What I have: a GLP-1 receptor agonist · 4 °C.
I am asking for verification rather than opinion, ideally with something I can read myself.
It is possible the evidence exists and I am searching for the wrong term.
How well supported is this claim?
Probably not at 4 °C specifically, because that is not where stability programmes take their readings. Accelerated work is conventionally run at 25 °C and 40 °C, with the refrigerated condition as the control, so 4 °C sits between or beyond the published points and what you will find is bracketing rather than a measurement. 4 °C is the condition the rule of thumb is anchored to, so it is the baseline rather than a multiplier: everything else in this thread is quoted relative to it. Whatever you find, check what was measured before you use it: a paper reporting purity at 4 °C has not measured content, and the two fail at different rates for different reasons.
The short version: water enables most of it, oxygen enables oxidation, surfaces enable adsorption, and agitation enables aggregation.
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.
| Pathway | Dominant when | Detected by |
|---|---|---|
| Deamidation | Solution, neutral to alkaline pH | RP-HPLC, +1 Da on MS |
| Oxidation | Light, trace metals, peroxides | RP-HPLC, +16 Da on MS |
| Hydrolysis | Solution, extremes of pH | RP-HPLC, fragment masses |
| Aggregation | Agitation, interfaces, high concentration | SEC, visual haze; often invisible on RP-HPLC |
| Freeze-concentration damage | Freeze-thaw of buffered solution | SEC, loss of recovered content |
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.
The caveat is that none of these pathways can be seen by looking at a vial, and a clear solution can be substantially degraded.
At dilute concentrations, suspect adsorption before you suspect chemistry.
Analytical standards and reagents with traceable certificates. Every quantitative result you read inherits the accuracy of the standard behind it.
Shop standardsMore usefully, this is answerable from the chemistry rather than from anecdote, which is unusual and welcome.
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.
Oxidation targets methionine, cysteine and tryptophan, adding sixteen daltons per oxygen. It is catalysed by trace metals and promoted by dissolved oxygen and by light.
Sequence decides which pathways are even available. Check the residues.
Answer first: the degradation pathways worth knowing are hydrolysis, deamidation, oxidation, aggregation and adsorption, and each has a different trigger and a different mitigation.
Light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations.
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.
Deamidation via the succinimide intermediate is well characterised, with sequence-dependent rates highest for asparagine-glycine motifs.
Apparent loss in a dilute preparation is usually adsorption rather than degradation and is worth ruling out first.
Cold, dry, dark, still. Those four words cover most of the mitigation.
edited 14 Aug 2025 by Dr_Otto_Lindqvist — corrected a unit error in the worked example
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.