On the subject in the title: Freeze-thaw and why one cycle is not the same as five Working notes rather than a conclusion.
Two things I would like separated before anyone answers on freeze-thaw, because they get bundled and then argued about as one thing.
The first is descriptive: what has actually been observed, by whom, and how. The second is causal: why. I am asking about the first only.
Freeze-thaw is worth one more sentence than it usually gets, and the sentence is the one about how the number was arrived at.
The arithmetic in post #2 is right; the assumption feeding it is the part to check.
Visible particulate is a strong signal in the other direction: it is a reason to stop and ask rather than to filter and proceed.
I would put this at better than even and not much better.
Understood. Thank you for being specific about the limits of it.
Taking post #2 at face value and following it one step further.
Freeze-thaw looks different depending on whether you are reading the primary literature or the summaries of it, and the difference is not in our favour.
Aggregation is the failure mode that most concerns anyone who works with peptides professionally and the one least visible to anyone who does not. It is also concentration-dependent.
The short version is the first sentence; the rest is why.
Everything in post #5 holds. The case it does not cover is the one I have.
A supplier stability statement tied to a named storage condition can be evaluated. One that says "store cool" cannot, and the difference between those two documents is larger than it looks.
The uncertainty is in the assumption, not in the calculation.
This follows post #6 rather than contradicting it.
Clarity is a weak test. A solution can lose a significant fraction of its active content to degradation or adsorption while remaining perfectly clear.
This is the sort of thing that ought to be settled and apparently is not.
Worth separating two things that post #8 runs together.
The honest summary: keep it dry until you need it, keep it cold once it is not, keep it dark, do not cycle the temperature, and treat any period at room temperature as spent whether or not anything visible happened.
This is the sort of thing the wiki should carry and currently does not.
The bit of freeze-thaw that nobody enjoys is that the answer changes depending on what you are trying to decide with it. Say what the decision is and the thread will converge.
Second-hand on freeze-thaw, so weight it accordingly — someone whose method I trust told me this and I have not verified it myself.
Freeze-thaw: some peptide solutions tolerate freezing poorly because ice crystals damage protein structure. Whether your specific solution tolerates it depends on the formulation and is not something to test empirically. The conservative position is not to freeze.
Adding the measurement that post #11 says would settle it.
Freezing a reconstituted peptide solution is not automatically protective. Freeze-thaw cycling is one of the harsher things you can do to a protein in solution, and a single freeze is different from repeated ones.
The arithmetic on freeze-thaw is the easy part and it is where the errors are, which is an uncomfortable combination. Show your working and someone will catch it.
Reading rather than contributing, but this is the most useful thread I have found on it.
I read post #15 twice before replying, because I had assumed the opposite.
My understanding of freeze-thaw is a few years old and may have been superseded. If it has been, I would genuinely like to know rather than keep repeating it.
Visible particulate is a strong signal in the other direction: it is a reason to stop and ask rather than to filter and proceed.
A supplier stability statement tied to a named storage condition can be evaluated. One that says "store cool" cannot, and the difference between those two documents is larger than it looks.
Anyone with a larger sample, please post it.
Post #20 answers the question as asked. The question underneath it is different.
A methods point on freeze-thaw rather than a substantive one: if the comparison is not like for like, the difference you are measuring is the difference in method.
I read post #22 twice before replying, because I had assumed the opposite.
Two people in this thread mean different things by freeze-thaw and are disagreeing about the definition while believing they are disagreeing about the facts. Worth pausing to define it.
Building on post #24 rather than restating it.
A beyond-use date on a home preparation is an inference rather than a measurement. It can be a reasonable inference and it should be described as one.
Clarity is a weak test. A solution can lose a significant fraction of its active content to degradation or adsorption while remaining perfectly clear.
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