DISPERSED SYSTEMS

Ingrid Žitňanová

DISPERSED SYSTEMS

Dispersed

phase

(water)Dispersionmedium

(oil)

SOLUTE

(DISPERSED PHASE )

SOLVENT

(DISPERSION MEDIUM )

Solute (NaCl) Solvent (water)

It has a non-uniform composition

There are two or more phases

They can be separated out physically

It has a uniform composition

It has only one phase

It can’t be separated out physically

Classification of the dispersed systems

according to the diameter of dispersed particles

1. Analytical (molecular, true solutions)

2. Colloids

3. Coarse / Crude dispersion (suspension)

< 1 nm

1 – 1000 nm

> 1000 nm

SolutionColloidsSolution Coarse dispersion

particle sizeType of dispersion

Properties of the dispersed systems

Dispersion Molecular (true solut.) Colloidal Coarse (crude)

Particles size 1 nm 1 – 1000 nm > 1000 nm (1 μm)

Particles Filterability Cannot be separated by

filtration

Can be separated by

semipermeabile

membrane

Can be separated by

filtration

Diffusion of particles rapid slow No diffusion

Visibility of particles Not visible under the

electrone microscope

Can be visible under

the electrone

microscope

Can be seen under

the low power

microscope or eye

Sedimentation of

particles

Particals do not sediment Sediment in the

strong centrifugal

field

Sediment under the

influence of gravity

Optical properties Transparent

No Tyndall effect

Tyndall effect Not transparent

Tyndall´s effect

is due to the scattering of light by colloidal particles, while showing

no light in a true solution.

This effect is used to determine whether a mixture is a true solution

or a colloid.

True

solution

Colloidal

solution

• when light is passed

through a colloidal

solution, the substance

in the dispersed phases

scatters the light in all

directions, making it

readily seen

TRUE SOLUTIONS(Analytical, molecular solutions)

TRUE SOLUTION

• a homogeneous mixture of two or more components

• particle size 1 nm

Liquid (vinegar)

Gas (carbon dioxide)

Solid (sugar)

e.g. water Acetic acid in water

CO2 in water

Sugar water

+

SolventsPolar

Nonpolar

Solutes

Polar

Nonpolar

• Polar solutes dissolve well in polar solvents

• Nonpolar solutes dissolve well in non-polar solvents

– e.g.water, ethanol, methanol,

– e.g. chloroform, hexane, benzene

- glucose, acetic acid, NaCl

- fats, steroids, waxes

Oil in water

Electrolytes, Nonelectrolytes

In water,

Strong electrolytes separate into ions making solutions that conduct electricity

Weak electrolytes produce a few ions

Nonelectrolytes produce molecules, not ions, do not conduct electricity

Electrolyte – when dissolved in water separates into cations and anions,

which disperse uniformly through the solvent.

Strong electrolytes

are compounds with ionic or very polar covalent bond

strong electrolyte

when dissolved in water, they dissociate 100% . They break up

into positive and negative ions in water

produced ions conduct an electrical current

Examples: KOH, HCl, HNO3, H2SO4...

Solutes that are weak electrolytes

Weak electrolytes

weak electrolyte

dissolve in water forming a few ions

produce solutions that conduct electricity weakly

Examples: HF, acetic acid, lactic acid, ammonia...

Nonelectrolytes

Solutes - nonelectrolytes are covalent compounds which:

nonelectrolyte

do not produce ions in water

form solutions that do not conduct an electrical current

Examples: sucrose, glucose, urea, ethanol, glycerol...

Average ion concentrations in blood plasma, ISF and ICF (mmol/L)

Electrolytes in body fluids

ICF – intracellular fluid

* Most of them are organic phosphates (hexose-P , creatine-P , nucleotides, nucleic acids)

ISF – interstitial fluid - the fluid in spaces between the tissue cells

Ionic composition of body fluids

Blood plasma and ISF (interstitial fluid) have almost identical

composition, ISF does not contain proteins

The main ions of blood plasma are Na+ and Cl-, responsible for

osmotic properties of ECF (extracellular fluid)

The main ions of ICF (intracellular fluid) are K+, organic

phosphates and proteins

Each body fluid is electroneutral total positive charge = total

negative charge

Interstitial

fluid

Water

Intracellular fluid ICF – inside cells – 25 - 30L

Extracellular fluid ECF – 15L - blood plasma, intersticial fluid,

lymph, fluid in gastrointestinal tract, urine...

