This group of compounds is often called plant phenols, since most of the aromatic natural derivatives contain a phenolic function or are formed from phenolic compounds, and these compounds are produced, as a rule, by plants. Indeed, the phenolic function is most common among aromatic derivatives of the benzene series (naphthalene and anthracene compounds with phenolic functions are somewhat less common), but most often the phenolic group accompanies other oxygen functions.
And in this regard, the main groups of this class of natural compounds can be represented by the following series: phenols - contain only hydroxy functions; phenolic acids - contain hydroxy and carboxy functions; aromatic compounds of the pyran series - a-pyrons, y-pyrons, pyrillium salts; quinones of benzene, naphthalene and anthracene series, also containing phenolic groups. The definition of "vegetable" can also be omitted at the present time, since various representatives of the above groups are found in microorganisms, in fungi, in marine organisms.
8.1. Phenols and phenolic acids
Simple phenols (Scheme 8.1.1) are not so widespread in nature: the most common is hydroquinone, sometimes catechol, as well as their derivatives. Since phenolic compounds (especially dihydroxy derivatives) are easily oxidized, in plants they are usually represented by the aglycone component of glycosides or esterified in another way: with alkyl and cycloalkyl radicals, for example. An interesting and important representative of the latter is the group of tocopherols vitamins E, which perform an antioxidant function in the cell membranes of animal organisms, including humans.
Aromatic carboxylic acids in their pure structural form are very rare in nature. Benzoic acid is found in sufficient quantities in cranberries and lingonberries, making them resistant to the action of microorganisms (berries are well stored without any additives and have been used as preservatives in other products since ancient times).
Phenolic acids in plants are found everywhere and in a fairly wide structural range. First, these are mono-, di-, and trihydroxybenzoic acids, which are widespread in plants, both accumulating and as intermediates in biosynthetic pathways. Another group is hydroxyphenylacetic acids, which are much less common. The third group is cinnamic acids, widespread, but usually present in low concentrations and lying on biosynthetic pathways to aromatic oxygen-containing heterocycles. Quite often, hydroxy acids are included in the composition of essential oils of many plants in the form of methyl (simple) ethers, and derivatives with a carboxyl group reduced to an aldehyde and alcohol group are also found (Scheme 8.1.2).
Scheme 8.1.1
(see scan)
Scheme 8.1.2.
(see scan)
Scheme 8.1.2 (continued).
(see scan)
The chemical properties of phenols and phenolic acids are due to the ability of phenolic compounds to oxidize to the corresponding quinones or similar compounds, forming a quinone-like system. What does this ability of phenolic compounds give to the plant organism?
First, since the oxidation of phenols proceeds by a radical mechanism, i.e. they have a certain affinity for free radicals, phenols act as traps for free radical particles (including oxygen). By donating their hydrogen atom from the hydroxyl function of the aromatic nucleus, they form a fairly stable phenolic radical, which, due to its stability and delocalized nature, does not participate in the radical chain process, i.e. it breaks the chain radical reaction, thus performing the role of an antioxidant and quencher of other radical processes, which usually lead to phenomena that accelerate cell death (aging) and mutagenic effects.
What are the direct products of the oxidation of natural phenolic compounds? First, these are ortho- and paraquinones, their formation is especially characteristic of simple phenols and low-substituted phenolic acids (Scheme 8.1.3).
Scheme 8.1.3
The second group of reactions is associated with the ability of the unpaired electron of the phenol radical to delocalize along the benzene ring, forming a significant spin density on carbon atoms in the ortho and para positions to the oxidized hydroxyl. Since carbon radicals are more active than oxygen radicals, they can enter into various reactions associated with a radical attack on another molecule or the same phenoxyl radical. The products of such reactions of oxidative coupling or oxidative condensation are melanins, the structure of which is composed of fragments of condensed quinones of type A, B, and C (Scheme 8.1.4).
Usually melanins are deeply colored - from dark brown to black tones, they are found in the seeds of Helianthus annuus and Citrullus vulgaris, in the spores of Ustilago maydis, in the ascomycete Daldinia concentrica. Melanin of the latter is formed by oxidative condensation of 1,8-dihydroxynaphthalene and presumably has structure D, it is accompanied by condensed black quinone E (Scheme 8.1.5).
Scheme 8.1.4
(see scan)
Scheme 8.1.5
(see scan)
Tannins are another group of aromatic derivatives that are formed in plants that contain phenolic acids. Tannins arise from gallic acid by various reactions: oxidative dimerization and esterification, both between the functions of gallic acid itself and with others
Scheme 8.1.6
(see scan)
hydroxy compounds - mainly with glucose. Accordingly, they are subdivided into hydrolyzable tannins - esters of gallic acid (or its oligomers) and carbohydrates and condensed tannins, i.e. non-hydrolyzable (Scheme 8.1.6).
Gallic acid forms oligomers in vivo of two types: dimers (or tetramers) with a carbon-carbon bond between phenyl rings (ellagic, hexahydroxydiphenoic acid, etc.), dimers and trimers with an ester bond between fragments (trigallic acids). In this regard, gallic acids themselves are divided into hydrolysable (esters) and non-hydrolysable (diphenyl derivatives). Both of them with carbohydrates form hydrolyzable tannins, since in an aqueous medium under conditions of acidic, alkaline or enzymatic catalysis, they form carbohydrates and phenolic acids.
