Formulating with copper peptides: pH, chelators and colour

Why copper peptides need care

In a copper peptide, copper is held by coordination bonds to the peptide. Anything in a formulation that competes for the copper, or changes the charge of the peptide, can weaken that bond. A formulation that works for a plain peptide therefore may not work for a copper complex.

Factors to test

• pH. Work in the range typical for your product type and confirm stability in your own system. Do not rely on a single pH figure from a general article.
• Chelating agents such as EDTA. They can pull copper away from the peptide. If your base needs a chelator, test the lowest level that does the job.
• Reducing agents. Strong reducing agents, including high levels of L-ascorbic acid, are commonly flagged as risks for copper(II) complexes.
• Low-pH actives. Exfoliating acids at low pH can change the charge of the histidine residue and destabilise the complex.
• Preservatives and surfactants. Check compatibility case by case.
• Light, heat and oxygen. Protect the raw material and the finished product during storage.

Colour is information

Copper peptides are blue, and finished products containing them are tinted. A shift away from blue during stability testing, toward green or brown, or a fading of the colour, is an early signal worth investigating.

Stability testing

Run stability studies under your own SOP and monitor colour, pH, peptide assay by HPLC and copper content over time. Your own data, in your own base, is the only reliable guide.

Responsibility

This article is general information for formulators. It does not replace your own stability testing, safety assessment or regulatory review. The brand owner is responsible for the safety substantiation, claims and labelling of the finished product in each market.