Aromatic amino acids are organic compounds that contain a carboxyl group, a benzene ring, an amino group. The presence of several functional groups explains the duality of the properties of these organic substances.
Being in nature
Aromatic amino acids are part of the tissues and cells of living organisms. Despite the diversity of representatives of this class, only 20 amino acids are monomers for the construction of proteins and peptides. Benzoic acid, for example, found in cranberries, has excellent antioxidant properties.
Many microorganisms and plants are able to independently synthesize some aromatic amino acids necessary for full functioning.
They take an active part in carbohydrate and protein metabolism, are part of nucleic acids, vitamins, hormones, pigments, alkaloids, antibiotics, toxins. Some are mediators in the transmission of nerve impulses.
Classification
There is a division of representatives of this class of organic oxygen-containing compounds according to structural features.
Given the location of amino and carboxyl functional groups, emit
α-, β-, γ-, δ-, ε- acids.
According to the number of groups, basic, neutral, acidic substances are distinguished.
Depending on the structure of the hydrocarbon radical, aromatic amino acids, aliphatic, heterocyclic, sulfur-containing substances are isolated.
Important information
In order to name these organic compounds, a systematic nomenclature is used. Aromatic amino acids are derivatives of benzene, in the side chain of which one or more carboxyl (acid) groups appear. The simplest representative of this class is benzoic acid. The introduction of a hydroxyl group into the side chain leads to the formation of salicylic acid.
Derivatives of aromatic amino acids - esters and amides - are used in the chemical industry.
Benzoic Acid Historical Background
Humanity has known benzoic acid since ancient times. In the sixteenth century, it was isolated by sublimation from resin. In the 19th century, German chemists studied the chemical properties of this compound, compared it with hippuric acid. Thanks to the antifungal and antimicrobial action, benzoic acid began to be used as a food preservative in the process of manufacturing food products. It is indicated on product labels as additive E 210.
Physical and chemical properties
In its appearance, benzoic acid is similar to oblong thin white needles with a specific shine. It is highly soluble in various environments: alcohols, fats, water. The melting point of this aromatic amino acid is 122 degrees Celsius. It passes from a solid state to a gas.
In large volumes, benzoic acid is obtained by the oxidation of toluene (methylbenzene).
It is a natural compound, as it is found in some berries: lingonberries, blueberries, cranberries. In addition, benzoic acid is formed in dairy products such as yogurt, yogurt. The compound is not toxic, not dangerous to humans, if you use it in small quantities.
Chemical properties
A qualitative reaction to aromatic amino acids is an electrophilic substitution in the aromatic ring (nitration with concentrated nitric acid). Xanthoprotein reaction is used to detect the following aromatic acids: tyrosine, phenylalanine, tryptophan, histidine. The process is accompanied by the formation of a product painted in bright yellow.
Another qualitative reaction to aromatic amino acids is ninhydrin, which is used in the quantitative and qualitative determination of not only amino acids, but also amines. When ninhydrin is heated in an alkaline solution with compounds in which primary amino groups are present, a product with a blue-violet color is obtained.
This chemical reaction is also used to detect secondary amino groups in aromatic acids: hydroxyproline and proline. Their presence can be judged by the formation of a stable product of bright yellow color. When conducting a modern chemical analysis of aromatic amino acids, the ninhydrin reaction is used.
The method of paper chromatography makes it possible to identify each amino acid in a taken mixture in an amount of from two to five micrograms.
Application
The food preservative E 210 (benzoic acid) is used in the confectionery, brewing, and baking industries. Here is a list of products whose production is inextricably linked with the use of benzoic acid: ice cream, canned vegetables, beer, liquors, sugar substitutes, pickled and salted fish, chewing gum, butter, margarine.
The manufacture of some cosmetics is not complete without this aromatic acid. Often it is added to medicines, for example, to antiseptic ointments. Pharmacists pay attention to benzoic acid because of its preservative properties.
This organic compound perfectly copes with a variety of fungi, microbes, simple parasites. That is why benzoic acid is added to cough syrups for children. It has an expectorant effect, softens sputum, removes it from the bronchi. The high efficiency of medical solutions intended for foot baths, which contain benzoic acid.
Organic compound helps eliminate excessive sweating in the legs. Benzoic acid is considered an effective means of combating fungal skin lesions. In the chemical industry, benzoic acid is used as the main reagent in the manufacture of many organic compounds.
Once in the human body, benzoic acid enters into a chemical interaction with protein molecules.
It transforms to hippuric acid, then it is excreted in the urine from the body.