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log-p values
Posted: Sat Mar 06, 2010 6:34 pm
by praveenpaliwal
Hellow
I have calculated Log-p value for my one of compound It was 1.29 and -0.99 what does it mean?
How we can approach towards right pH regarding to log-p values
praveen
Posted: Sat Mar 06, 2010 7:15 pm
by Uwe Neue
Log p is an index for the hydrophobicity of a compound. It is the logarithm of the octanol-water partition coefficient. It has nothing to do with pH or analyte pK.
Posted: Sun Mar 07, 2010 6:43 am
by praveenpaliwal
Ok sir,
Now I have calculated log-P value for isophthalic acid it was 1.66 + / - 0.23 means?
1.43 or 1.89 right .......
praveen
Posted: Sun Mar 07, 2010 9:28 am
by HW Mueller
What did you use for and how did you do the calculation? Seems to me one can not do this calculation without knowing where the values come from that one puts in the formular. I have used logP values the last time when I worked with a drug some 30 years ago . . . . isn´t one value for the acid and the other for the carboxylate in this case?
If that´s it then you can estimate the pH at which a given % is acid, etc. from the dissociation constant.
Posted: Sun Mar 07, 2010 2:57 pm
by praveenpaliwal
Sir,
I calculated this through software / ACD lab this shows the values 1.66 + / -0.23 .
I thought that it may be 1.43 or 1.89.
Now suggest us
Praveen
Posted: Sun Mar 07, 2010 3:09 pm
by HW Mueller
If you don´t tell what values you placed into the ACD software I can´t help you. Your second calc. seems to have delivered an avarage value with a standard deviation.
Posted: Sun Mar 07, 2010 6:58 pm
by Uwe Neue
Why do you need the log p? I have never used it for anything in chromatography...
Posted: Mon Mar 08, 2010 8:41 am
by HW Mueller
Neither have I. For drug design it also has limitet use.
Posted: Mon Mar 08, 2010 2:41 pm
by Alex Buske
I think the + / -0.23 is the uncertainness in calculation. So 1.66 is the calculated value and there is an 95% chance that the true value is between 1.43 and 1.89. I am sure there are Helpfiles ic ACD/Labs.
isn´t one value for the acid and the other for the carboxylate in this case
logD is always for the whole molecule.
BTW: Is there any decent way to estimate logD by chromatography? I tought of a nice generic gradient on a endcapped C18, doing a "logD calibration" with a series of ketones or so and the just run the analyte.
Organic solvents should be methanol as well as ACN to avoid a solvent bias. The aqueous part would be mixtures of dil. H3PO4 and aq. Na3PO4. I am having just a spare quarternary system. The whole thing should run overnight.
We are having problems to explain low bioavailibility of a substance. We suspect the solubility (decreasing with increasing pH) and logD values (unaffectet by pH) supplied from a contract lab.
Have a nice day...
Alex
Posted: Tue Mar 09, 2010 9:39 am
by HW Mueller
Alex, I was referring to the first question, just erroneously called it acid, we are not told what type of compound it is. (You seem not to have seen the following in one of my posts above: "Your second calc. seems to have delivered an avarage value with a standard deviation.").
Also one would think one can get the distribution coefficient of any entity that can be stabilized under the experimental conditions, the tables I have seen appear to confirm that.