disaccharides and polysaccharides. Chemical properties of disaccharides
Carbohydrates for diabetes
Sugars (saccharides, carbohydrates) are common in nature organic compounds. They are derivatives polyhydric alcohols. According to the size and structure of the molecules, they are divided into two groups: simple sugars (monosaccharides) and complex (these include disaccharides and polysaccharides).
By the presence of characteristic functional groups, in addition to polyatomic (hydroxyl) groups, which are part of all saccharides, they are distinguished: aldoses - having aldehyde groups, and - having ketone groups.
More about various types carbohydrates, read below in the articles I have collected on this topic.
Carbohydrates are organic compounds, most often of natural origin, consisting only of carbon, hydrogen and oxygen. Carbohydrates play a huge role in the life of all living organisms. This class of organic compounds got its name because the first carbohydrates studied by man had a general formula of the form Cx(H2O)y.
Those. they were conditionally considered compounds of carbon and water. However, later it turned out that the composition of some carbohydrates deviates from this formula. For example, a carbohydrate such as deoxyribose has the formula C5H10O4. At the same time, there are some compounds that formally correspond to the formula Cx(H2O)y, but are not related to carbohydrates, such as formaldehyde (CH2O) and acetic acid (C2H4O2).
Nevertheless, the term "carbohydrates" has historically been assigned to this class of compounds, and therefore is widely used in our time.
Classification of carbohydrates
Depending on the ability of carbohydrates to break down during hydrolysis into other carbohydrates with a lower molecular weight, they are divided into simple (monosaccharides) and complex (disaccharides, oligosaccharides, polysaccharides). As you might guess, from simple carbohydrates, i.e. monosaccharides, carbohydrates with an even lower molecular weight cannot be obtained by hydrolysis.
Hydrolysis of one disaccharide molecule produces two monosaccharide molecules, and complete hydrolysis of one molecule of any polysaccharide produces many monosaccharide molecules.
Chemical properties of monosaccharides on the example of glucose and fructose
As you can see, both in the glucose molecule and in the molecule there are 5 hydroxyl groups, and therefore they can be considered polyhydric alcohols. The glucose molecule contains an aldehyde group, i.e. in fact, glucose is a polyhydric aldehyde alcohol. In the case of fructose, a ketone group can be found in its molecule, i.e. fructose is a polyhydric ketoalcohol.
Chemical properties of glucose and fructose as carbonyl compounds
All monosaccharides can react in the presence of hydrogen catalysts. In this case, the carbonyl group is reduced to an alcohol hydroxyl group. The glucose molecule contains an aldehyde group in its composition, and therefore it is logical to assume that its aqueous solutions give qualitative reactions to aldehydes.
Attention!
Indeed, when an aqueous solution of glucose is heated with freshly precipitated copper (II) hydroxide, just as in the case of any other aldehyde, a brick-red precipitate of copper (I) oxide is observed from the solution. In this case, the aldehyde group of glucose is oxidized to carboxylic acid - gluconic acid is formed. Glucose also enters into the “silver mirror” reaction when it is exposed to an ammonia solution of silver oxide.
However, unlike the previous reaction, instead of gluconic acid, its salt is formed - ammonium gluconate, because. dissolved ammonia is present in the solution. Fructose and other monosaccharides, which are polyhydric ketoalcohols, do not enter into qualitative reactions to aldehydes.
Chemical properties of glucose and fructose as polyhydric alcohols
Since monosaccharides, including glucose and fructose, have several hydroxyl groups in their molecules. All of them give a qualitative reaction to polyhydric alcohols. In particular, freshly precipitated copper (II) hydroxide dissolves in aqueous solutions of monosaccharides. In this case, instead of a blue precipitate of Cu(OH)2, a dark blue solution of complex copper compounds is formed.
Disaccharides. Chemical properties
Disaccharides are called carbohydrates, the molecules of which consist of two monosaccharide residues linked together by the condensation of two hemiacetal hydroxyls or one alcohol hydroxyl and one hemiacetal. The bonds formed in this way between monosaccharide residues are called glycosidic bonds. The formula for most disaccharides can be written as C12H22O11.
The most common disaccharide is the familiar sugar, called sucrose by chemists. The molecule of this carbohydrate is formed by cyclic residues of one molecule of glucose and one molecule of fructose. The bond between the disaccharide residues in this case is realized due to the elimination of water from two hemiacetal hydroxyls.
Since the bond between monosaccharide residues is formed by the condensation of two acetal hydroxyls, it is impossible for a sugar molecule to open any of the cycles, i.e. transition to the carbonyl form is impossible. In this regard, sucrose is not able to give qualitative reactions to aldehydes.
Disaccharides of this kind, which do not give a qualitative reaction to aldehydes, are called non-reducing sugars. However, there are disaccharides that give qualitative reactions to the aldehyde group. This situation is possible when the hemiacetal hydroxyl from the aldehyde group of one of the initial monosaccharide molecules remains in the disaccharide molecule.
In particular, maltose reacts with an ammonia solution of silver oxide, as well as copper (II) hydroxide, like aldehydes.
Disaccharides as polyhydric alcohols
Disaccharides, being polyhydric alcohols, give the corresponding qualitative reaction with copper (II) hydroxide, i.e. when their aqueous solution is added to freshly precipitated copper(II) hydroxide, the water-insoluble blue precipitate of Cu(OH)2 dissolves to form a dark blue solution.
