I remember my mentor saying before that she decided to refrigerate her gentamycin stock solution instead of freezing it since that was the recommended storage condition.

Now, I'm dealing with Hygromycin B and I think I'm facing some issues with the antibiotic activity. The powder we have in our lab is stored at -20 degrees. I prepared aliquots of Hygromycin B after dissolving the powder and subsequently, I stored the aliquots of Hygromycin B solutions in -20 as well. I've read some papers and websites that reported a loss of activity when Hygromycin B is stored at -20.

My question is, how does freezing lead to this phenomenon? What is the mechanism behind this?