Ask how to store a peptide and you will be told −20 °C. That is correct and incomplete. Temperature is one of four variables that determine how long a preparation stays usable, and for a properly lyophilized powder it is often not the binding constraint.
Here is what actually degrades peptides, roughly in order of how much trouble each causes relative to the attention it receives.
Moisture
Water is the primary enemy of a dry peptide, and the mechanism is simple: hydrolysis requires water, so a genuinely dry powder cannot hydrolyse.
A well-lyophilized peptide with low residual moisture, sealed and desiccated at −20 °C, is stable for years. The same peptide that has picked up atmospheric water during careless handling has a dramatically shorter life, and the damage is cumulative and invisible.
The most common moisture failure is not storage — it is opening a cold vial. A vial at −20 °C is far below the dew point of room air. Open it directly and water condenses onto the cake immediately. Do that a few times across a vial's life and you have introduced enough moisture to matter.
Always let a vial reach room temperature, fully, before breaking the seal. Where a compound is particularly hygroscopic — NAD+ is a good example — handle it quickly and reseal with desiccant.
Oxidation
Three residues are vulnerable: methionine oxidises to the sulfoxide readily, cysteine forms disulfides and can scramble existing ones, and tryptophan oxidises under light exposure.
If your sequence contains any of these, oxidation is a live concern and the countermeasures are worth taking: minimise headspace air, store protected from light, and avoid prolonged storage in solution where dissolved oxygen is available.
Methionine oxidation is particularly insidious because it adds only 16 Da. It will not be visible in the vial, it may not separate well by HPLC, and the oxidised form frequently has reduced or altered activity. If a compound behaves inconsistently across a vial's life and it contains a methionine, this is the first thing to suspect.
Light
Tryptophan, tyrosine, and phenylalanine absorb UV, and prolonged exposure drives photodegradation. This is straightforward to eliminate: amber vials, foil overwrap, or simply a closed freezer. It matters most for compounds sitting on a bench during a long protocol.
Practical storage conditions
| State | Condition | Working life |
|---|---|---|
| Lyophilized, long term | −20 °C, desiccated, dark | Years |
| Lyophilized, extended | −80 °C, desiccated, dark | Longer, rarely necessary |
| Lyophilized, in transit | Ambient | 5–7 days without meaningful loss |
Two entries in that table surprise people.
Ambient transit is fine. A lyophilized peptide is a dry, stable solid. The stability data that produces the −20 °C recommendation concerns storage over months and years, not days. A vial that spent four days in a courier van at summer temperatures has lost very little. If it arrives dry, sealed, and intact, it is fine — put it in the freezer and proceed.
−80 °C is usually unnecessary. For a properly dried peptide, −20 °C is sufficient for any realistic working timeline. Reserve −80 °C for genuinely long-term archival storage or unusually labile sequences.
What to do when a shipment arrives warm
This generates more support email than any other topic, so it is worth stating plainly.
For a lyophilized powder, a warm shipment is almost never a problem. Dry peptides do not degrade rapidly at ambient temperature. Cold packaging is insurance against an unusually long or hot transit, not a requirement for the compound to survive a normal one.
What does warrant attention: outer packaging that was crushed or breached, a vial with a compromised or lifted seal, powder that has visibly changed — clumped, discoloured, or liquefied — or a cold-chain shipment where gel packs arrived fully thawed and warm and the contents were shipped in solution rather than lyophilized.
Any of those, photograph as received and contact us within 72 hours. Everything else, move it to the freezer.
Signs a preparation has degraded
- Powder that has clumped, changed colour, or gone tacky
- - Gradual loss of expected activity across a vial's working life
- A new or growing shoulder on the main HPLC peak
The last is the only definitive test. If a compound matters enough and its behaviour has drifted, re-assay it rather than guessing.
The short version
Keep it dry, keep it cold, and keep it dark. Of those, dry is where most real-world loss occurs, and it costs nothing but the patience to let a vial reach room temperature before opening it.
For laboratory research use only
This article is technical background for laboratory professionals. Nothing in it is medical advice, and nothing sold on this site may be administered to humans or animals.