General chemistry: textbook / A. V. Zholnin; ed. V. A. Popkova, A. V. Zholnina. - 2012. - 400 p.: ill.

Chapter 8. REDOX REACTIONS AND PROCESSES

Chapter 8. REDOX REACTIONS AND PROCESSES

Life is a continuous chain of redox processes.

A.-L. Lavoisier

8.1. BIOLOGICAL SIGNIFICANCE OF REDOX PROCESSES

The processes of metabolism, respiration, putrefaction, fermentation, photosynthesis are basically redox processes. In the case of aerobic metabolism, the main oxidizing agent is molecular oxygen, and the reducing agent is organic food substances. An indicator of the fact that redox reactions are the basis of the life of the body are the bioelectric potentials of organs and tissues. Biopotentials are a qualitative and quantitative characteristic of the direction, depth and intensity of biochemical processes. Therefore, the registration of biopotentials of organs and tissues is widely used in clinical practice in the study of their activity, in particular, in the diagnosis of cardiovascular diseases, an electrocardiogram is taken, and when measuring muscle biopotentials, an electromyogram is taken. Registration of brain potentials - encephalography - allows you to judge the pathological disorders of the nervous system. The source of energy for the vital activity of cells is the membrane potential equal to 80 mV, due to the occurrence of ionic asymmetry, i.e. uneven distribution of cations and anions on both sides of the membrane. The membrane potential has an ionic nature. In multinuclear complexes, there are processes associated with the transfer of electrons and protons between particles that resist

are driven by a change in the oxidation state of the reacting particles and the appearance of a redox potential. The redox potential has an electronic nature. These processes are reversible cyclic and underlie many important physiological processes. Michaelis noted the important role of redox processes in life: “The redox processes occurring in living organisms belong to the category of those that not only catch the eye and can be identified, but are also the most important for life, both biologically and from a philosophical point of view.

8.2. ESSENCE

REDOX PROCESSES

In 1913 L.V. Pisarzhevsky came up with the electronic theory of redox processes, which is currently generally accepted. This type of reactions is carried out due to the redistribution of electron density between the atoms of the reacting substances (electron transfer), which manifests itself in a change in the degree of oxidation.

Reactions, as a result of which the oxidation states of the atoms that make up the reactants change due to the transfer of an electron between them, are called redox reactions.

The redox process consists of 2 elementary acts or half-reactions: oxidation and reduction.

Oxidation- this is the process of loss (return) of electrons by an atom, molecule or ion. When oxidized, the oxidation state of the particles increases:

A particle that donates electrons is called reducing agent. The product of the oxidation of a reducing agent is called its oxidized form:

The reducing agent with its oxidized form constitutes one pair of the redox system (Sn 2 +/Sn 4 +).

A measure of the reducing ability of an element is ionization potential. The lower the ionization potential of an element, the stronger the reducing agent it is, s-elements and elements in the lower and intermediate oxidation states are strong reducing agents. The ability of a particle to donate electrons (donor ability) determines its reducing properties.

Recovery - is the process of electrons being attached to a particle. When reduced, the oxidation state decreases:

A particle (atoms, molecules, or ions) that accepts electrons is called oxidizing agent. The product of reduction of an oxidizing agent is called its restored form:

The oxidizer with its reduced form constitutes another pair (Fe 3+ /Fe 2+) of the redox system. A measure of the oxidizing power of particles is electron affinity. The greater the electron affinity, i.e. the electron-withdrawing ability of the particle, the stronger the oxidizing agent it is. Oxidation is always accompanied by reduction, and vice versa, reduction is associated with oxidation.

Consider the interaction of FeCl 3 with SnCl 2 . The process consists of two half-reactions:

The redox reaction can be represented as a combination of two conjugated pairs.

During the reactions, the oxidizing agent is converted into a conjugated reducing agent (reduction product), and the reducing agent is converted into a conjugated oxidizing agent (oxidation product). They are considered as redox pairs:

Therefore, redox reactions represent the unity of two opposite processes of oxidation and reduction, which in systems cannot exist one without the other. In this we see the manifestation of the universal law of unity and struggle of opposites. The reaction will occur if the electron affinity of the oxidizing agent is greater than the ionization potential of the reducing agent. For this, the concept electronegativity - a quantity that characterizes the ability of atoms to donate or accept electrons.

Drawing up the equations of redox reactions is carried out by the method of electronic balance and the method of half-reactions. The half-reaction method should be preferred. Its use is associated with the use of ions that actually exist, the role of the medium is visible. When drawing up equations, it is necessary to find out which of the substances that enter into the reaction act as an oxidizing agent, and which ones act as a reducing agent, the effect of the pH of the medium on the course of the reaction, and what are the possible reaction products. Redox properties are exhibited by compounds that contain atoms that have a large number of valence electrons with different energies. Compounds of d-elements (IB, VIIB, VIIIB groups) and p-elements (VIIA, VIA, VA groups) have such properties. Compounds that contain an element in the highest oxidation state exhibit only oxidizing properties.(KMnO 4, H 2 SO 4), in the lower - only restorative properties(H 2 S), in the intermediate - can behave in two ways(Na2SO3). After compiling the half-reaction equations, the ionic equation composes the reaction equation in molecular form:

Checking the correctness of the equation: the number of atoms and charges on the left side of the equation must be equal to the number of atoms and charges on the right side of the equation for each element.

8.3. THE CONCEPT OF ELECTRODE POTENTIAL. THE MECHANISM OF THE APPEARANCE OF ELECTRODE POTENTIAL. GALVANIC CELL. NERNST EQUATION

A measure of the redox ability of substances are redox potentials. Let us consider the mechanism of the emergence of the potential. When a reactive metal (Zn, Al) is immersed in a solution of its salt, for example Zn in a ZnSO 4 solution, the metal is additionally dissolved as a result of the oxidation process, a pair is formed, a double electric layer on the metal surface and the Zn 2 + / Zn ° pair potential appears .

A metal immersed in a solution of its salt, such as zinc in a solution of zinc sulfate, is called an electrode of the first kind. This is a two-phase electrode that is negatively charged. The potential is formed as a result of the oxidation reaction (according to the first mechanism) (Fig. 8.1). When low-active metals (Cu) are immersed in a solution of their salt, the opposite process is observed. At the interface between the metal and the salt solution, the metal is deposited as a result of the reduction of an ion with a high acceptor capacity for an electron, which is due to the high nuclear charge and the small radius of the ion. The electrode is positively charged, excess salt anions form a second layer in the near-electrode space, and an electrode potential of the Cu 2 +/Cu° pair arises. The potential is formed as a result of the recovery process according to the second mechanism (Fig. 8.2). The mechanism, magnitude and sign of the electrode potential are determined by the structure of the atoms involved in the electrode process.

