How to store peptides

How to store peptides in each of their three states

A peptide exists in three states between synthesis and the bench, and each has its own rules. Lyophilised powder, sealed and dry, is the most stable form and the one it ships in. Reconstituted solution is far less stable, because water is what lets hydrolysis and oxidation proceed. In transit it is neither: warm, moving, and out of your control.

How to store peptides matters most in the second of those states. Most of the material lost in a laboratory is lost there, held too long or cycled through a freezer repeatedly, rather than in the first.

The table below is the whole answer in one grid, in both units, because laboratory literature is written in Celsius and most of the equipment sold in the United States is labelled in Fahrenheit. Everything after it is the reasoning behind a row: what the chemistry is, which sequences are most exposed to it, and which cabinet, container and diluent make the difference.

The instruction is the same across the catalogue, which is worth saying plainly: every product page on this site carries −20°C long term in its specification table, and the compounds that are routinely held in solution add 2 to 8°C in use. There is no compound in the catalogue with a storage rule of its own that contradicts the grid below.

What is actually degrading, and what each condition does to it

How to store peptides makes more sense once you know what the rules are defending against. Five chemical routes account for very nearly everything that happens to a peptide in a vial, and each one is driven by a different condition.

Hydrolysis cleaves the backbone and needs water, which is why a dry cake outlasts a solution by an order of magnitude and why residual moisture rather than temperature is usually the limiting variable in a freezer. Oxidation attacks sulfur and aromatic side chains and needs oxygen, light or a trace metal. Deamidation converts asparagine and glutamine to their acids, shifts the mass by one unit per site and runs fastest in neutral to alkaline solution. Disulfide formation and exchange affects any free cysteine thiol. Aggregation is physical rather than chemical: hydrophobic sequences associate, come out of solution and do not readily go back in.

The physical conditions map onto those routes directly. Moisture feeds hydrolysis and deamidation, and a lyophilised cake is hygroscopic enough to pull water out of room air within seconds of the stopper coming off. Oxygen and light feed oxidation, which is why vials are filled under nitrogen or argon and why amber glass exists. Temperature multiplies every rate at once. Microbial growth is a separate problem that applies only to solutions, and it is the one a preservative addresses.

Two pieces of equipment follow from that list, and both appear on most published laboratory guidance: a desiccator, or simply a sealed box with fresh desiccant in it, which handles moisture; and an inert headspace, which handles oxygen. Neither is exotic, and between them they do more for a stored powder than the difference between −20°C and −80°C. Both belong in any working account of how to store peptides, and neither costs what a second freezer costs.

Note what is missing from that list. Nothing about it is visible. Every route above proceeds without changing the appearance of the vial until it is well advanced, which is why storage is managed by condition rather than by inspection.

How to store peptides varies by sequence

None of it applies evenly. Two compounds stored side by side in the same freezer can have very different shelf lives, because what degrades is a particular side chain rather than a peptide in general. The useful question is which residues a given sequence contains, and that is readable straight off the specification.

A molecular formula with no sulfur in it has neither cysteine nor methionine, and the two most-cited oxidation routes are closed. GLP-3 RT at C221H342N46O68 and GLP-1 at C187H291N45O59 are both in that position. Tesamorelin at C221H366N72O67S carries exactly one sulfur atom across 5,135.89 g/mol: a single methionine, and no cysteine at all.

MOTS-C is the opposite case and the one to keep darkest. Its sixteen residues, MRWQEMGYIFYPRKLR, include two methionines, which is the S2 in C101H152N28O22S2, one tryptophan and two tyrosines, which is five of the most readily oxidised side chains in one short chain.

BPC-157, GEPPPGKPADDAGLV, contains no cysteine, methionine, tryptophan or tyrosine whatever. There is nothing in it for oxygen or light to attack. That is a large part of why it has a reputation as forgiving material to keep, and it is a claim about chemistry rather than about a supplier.

