How to store research peptides: powder, solution and after opening
Peptides are chains of amino acids, and many of those amino acids react slowly with water, oxygen and light. Good storage is about slowing those reactions down. The rules are simple: keep peptides dry, cold and dark for as long as possible, and once they are in solution, handle them so they stay clean and are not frozen and thawed over and over.
Quick reference
| Form | Where | Notes |
|---|---|---|
| Lyophilised powder, long term | Freezer, −20 °C, or −80 °C for the longest storage | Sealed vial, in the dark, ideally with a desiccant |
| Lyophilised powder, short term | Refrigerator, 2–8 °C | Acceptable for short periods for many peptides; the freezer is safer |
| Powder in transit | Room temperature | Freeze-dried peptides tolerate normal shipping times |
| Reconstituted solution | Refrigerator, 2–8 °C | As a general guide, about a week; never leave at room temperature |
| Solution, longer term | Freezer, in single-use aliquots | Thaw each aliquot once; avoid repeated freeze–thaw |
| Capsules and tablets | Cool, dry place below 25 °C | Closed container, away from light |
| Pre-filled pens | Refrigerator, 2–8 °C | Do not freeze |
What damages a peptide
- Water: moisture lets slow chemical changes happen, such as deamidation (asparagine and glutamine residues change form) and hydrolysis (the chain breaks). This is why peptides are freeze-dried: with almost no water left, these reactions nearly stop.
- Oxygen: methionine, cysteine and tryptophan residues oxidise. Exposure to air, especially in solution, speeds this up.
- Heat: every degradation reaction runs faster when it is warmer. Cold storage is the single most effective protection.
- Light: UV and strong light can damage aromatic amino acids. Store vials in their box or in the dark.
- Freezing and thawing: each cycle stresses a peptide, above all in solution, where it can make it clump together (aggregate). Avoid repeated cycles for powder too: every time a cold vial is opened, moisture can get in.
- Contamination: bacteria introduced through repeated needle punctures can grow in a solution and break the peptide down.
Storing lyophilised powder
A sealed vial of freeze-dried peptide is the most stable form there is. Keep it in a freezer at −20 °C, or at −80 °C for the longest storage. Some peptides are stable for a while in a refrigerator at 2–8 °C, but the freezer is the safer default. Keep vials in the dark, and if possible in a closed container with a desiccant sachet to keep humidity away. Avoid frost-free freezers if you can: their defrost cycles swing the temperature and humidity.
Freeze-dried peptides are robust enough to travel at room temperature, which is why they are shipped without cooling. Put them in the freezer or refrigerator when they arrive.
One step people often miss: let a cold vial reach room temperature before you open it or pierce the stopper. Opening a cold vial draws in moist air, and the water condenses on the powder. Leave the closed vial on the bench, ideally in a desiccator, for 30–60 minutes first.
Reconstituting
- Bring the vial and the solvent to room temperature.
- Wipe the rubber stoppers with an alcohol swab and let them dry.
- Add the solvent slowly, letting it run down the inside wall of the vial rather than straight onto the powder.
- Swirl gently or roll the vial between your fingers until the powder dissolves. Do not shake: shaking creates foam and can make the peptide aggregate.
- Check that the solution is clear. A cloudy solution or visible particles usually means the peptide has not dissolved properly.
- Label the vial with the compound, the concentration and the date.
Which solvent
- Bacteriostatic water is sterile water with 0.9% benzyl alcohol. The benzyl alcohol stops bacteria from growing, so the vial can be punctured more than once. It is the usual choice when a solution will be used over several days or weeks.
- Sterile water without a preservative is for solutions used in one go, since nothing stops bacteria from growing once it is opened.
- Acetic acid water (dilute acetic acid) helps peptides that dissolve poorly or are unstable at neutral pH.
Always check the solubility information for the specific peptide: a few need a different solvent, and some are sensitive to particular additives.
Storing solutions
Once dissolved, a peptide degrades much faster than as powder. Keep solutions in the refrigerator at 2–8 °C, in the dark, and never leave them out at room temperature longer than needed. As a general guide, many peptide solutions stay stable for about a week in the refrigerator. Peptides containing asparagine, glutamine, cysteine, methionine or tryptophan are less stable in solution. How long a given solution stays usable depends on the peptide, the solvent and how clean the handling is, so follow the stability data for the compound where it exists.
If a solution must last longer, split it into single-use aliquots in clean low-binding tubes and freeze them. Thaw each aliquot once and do not refreeze it. This avoids repeated freeze–thaw cycles and repeated punctures of the same vial.
Signs a peptide has degraded
- Powder that has turned sticky, shrunk into a gel or changed colour, usually a sign that moisture got in.
- A solution that turns cloudy, forms particles or changes colour over time.
- Results that drift between experiments using the same stock.
When in doubt, prepare a fresh solution from a new vial. Purity at the time of manufacture is shown on the certificate of analysis; see our lab reports.
References
- Manning MC, Chou DK, Murphy BM, Payne RW, Katayama DS. Stability of protein pharmaceuticals: an update. Pharm Res 2010;27:544–575.
- Wang W. Lyophilization and development of solid protein pharmaceuticals. Int J Pharm 2000;203:1–60.
- Wang W. Instability, stabilization, and formulation of liquid protein pharmaceuticals. Int J Pharm 1999;185:129–188.
- Merck / Sigma-Aldrich. Handling and storage of synthetic peptides. Technical article.