So, the potential arises at the interface between the metal and the solution as a result of the oxidation and reduction processes occurring with the participation of the metal (electrode) and the formation of a double electric layer is called the electrode potential.

If electrons are removed from a zinc plate to a copper one, then the equilibrium on the plates is disturbed. To do this, we connect zinc and copper plates immersed in solutions of their salts with a metal conductor, near-electrode solutions with an electrolyte bridge (a tube with a solution of K 2 SO 4) to close the circuit. The oxidation half-reaction proceeds on the zinc electrode:

and on copper - the reduction half-reaction:

The electric current is due to the total redox reaction:

An electric current appears in the circuit. The reason for the occurrence and flow of electric current (EMF) in a galvanic cell is the difference in electrode potentials (E) - fig. 8.3.

Rice. 8.3. Electric circuit diagram of a galvanic cell

Galvanic cell is a system in which the chemical energy of a redox process is converted

into electrical. The chemical circuit of a galvanic cell is usually written as a short diagram, where a more negative electrode is placed on the left, the pair formed on this electrode is indicated by a vertical line, and the potential jump is shown. Two lines mark the boundary between solutions. The charge of the electrode is indicated in parentheses: (-) Zn°|Zn 2 +||Cu 2 +|Cu° (+) - diagram of the chemical circuit of a galvanic cell.

The redox potentials of a pair depend on the nature of the participants in the electrode process and the ratio of the equilibrium concentrations of the oxidized and reduced forms of the participants in the electrode process in solution, the temperature of the solution, and are described by the Nernst equation. The quantitative characteristic of the redox system is the redox potential that occurs at the interface between the phases of platinum - aqueous solution. The potential value in SI units is measured in volts (V) and is calculated from the Nernst-Peters equation:

where a(Ox) and a(Red) are the activities of the oxidized and reduced forms, respectively; R- universal gas constant; T- thermodynamic temperature, K; F- Faraday's constant (96,500 C/mol); n is the number of electrons involved in the elementary redox process; a - activity of hydronium ions; m- stoichiometric coefficient in front of the hydrogen ion in the half-reaction. The value of φ° is the standard redox potential, i.e. potential measured under the conditions a(Ox) = a(Red) = a(H +) = 1 and a given temperature.

The standard potential of the 2H + /H 2 system is taken equal to 0 V. The standard potentials are reference values ​​and are tabulated at a temperature of 298K. A strongly acidic environment is not typical for biological systems, therefore, to characterize the processes occurring in living systems, the formal potential is more often used, which is determined under the condition a(Ox) = a(Red), pH 7.4, and a temperature of 310 K (physiological level). When writing the potential, the vapor is indicated as a fraction, with the oxidizer being written in the numerator and the reducing agent in the denominator.

For 25 °C (298K) after substitution of constant values ​​(R = 8.31 J/mol deg; F= 96 500 C/mol) the Nernst equation takes the following form:

where φ° is the standard redox potential of the couple, V; with o.fu and with v.f. - the product of the equilibrium concentrations of the oxidized and reduced forms, respectively; x and y are stoichiometric coefficients in the half-reaction equation.

The electrode potential is formed on the surface of a metal plate immersed in a solution of its salt, and depends only on the concentration of the oxidized form [M n+ ], since the concentration of the reduced form does not change. The dependence of the electrode potential on the concentration of the ion of the same name with it is determined by the equation:

where [M n+ ] is the equilibrium concentration of the metal ion; n- the number of electrons involved in the half-reaction, and corresponds to the oxidation state of the metal ion.

Redox systems are divided into two types:

1) in the system only electron transfer Fe 3 + + ē = = Fe 2 +, Sn 2 + - 2ē = Sn 4 + is carried out. it isolated redox equilibrium;

2) systems where the transfer of electrons is supplemented by the transfer of protons, i.e. observed combined equilibrium of different types: protolytic (acid-base) and redox with possible competition of two particles of protons and electrons. In biological systems, important redox systems are of this type.

An example of a system of the second type is the process of utilizing hydrogen peroxide in the body: H 2 O 2 + 2H + + 2ē ↔ 2H 2 O, as well as the reduction in an acidic environment of many oxidizing agents containing oxygen: CrO 4 2-, Cr 2 O 7 2-, MnO 4 -. For example, MnО 4 - + 8Н + + 5ē = = Mn 2 + + 4Н 2 О. Electrons and protons participate in this half-reaction. The calculation of the potential of a pair is carried out according to the formula:

In a wider range of conjugated pairs, the oxidized and reduced forms of the pair are in solution in various degrees of oxidation (MnO 4 - /Mn 2 +). As measuring electrode

in this case, an electrode made of an inert material (Pt) is used. The electrode is not a participant in the electrode process and only plays the role of an electron carrier. The potential formed due to the redox process occurring in solution is called redox potential.

It is measured on redox electrode is an inert metal in solution containing oxidized and reduced forms of a pair. For example, when measuring E o pairs of Fe 3 + /Fe 2 + use a redox electrode - a platinum measuring electrode. The reference electrode is hydrogen, the potential of the pair of which is known.

The reaction taking place in the galvanic cell:

Chemical chain scheme: (-) Pt | (H 2 °), H + | | Fe 3 +, Fe 2 + | Pt (+).

The redox potential is a measure of the redox ability of substances. The value of the standard pair potentials is indicated in the reference tables.

In the series of redox potentials, the following regularities are noted.

1. If the standard redox potential of the pair is negative, for example φ ° (Zn 2+ (p) / Zn ° (t)) \u003d -0.76 V, then with respect to the hydrogen pair, the potential of which is higher, this pair acts as reducing agent. The potential is formed by the first mechanism (oxidation reactions).

2. If the potential of the pair is positive, for example φ ° (Cu 2 + (p) / Cu (t)) \u003d +0.345 V with respect to a hydrogen or other conjugated pair whose potential is lower, this pair is an oxidizing agent. The potential of this pair is formed according to the second mechanism (reduction reactions).