Volume of water in body is balanced (intake = output in urine, feces,

sweating, lungs)

Central regulatory organ of water volume – kidneys

Hydrogen

bond

Water – H2O – a polar solvent

O

O

O

O

HH

H

H

H

H

H

H

Average total body water (TBW) as body weight percentage

The water content of the body changes with:

• gender

• age

• body composition (a lean person has a higher TBW than an obese person)

True solutions

Ionic Molecular

NaCl Na+ +

H2OCl

-• solutions of nonelectrolytes

• contain molecules of compounds in

solution (glucose in water, urea)

• solution of electrolytes in which ions

are present, formed by electrolytic

dissociation of ionic compounds

H2O

H2O

H2O

Hydrated

ions

Electrolytic

dissociation

H2O

Cl-

Cl-

Cl-

Cl-

Cl-

H2OH2O

Na+

Na+

Na+

Na+

Solubility

A measure of how much of a solute can be dissolved in a solvent

Saturated Solutions - contain the maximum concentration of a

solute dissolved in the solvent (under a given set of pressure and

temperature). Additional solute will not dissolve in a saturated

solution

Super Saturated Solutions contains more dissolved solute

than could ordinarily dissolve into the solvent. Undissolved

solid remains in the flask.

Unsaturated Solutions – a solution containing less than the

maximum concentration of solute that will dissolve under a given

set of conditions (more solute can dissolve).

Unsaturated Saturated

Super saturated

Factors affecting solubility

• Temperature

• Pressure

• Polarity

Solubility

Temperature

For most solids and most liquids

Solubility increases when solution temperature increases

Temperature

For gases

Higher temperature reduces solubility of gases –

it drives gases out of solution

Examples:

Carbonated soft drinks are more bubbly if stored in the

refrigerator (more CO2 is inside the drink)

Warm lakes have less O2 dissolved in them than cool lakes

Pressure

• little effect on solubility of solids and liquids

• will greatly increase solubility of gases

• Henry's Law: The solubility of a gas in a liquid is directly proportional

to the pressure of that gas above the surface of the solution.

Polar substances tend to dissolve in polar solvents.

Nonpolar substances tend to dissolve in nonpolar solvents.

Examples

Polarity

Vitamin A is soluble in nonpolar compounds (e.g. fats)

Vitamin C is soluble in water

Vitamin A Vitamin C

Properties of true solutions

Colligative properties don´t depend on the chemical composition of a

solute, but depend only on the number of solute particles (molecules or

ions).

The processes based on colligative properties are:

• Diffusion

• Dialysis

• Osmosis

• Freezing point depression

• Boiling point elevation

Diffusion

is a process of spontaneous movement of particles of a dissolved

compound from a region of higher concentration to a region of lower

concentration, to distribute themselves uniformly = movement of a

substance down a concentration gradient

The rate of diffusion depends on the concentration gradient

Particles move until equilibrium is reached

Diffusion usually happens in a solution in gas or in a liquid.

Examples of diffusion:

A sugar cube is left in a beaker of water for a while.

The smell of food spread in the whole house

Biomedical importance of diffusion

Exchange of O2 and CO2 in lungs and in tissues

Certain nutrients are absorbed by diffusion in the gastrointestinal

tract e.g. water soluble vitamins, minerals...

Dialysis

Water and low molecular weight (LMW) compounds (not macromolecules)

are transported across a semipermeable membrane. LMW compounds go from

the more concentrated solution to the less concentrated solution till equilibrium is

reached.

Concentrated

sugar solutionDiluted

sugar solution

Movement of LMW solute

to equal concentrations

Semipermeable membrane

Biomedical importance of dialysis

Biological ultrafiltrates

Many extracellular fluids like interstitial fluids, CSF, glomerular filtrate of

kidneys are formed by ultrafiltration. Proteins do not appear in ultrafiltrates.

