Using antibodies to perturb the coordination sphere of a transition metal complex

METAL ions in the active sites of many metalloenzymes exhibit distinctive spectral and chemical features which are different from those of small inorganic complexes 1,2 . These features are the result of the unusual geometric and electronic constraints that are imposed on the metal ion within the protein environment 3 . Much effort has been invested to try to mimic this feature of metalloenzymes in synthetic systems, but this remains a formidable task. Here we show that one of the key lessons learned from the science of catalytic antibodies—that binding energy can be converted into chemical energy 4 —can be exploited to 'fine-tune' the physicochemical properties of a metal complex. We show that an antibody's binding site can reversibly perturb the coordination geometry of a metal ion, and can stabilize a high-energy coordinated species 5 . Specifically, antibodies designed to bind the organosilicon compound 1 (Fig. 1) also bind the geometrically similar Cu(I) complex 2. However, the antibody binds a slightly compressed form of 2, which is closer in size to 1. This distortion is manifested by a spectral shift—an 'immunochromic' effect.