A blend stores to its least stable component. GLOW carries GHK-Cu, BPC-157 and TB-500 in one vial and KLOW adds KPV, so the rule for the vial is whichever component needs the most care, not an average of them.

What freeze-thaw cycles cost, and how to store peptides in aliquots

Every freeze-thaw cycle concentrates solutes at the ice boundary and exposes the peptide to mechanical and chemical stress. The loss per cycle is small and it compounds, which is what makes it insidious: nothing looks wrong, and a later assay quietly disagrees with an earlier one.

Competitor pages in this subject quote a figure of twenty to fifty per cent loss per cycle. We are not going to repeat it, because it is asserted without a citation and it is far above what published stability work reports for buffered or lyophilised material. The honest statement is that the loss is real, measurable by assay, and dependent on the sequence and the buffer.

The practical answer, and the part of how to store peptides that is most often skipped, is aliquoting. Divide a reconstituted stock into single-use volumes at the point of preparation, so each one is thawed once. It costs a few minutes and removes the variable entirely.

Aliquot into low-binding polypropylene rather than glass if the solution is dilute. Peptide adsorbs onto surfaces, and at low concentration in a large glass vial the fraction lost to the wall stops being negligible. Polypropylene is also far less likely to fracture at −80°C than a glass vial filled near the shoulder.

A multi-vial order is where the discipline pays most, because it has to be decided once and applied to everything. A repair panel or a growth reference panel arrives lot-matched and dispatched together, and aliquoting the whole set the same way on the same day is what keeps later results comparable across it.

Choosing a freezer, and why frost-free is the wrong one

A domestic freezer runs at roughly −18°C, or 0°F, which is close enough to −20°C that the temperature itself is not the problem. The problem is how the cabinet holds that average.

Most modern upright freezers are frost-free. They stay dry by warming the evaporator on a cycle several times a day, and the cabinet warms with it. The setpoint is an average rather than a floor. Anything stored in one is being taken through a slow, repeated, low-amplitude freeze-thaw for as long as it sits there, which is precisely the process aliquoting exists to avoid, applied continuously and invisibly.

A manual-defrost chest freezer has no such cycle, holds its temperature better when opened because cold air sits in the well rather than falling out of the door, and costs a fraction of a laboratory unit. For sealed lyophilised material it is the sensible domestic answer. Whatever the cabinet, keep vials sealed and boxed: a domestic freezer carries far more water vapour than a laboratory one, and moisture is the variable that actually decides shelf life.

The same reasoning applies one appliance up. A refrigerator door is the warmest and most disturbed part of the unit, because it swings through room air every time it is opened and it vibrates, so refrigerated solution belongs at the back of a middle shelf, not in the door rack.

Containers, closures and the “peptide storage case”

The original vial is usually the best container the material will ever be in. It is borosilicate glass, filled under vacuum or an inert gas, and closed with a butyl stopper under an aluminium crimp, a seal more gas-tight than any screw cap achieves. The first rule of containers is not to move material out of it without a reason.

Once there is a reason, and aliquoting is the usual one, two properties decide the choice. The first is adsorption: peptide sticks to surfaces, and at dilute concentration the fraction lost to a tube wall is measurable, which is what low-binding polypropylene exists for. The second is closure integrity at temperature. A gasket that seals at room temperature may not seal at −80°C, and a cap that holds liquid in can still pass water vapour over months.

The storage case sold as a peptide accessory deserves a plain answer, because it is the most-searched part of this subject and the most misunderstood. A foam-lined case with a silicone gasket is an organiser and a shock absorber. It is not a preservation device: it does not cool, it does not exclude oxygen, and its gasket does not do what a crimped stopper does. It is genuinely useful for keeping labelled vials together, upright and unbroken on a freezer shelf or in a cool bag, and it is no substitute whatever for the temperature. A case organises the vials; how to store peptides is still decided by the cabinet they sit in.

