Why Research Peptides Are Supplied Freeze-Dried

Most research peptides are supplied as a white, freeze-dried (lyophilised) solid in a sealed vial. The reason is stability: many degradation reactions need water or proceed far faster in solution.

The process

Wang's review Lyophilization and development of solid protein pharmaceuticals (International Journal of Pharmaceutics, 2000) describes lyophilisation as three stages:

1. Freezing, which converts most of the water to ice.
2. Primary drying, in which ice is removed by sublimation under vacuum.
3. Secondary drying, which removes much of the remaining bound water.

Stresses during drying

The same review notes that freezing and drying themselves impose stresses — including concentration of solutes as ice forms and removal of the water that surrounds the molecule — and that formulation and process conditions are chosen to limit them.

What makes a stable solid

Residual moisture is an important factor in the stability of a lyophilised solid. A dry cake that is kept sealed, cold and protected from humidity retains its quality far longer than material that is repeatedly exposed to air.

Practical points

• Allow a vial to reach room temperature before opening, to avoid condensation on the solid.
• Reseal promptly and return to the stated storage temperature.
• Prepare solutions only as needed; a peptide in solution is generally less stable than the same peptide as a dry solid.