Polysaccharides. starch and cellulose
Polysaccharides are complex carbohydrates, the molecules of which consist of a large number of monosaccharide residues linked by glycosidic bonds. There is another definition of polysaccharides. Polysaccharides are called complex carbohydrates, the molecules of which are formed during complete hydrolysis big number monosaccharide molecules.
In general, the formula of polysaccharides can be written as (C6H11O5)n. Starch is a substance that is a white amorphous powder, insoluble in cold water and partially soluble in hot to form a colloidal solution, called starch paste in everyday life.
Starch is formed from carbon dioxide and water during photosynthesis in the green parts of plants under the influence of the energy of sunlight. The largest amounts of starch are found in potato tubers, wheat, rice and corn grains. For this reason, these sources of starch are the raw material for its production in industry.
Cellulose is a substance in its pure state, which is a white powder, insoluble neither in cold nor in hot water. Unlike starch, cellulose does not form a paste. Almost pure cellulose consists of filter paper, cotton wool, poplar fluff.
Both starch and cellulose are plant products. However, the roles they play in plant life are different. Cellulose is mainly a building material, in particular, it is mainly formed by the shells of plant cells. Starch, on the other hand, carries mainly a storage, energy function.
Source: https://scienceforyou.ru/teorija-dlja-podgotovki-k-egje/uglevody
Types of carbohydrates
There are three main types of carbohydrates:
- Simple (fast) carbohydrates or sugars: mono- and disaccharides
- Complex (slow) carbohydrates: oligo- and polysaccharides
- Indigestible, or fibrous, carbohydrates are defined as dietary fiber.
Sahara
There are two types of sugars:
- monosaccharides - monosaccharides contain one sugar group, such as glucose, fructose or galactose.
- disaccharides - disaccharides are formed by the residues of two monosaccharides and are represented, in particular, by sucrose (common table sugar) and lactose.
Complex carbohydrates
Polysaccharides are carbohydrates containing three or more simple carbohydrate molecules. TO this species carbohydrates include, in particular, dextrins, starches, glycogens and celluloses. Sources of polysaccharides are cereals, legumes, potatoes and other vegetables.
Source: http://sportwiki.to/%D0%92%D0%B8%D0%B4%D1%8B_%D1%83%D0%B3%D0%BB%D0%B5%D0%B2%D0%BE %D0%B4%D0%BE%D0%B2
Carbohydrates, monosaccharides, polysaccharides, maltose, glucose, fructose
Carbohydrates
Carbohydrates are an extensive group of organic compounds that play an important role in the life of the body. Carbohydrates are distributed mainly in flora. The human body requires 400-500 g of carbohydrates per day (including at least 80 g of sugars). They are an important source of energy.
The digestibility of carbohydrates contained in fruits is 90%; in and dairy products - 98; in table sugar - 99%. Examples of carbohydrates are glucose (C6H2O6), or grape sugar, so named because of its high content in; cane or beet sugar (С6Н22011); starch and cellulose (C6H10O5).
These substances are made up of carbon, hydrogen and oxygen. Moreover, the ratio of the last two elements is the same as in water, i.e., there is one oxygen atom for two hydrogen atoms. Thus, carbohydrates are, as it were, built from carbon and water, hence their name. Carbohydrates are divided into monosaccharides (such as glucose) and polysaccharides.
Polysaccharides, in turn, are divided into low molecular weight, or oligosaccharides (their representative is beet sugar), and high molecular weight, such as collapse - small and cellulose. Polysaccharide molecules are built from the remains of monosaccharide molecules and are broken down into simpler carbohydrates during hydrolysis.
Monosaccharides
Of the monosaccharides, glucose, fructose, galactose, etc. are of the greatest importance for the human body. All of them crystalline substances, soluble in water. Glucose in the free state is common in the fruits of many plants. In a bound state, it is found in plants in the form of polysaccharides (sucrose, maltose, starch, dextrin, cellulose, etc.). In industry, glucose is obtained from starch.
Anhydrous glucose melts at a temperature of 146 C, it is highly soluble in water. Glucose is about 2 times less sweet than sucrose. Under the action of strong oxidizing agents on glucose, sugar acid is formed. When restored, it passes into a six-atomic alcohol -.
Attention!
There are three types of carbohydrates:
- monosaccharides;
- disaccharides;
- polysaccharides.
The main monosaccharides are glucose and fructose, consisting of one molecule, due to which these carbohydrates are quickly broken down, instantly entering the bloodstream. Brain cells are “fueled” with energy thanks to glucose: for example, the daily norm of glucose necessary for the brain is 150 g, which is one-fourth of the total amount of this carbohydrate received per day with food.
The peculiarity of simple carbohydrates is that, when they are quickly processed, they do not transform into fats, while complex carbohydrates (if they are consumed excessively) can be deposited in the body in the form of fat. Monosaccharides are present in large quantities in many fruits and vegetables, as well as in honey.
These carbohydrates, which include sucrose, lactose and maltose, cannot be called complex, since they contain residues of two monosaccharides. Disaccharides take longer to digest than monosaccharides.
Interesting fact! Children and adolescents have been shown to respond to increased consumption of carbohydrates found in refined (or refined) foods with what is known as overactive (or hyperactive) behavior. When sequential exclusion eating foods such as sugar, white flour, pasta, and white rice will greatly reduce behavioral problems.
