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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
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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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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
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