The peptides we typically purchase usually come in the following physical states:

1. Low-density, large-volume powder: This is the most common form of peptides.

2. Colored powder: Often seen in peptides with fluorescent modifications.

3. Colorless, transparent crystals: Common in short peptides.

4. High-density, small-volume powder: Usually found in certain long peptides.

5. Other uncommon forms: These depend on the production process and peptide structure.

Regardless of the form, we should store the purchased peptides immediately. So how should they be stored?

Transportation and Storage Conditions for Peptides:

- For transportation: At room temperature or with ice packs (most peptides are not sensitive to room temperature).

- For long-term storage: Keep in a dark place at -20°C, with lower temperatures being better, such as -80°C (generally can be stored for 3 months to 3 years).

- For short-term storage: Keep in a dark place at 4°C.

- For peptide solutions: Maintain a slightly acidic pH, around 5-6, at -20°C, using sterile buffer solutions. (Generally, it is not recommended to store peptides after dissolution. It's recommended to package peptides in specific batch sizes based on your usage requirements.)

Regardless of the storage method, use sealing tape to cover the bottle cap and any air gaps to prevent moisture or air from entering the bottle. Also, avoid direct sunlight or high temperatures.

Peptide Sequences That Are Not Favorable for Storage:

- Peptides containing Cys, Trp, or Met are prone to oxidation. Peptide companies usually use nitrogen gas protection during bottling.
  
- Peptides containing Asn or Gln can also degrade, shortening their shelf life.

- Peptides with Gln at the N-terminus have an even shorter shelf life, so it is advisable to avoid having Gln at this position.