i want to do ITC experiment of protein (which is in phosphate buffer,water soluble) with a drug (which is soluble in organic solvent ).is this ok? or organic solvent can create a problm ?
High concentration of organic solvent or highly hydrophobic organic solvent will denature your protein. Use ethanol for instance at a low concentration, nonetheless I assume you want to study the interaction between the drug and the protein, if so any organic molecule could perturb or compete for the hydrophobic regions of the protein.
I agree with Omar. it would be a harsh condition for your protein. Nevertheless, if it is really needed you should dilute your organic buffer as low as possible with the buffer you use. Still, the presence of organic solvents in the buffer might cause signal artifacts.
Drug delivery technology can offer you an alternative in which the active pharmaceutical ingredient (API) is micro encapsulated in a water soluble molecular net. Example is hydroxyl propylated cyclodextrin in which the propyl groups wrap around the API, and the cyclodextrin provides water solubility. These components are available commercially.
You cannot maintain the drug in organic solvent and the protein in aqueous solution, because the background heats will be much larger than the contribution from the potential protein-drug interaction. You shold dilute the drug stock into buffer and keep the same residual low percentage of organic solvent in the protein solution in order to avoid even small mismatches in composition between both solutions, cell and syringe (and hoping that the protein will not suffer too much). For example, a difference of 0.1% DMSO or glycerol between both solutions will result in considerable background injection heats.
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