How to store lyophilized and reconstituted peptides
· Novatheris
Almost all the material lost in a small lab is lost by storing it wrong. Not because of a bad batch: because of a vial opened cold, a solution forgotten in the refrigerator door, ten trips in and out of the freezer.
Lyophilized powder and peptide in solution are two different worlds. It pays to treat them that way.
Lyophilized powder lives in the freezer
Lyophilized means dry: the water was pulled out of the peptide with cold and vacuum, and what is left is a powder.
That is its most stable form. Bachem, one of the largest peptide manufacturers in the world, recommends keeping the lyophilizate in a tightly closed container below -15 °C, and colder still for the long run, on the order of -50 °C or lower.
GenScript, another large manufacturer, gives a similar recommendation that is easier to hit in practice: -20 °C, away from bright light. And it adds that most lyophilized peptides stay stable for several years under those conditions.
Notice the detail: the sources say freezer. The refrigerator at 4 °C shows up only as a short-term option, not as the home of the powder.
The most expensive mistake: opening a cold vial
Peptides are hygroscopic. That means they pull moisture out of the air.
When you take a vial out of the freezer and open it right away, warm room air gets in and condenses water inside. That water does not leave. Bachem puts it plainly: absorbed moisture reduces the overall peptide content and may also decrease stability.
The rule is simple and costs nothing: leave the vial closed until it reaches room temperature. GenScript asks for the same thing. Bachem even suggests doing it inside a desiccator, a container holding material that absorbs moisture.
A couple of minutes of patience beat any storage trick, and they cost you nothing but the wait.
Not every peptide holds up the same
Composition matters. Peptides carrying asparagine, glutamine, methionine, cysteine or tryptophan have a shorter shelf life.
Cysteine, methionine and tryptophan oxidize easily. And the ones carrying aspartic acid, glutamic acid, lysine, arginine or histidine attract moisture, which is why GenScript recommends storing them in a desiccator with the cap tightly closed.
Bachem notes something useful about those same sensitive residues: they tend to tolerate shipping at room temperature, and the refrigerator at 4 °C works for short-term use. In other words, they are not made of glass, but they do not forgive steady carelessness either.
Solution is a different story
Here is the big difference. Powder holds for years in the cold. Solution holds for days or weeks.
Bachem recommends splitting the solution into aliquots, meaning small portions in separate vials, and freezing them below -15 °C. It also says long-term storage of solutions is not recommended, especially when the peptide carries asparagine, glutamine, cysteine, methionine or tryptophan. Frozen, it talks about a few weeks.
GenScript is even more direct: the shelf life of peptides in solution is very limited, and they do not recommend storing peptides in solution. If you have to anyway, they suggest a buffer at pH 5-6 and splitting into aliquots.
Why aliquots are not fussiness
Because freezing and thawing degrades. GenScript says it flat out: peptides that undergo freeze-thaw cycles are susceptible to degradation.
Every time you pull the same vial, let it reach temperature, take a little and put it back in the freezer, you are running a full cycle. Ten uses are ten cycles across all of the material.
With aliquots, each portion thaws once. The rest never finds out.
Another practical detail: if you suspect bacterial contamination in a solution, it can be filtered through a 0.2 micron filter.
A special case: free cysteine
If the peptide carries free cysteine, the thiol groups oxidize quickly to disulfide once the pH goes above 7. That is why Bachem recommends acidic, degassed buffers in those cases.
It is a small detail that explains why two peptides stored the same way do not always end up the same.
Bacteriostatic water: what it does and what it does not
Bacteriostatic water is sterile water with benzyl alcohol as a preservative. The Bacteriostatic Water for Injection USP label declares 0.9 % (9 mg/mL) in the 30 mL plastic presentation, and 1.1 % in the 20 mL glass one. It is a multi-dose container and it is stored between 20 and 25 °C.
What the preservative does is slow bacterial growth inside that container, which is going to be punctured several times. That is all.
What it does not do: it does not sterilize the peptide, it does not change its chemistry and it does not extend its shelf life. A peptide in solution degrades the same, in bacteriostatic water or not.
The label also warns against use in newborns, because benzyl alcohol has been associated with toxicity in neonates.
The 28 days of a multi-dose vial
Plenty of people believe an opened vial of bacteriostatic water lasts until the printed expiration date. It does not.
The 28-day rule does not come from the water label, it comes from USP chapter 797, and the CDC sums it up: once a multi-dose vial is opened, meaning needle-punctured, it should be dated and discarded within 28 days, unless the manufacturer states another date for that opened vial.
And a second part that also gets forgotten: that use date can never run past the manufacturer's original expiration date. If the vial expires in 15 days, it expires in 15 days, not in 28.
What we cannot tell you
Exactly how many days each of our peptides holds once reconstituted. We do not know it from our own study and we are not going to invent a number.
What we do know is the direction: powder in the freezer, closed and dry, lasts a long time. Solution, not long, and in aliquots. And that any figure you see out there for a finished pharmaceutical product, with its own formulation, does not transfer to a vial of powder.
The summary to tape on the door
- Powder: freezer, tightly closed container, away from bright light.
- Before opening: room temperature, with the vial still closed.
- Solution: aliquots, and as little time as possible.
- Never freeze and thaw the same vial over and over.
- Opened bacteriostatic water: date the vial, 28 days, and never past the expiration date.
If you want to see how each peptide is meant to be stored, every catalog page carries its own storage note.