Storing lyophilised peptides in the laboratory

Research peptides are supplied as a dry powder, not as a solution. That is not a packaging choice: it is the main reason they arrive in a usable state. This guide covers why, and how to keep them that way in the laboratory. It concerns handling and storage only and gives no instructions for use.

Why freeze-dried

In solution, peptides degrade through several routes. Peptide bonds can be hydrolysed, particularly next to aspartic acid. Methionine and cysteine residues oxidise. Asparagine and glutamine can deamidate. Some peptides aggregate. Water takes part in, or enables, most of these reactions. Lyophilisation, or freeze-drying, removes the water by freezing the solution and then turning the ice directly into vapour under vacuum, which slows these processes dramatically.

Storing unopened vials

Long term: in a freezer at −20 °C.
Protected from light; keep vials in their box.
Allow a cold vial to reach room temperature before opening, so moisture from the air does not condense on the powder.
A few days at room temperature during delivery is generally tolerated by lyophilised peptides; long-term storage should be cold.

After reconstitution

Once a peptide is dissolved, the clock starts again and runs much faster. Solutions are kept in a refrigerator at 2 to 8 °C, protected from light, and used within the period your protocol allows. Repeated freezing and thawing of solutions is best avoided; if a solution has to be kept longer, dividing it into single-use portions is common practice.

Choosing the diluent

Bacteriostatic water, with 0.9% benzyl alcohol as a preservative, is the usual diluent for vials that will be opened more than once. Dilute acetic acid helps with peptides that dissolve poorly at neutral pH. Some cell-based assays are sensitive to benzyl alcohol, and the choice of diluent should follow the experimental protocol.

Excipients

Some lyophilised products contain an excipient such as mannitol, which forms the structure of the dry cake and helps it dissolve evenly. Where a UKPeps lot contains mannitol, the certificate of analysis says so.

Signs that something is wrong

The powder has collapsed into a sticky film or changed colour (GHK-Cu is naturally blue; most peptides are white).
The vial seal is damaged.
A solution turns cloudy or shows particles when it should be clear.

If a vial arrives damaged, tell us within 14 days with a photo and the lot number.

Sources

Wang W et al. Lyophilization and development of solid protein pharmaceuticals. Int J Pharm, 2000. PubMed 10967427 · doi:10.1016/s0378-5173(00)00423-3
A review of freezing and drying stresses during lyophilisation, protection by excipients and solid-state stability.
Randolph TW et al. Phase separation of excipients during lyophilization: effects on protein stability. J Pharm Sci, 1997. PubMed 9383725 · doi:10.1021/js970135b
How excipient phase separation during lyophilisation affects protein stability.
Manning MC et al. Stability of protein pharmaceuticals: an update. Pharm Res, 2010. PubMed 20143256 · doi:10.1007/s11095-009-0045-6
A review of chemical and physical degradation pathways of protein and peptide pharmaceuticals.
Nugrahadi PP et al. Designing Formulation Strategies for Enhanced Stability of Therapeutic Peptides in Aqueous Solutions: A Review. Pharmaceutics, 2023. PubMed 36986796 · doi:10.3390/pharmaceutics15030935
A review of peptide degradation in aqueous solution and of formulation strategies to improve stability.

Published laboratory and preclinical research, cited for scientific context only. It is not evidence of safety or effect in people.