Wirt-Gast-Komplex β-Cyclodextrin und Phenolphthalein

1. Experiment is contained in the WAKER's Experimental Kit for Schools	yes
2. Experimental procedure has been modified	no
3. Video clip available	no
4. Flash animation available	no

3. Masking the Smell of Garlic

1 Materials, Chemicals, Time Needed

Snap-cap vial
Knife, chopping board
Scales
Spatula
Magnetic stirrer
Magnetic stir bar

Distilled water
β-Cyclodextrin
Garlic cloves

Allow approx ca. 10 minutes for this experiment.

2 Procedure and Observations

Variant I: Place half a diced garlic clove in a suspension of 0.2 g b-cyclodextrin and 20 ml water and shake or stir vigorously for five minutes. For comparison add the remainder of the diced garlic to 20 ml water and shake or stir this sample as well. Then smell each sample.
Variant II: Cut a clove of garlic in half and rub the cut surface onto the palm of your hand. Smell your palm and then rub a spatula tip of b-cyclodextrin in a little water onto the palm. Rinse briefly with water and smell it again.

The garlic smell decreases significantly in the sample with cyclodextrin. The palm of the hand no longer smells of garlic after washing with the cyclodextrin suspension.

3 Discussion of Results

The characteristic garlic smell has disappeared due to the formation of a host-guest complex with the aroma substance in the garlic. Allicin is one of the many sulfur-based compounds that are responsible for the garlic smell (see Fig. 2.24).

Fig. 2.24: Allicin is primarily responsible for the smell of garlic

4 Tips and Comments

It is advisable to blow into the snap-cap vials before smelling them to prevent the odor that has accumulated above the liquid from falsifying the experimental observations. Treat the surface of the hand with cyclodextrin as quickly as possible, because the intense smelling allicin is easily absorbed through the skin, thus preventing it from being encapsulated by cyclodextrins.

5 Supplementary Information

The sulfur-based compound allicin (see Fig. 2.24) can be used effectively in various medical applications. Allicin is antibacterial and also has a positive effect on cholesterol and blood lipid levels. In this way it can reduce the risk of arteriosclerosis. The use of garlic in pharmaceuticals was previously unpopular due to the strong smell of the active substance, but when encapsulated in cyclodextrins the allicin is rendered odor-neutral. Allicin is released when it reaches the stomach, where it passes through the gastric wall into the bloodstream. Complexation also prevents the extremely volatile allicin from rapidly evaporating or being oxidized by atmospheric oxygen. This odor-neutral allicin-cyclodextrin complex is used in garlic tablets, which have been on the market for several years.

6 References

Gröger, M.; Kretzer, E.K.; Woyke, A.; Reader mit Hintergrundinformationen zum Thema Cyclodextrine, 2001
Vollhardt, K.P.C.; Schore, N.E.; Organische Chemie; Wiley-VCH Weinheim, 2005, S. 423