Kharkiv National Medical University Department of Medical and

Kharkiv National Medical University Department of Medical and Bioorganic chemistry «Medical Chemistry» Lecture № 9 Micro geterogeneous systems. Colloidal solutions. Coarsely dispersed systems Lecturer: As. Professor, Department of Medical and Bioorganic Chemistry, , Ph. D. Lukianova L. V.

Plan of lecture 1. Dispersed systems: general aspects, classification. 2. Methods of preparation of colloidal solutions. 3. Methods of colloidal solutions purification. 4. Properties of colloidal solutions. 5. Structure of micelles. 6. Stability and coagulation of the dispersed systems. 7. Coagulation by means of electrolytes. 8. Coagulation in the biological systems. 9. Coarsely dispersed systems.

The most important biological liquids such as blood, urine and spinal fluid contain slightly soluble substances in colloid state: cholesterol, carbonate, phosphate, urate, and salts of other acids. Break of their stability causes their precipitation resulting in arteriosclerosis, holelithiasis, urolithiasis, etc. Knowledge of coagulation and stability of the dispersed, systems is necessary to understand processes taking place in the human organism, because a large number of biological fluids in the organism are colloidal systems. One of the most important characteristics of blood is red corpuscles sedimentation rate (RCSR) which increases if some kind of pathology takes place. Coagulation phenomena become clearly seen in the process of blood coagulation. The nature of blood coagulation must be taken into account during the blood conservation as well as in the process of creation of new medicinal materials possessing antithrombotic properties.

Colloidal chemistry – the science of surface phenomena and dispersed systems. Surface phenomena – a set of phenomena associated with the physical characteristics of the interfaces between contiguous phases. Dispersed Systems – heterogeneous system in which one phase is dispersed in the (fragmented state). 4

Colloidal solution Dispersed phase (fractured part dispersed system) Dispersion medium (continuous part of the dispersion system) Dispersed phase Dispersion medium

Dispersed system – is a system consisting of dispersed particles and the medium in which these are suspended. Dispersed systems are classified according to: Ø their dispersity; Ø the state of aggregation of the dispersed phase and the dispersion medium; Ø the intensity of the interaction between them; Ø the absence or formation of structures in the dispersed systems.

Classification of dispersed systems on the base of particles size Ø True solutions – size of particles is < 10 -9 m, particles of solute are molecules or ions Ø Colloids – size of particles is 10 -7 - 10 -9 m, particles of intermediate size Ø Coarsely dispersed systems – size of particles is > 10 -7 m, particles of solute are insoluble in a given solvent (suspensions, emulsions).

Classification of the state of aggregation of the dispersed phase and the dispersion medium Dispersed phase Dispersion medium Type of dispersed system Example Gas Liquid Foam soap lather, whipped cream, soda water Gas Solid foam bread, pumice, slag, foam concrete, lava Liquid Gas Aerosol fog, cloud, spray Liquid Emulsion milk, mayonnaise, oil in water Liquid Solid emulsion pearls, cheese, curd, jelly, butter Solid Gas Aerosol, powder smoke, haze, dust-laden air, flour Solid Liquid Suspension (coarsely dispersed) or sol (highly dispersed) paints, clay, starch dispersed in water Solid sol alloys, colored glass, gems (ruby,

Depending upon the nature of interactions between dispersed phase and dispersion medium, the colloidal solutions can be classified into two types as: lyophilic and lyophobic sols. 1. Lyophilic colloids – the colloidal solutions, in which the particles of the dispersed phase have a great affinity for the dispersion medium. 2. Lyophobic colloids – the colloidal solutions in which there is no affinity between particles of the dispersed phase and the dispersion medium.

Dispersed systems are very widely spread in nature! Soils, clays, natural water, air, clouds, dust, minerals (including precious stones), bread, milk, butter – are colloidal systems. Cells, genes, viruses – are colloidal particles. Biological liquids – blood, lymph, urine, cerebrospinal fluid – are colloidal dispersions. In these liquids substances, e. g. proteins, cholesterine, glycogen and others are present being in colloidal state. Finely dispersed substances easily penetrate through the pores of skin. Medicines in the form of colloids (emulsions, ointments, pastes, aerosols) are widely used in medicine.

Obtaining of colloidal solution 1. By the dispersion, i. e. comminution of large bodies. Comminution by crushing, grinding, or attrition yields comparatively coarsely dispersed powders (over 60 mm size). Finer comminution is achieved with the aid of special equipment named colloid mills, or by employing ultrasound. 2. By the condensation of substances forming molecular or ionic solutions. The condensation method consists in the obtaining of insoluble compounds by chemical reactions of exchange, hydrolysis, reduction, or oxidation.

3. Methods of colloidal solutions purification 1. Dialysis – the process of separating the particles of colloids from impurities by means of diffusion through a suitable membrane. Its principle is based upon the fact that colloidal particles cannot pass through a parchment or cellophane membrane while the ions of the electrolyte can pass through it. The ordinary process of dialysis is slow. To increase the process of purification, the dialysis is carried out by applying electric field. This process is called electrodialysis. 2. Ultra-filtration. It is the process of removing the impurities from the colloidal solution by passing it through graded filter papers called ultra-filter papers.

