I am testing a compound on RAW 264.7. the compound is soluble in DMSO. but to ensure that final concentration of dmso is not more than 0.1%, we are first dissolving it in dmso and then diluting it in pbs/ media which is leading to precipitation. I am aware that i can prepare highly concentrated stock, but because its an expensive compound i cant do that either, is there any other way that i can go ahead with?
You need to determine the solubility in PBS by adding to your DMSO solution the buffer stepwise, record the DMSO concentration. The solubility will be apparent due to [DMSO] > 0.1%. If your compound is not soluble at that pH, check the ionizable groups' pKa. You might need to lower the pH or you might have impurities precipitating.
First, kudos to you for visually determining that you have an aqueous solubility problem! A common paradigm in pharma screening is to dilute a 10mM DMSO stock at 1:1000 into medium (usually containing 10% FBS). How that's done might be important. One can simply inject a uL volume into a mL volume of medium, but this sometimes results in precipitation of the cmpd. Sometimes this can be averted by adding to a vigorously mixed system. We typically place 1-2uL of a 10-50mM DMSO stock in the cap if a microfuge tube containing a mL of medium, quickly cap, invert and immediately vortex the tube upside down. This might result in a supersaturated solution that could still ppt with time or simply produce smaller particles of ppt that are less visible to the naked eye. We also have determined for our assay that using up to 1% DMSO is not influential, so sometimes a lower stock concn and larger volume are diluted.
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