Separation Of Leaf Pigments

What causes those brilliant fall colors?

Each fall, we have the chance to enjoy the spectacular of our trees, shrubs and vines, even put on the screen. This makes the fall a popular time to travel can mean business tourism for many like us out viewing spectacle of nature. Wide variety of New York deciduous trees helps create a colorful display that each tree has its own palette of red, yellow, orange or gold.

While a colorful landscape can seem like magic, it all comes down to chemistry. Leaf pigments (chlorophyll, carotenoids and anthocyanins), longer nights and time are the three main things that influence the color of autumn leaves.

Chlorophyll is the pigment that makes leaves appear green. It is necessary for photosynthesis, the chemical reaction that enables plants to use sunlight to make food. The chlorophyll breaks down constantly during the summer and is regenerated in the leaves. As the nights lengthen, chlorophyll production slows down eventually stop, and breaking away from leaves.

Carotenoids are responsible for yellow, orange and brown in things like carrots, pumpkins and dandelions. Carotenoids are present in the cells of leaves during the growing season chlorophyll protect against damage.Carotene is more stable than chlorophyll, so it will remain in the leaves after the chlorophyll is gone, which goes around the yellow sheet.

Anthocyanin pigments are responsible for the colors red, purple and blue in many fruits, vegetables and flowers. Most anthocyanins are produced leaves in the fall in response to bright light and excess plant sugars within leaf cells.

The shortening days and cool nights cause changes to take place in the trees. Corky membrane begins to develop between the branch and the stem of the leaf. This membrane interferes with the flow of nutrients into the leaf.Because the nutrient flow is interrupted, the production of chlorophyll in leaves and lowers the melted green. If the leaf contains carotene, it will turn bright yellow as the chlorophyll fades. In some trees, such as sugar increases in the leaf, causing anthocyanin form leaves to turn red.

Each fall, is unique as the breadth and brilliance of the colors that develop are influenced by weather conditions that occur before and during the production of chlorophyll slows down. Low temperatures destroy chlorophyll, and if they stay above freezing, promote the formation of anthocyanins.The bright sun destroys chlorophyll and enhances anthocyanin production. The dry weather also increases the amount of anthocyanin production. Therefore, the brilliant fall colors occur when dry, sunny days followed by cool nights and dry.

SEPARATION OF LEAF PIGMENTS BY COLUMN CHROMATOGRAPHY

A solid stationary phase and a liquid mobile phase are used and the principle of separation is adsorption. When a mixture of components dissolved in the mobile phase is introduced in to the column, the individual components move with different rates depending upon their relative affinities. The compound with lesser affinity towards the stationary phase (adsorbent) moves faster and hence it is eluted out of the column first. The one with greater affinity towards the stationary phase (adsorbent) moves slower down the column and hence it is eluted later. Thus the compounds are separated. The type of interaction between the stationary phase (adsorbent) and the solute is reversible in nature. The rate of movement of a component (R) is given as follows: Homogenize 5gm of green leaves in a mortar and pestle, then the extract by shaking with a mixture of petroleum ether, methanol and benzene (45: 15: 5). Remove the residue by filtration and wash the filtrate four times with water to remove the methanol. Avoid vigorous shaking or an emulsion will form. Remove the last traces of water by adding anhydrous sodium sulphate, filter to remove the solid, and concentrate the extract to a few milliliters by careful evaporation in a fume chamber. Prepare slurries of the column materials ( alumina, calcium carbonate and sucrose) in petroleum ether and pack the column with alumina (5cm) ,calcium carbonate (7cm) and sucrose(7cm), inserting a filter paper disc between each adsorbent . Gentle suction may be applied to the bottom of the column to assist packing. Wash the column with several volumes of the eluting solvent, a mixture of benzene and petroleum ether (1:4).

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