One of the most challenging aspects of peptide handling, lies in its proper dissolution. To begin with, there is no universal solvent that can be used effectively which will not affect the compatibility and integrity of the peptides.
As such, it is always a game of trial and error in finding the right solvents, and this usually calls for a lot of patience if any worthwhile results are to be achieved. Discussed below is a brief look into some of the dissolution approaches normally used for charged peptides:
Dissolving acidic peptides
A peptide is acidic if its entire net charge turns out to be negative. For acidic peptides, or if the sum total of the charges at pH 7 turns out to be more than ¼ of the total number of peptide residues, you need to add 0.1M of ammonium bicarbonate so that you can dilute and dissolve the water to the recommended concentration. The resulting pH of the solution must near 7 and if not, continue adjusting appropriately.
Dissolving basic peptides
A peptide is basic when its overall net charge is positive. In this case, the total number of charges at pH 7 is between 10% and 25% of its total peptide residues. To dissolve such a peptide, use a small portion of ¼ acetic acid the dilute with water until it reaches the desired concentration.
Dissolving neutral peptides
A peptide is neutral if its overall net charge is zero. In this case, the total number of positive charges in the peptide is greater than ¼ of the total amount of residues in the peptide. For dissolving such a peptide, use the same method used for dissolving acidic peptides.
If the total number of charges in a peptide is less than 10% of the total number of residues, it is recommended that you use organic solvents for the dissolution.