Hemodialysis - Blood dialysis

- in patients with acute kidney injury blood is dialyzed in artificial

kidney to eliminate waste products (e.g. urea or creatinine) or toxins

Filtered blood

returning to body Blood flows to

dialyzer

Hemodialyzer

machine

Hemodialyzer

(where filtering takes place)

Biomedical importance of dialysis

Dialyzing

membrane

Dialysate

- solution isotonic with blood,

- it has the same concentrations of all the

essential substances that should be left in blood

Dialysate

Osmosis

Osmosis is the flow of solvent (e.g. water) across a semipermeable

membrane (with smaller pores than dialyzing membrane) from a

lower solute concentration to a higher solute concentration

semipermeable membrane is permeable only to solvent molecules,

not to solute molecules

Concentrated

solution

Diluted

solution

Semi-permeable

membrane

Osmotic pressure (π)

- external pressure that has to be applied on the more

concentrated solution to prevent osmosis

i – number of solute particles in solution to which the compound dissociates

c – amount of substance concentration (mol/L)

R – gas constant – 8.314 J K-1 mol-1

T – temperature in Kelvins (0 °C = -273.15 K)

π = i . c . R . T

π of blood - 780 kPa

Movement of solvent (water)

to equal concentrations

π

Osmolarity (cosm)

molar concentration of all osmotically active particles of solutes in

solution

cosm = i . c

cosm - osmolarity mol/L

i – number of solute particles in solution to which the

compound dissociates

c – amount of substance concentration (mol/L)

Osmolarity (cosm)

Blood serum osmolarity:

πblood = i . c . R . T

cosm

πblood

Blood cosm = = 0.3 mol/L R . T

• Osmolarity is kept constant by kidneys

.

= 780 kPa

Isotonic /isoosmotic solutions

Isotonic solutions are two solutions of equal osmolarity.

Hypertonic solution

Hypertonic solution is one of two solutions that has a higher

osmolarity.

Hypotonic solution

Hypotonic solution is one of two solutions that has a lower

osmolarity.

hemolysis

Crenation

Cells shrink

Solution of NaCl with concentration of 0.15 mol/L

Solution of NaCl with osmolarity of 0.3 mol/L

0.9% NaCl solution (9 g NaCl/L)

Physiological solution

Solution which osmotic pressure corresponds to blood plasma:

Any solution added in large quantity into the bloodstream has

to be isotonic with blood!!

Oncotic pressure

The capillary wall is permeable for small molecules and water but not

permeable for proteins

protein

Oncotic pressure

Oncotic pressure, or colloid osmotic pressure, is a form

of osmotic pressure exerted by proteins (e.g. albumin) in a blood

that usually tends to pull water into the circulatory system.

Water flow driven by

oncotic pressure

diference

Capilary

lumen

The significance of oncotic pressure

Small molecules and ions can be dialyzed in both directions between

blood and the interstitial compartment

Large protein molecules do not have this ability – their presence

produces excess osmotic pressure of blood (oncotic pressure)

compared to the interstitial fluid.

The hydrostatic pressure of the blood (at the arterial end of

capillary) tends to push water out of the capillary – filtration.

The oncotic pressure (at the venous end of capillary) pulls the

water from the interstitial space back into the capillary –

reabsorption.

Important function of oncotic pressure:to maintain water in capillaries

If capillaries become more permeable for proteins

(surgical procedures or extensive burns)

proteins migrate from blood

loss of blood oncotic pressure

total blood volume decreases

reduces the ability of blood to transfer oxygen and to eliminate CO2

Decrease of blood volume associated with insufficient brain oxygen supply

leads to shock

Biomedical importance of oncotic pressure

If plasma oncotic pressure is reduced (starvation, kidney disease)

Reduced force drawing water back into capillary from interstitium

Biomedical importance of oncotic pressure

Edema

Accumulation of excess fluid in tissue spaces

Colloidal dispersions

Colloidal dispersion

size of particles 1 – 1000 nm

almost all reactions in the organism proceed in colloid environment

True

solution

Colloid

High–molecular weight

(macromolecular) compounds

(e.g. proteins, polysaccharides)

Colloidal dispersion

Low–molecular weight compounds

by clustering of molecules into

aggregates – micelles

(e.g. soap solutions).