At the same time, it is important to increase consumption fresh vegetables and fruits, legumes, nuts, cheese. Disaccharides are present in dairy products, pasta and products containing refined sugar. Polysaccharide molecules include tens, hundreds, and sometimes thousands of monosaccharides.
Polysaccharides (namely starch, fiber, cellulose, pectin, inulin, chitin and glycogen) most important for the human body for two reasons:
- they are digested and absorbed for a long time (unlike simple carbohydrates);
- contain many useful substances including vitamins, minerals and proteins.
Many polysaccharides are present in plant fibers, as a result of which one meal, based on raw or boiled vegetables, can almost completely satisfy the daily norm of the body in substances that are sources of energy.
Thanks to polysaccharides, firstly, the required level of sugar is maintained, and secondly, the brain is provided with the nourishment it needs, which is manifested by increased concentration of attention, improved memory and increased mental activity. Polysaccharides are found in vegetables, fruits, grains, and animal livers.
The benefits of carbohydrates:
- Stimulation of peristalsis of the gastrointestinal tract.
- Absorption and excretion of toxic substances and cholesterol.
- Security optimal conditions for the functioning of normal intestinal microflora.
- Strengthening immunity.
- Normalization of metabolism.
- Ensuring the full functioning of the liver.
- Ensuring a constant supply of sugar in the blood.
- Prevention of the development of tumors in the stomach and intestines.
- Replenishment of vitamins and minerals.
- Providing energy to the brain, as well as the central nervous system.
- Promoting the production of endorphins, which are called “hormones of joy”.
- Relief of premenstrual syndrome.
Daily requirement of carbohydrates
The need for carbohydrates directly depends on the intensity of mental and physical activity, averaging 300-500 g per day, of which at least 20 percent should be easily digestible carbohydrates. Older people should include no more than 300 g of carbohydrates in their daily diet, while the amount of easily digestible carbohydrates should vary between 15 and 20 percent.
With obesity and other diseases, it is necessary to limit the amount of carbohydrates, and this should be done gradually, which will allow the body to adapt to the changed metabolism without any problems. It is recommended to start the restriction from 200-250 g per day for a week, after which the amount of carbohydrates supplied with food is brought to 100 g per day.
A sharp decrease in carbohydrate intake for a long time (as well as their lack in nutrition) leads to the development of the following disorders:
These phenomena disappear after eating sugar or other sweet foods, but the intake of such products should be dosed, which will protect the body from gaining extra pounds. Harmful to the body and an excess of carbohydrates (especially easily digestible) in the diet, which contributes to an increase in sugar, as a result of which part of the carbohydrates is not used, going to the formation of fat, which provokes the development of atherosclerosis, cardiovascular diseases, flatulence, diabetes mellitus, obesity, and caries.
What foods contain carbohydrates?
From the list of carbohydrates below, everyone can make a completely varied diet (given that this is not a complete list of foods that include carbohydrates). Carbohydrates are found in the following foods:
Only balanced diet provide the body with energy and health. But for this you need to properly organize your diet. And the first step to healthy eating will be a breakfast consisting of complex carbohydrates. So, a portion of whole grain porridge (without dressings, meat and) will provide the body with energy for at least three hours.
In turn, with the use of simple carbohydrates ( we are talking about sweet pastries, various refined products, sweet coffee and tea), we experience an instant feeling of fullness, but at the same time, a sharp rise in blood sugar occurs in the body, followed by a rapid decline, followed by a feeling again.
Why is this happening? The fact is that the pancreas is very much overloaded, because it has to secrete in order to process refined sugars. The result of such an overload is a decrease in sugar levels (sometimes below normal) and the appearance of a feeling of hunger.
In order to avoid these violations, we will consider each carbohydrate separately, determining its benefits and role in providing the body with energy.
20. Reducing disaccharides (maltose, lactose): structure, biochemical transformations (oxidation, reduction).
Reducing disaccharides. In these disaccharides, one of the monosaccharide residues is involved in the formation of a glycosidic bond due to the hydroxyl group, most often at C-4 or C-6, less often at C-3. The disaccharide has a free hemiacetal hydroxyl group, as a result of which the ability to open the ring is retained. The reducing properties of such disaccharides and the mutarotation of their freshly prepared solutions are due to the possibility of cyclo-oxo-tautomerism. Representatives of reducing disaccharides are maltose, cellobiose, lactose.
maltose (trivial name xmal sugar)" - product of enzymatic hydrolysis starch.
In this disaccharide, monosaccharide residues are linked by a glycoside-glycose bond (a-1,4-bond).
Due to the presence of a hemiacetal function in the maltose molecule, the a-anomer is in equilibrium with the p-anomer - p-maltose, 4-0-(a-D-glucopyranosyl)-p-0-glucopyranose. If it is subjected to acid hydrolysis, 2 moles of 0-(+)-glucose are obtained.
In contrast to sucrose, maltose is a reducing glycoside, since its structure contains a hemiacetal fragment. Maltose gives reactions with the Benedict-Fehling reagent and phenylhydrazine.
Maltose is a reducing sugar because it has an unsubstituted hemiacetal hydroxyl group. When maltose is boiled with dilute acid and under the action of the enzyme, maltase is hydrolyzed (two molecules of glucose C6H12O6 are formed).
Maltose contains a free glycosidic hydroxyl near the C-1-carbon atom, therefore it has reducing properties characteristic of reducing mono- and disaccharides. In solutions, maltose can exist in two forms - cyclic and aldehyde, which are in dynamic equilibrium. When maltose is hydrolyzed by the enzyme maltase, two molecules of alpha-D-glucose are formed. When the aldehyde group of maltose is oxidized, maltobionic acid is formed.
