I am buying some compounds for enzyme inhibtion assay. I want to use neutral compound and not salt form. I don't clearly understand if there is diff in assay with neutral or salt form but for now i am using neutral form. I need to know solubility but there is info on hydrate form only , not neutral forn, Can i assume neutral will form will have higher solubility slwsays
There seems to be some confusion in your question between salt form and hydrate form. They are not the same thing. I will discuss the neutral versus salt form.
I don't think there is a generally applicable rule that says the salt form is more (or less) soluble than the neutral form. The counterion in the salt can have a major effect on the solubility. Whether the substance is amorphous or crystalline can affect solubility, as can the crystal form.
It also matters what solvent you are using.
There are some predictable situations. You can expect the sodium salt to be more soluble in water than the (protonated) free acid when attempting to make a concentrated stock solution. Since the salt has already been at least partially neutralized, the pH of the solution will be higher than a solution of the free acid. Since the unprotonated acid is charged, it will be more soluble in water than the free acid. Conversely, you will have difficulty dissolving a highly charged substance in a nonpolar solvent, so the free acid is likely to be more soluble in such a solvent.
the assay solvent is water or it can be DMSO. I meant between hydrated vs non hydrated form. Dasatinib has no solubility data but Dasatinib hydrate is Soluble in water (5.06 mg/ml), ethanol (poorly), and DMSO (200 mg/ml). The later is not found in sigma Aldrich those dealership we have. Buying each compounds for my assay from diff vendor will be more expensive and inaccessible.
Thus can i expect similar or higher solubility for Dasatinib as compared to Dasatinib hydrate?
Thermodynamically (solubility) there is not any difference, however, hydrates can solulize faster in water. I suggest to avoid making concenrated stock solutions in DMSO, because its dilution does not always result in a true molecular solution (and not visible suspension).
As you said you would do an enzyme inhibition assay, so the drug must be dissolved in a buffer with resistance to the change of pH. IF your buffer could stabilize pH, neutral form and the salt form would have the same solubility as they would be the same form in the same buffer. (I have encountered the same question, these are my opinion on it)
As to the hydrate form, the solubility wouldn't change, but the dissolution rate would depend on the crystal form, and it's hard to say which form is faster.
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