Classification of colloids

Colloids are classified based on the following criteria:

Physical state of dispersed phase and dispersion medium

Affinity of dispersed molecules with dispersing media

Classification of colloids

1. Based on physical state of dispersed phase and

dispersion medium

• Sol – colloids with solid particles dispersed in a liquid

• Emulsion - liquid dispersed in liquid (immiscible liquids)

• Foam – gas particles dispersed in a liquid or solid

• Aerosol - small liquid particles or solid dispersed in a gas

Sauces and dressingsclouds

• Gel - liquid particles dispersed in a solid

gelatin

Sols

Are colloidal solutions made of globular proteins with normal

viscosity

Sol - a colloidal solution appears as fluid

Gels

.

they arise by swelling macromolecular compounds (e.g.proteins) in

solvent – acceptation of water by solid polymers

are formed from fibrous proteins (gelatin from collagen), polysaccharides

(gels – dextran, sephadex).

Gels - a colloidal solution appears as solid

Gels undergo aging - particles coagulate, gel volume diminishes and

water is displaced

Emulsions

are colloidal dispersions of two immiscible liquids (e.g. oil in water, or

water in oil) when are shaken together.

usually are not stable (e.g. the oil soon separates from the aqueous layer).

can be stabilized by a third component called emulsifying agent

(emulsifiers).

Biologically important emulsifying agents are salts of bile acids.

Emulsifiers

Hydrophilic

water-loving head Hydrophobic

water-fearing tail

• All emulsifiers have 2 components: hydrophilic head

hydrophobic tail

• enable fat to be uniformly dispersed in water as an emulsion (they

stabilize emulsions).

• Their action is similar to soap in washing

emulsifier

Emulsifiers

Oil droplets

Hydrophilic head will associate with water and its hydrophobic tail with oil droplets.

This prevents separation of two layers and thus stabilizes the emulsion.

emulsifier emulsifier

Hydrophobic groups

(nonpolar)

Hydrophilic groups

(polar)

Bile acids as emulsifiers

Fat

Fat

Fat

Fat

Fat Fat

Step 1: Emulsification of fat droplets

Step 2: Hydrolysis of triacylglycerols in emulsified fat droplets into fatty acid and monoacylglycerols

Sterp 3: Dissolving of fatty acids and monoacylglycerols into micelles to produce „mixed micelles“

Bile acids as emulsifiers

Foam

is composed of small bubbles of gas (usally air) dispersed in a liquid (e.g.

egg white foam)

As liquid egg white is whisked, air bubbles are incorporated.

If egg white is heated, protein coagulates and moisture is driven off. This

forms a solid foam, e.g. a meringue

Colloids

LyophilicLiquid-loving

Lyophobic

Liquid-hatingMicelles

2. Classification of colloids according to the affinity

of dispersed molecules with dispersing media

Macromolecular

compounds Low-molecular

weight compounds

Low-molecular

weight amphipatic

compounds (soaps)

1. Lyophilic colloids

• If water is the solvent (dispersing medium), it is known as a

hydrosol or hydrophilic colloids

• particles of a lyophilic colloid are stabilized in solution

(prevention of aggregation) by solvation (hydration) shell, i.e.

oriented solvent molecules

• are formed by spontaneous dissolving of macromolecular substances

(e.g. solutions of proteins, starch...)

1. Lyophilic colloids

The loss of hydration shell after excess of neutral salt (electrolyte) is

added into solution results in irreversible salting out (precipitation)

of particles from solution.

The living cells represent solutions of lyophilic colloids (as well as

coarse dispersions)

• solvent hating colloids, have no affinity for the dispersion medium

2. Lyophobic colloids

• unstable colloid systems in which the dispersed particles:

- tend to repel liquids,

- are easily precipitated

• require protective colloids (lyophilic colloids – gums, gelatin...) to

stabilize in water

Lyophobic soll particle

(particle being protected)

Lyophilic colloidal particle

(protecting particle)

Explanation: The particles of the hydrophobic sol adsorb the particles

of the lyophilic particles. The hydrophobic colloid, therefore, behaves

as a hydrophilic sol and is precipitated less easily by electrolytes.

