title: Retention behavior of amino acids and peptides on protoporphyrin-silica stationary phases with varying metal ion centers.
abstract: Various metalloprotoporphyrins (MProP) covalently linked to silica supports are examined as novel immobilized metal ion affinity chromatography (IMAC) stationary phases for separations of amino acids/peptides. Under reversed-phase HPLC conditions, the MProP-silicas exhibit high affinity toward L-histidine via metal-nitrogen axial ligation interactions, with an increasing degree of histidine retention highly dependent on the specific metal ion (M) in the center of the protoporphyrin (ProP) structure: Fe(III) > Ni(II) > Cu(II) > Zn (II) approximately Cd(II). Aromatic amino acids (i.e., L-trytophan and L-phenylalanine) are also retained on MProP columns through pi-pi interactions with the immobilized porphyrins, with the greatest affinity for L-trytophan observed on CuProP-silica columns. Peptides rich in L-histidine and L-tryptophan residues are selectively retained on most of the MProP-silica phases examined; however, the addition of an organic modifier and/or lowering the pH of the mobile phase can be used independently to attenuate the pi-pi and metal ion-nitrogen ligation interactions, respectively. Reproducible separations of His-Phe and trytophan releasing hormone are achieved on a FeProP-silica column even after extensive washing with 50 mM EDTA, demonstrating a fundamental advantage of the new MProP-silica over existing IMAC stationary phases, in which the metal ion is anchored weakly to the support via immobilized iminodiacetate and related ligands.
authors.affiliation: Department of Chemistry, University of Michigan, Ann Arbor 48109, USA.
authors.forename: J
authors.initials: J
authors.lastname: Xiao
authors.forename: M E
authors.initials: ME
authors.lastname: Meyerhoff
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry*; D002846:Chromatography, Affinity; D008670:Metals / Q000737:chemistry*; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D011524:Protoporphyrins / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D008670:Metals; D010455:Peptides; D011524:Protoporphyrins; D012822:Silicon Dioxide