Other examples of disaccharides include lactose (milk sugar) - a disaccharide containing a p-D-galactopyranose residue (in a fixed (3-form) and D-glucose and present in the milk of almost all mammals:
Hydrolysis of sucrose in the presence of mineral acids (H 2 SO 4, Hcl, H 2 CO 3):
Oxidation of maltose (reducing disaccharide), such as the "silver mirror" reaction:
21. Non-reducing disaccharides (sucrose): structure, inversion, application.
Sucrose is a disaccharide consisting of D-glucose and D-fructose residues linked by a glycosidic-glycosidic bond (a-1,-2-bond).
Sucrose is a non-reducing disaccharide (see Oligosaccharides), a widespread reserve in plants, formed during photosynthesis and stored in leaves, stems, roots, flowers or fruits. When loading above the melting temperature, decomposition and coloring of the melt (caramelization) occur. Sucrose does not reduce the Fehling reagent, it is quite stable to alkalis, but, being ketofuranoside, it is extremely easily (~ 500 times faster than trehalose or maltose) split (hydrolyzed) by acids into D-glucose and D-fructose. Hydrolysis of sucrose is accompanied by a change in the sign of beats. rotation of the solution and therefore called inversion.
A similar hydrolysis proceeds under the action of a-glucosidase (maltase) or b-fructofuranosidase (invertase). Sucrose is easily fermented by yeast. Being weak to-one (K approx. 10-13), sucrose forms complexes (saccharates) with hydroxides of alkali and alkaline earth metals, to-rye regenerate sucrose under the action of CO2.
The biosynthesis of sucrose occurs in the vast majority of photosynthetic eukaryotes, DOS. the mass of to-rykh is made up of plants (with the exception of representatives of red, brown, as well as diatoms and some other unicellular algae); its key stage is on loan. uridine diphosphate glucose and 6-phosphate-D-fructose. Animals are not capable of biosynthesis of sucrose.
Sucrose inversion. Acid hydrolysis of (+) sucrose or the action of invertase produces equal amounts of D (+) glucose and D (-) fructose. Hydrolysis is accompanied by a change in the sign of the specific rotation angle [α] from positive to negative, so the process is called inversion, and the mixture of D(+)glucose and D(-)fructose is called invert sugar.
Sucrose is obtained in prom. scales from sugar cane juice Saccharum officinarum or sugar beet Beta vulgaris; these two plants provide approx. 90% of the world's sucrose production (in a ratio of approx. 2:1), which exceeds 50 million tons / year. Chem. the synthesis of sucrose is very complex and economical. doesn't matter.
Sucrose is used as food. product (sugar) directly or as part of confectionery, and in high concentrations as a preservative; sucrose also serves as a substrate in prom. fermentation processes for obtaining ethanol, butanol, glycerin, citric and levulinic acid, dextran; also used in the preparation of lek. Wed-in; certain esters of sucrose with higher fatty acids are used as non-ionic detergents.
For qualities. detection of sucrose, blue staining with an alkaline solution of diazouracil can be used, a cut, however, also gives higher oligosaccharides containing a sucrose fragment in the molecule, raffinose, gentianose, stachyose.
The molecules of which consist of two simple sugars combined into one molecule by a glycosidic bond of a different configuration. The generalized formula of disaccharides can be represented as C 12 H 22 O 11 .
Depending on the structure of the molecules and their chemical properties, there are reducing (glycoside-glycosides) and non-reducing disaccharides (glycoside-glycosides). Reducing disaccharides include cellobiose, and non-reducing disaccharides include trehalose.
Chemical properties
Disugar are solid crystalline substances. Crystals of various substances are colored from white to brown. They dissolve well in water and alcohols, have a sweet taste.
During the hydrolysis reaction, glycosidic bonds are broken, as a result of which disaccharides break down into two simple sugars. In the reverse process of hydrolysis, condensation fuses several molecules of disaccharides into complex carbohydrates - polysaccharides.
Lactose - milk sugar
The term "lactose" is translated from Latin as "milk sugar". This carbohydrate is named so because it is found in large quantities in dairy products. Lactose is a polymer consisting of two molecules - glucose and. Unlike other disaccharides, lactose is not hygroscopic. Get this carbohydrate from dairy.
Application spectrum
Lactose is widely used in the pharmaceutical industry. Due to the lack of hygroscopicity, it is used for the manufacture of easily hydrolysable sugar-based drugs. Other carbohydrates, which are hygroscopic, quickly become damp and the active medicinal substance in them quickly decomposes.
Milk sugar in biological pharmaceutical laboratories is used in the manufacture of nutrient media for growing various cultures of bacteria and fungi, for example, in the production of penicillin.
Lactose isomerized in pharmaceuticals to produce lactulose. Lactulose is a biological probiotic that normalizes intestinal motility in constipation, dysbacteriosis and other digestive problems.
Beneficial features
Milk sugar is the most important nutritious and plastic substance vital for the harmonious development of the growing organism of mammals, including the human child. Lactose is a nutrient medium for the development of lactic acid bacteria in the intestine, which prevents putrefactive processes in it.
From useful properties lactose, it can be distinguished that, with a high energy intensity, it is not used for formation and does not increase the level in the blood.
