Colloids and macromolecular



All the properties of living systems are due to the existence of large molecules (in particular nucleic acids and proteins). These molecules are characterized by their large size.

The mass ratio and dimensions between macro and micro is very large.

Molecule Molecular weight Dimensions
urea 60 4
Hemoglobin 68000 42
ADN ~107 ~107



A colloid state is an intermediate state between the true solution and the suspension which has special properties.

In the presence of a catalyst, for example is observed increase in the viscosity of some solution from which small molecules, combine together to form a molecular chain or large molecules. This gives the new solution physicochemical properties.

When this process continues its evolution these large molecules strongly unite them and weave a network trapping the solvent in its meshes =>the solution turned into a gel.


The term colloid is the total dispersion of a solid in a liquid as it may be related to the dispersion of the bodies in the three states : gaseous, liquid and solid.

All these colloids states are characterized by the fact that the dispersant phase and the dispersed phase contact with an enormous surface.

Colloids are solutions macromolecule having a molecular weight and higher 5000 g / mol or atomic aggregate whose physico-chemical behavior is very different from the small molecule solutions.

Organic colloids are called biopolymers.

Suspension Colloids and macromolecular solutions Solutions


Not through a simple filter through an ordinary filter Through the filters and ultrafilters
Non dialysables Retained by ultrafilters and membranes dialysantes. dialysent
Settles quickly from the spontaneous precipitation up & rsquo; at 100,000 in lheure sediment slowly (several hours- dessusde 100,000 g) Do not settle d & rsquo; perceptibly.
Visible under the microscope Visible only to the & rsquo; ultramicroscope Invisible to the & rsquo; ultramicroscope
Dimensions > 1000 A° 10 A ° to 1000 A° < 10 A*
Numbers d & rsquo; atoms > 109 Between 103 and 109 carbon < 103 carbon


The colloidal solutions are characterized by two fundamental properties :

  1. The surface developed by the scattered molecules is considerable, it follows the phenomena of aggregation and new hydrodynamic properties ;
  2. Colloid solutions are electrically charged


Sol : A colloid in the liquid state is often called ground from which the molecules of the solution are not completely independent of each other (ex : gelatin).

The freeze : The cooling of certain solutions increases the bonds linking the molecules. It forms a network, that imprisons in its meshes, the liquid (solvent).

The concentration of the colloid was unchanged, but the network that has formed is endowed with a certain stiffness.

Soil turned into gel.

The amount of solvent molecules in the gel is up to considerable IE99% of total weight.


The stability of gels and stiffness depend on the number and strength of the bonds that unite the strings that constitute the.

  • Liaisons Van Der Vaals type : we are dealing with very unstable gels, a small increase in temperature, or a mechanical force by agitation or pressure can make them return to the ground state.
  • covalent type bonds : We are dealing with three-dimensional molecules (resin, silica gel) so the temperature rise does not destroy its links. These gels do not dissolve.


Despite the wide variety of colloidal systems, it has some well characterized properties.

  • Diffusion is slow in aqueous phase.
  • Osmotic phenomena are small but measurable.
  • Their optical properties are special.
  • Their solubilities vary widely, they depend on many factors.
  • They develop a tremendous solution contact surface.
  • The colloidal solution separates into two phases, the solvent containing the other colloidal.



  • A very low concentration solution deviate from ideality
  • The surface exposed to solvent is very large and heterogeneous
  • Many reagents (polar, hydrophobic, positively or negatively charged) will give these molecules a large number of new properties.
  • These properties are either :
  • In order structural (plasticity, elasticity, rigidity, fiber formation)
  • On the functional nature (supporting role, transport, enzymatic activity, storage and distribution of information.

– All of these properties depend on the nature of the chemical groups, which comprise these macromolecules, and configuration they adopt


All macromolecules are polymers characterized by the distribution of a basic structural pattern.

Polymers formed of chemically identical patterns are formed polymers Homopolymers of several types of United base units together ; are the copolymer.

The resulting channels can be linear, connected, interconnected by covalent bonds.

