At physiological pH, carboxy terminal of peptide is
Positive charged
Negative charged
Neutral
Infinitely charged
In ion-exchange chromatography, proteins interact with the stationary phase by charge-charge interactions. Proteins with a net positive charge at a given pH will tightly adhere to beads with negatively charged functional groups such as carboxylates or sulfates (cation exchangers).
 
Harper, Ed 30, Pg 27