Natural dyes are organic compounds produced by living organisms and stain animal and plant cells and connections tissue. They have mainly yellow, brown, black, and red colors of different shades, very little are blue and purple and green is usually absent.
To prepare a research peper on the topic, you should know that prior to the second half of the XIX century, natural dyes were the only dyes for dyeing the textile, perfumes, leather, paper, food, etc. With the development of organic synthesis industry, natural dyes were unable to compete with synthetic dyes and basically lost their former practical significance. Small amounts of natural dyes are used in the restoration work. They are also used in the food and perfume industries, in studies by optical and electron microscopy in cytology and histochemistry, in analytical chemistry. Many natural dyes have considerable physiological and antibiotic activity, and therefore are commonly used as medicaments. Some natural dyes are plant growth regulators, as well as signal substances that attract pollinators and pest repellents.
Natural dyes are widespread in nature and are extremely diverse. Often in different natural sources the same or similar in structure natural dyes are found, so the most useful way to classify them is by type of chemical compounds.
Aliphatic and alicyclic dyes
This type includes carotenoids that contribute to yellow, orange, and red tints in flowers and
fruits. With the lengthening of the conjugated double bonds chain, the coloring deepens. Among this
type of natural dyes there are hydrocarbons, such as lycopene (red) alyufa-, beta-, gamma-carotene
(purple); alcohols, such as xantofil cryptoxanthin and (yellow), zeaxanthin (yellow-red); ketones
such as rodoxanthin (bluish-black) and astitsin (purple); keto-alcohols, such as canthaxanthin and
astaxanthin (red), aldehydes, and other aldegido-alcohols.
Carotenoids are encountered in plant and animal world. Many of them, such as carotene, have a high
physiological activity, retinal (aldehyde formed from vitamin A) is part of the visual protein
rhodopsin. To include a number of polyene antibiotics (kanatsidin, gentamycin, trihomitsin etc.)
produced by actinomycetes.
Aromatic dyes
Basically it is a hydroxy-and alkoxy-substituted unsaturated ketones: 1) the derivatives of cinnamic
and ferulic acid-4.4-dihydrooxydicynnamoilmetan (yellow), diferuloilmetan or curcumin (orange-red),
appearing in the roots of turmeric etc.; 2) chalcone derivatives C6H5CH = SNSOS6H5 and quinones,
such as Lawson and juglone, isolated, respectively, from henna leaves and peel of unripe walnuts
– yellow dyes for wool and silk; Chrysarobin – yellow dye from Brazilian wood species,
emodinantron – yellow dye from zhostera White-naped wood; hypericin and pseudohypericin
– dark purple and dark red color dyes Hypericum perforatum, having the ability to kill
bacteria and protozoa even in low UV irradiation.
Many natural dyes have physiological activity, vitamin K-inflammatory action. Partially hydrogenated aromatic natural dyes include antibiotics tetracycline and hromomitsina, painted in yellow color. Some of the dyes of this series are still used for dyeing; for example, in the restoration Alizarin is used – basic dyestuff madder, or madder dye also containing purpurin – red dye, which is used in histochemistry for detection of Ca in frozen environments, as well as a reagent in analytical chemistry: kartamin – pollen yellow.
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