Kleurstofextractie uit planten
De kleurstoffen die in planten aanwezig zijn kunnen eruit geŽxtraheerd worden m.b.v. wasbenzine en spiritus
In planten en hun bladeren bevinden zich drie soorten kleurstoffen: chlorofyl, caroteen en xantofyl. Deze stoffen zijn op hun beurt echter ook weer mengsels van verschillende kleurstoffen.
Om de kleurstoffen zichtbaar te maken moeten we ze extraheren.
The bovenste laag bevat het chlorofyl dat beter oplosbaar is in benzine (een a-polair oplosmiddel). De onderste laag bevat de carotenen and xanthofyllen die beter oplosbaar zijn in spiritus(een polair oplosmiddel).
Bereiding van kleurloze spiritus:
|Contained in the chloroplasts of all higher
plants are two major kinds of pigments which absorb light energy effective
in photosynthesis. These are the green chlorophylls (a and b) and the
commonly red, orange or yellow carotenoids. The carotenoids, several types
of which typically occur in a single plant, are of two fundamental types,
the carotenes and the oxygenated carotenoids or xanthophylls. Structural
formulas of chlorophylls a and b; Beta-carotene, a representative
carotene; and lutein, a representative xanthophyll are shown in the Figure below.
Chlorophylls a and b possess a porphyrin structure, comprised of four pyrrole rings, with a chelated magnesium atom at its center, a fifth 5-carbon ring and a 20-carbon phytyl group attached to one of the pyrrole rings. The empirical formulas of chlorophylls a and b are C55H72O5N4Mg and C55H70O6N4Mg, respectively. The difference lies in the substituent on ring 3. Chlorophyll a has a methyl (-CH3) group in that position; chlorophyll b has an aldehyde (-CHO) group. In most higher plants and green algae chlorophylls a and b occur in a ratio of 2-3 : 1.
Carotenoids are 40-carbon compounds of which a large number of distinct types are known. The carotenes are pure hydrocarbons; Beta-carotene, for example, has the empirical formula C40H56. Xanthophylls contain oxygen in the terminal rings, and many, but not all, have the empirical formula C40H56O2. Carotenoids are NOT invariably red, orange or yellow. Some are green, others pink, and some quite black. Neither are carotenoids confined in occurrence to plants; indeed they occur in all major phyla of plants and animals. In higher plants they are not confined to chloroplasts, but often are found in other types of plastids, called chromoplasts, in fruits, flower parts, etc.
Chlorophylls and carotenoids occur in close association with each other and with the protein and lipid membrane constituents in the grana of chloroplasts. Whereas it was formerly believed that the photosynthetic pigments occur exclusively in grana lamellae, recent evidence indicates that chlorophyll at least occurs also in the stroma lamellae.
All photosynthetic plants, except photosynthetic bacteria, possess chlorophyll a, but many do not contain the combination of chlorophylls a and b, which is characteristic of green algae and higher plants. Photosynthetic bacteria possess unique forms of chlorophyll. Blue-green algae possess only chlorophyll a. Brown algae and diatoms possess chlorophylls a and c. Red algae commonlyhave chlorophylls a and d. The red and blue-green algae also possess phycobilin pigments, which, while not occurring in plastids, nevertheless absorb light energy which is effectively transferred to chlorophyll and therefore serve as photosynthetic pigments. All the pigments discussed above, other than chlorophyll a, often are termed accessory pigments.