GHK-Cu

GHK-Cu is not a peptide. It is a copper(II) coordination complex in which the tripeptide glycyl-L-histidyl-L-lysine acts as a chelating ligand around a metal centre. That distinction is not pedantry — it governs how the material looks, how it is characterised, how it degrades, and what a certificate of analysis for it should actually report.

Identity and classification

The free tripeptide GHK and the copper complex GHK-Cu are different substances with different registry numbers, different formulae and different masses. Free GHK is C₁₄H₂₄N₆O₄ at approximately 340.4 g/mol. Adding copper(II) and losing protons on coordination gives the complex at 401.91. A listing that quotes the peptide mass alongside the complex name has conflated them.

No receptor target is assigned to GHK-Cu in reference-supplier catalogue classification, and we make no claim about one. It is classified as a metallopeptide complex.

Structure and coordination

Copper(II) is held in an approximately square-planar arrangement by three nitrogen donors from a single GHK molecule:

• the α-amino nitrogen of the N-terminal glycine,
• the deprotonated amide nitrogen of the Gly–His peptide bond — note that coordination requires loss of the amide proton, which is why the complex formula has two fewer hydrogens than the free peptide,
• the imidazole nitrogen of the histidine side chain.

A carboxylate oxygen from a neighbouring complex completes a square-pyramidal geometry in the solid state. The lysine side chain is not involved in coordination and remains free and protonated, which is why the complex carries net positive charge and is freely water-soluble.

The histidine imidazole is the essential residue. It is the reason GHK binds copper at all and the reason no arbitrary tripeptide substitutes for it.

The colour check — a free identity test

GHK-Cu is blue to purple. Metal-free GHK is white to off-white. The colour arises from copper(II) d–d electronic transitions, with an absorbance maximum in the region of 620 nm that simply does not exist in the metal-free peptide.

This means the crudest possible inspection — looking at the powder — distinguishes the two. If a vial sold as GHK-Cu contains a white solid, it is not the copper complex, whatever the label says. No instrument is required to catch that particular substitution, and it is worth performing on receipt of every lot.

Specification and characterisation

A certificate for a coordination complex should report more than peptide purity. The appropriate panel:

• Copper content. By ICP-MS, ICP-OES or atomic absorption. This is the single most important number on a certificate for this material and the one most often absent. Stoichiometric copper for C₁₄H₂₂CuN₆O₄ is approximately 15.8% by mass. A result materially below that indicates incomplete complexation — free peptide contaminating the product.
• UV-visible spectroscopy. The d–d absorbance near 620 nm confirms the copper is coordinated rather than merely present as a separate salt. Copper content alone cannot distinguish a true complex from a physical mixture of GHK and a copper salt; the visible spectrum can.
• RP-HPLC. Chromatography of metal complexes is not straightforward — the complex can dissociate on an acidic mobile phase, and TFA-containing eluents in particular can strip the metal, so a chromatogram may report the free ligand rather than the intact complex. Any HPLC purity figure for this material should be read with that caveat.
• Ligand identity. Mass spectrometry or amino acid analysis confirming the Gly-His-Lys composition.
• Water content. Karl Fischer.

Handling and stability

Store sealed at 2–8 °C, dry, protected from light. The material is freely water-soluble.

The specific stability concern for this compound is complex integrity rather than peptide degradation. Copper coordination depends on the amide nitrogen remaining deprotonated, which makes the complex pH-sensitive: under acidic conditions the amide reprotonates and copper is released. Prolonged aqueous storage can therefore give both dissociation of the metal and hydrolysis of the now-unprotected peptide. Colour loss in solution — blue fading toward colourless — is a visible indication that the complex has dissociated.

Free copper(II) is also redox-active and can catalyse oxidation of other species in a shared solution, which is worth knowing if the material is used alongside oxidation-sensitive reagents.

Related compounds in this library

GHK-Cu is the only coordination complex in this catalogue; every other entry is a peptide, a cofactor or a diluent. The closest conceptual neighbour is glutathione, in that both are small tripeptides whose chemistry is dominated by a single reactive feature — a metal-binding site in one case, a free thiol in the other.

References

Chemical, specification and analytical sources. This list is deliberately limited to chemistry and analytical references.

• Cayman Chemical, GHK-Cu product record — formula, molecular weight, appearance
• Sigma-Aldrich, copper tripeptide record — registry and specification data
• PubChem, glycyl-L-histidyl-L-lysine copper complex — structure and coordination
• ChemicalBook, CAS 89030-95-5 — registry confirmation (note: this source lists C₁₄H₂₁CuN₆O₄ at 400.91, a deprotonation-state outlier against four other sources; the formula given above is the consensus value)

Cosmic Aminos supplies this material as a laboratory reagent for in-vitro research use only. It is not a drug, food, cosmetic or dietary supplement, is not approved by the Food and Drug Administration for any use, and is not for human or veterinary consumption. No dosing, administration or preparation guidance is provided.