Hi all,
I know there have been questions and answers on how to dissolve an acidic peptide. However, my questions will be:
a) Can I dissolve my peptide using a basic solvent such as NaOH instead of NH4OH? Are there any differences in dissolving the peptide in different basic solvents, for example ammonium hydroxide and ammonium bicarbonate?
b) What is the percentage of the basic solvents to be used to dissolve the peptide? How much ul to use in a 1ml pure water dissolved- peptide?
c) Better to reach ph7 in order to dissolve the peptide?
Thank you.
Mel
a) yes. The selection will depend on the application
b) it depends on the peptide concentration you want
c) yes
If you add 1 equivalent of base for each equivalent of acid, you should end up with a neutral pH solution, if the peptide dissolves. Whether or not the peptide is soluble will depend on the amino acid composition.
You could also try making a stock solution by dissolving the peptide in DMSO. Small amounts of DMSO (a few % by volume) are usually compatible with cells and proteins.
The solubility of a peptide is determined mainly by its polarity. Acidic peptides can be reconstituted in basic buffers, whereas basic peptides can be dissolved in acidic solutions. Hydrophobic peptides and neutral peptides that contain large numbers of hydrophobic or polar uncharged amino acids should be dissolved in small amounts of organic solvent such as DMSO, DMF, acetic acid, acetonitrile, methanol, propanol, or isopropanol, and then diluted using water. DMSO should not be used with peptides that methionine or free cysteine because it might oxidize the side-chain.
For more information:
https://www.lifetein.com/handling_and_storage_of_synthetic_peptides.html
You could always use a buffered solution...
Anyway, the ammonium hydroxide (or bicarbonate) is probably prefered, because it evaporates either in MS or during lyophilization, while NaOH will precipitate. But in principle, there should be no difference. OK, maybe in the ion size, but if you write about peptide, that should probably not matter.
I think NH4HCO3 is the best choice! I don't recommend to use any hydroxide as a solvent.
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