2. Lyophobic colloids

• are made artificially by aggregation of low molecular weight substances

• Examples: sols of metals and their insoluble compounds like sulphides and

oxides (e.g. gold, silver, platinum in water, cluster of inorganic molecules,

e.g. As2S3)

• Aplication in therapy: colloidal systems are used as therapeutic agents

Silver colloid – germicidal effects

Copper colloid – anticancer effects

Mercury colloid - antisyphilis

Colloidal gold

Colloidal silver

3. Association colloids – micelles

are formed by dissolving of low-molecular weight amphipathic compounds

Amphipathic compounds contain both polar (hydrophilic) and nonpolar

hydrophobic regions (e.g. fatty acids, phospholipids)

Polar part

Nonpolar part

when mixed with water, amphipatic compounds form colloidal particles –

micelles (e.g. soap, detergents)

Hydrophilic headHydrophobic tail

Biological importance of colloids

Biological compounds as colloidal particles: high-molecular weight proteins,

complex lipids and polysaccharides

Blood coagulation: when blood clotting occurs, the sol is converted finally

into the gel.

Biological fluids as colloids: these include blood, milk and cerebrospinal

fluid, lymph, mucus, cytosol, nucleus, cell membranes

Colloidal state is one of the most widespread in nature:

Reaction kinetics

Chemical reaction

Reaction means a change

Chemical reaction is a conversion of reactants to products

A + B C + DReactants Products

Reagents

Irreversible reactions

Reversible reactions

A + B C + D ReactantsProducts

Chemical kinetics

Kinetics of a chemical reaction can tell us:

how fast the concentration of A or B decreases

how fast the concentration of product C increases

A + B C

Rate equation(Guldberg Waage rate law)

The rate of a given chemical reaction (at constant temperature and

pressure) is proportional to product of reactants concentration.

Rate: v = k . [A]a . [B] b

k = rate constant

[A], [B]= molar concentrations of reactants (mol/L)

For the general reaction:

aA + bB cC

Rate constant

k = rate constant

A = Arrhenius constant for each chemical reaction (total number of collisions)

Ea = activation energy

R = gas constant (8.314 J K-1 mol-1)

T = Temperature in Kelvins

e = euler number (2.71828...)

Temperature has a dramatic effect on reaction rate.

For many reactions, an increase of 10°C will double the rate.

Effective collisions

For reactants to make products

They must collide in the correct orientation and with sufficient energy

The correct orientation of collisions

A B C D

A B A B

Effective collisions

For reactants to make products

They must collide in the correct orientation and with sufficient energy

The energy of collision must be greater than the bond energy

between the atoms

Activation energy

The minimum amount of energy required to start a chemical reaction

it is used to overcome the electrostatic repulsive forces between colliding

entities,

it is used to weaken the bonds of the reactants.

Activation energy

Activation energy

Transition state

(activated complex)

Activation energy

Reactants

Products

Factors which affect the rate of chemical

reactions

Rate of

reaction

The nature of

reactants

Temperature

Concentration

of reactants

Catalysts

Natu

reo

fre

acta

nts Number of bonds

• fewer bonds per reactant - faster reaction

Strength of bonds• Breaking of weaker bonds - a faster rate

(-C-C- / -C=C-)

The size and shape of a molecule• Complicated molecules or complex ions

are often less reactive

Less particles, less frequent

and successful collision

More particles, more frequent

and successful collision

Concentration of reactants

As the concentration of reactants increases, so does the likelihood that reactant

molecules will collide - the reaction rate will increase

A temperature increase of about 10°C will often double the rate of a reaction

Higher

temperatureHigher

speedMore high-energy

collisionsMore collisions

that break bonds

Faster

reaction

Temperature

Catalysts Catalysts speed up reactions by changing the mechanism of the reaction –

they reduce activation energy of reaction

Catalysts are not consumed during the course of the reaction

EaEa

Does a catalyst shift the location of the equilibrium position?

No! Catalysts do not affect the amounts of reactants and products present at

equilibrium, just the time it takes to establish equilibrium.

