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Topic

バイオケミストリー詳しい方

Problem / Need advice
#1
  • tasukete
  • 2006/09/17 05:44

宿題が出たのですが、なにから手をつけて良いのかまったくわかりません。
以下のものが問題です。

Aspirin is a weak acid with a pKa of 3.5 ( examine the structure and determine which H is titratable). It is absorbed into the blood through the cells lining the stomack and the samll intestine. Absorption requires passage through the plasma membrane, the rate of which determined by the polarity of the molecule: charged and highly polar molecules pass slowly, whereas netral hydrophobic ones pass rapidly. The pH of the stomach contents is about 1.5 and the pH of the contents of the small intestine 6.0. Calculate the relative ratios of the protonated and deprotonated forms of aspirin and determine: Is more aspirin absorbed into the blood stream from the stomach or from the small intestine?

アスピリンのどのHが始めにprotonate されるのかも解りません・・・。

よろしくお願いします。

#2

アスピリンの構造を見るとベンゼン環に-COOH基がついてますよね?

そのーCOOHがーCOO-に変わったりします。

つまり
-COOH⇔-COO-+ H+ (pKa=3.5)
ですね。

その後は自分で考えれますか?

pH=pKa+log[A-]/[HA] の式に
Stomachの場合はpH=1.5、pKa=3.5を代入して、[A-]/[HA]を求める。

Small intestineの場合はpH=6.0を代入。

といった具合です。

頑張ってください。

#3

Biochem Major さん、ありがとうございました。 

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