Properties of colloidal solutions 1. Colligative properties are negligible small. 2. Optical properties. Colloidal systems scatter the light (Tyndall effect). 3. Molecular-Kinetic properties: a) Brownian movement; b) diffusion; c) sedimentation 4. Electrical properties: a) electrophoresis; b) electroosmosis

Structure of colloidal particle (micelle) Pb(NO 3)2 + 2 Na. Cl → Pb. Cl 2↓ + 2 Na. NO 3 Pb(NO 3)2 Na. Cl [Pb. Cl 2]m nucleus

gegenions granule Na+ Na+ Cl. Cl- - + Cl Cl. Na + Na Cl-[Pb. Cl 2]m Cl. Cl Na+Clinner layer of ions Cl- Cl Na+ + Na Na+ diffuse layer of ions Na+ nucleus potentialdetermining ions granule {[Pb. Cl 2]m nucleus + -x + n. Cl (n-x)Na } x. Na potential-determining ions gegenions diffuse layer of ions inner layer of ions

Electrical double layer Micelle has electrical double layer. {[Pb. Cl 2]mn. Cl-(n-x)Na+}-x x. Na+ ζ-potential (electrokinetic potential) ε-potential (electrothermodynamic potential) ζ-potential determines the rate of movement of particles in the electric field. The granule of given micelle will move to the anode, while ions of diffuse layer will move to the cathode.

If all gegenions are in the inner layer, ζ-potential becomes equal zero and micelle is said to be in isoelectric state. {[Pb. Cl 2]mn. Cl-n. Na+}0 The thickness of electrical double layer and the value of ζ-potential depend on concentration of solution. ζ-potential decreases with increase in concentration. In isoelectric state colloidal systems are unstable. The movement of dispersed phase particles in electric field is called electrophoresis. The rate of movement depends on ζ-potential value. Electrophoresis is widely used for aminoacids, antibiotics, enzymes, antibodies and other objects separation. It is also used for plasma proteins investigations with diagnostic purposes.

Micelles with different charges of granule can be obtained depending upon the substance which is present in surplus. Pb(NO 3)2 + 2 Na. Cl → Pb. Cl 2↓ + 2 Na. NO 3 Pb(NO 3)2 Na. Cl Negatively charged sol surplus Na. Cl Pb(NO 3)2 surplus {[Pb. Cl 2]mn. Cl-(n-x)Na+}-xx. Na+ {[Pb. Cl 2]mn. Pb 2+(2 n-x)NO 3 -}+x x. NO 3 - Positively charged sol

Conditions for colloidal systems obtaining An essential condition for colloidal systems obtaining is the mutual insolubility of the substance being dispersed and the dispersion medium. 2. One reagent (it is stabilizer) must be in a small surplus 3. Nucleus of a colloidal micelle – is an insoluble product 4. Potential-determining ions are common for the nucleus and for the stabilizer 5. Gegenions come from the stabilizer. 1. Fe. SO 4 + Na 2 S → Fe. S↓ + Na 2 SO 4 surplus {[Fe. S]mn. Fe 2+(n-x)SO 42 -}+x x. SO 42 - {[Fe. S]mn. S 2 -(2 n-x)Na+}-x x Na+

Emulsions The various pharmaceuticals widely used in medicine are colloidal or coarsely dispersed systems. These are: suspensions, ointments, aerosols, powders, emulsions, pastes. Emulsions are the coarsely dispersed systems of two immiscible liquids in which the liquid acts as the dispersed phase as well as the dispersion medium. They are obtained by mixing an oil with water. Since the two do not mix well, the emulsion is generally unstable and is stabilized by adding emulsifier or emulsifying agent (gum, soap, glass powder, etc). There are two types of emulsions: 1. Oil-in-water emulsion (aqueous emulsions) 2. Water-in-oil emulsion (oily emulsions)

Stability and coagulation of dispersed systems Stability – constant in time the main parameters of the disperse system: the degree of dispersion and uniform distribution of the dispersed phase in the dispersion medium. Coagulation – the process of destruction of colloidal systems by sticking particles form larger aggregates and loss of stability, followed by separation. 21

Coagulation of sols with electrolytes Rules electrolyte coagulation • All electrolytes at certain concentrations can cause coagulation of the sol. • The rule of sign of the charge: the coagulation of the sol causes the ion electrolyte, the sign of the charge which is opposite to the charge of the colloidal particles. This ion is called an ioncoagulator. • Each electrolyte relative to the colloidal solution has a threshold of coagulation (coagulating ability). 22

Coagulation threshold (γ, C) – the lowest concentration of the electrolyte sufficient to cause coagulation of the sol Coagulation ability (P) – the inverse of the threshold of coagulation • Effect of ion charge-coagulator (Schulze-Hardy rule): coagulation ability of the electrolyte increases with increasing ion charge-coagulator n=2÷ 6 23