GHK-Cu: CAS Numbers, Molecular Weight, Copper Complex vs Free GHK and Why the Powder Is Blue

GHK-Cu has CAS number 89030-95-5: it is the number on the Pepta Labs GHK-Cu listing, and it is registered, together with UNII 6BJQ43T1I9, under the name prezatide copper. The listing's formula is C14H22CuN6O4 and its molecular weight 401.91 g/mol, the values PubChem records for the neutral 1:1 copper(II) complex at CID 165429100. The copper-free tripeptide GHK is a different entity, C14H24N6O4 at 340.38 g/mol (PubChem CID 73587). This page maps each name to its record, shows the arithmetic that links the numbers, and explains why the powder is blue.

Which name and which CAS number is which?

GHK, GHK-Cu, copper tripeptide-1, prezatide copper, prezatide copper acetate and AHK-Cu are six names for four different chemical entities. GHK-Cu, copper tripeptide-1 and prezatide copper all name the copper(II) complex of the tripeptide glycyl-L-histidyl-L-lysine (Gly-His-Lys); GHK is the tripeptide without copper; prezatide copper acetate names an acetate salt of the complex; and AHK-Cu is the copper complex of a different tripeptide, Ala-His-Lys. The table gives each name with its formula, mass and record, together with the related records PubChem holds.

GHK and related names: registry records and calculated values. Values marked "calculated" are computed on this page from the formula with standard atomic weights; every other value is the one held by the named record.

The Pepta Labs GHK-Cu listing uses the values for the neutral 1:1 complex: CAS 89030-95-5, UNII 6BJQ43T1I9, PubChem CID 165429100, C14H22CuN6O4 and 401.91 g/mol. Every other row describes a different chemical entity (the free tripeptide, a cation, a 2:1 complex, a salt or another sequence), or a formula that keeps the two hydrogen atoms displaced when copper binds. Each value belongs to a specific entity, so this page states which one the listing uses rather than ranking them. The peptide registry discrepancies page applies the same method to TB-500, BPC-157 and SNAP-8.

Why do some sources give GHK-Cu a different CAS number?

CAS 89030-95-5 is the CAS number on the Pepta Labs GHK-Cu listing, and it is registered under prezatide copper / copper tripeptide-1, the copper(II) complex of Gly-His-Lys. Some catalogue pages attach a different CAS number to the name GHK-Cu, sometimes together with a molecular weight near 403.9 g/mol, which matches C14H24CuN6O4 (calculated), and salt records such as an acetate carry numbers of their own. When two sources give two CAS numbers for "GHK-Cu", read the formula next to each number: C14H22CuN6O4 is the neutral 1:1 complex on the listing, C14H24N6O4 is copper-free GHK, and a formula that includes acetate or trifluoroacetate is a salt.

Are prezatide copper and prezatide copper acetate the same as GHK-Cu?

Prezatide copper is a registered name for the GHK copper(II) complex: CAS 89030-95-5 and UNII 6BJQ43T1I9 are assigned to the prezatide copper entry, and 89030-95-5 is the CAS number on the Pepta Labs GHK-Cu listing. Prezatide copper acetate adds the word "acetate" because it names an acetate salt of the same complex. A salt's formula and mass include the counter-ion, so an acetate record's molecular weight is higher than 401.91 g/mol; with one acetate per complex it is 461.97 g/mol (calculated).

GHK-Cu vs AHK-Cu: how do the two copper complexes differ?

AHK-Cu is a different compound from GHK-Cu: it is the copper(II) complex of the tripeptide Ala-His-Lys, and GHK-Cu is the copper(II) complex of Gly-His-Lys; the first residue is alanine instead of glycine. Alanine carries one more CH2 group than glycine, so AHK-Cu is C15H24CuN6O4 at 415.94 g/mol (calculated), 14.03 g/mol heavier than GHK-Cu at 401.91. AHK-Cu is not listed by Pepta Labs.

GHK vs GHK-Cu: why do listings show 340.38, 401.91 and 403.9?

GHK is not the same compound as GHK-Cu: GHK is the copper-free tripeptide glycyl-L-histidyl-L-lysine, C14H24N6O4, 340.38 g/mol, and GHK-Cu is its 1:1 copper(II) complex, C14H22CuN6O4, 401.91 g/mol, CAS 89030-95-5. The two differ by one copper atom and two hydrogen atoms. Free GHK is C14H24N6O4 at 340.38 g/mol; when the tripeptide binds one copper(II) ion it gives up two hydrogen ions, so the neutral complex is C14H22CuN6O4 at 401.91 g/mol. The arithmetic: 340.38 plus 63.55 for one copper atom, minus 2.02 for two hydrogen atoms, gives 401.91.

