Preparation
Peptide stability: what degrades, when, and why sources disagree
Hydrolysis, oxidation, deamidation, aggregation — the four degradation pathways, the variables that set the clock, and why a stability claim without conditions is not a claim.
Four ways peptides fall apart
Which pathway dominates depends on the sequence, which is why two peptides stored identically can have completely different stability profiles. Any blanket claim that “peptides last X” is ignoring one of the four above.
- —Hydrolysis — water breaks peptide bonds, especially next to acid- or base-sensitive residues. Faster in solution, faster when warm.
- —Oxidation — oxygen (and light, via photosensitized reactions) modifies sulfur- and indole-containing residues: methionine, cysteine, tryptophan.
- —Deamidation — asparagine and glutamine residues lose their amide group over time, changing the molecule's mass and charge without changing its sequence visibly.
- —Aggregation — peptides sticking together into larger assemblies; promoted by high concentration, agitation, and freeze/thaw cycling in solution.
The variables that set the clock
| Variable | Effect on stability |
|---|---|
| Temperature | Accelerates essentially every pathway; cold slows the whole set |
| Water / humidity | Enables hydrolysis even in powder (residual moisture); dominates in solution |
| Light | Drives photosensitized oxidation in vulnerable sequences |
| Oxygen | Oxidation partner; headspace in a vial is enough over long periods |
| pH | Different sequences have different stability optima; formulation chemistry |
| Concentration | Higher solution concentrations promote aggregation for some sequences |
| Freeze/thaw cycles | Mechanical and phase stress on solutions; aggregation promoter |
How to read a stability claim
A stability statement without conditions — “stable for 3 years” — is marketing. A verifiable one names the form (lyophilized/solution), temperature, container, and how stability was measured (assay over time, usually HPLC). Certificates that report degradation limits and expiry dates per lot are showing you the machinery; supplier pages that say “very stable” are not.
Where a supplier publishes actual stability data for a specific product, that belongs in Level 4 (industry reference) with the document linked — and where a manufacturer of an approved product publishes it in a label, it is Level 1. The tier matters: same-sounding sentences, different evidentiary weight.
Why this section has no compound tables
Because Therapept has not verified compound-specific stability studies for most of the library. Building that table is exactly the kind of work the research pipeline exists for — sourcing real stability literature per compound. Absence here is stated rather than papered over with borrowed numbers.
Sources
Updated 17 September 2026 · Therapept Editorial · How these guides are built