Why is GHK-Cu blue?
Open a vial of GHK-Cu and the cake is blue, from sky blue to a deep royal shade. Open a vial of plain GHK and it is white. The difference is one copper ion, and the color is the same chemistry that turns a copper sulfate solution blue. Here is what the color comes from, what the two materials weigh and what the shade can and cannot tell you.
GHK and its copper complex.
| Peptide | Gly-His-Lys (GHK), a tripeptide found in human plasma |
|---|---|
| Formula of GHK | C14H24N6O4 |
| Molecular weight of GHK | 340.4 g/mol |
| Formula of GHK-Cu | C14H22CuN6O4 |
| Molecular weight of GHK-Cu | 401.9 g/mol as the neutral complex (one Cu(II) replaces two protons); 400.9 g/mol for the anionic record the GHK-Cu page matches |
| Ratio | 1:1 peptide to copper in the complex supplied as GHK-Cu |
| Color | GHK: white. GHK-Cu: blue to blue-violet |
| PubChem | GHK CID 73587; the copper complex is listed as CID 165429100 (neutral, 401.9 g/mol) and CID 139035031 (anionic form, 400.9 g/mol) |
The copper is the difference.
GHK is the free tripeptide, glycine, histidine and lysine, and like most short peptides it is a white powder. GHK-Cu is the same tripeptide holding a copper(II) ion. In human plasma the peptide circulates partly in this copper-bound form, which is why the complex rather than the free peptide is the material most studied and most often sold. The GHK-Cu reference page lists the full identity data, and AHK-Cu vs GHK-Cu compares it with the other common copper peptide.
d-electrons and the ligand field.
Copper(II) has nine electrons in its 3d orbitals. On its own, the five d orbitals have the same energy; surrounded by the atoms that bind it, they split into two levels, and the gap between them matches the energy of orange and red light. The complex absorbs those wavelengths and passes the rest, so the eye sees blue. The same ligand-field effect makes aqueous copper sulfate blue, and the exact shade depends on what is bound to the metal. In GHK-Cu the copper is held by the amino nitrogen of glycine, the deprotonated amide nitrogen between glycine and histidine, and the imidazole nitrogen of histidine, with a water or a carboxylate completing the square around the ion. That arrangement shifts the absorption a little from copper sulfate's, which is why GHK-Cu leans violet.
Minus two hydrogens, plus copper.
When copper binds, it displaces two protons, one from the amino group and one from the amide nitrogen, so the complex's formula is the peptide's with two hydrogens fewer and one copper more: C14H22CuN6O4, 401.9 g/mol against 340.4 g/mol for the free peptide. PubChem lists the complex in more than one protonation state, C14H22CuN6O4 at 401.9 g/mol and the anion C14H21CuN6O4 at 400.9 g/mol, which is the record Helion's GHK-Cu page matches; the difference is one proton. A lab report for GHK-Cu identifies the peptide by mass spectrometry, where the copper-free peptide ion is usually what is detected, and may report copper content separately. The molecular weight calculator gives the free-peptide figure.
Copper present, nothing more.
A blue cake shows that copper is bound to the peptide. It does not show how pure the peptide is, how much is in the vial or whether the sequence is right, and the shade varies with how dry the cake is and how it was freeze-dried. A pale cake is not necessarily short of copper and a dark one is not necessarily purer. Those questions are answered by the lab report: identity, HPLC purity and content, as how to read a peptide COA explains.
A royal blue cake, reported per lot.
Helion's GHK-Cu 50 mg is supplied as the copper complex, a deep blue lyophilized cake in a sealed 3 mL vial, with a third-party report for each lot in the COA Portal.
Specs and storage by compound.
Questions (6)
Why is GHK-Cu blue?
Because copper(II) is bound inside the tripeptide. The ligand field around the copper splits its d orbitals so the complex absorbs orange and red light and looks blue, the same effect that colors copper sulfate.
Is plain GHK blue?
No. The free tripeptide is a white powder. Only the copper complex is blue.
What is the molecular weight of GHK-Cu?
About 401.9 g/mol for the neutral 1:1 complex, or 400.9 g/mol for the anionic form PubChem also lists, against 340.4 g/mol for the free peptide GHK.
Does a darker blue mean a better product?
No. The shade depends on dryness and the freeze-drying process. Purity, identity and content come from the lab report.
What is the formula of GHK-Cu?
C14H22CuN6O4: the peptide formula C14H24N6O4 with two hydrogens replaced by one copper.
Does Helion sell GHK or GHK-Cu?
GHK-Cu, the copper complex, as a 50 mg vial with a published lab report per lot.
Published studies (2)
- The human tri-peptide GHK and tissue remodeling
- GHK Peptide as a Natural Modulator of Multiple Cellular Pathways in Skin Regeneration
Citations from PubMed for reference. They describe the compound in the literature, not any Helion lot, and nothing here is guidance on use.