A purchasing analyst is comparing GHK-Cu listings from several suppliers. One quotes CAS 89030-95-5, another quotes CAS 49557-75-7, and a third gives a molecular weight of about 340 while calling the product a copper peptide. Prices per milligram look wildly different. Before anything can be compared, the analyst has to settle a basic question: is each listing describing the free tripeptide, or the copper complex? They are distinct substances, and nearly every number attached to them changes depending on which one is meant.
Peptide and complex are separate entries
GHK is the tripeptide glycyl-L-histidyl-L-lysine. GHK-Cu is that tripeptide with a copper(II) ion bound to it, which makes it a coordination complex rather than a simple peptide. Chemical registries list them as separate substances:
| Property | GHK (free tripeptide) | GHK-Cu (copper complex) |
|---|---|---|
| CAS registry number | 49557-75-7 | 89030-95-5 |
| Molecular formula | C14H24N6O4 | C14H23CuN6O4 (as commonly written) |
| Average molecular weight | about 340.4 g/mol | about 402.9 g/mol |
| Appearance | White to off-white solid | Blue solid |
A listing that quotes one registry number while supplying the other is describing a different substance from the one it sells. For that reason the CAS number is the first field to line up when comparing sources; names such as GHK-Cu, GHKCu, copper tripeptide-1 and “copper peptide” are used loosely. The general background on the compound is in what is GHK-Cu peptide.
Why the complex is not peptide plus copper
If the complex were simply the peptide with a copper atom added, its mass would be about 340.4 + 63.5, or roughly 403.9. The commonly cited figure is about one dalton lower. The missing hydrogen is chemically meaningful. Copper(II) in GHK-Cu is held by three nitrogen atoms from the peptide:
- the free N-terminal amine of glycine,
- the amide nitrogen of the glycine-histidine peptide bond, which loses its hydrogen when it binds the metal, and
- a nitrogen of the histidine imidazole ring.
Deprotonation of that backbone amide is what accounts for the lost hydrogen, and it also helps explain why such a small peptide forms a notably stable complex. The lysine side chain is not part of this core binding site; it projects away from the metal and contributes to the complex’s high water solubility.
Color as a first-look identity signal
The blue color of GHK-Cu is not an additive. It arises from d-d electronic transitions of copper(II) in this ligand environment, which absorb in the visible region. The free tripeptide has no such absorption and is essentially colorless. Few peptide materials offer an identity clue that can be checked by eye, and this one does: material sold as the copper complex that shows no blue color is worth a question to the supplier. Color cannot, however, say how much of the peptide is complexed.
What a label weight refers to
The two masses matter commercially. Copper makes up roughly 16 percent of the complex by mass, and the peptide portion roughly 84 percent. So if a label weight refers to the complex, the peptide content is correspondingly lower than the figure on the label. If it refers to the free peptide equivalent, the total solid in the container is higher. Neither convention is improper, but they are not interchangeable, and comparing prices per milligram across suppliers using different conventions gives a meaningless result. The general issue is discussed in what the mg on a peptide vial means and how to compare research peptide prices.
A worked example makes the gap concrete. Suppose one listing sells 100 mg of material defined as the complex and another sells 100 mg defined as peptide equivalent. The first container holds about 84 mg of tripeptide. The second, to deliver 100 mg of tripeptide in complexed form, must hold roughly 119 mg of complex. On paper the two items share a label figure; in practice their tripeptide content differs by about a fifth. A buyer who divides price by label milligrams without checking the convention is comparing different quantities.
Registry mismatches arise in a similar way. Catalogs are often assembled from older listings, and a CAS number, formula or molecular weight copied from a free-peptide entry can end up attached to a complex, or the reverse. When the three fields on a listing do not agree with each other, the listing itself is the first thing to question.
Reading an HPLC result for a complex
An HPLC purity figure for GHK-Cu reports the area of the main peak relative to everything else the detector recorded. By itself it does not prove that the copper is fully bound. Free tripeptide and incompletely complexed material can appear as separate peaks, depending on the method, and a chromatogram that resolves them says more than a single number.
Two further points apply to this compound specifically:
- Polarity. GHK is small and very polar, so it elutes early on reverse-phase columns. Separation from the void region and from early impurities deserves attention.
- Wavelength. The tripeptide contains no tryptophan, tyrosine or phenylalanine. Low-UV detection, where the peptide bond absorbs, is the meaningful choice; a figure taken where the peptide barely absorbs can flatter the result.
Copper content itself is a separate measurement, typically by an elemental technique such as atomic absorption or ICP, and it is not part of a routine HPLC purity report.
A quick comparison checklist
- Which CAS number does the listing quote, and does it match the product name?
- Is the stated molecular weight about 340 (peptide) or about 403 (complex)?
- Does the label weight refer to the complex or the peptide?
- Does the purity data state its detection wavelength?
- Is the material described as blue?
Battle Born supplies GHK-Cu as a laboratory reference material and publishes an independent reverse-phase HPLC result for the product, which can be read with the points above in mind.
Questions
Are GHK and GHK-Cu the same product?
No. GHK is the free tripeptide; GHK-Cu is its copper(II) complex. They have different formulas, molecular weights and CAS numbers.
Why is the complex about one dalton lighter than peptide plus copper?
Binding to copper removes a hydrogen from the backbone amide nitrogen between glycine and histidine.
Does an HPLC purity figure confirm copper content?
No. HPLC reports relative peak areas. Copper content requires a separate elemental measurement.
Why does the blue color matter?
It comes from copper(II) bound in the complex, so it is a simple first check that the material is the complex rather than the free peptide.
Research use only. All products supplied by Battle Born Peptides are laboratory reference materials for in-vitro research and analytical use by qualified professionals. They are not drugs, foods, dietary supplements, cosmetics or medical devices; they are not approved by the FDA or any other regulator for use in humans or animals; and they are not intended to diagnose, treat, cure, mitigate or prevent any disease, or to affect the structure or any function of the body of humans or animals. Nothing in this article is preparation, handling or dosing guidance. See our full research-use terms.