Peptide Research Glossary

The terms used across PeptideClock's calculators, database, and guides — including the evidence labels the site attaches to its own numbers. Definitions here favor precision over brevity: several of these words are routinely used loosely elsewhere, and the loose usage is where storage mistakes start.

Aggregation: The clumping of peptide molecules into dimers, larger assemblies, or visible particles. Aggregated peptide has typically lost biological activity, and the process is promoted by heat, agitation, and freeze-thaw stress — which is why cloudiness or visible particles in a vial are treated as a discard signal.
Aliquot: A portion of a reconstituted solution divided into a smaller, single-use container. Aliquoting exists to protect the bulk of a batch: each portion is thawed or opened once, so repeated freeze-thaw cycles and repeated septum punctures never touch the rest.
Bacteriostatic Water (BAC): Sterile water containing 0.9% benzyl alcohol, used to reconstitute peptides for multi-dose workflows. The benzyl alcohol inhibits bacterial growth between uses — it is a preservative, not a pH buffer, a distinction that is misstated surprisingly often.
Deamidation: A chemical reaction in which the amide group on an asparagine or glutamine side chain is converted to another functional group. It is one of the most common degradation pathways for stored peptides, and it proceeds faster at elevated temperature and unfavorable pH.
Decay Rate: The daily fractional loss of potency — the r in the first-order model PeptideClock uses, where potency declines by a percentage of whatever remains each day rather than by a fixed amount. Peptide-specific decay rates on this site are model estimates unless a cited source says otherwise.
Freeze-Sensitive: A classification for peptides treated as high-risk after freezing in reconstituted form. For these compounds the site assumes severe or complete loss of activity after a freeze event — a deliberately conservative stance, since direct freeze-thaw assay data does not exist for most research peptides.
Half-Life: The time required for a quantity to fall by half. Biological half-life describes how long a peptide persists in the body; storage stability is a separate question, which is why a compound can have a half-life of minutes in plasma and remain stable for weeks in a refrigerated vial.
Hydrolysis: The chemical breakdown of a compound by reaction with water. In peptides this means cleavage of the amide bonds holding the amino acid chain together — an unavoidable background process in any aqueous solution, and a core reason reconstituted peptides degrade faster than lyophilized powder.
In-Use Period: The FDA label term for how long an opened or reconstituted drug product may be used — for example, the 56-day window on the Ozempic label. An in-use period is a label-backed fact about a specific manufactured product, not a property of the molecule that transfers to research vials.
Lyophilization: Freeze-drying. Peptides are shipped and stored as lyophilized powder because removing water largely halts hydrolysis, giving far longer shelf life than any solution. The stability clock effectively restarts — and runs much faster — at reconstitution.
Mechanistic Extrapolation: An evidence tier used on this site for claims where no peptide-specific study exists but general protein chemistry supports the inference. It is real reasoning and visibly weaker than a direct study, which is why the site labels it rather than presenting it as measured fact.
Model Estimate: A number produced by PeptideClock’s internal decay model rather than by a published study or product label, always marked [Model Estimate — PeptideClock] where it appears. A model estimate is a calibrated judgment with uncertainty attached — no assay was run.
Oxidation: Degradation caused by reactive oxygen, which alters susceptible amino acid residues such as methionine, cysteine, and tryptophan. Light exposure and repeated air contact accelerate it, which is the practical reason behind opaque storage advice for light-sensitive compounds.
Peptide Bond: The covalent amide bond linking consecutive amino acids in a peptide or protein chain. Breaking these bonds — by hydrolysis, for instance — is degradation in the most literal sense.
Potency: The fraction of original biological activity remaining. In PeptideClock’s calculators, potency is expressed as the percentage of the starting material estimated to remain intact after storage — an estimate of activity, not a purity measurement.
Reconstitution: Dissolving lyophilized peptide powder in a solvent — typically bacteriostatic water — to produce a solution of known concentration. Reconstitution is the moment storage stakes change: the solution degrades faster than the powder did, and handling quality starts to matter.
Stability Class: PeptideClock’s grouping of peptides by how quickly they degrade in solution: Robust, Standard, Fragile, or Highly Volatile. The class sets the model’s baseline decay behavior for a compound and is a model-level classification, not a regulatory category.
Sterile Water: Water for injection with no preservative. It can dissolve a peptide just as well as bacteriostatic water, but with nothing to inhibit bacterial growth an opened vial has a much shorter practical window, which makes it a poor fit for multi-dose workflows.

Missing a term?

This glossary grows as the site does. If a term you expected is not here, or a definition seems off, write toresearch@peptideclock.com. To see the vocabulary in action, start with thepotency calculatoror browse the peptide database.