Module 3 - Benjamin-Mills

EP2.2
What’s in aspartame?
Is this activity you will apply your skills at
chromatography to help you investigate the conditions
needed for the hydrolysis of peptide bonds. You will be
looking at a simple example: aspartame, a dipeptide
used as an artificial sweetener. You will be
investigating what concentration of acid, and what
reflux time, are needed to hydrolyse the dipeptide.
Requirements
● aspartame, eg Searle ‘Canderel’ tablets (1–3 tablets)
● hydrochloric acid: various concentrations, eg 4 mol dm –3 ,
2 mol dm –3 , 1 mol dm –3 (25 cm 3 each)
● 10 cm 3 measuring cylinder
● apparatus for heating under reflux, eg 50 cm 3 pear-shaped
flask and water condenser
● anti-bumping granules
● apparatus for paper chromatography
● 250 cm 3 beaker
● butan-1-ol (20 cm 3 )
● glacial ethanoic acid (4 cm 3 )
● separating funnel
● aspartic acid solution,
0.01 mol dm –3 small amounts
● phenylalanine solution, for chromatography
0.01 mol dm –3
● ninhydrin in butan-1-ol, 0.5% solution in spray bottle
● mortar and pestle
● hair dryer
● protective gloves
Ï
Ì
Ó
butan-1-ol
ethanoic acid
hydrochloric acid
ninhydrin solution
CARE Eye protection
must be worn.
CARE Ninhydrin solution
must be used in a fume
cupboard. Gloves must be
worn. Wash the solution off
with lots of soap and water
if it contacts your skin.
HARMFUL
CORROSIVE
CORROSIVE
HARMFUL
WEAR EYE
PROTECTION
WEAR
PROTECTIVE
GLOVES
FLAMMABLE
FLAMMABLE
Introduction
Peptide bonds in proteins can be hydrolysed by refluxing with hydrochloric acid.
You will use the artificial sweetener aspartame as a substitute for a protein in this
activity. Aspartame is the methyl ester of the dipeptide Asp Phe. The ester link in
aspartame will also be hydrolysed under these conditions, so you will get
aspartic acid and phenylalanine just as you would from the dipeptide itself.
The skeletal formula for aspartame is shown below.
O
HO
H 2 N
N
H
O
OCH 3
O
aspartame
aspartame
„ Salters Advanced Chemistry 2000 – see Copyright restrictions
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