The absorption of drug molecules such as aspirin (acetylsalicylic acid) depends on their ability to penetrate nonpolar cell membranes. A large KP value indicates that the drug is able to do this efficiently. AH2O â Amembrane [A]membrane KP = â¯ï£§â¯ï£§â¯ï£§â¯ï£§ [A]H2O A. Aspirin has a carboxyl group with a pKa = 3.5 Calculate the exact percent of the drug in the uncharged (neutral) form at pH = 2. Calculate exactly the KP value in the stomach at pH = 2. Explain your reasoning and any simplifying assumptions. Show all work. B. If the large intestine has a pH = 5.5, estimate the percent in the uncharged form at this pH. What do you predict will be the ÎG°transfer into the membrane? Explain your reasoning and any assumptions and show all work. C. Do you expect aspirin to cross the cell membrane more efficiently in the stomach or in the intestine? Quantify how much better. Explain your reasoning and any assumptions.
The absorption of drug molecules such as aspirin (acetylsalicylic acid) depends on their ability to penetrate nonpolar cell membranes. A large KP value indicates that the drug is able to do this efficiently. AH2O â Amembrane [A]membrane KP = â¯ï£§â¯ï£§â¯ï£§â¯ï£§ [A]H2O A. Aspirin has a carboxyl group with a pKa = 3.5 Calculate the exact percent of the drug in the uncharged (neutral) form at pH = 2. Calculate exactly the KP value in the stomach at pH = 2. Explain your reasoning and any simplifying assumptions. Show all work. B. If the large intestine has a pH = 5.5, estimate the percent in the uncharged form at this pH. What do you predict will be the ÎG°transfer into the membrane? Explain your reasoning and any assumptions and show all work. C. Do you expect aspirin to cross the cell membrane more efficiently in the stomach or in the intestine? Quantify how much better. Explain your reasoning and any assumptions.
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