Proper peptide solubilization is one of the important factors for a successful peptide project. Improper peptide solubilization results in loss of peptide or failure of the experiment; however, finding the ideal solvent can sometimes be a challenge. The steps outlined below guide you through the processes for determining the best solvent for a synthetic peptide. It is best to test the peptide’s solubility using a minute amount of peptide first. Distilled, sterile water, should be used as solvent first especially when the peptides have less than five residues. For other specific peptides, optimum conditions for peptide solubility are based on the given peptide sequence.
Solubility test guideline:
Assign a value of -1 to acidic residues which include Asp (D), Glu (E), and the C-terminal -COOH. Assign a value of +1 to basic residues which include Arg (R), Lys (K), His (H), and the N-terminal -NH2. Calculate the overall charge of the entire peptide.
If the overall charge of the peptide is positive, try to dissolve the peptide in water first. If water fails, try 10%-30% acetic acid solution. If the peptide still does not dissolve, add TFA (< 50 μl) to solubilize the peptide and then dilute the peptide solution to the desired concentration.
If the overall charge of the peptide is negative, try to dissolve the peptide in water first. If water fails, add NH4OH (< 50 μl) and then dilute the peptide solution to the desired concentration. If the peptide contains Cys, then do not use basic solutions to dissolve it. Try the alternative method listed below.
Peptide whose overall charge is zero usually dissolves in organic solvent. First, try to add some acetonitrile, methanol, or isopropanol. For very hydrophobic peptides, try dissolving the peptide in a small amount of DMSO, and then dilute the solution with water to the desired concentration. For Cys-containing peptides, use DMF instead of DMSO. For peptides that tend to aggregate, add 6 M guanidine•HCl or 8 M urea, and then proceed with the necessary dilutions.
Above recommendations are schematically represented below: Please click on the bubbles showing different overall peptide charges for clearer illustration.
Note:
It is recommended that the concentration of the stock solution be around 1-2 mg of peptide per mL of solution. This is dilute enough to minimize the potential precipitation of the peptides during storage, but concentrated enough to take relatively small volumes (< 100 μL) of aliquots for the assay, and therefore minimizing the effect of the solvents initially used for solubilization.
Lyophilized peptides can be stored long-term at -20 °C and are stable for > 1 year. Once in solution we recommend that you aliquot them into tubes and store at -20 °C. It is recommended that peptides containing methionine, cysteine, or tryptophan residues be stored in oxygen-free atmosphere to avoid oxidation.
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). A 7% New Jersey sales tax will be applied to orders shipped to New Jersey. Your credit card will be billed under "GenScript USA Inc." Click here to download our 
