- Peptides degrade by chemistry, not by magic: oxidation, deamidation, hydrolysis and aggregation, all of which speed up with heat.
- 2–8°C is the standard because it slows those reactions without freezing — freezing a peptide *solution* can do more harm than a warm afternoon.
- Light matters for sequences containing tryptophan, tyrosine or methionine. Keep the carton.
- The cold chain is the vendor's storage problem until the parcel is in your hands. Ask how it is held and how it is shipped.
Every peptide carton says "store at 2–8°C". Fewer explain why, and almost none explain what happens if you don't. This is the chemistry behind the label, and what it means for the journey from a Swiss production line to a laboratory fridge in the UK.
What actually degrades a peptide
A peptide is a chain of amino acids held together by amide bonds, with side chains that have their own reactivity. Four processes account for most of the loss of a stored peptide:
- Oxidation. Methionine, cysteine and tryptophan side chains react with dissolved oxygen. Faster in solution, faster in light, faster when warm.
- Deamidation. Asparagine and glutamine residues lose an amide group, changing the mass and often the shape of the molecule. This is the classic slow degradation route and it is strongly temperature-dependent.
- Hydrolysis. Water attacks the backbone, particularly at aspartic acid residues. Again, faster in solution and faster when warm.
- Aggregation. Peptide molecules stick to each other. Some sequences are prone to it; heat, agitation and freeze–thaw cycles all encourage it.
None of these is instant. All of them roughly double in rate for every 10°C rise — the rule-of-thumb behind every stability study — which is why the difference between a fridge and a radiator is not a few percent but an order of magnitude.
Why 2–8°C and not colder
Refrigeration slows every reaction above without changing the physical state of the material. That's the point.
Freezing a lyophilised (freeze-dried) peptide is generally fine and often recommended for long-term storage — there's very little water present to form damaging ice.
Freezing a peptide in solution is a different matter. As water freezes, the peptide is concentrated into the shrinking liquid fraction between ice crystals, pH can shift, and the molecule can be physically stressed at the ice interface. Thawing and refreezing repeats the insult. For a pre-filled pen, which is already in solution, "do not freeze" is on the label for this reason. Pushed to the back of a fridge against the evaporator plate is the most common way it happens.
Light
Ultraviolet and even strong visible light can drive oxidation of aromatic residues — tryptophan especially, tyrosine and methionine to a lesser degree. The practical instruction is simple: keep the pen or vial in its carton. The cardboard is not packaging; it's a light shield.
How long things last
Manufacturers set shelf lives from real-time and accelerated stability studies, and the figure on the carton is the one to use. As a general shape:
| Form | Unopened, 2–8°C | After first use |
|---|---|---|
| Lyophilised powder in a sealed vial | Long — typically years, per the label | n/a until reconstituted |
| Reconstituted solution | Days to a few weeks depending on the sequence and buffer | Same |
| Pre-filled pen (solution, sealed) | Per the label — months | Manufacturer's in-use limit, typically 4–12 weeks |
Two things people miss. First, "after first use" limits exist because each puncture introduces a small risk of contamination and a small volume of air; they're not arbitrary. Second, a pen stored with a needle attached is an open system — the label says not to, and that's why.
The cold chain, from the vendor's side
The temperature history of a peptide before it reaches you is invisible in the box. This is what a vendor should be able to tell you about it:
- Manufacture and release. Material is held cold at the facility from release. The certificate of analysis reflects the batch at the time of testing; the cold chain is what keeps the batch matching its certificate afterwards.
- Transit to the vendor. Bulk shipments travel in insulated, temperature-logged containers. Ask whether the vendor receives a temperature log.
- Storage at the vendor. Stock should be held in a monitored fridge, not a stockroom. A vendor who holds stock in the UK controls this step; one who drop-ships single orders from overseas does not.
- Dispatch to you. Insulated packaging and a fast, tracked service. The goal is that the parcel spends as little time as possible outside refrigeration and none of it in a hot sorting facility. Next-day UK delivery is the practical minimum for a temperature-sensitive product.
- On arrival. Into the fridge, in the carton, away from the freezer plate.
What we do
Biovanta stock is manufactured in Switzerland and held refrigerated in the UK. Orders dispatch next working day by Royal Mail, tracked in insulated packaging. Every carton carries the 2–8°C instruction, and the product pages restate the storage conditions and in-use limits so nothing depends on reading the small print on the box. As with everything on the site, the products are supplied for laboratory research use only.
Sources
Questions this article answers
Can I freeze a peptide pen?
No. A pre-filled pen contains peptide in solution, and freezing a solution concentrates the peptide between ice crystals, shifts pH and stresses the molecule. The label says do not freeze; keep it in the main body of the fridge, away from the back wall.
What happens if a peptide is left at room temperature?
Degradation reactions run faster — roughly doubling for every 10°C. A few hours in transit at ambient temperature is within what stability studies allow; days on a warm windowsill are not. Return it to 2–8°C and keep it in the carton.
Why does the carton say to keep the peptide in the box?
Light drives oxidation of aromatic amino-acid residues. The carton is a light shield, so storing the pen or vial inside it protects the peptide.
Want the certificate for a real batch?
Name a compound and we'll send the manufacturer's HPLC-MS certificate for the batch you would receive — before you order, no account needed.