What minus twenty is actually for
Cold slows three different degradation routes at three different rates, and one of them is not slowed by cold at all.
Peptides do not have a single shelf life. They have several failure routes running in parallel, and storage conditions act on them unequally.
Hydrolysis
Water attacks the peptide bond, preferentially next to aspartate. This one is temperature-driven and water-driven, which is why the material is lyophilized, shipped with desiccant and kept cold. Dry and frozen, it is close to stopped.
Oxidation
Methionine, cysteine and tryptophan oxidise on exposure to air and light. Cold slows it. A sealed vial with the headspace displaced slows it more. Oxidation runs fastest in solution with oxygen present, which is why the material is shipped and stored dry and sealed.
Aggregation
The one cold does not stop, and can make worse. Freeze-thaw cycling drives aggregation directly, so a solution frozen and thawed repeatedly aggregates more than one frozen once, even if every hour was spent at minus twenty.
Moisture, light and repeated freezing each act on a different one of these routes. The valid-until date on a certificate describes the dry solid as supplied, and says nothing about the material once it is in solution.
Storage conditions for each product are on its own page: the specification block carries the temperature and the form as supplied.
Common questions
What causes a peptide to degrade over time?
There is no single cause. Peptides have several failure routes running in parallel: water attacks the peptide bond in hydrolysis, certain residues oxidise on exposure to air and light, and chains aggregate. Moisture, light and repeated freezing each act on a different one of these routes.
Which amino acids in a peptide are prone to oxidation?
Methionine, cysteine and tryptophan oxidise on exposure to air and light. Cold slows the reaction, and a sealed vial with the headspace displaced slows it more. Oxidation runs fastest in solution with oxygen present, which is why the material is shipped and stored dry and sealed.
Why are research peptides supplied lyophilized and with desiccant?
It is because of hydrolysis, in which water attacks the peptide bond, preferentially next to aspartate. That route is driven by temperature and by water, so the material is lyophilized, shipped with desiccant and kept cold. Dry and frozen, hydrolysis is close to stopped.
Does cold stop every kind of peptide degradation?
No. Aggregation is the one route cold does not stop, and can make worse. Repeated freezing and thawing drives aggregation directly, so cold acts unequally on the three routes: it nearly stops hydrolysis in a dry solid, slows oxidation, and does not stop aggregation.
For laboratory research use only. Not a drug, not a supplement, and nothing here is a claim about what any of this material does in a person or an animal.
