Storing and reconstituting lyophilized peptides

A lyophilized peptide is a dry, amorphous cake, and dry is why it is stable. Nearly every degradation route worth worrying about — hydrolysis, deamidation, oxidation, aggregation — needs water, so the practical question is how long the material spends wet and at what temperature.

Sealed vials

Store at -20 °C, protected from light. Sealed and dry, that is a shelf life measured in years for most sequences. Ambient temperature for the length of a domestic shipment is not a problem: the insulated packaging and gel packs in a shipment are margin, not necessity, and a mailer that arrives warm has not spoiled.

The real risk to a sealed vial is condensation. Bringing a cold vial straight into humid room air pulls moisture onto and into the cake. Let vials reach room temperature before breaking the seal — fifteen to twenty minutes on the bench, not under a lamp.

Choosing a solvent

Bacteriostatic water — sterile water with 0.9% benzyl alcohol — is the usual choice for bench storage, because the preservative allows a multi-use vial to sit refrigerated without becoming a culture. Preservative-free sterile water is appropriate where the benzyl alcohol would interfere with an assay, at the cost of a much shorter usable window.

Some sequences are poorly soluble in neutral aqueous buffer and need a small volume of dilute acetic acid to go into solution before dilution to working concentration. Highly basic peptides generally dissolve in slightly acidic solution; highly acidic peptides in slightly basic. When a compound needs this, it is noted on its product page.

Technique

• Run the solvent down the inside wall of the vial rather than directly onto the cake — a jet onto dry powder drives foaming, and foam means an air-liquid interface, which means denaturation.
• Swirl or roll gently. Do not vortex and do not shake; mechanical shear and interfacial stress are the two fastest ways to aggregate a peptide.
• Give it time. A cake that has not fully dissolved in thirty seconds is usually a cake that needs five minutes, not more force.
• Inspect the solution. Cloudiness or visible particulate after full dissolution time indicates incomplete solubility, not a defect in the material — revisit the solvent.

After reconstitution

Refrigerate at 2–8 °C and use within 30 days as a general working rule; individual sequences vary and compound-specific guidance is on each product page. Aliquot before freezing anything. Repeated freeze-thaw cycles are among the most reliable ways to lose activity, and a single vial thawed twenty times has had a very different history from twenty aliquots thawed once.

Label aliquots with the compound, the concentration, the lot number and the date. The lot number is the part people leave off, and it is the one that matters if a result ever needs to be traced back to the material that produced it.

Concentration arithmetic

Concentration is vial mass divided by solvent volume. A 10 mg vial in 2 mL of solvent is 5 mg/mL, which is 500 µg per 0.1 mL. Every product page here carries a calculator that does exactly this and nothing else — it reports concentration, because concentration is a property of a solution and anything beyond it would be guidance we do not give.