Possible harm
Lactose does not harm the human body. The only contraindication to the use of products containing milk sugar is lactose intolerance, which occurs in people with a deficiency of the lactase enzyme, which breaks down milk sugar into simple carbohydrates. Lactose intolerance is the cause of indigestion of dairy products by people, more often adults. This pathology manifests itself in the form of symptoms such as:
- nausea and vomiting;
- diarrhea;
- bloating;
- colic;
- itching and rashes on the skin;
- allergic rhinitis;
- puffiness.
Lactose intolerance is most often physiological, and it is associated with age-related lactose deficiency.
Maltose - malt sugar
Maltose, which consists of two glucose residues, is a disaccharide produced by cereals to build the tissues of their embryos. Less maltose is found in the pollen and nectar of flowering plants, and in tomatoes. Malt sugar is also produced by some bacterial cells.
In animals and humans, maltose is formed by the breakdown of polysaccharides - and - with the help of maltase.
Main biological role maltose is to provide the body with energy material.
Possible harm
Harmful properties are shown by maltose only in those people who have a genetic deficiency of maltase. As a result, in the human intestine, when eating foods containing maltose, starch or glycogen, underoxidized products accumulate, provoking severe diarrhea. Excluding these foods from the diet or taking enzyme preparations with maltase helps to level the manifestations of maltose intolerance.
Sucrose - cane sugar
, which is present in our daily diet both in pure form and as part of various dishes, this is sucrose. It consists of the residues of the molecule and .
In nature, sucrose is found in a variety of fruits: fruits, berries, vegetables, as well as in sugar cane, from where it was first mined. The breakdown of sucrose begins in the mouth and ends in the intestines. Under the influence of alpha-glucosidase, cane sugar is broken down into glucose and fructose, which are quickly absorbed into the blood.
Beneficial features
The benefits of sucrose are obvious. As a very common disaccharide in nature, sucrose serves as a source of energy for the body. Saturating the blood with glucose and fructose, cane sugar:
- ensures the normal functioning of the brain - the main consumer of energy;
- is a source of energy for muscle contraction;
- increases the efficiency of the body;
- stimulates the synthesis of serotonin, due to which it improves mood, being an antidepressant factor;
- participates in the formation of strategic (and not only) fat reserves;
- takes an active part in carbohydrate metabolism;
- supports the detoxification function of the liver.
The beneficial functions of sucrose appear only when it is consumed in limited quantities. It is considered optimal to consume 30-50 g of cane sugar in meals, drinks or in its pure form.
Harm when abused
Excess daily allowance consumption is fraught with manifestation harmful properties sucrose:
- endocrine disorders (diabetes, obesity);
- destruction of tooth enamel and pathologies on the part of the musculoskeletal system as a result of a violation of mineral metabolism;
- sagging skin, brittle nails and hair;
- deterioration of the skin condition (rash, acne formation);
- suppression of immunity (effective immunosuppressant);
- suppression of enzyme activity;
- increased acidity of gastric juice;
- violation of the kidneys;
- hypercholesterolemia and triglyceridemia;
- acceleration of aging.
Since sucrose (glucose, fructose) are actively involved in the process of absorption of sucrose breakdown products, excessive consumption of sweet foods is fraught with a deficiency of these vitamins. A prolonged lack of B vitamins is dangerous with persistent disorders of the heart and blood vessels, pathologies of neuropsychic activity.
In children, a passion for sweets leads to an increase in their activity up to the development of a hyperactive syndrome, neurosis, and irritability.
Cellobiose disaccharide
Cellobiose is a disaccharide consisting of two glucose molecules. It is produced by plants and some bacterial cells. Cellobiosis has no biological value for humans: in the human body, this substance does not break down, but is a ballast compound. In plants, cellobiose performs a structural function, as it is part of the cellulose molecule.
Trehalose - mushroom sugar
Trehalose is made up of two glucose molecules. It is found in higher fungi (hence its second name), lichens, some worms and insects. It is believed that the accumulation of trehalose is one of the conditions for increased cell resistance to desiccation. It is not absorbed in the human body, however, a large intake of it into the blood can cause intoxication.
Disaccharides are widely distributed in nature - in the tissues and cells of plants, fungi, animals, bacteria. They are included in the structure of complex molecular complexes and are also found in the free state. Some of them (lactose, sucrose) are an energy substrate for living organisms, others (cellobiose) perform a structural function.
An example of the most common disaccharides in nature (oligosaccharide) is sucrose(beet or cane sugar).
Oligosaccharides are the condensation products of two or more monosaccharide molecules.
disaccharides - These are carbohydrates that, when heated with water in the presence of mineral acids or under the influence of enzymes, undergo hydrolysis, splitting into two molecules of monosaccharides.
Physical properties and being in nature
1. It is a colorless crystals of sweet taste, highly soluble in water.
2. The melting point of sucrose is 160 °C.
3. When molten sucrose solidifies, an amorphous transparent mass is formed - caramel.
4. Contained in many plants: birch sap, maple, carrots, melons, as well as sugar beet and sugar cane.
Structure and chemical properties
1. The molecular formula of sucrose is C 12 H 22 O 11
2. Sucrose has a more complex structure than glucose. The sucrose molecule consists of glucose and fructose residues connected to each other through the interaction of hemiacetal hydroxyls (1→2)-glycosidic bond:
3. The presence of hydroxyl groups in the sucrose molecule is easily confirmed by the reaction with metal hydroxides.
If a solution of sucrose is added to copper (II) hydroxide, a bright blue solution of copper sucrose is formed (qualitative reaction of polyhydric alcohols).
