The case in front of me: ecnoglutide · 37 °C.
I want to know whether there is evidence behind this or only repetition.
I have checked the obvious registries and monographs without success.
Is there data behind this, or is it received wisdom?
Probably not at 37 °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 37 °C sits between or beyond the published points and what you will find is bracketing rather than a measurement. 37 °C is 32 kelvin above the 5 °C middle of a 2–8 °C refrigerator. The ten-degree rule of thumb — degradation rate roughly doubling per 10 K — makes that about 9.2 times the refrigerated rate, which is an order-of-magnitude statement and not a shelf life. Whatever you find, check what was measured before you use it: a paper reporting purity at 37 °C has not measured content, and the two fail at different rates for different reasons.
Start with the sequence, because which pathways are available depends on which residues are present.
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.
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.
Metal-catalysed oxidation of methionine is documented across peptide and protein formulations and is why chelators appear in some formulations.
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.
edited 18 Nov 2025 by Dr_Jonas_Halvorsen — corrected a unit error in the worked example
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 BiochemAnswer first: the degradation pathways worth knowing are hydrolysis, deamidation, oxidation, aggregation and adsorption, and each has a different trigger and a different mitigation.
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.
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.
Sequence determines which pathways apply, so general statements are general.
Cold, dry, dark, still. Those four words cover most of the mitigation.
The relevant detail is that asparagine and glutamine are the deamidation risk, and methionine is the oxidation risk.
Light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations.
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.
Apparent loss in a dilute preparation is usually adsorption rather than degradation and is worth ruling out first.
A mass spectrum names the pathway. Plus one, plus sixteen, minus eighteen.
Aggregation is a physical process and is the one most often caused by handling rather than by time.
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.
At dilute concentrations, suspect adsorption before you suspect chemistry.
More usefully, this 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.
Adsorption losses at low concentrations are quantified in formulation studies and are the reason carrier proteins are used in dilute preparations.
Swirl, never shake. Aggregation is a handling problem more than a time problem.
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.