PROTEIN SELECTIVITY WITH IMMOBILIZED METAL-ION TACN SORBENTS - CHROMATOGRAPHIC STUDIES WITH HUMAN SERUM-PROTEINS AND SEVERAL OTHER GLOBULAR-PROTEINS

The chromatographic selectivity of the immobilized chelate system, 1,4 ,7-triazocyclononane (tacn), complexed with the borderline metal ions Cu2+, Cr3+, Mn2+, Co2+, Zn2+, and Ni2+ has been investigated with hen egg white lysozyme, horse heart cytochrome c, and horse skeletal muscl e myoglobin, as well as proteins present in partially fractionated pre parations of human plasma, The effects of ionic strength and pH of the loading and elution buffers on protein selectivities of these new imm obilized metal ion affinity chromatographic (IMAC) systems have been e xamined. The results confirm that immobilized M(n;)pl-tacn sorbents ex hibit a novel type of IMAC behavior with proteins. In particular, the chromatographic properties of these immobilized Mn+-tacn ligand system s were significantly different compared to the IMAC behavior observed with other types of immobilized tri-and tetradentate chelating ligands , such as iminodiacetic acid, O-phosphoserine, or nitrilotriacetic aci d, when complexed with borderline metal ions. The experimental results have consequently been evaluated in terms of the additional contribut ions to the interactive processes mediated by effects other than solel y the conventional lone pair Lewis soft acid-Lewis soft base coordinat ion interactions, typically found for the IMAC of proteins with border line and soft metal ions, such as Cu2+ or Ni2+. (C) 1998 Academic Pres s.