How to Store Lyophilized Peptides: Temperature, Light and Moisture

Knowing how to store peptides comes down to keeping a lyophilized powder cold, dry, dark and sealed. Lyophilized peptides should be held at −20 °C or colder for long-term storage, warmed to room temperature before the vial is opened, kept away from light and air, and dissolved only as needed, because peptide solutions degrade much more quickly than the dry powder.

The guidance below draws on technical guides from two major chemical and peptide suppliers, Bachem and Sigma-Aldrich, and on peer-reviewed studies of how peptides degrade. It covers lyophilized vials and the solutions prepared from them for in-vitro assays, with residue notes for catalog peptides such as MOTS-c, Semax, GHK-Cu and TB-500.

Why are lyophilized peptides more stable than peptide solutions?

Lyophilization, or freeze-drying, removes most of the water from a peptide preparation and leaves a dry, porous powder. Water takes part in many of the reactions that break peptides down, so the dry powder changes far more slowly than the same peptide in solution. Bachem's handling guide states that peptides should not be stored in solution because they may slowly undergo chemical degradation (Bachem).

A dry powder still changes over time. A review of solid-state stability by Lai and Topp (1999) describes six chemical degradation pathways that still operate in solid peptides and proteins: deamidation, peptide bond cleavage, oxidation, the Maillard reaction, β-elimination, and dimerization or aggregation. Their rates depend on temperature, moisture content, excipients and whether the solid is amorphous or crystalline, which is why storage conditions matter even for a sealed vial.

Reactions in solution proceed much more quickly. In a model study, Geiger and Clarke (1987) found that the asparagine in a hexapeptide containing an asparagine-glycine (Asn-Gly) sequence deamidated with a half-life of about 1.4 days at 37 °C and pH 7.4. The practical rule follows: keep peptides dry until an experiment needs them.

How to store peptides at the right temperature

Colder is better for lyophilized peptides, and the two supplier guides agree on the range. Sigma-Aldrich recommends storing lyophilized peptides at −20 °C or preferably −80 °C (Sigma-Aldrich). Bachem recommends keeping the lyophilizate in a tightly closed container below −15 °C, with lower temperatures preferred for long-term storage, and notes that peptides may be kept in a refrigerator at 4 °C for short-term use and may be shipped at room temperature. Temperature is one of the factors that Lai and Topp identify as governing solid-state degradation rates, which is why freezer storage is preferred over refrigeration for anything beyond short-term use.

Brief ambient exposure in transit is normal for lyophilized material, and vials should go into the freezer on arrival. The table summarizes lyophilized peptide storage and solution storage in qualitative terms. There is no single peptide shelf life: neither guide gives one figure for lyophilized peptides, and Bachem notes that sequences containing asparagine, glutamine, methionine, cysteine or tryptophan have limited shelf lives.

How does moisture damage lyophilized peptides?

Lyophilized peptides are hygroscopic: the dry powder pulls water from the air. Bachem notes that absorbed moisture lowers the overall peptide content of the powder and may also lower its stability, and Sigma-Aldrich states that exposure to moisture greatly decreases long-term stability. Moisture content is also one of the main factors governing solid-state degradation rates (Lai and Topp, 1999).

The main risk comes at the moment of opening. A vial taken straight from the freezer is colder than room air, so water condenses on the glass and on the powder as soon as the cap comes off. A short routine avoids it:

1. Keep the vial sealed until it is needed.
2. Let the closed vial warm to room temperature before opening, ideally in a desiccator, as both Bachem and Sigma-Aldrich advise.
3. Weigh out material quickly and reseal the vial tightly.
4. For oxidation-prone sequences, replace the air in the vial with dry nitrogen or argon before resealing, a step Sigma-Aldrich describes.
5. Return the vial to frozen storage inside a sealed secondary container with desiccant.

Does light degrade peptides?

Light can degrade peptides, mainly through ultraviolet (UV) absorption and through reactive oxygen species generated by light. A review of photo-oxidation by Hipper et al. (2022) notes that the indole side chain of tryptophan absorbs light at wavelengths of 320 nm or shorter, that tyrosine absorbs in the UV with a maximum near 275 nm, and that tryptophan can oxidize rapidly because of its low oxidation potential. The same review notes that no proteinogenic amino acid absorbs visible light, and that most light-induced modifications come from other photosensitizing molecules that produce reactive oxygen species.

