Practice MT Ans

The neutral uncharged form is shown below o oh o c oh

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Unformatted text preview: artificial sweetener. The neutral, uncharged form is shown below. O OH O C OH C CH2 O CH2 O NH 2 CH C N CH C O CH3 CH2 O CH2 O + NH 3 CH C N CH C O CH3 H H PMS at pH = 3.5 (a) Draw the principle molecular species of aspartame expected to exist in Diet Coke (pH 3.5). Choose the most appropriate pKa values from the reference sheet. ( c) Estimate to the nearest 1% (eg. 18%, 76% etc) the % of aspartame molecules that exist as isoelectric zwitterions in Diet Coke (pH 3.5). NH3+/NH2 group: no calculation required: 100% NH3+ COOH/COO- group: pKa = 3.9 3.5-3.9 = log COO-/COOH COO-/COOH = 0.398/1 = 28% COOFinal answer = (0.28) (1) = 28% or 29% (d) Draw the structure of the average aspartame molecule at pH = 3.5. Give fractional charges to 2 decimal places. -0.28 O O O OH C C CH2 O CH2 O NH 2 CH C N CH C O CH3 H CH2 O CH2 O +1.00 NH 3 CH C N CH C O CH3 H Average molecule at pH = 3.5 Question #4 (6 points) “Cardophilin” is a brand-name drug used to treat cardiac arythmias. During initial studies of the drug, it was found that among persons taking the same daily dose of Cardophilin, some persons possessed slightly higher concentrations of Cardophilin in their blood if they were also taking another drug that increased the pH of their urine from 6 (normal) to 8. Which of the following structures is the likely structure of Cardophilin? O O (1) CN C CH 2 SH H CH3 CH 3 (3) C COOH H CH3 CH3 CH3 OH OH NC H CH 3 (4) NC HO CH3 O NC CC H CH3 NH 2 CH H C NH 2 OH (5) (2) H CN H CH 3 OH O (6) C HO NC CH H CH3 (a) First circle your answer. ( b) Now briefly explain the reasoning for your choice (a) in the space provided below. In your written explanation, do not refer to any of the structures you did not choose in (a). You must explain your choice (a) based solely on the merits of your choice alone. Use either “average molecule language” or “PMS language” in your explanation. Average molecule language: Passive rebasorption of a molecule from the urine into the blood occurs more readily if the molecule is uncharged. The net charge on a mo...
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