BINDING CONSTANTS AS A PROBE OF THE MICROENVIRONMENT IN POLYMER-SUPPORTED REAGENTS

A procedure is developed for quantifying the degree to which a ligand-substrate interaction is affected by the microenvironment surrounding the polymer-supported ligand. The binding constants between a series of substrates (such as substituted benzoic acids, anilines, phenols, etc.) and a ligand covalently bound to different polymer matrices are calculated through the Langmuir isotherms. The binding constants across different matrices quantify the effect of the microenvironment on each ligand-substrate interaction. A linear correlation of the binding constants with the substituent Hammett sigma-constants yields a slope that is a measure of the interaction's sensitivity to electron density changes within a given matrix; comparing the slopes across different matrices provides a measure of how the polymeric microenvironment influences that sensitivity. Matrix flexibility is thus found to have a major impact on the ligand-substrate interaction.