Hi everyone, I am preparing liposomes and I would like to know for how long lipids can be stored in a -20 °C freezer, please?
At the moment, I am working with DOTAP, DOPE, Cholesterol, and PEG, and they are all dissolved in ethanol. But, is there a general rule for other lipids as well?
Thank you!
There must be some references in data sheets also. But in my experience, lipids are good enough for one year (or even more) if they are properly stored at -20 C. I used to order them either in powder form, or in chloroform solution. In my experience, handling them in chloroform is easier. However, ethanol should be same I believe.
I would recommend using chloroform, since it is in principle possible that the hydroxyl group of ethanol will react with the ester bond to displace the fatty acids from glycerophospholipids. With common phospholipids and cholesterol a few years is typically fine, though the concentration should be checked at least once a year or more often if the stock is used frequently (solvent evaporates). Always use teflon capped tubes, since chloroform otherwise readily evaporates through the plastic.
In any case, in prolonged storage thin layer chromatography should also be done every year or two. I have observed very significant degradation in 20 year-old chloroform stock of phospholipids.
P.S. When checked by TLC, 20 years old phospholipids stored as dry powder are typically completely fine without any observable degradation. For this reason in the lab I worked in we used to order larger quantities as powder and then make chloroform stocks. The PI had had a company synthesizing and selling phospholipids and phospholipid derivatives in the 1980s, and they had studied the shelf-life, and we had a lot of old special lipids and lipid derivatives as dry powder as a leftover from the company in our lab, and if needed, we checked those, as they were often not commercially available from any source at the time. Chloroform stocks from the 1980s when checked in roughly years 2000-2008 tended to have very high level of degradation (in the order of 50% judging by eye on TLC), e.g. when comparing stereospecific DMPGs (1,2-dimyristoyl-sn-glycero-3-phospho-sn-1'-glycerol and 1,2-dimyristoyl-sn-glycero-3-phospho-sn-3'-glycerol) to the commonly available DMPG racemic for the headgroup glycerol (1,2-dimyristoyl-sn-glycero-3-phospho-rac-(1-glycerol). [Nowadays the naturally occurring stereospecific DMPG seems to available from a Chinese company, also supplied by SigmaAldrich.] The fresh stocks made from 20-year-old dry powder showed no detectable degradation.
So, the gist of the thing is that if you plan on long term storage, by dry powder and make chloroform stocks yourself.
Thank you Juha-Matti Alakoskela and Muhammad Saad Khan for the answers. They were very helpful!
Juha-Matti Alakoskela Can I dissolve DOPC powder in ethanol for immediate usage? And will not store as a stock solution.
Indraja Sundara Raju I have worked with DOPC and it works fine to dissolve it in absolute ethanol and use it straight away.
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