Peptide Solubility Guide — Solvent Selection and Troubleshooting¶
1. General Solubility by Peptide Character¶
| Peptide Character | First Choice | Alternative |
|---|---|---|
| Hydrophilic (net charge >0) | Water, PBS, or 10% ACN/H₂O | 0.1% TFA/H₂O |
| Hydrophobic (net charge 0 or low) | 50% ACN/H₂O or DMSO | 50% ACN/H₂O + 0.1% TFA |
| Basic (Lys, Arg, His-rich) | Water or 0.1% TFA/H₂O | 10% acetic acid |
| Acidic (Asp, Glu-rich) | Water or PBS | 0.1% NH₄OH/H₂O |
| High Cys content | 20% ACN/H₂O | Add TCEP or DTT |
2. Recommended Solvent Polarity¶
| Solvent | Polarity Index | UV Cutoff (nm) | Use |
|---|---|---|---|
| Water | 10.2 | 190 | Most polar peptides |
| PBS (pH 7.4) | — | 200 | Biological assays |
| 0.1% TFA/H₂O | ~10 | 210 | Acidic dissolution |
| 50% ACN/H₂O | ~7.5 | 200 | Hydrophobic peptides |
| DMSO | 7.2 | 265 | Universal solvent |
3. Troubleshooting¶
| Problem | Likely Cause | Solution |
|---|---|---|
| Peptide won't dissolve | Too hydrophobic | Add 10 – 20% ACN or 1 drop TFA |
| Solution cloudy | Aggregation | Add 6 M guanidine or heat briefly |
| Precipitation over time | π-stacking (Phe, Trp) | Lower concentration, add organic solvent |
| Gel formation | β-sheet formation | Add 0.1% SDS or 20% HFIP |