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Solubility FAQ

Solvent Best For Notes
Sterile Water for Injection (WFI) Most hydrophilic peptides pH ~5–7, first choice for most peptides
PBS (pH 7.4) Cell-based assays Buffered, physiological pH
0.9% Saline General research use Isotonic
0.1% Acetic Acid Hydrophobic/basic peptides Improves solubility for basic peptides
DMSO (≤0.1% final) Highly hydrophobic peptides Avoid >0.1% in cell assays

2. What is the typical solubility of research peptides?

Solubility is highly sequence-dependent. Most peptides dissolve at 1–10 mg/mL in WFI or PBS. Hydrophobic peptides or those with high β-sheet propensity may require acidic conditions or co-solvents.

3. How do I calculate the final concentration?

Concentration (mg/mL) = Mass of peptide (mg) / Volume of solvent (mL)

For molar concentration: Molarity (M) = Concentration (mg/mL) / Molecular Weight (g/mol)

Example: 5 mg peptide with MW 1500 g/mol dissolved in 2.5 mL of WFI: - Concentration = 5 / 2.5 = 2 mg/mL - Molarity = 2 / 1500 = 0.00133 M = 1.33 mM

4. What if the peptide doesn't dissolve?

Try these steps in order: 1. Allow more time (15–30 min with gentle swirling) 2. Warm to 25°C (do not exceed 37°C) 3. Sonicate in a water bath (30 seconds, avoid foaming) 4. Add a small volume of 0.1% acetic acid or DMSO 5. Adjust pH (use 0.1 M HCl or NaOH in small increments)

5. Can I use DMSO as the primary solvent?

DMSO is effective for hydrophobic peptides but should be used with caution. Final DMSO concentration in cell-based assays should not exceed 0.1%. For stock solutions in DMSO, prepare at 1000× the final assay concentration.

6. How does pH affect solubility?

Peptides are most soluble at a pH away from their isoelectric point (pI). For basic peptides (pI > 7), slightly acidic conditions improve solubility. For acidic peptides (pI < 7), slightly basic conditions are preferred.

For solubility inquiries: technical@rplpeptides.com