3. The higher the algebraic value of the standard potential of the pair, the higher the oxidizing ability of the oxidized form and the lower the reducing ability of the reduced form of this

couples. A decrease in the value of the positive potential and an increase in the negative potential corresponds to a decrease in the oxidative and an increase in the reduction activity. For example:

8.4. HYDROGEN ELECTRODE, REDOX MEASUREMENT

The redox potential of a pair is determined by the potential of the electrical double layer, but, unfortunately, there is no method for measuring it. Therefore, not an absolute, but a relative value is determined, choosing some other pair for comparison. Potential measurement is carried out using a potentiometric installation, which is based on a galvanic cell having a circuit: the electrode of the test pair (measuring electrode) is connected to the electrode of the hydrogen pair (H + / H °) or some other, the potential of which is known (reference electrode) . The galvanic cell is connected to an amplifier and an electric current meter (Fig. 8.4).

Hydrogen pair is formed on the hydrogen electrode as a result of the redox process: 1/2H 2 o (g) ↔ H + (p) + e - . The hydrogen electrode is a half cell consisting of

from a platinum plate coated with a thin, loose layer of platinum, dipped in a 1 N solution of sulfuric acid. Hydrogen is passed through the solution; in the porous layer of platinum, part of it passes into the atomic state. All this is enclosed in a glass vessel (ampoule). The hydrogen electrode is a three-phase electrode of the first kind (gas-metal). Analyzing the electrode potential equation for the hydrogen electrode, we can conclude that the potential of the hydrogen electrode increases linearly

Rice. 8.4. Hydrogen electrode

with a decrease in the pH value (increase in acidity) of the medium and a decrease in the partial pressure of hydrogen gas over the solution.

8.5. DIRECTION PREDICTION

ON CHANGE OF FREE ENERGY OF SUBSTANCES AND ON THE VALUE OF STANDARD REDOX POTENTIALS

The direction of the redox reaction can be judged by the change in the isobaric-isothermal potential of the system (Gibbs energy), free energy (ΔG) of the process. The reaction is fundamentally possible at ΔG o < 0. В окислительно-восстановительной реакции изменение свободной энергии равно электрической работе, совершаемой системой, в результате которой ē переходит от восстановителя к окислителю. Это находит отражение в формуле:

where F- Faraday's constant equal to 96.5 kK/mol; n- the number of electrons involved in the redox process, per 1 mol of substance; E o- the value of the difference in the standard redox potentials of two conjugated pairs of the system, which is called the electromotive force of reactions (EMF). This equation reflects the physical meaning of the relationship E o and free energy of the Gibbs reaction.

For the spontaneous occurrence of a redox reaction, it is necessary that the potential difference of conjugated pairs be a positive value, which follows from the equation, i.e. the pair, whose potential is higher, can act as an oxidizing agent. The reaction continues until the potentials of both pairs become equal. Therefore, in order to answer the question whether a given reducing agent will be oxidized by a given oxidizing agent or, conversely, one needs to know ΔE o : ∆Eo = φ°oxid. - φ°rest. The reaction proceeds in the direction that leads to the formation of a weaker oxidizing agent and a weaker reducing agent. Thus, by comparing the potentials of two conjugated pairs, one can fundamentally solve the problem of the direction of the process.

A task. Is it possible to reduce the Fe 3+ ion with T1+ ions according to the proposed scheme:

ΔЕ° of the reaction has a negative value:

The reaction is impossible, since the oxidized Fe 3+ form of the Fe 3+ / Fe 2 + pair cannot oxidize the T1+ of the T1 3 + / T1 + pair.

If the EMF of the reaction is negative, then the reaction goes in the opposite direction. The larger ΔE°, the more intense the reaction.

A task. What is the chemical behavior of FeC1 3 in a solution containing:

a) NaI; b) NaBr?

We compose half-reactions and find the potentials for pairs:

a) E reactions 2I - + 2Fe 3 + = I 2 + 2Fe 2 + will be equal to 0.771-0.536 = = 0.235 V, E has a positive value. Consequently, the reaction goes towards the formation of free iodine and Fe 2+.

b) E ° of the reaction 2Br - + 2Fe 3 + = Br 2 + 2Fe 2 + will be equal to 0.771-1.065 = = -0.29 V. Negative value E o shows that ferric chloride will not be oxidized by potassium bromide.

8.6. EQUILIBRIUM CONSTANT

REDOX REACTION

In some cases, it is necessary to know not only the direction and intensity of redox reactions, but also the completeness of the reactions (by what percentage the starting substances are converted into reaction products). For example, in quantitative analysis, one can rely only on those reactions that practically proceed 100%. Therefore, before using this or that reaction to solve any problem, determine the constant equal to

novesia (K R) of this island of the system. To determine Kp of redox processes, a table of standard redox potentials and the Nernst equation are used:

because the when equilibrium is reached, the potentials of the conjugated pairs of the oxidizing agent and the reducing agent of the redox process become the same: φ ° oxid. - φ°rest. = 0, then E o= 0. From the Nernst equation in equilibrium conditions E o reaction is:

where n- the number of electrons involved in the redox reaction; P.S. prod. district and P.S. ref. c-c - respectively, the product of the equilibrium concentrations of the reaction products and starting substances in the degree of their stoichiometric coefficients in the reaction equation.

The equilibrium constant indicates that the state of equilibrium of a given reaction occurs when the product of the equilibrium concentrations of the reaction products becomes 10 times greater than the product of the equilibrium concentrations of the starting materials. In addition, a large Kp value indicates that the reaction proceeds from left to right. Knowing Kp, it is possible, without resorting to experimental data, to calculate the completeness of the reaction.

8.7. REDOX REACTIONS IN BIOLOGICAL SYSTEMS

In the process of vital activity in cells and tissues, differences in electrical potentials can occur. Electrochemical transformations in the body can be divided into 2 main groups.

1. Redox processes due to the transfer of electrons from one molecule to another. These processes are electronic in nature.

2. Processes associated with the transfer of ions (without changing their charges) and with the formation of biopotentials. The biopotentials recorded in the body are mainly membrane potentials. They are ionic in nature. As a result of these processes, potentials arise between different layers of tissues in different physiological states. They are associated with different intensity of physiological redox processes. For example, the potentials formed in the tissues of the leaf surface on the illuminated and unlit side as a result of different intensity of the photosynthesis process. The illuminated area is positively charged in relation to the unlit area.

In redox processes that have an electronic nature, three groups can be distinguished.

