Peptide reconstitution, aliquoting and the cold chain

Before the vial is opened

Let the vial reach room temperature before breaking the seal. Cold glass condenses atmospheric moisture, and that water goes into a lyophilised cake that was dried specifically to exclude it. This single step prevents more degradation than any other handling choice.

Inspect the cake. A lyophilised peptide should be a discrete white cake or powder. Material that has collapsed into a film, shrunk away from the vial wall or developed a glassy appearance has taken up water or been through a thermal excursion in transit. Photograph it, and query the shipment before use rather than after an unexplained result.

Reconstitution technique

Direct the solvent down the inner wall of the vial rather than onto the cake. A jet of liquid striking the cake generates local shear and foaming, and the air–liquid interface is where peptides denature and aggregate.

Never vortex. Swirl gently and allow time. A peptide that resists dissolution is telling you something — usually moisture ingress, occasionally an unexpected salt form — and the correct response is to investigate, not to sonicate or warm it until it complies.

Choose the solvent deliberately. Bacteriostatic water suits multi-use vials; sterile water suits single-use aliquots. Peptides with poor aqueous solubility may need a small volume of dilute acetic acid or ammonium bicarbonate first, but confirm that the resulting buffer is compatible with your assay before committing the vial.

Aliquot immediately, and size the aliquots properly

Repeated freeze–thaw cycling is the most common and most avoidable cause of peptide potency loss. Each cycle concentrates solutes at the ice interface, shifts local pH and drives aggregation. Three cycles can measurably degrade a sensitive sequence.

Aliquot into single-use volumes at the moment of reconstitution, before any experiment has begun. The right aliquot size is the volume one experiment consumes — not a convenient round number.

Use low-binding tubes for dilute solutions. Peptides adsorb to polypropylene, and at low microgram-per-millilitre concentrations the fraction lost to tube walls is large enough to matter. Carrier protein at 0.1% BSA suppresses this where the assay tolerates it.

Storage and the sequence-specific risks

Lyophilised at −20 °C is adequate for most sequences; −80 °C extends it. Reconstituted material belongs at −20 °C or below in single-use aliquots, with short-term working solution at 2–8 °C only for the period the certificate supports.

Know your sequence's specific vulnerabilities. Methionine and cysteine oxidise — sermorelin and semax both carry methionine, and semax carries it at the N-terminus where it is most exposed. Tryptophan is photolabile, which makes amber glass a requirement rather than a preference for kisspeptin, melanotan 2 and PT-141. Asparagine and glutamine deamidate, shifting mass by one dalton. Disulfide-constrained peptides such as AOD9604 lose their conformation if a reducing agent is present.

None of these degradation routes produces a visible change. A solution that looks fine can be substantially oxidised, which is why storage discipline rather than inspection is the control.

Records that make a failed experiment interpretable

Record the reconstitution date, solvent, concentration and aliquot size on the tube and in the notebook. When a result is anomalous six weeks later, the question is always how old the solution is and how many times it has been thawed — and without a record, that question has no answer and the result cannot be salvaged.

References and authoritative sources

Chemical identity, regulatory status and anti-doping classification should be confirmed against primary sources rather than against this page. The records below are the ones to check first.

1. PubChem compound record (US National Library of Medicine)
2. PubMed indexed literature

These are database and regulatory sources. Citations to specific primary papers are being added to this page as part of ongoing scientific review; until they appear, treat the mechanism and literature sections above as a summary to verify rather than a citation of record.