German version
Chemicals and material:
| 1 M NaOH
| | 1 M aqueous copper(II) sulfate
| | glycine
| | egg albumen | | |
Glass wares:
| 3 conical measures, graduated 500 mL
| | 1 beaker 500 mL
| | 3 beakers 50 mL
| | measuring cylinder 100 mL
| | 2 volumetric pipettes 5 mL
| | 1 volumetric pipette 10 mL
| | 4 volumetric pipettes 20 mL
| | 7 pipette bulbs
| | 5 snap-cap vials 20 mL
| | 3 glass stirring rods | |
Hazards and safety precautions:
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Sodium hydroxide solution is very corrosive. Causes severe burns. May cause serious permanent eye damage.
Very harmful by ingestion. |
Safety glasses, protective gloves!
Experimental procedure:
Preparation of the egg albumen "solution": The albumem of an egg is mixed with 300 mL aqueous NaCl.
Three conical measures are set up as described in the following table. Each of the mixtures is mixed with a glass stirring rod.
conical measure
1
| 400 mL of water
| -
| 5 mL of 1 M copper sulfate solution
| 5 mL of 1 M NaOH
| conical measure
2
| 400 mL of water
| one spatula of glycine
| 5 mL of 1 M copper sulfate solution
| 5 mL of 1 M NaOH
| conical measure
3
| 400 mL of water
| 30 mL egg albumen "solution"
| 20 mL of 1 M copper sulfate solution
| 40 mL of 1 M NaOH |
Results:
conical measure
1
| water
| light blue precipitate
| conical measure
2
| glycin
| blue solution
| conical measure
3
| egg albumen
| blueviolet solution |
 Video clip (Download RealPlayer .rm
file)
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Discussion:
Peptides and proteins (long-chain polypeptides) react with Cu 2+ in alkalinity to create a blueviolet colored chelate
complex with an absorbance maximum at 540 nm (conical measure 3). The peptide must have three peptide bonds at least.
Amino acids and Cu 2+ ions form a blue complex (conical measure 2).
The biuret test is used for the quantitative photometrical determination of total protein concentration. The intensity of
the color produced in the biuret reaction is proportional to the number of peptide bonds participating in the reaction.
Index of Lecture Experiments
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