The first group includes processes associated with the transfer of electrons between substances without the participation of oxygen and hydrogen. These processes are carried out with the participation of electron transfer complexes - heterovalent and heteronuclear complexes. Electron transfer occurs in complex compounds of the same metal or atoms of different metals, but in different degrees of oxidation. The active principle of electron transfer is transition metals, which exhibit several stable oxidation states, and the transfer of electrons and protons does not require large energy costs, the transfer can be carried out over long distances. The reversibility of processes allows multiple participation in cyclic processes. These oscillatory processes are found in enzymatic catalysis (cytochromes), protein synthesis, and metabolic processes. This group of transformations is involved in maintaining antioxidant homeostasis and in protecting the body from oxidative stress. They are active regulators of free-radical processes, a system for the utilization of reactive oxygen species, hydrogen peroxide, and participate in the oxidation of substrates.

catalase, peroxidase, dehydrogenase. These systems carry out antioxidant, antiperoxide action.

The second group includes redox processes associated with the participation of oxygen and hydrogen. For example, the oxidation of the aldehyde group of the substrate into an acidic one:

The third group includes processes associated with the transfer of protons and electrons from the substrate, which are pH-dependent, proceed in the presence of dehydrogenase (E) and coenzyme (Co) enzymes with the formation of an activated enzyme-coenzyme-substrate complex (E-Co-S ), attaching electrons and hydrogen cations from the substrate, and cause its oxidation. Such a coenzyme is nicotinamide adenine dinucleotide (NAD +), which attaches two electrons and one proton:

In biochemical processes, combined chemical equilibria take place: redox, protolytic, and complex formation processes. The processes are usually enzymatic in nature. Types of enzymatic oxidation: dehydrogenase, oxidase (cytochromes, free radical oxidation-reduction). The redox processes occurring in the body can be conditionally divided into the following types: 1) reactions of intramolecular dismutation (disproportionation) due to the carbon atoms of the substrate; 2) intermolecular reactions. The presence of a wide range of oxidation states of carbon atoms from -4 to +4 indicates its duality. Therefore, in organic chemistry, redox dismutation reactions due to carbon atoms are common, which occur intra- and intermolecularly.

8.8. MEMBRANE POTENTIAL

Since the time of R. Virchow, it has been known that living cell- this is the elementary cell of the biological organization, providing all the functions of the body. The course of many physiological processes in the body is associated with the transfer of ions in cells and tissues and is accompanied by the appearance of a potential difference. A large role in membrane transport belongs to the passive transport of substances: osmosis,

filtration and bioelectrogenesis. These phenomena are determined by the barrier properties of cell membranes. The potential difference between solutions of different concentrations separated by a membrane with selective permeability is called the membrane potential. The membrane potential is ionic and not electronic in nature. It is due to the appearance of ionic asymmetry, i.e. unequal distribution of ions on both sides of the membrane.

The cationic composition of the intercellular medium is close to the ionic composition of sea water: sodium, potassium, calcium, magnesium. In the process of evolution, nature has created a special way of transporting ions, called passive transport, accompanied by a potential difference. In many cases, the basis of the transfer of substances is diffusion, so the potential that forms on the cell membrane is sometimes called diffusion potential. It exists until the ion concentration levels off. The potential value is small (0.1 V). Facilitated diffusion occurs through ion channels. Ionic asymmetry is used to generate excitation in nerve and muscle cells. However, the presence of ionic asymmetry on both sides of the membrane is also important for those cells that are unable to generate an excitatory potential.

8.9. QUESTIONS AND TASKS FOR SELF-CHECK

PREPARED FOR LESSONS

AND EXAMS

1. Give the concept of electrode and redox potentials.

2. Note the main patterns observed in the series of redox potentials.

3. What is a measure of the reducing ability of substances? Give examples of the most common reducing agents.

4. What is a measure of the oxidizing ability of a substance? Give examples of the most common oxidizing agents.

5. How can the redox potential be experimentally determined?

6. How will the potential of the Co 3+ /Co 2+ system change when cyanide ions are introduced into it? Explain the answer.

7. Give an example of reactions in which hydrogen peroxide plays the role of an oxidizing agent (reducing agent) in acidic and alkaline media.

8. What is the significance of the phenomenon of revealing the ligand environment of the central atom on the redox potential for the functioning of living systems?

9. The Krebs cycle in the biological oxidation of glucose is immediately preceded by the reaction:

where NADH and NAD + are the reduced and oxidized form of nicotinamide dinucleotide. In what direction does this redox reaction proceed under standard conditions?

10. What are the names of substances that reversibly react with oxidizing agents and protect substrates?

11. Give examples of the action of bactericidal substances based on oxidizing properties.

12. Reactions underlying the methods of permanganatometry and iodometry. Working solutions and methods for their preparation.

13. What is the biological role of reactions in which the oxidation state of manganese and molybdenum changes?

14. What is the mechanism of toxic action of nitrogen (III), nitrogen (IV), nitrogen (V) compounds?

15. How is superoxide ion detoxified in the body? Give the reaction equation. What is the role of metal ions in this process?

16. What is the biological role of half-reactions: Fe 3+ + ē ↔ Fe 2+; Cu 2+ + ē ↔ Cu + ; Co 3+ + ē ↔ Co 2+ ? Give examples.

17. How is the standard EMF related to the change in the Gibbs energy of the redox process?

18. Compare the oxidizing power of ozone, oxygen and hydrogen peroxide with respect to an aqueous solution of potassium iodide. Support your answer with tabular data.

19. What chemical processes underlie the neutralization of superoxide anion radical and hydrogen peroxide in the body? Give the equations of half-reactions.

20. Give examples of redox processes in living systems, accompanied by a change in the oxidation states of d-elements.

21. Give examples of the use of redox reactions for detoxification.

22. Give examples of the toxic effect of oxidizing agents.

23. In the solution there are particles of Cr 3+, Cr 2 O 7 2-, I 2, I -. Determine which of them interact spontaneously under standard conditions?

24. Which of the indicated particles is a stronger oxidizing agent in an acidic environment, KMnO 4 or K 2 Cr 2 O 7?

25. How to determine the dissociation constant of a weak electrolyte using the potentiometric method? Draw a diagram of the chemical circuit of a galvanic cell.

26. Is it possible to simultaneously introduce RMnO 4 and NaNO 2 solutions into the body?

8.10. TESTS

1. Which halogen molecules (simple substances) exhibit redox duality?

a) none, all of them are only oxidizers;

b) everything except fluorine;

c) everything except iodine;

d) all halogens.