The one thing an inexpensive case does very well is exclude light, because it is opaque. For a sequence like MOTS-C, with five oxidisable side chains, that is worth having, and an opaque box on a freezer shelf achieves what amber glass achieves.

How long each form actually lasts

Sealed lyophilised material at −20°C is stable for months to years, and the limiting factor is almost always residual moisture rather than temperature. A well-dried vial kept dry outlasts a poorly dried one at the same temperature, which is why water content appears on a thorough peptide certificate of analysis at all.

Reconstituted solution at 2 to 8°C is a matter of weeks. Water is what allows hydrolysis to proceed, and a preservative in the diluent addresses microbial growth rather than chemistry. There is no temperature at which a solution outlasts the powder it came from.

Frozen aliquots of solution sit in between: months at −20°C, longer at −80°C, provided each aliquot is thawed exactly once. That proviso is the whole benefit, and it disappears the moment a tube goes back into the freezer.

Published supplier figures agree closely enough to be worth setting out side by side. They are storage data for reagent material, they vary with sequence and buffer, and they are attributed below to whoever published them rather than presented as ours.

None of these numbers is a substitute for measuring. They describe what to expect, and the lot's own certificate describes where the material started, which is the only fixed point a later assay can be read against.

The diluent is not neutral: pH, preservative and whose clock is running

Once a peptide is in solution, the water around it sets the rate of most of the chemistry described above, and the published guidance converges on a window. GenScript and NIBSC specify pH 5 to 6 for stored solutions; SB-Peptide and Creative Peptides give pH 5 to 7; JPT recommends pH 4 to 6 to limit aggregation and deamidation. Bachem's general suggestion is phosphate-buffered saline at pH 7.0 to 7.4, at 1 mg/mL or below. The common ground is mildly acidic to neutral. Alkaline is where cysteine, asparagine and glutamine move fastest, and it is the condition to avoid.

Bacteriostatic water is sterile water carrying 0.9% benzyl alcohol as a preservative, 0.2µm filtered, and that preservative is the only thing that separates it from plain sterile water. It addresses microbial growth in a container that will be opened more than once. It does nothing about hydrolysis, oxidation or deamidation, which proceed at the same rate either way.

The 28-day figure attached to it belongs to the water, not to the peptide. It is the default beyond-use date USP General Chapter <797> applies to an entered multiple-dose container, reinforced by CDC injection-safety guidance, rather than anything derived from a peptide stability study. It is not on the FDA label for the reference product, which does not carry the number at all. The clock starts when the closure is first entered. Non-preserved sterile water carries no such window at all, which is why unpreserved solutions are treated as short-lived: sterile water vs bacteriostatic water is a microbiological difference before it is a chemical one.

The water has its own storage rule, and it is not the peptide's. Controlled room temperature, 20 to 25°C or 68 to 77°F, with permitted excursions to 15 to 30°C, upright, out of direct light, and not frozen, because freezing stresses the container closure rather than the liquid. Bacteriostatic water storage sets that out in full, and bacteriostatic water for peptides covers why it is the default diluent for lyophilised material.

How to store peptides once the vial has been opened

Let a vial reach room temperature before opening it. Cold glass pulls moisture out of the air and condensation lands directly on the powder, which is the one thing dry storage exists to prevent.

Work quickly once it is open, and reseal it. A lyophilised cake is hygroscopic, and the exposure that matters is measured in seconds of room air rather than hours on the bench. If material is being weighed out, weigh in as dry an environment as you have and return the stock vial to the freezer before doing anything further with the portion taken.

Dissolve gently. Swirling and slow inversion bring a cake into solution without shear; vigorous shaking introduces air and foam, and foam is an air-water interface, which is where peptides unfold and aggregate. Where a sequence resists, a sonication bath is the standard escalation and is still gentler than shaking. Hydrophobic sequences that will not go into water are a solubility problem rather than a storage one, and the laboratory answer is a different solvent first: 0.1% acetic acid, dilute ammonia for acidic peptides, or a small volume of DMSO or acetonitrile, before water is added.

