(1) To determine the specific charge of the polypeptide, set the acidic amino acids Asp (D), Glu (E) and C-terminal COOH to -1; the basic amino acids Lys (K), Arg (R), His (H) and N-terminal NH₂, is +1, and the charge of other amino acids is 0. Calculate the charge.
(2) If the net charge number > 0, the peptide is alkaline, dissolve it in water: if it does not dissolve or has little solubility, add acetic acid (above 10%); if the peptide is still insoluble, add a small amount of TFA (25 pL) to dissolve, Then add 500 uL of water to dilute.
(3) If the net charge number is <0, the peptide is acidic and dissolved in water; if it does not dissolve or has little solubility, add ammonia water (25 uL) to dissolve, and then add 50 u of water to dilute.
(4) If the net charge number = 0, the peptide is neutral, and generally needs to be dissolved with organic solvents such as acetonitrile, methanol or isopropanol, DMSO, etc. It has also been suggested that urea is required to dissolve very hydrophobic peptides. Keshengjingpeptide provides free peptide dissolution test service to help you dissolve peptides.