By Anonymous on Friday, June 22, 2001 - 01:31 am:
Where can I find the pKa values of some common compounds? Could someone suggest some free database.Thanks.
By Anonymous on Friday, June 22, 2001 - 04:05 am:
The pKa values for some drugs can be found at
http://promini.medscape.com/drugdb/search.asp.
I heard that the books Analytical Profiles of Drug Substances contain a lot of data including pKa values. Can someone tell me where we can buy the books?
By B.Buglio on Friday, June 22, 2001 - 06:05 pm:
This is a multivolume set of books printed by
Academic Press, NY. - very expensive. Why not use
a library?
By Anonymous on Saturday, June 23, 2001 - 01:43 pm:
I am confused that sometimes people use pKa to describe the basicity of a basic compound. As far as I learned, pKb should be used in this case. What is the relationship between pKa and pKb for a base?
THanks a lot.
By Tom M. on Monday, June 25, 2001 - 04:15 pm:
In aqueous solution Ka*Kb=Kw, where Kw=1*10^-14. I like to think in terms of pKa because of its relationship to pH and the Henderson-Hasselbalch equation.
pH = pKa + log ([A-]/[HA])
or
pH = pKa + log ([B]/[BH+]), where pKa is refering to the [BH+]
One of the things chromatographers usually care about it the charge state of their analyte. Thus if you have a primay amine with a pKa of about 9 the H-H equation tells you that at a pH = pKa the molecules of your analyte will be half charge and half uncharged. Chromatography will usually be more robust to small changes in pH if you are >/= 2 pH units from your analytes pKa. At a pH of 7 the analyte will be fully charged and at a pH of 11 the analyte will be uncharged.
Buffers are usually useful in a pH range of +/- 1 pH unit from their pKa...
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