The variety of molecular structures thus formed is considerable.


A- artificial polymers :

  1. homopolymers
  2. copolymers

B- biopolymers :

They are extremely varied, and their properties are fundamental include :

  1. Nucleic acids
  2. The proteins
  3. polysaccharides
  4. The isoprene polymers
  5. Biological copolymers


Simple : formed from identical monomer units (same size and weight), the polymer chain is uniform (oligomer). Case of starch, glycogen

Complexes : formed of several identical channels, For macromolecules quaternary conformation, such as hemoglobin, collagen.


  • Also called copolymers, they are formed of different monomer units ; another sub-category includes those formed by the association of polymers or chains of different chemical nature. These are glycoproteins, viruses, membrane systems, nucleoproteins, etc…
  • Homopolymers lead to monodisperse colloidal solutions, while hetero-polymers give rise to colloidal hetero-dispersed solutions.


Generally each macromolecule in solution a three-dimensional structure characterized call conformation, Chemical physical behavior depends largely on this conformation II excites two types of conformation :

A. Globulin form : where the molecules are folded over it same in spherical form.

B. The lunar shape : They resemble a real fiber macromolecule is closer to at least two of these forms. In practice the macromolecule are rigid rotations are possible in some places.


Because of the particle size the molar concentration of macromolecular is weak (to a solution of Cp = 70 g / l of albumin M = 70000g / mol, Cm = 1mM.

As a result, certain technical, such as tonometry or cryoscopy, unusable.

On the contrary, in many cases the measuring osmotic pressure proves to be great utility because the irregularities are of the order of a few centimeters or four inches of water.

Moreover it is easy to find adequate selective membranes, small molecules that pass and retains macromolecules.


Osmotic pressure : The osmotic pressure of a small molecule solution

π = ?RT = v CmRT = v RT/M Cp

= > Pi Cp = RTv / M

Experimentally, this ratio is a function of Pc for macromolecules :

π / CP =RTv/M = ßCp

Hence ß is the coefficient of Virielqui depends on the torque solute-solvent


Diffusion :

The spread is considered by the 1 is loi de Fick J d = dn / dt = D * S * (dC) Idx According to Einstein's relationship

D = kT/6 x π x µ x r = KTf = RTb

The diffusion coefficient is lower.

Diffusion of macromolecules is slow.

The real molecular weight as the inverse of the diffusion coefficient D M1/3 = cte

Provided consider macromolecules as spherical molecules. This is rarely.


A-Principe :

Is a particle volume V and density p, suspended in a liquid of density po.

The apparent mass (taking into account buoyancy) is V.(p – p0). It undergoes the action of gravity, and is therefore subject to a driving force :

Fm= V.(p – p0).G

It quickly reaches a limit speed v due to the friction it undergoes from the solvent molecules that exert a frictional force f.v(f friction coefficient)

vs = 2/9 g(p – Po) r2/m

The formula only applies to large particles.

In reality, thermal agitation opposes the spontaneous sedimentation of macromolecules.

Sedimentation B-Speed :

To overcome the tendency to homogeneous distribution of the particles in the scattering effect, we must increase the gravitational force field.

This is achieved through an ultracentrifuge.

The speed of sedimentation vs = 2/9 (p – p0)r2/μ is very low due to :

  • the low radius value macromolecule (micrometer),
  • the difference in density is very low.


To increase the sedimentation velocity, it must increase the value of g that is achieved by centrifugation with.

One puts the macromolecule has a distance x from the axis of rotation (rotor), then the macromolecule subjected to a uniform circular motion.

The rotation on itself of a rotor radius R at the speed of n revolutions per second results in a centrifugal acceleration :

? = ? 2 x R
with ? = 27m
therefore ? = (27??)2x R

acceleration is thus achieved in the order of 400000 times that of gravity, with rotors of ten cm in radius turning 60000 revolutions / min

s If the speed is less than 104 rd / min, was centrifuged. s If the speed is greater than is the ultracentrifugation.

electrophoresis :

Definition : the Greek phoêsis, Action to wear.

displacement, under the effect of an electric field of macromolecules, particles, beans charged in solution or in emulsion (we call anaphoresis migrate to the anode and the cataphoretic migration to the cathode).

