Storing peptides

• Moisture. Peptide powders take up water from the air. The water lowers the amount of peptide in whatever you weigh and shortens the powder's life. GenScript names sequences with aspartic acid, glutamic acid, lysine, arginine or histidine as the most prone, and advises keeping them in a desiccator in a tightly capped vial.
• Oxygen. Cysteine, methionine and tryptophan oxidise easily. Bachem notes that free cysteine thiols oxidise rapidly above pH 7.
• Time in water. In solution, bonds slowly hydrolyse and some residues change. GenScript lists shorter lives in solution for sequences with cysteine, methionine, tryptophan, aspartic acid, glutamine or an N-terminal glutamic acid.
• Heat and light. Warmth speeds every one of these reactions. GenScript advises storage away from bright light.
• Repeated freezing and thawing. Each cycle lets in air and condensation.
• Microbes, once a peptide is dissolved in a liquid that is not sterile.

A lyophilised peptide (in American spelling, a lyophilized peptide) has been freeze-dried. The purified solution is frozen and the ice is removed under vacuum, leaving a dry powder or a compact cake at the bottom of the vial. It is the most stable form in which to keep a peptide, provided it stays dry and sealed.

1. Take the vial from the freezer and let it reach room temperature before opening it, in a desiccator if you have one (Bachem). A cold vial opened in humid air collects condensation on the powder.
2. Weigh out what you need without delay.
3. Close the vial tightly and return it to the freezer.

GenScript advises keeping oxygen-sensitive sequences, those with cysteine, methionine or tryptophan, under anaerobic conditions. If a peptide will be used many times, divide it into single-use portions at the first opening, so that each portion is thawed only once.

Both manufacturers say the same thing: avoid it where you can. Where you cannot:

• use a buffer at pH 5 to 6 (GenScript);
• divide the solution into single-use aliquots and freeze them;
• never refreeze an aliquot that has thawed;
• consider a 0.2 µm filter to remove bacteria (GenScript);
• dissolve oxygen-sensitive sequences in oxygen-free water or buffer (Bachem).

For preparing solutions for laboratory experiments only.

No single solvent suits every peptide. Solubility depends on the sequence: its overall charge and how many water-repelling residues it carries. Bachem's approach:

Try a small portion before committing the whole batch. A few minutes in a sonicating water bath helps larger particles dissolve; avoid warming the sample much.

A milligram of powder is not a milligram of peptide, because the powder also holds counter-ions and water. To know the concentration you have made, use the batch certificate: GenScript's rule is gross weight × net peptide content × HPLC purity. Peptide purity explained works through an example, and the peptide calculator does the arithmetic.

The controlled room temperature printed on pharmacopoeial labels is 20 to 25 °C. An Iraqi summer is far above it. On 10 August 2025 weather stations recorded 52.6 °C near Basra International Airport and 49.2 °C at Baghdad International Airport (Shafaq News). A sealed vial tolerates a short time at ambient temperature. A day in a parked vehicle, on a loading bay or in a store room without cooling is another matter.

• Give a business address where someone receives goods during working hours, Sunday to Thursday, and tell us who that person is.
• Ask whoever signs for the box to put it in the freezer or fridge at once, not on a shelf to wait.
• Keep the outer packaging until the contents have been checked.
• If your freezer depends on a generator during power cuts, keep a minimum and maximum thermometer in it. The reading after a long cut tells you what the stock went through.

We deliver to your business address in Iraq, in Baghdad, the provinces and the Kurdistan Region. Delivery and storage explains how goods travel.

1. Look at the outer box for damage, and at any temperature indicator, before opening it.
2. Match the paperwork: the batch number and expiry on each vial or box must match the delivery note and the certificate of analysis. If they do not, set the goods aside and contact us.
3. Move each product to the storage condition on its label straight away.
4. Write the date of receipt next to the batch number in your stock record.

Work to the expiry or retest date on the label and the certificate. It applies to the material as supplied and stored as the label says. Once a peptide is dissolved, that date no longer describes it: a solution's life is weeks at best, and only if frozen.

Label every aliquot with the peptide name, batch number, concentration, solvent and date of preparation. Keep a log of which aliquots have been thawed. When a result looks wrong months later, the log separates a stability problem from a pipetting error.