Three other figures follow from the same arithmetic:

• About 403.9 g/mol is 340.38 plus 63.55 with no hydrogens removed, the formula C14H24CuN6O4 (calculated 403.93). It is 2.02 g/mol above the listing value, exactly two hydrogen atoms.
• 402.92 g/mol, the PubChem cationic record (CID 71587328), is 1.01 g/mol above 401.91, the mass of one hydrogen atom.
• 744.3 g/mol, the 2:1 record (CID 133697840), holds two GHK units per copper ion, C28H48CuN12O8.

A listing that pairs the name GHK-Cu with 340.38 g/mol or C14H24N6O4 is quoting the copper-free tripeptide. The CAS numbers and molecular weights reference lists the same fields for every compound in the catalog.

How much of the GHK-Cu molecular weight is copper?

Copper is 15.81% of the GHK-Cu formula mass: one copper atom at 63.55 g/mol in C14H22CuN6O4 at 401.91 g/mol (calculated). That percentage describes the formula of the complex, not the powder in a vial, because the weighed solid also contains counter-ion and residual water.

Why is GHK-Cu powder blue?

GHK-Cu is blue to blue-violet because its copper(II) ion absorbs part of the visible spectrum through d-d electronic transitions, and the colour observed is that of the light that is not absorbed. Copper(II) has nine d electrons. When the peptide's donor atoms surround the ion, the five d orbitals split into levels of different energy, and an electron can move from a lower d level to the half-filled upper one by absorbing a photon of visible light. The absorbed light lies toward the yellow, orange and red end of the spectrum, so the transmitted and reflected light is blue to violet.

Why does the nitrogen coordination matter?

In GHK-Cu the copper(II) ion is chelated by three nitrogen atoms of the tripeptide: the glycine amino nitrogen, the deprotonated peptide amide nitrogen and the histidine imidazole nitrogen. Nitrogen donors split the d orbitals more widely than water or other oxygen donors, which moves the absorption toward shorter wavelengths. That is why copper(II) bound to peptide nitrogens looks deeper blue to violet than the pale blue of copper(II) surrounded only by water. The same chemistry gives the violet colour of the biuret test, in which copper(II) binds deprotonated amide nitrogens of a peptide chain.

Why is free GHK white?

Free GHK is white because it contains no transition-metal ion and no group that absorbs visible light; its amide bonds and imidazole ring absorb only in the ultraviolet. The colour of GHK-Cu comes from the copper(II) complex, not from the tripeptide alone. Copper(I), with a full set of ten d electrons, has no d-d transition, so the blue colour also marks the copper as copper(II).

Does the colour show purity or copper content?

No. The colour shows that a copper(II) complex is present; it does not measure purity, the copper-to-peptide ratio or the share of free GHK in the powder. The shade of a powder also varies with particle size, moisture and how densely it is packed. Purity comes from RP-HPLC and identity from mass spectrometry on the analytical report.

What should a GHK-Cu mass spectrum show?

A GHK-Cu mass spectrum should show an ion consistent with the copper complex, not only with free GHK. For C14H22CuN6O4 the monoisotopic mass with copper-63 is 401.100 Da, so the singly charged ion [M+H]+ falls at m/z 402.107 (calculated with a proton mass of 1.007276). Copper has two stable isotopes, so that ion appears as a pair: m/z 402.107 for copper-63 and m/z 404.105 for copper-65, the heavier peak at about 45% of the height of the lighter one (calculated from natural copper isotope abundances).

The complex can partly dissociate in the ion source, so a peak at m/z 341.19 for free GHK can also appear; check which ion the laboratory used to assign identity. The expected mass table lists computed ions for every listed compound, the HPLC vs mass spec guide explains what each instrument measures, and the COA verification guide walks through each line of a report.

What does the salt form change?

The salt form changes the mass of the weighed solid, not the identity of the complex. The Pepta Labs listing states the formula and mass of the neutral 1:1 complex, and the powder is supplied as the copper(II) complex, usually as an acetate or trifluoroacetate salt of it. The label quantity is a supplier-stated nominal quantity of that powder, so it includes counter-ion and residual water. The TFA vs acetate guide explains how salt form and water change net peptide content, which is not reported per listing.

Where are price per mg, reports, storage and FDA status covered?

