GHK-Cu is a coordination complex, not a conventional peptide. The copper ion is central to its chemistry — and central to how a research-grade reference standard is qualified.
The Tripeptide and the Copper
GHK is the tripeptide Gly-His-Lys (C14H24N6O4; 340.39 g/mol). GHK-Cu is the copper(II) complex of this tripeptide, with Cu(II) coordinated via the imidazole nitrogen of His, the deprotonated peptide amide between Gly and His, and the α-amino nitrogen of the N-terminal Gly. The ε-amine of Lys is not part of the primary coordination sphere but contributes to solubility.
With copper, the empirical formula becomes C14H24CuN6O4 and the molecular weight rises to 403.93 g/mol. CAS: 49557-75-7.
Why the Copper Matters for Reference Standards
Two peptides can have identical Gly-His-Lys sequences and behave completely differently if the copper is missing, oxidized, or stoichiometrically inconsistent. For a qualified research-grade GHK-Cu, the COA should report:
- Copper content by ICP-MS or AAS — typically quantified as % Cu or as mol Cu per mol peptide.
- Cu(II) vs Cu(I) speciation indirectly via color and UV-Vis absorbance — GHK-Cu has a characteristic blue color (λmax ~ 550 nm).
- Analytical HPLC purity of the peptide backbone ≥ 99%.
- ESI-MS showing the expected mass with Cu isotope pattern.
Missing any of these and the material is either a plain Gly-His-Lys tripeptide or a poorly characterized Cu-adduct.
Synthesis
Research-grade GHK-Cu is produced by:
- Standard Fmoc SPPS of the Gly-His-Lys tripeptide.
- Preparative HPLC purification of the apopeptide.
- Controlled complexation with copper(II) acetate or sulfate in a buffered aqueous system, monitored by UV-Vis.
- Purification of the copper complex, lyophilization, and release testing.
Because the apopeptide is only three residues, coupling yields are high (> 98% per residue). The critical chemistry step is the copper complexation — insufficient stoichiometry yields a mixture of apo and Cu-peptide; excess copper yields free-copper contamination.
Stability
GHK-Cu lyophilized at −20 °C is stable for 24+ months in sealed form. In aqueous solution:
- Stable at pH 5–8; degrades outside this range.
- Photodegradation if exposed to UV for extended periods — store in amber.
- Freeze-thaw cycles can destabilize the copper-peptide bond; aliquot before freezing.
BioFusion Aminos publishes stability data per lot in the public COA library.
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