A catalyst speeds up the forward and reverse reactions exactly the same

Oxidation – reduction reactions

(redox reactions)

Oxidation – reduction reactions

(redox reactions)

Oxidation is the loss of electrons (or hydrogen), the species which loses

the electrons is oxidized, it becomes more positive

Reduction is the gain of electrons (hydrogen), the species which gains

electrons is reduced, becomes less positive.

Na0 → Na+ + 1e-

Cl20 + 2e- → 2Cl-

Oxidation and reduction reactions occur simultaneously

chemical reactions where one of the reactants is oxidized and one of the

reactants is reduced

Biological oxidation-reduction reactions

In biological systems, oxidation is often synonymous with dehydrogenation

Many enzymes that catalyze oxidation reactions are oxidoreductases, called

dehydrogenases.

O : H ratio1 : 6

O : H ratio1 : 4

O : H ratio1 : 2

More reduced compounds are richer in hydrogen

Oxidizing agent – oxidant - is the chemical species causing the

oxidation. This species is reduced and can also be called the

electron acceptor.

2Na0 + Cl20 2Na+Cl-

oxidant

Reducing agent – reductant- is the species causing the

reduction. This species is oxidized and can be called the electron

donor.

reductant

The number of electrons lost by the reductant must be equal to the

number of electrons gained by the oxidant.

e-

Electrons are transferred from one molecule (electron donor) to another

(electron acceptor) in one of four different ways:

1. Directly as electrons Fe2+ + Cu2+ Fe3+ + Cu+

2. As hydrogen atoms

H = H+ + 1e- AH2↔ A + 2 eˉ + 2 H+

AH2+ B ↔ A + BH2

Hydrogen/electron donor

Reduced

3. As a hydride ion (Hˉ), which has two electrons (H+ + 2e-)

This occurs in the case of NAD+-linked dehydrogenases

4. Through the direct combination with oxygen

R−CH3+ ½O2 R−CH2OH

Dismutation (disproportionation)

The special case of oxidation – reduction reaction

a compound of intermediate oxidation state converts to two different

compounds, one of higher and one of lower oxidation states.

Examples:

The dismutation of superoxide free radical to hydrogen peroxide and oxygen,

catalysed in living systems by the enzyme superoxide dismutase

2O2. − + 2H+ → H2O2 + O2

With oxidation numbers:

2 O2. −1 + 2 H+1 → H2

+1 O2-2 + O2

0

SOD

Oxidation-reduction reactions

Oxidation – reduction reactions occur together

Fe2+ + Cu2+ Fe3+ + Cu+

This reaction can be described in two half-reactions:

(1) Fe2+ Fe3+ + 1e-

(2) Cu2+ + 1e- Cu+

Which ion is a reducing agent (reductant)?

Reductant – donates electrons

Which ion is an oxidizing agent (oxidant)?

Oxidant – accepts electrons

Electron donor e- + electron acceptor

Conjugate redox pair

Reduction potentials

When two conjugate redox pairs are together in solution, electron transfer from the electron donor of one pair to the electron acceptor of the other may occur spontaneously.

The tendency for a reaction depends on the relative affinity of the electron

acceptor of each redox pair for electrons.

The standard reduction potential (E0) is the tendency for a chemical

species to be reduced, and is measured in volts at standard conditions

H+ + eˉ ½ H2 E0 = 0 V

The electrode at which this half-reaction occurs is arbitrarily assigned a

standard reduction potential of 0.00V.

Fe2+ + Cu2+ Fe3+ + Cu+

Element with the more positive redox potential has a higher

affinity towards electrons – it has an oxidizing property

Element with the more negative redox potential has a lower

affinity towards electrons – it can easily donate electrons – it has

an reducing property

R is gas constant (8.314 JKˉ1molˉ1

T is temperature (in Kelvins)

n is the number of electrons transferred per molecule

F is the Faraday constant (9.68 . 104 Cmolˉ1).

The Nerst – Peterson equation:

The reduction potential of a half-cell depends on:

the chemical species present

on their concentrations

Reduction potentials in medicine

Known oxidation-reduction potentials of biological redox systems allow to

determine the direction and sequence of oxidation-reduction reactions in

biological systems.

The strict sequence of enzymatic reactions in “respiratory chain” allows a

gradual release of energy during biological oxidation.

Electron transport chain

Thank you for your attention...