Video experiment "Proof of the presence of hydroxyl groups in sucrose"
4. There is no aldehyde group in sucrose: when heated with an ammonia solution of silver (I) oxide, it does not give a “silver mirror”, when heated with copper (II) hydroxide, it does not form red copper (I) oxide.
5. Sucrose, unlike glucose, is not an aldehyde. Sucrose, being in solution, does not enter into the "silver mirror" reaction, since it is not able to turn into an open form containing an aldehyde group. Such disaccharides are not capable of being oxidized (i.e., being reducing agents) and are called non-reducing sugars.
Video experience "Lack of reducing ability of sucrose"
6. Sucrose is the most important of the disaccharides.
7. It is obtained from sugar beet (it contains up to 28% of sucrose from dry matter) or from sugar cane.
Reaction of sucrose with water.
An important chemical property of sucrose is the ability to undergo hydrolysis (when heated in the presence of hydrogen ions). In this case, from one sucrose molecule, a glucose molecule and a fructose molecule are formed:
C 12 H 22 O 11 + H 2 O t , H 2 SO 4 → C 6 H 12 O 6 + C 6 H 12 O 6
Video experience "Acid hydrolysis of sucrose"
Among the isomers of sucrose having the molecular formula C 12 H 22 O 11, maltose and lactose can be distinguished.
During hydrolysis, various disaccharides are split into their constituent monosaccharides by breaking the bonds between them ( glycosidic bonds):
Thus, the hydrolysis reaction of disaccharides is the reverse of the process of their formation from monosaccharides.
Application of sucrose
· Food product;
· In the confectionery industry;
Obtaining artificial honey
Carbohydrates- organic matter, whose molecules consist of carbon, hydrogen and oxygen atoms, and hydrogen and oxygen are in them, as a rule, in the same ratio as in the water molecule (2: 1).
The general formula for carbohydrates is C n (H 2 O) m, i.e. they seem to consist of carbon and water, hence the name of the class, which has historical roots. It appeared on the basis of the analysis of the first known carbohydrates. Later it was found that there are carbohydrates in the molecules of which the indicated ratio (2: 1) is not observed, for example, deoxyribose - C 5 H 10 O 4. Organic compounds are also known, the composition of which corresponds to the given general formula, but which do not belong to the class of carbohydrates. These include, for example, formaldehyde CH 2 O and acetic acid CH 3 COOH.
However, the name "carbohydrates" has taken root and is now generally accepted for these substances.
Carbohydrates according to their ability to hydrolyze can be divided into three main groups: mono-, di- and polysaccharides.
Monosaccharides- carbohydrates that are not hydrolyzed (not decomposed by water). In turn, depending on the number of carbon atoms, monosaccharides are divided into trioses (the molecules of which contain three carbon atoms), tetroses (four carbon atoms), pentoses (five), hexoses (six), etc.
In nature, monosaccharides are predominantly pentoses and hexoses.
TO pentoses include, for example, ribose - C 5 H 10 O 5 and deoxyribose (ribose, from which the oxygen atom was "taken away") - C 5 H 10 O 4. They are part of RNA and DNA and determine the first part of the names of nucleic acids.
TO hexoses having the general molecular formula C 6 H 12 O 6 include, for example, glucose, fructose, galactose.
disaccharides- carbohydrates that are hydrolyzed to form two molecules of monosaccharides, such as hexoses. The general formula of the vast majority of disaccharides is not difficult to deduce: you need to “add” two formulas of hexoses and “subtract” from the resulting formula a water molecule - C 12 H 22 O 11. Accordingly, one can write general equation hydrolysis:
Disaccharides include:
1. sucrose(ordinary food sugar), which, when hydrolyzed, forms one glucose molecule and a fructose molecule. It is found in large quantities in sugar beet, sugar cane (hence the name - beet or cane sugar), maple (Canadian pioneers extracted maple sugar), sugar palm, corn, etc.
2. Maltose(malt sugar), which is hydrolyzed to form two molecules of glucose. Maltose can be obtained by hydrolysis of starch under the action of enzymes contained in malt - germinated, dried and ground barley grains.
3. Lactose(milk sugar), which is hydrolyzed to form glucose and galactose molecules. It is found in the milk of mammals (up to 4-6%), has a low sweetness and is used as a filler in pills and pharmaceutical tablets.
The sweet taste of different mono- and disaccharides is different. So, the sweetest monosaccharide - fructose - is 1.5 times sweeter than glucose, which is taken as a standard. Sucrose (disaccharide), in turn, is 2 times sweeter than glucose and 4-5 times sweeter than lactose, which is almost tasteless.
Polysaccharides- starch, glycogen, dextrins, cellulose, etc. - carbohydrates that are hydrolyzed to form many monosaccharide molecules, most often glucose.
To derive the formula of polysaccharides, you need to “take away” a water molecule from a glucose molecule and write an expression with the index n: (C 6 H 10 O 5) n, because it is due to the elimination of water molecules that di- and polysaccharides are formed in nature.
The role of carbohydrates in nature and their importance for human life is extremely great. Formed in plant cells as a result of photosynthesis, they act as a source of energy for animal cells. First of all, this applies to glucose.
Many carbohydrates (starch, glycogen, sucrose) perform a storage function, the role of the nutrient reserve.