2. Which halide ion has the highest reducing activity?

a) F - ;

b) C1 - ;

c) I - ;

d) Br - .

3. Which halogens undergo disproportionation reactions?

a) everything except fluorine;

b) everything except fluorine, chlorine, bromine;

c) everything except chlorine;

d) none of the halogens is involved.

4. Two tubes contain KBr and KI solutions. FeCl 3 solution was added to both tubes. In which case is the halide ion oxidized to free halogen if E o (Fe 3+ / Fe 2+) = 0.77 V; E ° (Br 2 /2Br -) \u003d 1.06 V; E o (I2 / 2I -) \u003d 0.54 V?

a) KBr and KI;

b) KI;

c) KVR;

d) not in any case.

5. The most powerful reducing agent:

6. In which of the reactions involving hydrogen peroxide, gaseous oxygen will be one of the reaction products?

7. Which of the proposed elements has the highest value of relative electronegativity?

a)O;

b)C1;

c)N;

d)S.

8. Carbon in organic compounds exhibits the following properties:

a) an oxidizing agent;

b) reducing agent;

Acidic waste products are a natural by-product of cellular metabolism. There are over 60 trillion cells in the human body, with an average life cycle of 4 weeks. At the end of the cycle, each cell divides into two genetically equivalent units. However, only half of the newly formed cells are destined for further development. The rest of the weak, damaged and polluted cells simply die. Other millions of cells become acid waste.

The natural aging process is also taking its toll - the body's internal environment tends to oxidize over the years. It often happens that after 45 years the body loses the ability to get rid of accumulated acid waste and begins to store it in various parts of the body, subsequently causing illness.

Considering each disease, we must necessarily analyze its causes and effects. A surprising number and variety of physical problems and diseases can be caused by the oxidation of the body. Today, the vast majority of the population suffers from problems caused by acidification - due to special eating habits and lifestyles, without even knowing it. Let's look at the oxidation factors:

• Increased consumption of acidic foods.

The modern diet contains more acidic foods (ph below 7), so our initially alkaline body gradually begins to oxidize.

• Drinks that we drink daily are also acidic (Coffee, water

without gas, tea, beer, etc.)

• Decreased secretion (excretion) of acid.

During exercise, sweat releases a large amount of acids from the body, but nowadays people do not always have enough time to play sports.

Let's look at nutrition - the number one cause of body oxidation. All foods provide essential nutrients and energy needed for the development and growth of the human body. The difference between good and bad food is determined by the relative amount of hazardous waste generated by its consumption. Keep in mind that alkaline substances neutralize acid waste and cleanse the body, and acid substances lead to oxidation and contamination.

One of the main foundations of good health is acid-base balance. Unfortunately, the foods that we eat every day are acidic (Ph below 7). Alkaline foods such as vegetables and fruits are eaten in much smaller quantities. Let's take a look at the products we use.

The table shows that the bulk of the products are acidic and have an acidic ph, as a result of which acidification of the body occurs, which subsequently causes various diseases. For example: acidic wastes have accumulated in the body near the pancreas, and alkaline calcium ions are not enough to neutralize them, a person becomes ill with diabetes. Of course, you shouldn’t eat melon, carrots, pears all day long (which refers to alkali), but it’s enough to use alkaline water, which you can get with help, to maintain the acid-base balance of the body.

Let's look at a specific example of how the body's oxidation affects our blood.

Blood picture of a healthy person (Fig. 1) Blood during oxidation of the body (Fig. 2)

In the right picture, we see blood cells that look like coins stuck together - these are red blood cells, but they should not look like this. They need to be separated, circulate freely in the blood and distribute oxygen. But that doesn't happen here. The blood here is so oxidized that the cells are trying to protect themselves from the acidic environment. This person has an oxygen distribution disorder. If you pay attention, you will also see black dots - this is cholesterol that clogs the capillaries. This is how blood clots occur in the heart, in the brain.

In Figure 1, we see an already changed picture 20 minutes after taking live (alkaline water). The erythrocytes have separated, which means alkalization of the blood. They began to "transport" oxygen and began to feel great.

Healthy cells need an alkaline environment. Evidence suggests that excess acidity is the root cause of all disease. Any disease, from the common cold to cancer, manifests itself when the body becomes unable to cope with the accumulation of acid waste.

There are many ways to show that alkaline water has a significant impact on the health and functionality of the human body. For now, let's summarize a few things - as it's very important to minimize visits to the doctor:

• It's your
• Temperature
• General well-being

These 3 parameters are indicators of your general condition. Because as soon as you start drinking living water, or anything else that can adjust your pH to the alkaline side, you will feel better, and your body will feel much better due to detoxification, cleansing and regeneration. What does it mean to reduce your medication intake?

In contact with

Biological oxidation - it is a set of redox transformations of various substances in living organisms. Redox reactions are called reactions that occur with a change in the oxidation state of atoms due to the redistribution of electrons between them.

Types of biological oxidation processes:

1)aerobic (mitochondrial) oxidation is designed to extract the energy of nutrients with the participation of oxygen and its accumulation in the form of ATP. Aerobic oxidation is also called tissue respiration, since during its course the tissues actively consume oxygen.

2) anaerobic oxidation- this is an auxiliary way to extract the energy of substances without the participation of oxygen. Anaerobic oxidation is of great importance when there is a lack of oxygen, as well as when performing intense muscular work.

3) microsomal oxidation It is intended for the neutralization of drugs and poisons, as well as for the synthesis of various substances: adrenaline, norepinephrine, melanin in the skin, collagen, fatty acids, bile acids, steroid hormones.

4) free radical oxidation necessary for the regulation of renewal and permeability of cell membranes.

The main pathway of biological oxidation is mitochondrial associated with providing the body with energy in an accessible form. Energy sources for humans are a variety of organic compounds: carbohydrates, fats, proteins. As a result of oxidation, nutrients decompose to final products, mainly to CO 2 and H 2 O (during the breakdown of proteins, NH 3 is also formed). The energy released in this case is accumulated in the form of the energy of chemical bonds of macroergic compounds, mainly ATP.

