Storage
Oxidation
Research use only. For in vitro research use only. Not for human or animal consumption. Not for human consumption, medical use, or personal application.
Oxidation is a degradation route in which oxygen adds to susceptible side chains, altering the molecule without cleaving the peptide backbone. Methionine is usually the first casualty, converting to its sulfoxide, and tryptophan, histidine, tyrosine and cysteine are also exposed. The reaction needs no heat to proceed. Dissolved oxygen, trace metal ions, light and peroxide contaminants carried in solvents all promote it, which is why an oxidation problem can turn up in material that never left the cold.
Conditions that drive side-chain oxidation
Solution is the high-risk state: dissolved oxygen is freely available, and metal traces from glassware, water or buffers act catalytically. Light adds energy to the same reactions, so amber vials or foil wrapping appear in procedures for sequences with photo-labile residues.
Diluent quality carries more weight than it appears to. Choosing between bacteriostatic water and other laboratory water is partly a contamination decision and partly a question of what trace species arrive with the fluid.
How oxidation shows up analytically
It adds mass in defined increments, so mass spectrometry identifies it well: a methionine sulfoxide sits sixteen mass units above the parent molecule. By HPLC the oxidised form commonly resolves as a separate peak at a different retention time.
That makes oxidation one of the more traceable routes. A stored vial compared against its release record shows a shrinking main peak with a matching new peak, rather than a diffuse loss with nothing to point at.
Frequently asked questions
- Which sequences deserve extra care?
Any containing methionine, tryptophan or a free cysteine. Copper-bound sequences such as GHK-Cu carry a redox-active metal within the molecule, so their handling notes repay close reading.
- Can oxidised material be recovered?
Not in practice. Reduction chemistry exists but it is not a storage operation, so the oxidised fraction is best regarded as lost.
- Does headspace air in a sealed vial matter?
Far less than exposure in solution, because a dry cake offers little molecular mobility. Repeated opening is the greater issue, since it exchanges headspace and admits moisture.
Updated 2026-06-01