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THE CHEMISTRY OF AUTUMN COLORS

Martin Drastík

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Why would I like to speak about this topic? Sad but beautiful

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Pigments

Chlorophyll – green Carotene – orange Anthocyanin – red, purple

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Chlorophyll Molecule is large

(C55H70MgN4O6)

Porphyrin ring + magnesium

Situated in leafs – organelles

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Chlorophyll Chloroplasts Not soluble in

the aqueous solution of cells

Photosynthesis of sugars and starches

tescarbohydraOOHCO 2lchlorophyllight

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Chlorophyll Why do the leaves seem to be green? Absorption spectrum

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Chlorophyll

Not a very stable

compound;

decomposed

by bright sunlight

Continuously synthesized in leaves (requires sunlight and temperatures) until autumn

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Carotene Large molecule (C40H36)

Situated in the chloroplasts Function: accessory absorber - energy transferred to chlorophyll

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5

1

4

2

3

7

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CH318

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10

11

12

13

14

15

15'

14'

13'

CH320'

12'

11'

10'

9'

CH319'

8'

7'

CH317

CH316

CH319

CH320

1'

6' 2'

3'5'

4'CH318'

CH316'

CH317'

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Carotene Absorption spectrum Much more stable than chlorophyll Carotene persists in leafs even when chlorophyll has disappeared

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Anthocyanin Various structures –

diff. is „B“ benzenoid ring

Disolved in the aqueous solu-

tion of cells

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Anthocyanin Absorption spectrum

Color is sensitive to the pH of the cell sap

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Anthocyanin If the sap is acidic – bright red If the sap is neutral – purple If the sap is alkaline – orange

alkaline; neutral; acidic

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Anthocyanin Formed by a reaction between sugars and

certain proteins in cell. Occurs when concentration of sugar in the sap is high enough.

Requires light Red side insolate

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Conclusion Summer:

Autumn: stop of producing chlorophyll, storing energy in fruit

and nuts

changing color of leaves

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Thank you for your attention

The biggest source of information:

Prof. Shakhashiri, University of Wisconsin-Madison Chemistry: Chemical of the Week

Pictures – internet