Every GHK-Cu size with a live listing is the same copper complex, CAS 89030-95-5:

Prices are read from the catalog when this page loads; price per mg divides the single-unit price by the supplier-stated quantity. Multi-unit pack prices are shown on each product page.

• Price per mg: the table above gives the price per milligram of each GHK-Cu size from the live catalog; the research peptide price per mg page compares every listing by vial size, and each product page shows the current price.
• Analytical report: Pepta Labs represents independent third-party HPLC purity analysis and mass-spectrometry identity confirmation, commissioned through the purchasing group on a sampled production run from the source; Pepta Labs does not test in-house. The report is sent by email on request, before you order if you want to see it first: use the report request form and name GHK-Cu. Vial labels identify the compound, quantity and research-use designation and do not carry lot or batch numbers.
• Storage: the dry powder as supplied is stored at 2-8 C on arrival or at -20 C for the long term, protected from light and moisture; the peptide storage guide covers sealed-vial handling.
• FDA status: the GHK-Cu entries on the FDA compounding lists, with their dates, are on the FDA Category 2 peptides 2026 page.
• Background: what research peptides are and how they are sold as laboratory reference materials.

Frequently asked questions

Is GHK-Cu the same as GHK?

No. GHK is the copper-free tripeptide Gly-His-Lys, C14H24N6O4, 340.38 g/mol (PubChem CID 73587), and GHK-Cu is the same tripeptide bound to one copper(II) ion, C14H22CuN6O4, 401.91 g/mol, CAS 89030-95-5, the entity on the Pepta Labs listing; a listing that pairs the name GHK-Cu with 340.38 g/mol is quoting the copper-free tripeptide.

What is the difference between GHK and GHK-Cu?

GHK is the free tripeptide glycyl-L-histidyl-L-lysine, C14H24N6O4, 340.38 g/mol (PubChem CID 73587), and GHK-Cu is the same tripeptide bound to one copper(II) ion, C14H22CuN6O4, 401.91 g/mol (PubChem CID 165429100, CAS 89030-95-5); the two hydrogen atoms given up when copper binds account for the formula difference, and GHK-Cu is a blue to blue-violet solid whereas GHK is white.

Is the copper included in the GHK-Cu molecular weight?

Yes. The listing formula C14H22CuN6O4 at 401.91 g/mol includes one copper atom at 63.55 g/mol, 15.81% of the formula mass (calculated); the label quantity of powder in a vial also includes counter-ion and residual water, so that percentage describes the formula, not the vial.

Which CAS number belongs to GHK-Cu?

CAS 89030-95-5, registered under prezatide copper / copper tripeptide-1 with UNII 6BJQ43T1I9, is the CAS number on the Pepta Labs GHK-Cu listing, which uses C14H22CuN6O4 and 401.91 g/mol; catalogue pages that attach a different CAS number to GHK-Cu sometimes pair it with a figure near 403.9 g/mol, which matches C14H24CuN6O4 (calculated), and salt records carry numbers of their own, so compare the formula next to each number.

Why is GHK-Cu powder blue?

GHK-Cu is blue to blue-violet because its copper(II) ion, chelated by three nitrogen atoms of the tripeptide, absorbs yellow to red visible light through d-d electronic transitions, so the transmitted and reflected light is blue to violet; free GHK has no copper and is white.

Is prezatide copper the same as GHK-Cu?

Yes: prezatide copper is a registered name for the GHK copper(II) complex, and CAS 89030-95-5 and UNII 6BJQ43T1I9 are assigned to the prezatide copper entry, the same CAS number the Pepta Labs GHK-Cu listing shows; prezatide copper acetate names an acetate salt of that complex, 461.97 g/mol for a 1:1 acetate (calculated).

Is AHK-Cu the same as GHK-Cu?

No. AHK-Cu is the copper(II) complex of Ala-His-Lys, C15H24CuN6O4 at 415.94 g/mol (calculated), while GHK-Cu is the copper(II) complex of Gly-His-Lys, C14H22CuN6O4 at 401.91 g/mol; the sequences differ in the first residue, and AHK-Cu is not listed by Pepta Labs.

Sources

• PubChem compound records: CID 73587, 165429100, 71587328 and 133697840.
• FDA Global Substance Registration System: UNII 6BJQ43T1I9, the prezatide copper entry to which CAS 89030-95-5 is assigned.
• Calculated values: average masses from standard atomic weights; monoisotopic masses and ion m/z values from isotope masses (carbon-12, hydrogen-1, nitrogen-14, oxygen-16, copper-63 and copper-65) with a proton mass of 1.007276.

All products are supplied for laboratory research use only and are not for human or animal use.