title: Copper dynamics in doped metal-bis(histidine) complexes.
abstract: Electron paramagnetic resonance (EPR) temperature-dependent measurements were undertaken on three Cu(II)-doped metal-histidine complexes to assess copper site dynamic behavior. Previous single-crystal EPR analysis on two of these, zinc d,l-histidine pentahydrate (ZnDLH) and bis(l-histidinato)cadmium dihydrate (CdLH), found that doped Cu(2+) can be modeled as hopping between two neighboring conformational states, with a temperature-dependent rate becoming large enough at room temperature to produce an "averaged" spectrum. By comparing spectra from their powdered form, we show that Cu(2+) doped into a third system, Cd(2+)-d,l-histidine (CdDLH), also exhibits temperature-dependent EPR with features indicating a similar motional-averaging process. In addition, the change of g and copper hyperfine parameters from low to high temperature for CdDLH resembles that in ZnDLH, whereas the change in these parameters for CdLH is like that found in a fourth copper-doped system, zinc l-histidine dihydrate (ZnLH). Taken together, these results suggest that averaging motion between neighboring copper sites is common in metal-bis(histidine) compounds. More detailed studies on biological models are thus warranted, especially because they reveal unique relationships between structure, dynamic processes, and stability and can lead to a better understanding of the role played by site flexibility in copper proteins.
authors.affiliation: Department of Chemistry and Physics, State University of New York at Old Westbury , Old Westbury, New York 11568, United States.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Colaneri
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Vitali
mesh_terms: D001665:Binding Sites; D002104:Cadmium / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006639:Histidine / Q000737:chemistry*; D008968:Molecular Conformation; D013816:Thermodynamics; D015032:Zinc / Q000737:chemistry
chemical_list: D056831:Coordination Complexes; D002104:Cadmium; D006639:Histidine; D003300:Copper; D015032:Zinc