Magnetic circular dichroism study of a dicobalt(II) complex with mixed 5- and 6-coordination: a spectroscopic model for dicobalt(II) hydrolases.

The magnetic circular dichroism (MCD) study of [Co(2)(mu-OH)(mu-Ph(4)DBA)(TMEDA)(2)(OTf)], in which Ph(4)DBA is the dinucleating bis(carboxylate) ligand dibenzofuran-4,6-bis(diphenylacetate) and TMEDA is N,N,N',N'-tetramethylethylenediamine, is presented. This complex serves as an excellent spectroscopic model for a number of dicobalt(II) enzymes and proteins that have both the mu-hydroxo, mu-carboxylato bridging and asymmetric 6- and 5-coordination. The low-temperature MCD spectrum of the model complex shows bands at 490, 504, and 934 nm arising from d-d transitions on the 6-coordinate Co(II) and bands at 471, 522, 572, 594, and 638 nm arising from d-d transitions on the 5-coordinate Co(II).

Magnetic circular dichroism study of a dicobalt(II) methionine aminopeptidase/fumagillin complex and dicobalt II-II and II-III model complexes.

The dicobalt form of the metallohydrolase methionine aminopeptidase from Escherichia coli (CoCo EcMetAP) has an active site with one 5-coordinate Co (II) and a more weakly bound 6-coordinate Co (II). These metal ions are bridged by two carboxylate amino acid side chains and water or hydroxide, potentially enabling magnetic exchange coupling between the metals. We used variable-temperature, variable-field magnetic circular dichroism to determine whether such coupling occurs.