Laboratory Storage of Lyophilised Peptides

Freeze-drying removes water from a frozen solution by sublimation under vacuum, leaving a porous solid. Without water, the hydrolysis and microbial growth that degrade peptides in solution essentially stop. A lyophilised peptide in a sealed vial, kept cold and dry, typically remains within specification for years; the same peptide in solution may degrade in days.

For short-term storage, 2–8 °C in a refrigerator is adequate for most lyophilised peptides. For long-term storage, −20 °C is the usual recommendation, and some laboratories use −80 °C for particularly labile sequences. Unopened vials can be shipped at ambient temperature for a few days without measurable loss, which is why tracked 24-hour delivery is sufficient; what matters is that the vial goes into cold storage on arrival.

Residues such as tryptophan, methionine and cysteine are sensitive to light and oxidation. Vials should be kept in the dark, in their box or an opaque container. Keep the stopper sealed until use; once a vial is opened, the headspace contains air and the clock starts on oxidation-sensitive sequences.

The most common cause of avoidable degradation is condensation. A cold vial opened in warm air immediately collects moisture on the powder, and that water begins hydrolysis. Always allow a vial to reach room temperature before opening it, which takes fifteen to thirty minutes on the bench. The same applies to the diluent.

Once dissolved, a peptide is far less stable. Prepared solutions should be refrigerated at 2–8 °C, protected from light and used within the period supported by the laboratory's own stability data; a few weeks is typical, longer for some sequences, shorter for others. Repeated freeze–thaw cycles damage peptides, so if a solution must be frozen it should be divided into single-use aliquots first. Label every prepared solution with compound, concentration, solvent, date and batch reference.

A lyophilised cake that has collapsed, discoloured, or become sticky has likely taken on moisture. A solution that is cloudy or contains particulates should not be used. GHK-Cu is the exception that proves the rule: its blue colour is expected and a loss of colour, not its presence, is the warning sign.