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How to dissolve a peptide?
Please see our Technical Note “Solubilization of Peptides”, which can be downloaded from our website.
The solubility of a peptide in a solvent or buffer is determined mainly by its polarity, which results from the amino acid composition, and its conformation.
Solubility in water can be expected for peptides containing a large proportion of charged amino acids. As the peptides are usually produced as trifluoroacetate salts, the basic amino acids (Arg, Lys, His) and the N-terminal amino group will be protonated. The aqueous solubility of peptides containing Asp and/or Glu can be improved by adding diluted ammonia, which will generate the ammonium salts.
Polar amino acids as Asn, Gln, Gly, Ser, Thr facilitate reconstitution in water.
DMSO (dimethyl sulfoxide) is a highly suitable solvent for dissolving non-polar peptides (peptides containing a large proportion of Ile, Leu, Met, Phe, Pro, Trp, Val; most fluorophoric and chromophoric peptide substrates), it will also disrupt aggregates. Addition of DMSO (or DMF, acetonitrile, or other highly polar water-miscible solvents) may help to reconstitute a peptide, which is scarcely soluble in water. DMSO should not be used in combination with strong acids as trifluoroacetic acid. Most peptides will dissolve in acetic acid. Cys- and Met-containing peptides require special attention to prevent oxidation of the sulfur.
Reconstitution of peptides, especially long peptides or inner salts, may take time. Gentle warming or short repetitive sonication to accelerate dissolution is usually tolerated.
The intended use may limit the choice of solvents.
We advise against dissolving peptides directly in assay buffer, except if they show a high water-solubility. |
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