Research-use information only. The peptides discussed are laboratory reference materials, not for human or animal consumption.
Most reconstitution problems are solubility problems. A peptide that will not fully dissolve, goes cloudy, or leaves visible particulate has almost always met the wrong diluent — not a defective vial. Peptide solubility is governed by the amino acid sequence, and a short look at that sequence tells you which diluent to reach for.
Read the sequence first
Peptides carry a net charge determined by their acidic and basic residues at a given pH. That charge is what keeps them in solution.
- Basic peptides (net positive; rich in Lys, Arg, His) dissolve readily in slightly acidic aqueous solution.
- Acidic peptides (net negative; rich in Asp, Glu) dissolve readily in slightly basic solution.
- Neutral or hydrophobic peptides (rich in Ala, Val, Leu, Ile, Phe, Trp) resist water entirely and need an organic co-solvent to start.
A peptide sitting at its isoelectric point — the pH where net charge is zero — is at its least soluble. Moving pH away from that point in either direction is usually all that is required.
The diluent ladder
Work down this list, stopping at the first that works. Always start with the gentlest option.
- Bacteriostatic water. The default for most research peptides supplied as acetate salts. Multi-use, preserved. See bacteriostatic vs sterile water.
- Sterile water. Where the assay cannot tolerate benzyl alcohol.
- Dilute acetic acid (0.1–1%). For stubborn basic peptides. Dissolve in the smallest volume that works, then bring to final volume with water.
- Dilute ammonium hydroxide or ammonium bicarbonate. For acidic peptides that resist water. Avoid with peptides containing Cys, Met or Trp, which oxidise readily.
- DMSO, then dilute. Last resort for hydrophobic sequences. Dissolve in minimal DMSO, then add aqueous buffer slowly. Note that DMSO is incompatible with many downstream assays and with Cys-containing peptides.
Rules that prevent most failures
- Test on a small amount first when a peptide is unfamiliar. Sacrificing 1 mg beats ruining 10 mg.
- Never sonicate or vortex to force dissolution. If it needs force, the diluent is wrong. Agitation shears and denatures.
- Let it sit. Many peptides simply need 10–20 minutes of gentle swirling at room temperature.
- Cloudiness is not dissolved. A properly reconstituted solution is clear. Cloudy means suspended, and concentration is then unreliable.
- Once solubilised, do not re-lyophilise and expect identical behaviour.
Quick reference
- Basic sequence: water, then dilute acetic acid.
- Acidic sequence: water, then dilute base — unless Cys/Met/Trp present.
- Hydrophobic sequence: minimal DMSO, then dilute out.
- Clear solution: proceed. Cloudy or particulate: stop, reassess diluent.
Getting the right diluent
Product pages list the molecular formula and weight where available, and a batch COA states the salt form — the two facts you need to pick a diluent. Browse the catalogue, or ask us which diluent suits a specific batch. Related: how to read a peptide COA.