Recent advances in understanding blue copper proteins

The type 1 (T1) or blue Cu (BC) proteins are a highly studied group of electron transfer (ET) active sites in bioinorganic chemistry. In this review, we cover several more recent results which extend the understanding of the geometric and electronic structure of these interesting Cu ET sites. Spectroscopic methods in tandem with density functional theory (DFT) and time dependent-DFT (TD-DFT) calculations have been used in studies of S → Se variants as well as a series of metal-varied model complexes (M = Mn²⁺ → Zn²⁺). The ligand and metal perturbations further defined the origins of the unique spectral features of BC proteins. These unique spectral features show different temperature dependencies in different T1 sites, and contrasts drawn between their behaviors define the role of the protein in tuning the geometric and electronic structure of the BC site for function. This has been termed the ‘entatic’ or ‘rack-induced’ state in bioinorganic chemistry.