These tannins, first of all, should include esters of monosaccharides (usually glucose) with gallic or trigallic acids. Whereas glucose esters with condensed gallic acids (ellagovs, etc.) can be considered tannins of a dual nature, since they contain hydrolysable and non-hydrolysable fragments. Fully non-hydrolyzed tannins have nothing to do with gallic acid (except that they are also polyphenolic substances), but are derivatives of flavanols - pyranic compounds, which will be discussed in the next section.
Tannins are obtained from the bark of acacia, spruce, oak, chestnut and other plants. They are also found in tea. This is a fairly active substance in relation to many pathogenic microbes, their tanning effect is due to the ease of interaction with proteins, and phenolic groups provide a significant antioxidant effect. Tannins inactivate many enzymes.
Tannins have the property of tanning leather, and are also pro-pigments, since under the action of oxidants (even oxygen in the air) they form dyes of stable black color.
The third group of phenolic acid derivatives, or rather phenol alcohols, is formed by dimerization and polymerization of compounds such as coniferyl alcohol. These are lignans and lignins. Lignans are dimers of coniferyl alcohol, the dimerization of which, apparently, can proceed (judging by the structure of the products) in different ways and with different numbers of subsequent modifying stages. But in general terms, these are phenyl-propane dimers, the units of which are interconnected by bonds between the middle carbons of the side-units. The structural diversity of lignans is due to the nature of the bond between monomeric molecules (“head to tail” or “tail to tail”), the degree of oxidation of y-carbon atoms, etc. In plants, they accumulate in all organs, are dissolved in essential oils, resins, especially often found in the seeds of pine, barberry, Compositae, and aralia.
Lignins are polymers based on the same phenylpropane blocks of coniferyl alcohol with the same method of connecting these blocks to each other, and the formation of the polymer structure is characterized by randomness, i.e. there are different ways of connecting fragments and the fragments themselves are usually not identical. Therefore, it is difficult to study the structure of lignins, and even more so to depict. Usually these are hypothetical structures (Figure 8.1.7). In plants, lignins are important components of the cell wall of supporting and conducting tissues, performing a dual role in this: mechanical strengthening of the tissue and protection of the cell from chemical, physical, and biological influences.
16. The concept of simple phenolic compounds (glycosides), their classification. Physical and chemical properties. Features of preparation, drying, storage of raw materials. Assessment of the quality of raw materials, methods of analysis. Uses of raw materials, medical applications.
Phenolic compounds
Natural phenolic compounds- plant substances containing one or more aromatic rings with one or more free or linked hydroxyl groups.
Phenolic compounds are universally distributed in the plant kingdom. They are characteristic of every plant and even every plant cell. Currently, over two thousand natural phenolic compounds are known. Substances of this group account for up to 2-3% of the mass of organic matter in plants, and in some cases - up to 10% or more. Phenolic compounds are also found in fungi, lichens, and algae. Animals consume phenolic compounds ready-made and can only transform them.
In plants, phenolic compounds play a very important role. They are indispensable participants in all metabolic processes: respiration, photosynthesis, glycolysis, phosphorylation.
1. Research of the Russian scientist-biochemist V.I. Palladin (1912, St. Petersburg) established and confirmed by modern research that phenolic compounds are involved in the process of cellular respiration. Phenolic compounds act as acceptors (carriers) of hydrogen at the final stages of the respiration process, and then are re-oxidized by specific enzymes, oxidases.
2. Phenolic compounds are regulators of plant growth, development and reproduction. In this case, they have both a stimulating and an inhibiting (slowing down) effect.
3. Phenolic compounds are used by plants as an energetic material, perform structural, support and protective functions (increase plant resistance to fungal diseases, have antibiotic and antiviral effects).
Classification of phenolic compounds
The classification of natural phenolic compounds is based on the biogenetic principle. In accordance with modern concepts of biosynthesis and based on the structural features of the carbon skeleton, the following classes of plant phenols can be distinguished.
Physical and chemical properties of simple phenolic compounds
Physical properties.
Simple phenolic compounds are colorless, less often slightly colored, crystalline substances with a certain melting point, optically active. They have a specific smell, sometimes aromatic (thymol, carvacrol). In plants, they are more often found in the form of glycosides, which are readily soluble in water, alcohol, acetone; insoluble in ether, chloroform. Aglycones are slightly soluble in water, but readily soluble in ether, benzene, chloroform, and ethyl acetate. Simple phenols have characteristic UV and visible absorption spectra.
Phenolic acids are crystalline substances, soluble in alcohol, ethyl acetate, ether, aqueous solutions of sodium bicarbonate and acetate.
Gossypol is a fine-crystalline powder from light yellow to dark yellow in color with a greenish tinge, practically insoluble in water, slightly soluble in alcohol, well soluble in lipid phases.
Chemical properties.
