Storage, stability and degradation
Peptides do not fail all at once. They break down by four routes, each on its own clock, and the sequence tells you which one matters most for a given compound.
Dry is the stable state
Nearly every degradation route below needs water. Removing it is why peptides ship as freeze-dried powder, and why the difference between storage conditions is measured in years for a powder and days for a solution.
Beyond water, the three variables are temperature, oxygen and light, and they act on different residues. A sequence with no methionine, no cysteine and no tryptophan is largely indifferent to oxygen. A sequence with an asparagine followed by a glycine has a deamidation problem no storage condition fully solves.
The four routes
Deamidation
Asparagine and glutamine lose an amide group and convert to aspartate or glutamate, adding roughly one mass unit. Asn-Gly is the fastest motif because the succinimide intermediate forms easily. Rate rises with pH above about 6 and with temperature. It is usually the first thing to go in solution.
Oxidation
Methionine picks up an oxygen at the sulfur and gains 16 mass units. Cysteine oxidizes to disulfides, which can cross-link separate molecules. Tryptophan oxidizes under light. Trace metals and peroxide in buffers catalyze all of it.
Hydrolysis
The backbone breaks. Asp-Pro is the classic weak bond, Asp-Gly close behind, and acidic conditions accelerate both. This is the route that a dry powder is essentially immune to and a solution is not.
Aggregation
Molecules associate rather than change chemically, and once they do it is generally not reversible. Driven by concentration, by interfaces from shaking, by freeze-thaw cycling and by sequences with long hydrophobic stretches. Mass spectrometry on a filtered sample can miss it entirely.
Storage, and what each condition buys
- Lyophilized, minus 20 C, sealed and desiccated
- Years. This is the reference condition every retest date is written against.
- Lyophilized, 2 to 8 C
- Months to a year or more for most sequences.
- Lyophilized, room temperature
- Weeks to months. Acceptable for transit, not for storage.
- In solution, 2 to 8 C
- Days to a few weeks, sequence dependent.
- In solution, room temperature
- Hours to days. Working condition only.
- Freeze-thaw cycles
- Each one costs material to aggregation. Aliquot instead.
General guidance for lyophilized synthetic peptides. Individual sequences differ and a supplier's retest date assumes the condition printed on the certificate.
Reading a sequence for its weak points
Look for asparagine followed by glycine, which is the fast deamidation motif. Look for aspartate followed by proline, the weak backbone bond. Count the methionine, cysteine and tryptophan residues, which are the oxidation targets. Look for long hydrophobic runs, which predict aggregation.
None of that is a claim about what the compound does. It is arithmetic on a string of letters, and it tells you which storage variable to worry about for a given vial.
Questions
Common questions
What does a retest date mean on a certificate?
The point at which the supplier expects the stated specification to need re-confirming, under the storage condition printed alongside it. It is not an expiry, and it is void if the material was stored differently.
Is discoloration a reliable warning?
It is a warning when present and it is not reliable when absent. Yellowing suggests oxidation and a collapsed or shrunken cake suggests moisture or a thermal excursion, but most degradation produces no visible change at all. Looking fine is not proof that a lot is fine.
Does a sequence with no methionine still need protecting from oxygen?
Less. Cysteine and tryptophan are also oxidation targets, and tryptophan specifically responds to light. A sequence with none of the three has a small oxidation risk, and the effort belongs on water and temperature instead.
Why is minus 20 the usual recommendation rather than minus 80?
For a dry lyophilized powder the marginal gain from minus 80 is small, because the dominant degradation routes need water that is not present. Minus 80 matters more for material already in solution, where the routes are live.
In the catalog
Compounds this applies to
Cite as: SBz Industries research library, "Storage, stability and degradation", https://www.sbzindustries.com/research/stability, updated 2026-09-11.
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