Peptide solubility characteristics vary strongly from one peptide to another.
Residues such as Ala, Cys, Ile, Leu, Met, Phe, and Val will increase the chance of the peptide having solubility problems.
The best solvent to use will depend on the solubility properties of the peptide and solvent requirements of your assay. We recommend predicting the physical properties of the peptide, dissolving the peptide as a function of these physical properties and then adapting the solubility results experimentally.
Use distilled solution
In order to reconstitute the peptide, distilled water or a buffer solution should be utilised. Some peptides have low solubility in water and must be dissolved in other solvents such as 10% acetic acid for positively charged peptides or 10 % ammonium bicarbonate solution for negatively charged peptides.
Select the best solvent
Other solvents that can be used for dissolving peptides are acetonitrile, DMSO, DMF, or isopropanol. Use the minimal amount of these non-aqueous solvents and add water or buffer to make up the desired volume.
Always use pure solvent first, then dilute by adding water stepwise until you reach a solvent concentration compatible with your assay.
Use and storage
After peptides are reconstituted, they should be used as soon as possible to avoid degradation in solution.
Unused peptide should be aliquoted into single-use portions, relyophilized if possible, and stored at -20 °C. Repeated thawing and refreezing should be avoided.
For peptides that tend to aggregate (usually peptides containing cysteines), add 6 M urea, 6 M urea with 20 % acetic acid, or 6 M guanidine - HCl to the peptide, then proceed with the necessary dilutions. Please note that urea irreversibly alters the side chain of lysines. If this is to be avoided, use of guanidium chloride is advised.
A major problem associated with the dissolution of a peptide is secondary structure formation. This formation is likely to occur with all but the shortest of peptides and is even more pronounced in peptides containing multiple hydrophobic amino acid residues. Secondary structure formation can be promoted by salts.