Powerful New Metal-Chelating Agents Developed

Abstract

For years chemists have considered EDTA (ethylenediaminetetraacetic acid) the classic metal-chelating agent. But EDTA and similar compounds employ a flawed strategy for binding cations, work by University of Pittsburgh researchers now makes clear. New chelating agents designed by chemistry professor Julius Rebek Jr. and his coworkers offer dramatic improvements over classic chelators in tying up metal atoms. EDTA and similar compounds capture small metal ions by forming noncovalent bonds to the cations with unshared electrons on nitrogen atoms and carboxylate oxygens. Because of the molecular shapes of the chelating agents, only the anti lone pairs of the carboxylate oxygens—that is, the unshared electrons on the side opposite the carbonyl—contact the metal ions in the complex. Rebek's new chelating agents are constructed so they are forced to form complexes with the more basic syn lone pairs, those on the same side of the carbonyl oxygen. The result is molecules that are extraordinarily effective in ...