Accepted answer
Forty-two days at minus 80 °C. minus 80 °C is 85 kelvin below a refrigerator, and below the glass transition of a lyophilised cake the ten-degree rule of thumb stops applying at all — solid-state chemistry is not slow liquid chemistry, it is a different regime, and the failure modes that survive it are mechanical rather than chemical. The thing to establish is how many times it froze and thawed, not how long it sat: forty-two days at one stable temperature is gentler than a single uncontrolled transition. Either way, record the forty-two days and the temperature now, while you still know them; an excursion you did not write down is an excursion you cannot interpret later.
On the detail: the domestic leg after arrival is the part most often left in a warm hallway and least often worried about.
Anything shipped in solution is a different risk category, because hydrolysis and deamidation proceed in the aqueous phase and are strongly temperature-dependent.
Specifically, once the parcel arrives, the domestic leg is the controllable part: get it into the refrigerator promptly rather than leaving it in a warm hallway for a day.
Solid-state stability of lyophilised peptides at ambient temperature is documented in formulation studies with residual moisture as the dominant variable.
Nothing here is medical advice, and research-use compounds are not approved for human use.
Buy a logger if you actually want to know. Everything else is inference.
8I would add a sentence about light, since tryptophan-containing sequences care. – Dr_Bram_Verhoeven 3 months ago add a comment