Storing and reconstituting lyophilised peptides

A peptide as a lyophilised cake and the same peptide in solution are, as far as stability goes, two different materials. What follows are the rules that in practice decide whether a sample still matches its certificate of analysis a few weeks later.

Why a lyophilisate keeps

Freeze-drying removes water under reduced pressure and leaves a porous cake behind. With no water present hydrolysis effectively stops, and molecular mobility is low enough that degradation slows by orders of magnitude. A sealed vial at -20 °C therefore holds its declared purity for a long time, while the same peptide in solution measures its life in days or weeks.

The enemy of a cake is moisture from the air. A vial taken straight from the freezer and opened immediately collects condensation on cold glass, and that water goes into the cake. Hence the habit of letting a vial reach room temperature before it is opened — usually 20 to 30 minutes, still closed.

Temperature and light

For research material as a lyophilisate, -20 °C is the usual long-term condition. Over a few days a refrigerator is often enough, but that decision should follow the documentation for the specific batch rather than a general rule.

Light is a separate question. Some sequences carry residues prone to photo-oxidation — tryptophan, tyrosine, methionine, cysteine. Amber glass, or simply keeping the vial in its box, solves that at no cost.

Reconstitution

The solvent follows the material, not the other way round. Bacteriostatic water with 0.9% benzyl alcohol is the usual choice where a solution will be drawn from repeatedly over some weeks; preservative-free water for injection where the preservative would interfere with the assay.

Direct the stream at the wall of the vial rather than onto the cake. Peptides denature mechanically without much provocation: shaking and foaming do real damage, gentle swirling does not. A cake normally dissolves in under a minute; material that is still not going into solution after several minutes is telling you about solvent choice, not about how hard to shake it.

After reconstitution

Keep the solution refrigerated and treat it as a material with a limited life. The single largest mistake is repeated freezing and thawing: every cycle adds aggregates and removes active material. Split the solution into working aliquots immediately after preparing it — one assay's worth each — and freeze those separately.

Write the reconstitution date on the vial. It is one line, and it is the difference between a result and the question "how long has this been sitting here".

What this does not cover

The materials described in this shop are supplied for research use only. They are not medicines, dietary supplements or cosmetics, they are not approved as such, and they are not for human or veterinary use. Everything above concerns handling a reagent in a laboratory and nothing beyond that.