Peptide Formation in the Presence of Metal Ion Protecting Groups: III. The Separation of [(NH3)5Co(III)-] Amino Acids and Peptides by Reverse Phase High Pressure Liquid Chromatography

Pentaammine cobalt(III) amino acid and peptide complexes of the type can be separated rapidly under mild conditions by high pressure liquid chromatography (HPLC) using octadecyl silane derivatized columns (RP-18) with 0.2% sodium trifluoroacetate (NaTFA) in aqueous-methanol at pH 2.5. The retention time of these cobalt(III) complexes is a function of the hydrophobicity of the amino acid or peptide ligand and the total charge on the complex. In the trifluoroacetate media used for these separations, the hydrophobic ligand and the number of trifluoroacetate counter ions on the cobalt complex contribute to the selective elution of these complexes.