Most research peptides arrive as a small cake of white powder at the bottom of a vial. That powder is the result of lyophilization, or freeze-drying, and it is the main reason peptides can be shipped and stored at all.
What lyophilization does
The peptide is dissolved, frozen, and then placed under a vacuum so the ice turns directly into vapor without melting. What remains is a dry, porous solid with very little water left in it.
Why water matters
Almost every way a peptide breaks down needs water or happens much faster in solution:
- Hydrolysis: water molecules split the bonds that hold amino acids together.
- Deamidation: the amino acids asparagine and glutamine slowly convert into different structures, changing the peptide.
- Oxidation: methionine, cysteine and tryptophan react with dissolved oxygen.
- Aggregation: peptide chains stick together into clumps that no longer behave like the original molecule.
Removing the water slows all of these reactions dramatically. Cold temperatures slow them further.
What changes after reconstitution
The moment you add bacteriostatic water, the clock starts running faster. That is why common lab practice is to refrigerate a reconstituted vial at 2 to 8 °C, keep it out of light, avoid repeated freezing and thawing, and use it within the time the supplier recommends. Formal stability data in solution do not exist for most research peptides, so the label is your best guide.
A simple rule
Keep unopened vials dry, cold and dark. Reconstitute only what you plan to use, and label every vial with the date you mixed it. For the full steps, see the reconstitution guide.