Since many of
the products sold by PolySciTech Division of Akina, Inc. (www.polyscitech.com) are used in
reactions, I often receive questions about their usage and subsequent
purification techniques. One common solvent for performing conjugations and
other reactions in is dimethylsulfoxide (DMSO). This solvent is a highly versatile
polar aprotic solvent with low toxicity. It has some drawbacks however in that
its boiling point is extremely high (189 °C) and it has very bad miscibility
with typical non-solvents used for polymer purification such as hexane or
diethyl ether. Attempts at ‘precipitating’ a PLGA based conjugate material from
DMSO into one of these non-solvents typically result in the formation of two
separate layers and minimal DMSO removal. We have used this solvent at Akina
for a variety of applications and have two methods which are used for DMSO
removal both of which have pros and cons:
1. Rotovap: with deep
vacuum and heat about 50 C. For this one deep vacuum is important and typical
peristaltic vacuums or aspirators are insufficient. My personal favorite for
this one is the Welch Duoseal type vacuum because of its robustness but it can
also be accomplished using a direct-drive type vacuum or other capable of
dropping the pressure very low (mTorr range). After rotovap, to purify
redissolve in either dichloromethane (DCM) or another more convienent solvent
with low boiling point and precipitate in a traditional non-solvent such as
hexane or diethyl ether. The pro’s to this method are that it’s effective,
fast, and simple with no additional solvents/chemicals added. The con of this
method is heat. Heat exposure won't damage the polyester under deep vacuum, but
if you have something delicate attached (peptide, protein, etc.) then it could
be damaged by heating.
2. Dialysis: Dialyze
against deionized water. Since DMSO is water soluble it will go into the
deionized water easily. Subsequently this can be dialyzed against acetone to
replace the water with acetone. If doing dialysis make sure to use a MWCO
membrane lower than the molecular weight of the polymer. To prevent premature
degradation it is best to dialyze in refrigerator (4C) and not for extensive
periods of time (no more than 1-2 days). Afterwards rotovap away the much more
volatile solvent at room temperature or precipitate in a non-solvent. The pro
to this method is no heating is involved. The con to it is that it is a slow
process with lots of water exposure.
These are just two methods
but there are many ways to remove DMSO. Keep in mind all the parameters of your
particular research prior to deciding the best method to desolvate your system.
