Freeze-Thaw Cycle
Definition
One round of freezing and thawing, during which ice crystal growth and the concentration of solutes at the freezing front push peptide molecules together. Repeated rounds degrade a material measurably, and aliquoting is the standard way to avoid them.
What this means for research sourcing
Correct storage preserves peptide integrity between experiments. Volta product pages list compound-specific storage conditions and shelf life.
Related Terms in Storage & Stability
Aggregation
Peptide molecules associating into clumps under heat, agitation or repeated freezing. Aggregates lose activity, scatter light enough to make a solution look faintly cloudy, and are more immunogenic than the monomer.
Deamidation
A degradation route in which an asparagine or glutamine side chain loses its amide group, often via a cyclic intermediate that can also rearrange the backbone. Heat and alkaline pH speed it up and it shows on a chromatogram as a close-running impurity.
Oxidation
Reaction of methionine, cysteine or tryptophan side chains with oxygen, accelerated by light, air and trace peroxides. It costs activity, and a sequence containing none of those three residues has no oxidation liability to begin with.
Hydrolysis
Cleavage of the peptide backbone by water, which proceeds slowly in solution and faster at extremes of pH or temperature. It is the reason a lyophilised powder outlasts the solution made from it by a wide margin.
Desiccant
A moisture-absorbing material, usually silica gel, packed alongside a dry product to keep ambient humidity away from it. Residual moisture is what drives hydrolysis in a powder, so the sachet is doing real work.
Shelf Life
How long a material stays within its specification under stated storage conditions. The figure is meaningless without the conditions attached, and it is established by stability study rather than estimated.
Beyond-Use Date (BUD)
The date after which a compounded preparation should no longer be used, set by the compounder from applicable stability data. It is not an expiry date, which is assigned to a manufactured product from its own stability programme.
Retest Date
The date by which stored material should be re-examined against its specification rather than discarded. It is used where stability data support continued use after confirmation, and it is a different claim from an expiry date.
