10.1021/ic0497679.s001 Amy K. Petros Amy K. Petros Sarah E. Shaner Sarah E. Shaner Alison L. Costello Alison L. Costello David L. Tierney David L. Tierney Brian R. Gibney Brian R. Gibney Comparison of Cysteine and Penicillamine Ligands in a Co(II) Maquette American Chemical Society 2004 EXAFS coordination spheres NH ferredoxin maquette ligand IGA Co exogenous H 2 O UV KL 2004-08-09 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Comparison_of_Cysteine_and_Penicillamine_Ligands_in_a_Co_II_Maquette/3329455 l-Penicillamine (Pen) has been investigated as a ligand for metalloprotein design by examining the binding of Co(II) to the sequence NH<sub>2</sub>−KL(Pen)EGG·(Pen)<b>IG</b>(Pen)G<b>A</b>(Pen)·GGW−CONH<sub>2</sub>. For comparison, we have studied Co(II) binding to the analogous sequence with Cys ligands, the ferredoxin maquette ligand <b>IGA</b> that was originally designed to bind a [4Fe-4S] cluster. The Co(II) affinity and UV−vis spectroscopic properties of <b>IGA</b> indicate formation of a pseudotetrahedral tetrathiolate ligated Co(II). In contrast, <b>IGA-Pen</b> showed formation of a pseudotetrahedral complex with Co(II) bound by three Pen ligands and an exogenous H<sub>2</sub>O. EXAFS data on both Co(II) complexes confirms not only the proposed primary coordination spheres but also shows six Co(II)-C<sub>β</sub> methyl group distances in Co(II)-<b>IGA-Pen</b>. These results demonstrate that ligand sterics in simple peptides can be designed to provide asymmetric coordination spheres such as those commonly observed in natural metalloproteins.