Reading time: ~2 min · Part of the free certification in peptide science
Lyophilization is the reason a peptide can travel at room temperature and keep for years. Understanding the process explains what a vial actually contains.
Freezing
The solution is frozen completely. The peptide is trapped between the ice crystals in an amorphous matrix.
Primary drying
Under vacuum, the ice sublimates: it passes directly from solid to vapor without melting. Most of the water is removed.
Secondary drying
At a somewhat higher temperature, the remaining bound water is desorbed, down to a low residual content.
The result is a dry, porous cake that dissolves quickly. Without water, deamidation, isomerization and hydrolysis reactions practically stop.
What each component does
| Component | Function |
|---|---|
| Mannitol, sucrose, trehalose | Bulking agents and cryo/lyoprotectants: they give structure to the cake and protect the peptide during freezing and drying |
| Buffers (acetate, phosphate, histidine) | They keep the pH in the range where the peptide is most stable |
| Preservatives (benzyl alcohol, m-cresol) | They inhibit microbial growth in multi-dose containers; 0.9% benzyl alcohol is the one in bacteriostatic water |
| Surfactants (polysorbate) | They reduce aggregation at interfaces |
| Counterion (acetate, TFA) | Part of the peptide's salt; it is not active |
The pH of the reconstituted solution
Each peptide has a pH range of maximum stability and minimum solubility around its isoelectric point. That is why some compounds reconstitute better in a slightly acidic medium (dilute acetic acid) than in bacteriostatic water: it is not a preference, it is chemistry.
A lyophilized vial is stable; a reconstituted solution starts to degrade from the first minute. Reconstitution should be done close to the time of use and the solution should be refrigerated immediately.
Catalogue compounds mentioned in this lesson
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