1. How can the acidity or basicity of a peptide be predicted?

Assignment Rules

• Acidic amino acids: Aspartic acid (D), Glutamic acid (E), C-terminal –COOH → −1
• Basic amino acids: Arginine (R), Lysine (K), Histidine (H), N-terminal –NH₂ → +1

Determination Method

• Sum > 0 → The peptide carries a net positive charge, classified as basic
• Sum < 0 → The peptide carries a net negative charge, classified as acidic
• Sum = 0 → The peptide is neutral

2.What factors affect the solubility of a peptide?

Peptide solubility depends on its amino acid composition:

• Hydrophilic amino acids: Lys, His, Arg (basic hydrophilic), Glu, Asp (acidic hydrophilic)
• Hydrophobic amino acids: Leu, Ile, Val

3.What strategies are generally used for peptide dissolution?

• Preferred choice: Sterile distilled water or deionized water 
• For acidic peptides: If solubility is poor, add a mild base (e.g., 0.1% NH₃·H₂O) to assist dissolution
• For basic peptides: If solubility is poor, add a mild acid (e.g., 0.1% acetic acid or 0.1% TFA) to assist dissolution
• For hydrophobic peptides: Dissolve in DMF/DMSO first, then dilute with water, and after complete dissolution, add buffer solution

4.What precautions should be taken during the dissolution process?

• DMF and DMSO can disrupt the secondary structure of peptides and aid in dissolution, but they may affect peptide activity and subsequent experiments
• Ultrasonic treatment can further promote dissolution, especially when using organic solvents, and can assist in both dissolution and dilution processes

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