Dilute acetic acid solution supplied as a laboratory dilution standard. CAS 64-19-7, molecular formula CH3COOH (C2H4O2), molecular weight 60.05 g/mol. Clear liquid, miscible with water.
When acidic reconstitution is required
Not every peptide dissolves in neutral water, and forcing one that doesn’t is a common source of failed preparations.
Solubility depends on the net charge of the sequence at a given pH. Peptides rich in basic residues — lysine, arginine, histidine — carry a net positive charge under acidic conditions, and that charge keeps individual molecules repelling one another rather than aggregating. Near the isoelectric point, net charge approaches zero, and the peptide is at its least soluble.
A dilute acid brings the pH away from the isoelectric point for basic sequences and restores solubility. IGF-1 LR3 is the clearest example in this catalogue — it is specified for dilute acetic acid rather than bacteriostatic water.
Practical use
Dissolve in the acid first, then dilute into your working buffer. The peptide stays in solution through the transition, whereas adding acid to an already-cloudy aqueous preparation rarely recovers material that has already aggregated.
Check the compound’s specification before choosing a diluent. Most peptides in this catalogue reconstitute in bacteriostatic water; only those specified for acidic conditions need this. Note also that acetic acid contains no preservative, so it does not confer the multi-dose stability that benzyl alcohol provides.
Handling
Store at room temperature and protect from freezing. Prepare working dilutions fresh where the protocol allows.
For a fuller treatment of reconstitution technique and diluent selection, see the reconstitution and storage guide.
Frequently asked questions about acidic reconstitution
Why won’t some peptides dissolve in water?
Because of net charge. A peptide is least soluble near its isoelectric point, where positive and negative charges balance and molecules stop repelling one another — at which point they aggregate instead of dispersing. Sequences rich in basic residues such as lysine, arginine and histidine sit near neutral pH at their isoelectric point, so plain water is close to the worst possible solvent for them.
How does dilute acid help?
It shifts the pH away from the isoelectric point. Under acidic conditions a basic sequence carries a net positive charge, and that mutual repulsion keeps individual molecules in solution rather than clumping. The peptide is not chemically altered — the acid changes the environment, not the molecule.
Should I add acid to a cloudy solution to fix it?
It rarely works. Once material has aggregated, adding acid seldom recovers it. The correct order is to dissolve in the acid first, then dilute into your working buffer — the peptide stays in solution through the transition. Prevention is far more reliable than rescue here.
Can I use acetic acid instead of bacteriostatic water generally?
No. Use it only where the compound’s specification calls for acidic conditions. It contains no preservative, so it does not provide the multi-dose stability that benzyl alcohol in bacteriostatic water gives you across repeated withdrawals — and unnecessary acid exposure is a variable you do not want in an experiment that did not require it.
Research use only. Not for human or veterinary use, not for use in diagnostic procedures, and not evaluated by the U.S. Food and Drug Administration.