Keep material out of light, particularly compounds containing tryptophan, tyrosine or methionine, which are the residues most readily oxidised. Amber vials and a closed box do most of that work. Static is a genuine nuisance with freeze-dried solids, which will climb a plastic spatula given the chance; glass and a grounded surface help.

Label every aliquot with the compound, the concentration, the lot and the date it was prepared. The concentration written there is mass over volume in that vial, and the peptide calculator works it out from the vial strength in mg and the diluent volume in mL. Storage discipline fails at identification long before it fails at temperature, and an unlabelled tube has already defeated everything else in this article.

How to tell whether material has degraded

Mostly you cannot, and that is the honest answer. A sound lyophilised cake is white, or deep blue for GHK-Cu where the copper complex is the colour, and it is dry, porous, and either intact or shaken loose inside the vial. Clumping, stickiness, shrinkage, or a cake that has slumped into a glassy film means moisture has reached it. Yellowing points at oxidation. In solution, cloudiness, visible particulate or a film on the glass means aggregation or contamination.

Colour is the one readout that comes free, and only for some compounds. GHK-Cu is blue because copper(II) is coordinated by the tripeptide; every certificate we hold records the appearance as a blue lyophilised powder, and a pale or colourless lot indicates incomplete complexation rather than a lighting problem. The same applies to the blends built on it.

What none of this catches is the case that matters. A lot that has lost two per cent purity looks exactly like a lot that has not. Purity is invisible in the vial. The only way to know is to assay the material and read the result against the figure the lot was released at, which is what peptide purity testing measures and what a peptide certificate of analysis records.

The two methods answer different questions. RP-HPLC at 214 nm gives the purity figure, because it separates the intact peptide from everything that is no longer it. LC-MS confirms identity by mass, which is how deamidation is caught: it adds one mass unit per site and changes nothing you can see.

Transit, and what a warm parcel really means

The most common anxiety about storage is not about storage at all. It is a parcel that has spent three days in a hot van, and the answer is usually that it does not matter much.

Lyophilised material ships dry for exactly this reason. Sealed powder tolerates ambient conditions for days, because the route temperature accelerates most is hydrolysis, and hydrolysis needs water that a dried cake does not contain. Standard ground transit of three to seven days at ambient temperature is not the exposure people picture when they feel a warm box.

There is a limit, and it is worth naming rather than glossing. Sustained heat accelerates every route at once, and the interior of a parked car in summer sun is documented to exceed 60°C, or 140°F, which is a genuinely different exposure from a warm porch or a warm van. A parcel left in a vehicle for an afternoon is worth noting on the label; an ordinary warm delivery is not.

How orders are packed and shipped is the same logic applied at our end: dry, sealed, and documented, so that the state the material arrives in is the state it was released in. How to store peptides on arrival is two steps in order: bring the vial to −20°C, and let it come fully back to room temperature before it is opened for the first time. Those two steps, in that order, cover almost every transit scenario anyone writes in about.

Why the lot number matters to storage

How to store peptides well assumes you know what you started with. A certificate of analysis records peptide purity for a specific lot at the point of release. That is your baseline, and without it a later measurement has nothing to be compared against.

Every batch we release is assayed by an independent laboratory and the certificate published against the lot number printed on the vial, so the material in your freezer can always be traced back to its own data.

That is also what makes an excursion recoverable rather than simply worrying. A vial left out overnight, a parcel that arrived hot, a freezer that failed over a weekend: none of these is answerable by looking at the vial, and all of them are answerable by assay against the release figure. Note the excursion on the label, keep the lot number, and match the vial to its certificate when you want to settle it. If the supplier cannot produce that document, there is nothing to settle it against, which is the first of the checks in vetting a research peptide supplier.