I dissolved 5 mM L or D-amino acid in PBS 1X solution which is commonly used as cell culture media. Initially, both amino acid solutions remained clear after the amino acids were dissolved by sonication.
After couple days later, I observed only L-amino acid solutions get cloudy or show some precipitated powder at the bottom while the D-amino acid solutions were still clear. It happened to trp, phe, pro, val, his except threonine so far. They are not from the same vendor.
Here are possible reasons I can think of:
1. different ways of amino acid crystallization: I also noticed the enantiopure amino acid products have different crystals. For example, L-trp was more powdery than D-trp. Maybe both L and D amino acids got precipitated due to a cooled temperature (still around 20C though) a while after sonication, but only L-amino acid was visible?
2. Impurities: I doubt this because the amino acids were purchased from 3-4 different vendors, meaning they should have different degrees or kinds of impurities. Also, the purities of the amino acids are above 98%.
It'd be very grateful if you can share any thoughts.
Thanks in advance!
I'd imagine that seed crystals of the L-amino acids (and salts) are much more likely to be floating about than those of D-amino acids. In the absence of seeds to get things started, the D-amino acid solutions would be more likely to remain super-saturated.
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