Storage and stability of lyophilised peptides
Peptides degrade by hydrolysis, oxidation, deamidation and aggregation. Every one of those is accelerated by water, heat, light or oxygen, which is what storage practice is trying to exclude. The dry powder and the reconstituted solution are two different problems with two different answers.
Before reconstitution
| Factor | Practice |
|---|---|
| Temperature | −20 °C for long-term storage. 2–8 °C is adequate for weeks. Ambient temperature is acceptable for the days a shipment is in transit, which is why lyophilised material can be sent without a cold chain. |
| Moisture | The dominant variable. Store in a desiccated environment and allow vials to reach room temperature before opening, so that atmospheric moisture does not condense onto cold glass and powder. |
| Light | Store in the dark. Tryptophan, tyrosine, methionine and cysteine residues are photosensitive. |
| Oxygen | Vials are supplied sealed under partial vacuum. Leave them that way until needed; there is no benefit to opening one early. |
Kept dry, cold and dark, lyophilised material is stable for a long time — commonly quoted as years at −20 °C. That figure assumes the seal is intact and the powder has never been exposed to humid air.
After reconstitution
Once in solution, the timescale shortens from months to days or weeks. Refrigerate at 2–8 °C and keep the vial out of light.
How long a solution remains usable depends on the sequence, the diluent and the concentration, so treat any general figure as a starting point rather than a specification. Where it matters, the honest approach is to verify rather than assume: retain a sample and re-analyse it, or prepare fresh material.
Aliquot before freezing
Repeated freezing and thawing is one of the most reliable ways to damage a peptide in solution. Ice formation concentrates solutes in the remaining liquid, shifts pH as buffer components crystallise at different rates, and drives aggregation at the ice–water interface. Each round does more damage.
Divide the solution into single-use aliquots first, then freeze. A frozen stock split into ten portions is thawed once each; the same stock in one vial is thawed ten times. Use low-binding tubes where the concentration is low enough for adsorption to the vessel wall to matter.
Recognising degraded material
- Cloudiness or visible particulates in a solution that was previously clear — usually aggregation.
- Discolouration. Lyophilised peptide is normally white to off-white. Yellowing suggests oxidation.
- A cake that has collapsed, shrunk or gone glassy. Ordinarily a sign of moisture ingress or a failed seal.
- Material that will no longer dissolve in a diluent that previously worked.
None of these is sensitive. A peptide can lose a large fraction of its integrity with no visible change at all, which is the argument for dated records and, where the result matters, for re-analysis rather than inspection.
Records
Storage practice is only as good as the paperwork attached to it. For each vial and each aliquot, keep the compound, the lot number, the concentration, the diluent, the date of reconstitution and the storage location. The lot number is the link back to the certificate of analysis, and it is the first thing lost when the original packaging is discarded.
Freezers fail. If a stock matters, knowing when it was prepared and where it sits is the difference between a contained problem and starting again.