RNA and DNA acids, which include some carbohydrates (pentose-ribose and deoxyribose), perform the functions of transmitting hereditary information.
Cellulose- construction material plant cells - plays the role of a framework for the membranes of these cells. Another polysaccharide, chitin, performs a similar role in the cells of some animals: it forms the outer skeleton of arthropods (crustaceans), insects, and arachnids.
Carbohydrates are the ultimate source of our nutrition, whether we eat starchy grains or feed them to animals that convert starch into proteins and fats. The most hygienic clothing is made from cellulose or products based on it: cotton and linen, viscose fiber, acetate silk. Wooden houses and furniture are built from the same pulp that forms wood.
At the heart of the production of photographic and film is the same cellulose. Books, newspapers, letters, banknotes - all these are products of the pulp and paper industry. This means that carbohydrates provide us with everything necessary for life: food, clothing, shelter.
In addition, carbohydrates are involved in the construction of complex proteins, enzymes, hormones. Carbohydrates are also such vital substances as heparin (it plays essential role- prevents blood clotting), agar-agar (it is obtained from seaweed and used in the microbiological and confectionery industries - remember the famous Bird's Milk cake).
It should be emphasized that the only type of energy on Earth (besides nuclear, of course) is the energy of the Sun, and the only way to accumulate it to ensure the vital activity of all living organisms is the process photosynthesis, which occurs in the cells of living plants and leads to the synthesis of carbohydrates from water and carbon dioxide. It is during this transformation that oxygen is formed, without which life on our planet would be impossible:
Monosaccharides. Glucose
glucose and fructose- solid colorless crystalline substances. Glucose, found in the juice of grapes (hence the name "grape sugar"), together with fructose, which is found in some fruits and vegetables (hence the name "fruit sugar"), makes up a significant portion of honey. The blood of humans and animals constantly contains about 0.1% glucose (80-120 mg per 100 ml of blood). Most of it (about 70%) undergoes slow oxidation in the tissues with the release of energy and the formation of end products - carbon dioxide and water (glycolysis process):
The energy released during glycolysis largely provides the energy needs of living organisms.
Exceeding the level of glucose in the blood of 180 mg in 100 ml of blood indicates a violation of carbohydrate metabolism and the development of a dangerous disease - diabetes mellitus.
The structure of the glucose molecule
The structure of the glucose molecule can be judged on the basis of experimental data. It reacts with carboxylic acids to form esters containing 1 to 5 acid residues. If a glucose solution is added to freshly obtained copper (II) hydroxide, then the precipitate dissolves and a bright blue solution of the copper compound is formed, i.e., a qualitative reaction to polyhydric alcohols occurs. Therefore, glucose is a polyhydric alcohol. If, however, the resulting solution is heated, a precipitate will again form, but already of a reddish color, i.e., a qualitative reaction to aldehydes will occur. Similarly, if a glucose solution is heated with an ammonia solution of silver oxide, then a “silver mirror” reaction will occur. Therefore, glucose is both a polyhydric alcohol and an aldehyde - an aldehyde alcohol. Let's try to derive the structural formula of glucose. There are six carbon atoms in the C 6 H 12 O 6 molecule. One atom is part of aldehyde group:
The remaining five atoms bind to five hydroxyl groups.
And finally, we will distribute the hydrogen atoms in the molecule, taking into account the fact that carbon is tetravalent:
However, it has been established that, in addition to linear (aldehyde) molecules, in a glucose solution there are molecules of a cyclic structure that make up crystalline glucose. The transformation of molecules of a linear form into a cyclic one can be explained if we remember that carbon atoms can freely rotate around σ-bonds located at an angle of 109° 28'. In this case, the aldehyde group (1st carbon atom) can approach the hydroxyl group of the fifth carbon atom. In the first, under the influence of the hydroxy group, the π-bond is broken: a hydrogen atom is attached to the oxygen atom, and the oxygen of the hydroxy group that “lost” this atom closes the cycle:
As a result of this rearrangement of atoms, a cyclic molecule is formed. The cyclic formula shows not only the order of bonding of atoms, but also their spatial arrangement. As a result of the interaction of the first and fifth carbon atoms, a new hydroxyl group appears at the first atom, which can occupy two positions in space: above and below the cycle plane, and therefore two cyclic forms of glucose are possible:
a) α-form of glucose- hydroxyl groups at the first and second carbon atoms are located on one side of the ring of the molecule;
b) β-form of glucose- hydroxyl groups are located on different sides molecule rings:
V aqueous solution glucose is in dynamic equilibrium in its three isomeric forms - the cyclic α-form, the linear (aldehyde) form and the cyclic β-form:
In the established dynamic equilibrium, the β-form predominates (about 63%), since it is energetically preferable - it has OH groups at the first and second carbon atoms on opposite sides of the cycle. In the α-form (about 37%), the OH-groups of the same carbon atoms are located on one side of the plane, therefore it is energetically less stable than the β-form. The share of the linear form in equilibrium is very small (only about 0.0026%).
The dynamic balance can be shifted. For example, when an ammonia solution of silver oxide acts on glucose, the amount of its linear (aldehyde) form, which is very small in solution, is replenished all the time due to cyclic forms, and glucose is completely oxidized to gluconic acid.
An isomer of glucose aldehyde alcohol is keto alcohol - fructose:
Chemical properties of glucose
Chemical properties Glucose, like any other organic substance, is determined by its structure. Glucose has a dual function, being and aldehyde, and polyhydric alcohol, therefore, it is characterized by the properties of both polyhydric alcohols and aldehydes.