The chemical properties of simple phenolic compounds are due to the presence of:
- aromatic ring, phenolic hydroxyl, carboxyl group;
- glycosidic bonds.
Phenolic compounds are characterized by chemical reactions:
1. Hydrolysis reaction(due to the glycosidic bond). Phenolic glycosides are readily hydrolyzed by acids, alkalis or enzymes to aglycone and sugars.
2. Oxidation reaction. Phenolic glycosides are easily oxidized, especially in an alkaline environment (even with atmospheric oxygen), forming quinoid compounds.
3. Salting reaction. Phenolic compounds, possessing acidic properties, form water-soluble phenolates with alkalis.
4. Complexation reactions. Phenolic compounds form complexes with metal ions (iron, lead, magnesium, aluminum, molybdenum, copper, nickel), colored in different colors.
5. Azo coupling reaction with diazonium salts. Phenolic compounds with diazonium salts form orange to cherry red azo dyes.
6. The reaction of the formation of esters (depsides). Depsides form phenolic acids (digalic and trigallic acids).
Features of collection, drying and storage of raw materials containing simple phenolic compounds
The harvesting of raw materials for lingonberry and bearberry is carried out in two periods - in early spring before flowering and in autumn from the beginning of fruit ripening until the appearance of snow cover. Air-shadow or artificial drying at a temperature of no more than 50-60 ° C in a thin layer. Re-harvesting on the same thickets is possible in 5-6 years.
Raw materials of Rhodiola rosea (golden root) are harvested at the end of flowering and fruiting phases. Dried at a temperature of 50-60 ° C. Re-harvesting on the same thickets is possible in 10-15 years.
The raw material of male foxwort (Rhizomata Filicismaris) is harvested in autumn, do not wash, dry in the shade or in dryers at a temperature not exceeding 40 ° C. Re-harvesting on the same thickets is possible in 20 years.
The raw material of cotton - root bark (Cortexradicum Gossypii) - is harvested after the cotton harvest.
Store raw materials according to the general list in a dry, well-ventilated area. Shelf life is 3 years. Male fern rhizomes are stored for 1 year.
Evaluation of the quality of raw materials containing simple phenolic compounds. Analysis methods
The qualitative and quantitative analysis of raw materials is based on physical and chemical properties.
Qualitative analysis.
Phenolic compounds are extracted from plant materials with water. Aqueous extracts are purified from accompanying substances by precipitating them with a solution of lead acetate. Qualitative reactions are performed with the purified extract.
Phenologlycosides, which have free phenolic hydroxyl, give all reactions characteristic of phenols (with salts of iron, aluminum, molybdenum, etc.).
Specific reactions (GF XI):
- for arbutin (raw lingonberry and bearberry):
a) with crystalline ferrous sulfate. The reaction is based on obtaining a complex that changes its color from lilac to dark violet, with the further formation of a dark violet precipitate.
b) with a 10% solution of sodium phosphoromolybdic acid in hydrochloric acid. The reaction is based on the formation of a blue complex compound.
- for salidroside (raw material of Rhodiola rosea):
a) azo coupling reaction with diazotized sodium sulfacyl with the formation of a cherry red azo dye
Chromatographic study:
Various types of chromatography are used (paper, thin-layer, etc.). In chromatographic analysis, solvent systems are usually used:
- n-butanol-acetic acid-water (BUV 4: 1: 2; 4: 1: 5);
- chloroform-methanol-water (26: 14: 3);
- 15% acetic acid.
Chromatographic study of alcoholic extraction from raw materials of Rhodiola rosea.
Thin layer chromatography is used. The sample is based on the separation in a thin layer of silica gel (Silufol plates) of methanol extraction from raw materials in a solvent system chloroform-methanol-water (26: 14: 3) with subsequent development of the chromatogram with sodium diazotized sulfacyl. The salidroside spot with Rf = 0.42 turns reddish.
Quantitation.
For the quantitative determination of phenological glycosides in medicinal plant raw materials, various methods are used: gravimetric, titrimetric and physicochemical.
1. Gravimetric method determine the content of phloroglucides in the rhizomes of the male fern. The method is based on the extraction of phloroglucides from raw materials with diethyl ether in a Soxhlet apparatus. The extract is purified, ether is distilled off, the resulting dry residue is dried and brought to constant weight. In terms of absolutely dry raw materials, the content of phloroglucides should be at least 1.8%.
2. Titrimetric iodometric method used to determine the content of arbutin in raw lingonberry and bearberry. The method is based on the oxidation of aglycone hydroquinone to quinone with 0.1 M iodine solution in an acidic medium and in the presence of sodium bicarbonate after obtaining a purified aqueous extract and carrying out acid hydrolysis of arbutin. Hydrolysis is carried out with sulfuric acid concentrated in the presence of zinc dust so that the liberated free hydrogen prevents its own oxidation of hydroquinone. A starch solution is used as an indicator.
3. Spectrophotometric method used to determine the content of salidroside in raw materials of Rhodiola rosea. The method is based on the ability of colored azo dyes to absorb monochromatic light at a wavelength of 486 nm. Determine the optical density of the colored solution obtained by the reaction of salidroside with diazotized sodium sulfacyl using a spectrophotometer. The content of salidroside is calculated taking into account the specific absorption rate of the GSO of salidroside E 1% 1 cm = 253.
