Chemistry of Macrocyclic Polyamine Complexes

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This grant in the Organic and Macromolecular Chemistry Program supports research by Prof. Cynthia Burrows, which is aimed at characterizing the binding and catalytic properties of protonated macrocyclic polyamines. This work falls in the general area of "host- guest" chemistry and constitutes a "biomimetic" approach to replication of enzyme binding and catalysis in man-made chemical systems. Macrocyclic polyamines can participate in both cation and anion complexation phenomena. Tetraamines of 18-membered ring size are easily tetra-protonated in aqueous media, and their high positive charge density accounts for their ability to form strong association complexes with various organic and inorganic anions. In this context, the Burrows group will investigate optically active macrocyclic spermine analogs which possess functionalized side chains. Phosphate esters and carboxylates will be studied in various media in order to define the parameters important for strong association. Macrocycles bearing a pendant imidazole group have been designed as potential catalysts for phophate ester hydrolysis. Tetraamines of 14-membered ring size (cyclams) form stable complexes with transition metal cations, especially divalent cobalt, nickel, and copper ions. Like porphyrins, the cyclams stabilize high oxidation states of certain metals. Burrows has recently discovered the first nickel-catalyzed olefin epoxidations in which cyclam is the key to accessibility of the Nickel(III) oxidation state. Optically active cyclams bearing pendant ligating groups are under study in order to further modify the reactivity of the metal and to investigate the potential for asymmetric epoxidation of olefins. These studies will enhance understanding of intermolecular interactions in molecular recognition complexes and catalysis.