Counterion
Counterion — An ion that accompanies and balances the charge of a peptide in its salt form. Common counterions include trifluoroacetate (TFA) and acetate.
What Is a Counterion?
A counterion is the charged species associated with a peptide salt form to maintain electrical neutrality. Most synthetic peptides are supplied as TFA (trifluoroacetate) salts because TFA is the cleavage and HPLC mobile phase acid. The counterion affects peptide solubility, net peptide content, stability, and suitability for biological assays.
Common Counterions
- TFA (CF3COO⁻): Default from HPLC purification. Can interfere with NMR (19F signal), cell culture (cytotoxic at high concentrations), and some MS applications
- Acetate (CH3COO⁻): Milder, biocompatible. Obtained by TFA-to-acetate salt exchange on preparative HPLC or SPE
- Hydrochloride (Cl⁻): Pharmaceutical standard. Higher NPC than TFA salt
Frequently Asked Questions
What is Counterion?
An ion that accompanies and balances the charge of a peptide in its salt form. Common counterions include trifluoroacetate (TFA) and acetate.
Why is Counterion important in peptide research?
Counterion is a fundamental concept in chemistry as it relates to peptide science. It directly influences experimental design, compound characterization, and the reliability of research outcomes across biochemistry and molecular biology disciplines.