Ways of using raw materials containing simple phenolic compounds
Raw materials of lingonberry, bearberry, Rhodiola rosea are released from the pharmacy without a doctor's prescription - order of the Ministry of Health and Social Development of the Russian Federation No. 578 of 13.09.2005 - as medicines. Rhizomes of male fern, rhizomes and roots of Rhodiola rosea, bark of cotton roots are used as raw materials for obtaining finished medicines.
From medicinal plant materials containing phenologlycosides, get:
1. Extemporal dosage forms:
- decoctions (raw lingonberry, bearberry, Rhodiola rosea);
- fees (raw lingonberry, bearberry, Rhodiola rosea).
2. Extraction (galenic) preparations:
Extracts:
- liquid extract (rhizomes and roots of Rhodiola rosea);
- thick ethereal extract (male fern rhizomes).
3. Novogalenic drugs:
- "Rodascon" from Rhodiola rosea raw materials.
4. Preparations of individual substances:
Gossypol 3% liniment and eye drops - 0.1% gossypol solution in 0.07% sodium tetraborate solution (bark of cotton roots).
Medical use of raw materials and preparations containing simple phenolic compounds
1. Antimicrobial, anti-inflammatory, diuretic (diuretic) the action is typical for raw lingonberry and bearberry. It is due to the presence of arbutin in the raw material, which, under the influence of enzymes of the gastrointestinal tract, is split into hydroquinone and glucose. Hydroquinone, excreted in the urine, has an antimicrobial and irritant effect on the kidneys, which causes a diuretic effect and anti-inflammatory effect. The anti-inflammatory effect is also due to the presence of tannins.
Dosage forms from raw lingonberry and bearberry are used to treat inflammatory diseases of the kidneys, bladder (cystitis, urethritis, pyelitis) and urinary tract. Decoctions of lingonberry leaves are used to treat diseases associated with a violation of mineral metabolism: urolithiasis, rheumatism, gout, osteochondrosis.
Side effect: when taking large doses, an exacerbation of inflammatory processes, nausea, vomiting, diarrhea is possible. In this regard, it is recommended to take dosage forms from raw lingonberry and bearberry in combination with other plants.
2. Antiviral the action is characteristic of phenolic compounds of the bark of cotton roots. "Gossypol" is used in the treatment of herpes zoster, herpes simplex, psoriasis (liniment); with herpetic keratitis (eye drops).
3. Adaptogenic, stimulating and tonic the effect is exerted by preparations of rhizomes and roots of Rhodiola rosea. The drugs increase efficiency during fatigue, hard physical work, and have an activating effect on the cerebral cortex. Phenolic compounds of rhodiola are able to inhibit lipid peroxidation, increasing the body's resistance to extreme stress, thereby exhibiting an adaptogenic effect. Used to treat patients with neuroses, hypotension, vegetative-vascular dystonia, schizophrenia.
Contraindications: hypertension, fever, agitation. Do not appoint in the summer in hot weather and in the afternoon.
Contraindications: disorders of the circulatory system, diseases of the gastrointestinal tract, liver, kidneys, pregnancy, not prescribed to children under two years of age.
PHENOLIC COMPOUNDS are aromatic substances that contain one or more hydroxyl groups bonded to the carbon atoms of the aromatic nucleus. Among the products of secondary origin
Phenolic compounds are the most common and characteristic of every plant and even every plant cell. By the number of OH groups, monoatomic (for example, phenol itself), diatomic (pyrocatechol, resorcinol, hydroquinone) and polyatomic (pyrogallol, phloroglucinol, etc.) phenolic compounds are distinguished.
Phenolic compounds can be in the form of monomers, dimers, oligomers and polymers; the biogenetic principle is the basis for the classification of natural phenols. In accordance with modern concepts of biosynthesis, they can be divided into several main groups:
- compounds of the C 6-row - simple phenols;
- compounds C 6 - C 1 -series - derivatives of benzoic acid (phenolic acids);
- compounds C 6 - C 2 - phenol alcohols and phenylacetic acids;
- compounds C 6 - C 3 - derivatives of phenylpropane (hydroxycinnamic acids and alcohols, coumarins);
- compounds C 6 - C 3 - C 6 - flavonoids and isoflavonoids;
- compounds C 6 - C 3 - C 3 - C 6 -series - lignans;
- derivatives of anthracene;
- polymeric phenolic compounds - lignin, tannins, melanins.
Phenolic compounds are colorless or colored crystals or amorphous substances with a characteristic odor, less often liquids, readily soluble in organic solvents (alcohol, ether, chloroform, ethyl acetate) or in water. Possessing acidic properties, they form salt-like products with alkalis - phenolates. The most important property of phenolic compounds is their ability to oxidize with the formation of quinone forms. Polyphenols are especially easily oxidized in an alkaline environment under the influence of atmospheric oxygen. Phenols are capable of producing colored complexes with heavy metal ions, which is typical for o-dioxy derivatives. Phenolic compounds enter into coupling reactions with diazonium compounds. In this case, products with various colors are formed, which is often used in analytical practice. In addition to the qualitative reactions common to all phenols, there are specific group reactions.
