a problem about predicting the logP.

Hi:


I used ChemAxon to predict some characters based on the molecular structure, and I think it is very useful to my research.


But, I encountered a little problem. That's how to predict the LogP of ionic molecular, such as Montelukast Sodium (see pic below). In theory, the LogP of Montelukast Sodium should be negative value, but using the calculator, it predicted the LogP is 8.99. I don't know the reason.





Sincerely


Rong

Hi,





I calculated the logP of Montelukast Sodium as an ion.


And I obtained logP=5.0.





This is a large positive number.





Why do you think that the logP should be negative?











Jozsi

Hi, Jozsi:


Thank you for you reply.


I calculated the LogP of Montelukast Sodium is 5.0, too. But you know, it is very easy for Montelukast Sodium to be dissolved into the water. In my opinion, it is a hydrophilic molecular, so it is more possible for this molecular to diffusion into the water phase rather than the octanol phase. Therefore, the logP value should be negative.





Rong

Hi,








Do you have an experimental logP data for Montelukast?





The intrinsic solubility ( logS0 ) may depends on the structural features of the molecule as well.


This is why the high solubility is not a perfect evidence for the very low logP.








Jozsi