Macroergic organic compounds of living cells containing energy-rich bonds are called. During the hydrolysis of macroergic bonds (indicated by a sinuous line ~), more than 4 kcal / mol (20 kJ / mol) is released. Macroergic bonds are formed as a result of the redistribution of the energy of chemical bonds in the process of metabolism. Most high-energy compounds are phosphoric anhydrides, such as ATP, GTP, UTP, etc. Adenosine triphosphate (ATP) occupies a central place among substances with macroergic bonds.

adenine - ribose - P ~ P ~ P, where P is a phosphoric acid residue

ATP is found in every cell in the cytoplasm, mitochondria and nuclei. Biological oxidation reactions are accompanied by the transfer of a phosphate group to ADP with the formation of ATP (this process is called phosphorylation). Thus, energy is stored in the form of ATP molecules and, if necessary, used to perform various types of work (mechanical, electrical, osmotic) and to carry out synthesis processes.

The system of unification of oxidation substrates in the human body

The direct use of the chemical energy contained in the molecules of food substances is impossible, because when intramolecular bonds are broken, a huge amount of energy is released, which can lead to cell damage. In order for nutrients that enter the body, they must undergo a series of specific transformations, during which there is a multi-stage decomposition of complex organic molecules into simpler ones. This makes it possible to gradually release energy and store it in the form of ATP.

The process of converting various complex substances into one energy substrate is called unification. There are three stages of unification:

1. Preparatory stage occurs in the digestive tract, as well as in the cytoplasm of body cells . Large molecules break down into their constituent structural blocks: polysaccharides (starch, glycogen) - to monosaccharides; proteins - to amino acids; fats - to glycerol and fatty acids. This releases a small amount of energy (about 1%), which is dissipated in the form of heat.

2. tissue transformations starts in the cytoplasm of cells and ends in mitochondria. Even simpler molecules are formed, and the number of their types is significantly reduced. The resulting products are common to the metabolic pathways of various substances: pyruvate, acetyl-coenzyme A (acetyl-CoA), α-ketoglutarate, oxaloacetate, etc. coenzyme A - the active form of vitamin B 3 (pantothenic acid). The processes of breakdown of proteins, fats and carbohydrates converge at the stage of formation of acetyl-CoA, subsequently forming a single metabolic cycle. This stage is characterized by a partial (up to 20%) release of energy, part of which is accumulated in the form of ATP, and part is dissipated in the form of heat.

3. Mitochondrial stage. The products formed in the second stage enter the cyclic oxidizing system - the tricarboxylic acid cycle (Krebs cycle) and the associated mitochondrial respiratory chain. In the Krebs cycle, acetyl-CoA is oxidized to CO 2 and hydrogen associated with carriers - NAD + H 2 and FAD H 2. Hydrogen enters the respiratory chain of mitochondria, where it is oxidized by oxygen to H 2 O. This process is accompanied by the release of approximately 80% of the energy of chemical bonds of substances, part of which is used to form ATP, and part is released in the form of heat.

Classification and characterization of the main oxidoreductases in tissues

An important feature of biological oxidation is that it proceeds under the action of certain enzymes. (oxidoreductase). All the necessary enzymes for each stage are combined into ensembles, which, as a rule, are fixed on various cell membranes. As a result of the coordinated action of all enzymes, chemical transformations are carried out gradually, as if on a conveyor belt. In this case, the reaction product of one stage is the starting compound for the next stage.

Classification of oxidoreductases:

1. Dehydrogenases carry out the elimination of hydrogen from the oxidized substrate:

SH 2 + A → S +AH 2

In processes associated with the extraction of energy, the most common type of biological oxidation reactions is dehydrogenation, that is, the elimination of two hydrogen atoms from the oxidized substrate and their transfer to the oxidizing agent. In fact, hydrogen in living systems is not in the form of atoms, but is the sum of a proton and an electron (H + and ē), the routes of movement of which are different.

Dehydrogenases are complex proteins, their coenzymes (non-protein part of a complex enzyme) can be both an oxidizing agent and a reducing agent. By taking hydrogen from substrates, coenzymes are converted into a reduced form. Reduced forms of coenzymes can donate hydrogen protons and electrons to another coenzyme that has a higher redox potential.

1) OVER + - and NADP + -dependent dehydrogenases(coenzymes - OVER + and NADP + - active forms of vitamin PP ). Two hydrogen atoms are attached from the oxidized substrate SH 2, and the reduced form is formed - NAD + H 2:

SH 2 + OVER + ↔ S + OVER + H 2

2) FAD-dependent dehydrogenases(coenzymes - FAD and FMN - active forms of vitamin B 2). The oxidizing abilities of these enzymes allow them to accept hydrogen both directly from the oxidized substrate and from reduced NADH 2 . In this case, reduced forms of FAD·H 2 and FMN·H 2 are formed.

SH 2 + FAD ↔ S + FAD H 2

OVER + N 2 + FMN ↔ OVER + + FMN N 2

3) coenzymeQor ubiquinone, which can dehydrogenate FAD H 2 and FMN H 2 and add two hydrogen atoms, turning into KoQ H 2 ( hydroquinone):

FMN N 2 + KoQ ↔ FMN + KoQ N 2

2. Iron-containing electron carriers of hemic nature – cytochromesb, c 1 , c, a, a 3 . Cytochromes are enzymes belonging to the class of chromoproteins (stained proteins). The non-protein part of cytochromes is represented by heme containing iron and similar in structure to the heme of hemoglobin. One cytochrome molecule is able to reversibly accept one electron, while the oxidation state of iron changes:

cytochrome (Fe 3+) + ē ↔ cytochrome (Fe 2+)

Cytochromes a, a 3 form a complex called cytochrome oxidase. Unlike other cytochromes, cytochrome oxidase is able to interact with oxygen, the final electron acceptor.

Redox reactions. The role of redox processes in the body. Redox potential. Nernst equation.