In plants, phenolic compounds play an important role in some intermediate stages of the respiration process. Taking part in redox reactions, they serve as a link between the hydrogen of the respiratory substrate and the oxygen of the atmosphere. It was found that some phenolic compounds play an important role in photosynthesis as cofactors. They are used by plants as an energetic material for a variety of vital processes, are regulators of growth, development and reproduction, while exerting both a stimulating and an inhibitory effect. The antioxidant activity of many phenols is known; they are increasingly used in the food industry to stabilize fats.
Preparations based on phenolic compounds are used as antimicrobial, anti-inflammatory, choleretic, diuretic, antihypertensive, tonic, astringent and laxative agents.
Other definitions for the letter "F":
Phenolic compounds are substances containing aromatic rings with a hydroxyl group, as well as their functional derivatives. Phenolic compounds with more than one hydroxyl group in the aromatic ring are called polyphenols.
Classification of phenolic compounds
The classification of phenolic compounds is based on the main carbon skeleton - the number of aromatic rings and carbon atoms in the side chain. On these grounds, phenolic compounds are subdivided into groups: simple phenols; phenolic acids; phenolic alcohols, phenylacetic acids, acetophenols; hydroxycinnamic acids, coumarins, chromones; lignans; flavonoids; tannins.
Properties
Phenolic compounds are colored or colorless substances with a characteristic odor, solid, crystalline or amorphous, less often liquid. As a rule, they are highly soluble in ethyl alcohol, diethyl ether, chloroform, less often in water. They have acidic properties, form phenolates with alkalis.
The most important property of phenolic compounds is the ability to oxidize with the formation of forms such as quinones. Polyphenols are especially easily oxidized by atmospheric oxygen in an alkaline medium. Complexes of phenols with heavy metal ions are brightly colored. This property of phenol is widely used to determine their qualitative content in solutions.
The biological role of phenols in plants is diverse. Redox reactions in the process of respiration and photosynthesis take place with the obligatory participation of phenolic compounds, which are components of the respiratory chain.
Many phenolic compounds are activators and inhibitors of plant growth and development. Known antioxidant activity of many phenols used in the food industry as antioxidants.
Polyphenolic compounds significantly affect the quality and nutritional value of fruits, berries, vegetables. The change in polyphenols in plant raw materials under the influence of technological influence during canning is one of the main reasons for the change or even loss of color, aroma, and taste characteristic of the original fresh raw material in fruits and vegetables.
Violation of the integrity of cells of tissues of fruits and vegetables and the resulting darkening, the development of oxidative processes when heating canned raw materials is largely the result of measuring the chemical structure of polyphenolic compounds.
Alkaloids
Alkaloids are complex nitrogen-containing organic compounds of a basic nature with a strong physiological effect on the body. Their chemical structure is very diverse and complex. Alkaloids are found in the form of salts with organic acids - oxalic, malic, citric in a dissolved state in the cell sap. They accumulate in all parts of plants, but more often they predominate in only one organ, for example, in tea leaves, in celandine herb, Indian dope fruits, in the rhizome of scopolia, and cinchona bark. Most plants contain not one, but several alkaloids in their composition. Thus, over 30 different alkaloids are found in ergot, and about 50 in rauwolfia serpentine. Most often, one or 2-3 alkaloids quantitatively predominate in one plant, while others are contained in smaller quantities.
Alkaloids- These are natural nitrogen-containing organic compounds of a basic nature, which have a complex composition and have a strong specific effect. Most of them belong to compounds with a heterocyclic nitrogen atom in the ring, less often nitrogen is in the side chain. Synthesized mainly by plants.
In translation, the term "alkaloid" (from Arabic "alkali" - alkali and Greek "eidos" - similar) means alkali-like. Like alkalis, alkaloids form salts with acids.
Spreading.
Distributed unevenly in the plant kingdom. There are few of them in the lower plants. They are found in the Lamb family (Lamb-baranets). They are rare in cereals and sedge plants. Plants of the families of poppy, solanaceous, lily, madder, celery, amaryllis, legumes, buttercups are richest in alkaloids. In plants, alkaloids are dissolved in the cell sap. The content ranges from thousandths of a percent to several percent, and in the bark of the cinchona tree from 15 to 20%.
Phenols are compounds whose molecules contain an aromatic (benzene) ring bonded to one or more -OH groups. A high content of phenols is characteristic of plant cells.
In the animal body, benzene rings are not synthesized, but can only be transformed, so they must constantly enter the body with food. However, many phenolic compounds in animal tissues perform important functions (ubiquinone, adrenaline, thyroxine, serotonin, etc.).
Currently, several thousand different phenolic compounds have already been found in plants. They are classified according to the structure of the carbon skeleton:
1.C 6 -phenols
2.C 6 -C 1 -phenolic acids
3.C 6 -C 3 -hydroxycinnamic acids and coumarins
4.C 6 -C 3 -C 6 -flavonoids
5. Oligomeric phenolic compounds.
6. Polymer phenolic compounds.
C 6 -Phenols. Compounds whose benzene ring is linked to several hydroxyl groups are called polyphenols.
