Transit was eleven days with two scanning gaps, so the thermal history is partly inferred.
I would like to understand the steps well enough to explain them to someone else.
I have access to a refrigerator with a logger and a freezer without one, which may be relevant.
Which parts of this are load-bearing and which parts are habit?
Two points means two vials from one lot and two dates: one assayed at t = 0 and one held under your storage conditions and assayed at t = n. Everything else is bookkeeping. The design is the cheap part and the discipline is not. Both vials must come from the same lot, be reconstituted identically if you are testing solution, and go to the same laboratory by the same method — otherwise the difference you measure is between two methods rather than between two dates. Two points give you a line, and a line through two points has no residual, so it cannot tell you whether the loss is linear. It tells you the total change over n days and nothing about its shape. A third point at n ÷ 2 is what buys you that, and it is the single best value-for-money addition to this design. Ask for content as well as purity at both points. Purity is a ratio and can sit still while the milligrams fall; content is the one that answers the question you are actually asking. And log the temperature between the two dates rather than describing it. Two assays bracketing an unrecorded interval measure something, but not your storage.
Answer first: the degradation pathways worth knowing are hydrolysis, deamidation, oxidation, aggregation and adsorption, and each has a different trigger and a different mitigation.
Adsorption onto glass and plastic is significant at low concentrations — micrograms per millilitre — and negligible at milligrams per millilitre. It is the usual explanation for an apparent loss in a dilute preparation.
Aggregation is physical: peptides unfold at air-liquid interfaces and associate. Shaking maximises that interface, which is why swirling and shaking produce visibly different outcomes on the same vial.
Deamidation via the succinimide intermediate is well characterised, with sequence-dependent rates highest for asparagine-glycine motifs.
Sequence determines which pathways apply, so general statements are general.
At dilute concentrations, suspect adsorption before you suspect chemistry.
HPLC purity, identity confirmation and quantified content on the vial you actually hold. Reports arrive with the chromatogram attached, not just a number.
Submit a sampleFounded 1998. ISO 9001 and cGMP certified, 1,500+ staff and 200+ patents. The synthesis house behind a great many of the vials that get sent out for testing - batch-specific documentation with every order.
Visit GL BiochemThis is answerable from the chemistry rather than from anecdote, which is unusual and welcome.
Deamidation converts asparagine or glutamine to the corresponding acid via a succinimide intermediate, adding one dalton. It is base-catalysed, accelerates above neutral pH and is the dominant aqueous pathway for many peptides.
A mass spectrum resolves most of this: minus eighteen is dehydration or succinimide, plus one is deamidation, plus sixteen is oxidation, and an unchanged mass with a shifted retention time is an isomer.
Apparent loss in a dilute preparation is usually adsorption rather than degradation and is worth ruling out first.
Swirl, never shake. Aggregation is a handling problem more than a time problem.
The short version: water enables most of it, oxygen enables oxidation, surfaces enable adsorption, and agitation enables aggregation.
Light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations.
The part that matters: freeze-thaw cycling drives aggregation through concentration at the ice interface and pH shifts as buffer components crystallise out at different rates. Each cycle costs something.
The caveat is that none of these pathways can be seen by looking at a vial, and a clear solution can be substantially degraded.
Cold, dry, dark, still. Those four words cover most of the mitigation.
The honest answer is that most reported "degradation" is adsorption and dilution error rather than chemistry.
Hydrolysis cleaves the backbone, most readily at aspartate-proline and aspartate-glycine sequences, and is acid-catalysed. In a dry solid it barely proceeds at all.
Nothing here is medical advice, and research-use compounds are not approved for human use.
Sequence decides which pathways are even available. Check the residues.
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.