Respiration and metabolism, putrefaction and fermentation, photosynthesis and nervous activity of living organisms are associated with redox reactions. Redox processes underlie fuel combustion, metal corrosion, electrolysis, metallurgy, etc. Reactions that occur with a change in the oxidation state of the atoms that make up the reacting molecules are called redox reactions. The processes of oxidation and reduction proceed simultaneously: if one element participating in the reaction is oxidized, then the other must be reduced. An oxidizing agent is a substance containing an element that accepts electrons and lowers the oxidation state. The oxidizing agent is reduced as a result of the reaction. So, in the reaction 2Fe +3 Cl - 3 + 2K + I - -> I 2 0 + 2Fe +2 Cl 2 - + 2K + Cl -. Reducing agent - a substance containing an element that donates electrons and increases the oxidation state. The reducing agent is oxidized as a result of the reaction. The reducing agent in the proposed reaction is the ion I - . The source of electrical energy in the element is the chemical reaction of displacement of copper by zinc: Zn + Cu 2+ + Cu. The work of zinc oxidation, equal to the loss of the isobaric-isothermal potential, can be represented as the product of the transferred electricity and the value of e. d.s.: A \u003d - - dG 0 \u003d p EF, where p is the charge of the cation; E- h. d.s. element and F- Faraday number. On the other hand, according to the reaction isotherm equation. Redox potentials are of great importance in human and animal physiology. The redox systems include such systems in the blood and tissues as heme/hematia and cytochromes, which contain bi- and trivalent iron; ascorbic acid (vitamin C), which is in oxidized and reduced forms; the system of glutathione, cystine-cysteine ​​of succinic and fumaric acids, etc. The most important process of biological oxidation, namely the transfer of electrons and protons from an oxidized substrate to oxygen, carried out in tissues using a strictly defined series of intermediate carrier enzymes, is also a chain of redox processes . Each link in this chain corresponds to one or another redox system, which is characterized by a certain redox potential.

Determining the direction of redox reactions by standard values ​​of the free energy of formation of reagents and by the values ​​of redox potentials.

Various life processes are accompanied by the occurrence in the body of electrochemical processes that play a significant role in metabolism. Electrochemical transformations in the body can be divided into two main groups: processes associated with the transfer of electrons and the occurrence of redox potentials; processes associated with the transfer of ions (without changing their charges) and with the formation of bioelectric potentials. As a result of these processes, potential differences arise between different layers of tissues in different physiological states. They are associated with different intensity of redox biochemical processes. These include, for example, photosynthesis potentials that arise between illuminated and unilluminated areas of the leaf, and the illuminated area turns out to be positively charged with respect to the unlit area. Redox processes of the first group in the body can be divided into three types: 1. Direct transfer of electrons between substances without the participation of oxygen and hydrogen atoms, for example, electron transfer in cytochromes: cytochrome (Fe 3+) + e -> cytochrome (Re 2+ ) and electron transfer in the enzyme cytochrome oxidase: cytochrome oxidase (Cu 2+) + e -> cytochrome oxidase (Cu 1+). 2. Oxidative, associated with the participation of oxygen atoms and oxidase enzymes, for example, the oxidation of the aldehyde group of the substrate into an acid one: RСОН + O ó RСООН. 3. pH-dependent, occurring in the presence of dehydrogenase (E) and coenzymes (Co) enzymes, which form an activated enzyme-coenzyme-substrate complex (E-Co-5), attaches electrons and hydrogen cations from the substrate and causes its oxidation. coenzymes are nicotinamide-adenine-nucleotide (NAD +), which attaches two electrons and one proton: S-2H - 2e + NAD * ó S + NADH + H +, flavin-adenine dinucleotide (FAD), which attaches two electrons and two protons: S - 2H - 2e + FAD óS + FADH 2, and ubiquinone or coenzyme Q (CoO), which also attaches two electrons and two protons: S-2H - 2e + KoQ ó S + KoQH 2.

66. Oxidometry, iodometry, permanganatometry. Application in medicine.

Depending on the titrants used, there are several types of redox titration: permanganometric, iodimetric, bichromatometric, and others. Permanganometric titration is based on the interaction of a standard solution of potassium permanganate with a reducing agent solution. Oxidation with potassium permanganate can be carried out in acidic, alkaline, and neutral media, and the products of KMnO reduction are different in different media. Permanganometric titration is recommended to be carried out in an acidic environment. First, as a result of the reaction, colorless Mn 2+ ions are formed, and one excess drop of KMnO 4 titrant will color the titrated solution pink. When oxidized in a neutral or alkaline medium, a dark brown precipitate precipitates, or dark green MnO 2-4 ions are formed, making it difficult to fix the equivalence point. Secondly, the oxidizing ability of potassium permanganate in an acidic environment is much greater (E ° MnO 4 / Mn 2+ \u003d + 1.507v) than in an alkaline and neutral environment. The standard oxidation potential of the pair E) / 2G - is 0.54 V. Therefore, substances whose oxidation potential is below this value will be reducing agents. And, therefore, they will direct the reaction from left to right, "absorbing" iodine. Such substances include, for example, Na 2 83Oz, tin (II) chloride, etc. Substances whose oxidation potential is higher than 0.54 V will be oxidizing agents with respect to the ion and will direct the reaction towards the release of free iodine: 2I + 2e \u003d I 2. The amount of released free iodine is determined by titrating its solutions of Na 2 S 2 O 3 thiosulfate: I + 2e -> 2I - Sodium thiosulfite absorbs free iodine, shifting the reaction equilibrium to the right. For the reaction to proceed from left to right, an excess of free iodine is needed. Usually a back titration is carried out. To the reducing agent, which is determined, immediately add an excess of titrated iodine solution. Part of it reacts with the reducing agent, and the remainder is determined by titration with a solution of sodium thiosulfate.

67. Quantum - mechanical model of the atom.

Quantum (or wave) mechanics is based on the fact that any material particles simultaneously have wave properties. This was first predicted by L. de Broglie, who in 1924 theoretically showed that a particle with mass m and speed v can be associated with wave motion, the wavelength of which X is determined by the expression: L \u003d h / m v, where h (Planck's constant ) = 6.6256-10-27 erg-s = 6.6256-10 34 J-s. Soon this assumption was confirmed by the phenomena of electron diffraction and interference of two electron beams. The dual nature of elementary particles (particle-wave dualism) is a particular manifestation of the general property of matter, but it should be expected only for micro-objects. The wave properties of microparticles are expressed in the limited applicability to them of such concepts that characterize a macroparticle in classical mechanics as coordinate (x, y, z) and momentum (p = m v). ​​For microparticles, there are always uncertainties in the coordinate and momentum, related by the Heisenberg relation : d x d p x > = h, where d x is the uncertainty of the position, and d p x is the uncertainty of the momentum. According to the uncertainty principle, the motion of a microparticle cannot be described by a certain trajectory and it is impossible to represent the motion of an electron in an atom in the form of motion along a specific circular or elliptical orbit, as was accepted in the Bohr model. The description of the motion of an electron can be given with the help of de Broglie waves. The wave corresponding to the microparticle is described by the wave function y(x, y, G). It is not itself that has physical meaning; wave function, but only the product of the square of its modulus and the elementary volume |у| 2 -dу, equal to the probability of finding an electron in an elementary volume dv = dx -dу-dz. The Schrödinger wave equation is a mathematical model of an atom. It reflects the unity of corpuscular and wave properties of an electron. Without going into the analysis of the Schrödinger equation.

