Almost every synthetic peptide is supplied as a lyophilized (freeze-dried) powder, and almost every purity problem that is not the manufacturer’s fault happens after the vial is opened. This note covers what lyophilization does, the four degradation routes that matter for peptides, and a storage protocol that keeps a lot at its certified purity.
Why peptides are freeze-dried
Peptides in solution hydrolyze, oxidize and aggregate at rates that depend on temperature, pH and sequence. Removing the water stops most of these reactions and leaves a stable, low-density cake that can be weighed accurately and stored for years. The trade-off is that the cake is hygroscopic: it will pull moisture from the air the moment the seal is broken, and moisture restarts the chemistry that lyophilization stopped.
The four degradation routes
Hydrolysis. Peptide bonds, and particularly Asp-Pro and Asp-Gly bonds, cleave in the presence of water. Sequences with aspartate — epitalon (Ala-Glu-Asp-Gly) is an example — are the ones to keep driest.
Oxidation. Methionine, cysteine and tryptophan are the oxidation-sensitive residues. Methionine oxidizes to methionine sulfoxide, which appears on an HPLC trace as a slightly earlier-eluting shoulder on the main peak and adds 16 Da on the mass spectrum. Semax (N-terminal Met) and MOTS-c (two Met residues plus a Trp) are the sequences in this catalog where oxidation is the dominant degradation route; GHK-Cu’s copper centre is itself redox-active. Light and dissolved oxygen accelerate all of these.
Deamidation. Asparagine and glutamine residues convert slowly to their acidic counterparts, changing the mass by 1 Da and shifting retention time. It is slow in the solid state and much faster in solution at neutral or basic pH.
Aggregation and adsorption. Hydrophobic peptides stick to plastic and to each other. This does not show up as an impurity peak — it shows up as a lower-than-expected concentration when the solution is assayed.
A storage protocol
For long-term storage keep sealed vials at −20 °C, in the dark, ideally with a desiccant. For working stock over days to a few weeks, 2–8 °C is adequate. Before opening any vial let it warm to room temperature for 20–30 minutes; opening a cold vial condenses atmospheric water directly onto the cake. Weigh and dispense quickly, reseal, and return to storage. If a lot will be used over an extended period, divide it into single-use aliquots so that the bulk is never repeatedly exposed to air.
Once in solution, most short peptides are stable for a few days refrigerated and for months frozen in aliquots; avoid repeated freeze–thaw cycles, which drive both aggregation and oxidation. Solutions of methionine- or tryptophan-containing peptides should be protected from light and, where the experiment allows, prepared in degassed buffer.
How to tell whether a lot has degraded
Run it. An HPLC injection against the lot’s certificate of analysis will show any new peaks or loss of main-peak area; a mass spectrum will show +16 Da (oxidation), +1 Da (deamidation) or fragment masses (hydrolysis). If the trace still matches the COA, the lot is still the lot. If it doesn’t, the certificate no longer describes what is in the vial, and the material should be re-qualified or discarded.
Alpha Forge Prime supplies synthetic peptides for in-vitro laboratory research only. Nothing on this page describes or recommends any use in humans or animals. Products are not drugs and have not been evaluated by the FDA.
