ORGN 593

We have prepared and examined the anion binding behavior of a series of tetra-, tri-, and di-urea-picket porphyrins shown in Figure 1.  A comparison of the binding data shows a remarkable reversal in the selectivity of anion complexation.  Porphyrin A binds chloride anion selectively, porphyrin B binds no anions selectively, and porphyrin C binds acetate anion selectively.  The binding constant ratios for chloride to phosphate anion changes over 3 orders of magnitude, and for that of chloride to acetate anion over 5 orders of magnitude, respectively, as the receptor’s number of urea pickets are changed from four to three to two.  This change in binding constants occurs despite the fact that the binding motif for the anions stays the same among the receptors.  The role of solvent in the observed change in selectivity of anion complexation will be discussed.