68. Electron cloud orbital.

The idea of ​​an electron as a material point does not correspond to its true physical nature. Therefore, it is more correct to consider it as a schematic representation of an electron “smeared” over the entire volume of the atom in the form of the so-called electron cloud: the denser the points are located in one place or another, the greater the density of the electron cloud here. In other words, the electron cloud density is proportional to the square of the wave function. E the energy of an electron in an atom depends on the principal quantum number P. In a hydrogen atom, the energy of an electron is completely determined by the value P. However, in many-electron atoms the electron energy also depends on the value of the orbital quantum number. Therefore, the states of an electron, characterized by different values, are usually called the energy sublevels of an electron in an atom. In accordance with these notations, they speak of s - sublevel, p-sublevel, etc. Electrons characterized by the values ​​of the side quantum number O, 1, 2 and 3, respectively, are called s-electrons, p-electrons, d - electrons and f - electrons. For a given value of the principal quantum number P s-electrons have the lowest energy, then p-, d - and f-electrons. The state of an electron in an atom that corresponds to certain values P and l, is written as follows: first, the number indicates the value of the main quantum number, and then the letter indicates the orbital quantum number. Thus, the designation 2p refers to an electron for which P= 2 and l = 1, the designation 3d - to an electron with n = 3 and l == 2. The electron cloud has no boundaries sharply defined in space. Therefore, the concept of its size and shape requires clarification.

69. Characterization of the electrical state of an electron by a system of quantum numbers: principal, orbital, magnetic and spin quantum numbers.

In a one-dimensional model of an atom, the energy of an electron can only take on certain values, in other words, it quantized. The energy of an electron in a real atom is also a quantized quantity. Possible energy states of an electron in an atom are determined by the value of the main quantum number P, which can take positive integer values: 1, 2, 3... etc. The electron has the lowest energy at n = one; with increasing P. the energy of the electron increases. Therefore, the state of an electron, characterized by a certain value of the main quantum number, is usually called the energy level of the electron in the atom: at n = 1, the electron is at the first energy level, at n = 2 at the second, etc. The main quantum number determines and size of the electron cloud. In order to increase the size of the electron cloud, it is necessary to move part of it to a greater distance from the nucleus. The shape of the electron cloud cannot be arbitrary either. It is determined by the orbital quantum number (also called side or azimuthal quantum number), which can take integer values ​​from 0 to (P- 1), where P is the principal quantum number. different meanings P corresponds to a different number of possible values. Thus, for i = 1, only one value is possible; orbital quantum number - zero (/ = 0), at n= 2l can be equal to 0 or 1, for i = 3 the values ​​/ equal to 0, 1 and 2 are possible; in general, given the value of the principal quantum number P correspond P different possible values ​​of the orbital quantum number. It follows from the Schrödinger equation that the orientation of the electron cloud in space cannot be arbitrary: it is determined by the value of the third, the so-called magnetic quantum number, etc. The magnetic quantum number can take on any integer values, both positive and negative, ranging from + L to - L. Thus, for different values, the number of possible values ​​m is different. So, for s-electrons (l = 0) only one value of m (m - 0) is possible; for p-electrons (L=1) three different values ​​are possible t. P besides quantum numbers n, I and m, the electron is characterized by another quantized quantity, not related to. by the motion of an electron around the nucleus, but by determining its own state. This quantity is called the spin quantum number or simply spin; spin is usually denoted by the letter S. The spin of an electron can only have two values. Thus, as in the case of other quantum numbers, the possible values ​​of the spin quantum number differ by one.

Oxidation is the process by which atoms and molecules lose electrons, a chemical reaction in which something reacts with oxygen to form oxides.

This is the most important chemical reaction in the body. The reaction is natural and normal. The energy necessary for a person is formed by the oxidation of organic compounds that come with food. As a result of biological oxidation or cellular respiration, heat, water, carbon dioxide are formed, amino acids are converted, hormones are formed.

However, excessive uncontrolled oxidation is a destructive process, it is diseases and early aging.

Antioxidants are chemical compounds that prevent excessive oxidation. Free radicals are chemical compounds that result from excessive oxidation.

The danger of free radicals

Free radicals are harmful substances that are formed as a result of inadequate oxygen reduction, these are active "pollutants". They can cause a chain reaction and lead to damage to the cells of the body. Our body is able to resist free radicals, neutralize the effects of toxic and foreign substances as much as possible, but when the oxidative process exceeds the protective capabilities of the body, a disease begins.

Free radicals are the causative agents of cancer. Under their influence, strokes and heart attacks, a whole range of autoimmune and mental diseases occur. Including a number of addictions or psychological addictions.

One of the main reasons for the increase in free radicals in the body is eating. Many leading doctors and scientists have worked and are working in this direction, academician neurosurgeon G.Shatalova, academician physiologist A.Ugolev, professor oncologist I. Petrov, biochemist K.Kembel, cardiologist D Ornish, cardiosurgeon E. Wareham, Ph.D. oncologist V. Elburg.

What is needed to avoid an increase in free radicals in the body?

We need antioxidants!
Antioxidants can be artificial in the form of vitamins and dietary supplements, and natural.
Natural antioxidants are all types of plants, fruits, vegetables, cereals.

Antioxidants are found ONLY in live plant foods, and excess animal protein causes an increase in free radicals.

The richest in antioxidants are fresh fruits and vegetables with a bright, saturated color, with pronounced pigmentation. Antioxidants are usually colored because the same chemical responsible for absorbing excess electrons also creates visible colors. Some antioxidants are called carotenoids, and there are hundreds of types. They range in color, from yellow beta-carotene (pumpkin) to red lycopene (tomatoes) and orange cryptoxanthin (oranges). Other antioxidants are colorless, such as chemicals such as ascorbic acid (citrus fruits, greens) and vitamin E (nuts, grains).

Many believe that taking artificial antioxidant preparations will protect them from the harmful effects of other factors. However, we firmly declare that in the course of numerous studies, scientists have found that antioxidants in the dosage form do not prevent the destructive effects of free radicals on cells and do not slow down the aging process of the body. Unfortunately, there is no point in taking vitamins while maintaining a high-protein diet. In this case, it is necessary.

All tastes in a person are acquired, except for breast milk, which means that at any age a person can change his taste preferences.
Wall Street Journal (2014.1)