Almost every research peptide ships as a lyophilised powder. The reason is straightforward: in aqueous solution a peptide is subject to hydrolysis, deamidation, oxidation and aggregation, all of which need water to proceed. Take the water away and the reactions largely stop. A peptide stable for weeks in solution is stable for years dry.
What is less widely understood is that lyophilisation is not simply evaporation. It is a controlled physical process, and the state of the material you receive is a direct product of how that process was run.
What actually happens
The peptide solution is frozen, then placed under vacuum. Ice does not melt under those conditions; it sublimes, passing straight from solid to vapour. This is primary drying, and it removes the bulk of the water while the material stays frozen — which is the point, because a frozen matrix cannot undergo the reactions that a liquid one can.
A second stage, secondary drying, runs at slightly higher temperature to remove water bound to the peptide itself. That residual water is what a Karl Fischer titration measures, and it is typically 3 to 8% in a well-dried product.
What is left behind is a porous solid occupying roughly the volume of the original frozen liquid — the cake. Its structure is a cast of where the ice crystals were.
Why the vial can look empty
This is the most common question suppliers receive, and it is almost always a non-problem.
At low fill weights — 5 or 10 mg is a small amount of solid — the cake often forms as a thin translucent film on the vial wall rather than a visible pellet in the base. Handling in transit can dislodge it. Under normal lighting it can be genuinely difficult to see.
Fill weight is verified gravimetrically at packing, so the material is there. If you have real doubt, quote the batch code and ask for the packing record.
Reconstitution, and how to get it wrong
Four mistakes account for most losses at this stage.
Opening a cold vial
A vial straight from a −20 °C freezer is well below the dew point of room air. Break the seal and moisture condenses onto a hygroscopic powder immediately. Let the vial reach room temperature sealed — twenty to thirty minutes — before opening it.
Firing the diluent in
Directing a jet of diluent straight onto the cake causes localised high concentration and mechanical shear, both of which promote aggregation. Add the diluent slowly against the inner wall so it runs down and reaches the cake gently.
Shaking or vortexing
This is the one that costs most. Peptides denature at air-liquid interfaces, and agitation creates enormous interfacial area. Lipidated peptides — retatrutide, semaglutide, tirzepatide — are particularly susceptible, and aggregation shows up on re-assay as new early-eluting peaks.
Swirl gently. If it has not dissolved, wait longer. Time is free; a degraded vial is not.
The wrong diluent
Bacteriostatic water contains 0.9% benzyl alcohol and suits solutions held for weeks. Sterile water suits prompt use and avoids the preservative interfering with UV detection. Hydrophobic peptides — humanin, dihexa — need a DMSO stock and aqueous dilution, and going straight into water gives a suspension and a concentration that reads low.
Compounds that need something different
| Compound | Consideration |
|---|---|
| Humanin | Hydrophobic central run. DMSO stock, then dilute. |
| Dihexa | Poorly water-soluble. DMSO stock required. |
| LL-37 | Strongly cationic. Adsorbs to glass and untreated plastic — use low-binding consumables. |
| NAD+ | Strongly hygroscopic. Weigh fast, reseal, keep below pH 7. |
| MOTS-c | Two methionines. Minimise headspace and air exposure. |
| GHK-Cu | Copper coordination is pH-dependent. Check buffer compatibility. |
After reconstitution
- Aliquot at first reconstitution if more than a few withdrawals are planned. Repeated freeze-thaw and repeated air exposure both cost purity.
- Label with the compound, concentration, diluent and date. Concentration drift from evaporation is the usual explanation for unexplained variance between runs.
- Hold at 2–8 °C for routine use; −80 °C for aliquots kept longer.
- Do not return a thawed aliquot to the freezer for a second cycle.
A note on excipients
Pharmaceutical lyophilised products usually contain bulking agents and cryoprotectants — mannitol, sucrose, trehalose — which form the cake structure and protect the molecule during freezing. Research-grade peptides generally do not, because an excipient is one more thing to control for in an assay.
The trade-off is that a peptide lyophilised without a bulking agent produces a less robust cake, which is part of why low-fill vials look sparse. It also means what is in the vial is the peptide, its counter-ion and residual water, and nothing else — which is the right choice for research material.
This guide is written for laboratory practitioners and describes analytical and handling practice. It is not medical advice, and it contains no dosing or administration guidance. Material supplied by Ryzen Research Ltd is for research use only and is not for human or veterinary use.