Tashkent Medical Academy Department of Bioorganic and Biological Chemistry Subject: bioinorganic and physical–colloidal chemistry The lecture "Physics and Chemistry of Surface Fenomena" (Lectures on bioinorganic chemistry and fizkolloidnoy for students 1st year) Lecture number 7 Author: Professor Kasimova S.S. Tashkent - 2013

Surface phenomena and their role in biology and medicine The role and importance of adsorption processes in the body, it is easy to understand, for example, when considering the adsorption capacity of red blood cells in human blood. Red blood cells are the carriers of various substances, including amino acids, which they spread and transmit the various cells and tissues. Number of red blood cells in the blood of adult humans is approximately 5,000,000 to 1 mm3. On average, 1 kg in healthy men have 450 billion. erythrocytes or 27 trillion for the whole body

Knowing the diameter of the red blood cell (7-8 microns), we can calculate the total surface of the red blood cells of the blood of man, which is about 3,200 m2. On average, 1 kg in healthy men have 450 billion. erythrocytes or 27 trillion for the whole body.

Number of red blood cells in the blood of adult humans is approximately 5,000,000 to 1 mm3. On average, 1 kg in healthy men have 450 billion. erythrocytes or 27 trillion for the whole body. Knowing the diameter of the red blood cell (7-8 microns), we can calculate the total surface of the red blood cells of the blood of man, which is about 3,200 m2.

The surface energy and surface tension Important properties of colloidal and microheterogeneous systems due to the presence of the interface between the particles of the dispersed phase and the dispersion medium. The specific surface area of the dispersed system of particles per unit volume of the dispersed phase. The smaller the particles of the dispersed phase, the greater the surface area of the system, ie the specific surface area of the dispersed or colloidal system is inversely proportional to the linear dimensions of the particles of the dispersed phase. With a decrease in their size, the specific surface of dispersed, particularly in colloidal systems is increasing rapidly.

Not all of the molecules occupying the body volume, equally define its properties. Thus, the molecules in the thin surface layers at the interface to behave differently than in the volume of each phase. For example, if the molecule is in the bulk liquid (Fig. 1a), it is attracted by molecules within the scope of its influence and the resultant force is zero due to the symmetry of the force field.

If the molecule is from the surface to a distance less than the radius of interaction, the attraction felt by a molecule from all sides, not the same, the molecule near the surface weakened gravity acting in the direction of the interface. As a result, the forces are not fully compensated and there is the resultant force (Fig. 1b), which aims to "draw" the molecule back into the bulk liquid. This force is a maximum when the molecule is on the surface (it only apply forces directed inward) (Fig. 1, B). To move a molecule from the bulk to the surface of the liquid should accomplish the work against the forces pushing it back into the volume.

To move the molecules of the liquid from the bulk to the surface layer must be expended work associated with overcoming the internal pressure

Due to the molecular forces neskompensirovannosti surface layer has excess free energy compared to the amount of liquid. This surplus per unit surface, is called the specific surface free energy and is denoted by the letter σ. The value of σ is also called surface tension, as the specific surface free energy numerically equal surface tension (only single-component liquid).

Surface free energy G of a heterogeneous system is defined as a product of the area of the interface on the surface tension: G= σ · S, where G - the surface free energy, J; σ - surface tension, J/m2; S - surface interface, m2. The value of G determines the possibility of occurrence of many processes and is an important thermodynamic characteristics.

Adsorption, types of adsorption The more highly developed material surface, the stronger the flow processes related to surface phenomena, and in the first adsorption. For the first time the phenomenon of gas adsorption charcoal observed in 1777 D. Fontana, then T.E.Lovits used it, to clean coal solutions. The subsequent investigation of the nature of adsorption phenomena and their practical application study Russian and foreign scientists M.S.Tsvet, NDZelinskii N.A.Shilov, M.M.Dubinin, Dzh.Gibbs, I.Lengmyur, and G.Freyndlih etc.

Adsorption is a spontaneous isothermal process condensed mass of solute in the surface layer, caused by an excess of free energy and is accompanied by a decrease in surface tension.

Adsorption is a reversible process Adsorption is a reversible process. Reverse process of adsorption, desorption is called. Substance on the surface of which adsorption takes place is called the adsorbent, and the absorbed substance - adsorptive. Adsorption depends on the chemical and physical nature of the adsorbent and the adsorptive.

When molecules of gaseous or vaporous substances diffuse into the interior of the adsorbent, forming with it a smooth paste, the process of absorption of the adsorptive called absorption. The dissolution process of any gas in a liquid is an example of absorption. Therefore, absorption - the phenomenon of volume, and adsorption - purely superficial. In some cases, when absorbed by a substance chemically reacts with the adsorbent, such a process as opposed to physical adsorption is called chemisorption. Chemisorption can occur in the surface layer, and in the thickness of the adsorbent.

All of these concepts - adsorption, absorption and chemisorption is the general name of sorption processes and characterize the absorption of gases, vapors and solutes by solids and liquids. Adsorption can take place at any of the interface: the liquid - gas, solid-gas, liquid - liquid, solid - liquid. Adsorption is denoted by the Greek letter r (gamma).

