Peptide degradation is not dramatic. Material does not usually go visibly bad. It drifts — a percentage point of purity here, a new small peak there — and the first sign is often an experiment that will not reproduce against results from six months earlier.
Four variables drive it, and all four are cheap to control.
Temperature
Degradation chemistry follows the usual Arrhenius relationship: rates roughly double for every 10 °C rise. The practical consequence is that the difference between a fridge and a freezer is not marginal.
| Condition | Form | Typical working life |
|---|---|---|
| −80 °C | Lyophilised | 5 years or more |
| −20 °C | Lyophilised | 24 months |
| 2–8 °C | Lyophilised | Weeks to a few months |
| Room temperature | Lyophilised | Days to weeks; shipping only |
| 2–8 °C | In solution | 7–28 days, compound-dependent |
| −80 °C | Aliquoted solution | Several months, single thaw |
For most laboratories, −20 °C for lyophilised stock and 2–8 °C for working solutions is the right balance. Reserve −80 °C for long-term reserve and for aliquoted solution.
Water
Water is a reactant in hydrolysis and deamidation, so residual moisture sets a floor on how stable dry material can be. It arrives from two directions: what the lyophilisation left behind, and what the powder picks up afterwards.
The second is entirely under your control and is routinely mishandled. Opening a cold vial condenses room moisture directly onto the powder. Every subsequent opening exchanges the dry headspace for room air. A vial opened weekly on a humid bench will hold specification for a fraction of the time a properly handled one does.
- Equilibrate sealed vials to room temperature before opening — twenty to thirty minutes.
- Store with desiccant, and replace it when the indicator changes.
- Weigh quickly and reseal. For hygroscopic compounds such as NAD+, mass gain is measurable within minutes.
- Aliquot at first opening rather than returning repeatedly to a stock vial.
Air
Oxidation is the dominant degradation route for peptides containing methionine, cysteine or tryptophan. Methionine oxidises to the sulfoxide, adding 16 daltons and producing a peak that elutes just ahead of the parent on reversed-phase. Cysteine forms disulfides, which can dimerise the peptide.
MOTS-c is the clearest case in the catalogue — two methionines, and a solution shelf life we specify at fourteen days rather than twenty-eight precisely because of it. Semax and its analogues carry one. HGH fragment 176-191 contains cysteine and can dimerise on ageing.
Where your facility allows it, purging headspace with nitrogen or argon measurably extends solution life. Where it does not, minimising the number of openings does most of the same work.
Light
Photodegradation matters for aromatic residues — tryptophan particularly — and for chromophoric compounds. GHK-Cu is a copper coordination complex and is genuinely light-sensitive; NAD+ degrades measurably in light over days in solution.
Amber vials, foil overwrap or simply a closed box handles this. It is the cheapest of the four controls and the most often skipped.
Freeze-thaw
Each cycle concentrates solutes as ice forms, shifts local pH, and creates ice-liquid interfaces where peptides denature. Aggregation from freeze-thaw is cumulative and irreversible.
The fix is aliquoting at first reconstitution, sized so each aliquot is used in one session. It takes ten minutes once and removes the problem entirely. Do not refreeze a thawed aliquot.
Compound-specific notes
| Compound | Watch | Solution life at 2–8 °C |
|---|---|---|
| MOTS-c | Two methionines — oxidation | 14 days |
| NAD+ | Hygroscopic; unstable above pH 7 | 7 days, below pH 7 |
| N-Acetyl Semax Amidate | One methionine | 21 days |
| GHK-Cu | Light; pH-dependent coordination | 14 days, dark |
| LL-37 | Adsorbs to glass and plastic | 14 days, low-binding tubes |
| Retatrutide | Aggregation under agitation | 28 days |
| Humanin | Aggregation; prepare fresh | Prepare per session |
Practical setup
- Manual-defrost −20 °C freezer for lyophilised stock, with desiccant in the storage box.
- Equilibrate sealed vials to room temperature before every opening.
- Aliquot at first reconstitution, sized for single-session use.
- Label every aliquot with compound, concentration, diluent and date.
- Keep light-sensitive material in amber vials or a closed box.
- Record the batch code in your notebook alongside results, so material can be traced later.
- Observe the retest date on the certificate rather than assuming indefinite stability.
None of this is expensive or slow. It is the difference between results that reproduce across a year and results that quietly stop agreeing with each other for reasons nobody can identify.
This guide is written for laboratory practitioners and describes analytical and handling practice. It is not medical advice, and it contains no dosing or administration guidance. Material supplied by Ryzen Research Ltd is for research use only and is not for human or veterinary use.