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hi i need help and currently pursuing my bsc I need help in a question.

Determine the % ionisation of ibuprofen in blood(ph 7.4).
The pka of thiol group in of an active site cysteine residue if determined to be 8.5. Determine the ratio of
protonated(thiol) to deprotonated (thiolate) groups at pH 7.

Would sincerely appreciate your help.


Hi Shantini,
That is a really difficult question.None the less let me attempt it.
pKa of Ibuprofen is 4.91 as reported by Sangster (1994)it is a weak acid. For such compounds the formula is :
%ionized= 10pH-pKa/(1+ 10pH-pKa) *100
       = 7.4-4.91/(1+7.4-4.91)*100
       = 2.49\3.49X100
       = 71.34%
The second part of your question is something I have forgotten. It is over 40 years since I learnt all this. I am sorry I am unable to recall the formula.
Best wishes
Ravi Ghooi


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Dr. Ravindra Bhaskar Ghooi


I can provide information on drugs and medicines, their actions, uses, interactions and adverse effects. To avoid confusion, generic names of medicines may please be provided. I am a pharmacologist, having worked on animal and human pharmacology, and presently I am the Dean of Bilcare Research Academy, where we teach courses on clinical research. We dont work on saturdays and sundays, hence questions reachng me on these days will be replied on Monday, please bear with me.

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