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PEG molecular weight ? - (May/08/2006 )

Hi everyone. I am doing some experiments using Polyethilene glycol. I learnt that there are at least 3 types of polyethilene glycol diferenciated by its molecular weight so you have PEG 4000, PEG 6000 and PEG 8000. PEG is used for nucleic acids precipitation i think. For precipitate s RNA many people is using PEG 8000, while or DNA the are using 4000. My question is, why the MW is important. I would appreciate if anyone can help with this doubt.

Thanks wink.gif


We use PEGs in protein crystallization. I think PEG mol wt is to do with osmotic pressure within the solution and environment. Kind of similar to the osmotic effect of albumin in blood. Not sure how well that correlates to nucleic acids, though. (You are right, there are many more PEGs than 4k, 6k and 8k. There are PEGs in the hundreds..PEG200, PEG 400 etc).


PEG 4000 o PEG 8000 are polymers of polyethylene glycol. If you use higher polymers, the resulting carrier effect will be better. that's why, PEG 8000 is used for small RNA precipitation. PEG 4000 is cheaper and is sufficent for DNA precipitation.


the number associated with the various pegs indicate the average molecular weight of the polymer. peg6000 and 8000 are the same, peg6000 was found to have an average fw of 8000 and was renamed.


The clue is in the name - POLYethylene glycol!

-John Buckels-

hi solmaniar! PEG is a polymer and has high affinity towards water. affinity increases with the molecular wt. of the polymer. High mol. wt PEG is a solid at Room Temp.
due to its affinity for water it precipitates DNA. it is also used in concentration liquids (solid PEG).