GHK versus GHK-Cu: free tripeptide and copper complex
Two different reagents sold side by side. What the copper changes about weight, colour, handling and chemistry, and how to be sure which is in the vial.
GHK and GHK-Cu are sold side by side, sometimes interchangeably, and they are different reagents: the free tripeptide glycyl-histidyl-lysine and its copper(II) complex. The copper changes the chemistry, the appearance, the molecular weight, the handling and much of the reported activity. This note explains the relationship, the practical differences, and how to be sure which one is in the vial. All Alphex products are for laboratory and in-vitro research only.
The free tripeptide, GHK
Gly-His-Lys, molecular weight 340.4 g/mol. A white to off-white lyophilised solid, freely water-soluble, colourless in solution. Isolated originally from human plasma, where it circulates and where its concentration declines with age. On its own it is a small, unremarkable-looking peptide; its notable property is its very high affinity for copper(II), which it binds through the histidine imidazole nitrogen, the glycine alpha-amino group and a backbone amide nitrogen.
The copper complex, GHK-Cu
GHK coordinated to Cu(II), molecular weight 403.9 g/mol as the 1:1 complex (the difference from 340.4 being copper's atomic mass, 63.5). A blue to blue-violet solid and solution; the colour is the copper's d-d absorption in the peptide's coordination environment and is the immediate visual sign of the complex. It is the form used in the great majority of the research literature, and it is what Alphex supplies. See the GHK-Cu guide.
Practical differences
- Colour: GHK colourless; GHK-Cu blue. The single quickest identity check.
- Molecular weight: 340.4 versus 403.9. Molar calculations must use the right one. See molecular weight and molar calculations.
- Light sensitivity: the copper complex is light sensitive and can photo-oxidise; the free peptide much less so. See light-sensitive peptides.
- Buffer compatibility: GHK-Cu must be kept away from chelators (EDTA, citrate) and from phosphate at high concentration, which strip or precipitate the copper. GHK does not care.
- pH: copper coordination is pH-dependent; strongly acidic conditions release the copper. See buffers for reconstitution.
- Redox chemistry: the complex participates in copper redox chemistry; the free peptide does not. This is central to much of the literature and to why the two are not interchangeable in an assay.
Can you make GHK-Cu from GHK?
Chemically, yes: adding a copper(II) salt to GHK in solution at appropriate pH forms the complex, and some laboratories do this to control the copper stoichiometry precisely. In practice, buying the characterised complex is simpler and avoids questions about excess free copper, which is itself active in many assays and confounds results. A product sold as "GHK-Cu" that is actually GHK plus a copper salt mixed in the vial is not the same reagent as a purified, characterised complex, and its COA should make clear which it is.
Being sure which you have
- Colour: blue solid and solution means copper is present.
- COA mass: the peptide component (340.4) is what ESI-MS typically reports, since the copper may dissociate in the electrospray; a good certificate states the form and reports copper content or the complex explicitly.
- Price: the complex costs more than the free peptide; a "GHK-Cu" listing at free-peptide prices deserves the questions in questions to ask before ordering.
Frequently asked questions
Which does the literature use?
Overwhelmingly the copper complex, particularly the gene-expression and dermal-fibroblast work.
Does Alphex sell free GHK?
No; the catalogue item is the copper complex.
Why is the powder sometimes more violet than blue?
Coordination geometry and hydration state shift the shade slightly between batches; blue through blue-violet is normal, green or brown is not. See recognising degradation.
Alphex research peptides are supplied for laboratory and in-vitro research by qualified researchers only. They are not authorised for human or veterinary use.
Research use only. Alphex products are supplied exclusively for laboratory and in-vitro research by qualified researchers. They are not authorised for human or veterinary use, and nothing in this note is advice on any such use.
Published 6 March 2026. Alphex reviews research notes when the testing method, the catalogue or UK guidance changes.