Accepted answer
twelve weeks is 84 days, which at room temperature is on the order of 283 refrigerated days. Room temperature is not a number, so take the pharmacopoeial 20–25 °C and its 22.5 °C midpoint: 17.5 kelvin above the 5 °C middle of a 2–8 °C refrigerator. The ten-degree rule of thumb — degradation rate roughly doubling per 10 K — puts that at about 3.4 times the refrigerated rate. It is an order-of-magnitude statement about a rate, not a shelf life, and the top of the 20–25 °C band runs about 1.4 times faster than the bottom of it. In solution the routes that matter are hydrolysis of the backbone, deamidation at Asn, and physical association — the first two cost content, the third costs neither until it precipitates. Over 84 days at room temperature you should expect all three to have moved, and a purity figure to have noticed only some of them. Reconstituted material has no certificate; the one in the box describes the powder.
Start with the sequence, because which pathways are available depends on which residues are present.
Hydrolysis cleaves the backbone, most readily at aspartate-proline and aspartate-glycine sequences, and is acid-catalysed. In a dry solid it barely proceeds at all.
Aggregation is physical: peptides unfold at air-liquid interfaces and associate. Shaking maximises that interface, which is why swirling and shaking produce visibly different outcomes on the same vial.
Adsorption losses at low concentrations are quantified in formulation studies and are the reason carrier proteins are used in dilute preparations.
A mass spectrum names the pathway. Plus one, plus sixteen, minus eighteen.
5This should be linked from the help pages. – tri_gly_ala 2 months ago 4Small correction: it is the number of cycles rather than the freezer temperature that does the damage. – mz_4113 10 months ago add a comment