Copper peptide storage needs a little more thought than storage of an ordinary linear peptide. GHK-Cu and blends that contain it carry a copper(II) ion held in a peptide binding site, and that metal centre brings its own sensitivities alongside the usual concerns of moisture, heat and light. This article covers what the colour of copper peptides tells you, what affects their stability, and how to keep them in good condition in the laboratory.
For laboratory research use only. Not for human or veterinary use. See our research use only policy.
At a glance
- Name: GHK-Cu (glycyl-L-histidyl-L-lysine copper(II) complex)
- Synonyms: Copper peptide, copper tripeptide-1
- Sequence: Gly-His-Lys, copper(II) complex
- Molecular formula: C14H22CuN6O4 (neutral complex, per PubChem)
- Molecular weight: approximately 401.9 g/mol (neutral complex, per PubChem)
- CAS number: 89030-95-5
- Form: Lyophilised powder
- Storage: 2-8°C, dark, upright - do not freeze. Keep sealed until use.
For background on structure and research history, see our GHK-Cu copper peptide overview.
Colour: what it tells you
Why copper peptides are blue
Copper(II) ions absorb light in the visible region when they are surrounded by ligands. In GHK-Cu, the copper is coordinated by nitrogen atoms from the glycine amine, the peptide backbone and the histidine ring. That nitrogen-rich environment shifts the absorption so that the complex appears blue to violet. The free GHK peptide, with no copper, is colourless.
What a normal sample looks like
A lyophilised GHK-Cu sample is typically a uniform blue to violet powder or cake. The exact shade can vary with particle size, residual moisture and the counterion present, so minor differences between batches are not in themselves a concern. Blends that contain GHK-Cu alongside colourless peptides, such as those discussed in Glow vs Klow peptide blends, appear paler in proportion to their copper peptide content.
Colour changes worth noting
- Fading towards colourless can indicate that copper has been lost from the complex, for example through contact with a stronger chelating agent.
- A shift towards green can indicate a change in the copper's coordination environment, such as hydrated copper salts not bound to the peptide.
- Brown or dark discolouration can suggest decomposition or contamination.
- Clumping, stickiness or a shrunken cake usually indicates moisture uptake.
Colour is a screening observation, not an analytical finding. Any concern should be followed up with appropriate testing such as HPLC, mass spectrometry or copper determination.
Stability considerations
Moisture
Lyophilised peptides are hygroscopic: they absorb water from the air. Moisture accelerates hydrolysis of peptide bonds and can encourage aggregation. For copper complexes, water uptake can also alter the coordination sphere of the metal. Keeping vials sealed until use, and allowing a refrigerated vial to reach room temperature before opening to avoid condensation, are standard precautions.
Temperature
Our guidance for GHK-Cu is storage at 2-8°C. We advise against freezing. Repeated freezing and thawing can draw moisture into a vial each time it is handled, and temperature swings are a common source of degradation in stored peptides. A stable refrigerated environment is the aim.
Light
Light exposure can drive photo-oxidation of susceptible amino acid residues, and histidine is among those that can be affected. Storing vials in the dark, or in their outer packaging, limits this. Amber vials or opaque secondary containers are common laboratory practice for light-sensitive materials.
Chelating and reducing agents
This is the consideration most specific to copper peptides. Strong chelating agents such as EDTA can bind copper more tightly than GHK does and strip it from the complex, converting GHK-Cu back towards the free peptide. Reducing agents, including thiol compounds such as dithiothreitol, can reduce copper(II) to copper(I), which changes its coordination and colour. Keeping copper peptides away from these reagents, and being aware of them in any buffer or medium, avoids unintended changes to the material.
pH
Solution chemistry studies, including the 1981 work of Lau and Sarkar in the Biochemical Journal, showed that the copper binding mode of GHK depends on pH. Under strongly acidic conditions, protonation of the binding groups weakens copper binding. This is why reversed-phase HPLC with acidic mobile phases can partially dissociate the complex during analysis, a point covered in GHK vs GHK-Cu.
Storage checklist
- Store at 2-8°C in a stable refrigerator, not in a door shelf where temperature fluctuates.
- Keep in the dark, in outer packaging or an opaque container.
- Keep vials upright and sealed until use.
- Do not freeze.
- Let a refrigerated vial reach room temperature before opening to limit condensation.
- Keep away from chelating agents and reducing agents.
- Record the receipt date, storage location and any observations about appearance.
These points build on the general principles in our guide to how to store lyophilised peptides, which applies to all freeze-dried research peptides.
Handling and documentation
Good handling is mostly about minimising exposure and keeping clear records. Open vials only when needed and in a clean, dry environment. Use clean, dry tools. Note the appearance of the material on receipt so that any later change can be recognised. Keep identity documents with the CAS number 89030-95-5 for the copper complex, and check that the form described matches the material in hand.
Standard laboratory safety applies throughout. Copper compounds and peptides should be handled with appropriate personal protective equipment, and waste should be disposed of according to local laboratory rules for metal-containing materials.
Our GHK-Cu
Compound Cave GHK-Cu is supplied as a lyophilised powder at >99% purity by HPLC, with the storage guidance set out above. View GHK-Cu 100mg in the catalogue.
Frequently asked questions
What colour should copper peptides be?
GHK-Cu is typically a blue to violet powder. Blends containing GHK-Cu appear paler depending on how much copper peptide they contain. The free GHK peptide is colourless.
What temperature should GHK-Cu be stored at?
Our guidance is 2-8°C, in the dark, upright, sealed until use, and not frozen.
Why should copper peptides be kept away from EDTA?
EDTA and similar chelating agents can bind copper more strongly than GHK does, stripping the metal from the complex and changing the material.
What does a green or faded colour mean?
A green tint or fading can indicate a change in the copper's environment or loss of copper from the complex. It is a prompt for analytical checking rather than a conclusion in itself.
Can GHK-Cu be frozen?
We advise against freezing. Repeated freezing and thawing can introduce moisture and temperature stress, both common sources of degradation.
References
- Lau SJ, Sarkar B. The interaction of copper(II) and glycyl-L-histidyl-L-lysine, a growth-modulating tripeptide from plasma. Biochemical Journal, 1981.
- Pickart L, Margolina A. Regenerative and protective actions of the GHK-Cu peptide in the light of the new gene data. International Journal of Molecular Sciences, 2018.
- PubChem compound records for glycyl-L-histidyl-L-lysine and its copper(II) complex, National Center for Biotechnology Information.
For laboratory research use only. Not for human or veterinary use. See our research use only policy.