic molecules in aqueous solution

A general nuclear magnetic resonance analysis of a statistical-thermodynami cal model of hetero-association of aromatic molecules in solution has been developed to take "edge effects" into consideration, i.e., the dependence o f proton chemical shifts on the position of the molecule situated inside or at the edge of the aggregate. This generalized approach is compared with a previously published model, where an average contribution to proton shield ing is considered irrespective of the position of the molecule in the stack . Association parameters have been determined from experimental concentrati on and temperature dependences of 500 MHz proton chemical shifts of the het ero-association of the acridine dye, proflavine, and the phenanthridinium d ye, ethidium bromide, in aqueous solution. Differences in the parameters in the range 10%-30% calculated using the basic and generalized approaches ha ve been found to depend substantially on the magnitude of the equilibrium h etero-association constant K-het-the larger the value of K-het, the higher the discrepancy between the two methods. (C) 2001 American Institute of Phy sics.