A well-stored lyophilized peptide keeps its integrity for a long time. Most problems come later: moisture when the vial is opened, unsuitable solvents or repeated freeze-thaw cycles.
When the shipment arrives
- Check the temperature logger reading before storing the material.
- Match the batch numbers on the vials with their certificates.
- Store the vials immediately at −20 °C or below, protected from light.
- If the logger shows a cold-chain breach, report it within 48 hours with the reading and photos of the shipment.
The lyophilisate
Dry and at −20 °C, most peptides are stable for months. Their main enemy is moisture: the powder is hygroscopic and absorbs water from the air, which speeds up degradation. Before opening a cold vial, let it reach room temperature inside a desiccator for 15 to 30 minutes to prevent condensation. Weigh quickly, close the vial and put it back in the cold.
Choosing the solvent
Solubility depends on the sequence. Always test a small aliquot first:
- Net positive charge (rich in lysine, arginine or histidine): analytical-grade water and, if it does not dissolve, dilute acetic acid.
- Net negative charge (rich in aspartic or glutamic acid): water or a mildly basic buffer such as ammonium bicarbonate.
- Hydrophobic: a small amount of DMSO, then dilution in buffer, checking the assay tolerance to the solvent.
Brief sonication helps dissolution. Avoid vigorous shaking, which promotes aggregation.
Solutions
- Peptides are much less stable in solution. Prepare a concentrated stock, split it into single-use aliquots and freeze them at −20 °C or −80 °C.
- Avoid freeze-thaw cycles: each one degrades part of the material.
- Methionine, cysteine and tryptophan oxidise easily. Use degassed solvents and minimise air in the vial. Semax, for example, contains methionine.
- For GHK-Cu, avoid chelators such as EDTA in the buffer, which would strip copper from the complex.
Records and traceability
Label each aliquot with batch, concentration, solvent and date, and log it in the lab notebook. If a result looks unexpected, that record tells you which batch and which preparation it came from.
Safety and disposal
Work with personal protective equipment and single-use material, and dispose of waste according to your institution's biosafety rules.