Peptide storage and handling

• Moisture. Peptide powders are hygroscopic: they take water from the air. The water lowers the amount of peptide in whatever you weigh and shortens the powder's life. Sequences rich in aspartic acid, glutamic acid, lysine, arginine or histidine take it up most readily.
• Oxygen. Cysteine, methionine and tryptophan oxidise easily. Free cysteine thiols oxidise quickly above pH 7.
• Time in water. In solution, peptide bonds slowly hydrolyse and some residues change. Sequences containing asparagine or glutamine are known for shorter lives.
• Heat and light. Warmth speeds up every one of these reactions. Bright light is best avoided.
• Repeated freezing and thawing. Each cycle lets in air and condensation.
• Microbes, once a peptide is dissolved in a liquid that is not sterile.

Each rule below keeps one of these out.

GenScript advises against repeated freezing and thawing. Use a laboratory freezer where you have one, and keep peptides away from the door.

A lyophilised 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 a peptide can be kept in, as long as it stays dry and sealed.

1. Take the vial from the freezer and let it reach room temperature before opening it, inside a desiccator if you have one. 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 you will use a peptide many times, divide it into single-use portions on the first opening, so each portion is thawed once.

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

• dissolve in a buffer at pH 5 to 6 (GenScript);
• divide the solution into single-use aliquots and freeze them at −20 °C or below;
• never refreeze an aliquot once it has thawed;
• consider passing the solution through a 0.2 µm filter to remove bacteria (GenScript);
• dissolve oxygen-sensitive sequences in oxygen-free water or buffer.

For preparing solutions for experiments in the laboratory only.

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

Test a small portion before committing the whole batch. Dissolution can take time, and a few minutes in a sonicating water bath helps; avoid warming the solution much.

To know the concentration you have made, you need the batch certificate. A milligram of powder is not a milligram of peptide, because the powder also holds counter-ions and water. 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.

"Room temperature" in a handling guide means about 20 to 25 °C. A summer afternoon in Cairo, or a parked vehicle anywhere in Upper Egypt, is well above that. Peptides tolerate a short time at ambient temperature; they do not tolerate a day in a hot van or on a loading bay.

• Give a business address where someone receives goods during working hours, and tell us who that is.
• Ask the person who signs for the box to put it in the freezer or fridge straight away, not in a store room.
• Keep the outer packaging until you have checked the contents.

We deliver to your business address in Egypt. Shipping 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 should 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.

The expiry or retest date on the label and the certificate is the one to work to. It applies to the material as supplied, 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 it is frozen.

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