Storing peptides: powder vs mixed
Peptides are stable as a dry powder and fragile once dissolved. Almost every storage rule follows from that one fact, so the habits for a sealed vial and a mixed stock are quite different.
At a glance
| Powder (lyophilized) | Mixed (in solution) | |
|---|---|---|
| Long-term temperature | -20 °C (-4 °F), or -80 °C (-112 °F) where available | Frozen in single-use portions at -20 °C or colder |
| Short-term | Tolerates short periods at room temperature, such as shipping | Refrigerated at 2–8 °C (36–46 °F) |
| Main threats | Moisture, light, heat | Bacteria, oxidation, freeze-thaw cycles, time |
| Typical lifetime | Long, often a year or more when kept cold, dry and sealed | Days to months, depending on the sequence and conditions |
Storing powder
Freeze-drying removes the water that most degradation reactions need, which is why a sealed vial of powder keeps so well.
- Cold: for long-term storage, keep vials at -20 °C or colder. A manual-defrost freezer is better than a frost-free one, because frost-free models warm up briefly during their defrost cycles.
- Dry: peptide powder readily absorbs moisture from the air. Let a cold vial reach room temperature before you open it, ideally in a desiccator, so water does not condense on the powder.
- Dark: keep vials in their box or another light-proof container.
- Sealed: open a vial as few times as possible and reseal it promptly.
Short spells at room temperature, such as time in transit, are generally well tolerated by dry peptide. Move vials to cold storage when they arrive.
Storing a mixed solution
In solution, peptides are exposed to water, oxygen and any microbes that get in. Shelf life drops sharply, so plan to make only what you will use.
- Short term: keep the solution refrigerated at 2–8 °C and protected from light.
- Longer term: divide the stock into single-use portions (aliquots) and freeze them at -20 °C or colder. Thaw only what you need.
- Avoid repeated freezing and thawing. Each cycle can damage the peptide, which is the main reason to aliquot.
- Keep it sterile. Use sterile liquid and clean technique. A slightly acidic to neutral pH (around 5 to 7) is generally kinder to peptides in solution than alkaline conditions.
Published handling guidance varies on how long solutions last, from about a week to several months, because it depends heavily on the sequence and conditions. Where it matters, test stability for your own peptide and setup rather than relying on a general rule.
Some sequences need extra care
| Contains | Risk in solution |
|---|---|
| Cysteine (C), methionine (M), tryptophan (W) | Oxidation by air. Use oxygen-free liquid where practical and keep headspace small. |
| Asparagine (N), glutamine (Q) | Deamidation, which changes the molecule over time, faster at higher pH and temperature. |
| Glutamine (Q) at the start of the chain | Can convert to pyroglutamate, changing the molecule. |
The diluent vial
A multi-use vial of bacteriostatic water contains a preservative, but it does not last indefinitely once opened. A common rule for preserved multi-use vials is to discard them 28 days after the first puncture unless the label states otherwise. Unopened, follow the expiry date on the vial.
Signs a solution has degraded
- Cloudiness, particles or a film that was not there before.
- A yellow or brown tint in a solution that was clear.
- Results drifting between experiments that use the same stock.
A clear solution is not proof that a peptide is intact, so date every vial and stick to the time limits you set. For how to make the stock in the first place, see how to reconstitute research peptides: the math.