Free phenols in plants are rare and in small quantities. Thus, phenol was found in pine needles and cones, in blackcurrant essential oil, pyrocatechin - in onion scales, in berry leaves, hydroquinone - in pear bark and leaves, and berry leaves. Derivatives of phenols are more common, where they are linked to some kind of carbon chain or cycle. For example, urushiol and tetrahydrocannabinol.
Urushiol is a toxic substance from sumac leaves. Tetrahydrocannabinol is the hallucinogenic origin of cannabis.
When phenols are oxidized, quinones (benzoquinones) are formed. In the free state, quinones are not found in plants, but their derivatives are widespread. For example, derivatives of benzoquinones are electron carriers in the ETC of photosynthesis and respiration - plastoquinone and ubiquinone. Derivatives of benzoquinone also include the burning substance of primrose - primin and the red pigment of the fly agaric - muscarufin.
C 6 -C 1 -phenolic acids. Phenolic acids are common in plants. They are more often found in tissues in a bound state and are released during excretion and hydrolysis.
Salicylic acid is released as an allelopathic agent into the environment. In addition, it has now been found to have a regulatory effect on a number of physiological and biochemical processes in a plant (formation of ethylene, reduction of nitrates, etc.).
Protocatechuic acid is found in onion scales.
Vanilla and gallic acids are found in wood. The latter is a part of some tannins and can form dimers - digalic acid, in the molecule of which 2 gallic acid residues are connected by an ester bond.
Found in plants derivatives of phenolic acids - aldehydes and alcohols. For example, salicylic alcohol is present in the bark of willow. But vanillin is especially famous - vanilla aldehyde. It has a very pleasant smell and in the form of a glycoside - glucovanillin is found in the fruits and branches of the vanilla tree. Glycoside and vanillin itself are widely used in the confectionery, soap and perfume industries.
Phenolic acids can bind with ester bonds with sugars, more often with glucose. Glycogallin has been isolated from a number of plants (rhubarb, eucalyptus), in which the carboxyl group of gallic acid is linked to the glycosidic hydroxyl of glucose.
C 6 -C 3 -hydroxycinnamic acids and coumarins. Hydroxycinnamic acids are widespread in plants. Usually they are in a tied state, and in a free state, except for coffee, they are rare.
It was shown that the cis-isomers of hydroxycinnamic acids are activators of plant growth processes, while the trans-isomers do not possess such properties.
In plants, hydroxycinnamic alcohols are found - derivatives of the corresponding acids: coumaric - coumaric alcohol, ferulic - coniferyl alcohol, sinapic - synapic alcohol. Alcohols usually do not accumulate, but, obviously, are used to form lignin, of which they are monomers.
Hydroxycinnamic acids can form esters with organic acids of the aliphatic series. So, caffeic acid forms esters with malic and tartaric acids. The first ester is called phaseolinic acid. It is found in bean leaves. The second is chicoric acid. It is found in chicory leaves.
Esters of hydroxycinnamic acids and sugars, more often glucose, are widespread in plants. So, in the flowers of petunia and snapdragon, esters of coffee, coumaric, ferulic acids were found, and in cereals in general, most hydroxycinnamic acids are represented by esters. In addition, hydroxycinnamic acids are found in polysaccharides and proteins. For example, ferulic acid is found in wheat flour xylans and pineapple polysaccharides.
Coumarins are lactones that are formed when the ring closes between the hydroxyl and carboxyl groups in the hydroxycinnamic acid molecule.
Coumarin is a colorless crystalline substance with a pleasant smell of freshly cut hay. Free coumarin is not found in plants. It is usually found in the form of glycosides (flowers and leaves of sweet clover). In herbaceous plants, the cell sap contains a glycoside containing ortho-coumaric acid. During haymaking, plant tissues are damaged, membrane permeability is impaired. Glycosides from cell sap come into contact with cytoplasmic enzymes. Sugars are cleaved from glycosides, and coumaric acid, after trans-cis-isomerization, is closed into lactone-coumarin. In this case, the wilting grass acquires the smell of hay.
In plants, hydroxylated coumarins are often found in the composition of glycosides. For example, esculetin from the horse chestnut pericarp and scopoletin from the roots of Japanese scopolia. Both of these coumarins have P-vitamin activity and are used in medicine as capillary-strengthening agents.
Dicumarin was found in white melilot, which prevents blood clotting. This and other dicoumarins are used as drugs to prevent blood clots.
C 6 -C 3 -C 6 -flavonoids... It is one of the most diverse and widespread groups of phenolic compounds. The structure of flavonoid molecules is based on the structure of flavan, which consists of two benzene rings and one heterocyclic (pyran) ring.
Flavonoids are divided into several groups.
1. Catechins.
2. Anthocyanins.
3. Chalcones.
Catechins- the most reduced flavonoids. They do not form glycosides. Catechin was first isolated from Acacia catechu wood, hence its name. Catechins have been found in over 200 plant species. Among the catechins, the best known are catechin and gallocatechin.