The storage practice is simple. Keep vials in their carton or an opaque box, use amber tubes for aliquots where practical, and avoid leaving material on a sunlit or brightly lit bench; Sigma-Aldrich advises storing peptides away from bright light. Tryptophan-containing catalog peptides include MOTS-c and DSIP (emideltide), whose sequence begins with tryptophan.

Which residues make a peptide prone to oxidation and deamidation?

A peptide's sequence determines which degradation pathways matter most for it. Three are worth checking against every sequence:

• Oxidation. A review by Li, Schöneich and Borchardt (1995) identifies methionine (Met), cysteine (Cys), histidine (His), tryptophan (Trp) and tyrosine (Tyr) as the residues most susceptible to oxidation. Oxidation can be driven by contaminating oxidants, trace transition-metal ions or light, and is influenced by pH, temperature and buffer composition. Sigma-Aldrich singles out sequences containing Cys, Met or Trp as prone to air oxidation.
• Deamidation and isomerization. Asparagine (Asn) can cyclize into a succinimide intermediate that opens to a mixture of aspartyl and isoaspartyl forms, with some racemization. In Geiger and Clarke's model peptide, replacing the glycine after Asn with leucine or proline slowed degradation 33- to 50-fold, and an aspartate (Asp) in place of the Asn formed the succinimide 34 times more slowly. Bachem also lists glutamine (Gln) among the residues that limit shelf life.
• Disulfide formation. Free cysteine thiols oxidize to disulfides, and Bachem notes that this happens rapidly above pH 7. None of the catalog sequences below contains cysteine.

The table applies these rules to catalog peptides, using the sequences on their product pages.

BPC-157's sequence, salt forms and regulatory status are covered in What Is BPC-157? Sequence, Salt Forms and Regulatory Status.

How should peptide solutions for in-vitro assays be handled?

Peptide solutions are the least stable form of a peptide, so the aim is to keep each one short-lived and to spare a stock repeated temperature swings. Bachem advises against long-term storage of peptide solutions, especially for sequences containing Asn, Gln, Cys, Met or Trp, and recommends aliquoting solutions and keeping them frozen below −15 °C. Sigma-Aldrich advises against repeated freezing and thawing of both lyophilized peptides and peptide solutions, and recommends preparing a series of working aliquots from a stock.

In practice, the routine for solutions prepared for in-vitro work looks like this:

• Dissolve only the amount a planned series of experiments needs.
• Divide a fresh stock into single-use aliquots, freeze them, and thaw one aliquot per experiment.
• Discard any thawed remainder instead of refreezing it.
• Keep the rest of the lyophilized powder sealed and frozen, since the powder remains the most stable form.

How should peptide vials and aliquots be labeled and tracked?

Labeling turns storage rules into a record. Each vial and aliquot label should carry the compound name, the lot number, the date received or prepared, and the storage condition, so that any unexpected finding can be traced to the source lot and its certificate of analysis (COA). An inventory log listing each lot, its COA, its freezer location and any temperature excursions, such as a power cut or a freezer left open, makes that trace quick.

When an excursion happens, note its duration and the temperature reached, return sealed vials to frozen storage, and decide whether the affected material needs re-testing before it goes into a sensitive assay. Sealed lyophilized vials tolerate ambient temperature in transit, so a short excursion of a sealed vial is less concerning than one involving an opened vial or a solution. Where doubt remains, a high-performance liquid chromatography (HPLC) purity check compared against the lot's COA shows whether new impurity peaks have appeared.

Rotate stock first in, first out, so older lots are used before newer ones, and keep each lot's COA with the inventory record. PeppedCo prints the lot number on every vial, and the COA for each released lot is published on the Lab Testing page. How to Read a Peptide COA explains how to match a report to a vial, and How to Vet a Research Peptide Supplier covers the checks to run before ordering.

Sourcing lyophilized peptides for laboratory research

PeppedCo products are supplied as lyophilized powder in sealed glass vials, with full spec sheets (Chemical Abstracts Service registry number, sequence, formula and molecular weight) on every product page. PeppedCo ships within the United States and provides no dosing, administration or reconstitution guidance.