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GHK-Cu 1:1 and 2:1: what the ratio on a COA means, and how to compare offers
Published October 7, 2026 · Facts checked October 9, 2026
Short answer
There is no standard for copper-peptide 'grades'. Two batches sold as GHK-Cu can differ in peptide-to-copper ratio (1:1 at 15.81 % copper, 2:1 at 8.56 %) and in acetate and water content. Compare offers by these measurable points and by the batch COA, not by a grade name.
Compare offers on these points
| Point | What differs | What to ask for |
|---|---|---|
| Peptide-to-copper ratio | 1:1 complex (401.91 g/mol, 15.81 % Cu) or 2:1 (742.3 g/mol, 8.56 % Cu) | Which form, and the measured Cu²⁺ : peptide ratio |
| As-is composition | Acetate and water add mass, so as-is copper is below the theoretical figure | Peptide content, water and acetate alongside HPLC purity |
| Purity vs content | HPLC purity is the share of the peptide signal; it is not the share of the powder that is peptide | Both numbers, labelled |
| Colour | Blue; a shift towards violet means the copper's surroundings changed | Appearance on the COA, UV-Vis λmax |
| Documents | A generic specification sheet, or a COA for the batch you receive | A batch COA with the batch number of your vials |
Sources: PubChem CID 165429100 · PubChem CID 9831891
1:1 or 2:1
In solution at neutral pH, GHK and copper(II) form a 1:1 complex. A 2:1 material carries a second GHK per copper, so the same weight of powder holds about half the copper (8.56 % against 15.81 % for the pure forms) and more peptide. They are different specifications: check the copper content against the form you ordered.
Sources: Freedman et al., Biochemistry 1982 · Trapaidze et al., J Biol Inorg Chem 2012 · PubChem CID 9831891
Reading the ratio
The Cu²⁺ : peptide ratio on a COA, or the one you calculate from copper and peptide content, is close to 1.0 for a 1:1 batch and close to 0.5 for a 2:1 batch. Below the expected value, part of the peptide carries no copper; above it, there is copper the binding site cannot hold.
Sources: Trapaidze et al., J Biol Inorg Chem 2012
Calculator
Cu²⁺ : peptide ratio from your COA
Enter copper content and peptide content as percentages (0–100).
Colour: blue, violet, white
The colour comes from the copper's d–d band, near 606 nm for the 1:1 complex. When another ligand joins the copper — imidazole is a studied example — the band moves to about 565 nm and the colour shifts. Uncomplexed aqua copper absorbs near 816 nm. Colour is a fast first check; UV-Vis puts a number on it.
Sources: Bossak-Ahmad et al., Int J Mol Sci 2020 · Ufnalska et al., Inorg Chem 2021
Questions
- What is GHK-Cu 2:1?
- GHK-Cu with two GHK molecules per copper ion (C28H46CuN12O8, 742.3 g/mol). Pure, it is 8.56 % copper by mass, against 15.81 % for the 1:1 complex.
- Is 'research-grade' GHK-Cu a defined standard?
- No. Grade names are not standardised. Compare the ratio, copper content, HPLC purity, peptide content, water and acetate on the batch COA instead.
- Why is my GHK-Cu purple rather than blue?
- A colour shift means the copper's surroundings changed — for example another ligand joined it or the pH moved. UV-Vis shows it as a shift of the band near 606 nm.
References
- PubChem CID 165429100 — GHK copper complex (C14H22CuN6O4, 401.91) — formula and molecular weight of the neutral 1:1 complex
- PubChem CID 9831891 — bisprezatide copper (C28H46CuN12O8, 742.3) — the 2:1 peptide-to-copper record
- Freedman et al., Biochemistry 1982 — structure of the GHK–copper(II) complex in solution — mononuclear 1:1 complex at neutral pH; pH transitions at pK 3.6, 9.2 and 11.4
- Trapaidze et al., J Biol Inorg Chem 2012 — Cu²⁺ binding to DAHK and GHK by ITC — 1:1 stoichiometry; conditional Kd 7.0 × 10⁻¹⁴ M at pH 7.4
- Bossak-Ahmad et al., Int J Mol Sci 2020 — ternary Cu(II) complex with GHK — d–d band of Cu(GHK) at 605–606 nm; aqua copper absorbs near 816 nm
- Ufnalska et al., Inorg Chem 2021 — reduction of Cu(II)GHK by glutathione — Cu(II)GHK d–d band at 606 nm; imidazole adduct at 565 nm; glutathione reduces the complex
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