They can form esters with gallic acid - catechin gallates and gallocatechin gallates. Catechins are found in many fruits (apples, pears, quince, cherries, plums, apricots, strawberries, blackberries, currants, lingonberries, grapes), in cocoa beans, coffee beans, in the bark and wood of many trees (willow, oak, pine, fir , cedar, cypress, acacia, eucalyptus). There are especially many catechins in the leaves and young shoots of tea (up to 30%). Oxidative transformations of catechins play an important role in tea production and winemaking. The oxidation products, which are mainly catechin dimers, have a pleasant, slightly astringent taste and a golden brown color. This determines the color and taste of the final product. At the same time, catechins have high P-vitamin activity, strengthen capillaries and normalize the permeability of the vascular walls. Dimers of catechins in tea have the same activity. Catechins are monomers in condensed tannins.
Anthocyanins- the most important plant pigments. They color the petals of flowers, fruits, and sometimes leaves in blue, blue, pink, red, purple colors with various shades and transitions. All anthocyanins are glycosides. Their aglycones are anthocyanidins. Anthocyanins are water soluble and are found in the cell sap.
More than 20 anthocyanidins are currently known, but 4 are the most widespread: pelargonidin, cyanidin, delphinidin, and malvidin (a methylated derivative of delphinidin).
As monosaccharides in anthocyanins, glucose, galactose, rhamnose, xylose, less often arabinose are found, and as disaccharides - most often rutinose, sophorosis, sambubiose. Sometimes anthocyanins contain trisaccharides, usually branched. For example, in berries of currants and raspberries, anthocyanins are found, in which a branched trisaccharide is associated with cyanidin.
The coloration of anthocyanins depends on a number of factors:
1. the concentration of anthocyanins in the cell sap;
2. pH of cell sap;
3. complexation of anthocyanins with cations;
4. copigmentation - a mixture of anthocyanins and the presence of other phenolic substances in the cell sap;
5. Combinations with coloring of plastid pigments.
Let's consider these factors in more detail.
1. The concentration of anthocyanins in the cell sap can vary over a wide range - from 0.01 to 15%. For example, an ordinary blue cornflower contains 0.05% cyanine anthocyanin, and dark purple its 13-14%.
2. Due to the fact that there is free valence in anthocyanin molecules, the color can change depending on the pH value. Usually, in an acidic medium, anthocyanins have a red color of varying intensity and shades, and in an alkaline medium, they are blue. Such changes in the color of anthocyanins can be observed by adding acid or alkali to the colored juice of currant, cherry, beetroot or red cabbage. In nature, sharp changes in the pH of the cell sap do not occur, and this factor does not play a large role in the color of anthocyanins. You can only notice that some pink and red flowers turn blue when wilted. This indicates a change in pH in dying cells.
3. Of great importance in the color of flowers and fruits is the ability of anthocyanins to chelate with metal ions. This is clearly seen in the example of cornflower and rose. Their petals contain the same anthocyanin - cyanine. In the petals of blue cornflower, cyanine forms a complex with Fe ions (4 cyanine molecules are linked to one Fe atom). Free cyanine is present in the petals of red roses. Another example. If an ordinary hydrangea with pink flowers is grown in a mineral medium containing aluminum and molybdenum, then the flowers become blue in color.
4. Usually in the cell sap of many flowers and fruits there is not one, but several pigments. In this case, the color depends on their mixture, and it is called copigmentation. So, the color of blueberry fruits is due to the copigmentation of dolphinin and malvin. There are 10 different anthocyanins found in purple potato flowers.
The color pattern of the petals of many flowers is determined either by a local increase in the concentration of one pigment (foxglove), or by the superposition of an additional pigment on the main one (a high concentration of cyanine is superimposed in the center of the poppy flowers against the general background of pelargonin).
The color is also influenced by the copigmentation of anthocyanins with other substances, for example, with tannins. So, purple and dark red roses contain the same cyanine, but in dark red roses it is copigmented with a lot of tannin.
5. Combination of blue anthocyanins of cell sap and yellow-orange carotenoids of chromoplasts results in brown color of petals of some flowers.
Tab. Some plant anthocyanins
Chalcones, or anthochlores, are flavonoids with an open heterocycle. They give the flower petals a yellow color. Their distribution is limited to nine families. They are found in the form of glycosides. Chalcones, for example, are isosalipurposide from yellow carnation flowers, Floridzin from apple bark and leaves. Floridzin is an apple tree growth inhibitor. When ingested by humans, it causes a one-time intense release of glucose into the blood - "phloridzin diabetes".
Oligomeric phenolic compounds. This includes lichen acids. They are formed in lichens from two or more residues of orsellic acid. Lekanoric and evernic acids are composed of two residues of orsellic acid. Evernic acid is the main component of the evernia acid complex ("oakmoss"), which is used in perfumery as a fragrant substance and at the same time as a fixative in the manufacture of the best sorts of perfumes.
Among lichen acids, there are colored ones. They give a varied color to lichens - yellow, orange, red, purple. Lichen contains usnic acid, which is an effective bactericidal agent.
