Storage and Stability

Once a peptide has been synthesized and purified, it exists in a highly vulnerable state. Because peptides are essentially “mini-proteins,” they are susceptible to various forms of degradation, including oxidation, hydrolysis, and aggregation. Proper storage is the difference between a successful experiment and a failed one.

The Stabilization Process: Lyophilization

Peptides are rarely shipped or stored in a liquid state because water facilitates the very chemical reactions that break them down. Instead, they undergo Lyophilization, or freeze-drying.

  • The Science: The peptide solution is frozen, and then the surrounding pressure is reduced. Through a process called sublimation, the ice turns directly into water vapor without ever passing through a liquid phase.

  • The Result: This leaves behind a “lyophilized cake”—a stable, fluffy, white powder. In this dehydrated state, the peptide bonds are “locked” in place, and the lack of moisture prevents bacteria from growing and enzymes from breaking the chain.

Critical Storage Conditions

To maintain a peptide’s “shelf life,” researchers must control three primary variables: Temperature, Light, and Moisture.

1. Temperature Control

Temperature is the most significant factor in peptide degradation.

  • Long-Term (1–2+ years): Peptides should be stored in a high-quality freezer at $-20°C$ or, ideally, $-80°C$. This near-total reduction in thermal energy stops most chemical degradation.

  • Short-Term (Weeks to Months): For peptides that will be used soon, a standard refrigerator at $4°C$ is typically sufficient for the lyophilized powder.

  • Room Temperature: While many peptides are stable at room temperature for transit (shipped in “cool packs”), they should not be left out for extended periods as this accelerates the breakdown of sensitive amino acids like Cysteine and Tryptophan.

2. Protection from Moisture (Desiccation)

Peptides are hygroscopic, meaning they naturally attract and absorb moisture from the air.

  • The Danger: If you open a frozen vial immediately after taking it out of the freezer, water vapor from the air will condense on the cold powder, leading to rapid hydrolysis.

  • The Protocol: Vials must be allowed to reach room temperature in a desiccator (a container that removes moisture) before being opened.

3. Light and Oxidation

Certain amino acids are “photo-sensitive.” Exposure to UV light can cause the peptide to turn yellow or lose its biological activity.

  • Storage Tip: Peptides are almost always stored in amber-tinted vials or kept in dark boxes to prevent light-induced oxidation.

Reconstitution: The Transition to Liquid

When a researcher is ready to begin a study, the powder must be turned back into a liquid. This is called reconstitution.

  • The Solvent: The most common solvent is Bacteriostatic Water (0.9% benzyl alcohol), which prevents bacterial growth. Some hydrophobic peptides may require a tiny amount of Acetic Acid or DMSO to fully dissolve.

  • The “No-Shake” Rule: Peptides are physically fragile. When adding the solvent, the liquid should be let to run down the side of the glass. The vial should be Gently Swirled, never shaken. Shaking can create shear forces that physically “denature” or break the delicate 3D structure of the peptide.

  • The Reconstituted Shelf Life: Once liquid, the peptide is on a “ticking clock.” It must be kept refrigerated ($2°C$ to $8°C$) and typically used within 30 days before its potency begins to drop significantly.