I am collaborating with a microbiologist to test some compounds to see whether or not they possess antibacterial properties. These compounds are either neutral or bear a single negative charge near pH 7, and they have aromatic rings. The compounds we have tested so far are soluble in DMSO, but modestly soluble in ethanol (less than 10 mg/mL), and probably not soluble in unbuffered water. The assay begins with adding the compound to a disk that is placed in contact with bacteria.
My question concerns solvents that would be appropriate to use to dissolve the compounds. I assume that one control is to try the solvent without the compound of interest. Are there any solvents that are known to be so toxic in this sort of assay that they are best avoided altogether? If two solvents had about the same polarity, is it better to choice the more volatile or less volatile solvent? Is there any other property that we should consider? So far I looked in a microbiology laboratory manual, but I did not find anything. Perhaps there is a good reference that someone could suggest. Thank you.