It is not always necessary but YES, it is recommended to do this. Biological effect first of all depends on dose, and not on mass dose but on the quantity of substance. That is becouse "one (quantity) molecule interacts with biotarget" but not "one nanogram of molecules interacts with some mass of biotarget". Since compounds has different molecular weights, two same IC50 in mcg/ml represent effect of different number of molecules. Converting to mcm/ml solves this problem. For sure, if your molecules have similar molecular weights and IC50 ranges significantly (few orders of magnitude) the question of units choice has little effect and you can ignore it safely.
In regression analysis of QSAR the IC50 value ( or any other biological activity data like EC50, MIC etc) which is used as dependent variable must be converted to pIC50 value i.e negative log of IC50 . My question is, if the IC50 value is given in μg/ml then do we need to convert it to μm/ml? Since many of the published article changed μg/ml to μm/ml before converting the IC50 to pIC50 values I guess it is necessary to change the microgram to micromolar. Could anyone tell me why??
It is not always necessary but YES, it is recommended to do this. Biological effect first of all depends on dose, and not on mass dose but on the quantity of substance. That is becouse "one (quantity) molecule interacts with biotarget" but not "one nanogram of molecules interacts with some mass of biotarget". Since compounds has different molecular weights, two same IC50 in mcg/ml represent effect of different number of molecules. Converting to mcm/ml solves this problem. For sure, if your molecules have similar molecular weights and IC50 ranges significantly (few orders of magnitude) the question of units choice has little effect and you can ignore it safely.
I would recommend to convert it. The biological activity and potency depends on how much molecules are in your dose that affect or bind to a receptor, but not on the concentration itself. This would be very important when you compare to molecules regarding their potency specially if the molecules have high molecular weieghts.
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