Dimers of hydroxycinnamic alcohols are found in the bark, wood, fruits and leaves of many plants. Form oligomers and flavonoids, especially catechins. Catechin dimers are found in apples, chestnuts, hawthorns, cocoa beans, and eucalyptus wood.
Polymeric phenolic compounds. Polymeric phenolic compounds include tannins, or tannins, lignins and melanins.
Tannins, or tannins. They got their name due to the ability to tan the skin of animals, turning it into leather. Tanning is based on the interaction of tannins with the skin protein collagen. In this case, numerous hydrogen bonds are formed between the protein and tannin.
Natural tannins are a complex mixture of similar compounds with a molecular weight of 500-5000.
Many tannins are found in the bark and wood of oak, eucalyptus, chestnut wood, in the rhizome of sorrel, rhubarb, and sumac leaves. There are many of them in the bark and wood of legumes, myrtle, pink. Galls, which are formed on leaves when damaged by nut-working (up to 50-70%), are distinguished by a particularly high content of tannins.
Tanning (more often food tanning) is also called lower molecular weight substances that have a pleasant astringent taste, but are not capable of real tanning. They are present in many fruits (quince, apples, persimmons, grapes), in tea leaves.
Tannins are widely used not only in the leather industry. They are used in the production of plastics, binders in the manufacture of plywood and sawdust boards, as a stain for dyeing. They are used in installations for boiling water as stabilizers of colloids, for adjusting the viscosity of solutions when drilling wells.
The use of tannins in winemaking is associated with their inhibitory effect on enzymes and microorganisms, which prevents clouding of wines and improves their quality. Tea tannin is used to stabilize betacyanin, a food red color obtained from beetroot.
In medicine, tannins are used as astringent, bactericidal, antiradiation and antineoplastic agents.
Lignin is a part of the cell walls of wood tissues. It is deposited between cellulose microfibrils, which gives the cell walls hardness and strength. However, in this case, the communication between cells is disrupted, which leads to the death of living contents; therefore, lignification is the final stage of cell ontogenesis.
Lignin is an amorphous substance, insoluble in water, organic solvents, and even concentrated acid.
Lignin has another important property: it is resistant to microorganisms. Only a few microorganisms, and then very slowly, decompose it.
Lignin is a three-dimensional polymer, the monomers of which are hydroxycinnamic alcohols. Thus, in conifers, lignin is dominated by coniferyl alcohol, in cereals - coumaric, in many deciduous trees - synap.
The pulp and paper industry and hydrolysis plants accumulate large amounts of lignin as waste. It is used to produce activated carbon, plastics, and synthetic resins.
Melanins- polymers of phenolic nature, which are a product of tyrosine oxidation. Their structure has not yet been fully elucidated.
Melanins are black or brown-black in color. Their formation is explained by the rapid darkening of the surface of the cut apple, potato tuber, and some mushrooms. Melanins are also present in animal organisms, causing the color of the coat and hair. However, plant and animal melanins differ in monomer composition. During hydrolysis, plant melanins form pyrocatechol, and animals form dihydroxyindole. In other words, plant melanins, unlike animals, are nitrogen-free substances.
Functions of phenolic compounds in a plant. 1. Phenols are involved in redox processes: phenols are converted into quinones and vice versa with the participation of the enzyme polyphenol oxidase. In this case, along the way, various compounds (amino acids, organic acids, phenols, cytochromes, etc.) can be oxidized in a non-enzymatic way.
2. Some phenolic compounds are carriers of electrons and protons in the ETC of photosynthesis and respiration (plastoquinone, ubiquinone).
3. A number of phenols have an effect on the growth processes of plants, sometimes activating, more often inhibiting. This influence is mediated by the action on phytohormones. Thus, it is known that some phenolic compounds are necessary for the synthesis of auxin, while others are necessary for its decomposition. For the formation of ethylene, the presence of an ester of coumaric acid is necessary. It was found that under stress, plants accumulate a large amount of phenols, which leads to inhibition of growth processes and an increase in their resistance to unfavorable conditions.
4. Phenols have a protective function in plants: Phenolic compounds give plants resistance to diseases. For example, resistance to a number of diseases of onions with colored husks is associated with the presence of protocatechuic acid in it. In case of mechanical damage to plant tissues, phenols accumulate in the cells and, condensing, form a protective layer. Some plants, in response to infection by pathogenic fungi, form protective substances - phytoalexins, many of which are phenolic in nature.
5. Many phenols are antioxidants and protect membrane lipids from oxidative degradation. Some of them are used in the food industry to prevent fats from going rancid (gallic acid esters, flavonoids, etc.).
6. The role of phenolic compounds in the process of plant reproduction is very important. This is not only associated with the color of flowers and fruits, but also with the direct participation of phenols in fertilization. So, in the process of fertilization of the algae Chlamydomonas and the higher plant forsythia, flavonoids take part.
7. Phenols can act as allelopathic substances in some plants. For example, salicylic acid can be such a substance in oak.
8. Some phenols act as activators or inhibitors of certain processes and enzymes (cell division, protein synthesis, oxidative phosphrilation, etc.).
Loading ...