Why does aggregation accelerate at 37 °C rather than proceeding linearly?

What I am working with: aggregation · 37 °C.

I keep seeing this stated as a fact with no explanation attached, and unexplained facts make me suspicious.

My background is quantitative but not chemical, so I can follow an equation more easily than a hand-wave.

Is the standard explanation correct, and if so, what is the evidence for it?

Because temperature enters the rate constant through an exponential, so equal steps in temperature multiply the rate instead of adding to it. Arrhenius puts the rate proportional to exp(−Ea/RT); the working approximation is a doubling per 10 K, which takes 5, 15, 25 and 35 °C to multipliers of 1, 2, 4 and 8. The steps in temperature are equal and the steps in rate are not, and that is the whole of the observation. At 37 °C the same rule gives about 9.2 times the refrigerated rate, and another 10 K would roughly double it again. Molecules associate without any covalent change, so the mass is unchanged and a reversed-phase run — which is performed in organic solvent — mostly dissolves the evidence before it can be measured. Ea differs by route, so the ranking of routes changes with temperature too — which is why accelerated data extrapolates badly and why nobody should read a 40 °C study as a fast version of a 5 °C one.

Stated carefully, aggregation is a physical process and is the one most often caused by handling rather than by time.

A mass spectrum resolves most of this: minus eighteen is dehydration or succinimide, plus one is deamidation, plus sixteen is oxidation, and an unchanged mass with a shifted retention time is an isomer.

It helps to be literal here: adsorption onto glass and plastic is significant at low concentrations — micrograms per millilitre — and negligible at milligrams per millilitre. It is the usual explanation for an apparent loss in a dilute preparation.

Metal-catalysed oxidation of methionine is documented across peptide and protein formulations and is why chelators appear in some formulations.

Sequence decides which pathways are even available. Check the residues.

edited 8 Dec 2025 by lyoph_cake — added the citation requested in comments

The honest answer is that most reported "degradation" is adsorption and dilution error rather than chemistry.

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.

To be exact about it, 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.

A mass spectrum names the pathway. Plus one, plus sixteen, minus eighteen.

edited 7 Jan 2026 by halvard_ness — clarified the distinction between purity and content

The short version: water enables most of it, oxygen enables oxidation, surfaces enable adsorption, and agitation enables aggregation.

Freeze-thaw cycling drives aggregation through concentration at the ice interface and pH shifts as buffer components crystallise out at different rates. Each cycle costs something.

Deamidation converts asparagine or glutamine to the corresponding acid via a succinimide intermediate, adding one dalton. It is base-catalysed, accelerates above neutral pH and is the dominant aqueous pathway for many peptides.

Apparent loss in a dilute preparation is usually adsorption rather than degradation and is worth ruling out first.

Swirl, never shake. Aggregation is a handling problem more than a time problem.

This is answerable from the chemistry rather than from anecdote, which is unusual and welcome.

Oxidation targets methionine, cysteine and tryptophan, adding sixteen daltons per oxygen. It is catalysed by trace metals and promoted by dissolved oxygen and by light.

The caveat is that none of these pathways can be seen by looking at a vial, and a clear solution can be substantially degraded.

Cold, dry, dark, still. Those four words cover most of the mitigation.

Start with the sequence, because which pathways are available depends on which residues are present.

Light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations.

At dilute concentrations, suspect adsorption before you suspect chemistry.