Reactions of glucose as a polyhydric alcohol.
Glucose gives a qualitative reaction of polyhydric alcohols (remember glycerol) with freshly prepared copper (II) hydroxide, forming a bright blue solution of a copper (II) compound.
Glucose, like alcohols, can form esters.
Reactions of glucose as an aldehyde
1. Oxidation of the aldehyde group. Glucose as an aldehyde can be oxidized to the corresponding (gluconic) acid and give qualitative reactions of aldehydes.
The reaction of the "silver mirror":
Reaction with freshly obtained Cu(OH) 2 when heated:
Recovery of the aldehyde group. Glucose can be reduced to the corresponding alcohol (sorbitol):
Fermentation reactions
These reactions proceed under the action of special biological catalysts of protein nature - enzymes.
1. Alcoholic fermentation:
has long been used by man to produce ethyl alcohol and alcoholic beverages.
2. Lactic fermentation:
which forms the basis of the vital activity of lactic acid bacteria and occurs during the souring of milk, the pickling of cabbage and cucumbers, and the ensiling of green fodder.
Chemical properties of glucose - compendium
Polysaccharides. starch and cellulose.
Starch- white amorphous powder, insoluble in cold water. In hot water, it swells and forms a colloidal solution - a starch paste.
Starch is found in the cytoplasm of plant cells in the form of grains of a reserve nutrient. Potato tubers contain about 20% starch, wheat and corn grains - about 70%, and rice - almost 80%.
Cellulose(from lat. cellula - cell), isolated from natural materials (for example, cotton wool or filter paper), is a solid fibrous substance that is insoluble in water.
Both polysaccharides are of plant origin, but they play different roles in the plant cell: cellulose is a building, structural function, and starch is a storage one. Therefore, cellulose is obligatory element plant cell wall. Cotton fibers contain up to 95% cellulose, flax and hemp fibers - up to 80%, and its wood contains about 50%.
The structure of starch and cellulose
The composition of these polysaccharides can be expressed by the general formula (C 6 H 10 O 5) n. The number of repeating units in a starch macromolecule can vary from several hundred to several thousand. Cellulose is different a large number links and, consequently, a molecular weight that reaches several million.
Carbohydrates differ not only in molecular weight, but also in structure. Starch is characterized by two types of macromolecular structures: linear and branched. Smaller macromolecules of that part of starch, which is called amylose, have a linear structure, and molecules of another constituent of starch, amylopectin, have a branched structure.
In starch, amylose accounts for 10-20%, and amylopectin accounts for 80-90%. Starch amylose dissolves in hot water, while amylopectin only swells.
The structural units of starch and cellulose are built differently. If the starch unit includes residues α-glucose, then cellulose - residues β-glucose oriented in natural fibers:
Chemical properties of polysaccharides
1. The formation of glucose. Starch and cellulose undergo hydrolysis to form glucose in the presence of mineral acids, such as sulfuric:
In the digestive tract of animals, starch undergoes a complex stepwise hydrolysis:
The human body is not adapted to the digestion of cellulose, since it does not have the enzymes necessary to break bonds between β-glucose residues in the cellulose macromolecule.
Only in termites and ruminants (for example, cows) in digestive system live microorganisms that produce the necessary enzymes.
2. Esters formation. Starch can form esters at the expense of hydroxy groups, but these esters have not found practical application.
Each cellulose unit contains three free alcohol hydroxyl groups. Therefore, the general formula for cellulose can be written as follows:
Due to these alcohol hydroxy groups, cellulose can form esters, which are widely used.
When processing cellulose with a mixture of nitric and sulfuric acids, mono-, di- and trinitrocellulose are obtained, depending on the conditions:
The use of carbohydrates
A mixture of mono- and dinitrocellulose is called colloxylin. A solution of colloxylin in a mixture of alcohol and diethyl ether - collodion - is used in medicine for sealing small wounds and for gluing bandages to the skin.
When a solution of colloxylin and camphor in alcohol dries, it turns out celluloid- one of the plastics that first became widely used in Everyday life a person (from it they make photo and film, as well as various consumer goods). Solutions of colloxylin in organic solvents are used as nitro-varnishes. And when dyes are added to them, durable and aesthetic nitro-paints are obtained, which are widely used in everyday life and technology.
Like other organic substances containing nitro groups in their molecules, all types of nitrocellulose are flammable. Particularly dangerous in this respect trinitrocellulose- the strongest explosive. Under the name "pyroxylin" it is widely used for the production of weapons shells and blasting, as well as for obtaining smokeless powder.
With acetic acid (in industry, a more powerful esterifying agent, acetic anhydride, is used for these purposes), similar (di- and tri-) esters of cellulose and acetic acid are obtained, which are called cellulose acetate:
cellulose acetate used to obtain varnishes and paints, it also serves as a raw material for the manufacture of artificial silk. To do this, it is dissolved in acetone, and then this solution is forced through thin holes of spinnerets (metal caps with numerous holes). The flowing streams of the solution are blown with warm air. At the same time, acetone quickly evaporates, and drying cellulose acetate forms thin, shiny threads that are used to make yarn.
Starch, unlike cellulose, gives a blue color when interacting with iodine. This reaction is qualitative for starch or iodine, depending on which substance is to be proven.
Reference material for passing the test:
Mendeleev table
Solubility table
