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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
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
O OH C C
CH2 O CH2 O NH 2 CH C N CH C O CH3
H CH2 O
NH 3 CH C N CH C O CH3
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?
(1) CN C CH 2 SH H
(3) C COOH H CH3 CH3 CH3 OH OH NC
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
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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- Winter '13