Peptide Storage

General Storage Principles

Proper peptide storage is essential for maintaining compound integrity and ensuring reliable research results. The fundamental principle is to minimize exposure to factors that accelerate degradation: heat, moisture, oxygen, and light. Most peptides are supplied as lyophilized (freeze-dried) powders, which provides maximum stability. Once reconstituted, peptides enter a less stable state requiring refrigeration or freezing. Storage conditions should be based on the specific peptide's characteristics and manufacturer recommendations.

Lyophilized Peptide Storage

Lyophilized peptides should be stored at -20°C or colder for long-term storage (months to years). At -80°C, most peptides remain stable for several years. Some stable peptides can be stored at 4°C for weeks to months. Critical factors include: (1) Keep containers tightly sealed to exclude moisture; (2) Use desiccant if available; (3) Store in the dark or amber vials; (4) Minimize container opening frequency; (5) Allow vials to equilibrate to room temperature before opening to prevent condensation. Properly stored lyophilized peptides can maintain >95% purity for years.

Reconstituted Peptide Storage

Reconstituted peptides have significantly reduced stability compared to lyophilized forms. General guidelines: (1) Store at 4°C for short-term use (days to 1-2 weeks); (2) Store at -20°C for medium-term (weeks to months); (3) Store at -80°C for longer periods. Avoid repeated freeze-thaw cycles by aliquoting into single-use portions before freezing. Use sterile reconstitution fluids and aseptic technique to prevent microbial contamination. Some peptides are unstable in solution even when frozen and should be used promptly after reconstitution.

Reconstitution Fluids

Common reconstitution fluids include: (1) Bacteriostatic water (0.9% benzyl alcohol)—preferred for multi-use, prevents microbial growth; (2) Sterile water for injection—for single-use applications or benzyl alcohol-sensitive work; (3) Acetic acid (0.1-1%)—improves solubility of basic peptides; (4) DMSO—for hydrophobic peptides, use minimal volume then dilute; (5) Buffer solutions—PBS, sodium acetate, or other buffers for pH-sensitive peptides. Avoid buffers with primary amines (Tris) for long-term storage as they can react with peptides.

Container Selection

Container choice affects peptide stability: (1) Polypropylene—preferred for most peptides, low adsorption, siliconized versions available; (2) Glass—may cause adsorption of hydrophobic peptides, use silanized glass for sensitive peptides; (3) Low-binding plastics—specialized tubes designed to minimize peptide adsorption; (4) Amber containers—block light for photo-sensitive peptides. For very low concentrations (<10 μg/mL), surface adsorption becomes significant regardless of container type.

Documentation and Best Practices

Maintain records of: storage dates, reconstitution dates and volumes, number of freeze-thaw cycles, and observed changes (color, precipitation). Label all containers with peptide identity, concentration, date, and lot number. Implement first-in-first-out inventory management. Periodically verify purity of stored peptides by HPLC if available. When in doubt about stability, prepare fresh solutions rather than risk using degraded material that could compromise experiments.

Key Takeaways