This phenomenon is increasingly used as technical analysis and above all as separation technique. In the first case, using the free electrophoresis (Tisel) In the second, using a variety of electrophoretic techniques carrier.


A charged particle, placed in the electric field E is subjected to the force displacement Coulomb :

F = Z x to x E

With a speed v, in a solution (friction force) fxv

Equilibrium : v = ZeE / f = ZeE /????

(? solvent viscosity, r rayon shérique)

We define the electrophoretic mobility by the ratio :

U = v / E = Ze / ???? (for a sphere)


  • Mobility depends only on the load and the friction coefficient of the particle.
  • Electrophoresis is used to evaluate the conformation of macromolecules such as sedimentation or dissemination, since the friction coefficient f is itself a function of the form (spheres ellipsoids, sticks, balls, statistics).
  • In reality, the particles are surrounded by an ionic atmosphere 'thickness e, which varies with the ionic strength, and velocity of the particle ; therefore their actual load is reduced

U = ??/????

? : the middle dielectric constant

? : is always close (difficult to calculated) => it is difficult to draw any information about the shape and particle charge.

électrophorèse FREE :

• The principle of this technique is based on the movement of macromolecules charged under the effect of an electric field, the gradient of the gravitational field g sedimentation is replaced by an electrical gradient results of separation will depend on the load.

• It is used as technical analysis and separation which allows measurement of the electrophoretic mobility.
• This separation technique allows :
– The identification of certain substances found in a mixture.
– Used as a separation technique for obtaining substances.
• There are two types of techniques : on liquid phase and on filter paper.


• Quantitative analysis of a macromolecular solution allows measured mobilities of the various constituents, Identification and determination of concentrations of substances.
• The separation of substances (slower, faster).


• A fairly difficult technique to maintain the boundaries for observation.
• The diffusion phenomenon remains important for such kinds as electrophoresis can be applicable only for large molecules


• To overcome the difficulties of the previous technique using electrophoresis support is paper, slide, or gel.

• The difference between the two techniques :

  • The diffusion phenomenon is eliminated, allowing a good observation of the separated substances.
  • The electrophoretic mobility does not depend on the nature of particle but the nature of the solvent.
  • This produces another phenomenon called electroendosmosis.
  • Media (the extremities) deceived in a buffer solution Migrating negative proteins to the positive pole and conversely there will be a plurality of layers, these layers are called layers HELMOLTEZ.


  • Absorption spectroscopy (ultraviolet and visible):

Method for calculating the concentration using the Beer-Lambert

A = log I0/I = ??? = ???

  • Emission spectroscopy :

The study of emission properties of molecules excited provides interesting information on their structure, and allowed to check and improve the quantum theory of atomic bonds


Although its radiation energy E-M is insufficient for passing an electron from the ground state to the excited state; it interacts with the different quantum levels of vibration or rotation of atoms in molecules.

The infrared spectrum gives very precise information on the nature of the atomic bonds, So chemical functions present in molecules.

It is a spectroscopic technique widely used to identify compounds and to check the purity.


Using an E-M radiation energy is very low placing the molecules in a strong magnetic field ; this type of spectroscopy has numerous applications in the study of the shape and properties of biological macromolecules and even membranes.


1- nucleic acids :


  • Store and transmit genetic information.
  • Allows the evolution of species.


  • Mediates the transmission of genetic information.
  • Can catalyze chemical reactions -servent cofactors for enzymes.
  • Regulate the & rsquo; gene expression.

2- protein :

  • Create and maintain a structure (cytosquelette).
  • specifically recognize a ligand to defend the cell (immuno).
  • carry (hemoglobin, PMB).
  • transform (enzymes).
  • Involved in cell movement (myosine).
  • Inform and report ("Molecular switches").

Course of Dr Allouache – Faculty of Constantine