Surfactants and surface-inactive substances Solutes alter the surface tension of the liquid, those that significantly lower the surface tension is called surface-active agents (surfactants), and those that increase the surface tension of a few, are called surface-inactive substances (IRP). Molecule surfactants able to concentrate in the surface layer, and thus there is a positive adsorption, ie T> 0.

Surfactants are organic compounds whose molecules are built asymmetrically, and at the same time contain: active polar hydrophilic group interacts well with water molecules, such as:-OH,-COOH,-NH2-, -NO2,-SO3N,-SO3Na,-COONa, etc. and   nonpolar hydrophobic group - a hydrocarbon radical. So, in the molecule of butyric acid CH3-CH2-CH2-COOH group is the polar-COOH, and the non-polar - the hydrocarbon chain. Therefore, these molecules are called diphilic ("loving" the two solvents - the polar and non-polar). Diphilic molecules are usually portrayed as a symbol

where the circle corresponds to the polar group and the bar - nonpolar radical.

On dissolution of the surfactant in the polar and non-polar solvent molecule is energetically more favorable to move from the bulk to the surface layer (like dissolves like).

This important relationship has been formulated in the form of a rule-Duclos Traube: "For the lower members of the homologous series of fatty acids, alcohols and amines with increasing hydrocarbon chain to the group-CH 2-surface active agents at the liquid-gas increases by 3-3.5 times at the same molar concentration."

Qualitatively, this rule can be explained by the decrease "specific gravity" of the polar group in the molecule with increasing chain length. With the lengthening of the chain in the homologous series of adsorption increases, but for all members of a number of curves tend to the same limit value of G00, called the limiting adsorption (Fig. 2).

Fig.2. The family of adsorption isotherms on the border solution – gas for a homologous series of surfactants - organic acids: 1 - propionic acid, 2 - oil 3 - valeric 4 - Nylon

SAW - is the most popular and the most common source of pollution of the biosphere today (sewers, factories, laundries, etc.). The presence of surfactants in natural waters violates their oxygen conditions - leads to the death of flora and fauna, water quality changes, foam surfactant can be a source of infection. In this regard, the SAW introduced stringent maximum permissible concentration (MPC) - 0.5 mg / L, and the industry is allowed to use only those surfactants that almost decomposed in natural conditions.

Adsorption at the liquid - gas and liquid - liquid Adsorption at the liquid - gas and liquid - liquid. Gibbs adsorption isotherm equation and Langmuir Adsorption can be characterized by the dependence of the adsorbate from the equilibrium pressure or concentration at constant temperature. Dependence D = f (R) and T = f (C) at a constant temperature are called adsorption isotherms.

The constancy of T for all members of a homologous series has allowed American scientist I.Lengmyuru in 1915 to put forward ideas about the structure of the surface layers and the orientation of the adsorbed molecules in the surface layer. He formulated the principle of the independence of the surface, which consists in the fact that the adsorption at the interface diphilic surfactant molecules orient themselves: their polar groups facing the more polar and non-polar - a less polar phase (Fig. 3)

Fig. 3. The structure of the surface layer of the adsorption of the surfactant at the interface water - air a, b - unsaturated adsorption bed, in - saturated adsorption layer

Adsorption of the gaseous medium (maximum adsorption saturation) describes the adsorption equation proposed in 1919 I.Lengmyurom: where Г - maximum value of adsorption (the extreme concentration of gas at the surface of 1m2) kmol/m2 C - equilibrium concentration of the gas, ie, gas concentration, is still free after the adsorption equilibrium, kmol/m3, K - adsorption coefficient, which depends on the nature of the adsorbent and the adsorbed substance.

Equation (I) shows that if the concentration of adsorbed gas from small, then it can be neglected in the denominator of the equation becomes: ie between the adsorption and concentration there is a direct proportionality.

ie in this case the maximum possible amount of adsorbed gas.

Fig.4. Adsorption isotherm I.Lengmyura

Gibbs equation. The ratio of the concentration of solute in solution C, D adsorption (excess of matter in the surface layer) and surface tension σ on the boundary solution - gas (Fig. 5) derived in 1878 by thermodynamic Dzh.U.Gibbs. He proposed an equation that bears his name:

where C - the concentration in mol / L or kmol/m3, T - absolute temperature, K; R - gas constant, equal to 8.31 J / K mol; (dσ / dC) m - surface activity, showing the change in surface tension solution with a concentration J/m2. The sign and magnitude of the solute adsorption on the surface of a dilute solution determined derivative (dσ / dC) t Adsorption is positive (r> 0) for (dσ / dC) m <0, ie, with increasing concentration of solute surface tension decreases. This is true for products less polar than the solvent, and lower surface tension.

Models of biological membranes Models of biological membranes. a- the first model of the unit membrane Danielli, Davson, Robertson, b - a universal model of the membrane Capaldi, Green's model of the membrane c,d-subunit structures.

Fig. 8. Chromatographic column Fig. 8. Chromatographic column. 1 - fluid level (minimum), 2 - sand, 3 - Alumina Al2 O3 4 - glass wool, 5 - clamp.