Storage & Handling of Lyophilised Peptides
Lyophilised peptides are more robust than their reputation suggests and more fragile than convenient assumptions allow. Most degradation researchers encounter is avoidable and comes from a small number of handling errors.
Cold storage, and why desiccation matters more
The standard recommendation is −20 °C, desiccated, protected from light. Of those three conditions, desiccation is the one most often neglected and the one that does the most damage. Water is the substrate for hydrolysis of the peptide backbone; a cake stored cold but humid degrades faster than one stored cool and dry.
A vial taken from −20 °C and opened immediately pulls ambient moisture straight onto the cold cake. Always allow a sealed vial to equilibrate fully to room temperature before breaking the seal — typically 20 to 30 minutes.
Transit excursions
Lyophilised material shipped at ambient temperature over a few days does not measurably degrade. The dry powder form exists precisely to make the material transport-stable. Cold-chain shipping for lyophilised peptides is largely theatre; it matters for solutions, and it matters for a small number of unusually labile sequences, and otherwise it is expensive reassurance.
Light
Sequences containing tryptophan, tyrosine, phenylalanine, methionine or cysteine are photosensitive to varying degrees. Amber vialware and opaque secondary packaging handle this; the practical rule is to keep material in its original container and out of the light of the bench.
Freeze-thaw cycles
Every freeze-thaw cycle on a prepared solution is an opportunity for aggregation, adsorption to vessel walls, and concentration drift as ice forms. Aliquot into single-use volumes before the first freeze. The discipline costs ten minutes once and prevents a class of irreproducibility that is very difficult to diagnose after the fact.
Adsorption
At low concentrations, peptides adsorb to glass and to some plastics, and the loss can be substantial — enough to shift a dilution series by a meaningful factor. Low-bind vessels, or a carrier protein where the assay permits one, mitigate it. If a dilution series behaves non-linearly at the bottom end, adsorption is the first hypothesis to test.
Records
Record the lot number in the notebook alongside every result generated from the material. When a result cannot be reproduced six months later, the lot number is the thread that lets you determine whether the material changed or the experiment did. Suppliers that hold retention samples can then be asked a specific, answerable question.