How to Store Lyophilised Peptides

To store lyophilised peptides, keep the sealed vial cold, dry and dark: 2–8 °C for short-term storage, or −20 °C and below for long-term storage, protected from light and without repeated freeze–thaw cycles. Lyophilised peptides are often hygroscopic, so a vial taken out of cold storage should reach room temperature before it is opened, to stop moisture condensing on the solid.

This guide covers the sealed vial as supplied. It explains the chemistry behind each part of that storage statement and what to check when a vial arrives.

The storage statement at a glance

Every lyophilised compound in our catalogue carries the same statement on its product page. Each part answers a specific chemical risk.

Why a dry peptide still needs cold storage

Freeze-drying removes most of the water from a peptide, and that is why the lyophilised solid keeps well. It does not make the solid inert. A review of solid-state chemistry by Lai and Topp lists the reactions that continue in dry peptides and proteins: deamidation, cleavage of peptide bonds, oxidation, β-elimination and dimerisation or aggregation. Their rates depend on temperature, on moisture content and on the physical state of the solid; a lyophilised peptide is usually amorphous rather than crystalline, which leaves its molecules some mobility.

How much this matters depends on the sequence. Manufacturers' handling notes single out asparagine, glutamine, methionine, cysteine and tryptophan as residues that shorten the shelf life of a peptide.

Two catalogue peptides show the range. MOTS-c, Met-Arg-Trp-Gln-Glu-Met-Gly-Tyr-Ile-Phe-Tyr-Pro-Arg-Lys-Leu-Arg, contains two methionines, a tryptophan and a glutamine. BPC-157, Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val, contains none of those five residues. The catalogue applies one conservative statement to both, so the sealed vial is kept cold whatever the sequence. How these mass shifts are detected is explained in mass spectrometry and peptide identity.

Temperature: short term and long term

The two temperatures correspond to ordinary laboratory equipment: 2–8 °C is a laboratory refrigerator, and −20 °C and below is a freezer. Chemical reactions slow as the temperature falls, so the longer a sealed vial will be kept, the colder it should be. Bachem advises storing lyophilised peptides below −15 °C for long periods, and prefers lower temperatures still, such as −50 °C or below.

A stable temperature matters as much as a low one:

• Keep vials towards the back of a shelf rather than in the door, where the temperature swings each time the door opens.
• Prefer a freezer without an automatic defrost cycle, because each defrost warms the contents for a while.
• Store vials in a closed box inside the refrigerator or freezer, which also keeps them dark and shields them from condensation elsewhere in the unit.

Short periods at ambient temperature are tolerated by a dry lyophilisate. Bachem ships peptides at room temperature and notes that, with few exceptions, lyophilisates in sealed vials tolerate one to two days at ambient temperature; on receipt they go to their recommended storage temperature. The storage statement applies from the moment the vial is received.

Moisture and hygroscopicity

A freeze-dried solid holds very little water, and the vial is sealed to keep it that way. The solid is also hygroscopic: given the chance, it takes up water vapour from the air. Bachem notes that short peptides and arginine-rich peptides can be very hygroscopic, and charged residues and their counter-ions attract water too.

Water that gets into the solid causes two separate problems. It adds mass that is not peptide, so the net peptide content of the material falls; see peptide purity vs net peptide content. It also acts as a plasticiser in the amorphous solid, giving the molecules more mobility and so speeding up the reactions described above.

Bringing a vial to room temperature before opening

A vial straight from a refrigerator or freezer is colder than the dew point of room air. Moisture condenses quickly on its outer glass, and if the vial were opened at that point it would condense on the solid inside as well. Bachem advises letting the closed container reach ambient temperature in a desiccator before it is opened.

• Leave the vial closed until it has reached room temperature. The time depends on the vial and on how cold it was.
• Do not warm it with a heat source; let it equilibrate on the bench or in a desiccator.

Light

Ultraviolet and short-wavelength visible light can drive oxidation in some amino acids. Kerwin and Remmele identify tryptophan, tyrosine, phenylalanine and cysteine or cystine as the residues that undergo primary photo-oxidation in proteins, and the same chemistry applies to peptides that contain them. The storage statement therefore asks for protection from light as well as cold. The short flash of a refrigerator light is not the concern; hours on a bench under daylight or strong laboratory lighting are. Keeping vials in a closed, opaque box covers this.

Freeze–thaw and temperature cycling

For a lyophilised solid, a freeze–thaw cycle is a warm-up and cool-down rather than the melting of ice, but it still counts. Each cycle is a temperature swing, and each time the cold vial meets room air there is a chance of condensation on the glass and, if the seal is imperfect, inside the vial. Lai and Topp list temperature and moisture content among the factors that govern degradation in the solid state, and repeated cycling works on both.

The practical answer is to decide on a storage location when a vial arrives and leave it there. Take out single vials rather than warming a whole box, and avoid moving vials back and forth between the refrigerator and the freezer.

Checking a sealed vial on arrival

A short check on receipt confirms that the vial is still in the state the storage statement assumes:

1. Closure. The aluminium crimp cap should be tight and the stopper seated. A loose or damaged cap means the solid may have met room air.
2. Contents. A lyophilised peptide is usually a white to off-white solid, while a metal complex such as GHK-Cu is coloured. It may be a solid disc, a loose powder or a thin film on the glass, and it can move around in transit; what is a lyophilised peptide? explains why. Visible liquid or a sticky, glassy residue is not what a dry lyophilisate looks like and is worth reporting to us.
3. Label. Check the product name and presentation, and the batch or lot number where one is printed.
4. Storage. Move the vial to its storage temperature promptly, in a closed box away from light.

Certificate status is shown on every product page, certificates of analysis are published in the COA Library where available, and a batch certificate is available on request. How storage and specifications are documented across the catalogue is set out on the quality page, and terms such as hygroscopic, freeze–thaw cycle and crimp cap are defined in the glossary.