Peptide solubility depends on the amino acid composition and the overall charge of the molecule. Hydrophilic peptides (those rich in charged or polar residues like Arg, Lys, Asp, Glu) are generally soluble in aqueous solutions, while hydrophobic peptides may require organic co-solvents.
As a general rule, first attempt to dissolve the peptide in sterile water or a dilute buffer at the desired concentration. If the peptide does not dissolve, a small amount of dilute acetic acid (for basic peptides) or dilute ammonium hydroxide (for acidic peptides) can be added.
For highly hydrophobic peptides, initial dissolution in a small volume of DMSO, DMF, or acetonitrile followed by dilution into an aqueous buffer is often effective. The organic solvent should be kept below 10% of the final volume to minimize interference with biological assays.
It is important to note that sonication should be avoided as it can cause peptide degradation. Gentle vortexing or swirling is the preferred method for mixing. Always prepare peptide solutions fresh when possible for optimal results.