Color, pigments chlorophylls

Phthalocyanines are analogues of the natural pigments chlorophyll and heme. However, unlike these natural pigments, which have extremely poor stabihty, phthalocyanines are probably the most stable of all the colorants ia use today. Substituents can extend the absorption to longer wavelengths, iato the near iafrared, but not to shorter wavelengths, and so their hues are restricted to blue and green. 

A similar result is accomplished by using as one phase a solid powder or fine "beads" packed in a vertical column or spread in a thin layer on a plate of glass. The methods are usually referred to as chromatography, a term proposed by Tswett to describe separation of materials by color. In 1903 Tswett passed solutions of plant leaf pigments (chlorophylls and carotenes) in nonpolar solvents such as hexane through columns of alumina and of various other adsorbents and observed separation of colored bands which moved down the column as more solvent was passed through. Individual... 

Pigment Any colorful molecule chlorophyll is the dominant pigment in most plants. 

Approximately 1500 colored compounds, also known as natural food pigments, have been isolated from foodstuffs. On the basis of their chemical structure, these food pigments can be grouped in the following six classes heme pigments, chlorophylls, carotenoids, flavonoids, betalains, and miscellaneous pigments. 

Porphyrins are everywhere, as far as the living world is concerned. Their best-known forms (Figure 3.1) are heme, the red pigment that gives hemoglobin its red color, and chlorophyll, a reduced porphyrin, which is responsible for the green color of plants. The basic skeleton... 

Green coloration, present in many vegetable oils, poses a particular problem in oil extracted from immature or damaged soybeans. Chlorophyll is the compound responsible for this defect. StmcturaHy, chlorophyll is composed of a porphyrin ring system, in which magnesium is the central metal atom, and a phytol side chain which imparts a hydrophobic character to the stmcture. Conventional bleaching clays are not as effective for removal of chlorophylls as for red pigments, and specialized acid-activated adsorbents or carbon are required. 

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